Adiponectin levels do not change with moderate dietary induced weight loss and exercise in obese postmenopausal women

OBJECTIVE

The purpose of this study was to determine changes in adiponectin levels with moderate weight loss, weight loss plus aerobic exercise, or weight loss plus resistive exercise in overweight and obese, sedentary postmenopausal women.

DESIGN

Longitudinal, clinical intervention study of 6-month (3 x /week) program of either weight loss (WL, n=15), weight loss + aerobic exercise (WL+AEX, n=16), or weight loss + resistive exercise (WL+RT, n=9)

SUBJECTS

We studied 40 sedentary, overweight and obese (body mass index, BMI=32+/-1 kg/m(2), X+/-s.e.m.) postmenopausal (57+/-1y) women.

MEASUREMENTS

Fat mass and fat-free mass (FFM) by dual-energy X-ray absorptiometry, plasma insulin, leptin, and adiponectin by radioimmunoassay.

RESULTS

Age, body weight, BMI, waist and hip circumferences, waist-to-hip ratio, VO(2)max, percent fat, total body fat mass, FFM, and fasting plasma glucose, insulin, leptin, and adiponectin concentrations were similar among WL, WL+AEX, and WL+RT groups before the interventions. In all women combined, body weight, BMI, and waist and hip circumferences decreased (P < 0.001). There was a significant absolute decrease in percent body fat from 47 to 44%, representing a 13% decrease in total fat mass and a -1.6% change in FFM. Fasting concentrations of plasma adiponectin did not change (40+/-16%, P=NS), whereas fasting plasma glucose, insulin, and leptin all decreased (P<0.001).

CONCLUSIONS

Plasma adiponectin levels do not change with a 6-month moderate weight reduction program even when accompanied by aerobic or resistive exercise training in overweight and obese postmenopausal women.

Does waist circumference add to the predictive power of the body mass index for coronary risk?

OBJECTIVES

To examine the power of the combined measurements of body mass index (BMI) and waist circumference (WC) for the prediction of abnormality in coronary heart disease risk factors and to determine whether the additional measurement of WC is predictive in older men and women.

RESEARCH METHODS AND PROCEDURES

1190 men and 751 women of the Baltimore Longitudinal Study of Aging were dichotomized into younger (<65 years) and older (65+ years) age groups. Coronary risk factors in the realms of glucose/insulin metabolism, blood pressure, and plasma lipids were assessed. The relationship of BMI and WC, singly and combined, to 10 risk factors for coronary heart disease was examined.

RESULTS

In younger and older men and women, BMI and WC are highly correlated (0.84 to 0.88). BMI and WC are also significantly correlated to all 10 coronary risk factors in younger men and women and to 8 of the 10 in the older men and women. Both partial correlation and logistic regression analyses revealed a modest but significant improvement in the prediction of coronary risk in younger men and women by WC after controlling for the level of BMI. There was no improvement in the older subjects.

DISCUSSION

WC adds only modestly to the prediction of coronary risk in younger subjects once BMI is known, and adds nothing to the production of risk in older subjects.

Effect of glucagon-like peptide 1 on non-insulin-mediated glucose uptake in the elderly patient with diabetes

An important cause of elevated glucose levels in elderly patients with diabetes is an alteration in non-insulin-mediated glucose uptake (NIMGU). Glucagon-like peptide 1 (GLP-1) is an intestinal insulinotropic hormone. It has been proposed that this hormone also lowers glucose levels by enhancing NIMGU. This study was conducted to determine whether GLP-1 augments NIMGU in elderly patients with diabetes, a group in which NIMGU is known to be impaired. Studies were conducted on 10 elderly patients with type 2 diabetes (aged 75 +/- 2 years, BMI 27 +/- 1 kg/m(2)) who underwent paired 240-min glucose clamp studies. In each study, octreotide was infused to suppress endogenous insulin release, and tritiated glucose methodology was used to measure glucose production and disposal rates. For the first 180 min, no glucose was infused. From 180 to 240 min, glucose was increased to 11 mmol/l using the glucose clamp protocol. In the GLP-1 study, GLP-1 was infused from 30 to 240 min. In a subsequent control study, insulin was infused using the glucose clamp protocol from 30 to 240 min to match the insulin levels that occurred during the GLP-1 infusion study. During hyperglycemia, GLP-1 enhanced glucose disposal (control study: 2.52 +/- 0.19 mg x kg(-1) x min(-1); GLP-1 study: 2.90 +/- 0.17 mg x kg(-1) x min(-1); P < 0.0001). Hepatic glucose output was not different between studies. We conclude that GLP-1 may partially reverse the defect in NIMGU that occurs in elderly patients with diabetes.

Glucagon-like peptide-1 (7-37) augments insulin-mediated glucose uptake in elderly patients with diabetes

BACKGROUND

Glucagon-like peptide-1 (GLP-1) is an intestinal insulinotropic hormone that augments glucose-induced insulin secretion in patients with type 2 diabetes. It has also been proposed that a substantial component of the glucose-lowering effects of GLP-1 occurs because this hormone enhances insulin-mediated glucose disposal. However, interpretations of the studies have been controversial. This study determines the effect of GLP-1 on insulin-mediated glucose disposal in elderly patients with type 2 diabetes.

METHODS

Studies were conducted on 8 elderly patients with type 2 diabetes (age range, 76 +/- 1 years; body mass index, 28 +/- 1 kg/m(2)). Each subject underwent two 180-minute euglycemic (insulin infusion rate, 40 mU/m(2)/min) insulin clamps in random order. Glucose production (Ra) and disposal (Rd) rates were measured using tritiated glucose methodology. In one study, glucose and insulin alone were infused. In the other study, a primed-continuous infusion of GLP-1 was administered at a final rate of 1.5 pmol x kg(-1) x min(-1) from 30 to 180 minutes.

RESULTS

Glucose values were similar between the control and GLP-1 infusion studies. 120- to 180-minute insulin values appeared to be higher during the GLP-1 infusion study (control, 795 +/- 63 pmol/l; GLP-1, 1140 +/- 275 pmol/l; p = not significant [NS]). The higher insulin values were largely due to 2 subjects who had substantial insulin responses to GLP-1 despite euglycemia and hyperinsulinemia. The 120- to 180-minute insulin values were similar in the other 6 subjects (control, 746 +/- 35 pmol/l; GLP-1, 781 +/- 41 pmol/l; p = NS). Basal (control, 2.08 +/- 0.05 mg/kg/min; GLP-1, 2.13 +/- 0.04 mg/kg/min; p = NS) and 120- to 180-minute (control, 0.50 +/- 0.18 mg/kg/min; GLP-1, 0.45 +/- 0.14 mg/kg/min; p = NS) Ra was similar between studies. The 120- to 180-minute Rd values were higher during the GLP-1 infusion studies (control, 4.73 +/- 0.39 mg/kg/min; GLP-1, 5.52 +/- 0.43 mg/kg/min; p <.01). When the 2 subjects who had significant insulin responses to GLP-1 during the euglycemic clamp were excluded, the 120- to 180-minute Rd values were still higher in the GLP-1 infusion study (control, 5.22 +/- 0.32 mg/kg/min; GLP-1, 6.05 +/- 0.37 mg/kg/min; p <.05).

CONCLUSIONS

We conclude that GLP-1 may enhance insulin sensitivity in elderly patients with diabetes.

Effect of aging and diabetes on the enteroinsular axis

BACKGROUND

The current studies were designed to examine the effect of aging and diabetes on the enteroinsular axis.

METHODS

Healthy young control subjects (n = 10 young; age 23 +/- 1 years; body mass index [BMI] 24 +/- 1 kg/m(2)), healthy elderly subjects (n = 10; age 80 +/- 2 years; BMI 26 +/- 1 kg/m(2)), and elderly patients with type 2 diabetes (n = 10; age 76 +/- 2 years; BMI 26 +/- 2 kg/m(2)) underwent a 3-hour oral glucose tolerance test (glucose dose 40 gm/m(2)).

RESULTS

Insulin responses were not different between young controls and elderly patients with diabetes but were significantly lower in elderly patients with diabetes and young controls than in elderly controls (young control: 178 +/- 27 pM; elderly control: 355 +/- 57 pM; elderly diabetes: 177 +/- 30 pM; p <.05 elderly control vs young control and elderly diabetes). Total glucagon-like peptide 1 (GLP-1) responses were not significantly different between young and elderly controls and patients with diabetes (young control: 15 +/- 2 pM; old control: 8 +/- 2 pM; elderly diabetes: 12 +/- 3 pM; p = ns). Active GLP-1 responses were also not different between young and elderly controls and patients with diabetes (young control: 5 +/- 1 pM; old control: 6 +/- 1 pM; elderly diabetes: 7 +/- 1 pM; p = ns). However, the difference between total and active GLP levels was significantly greater in the young controls (young control: 10 +/- 2 pM; old control: 2 +/- 2 pM; elderly diabetes: 4 +/- 2 pM; p <.05, young vs elderly). Glucose-dependent insulinotropic polypeptide responses were not different between young and elderly controls and between elderly controls and patients with diabetes but were significantly higher in elderly patients with diabetes than in young controls (young control: 97 +/- 12 pM; elderly control: 121 +/- 16 pM; elderly diabetes: 173 +/- 27 pM; p <.05, young vs elderly diabetes). Glucagon responses were reduced in elderly controls but were similar in young controls and elderly patients with diabetes (young control: 15 +/- 1 pM; elderly control: 9 +/- 1 pM; elderly diabetes: 16 +/- 1 pM; p <.01 elderly control vs young control and elderly diabetes). Dipeptidyl peptidase IV levels were lower in both elderly controls and patients with diabetes when compared with young controls (young control: 0.17 +/- 0.01; elderly control: 0.15 +/- 0.01; elderly diabetes: 0.15 +/- 0.01 DeltaOD/20 minutes; p <.05, elderly vs young).

CONCLUSIONS

We conclude that normal aging and diabetes are associated with multiple changes in the enteroinsular axis.

Sequential hyperglycemic-euglycemic clamp to assess beta-cell and peripheral tissue: studies in female athletes

Insulin secretion and rate of utilization (R(d)) of glucose were tested during a newly developed sequential clamp in 42 highly trained female athletes (A; 18-69 yr old) and 14 sedentary control women (C; 18--50 yr old; body mass index <25 kg/m(2)). The A women were categorized into four age groups: 18--29, 30--39, 40--49, and 50--69 yr old. The C women were also grouped by age (18--29 and 40--50 yr old). During the three-step clamp (hyperglycemia, return to euglycemia, and hyperinsulinemia), glucose turnover was assessed with [3-(3)H]glucose. Among the A, the youngest group had the largest first- and second-phase insulin response, which was significantly different from the oldest A (P < 0.05). Among the two C groups, first-phase response of both groups and second-phase response of the older group was higher than respective age-matched A (P < 0.05). During the hyperglycemic period, glucose R(d) was similar among A groups and between A and C. Despite similar levels of insulin between groups during the hyperinsulinemic period (approximately 400 pmol/l), A utilized 36% more glucose than C (P < 0.001). Glucose R(d) was not different across the age groups of A. This newly developed sequential clamp procedure allows assessment of both beta-cell sensitivity to glucose and peripheral tissue sensitivity to insulin in a single session. We have shown that physical activity improves beta-cell efficiency across the age span in women and ameliorates the effect of age on the decline of peripheral tissue sensitivity to insulin.

The effect of intraislet somatostatin immunoneutralization on insulin secretion in the isolated perfused rat pancreas

BACKGROUND

There is evidence of a local inhibitory effect of somatostatin on insulin secretion in the isolated human pancreas, but this has not been shown in a rat model. The possible phasic effect of somatostatin on insulin secretion has not been demonstrated.

AIMS

This study was undertaken to determine if somatostatin has a local regulatory effect on phasic insulin secretion within a rat pancreas model.

METHODS

The basal and glucose stimulated secretion of insulin was compared with and without immunoneutralization of somatostatin using a somatostatin antibody in an isolated perfused rat pancreas model. High concentration, high affinity monoclonal somatostatin antibody was perfused through isolated rat pancreata. Radioimmunoassay for insulin was performed on the portal effluent.

RESULTS

Immunoneutralization of somatostatin during basal insulin secretion produced a rise in insulin secretion of 551 +/- 163% that approached significance. Immunoneutralization during glucose stimulated insulin secretion produced a significant rise in insulin secretion compared to the control group of 2,678 +/- 187% vs. 535 +/- 39% (p < 0.05). The phase I vs. the phase II response in the glucose stimulated pancreas was similar in the presence of control antibody, 867 +/- 351% vs. 900 +/- 398% (p = NS). With somatostatin immunoneutralization, the glucose stimulated pancreas had a significantly higher phase II response than phase I; 3,832 +/- 688% vs. 2,516 +/- 431% (p < 0.05).

CONCLUSION

These data indicate that intraislet somatostatin is an inhibitor of insulin secretion in the isolated perfused rat pancreas. This effect occurs primarily in phase II of insulin secretion.

Whole organ transplantation and glucose regulation

Pancreas transplantation has gained clinical acceptance since its initial application more than 30 years ago. A constellation of surgical, pharmacologic, and metabolic alterations occur with transplantation, particularly if pancreatic transplantation is performed in addition to renal transplantation in a uremic diabetic. Increasingly sophisticated studies have allowed analysis of the performance of the transplanted organ and have enhanced our basic understanding of insulin's complex interplay in peripheral glucoregulatory processes.

A test of recently proposed BMI standards with respect to old age

The purpose of this study was to investigate the effects of age on the relationship between BMI and multiple coronary risk factors, and to determine whether the BMI classification by NHLBI and WHO is applicable as a predictor of coronary risk factors in older (>65 years) as well as in younger (<65 years) men and women. Effects of age on ten coronary risk factors were examined. Sex differences in the slopes of BMI on risk factors were compared between younger and older subjects in order to examine the effects of age on these relationships. The frequency of risk factor abnormality in individual BMI groups (18.5-24.9, 25.0-29.9, 30.0+) was examined for four age-sex groups. The significance of an age group-BMI interaction term was tested by the logistic regression model to see whether there is a significant difference in the relationship between BMI and the individual risk factor abnormalities between younger and older subjects. Older subjects had significantly higher values for most risk factors than younger subjects. The slopes of BMI on risk factors were different between younger and older subjects for fasting glucose, total, HDL- and LDL-cholesterol in men, and for diastolic blood pressure, total and LDL-cholesterol in women. The proportion of subjects with abnormal risk factor levels in each of the three BMI groups was higher in older than in younger subjects for most risk factors. There was generally a progressive worsening of the risk factor levels with increasing BMI in both age groups. There was no consistent age difference in the relationship between BMI groups and the frequency of risk factor abnormality. We conclude that, although age increases the frequency of most cardiovascular risk factor abnormalities, in general, it does not affect the trend of the relationship between the risk factors and the normal, overweight and obese BMI groups defined by NHLBI and WHO. Therefore, these BMI categories are applicable as predictors of risk factor levels in older as well as in younger men and women.

Impaired insulin secretion and increased insulin sensitivity in familial maturity-onset diabetes of the young 4 (insulin promoter factor 1 gene)

Diabetes resulting from heterozygosity for an inactivating mutation of the homeodomain transcription factor insulin promoter factor 1 (IPF-1) is due to a genetic defect of beta-cell function referred to as maturity-onset diabetes of the young 4. IPF-1 is required for the development of the pancreas and mediates glucose-responsive stimulation of insulin gene transcription. To quantitate islet cell responses in a family harboring a Pro63fsdelC mutation in IPF-1, we performed a five-step (1-h intervals) hyperglycemic clamp on seven heterozygous members (NM) and eight normal genotype members (NN). During the last 30 min of the fifth glucose step, glucagon-like peptide 1 (GLP-1) was also infused (1.5 pmol x kg(-1) x min(-1)). Fasting plasma glucose levels were greater in the NM group than in the NN group (9.2 vs. 5.9 mmol/l, respectively; P < 0.05). Fasting insulin levels were similar in both groups (72 vs. 105 pmol/l for NN vs. NM, respectively). First-phase insulin and C-peptide responses were absent in individuals in the NM group, who had markedly attenuated insulin responses to glucose alone compared with the NN group. At a glucose level of 16.8 mmol/l above fasting level, GLP-1 augmented insulin secretion equivalently (fold increase) in both groups, but the insulin and C-peptide responses to GLP-1 were sevenfold less in the NM subjects than in the NN subjects. In both groups, glucagon levels fell during each glycemic plateau, and a further reduction occurred during the GLP-1 infusion. Sigmoidal dose-response curves of glucose clearance versus insulin levels during the hyperglycemic clamp in the two small groups showed both a left shift and a lower maximal response in the NM group compared with the NN group, which is consistent with an increased insulin sensitivity in the NM subjects. A sharp decline occurred in the dose-response curve for suppression of nonesterified fatty acids versus insulin levels in the NM group. We conclude that the Pro63fsdelC IPF-1 mutation is associated with a severe impairment of beta-cell sensitivity to glucose and an apparent increase in peripheral tissue sensitivity to insulin and is a genetically determined cause of beta-cell dysfunction.

Effect of acarbose on insulin sensitivity in elderly patients with diabetes

OBJECTIVE

To study the effect of acarbose, an alpha-glucosidase inhibitor, on insulin release and insulin sensitivity in elderly patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Elderly patients with type 2 diabetes were randomly treated in a double-blind fashion with placebo (n = 23) or acarbose (n = 22) for 12 months. Before and after randomization, subjects underwent a meal tolerance test and a hyperglycemic glucose clamp study designed to measure insulin release and sensitivity.

RESULTS

After 12 months of therapy there was a significant difference in the change in fasting plasma glucose levels (0.2 +/- 0.3 vs. -0.5 +/- 0.2 mmol/l, placebo vs. acarbose group, respectively; P < 0.05) and in incremental postprandial glucose values (-0.4 +/- 0.6 vs. -3.5 +/- 0.6 mmol/l, placebo vs. acarbose group, P < 0.001) between groups. There was a significant difference in the change in HbA(1c) values in response to treatment (0.4 +/- 0.2 vs. -0.4 +/- 0.1%, placebo vs. acarbose group, P < 0.01). The change in fasting insulin in response to treatment (-2 +/- 2 vs. -13 +/- 4 pmol/l, placebo vs. acarbose group, P < 0.05) and incremental postprandial insulin responses (-89 +/- 26 vs. -271 +/- 59 pmol/l, placebo vs. acarbose group, P < 0.01) was also significantly different between groups. During the hyperglycemic clamps, glucose and insulin values were similar in both groups before and after therapy However, there was a significant difference in the change in insulin sensitivity in response to treatment between the placebo and the acarbose groups (0.001 +/- 0.001 vs. 0.004 +/- 0.001 mg/kg x min(-1) [pmol/l](-1), respectively, P < 0.05)

CONCLUSIONS

Acarbose increases insulin sensitivity but not insulin release in elderly patients with diabetes.

Effect of aging on the relationship between multiple risk factors and waist circumference

OBJECTIVE

To examine the relationship between various coronary risk factors and the different levels of fat distribution in younger (<65 years) and older (> or = 65 years) men and women, using the classifications proposed by the National Heart, Lung and Blood Institute (NHLBI) and the World Health Organization (WHO).

DESIGN

Cross-sectional study of subjects enrolled in the Baltimore Longitudinal Study of Aging.

MEASUREMENTS

Systolic blood pressure, diastolic blood pressure, fasting glucose, 2-hour glucose, fasting insulin, homeostasis model assessment insulin resistance (HOMAIR), triglyceride, total cholesterol, high-density lipoprotein (HDL)-cholesterol, and low-density lipoprotein (LDL)-cholesterol were measured as risk factors. The proportion of subjects with abnormal risk factor levels by waist circumference classifications was determined in the age and gender subgroups.

RESULTS

There were significant adverse effects of age per se on all risk factors with the exception of fasting insulin and HOMAIR in both men and women, total cholesterol in men, and diastolic blood pressure in women. HDL-cholesterol was higher in older subjects. There were significant correlations between waist circumference and all of the risk factors in the younger group. Waist circumference did not have a significant correlation with total cholesterol in older men, or with total cholesterol and LDL-cholesterol in older women. The proportion of subjects with an abnormal risk factor level increased with increasing waist circumference for most risk factors in both younger and older subjects, but proportions of subjects in each individual waist group were higher in older than in younger groups for systolic blood pressure, diastolic blood pressure, fasting glucose, and 2-hour glucose in men, and for systolic blood pressure, fasting glucose, 2-hour glucose, total and LDL-cholesterol, and triglyceride in women.

CONCLUSIONS

Our data indicate that the waist circumference cutpoints proposed by NHLBI and WHO standards are useful for the prediction of cardiovascular disease risk factors in older as well as in younger men and women.

Carbohydrate metabolism in the elderly

In this short review we summarize the effect of age on glucose homeostasis. The concept of decreased glucose tolerance with increasing age is introduced, followed by evidence for this phenomenon. Specifically we review the evidence for changes in fasting glucose as a function of age and the effect of age on HbA1c. The role of age on hepatic glucose production and glucose uptake is then discussed in detail and we review the evidence that supports the concept that with advancing age hepatic glucose sensitivity to insulin is unaltered. We then review the large evidence for the role of age on the purported decrease in peripheral tissue sensitivity to insulin and conclude that the issue is unsettled. The decrease attributed to age is no longer significant when confounders are controlled for, the largest being obesity. We next present evidence that beta-cell sensitivity to glucose remains intact with aging. A review of age-related disorders due to hyperglycemia and confounding effects on the relationships of age and glucose tolerance is presented next. Finally we present new evidence that when the revised criteria for the diagnosis of type 2 diabetics as proposed by the American Diabetes Association and WHO are used, a greater percentage of the elderly will not be diagnosed. We conclude that, although glucose intolerance increases with aging, which is accompanied with other disorders, it is possible to ameliorate this effect with alteration of diet and exercise.

Changes in plasma leptin and insulin action with resistive training in postmenopausal women

OBJECTIVE

To determine the effects of 16 weeks of resistive training alone (RT) and with weight loss (RT+WL) on insulin action, plasma leptin concentrations and leptin's relationship to beta-cell sensitivity to glucose, resting metabolic rate (RMR), and plasma catecholamines in older women.

SUBJECTS

Fifteen obese postmenopausal women aged 50-69 y.

MEASUREMENTS

Body composition (by dual-energy X-ray absorptiometry), RMR (by indirect calorimetry), insulin action (by 2 h hyperglycemic clamps; 7.9 mmol/l above basal plasma glucose levels), plasma leptin and insulin (by RIA), and plasma catecholamines (by enzymatic methods).

RESULTS

RT and RT+WL resulted in significant improvements in muscular strength (P<0.01) with no changes in maximal oxygen consumption. Body weight, fat mass and percent body fat did not change with RT, but decreased with RT+WL (P<0.001). Fat-free mass and RMR increased after training when both groups were combined (P<0.05). The insulin response during the last 20 min of the 2 h hyperglycemic clamps decreased 16% after RT (P=0.05), 43% after RT+WL (P<0.05), and 29% in the entire group (P<0. 01) without any changes in glucose utilization. Plasma leptin levels did not change after RT, but decreased by 36% after RT+WL (P<0.05). Baseline leptin levels correlated with body weight (r=0.68, P<0.01), body fat mass (r=0.77, P<0.001), and RMR (kcal/d; (r=0.69, P<0.005), but not with baseline norepinephrine or epinephrine levels. Plasma leptin levels correlated with basal insulin (r=0.73, P<0.005), and approached significance with the 0-10 min and 100-120 min insulin response to hyperglycemia before training (both r=0.51, P=0.07). In the entire group, the change in insulin response from 100-120 min during the clamp correlated with the change in leptin levels (r=0.60, P<0.05), but this was not independent of changes in fat mass.

CONCLUSIONS

Although changes in leptin levels were not related to changes in RMR or plasma catecholamines after RT with and without weight loss, the increase in insulin action after training and weight loss may be related to the decrease in leptin levels that were mediated by the loss of body fat in the obese, postmenopausal women. International Journal of Obesity (2000)24, 27-32

Disruption of the pulsatile and entropic modes of insulin release during an unvarying glucose stimulus in elderly individuals

Insulin is secreted in a pulsatile fashion with measurable orderliness (low entropy). Aging is characterized by alterations in pulsatile insulin release in the fasting state. We undertook the current studies to determine whether disruptions in pulsatile insulin release in response to sustained glucose infusion also accompany the age-related changes in carbohydrate metabolism. Healthy young (n = 10; body mass index, 23 +/- 1 kg/m2; age, 23 +/- 1 yr) and old (n = 10; body mass index, 24 +/- 1 kg/m2; age, 80 +/- 2 yr) volunteers underwent a 600-min hyperglycemic glucose clamp. During the entire 600 min, insulin was sampled every 10 min, and insulin release was evaluated by Cluster analysis. From 240-360 min, insulin was sampled every 1 min, and secretory pulse analysis was conducted using a multiparameter deconvolution technique. During the 1-min sampling interval, basal insulin secretion (P < 0.01), insulin production rate (P < 0.01), pulsatile mean and integrated insulin concentration (P < 0.01), insulin secretory burst mass (P < 0.01), and burst amplitude (P < 0.05) were reduced in the elderly. In addition, interpulse interval was increased in the aged (P < 0.05). In the 600-min studies, interpulse interval was greater in the aged (P < 0.01) and burst number (P < 0.01), basal concentration (P < 0.01), and burst increment (P < 0.05) were less. Approximate entropy, a measure of irregularity of insulin release, was increased in the aged, signifying the loss of orderliness of insulin secretion (P < 0.05). We conclude that in response to a sustained (10-h) glucose infusion, normal aging is characterized by a reduction in mass and amplitude of rapid insulin pulses and a decrease in the frequency, amplitude, and regularity of ultradian pulses. Whether these changes in insulin pulsatility contribute directly to the age-related changes in carbohydrate metabolism will require further clinical studies.

Loss of bone mineral density in women athletes during aging

Total and regional bone mineral density (BMD) by dual-energy-X-ray absorptiometry (DXA) and bone turnover were tested in 50 highly trained women athletes and 21 sedentary control women (18-69 years; BMI < 25 kg/m2). VO2max (ml . kg-1 . min-1) and lean tissue mass (DXA) were significantly higher in the athletes versus controls (both P < 0.0001). Total body BMD did not decline significantly with age in the athletes whereas lumbar spine (L2-L4) BMD approached statistical significance (r = -0.26; P = 0.07). Significant losses of the femoral neck (r = - 0.42), Ward's triangle (r = -0.53), and greater trochanter BMD (r = -0.33; all P < 0.05) occurred with age in the athletes. In the athletes, total body BMD, L2-L4 BMD, and BMD of all sites of the femur were associated with lean tissue mass (r = 0.32 to r = 0.57, all P < 0.05) and VO2max (r = 0.29 to r = 0.48, all P < 0.05). Femoral neck and greater trochanter BMD were higher in the athletes than in controls (both P < 0.05) and lumbar spine and Ward's triangle BMD approached statistical significance (both P = 0.07). Bone turnover was assessed by serum bone-specific alkaline phosphatase (B-ALP), urinary deoxypyridinoline cross-links (Dpd), and urinary aminoterminal cross-linked telopeptides (NTX). There were no relationships between B-ALP or Dpd with age whereas NTX increased with age (r = 0.46, P < 0.05) in the entire group. Levels of B-ALP and NTX were negatively associated with total body, L2-L4, femoral neck, Ward's triangle, and greater trochanter BMD (P < 0.05). B-ALP and Dpd were not significantly different between athletes and controls whereas NTX was lower in the athletes than in controls (P < 0.001). The high levels of physical activity observed in women athletes increase aerobic capacity and improve muscle mass but are not sufficient to prevent the loss of bone with aging.

The effect of age and glycemic level on the response of the beta-cell to glucose-dependent insulinotropic polypeptide and peripheral tissue sensitivity to endogenously released insulin

Normal aging is characterized by a progressive impairment in glucose tolerance. An important mechanism underlying the glucose intolerance of aging is an impairment in glucose-induced insulin release. These studies were conducted to determine whether the age-related impairment in insulin release was caused by a decreased beta-cell sensitivity to glucose-dependent insulinotropic polypeptide (GIP). Thirty-one Caucasian men were divided into four groups: two young groups (age range: 19-26 yr, n = 15) and two old groups (age range: 67-79 yr, n = 16). Each volunteer participated in three studies (n = 93 clamps). Hyperglycemic clamps were conducted at two doses [basal plasma glucose (G) + 5.4 mmol/L and G + 12.8 mmol/L] for 120 min. In the initial hyperglycemic clamp, only glucose was infused. In subsequent studies, GIP was infused at a final rate of 2 or 4 pmol/ kg(-1) x min(-1) from 60-120 min. Basal plasma insulin and GIP levels were similar in the young (41 +/- 6 and 51 +/- 6 pmol/L) and the old subjects (42 +/- 6 and 66 +/- 12 pmol/L) in all studies. First- and second-phase insulin responses were similar during the control study and during the first 60 min of each GIP infusion study in both groups. The 90-120 min GIP values were similar between groups and between hyperglycemic plateaus during the 2 and 4 pmol/kg(-1) x min(-1) GIP infusion (young: 342 +/- 28 and 601 +/- 44 pmol/L, old: 387 +/- 45 and 568 +/- 49 pmol/L). In response to the GIP infusions, significant increases in insulin occurred in young and old at both glucose levels (P < 0.01). The potentiation of the insulin response caused by GIP was greater in the young subjects than in the old, in the G + 5.4 mmol/L studies (P < 0.05). However, the insulin response to GIP was similar in both young and old during the G + 12.8 mmol/L clamps. The insulinotropic effect of the incretin was higher in the young and in the old, in the G + 12.8 mmol clamps, than in the G + 5.4 mmol/L clamps. We conclude that normal aging is characterized by a decreased beta-cell sensitivity to GIP during modest hyperglycemia, which may explain, in part, the age-related impairment in glucose-induced insulin release. We also find that the insulinotropic effect of GIP is increased with increasing levels of hyperglycemia.

Physiological importance of first-phase insulin release in elderly patients with diabetes

OBJECTIVE

To assess the physiological role of first-phase insulin release in obese elderly patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Moderately obese elderly patients (n = 14, mean age 77 +/- 2 years, BMI 28.4 +/- 0.7 kg/m2) with type 2 diabetes underwent three 180-min hyperglycemic clamp studies. In the control study, glucose alone was infused. In the first-phase study, human insulin was infused for the first 4 min at 12 mU/m2 to mimic first-phase insulin release. In the first-phase enhanced study, insulin was infused for the first 4 min at 24 mU.m-2 .min-1. Tritiated glucose methodology was used in all studies to measure glucose production and disposal rates.

RESULTS

Glucose values were similar in all studies. In the control study, first-phase insulin response was absent. The peak insulin response occurred at 4 min in the first-phase and first-phase enhanced studies, but insulin values were substantially higher in the latter study (528 +/- 40 vs. 340 +/- 24 pmol/l, P < 0.0001). Second-phase insulin responses were not different among the studies. Glucose production and disposal rates were not significantly different among the studies.

CONCLUSIONS

While absent first-phase insulin secretion is a marker of abnormal pancreatic function in obese elderly patients with type 2 diabetes, it is not important in the regulation of hepatic glucose output or peripheral glucose disposal.

Insulinotropic hormone glucagon-like peptide-1-(7-37) appears not to augment insulin-mediated glucose uptake in young men during euglycemia

Glucagon-like peptide-1 (GLP-1) is an intestinal insulinotropic hormone that augments insulin secretion in response to meals and lowers blood glucose levels in both type 1 and type 2 diabetic subjects. It has been proposed that a substantial component of the glucose-lowering effects of GLP-1 occurs via insulin-independent mechanisms. However, the interpretations of the studies have been controversial. This study was conducted to examine whether glucagon-like peptide (GLP-1) has an insulin-like effect during euglycemia. Nine young lean men (age, 25 +/- 1.4 yr; body mass index, 24.0 +/- 0.7 kg/m2) volunteered to participate in two euglycemic clamp studies (n = 18 clamps) for 120 min. The initial clamp was performed with a primed continuous infusion of GLP-1 at a final rate of 1.5 pmol/kg.min from 0-60 min. At 60 min, the GLP-1 infusion was terminated, and euglycemia was maintained from 60-120 min. After the GLP-1 study, each individual's plasma insulin level was measured. A second study was performed that was identical to the first, with the infusion of regular insulin in place of GLP-1. Insulin infusion rates were designed in each individual to simulate plasma insulin levels produced during the GLP-1 infusion. The rate of disappearance of glucose was calculated for each subject. Basal plasma insulin levels were similar between studies and averaged 49 +/- 5 pmol/L. Basal GLP-1 levels were also similar (6.0 +/- 1.0 pmol/L). In response to the GLP-1 infusion, although basal plasma glucose levels were clamped, significant increases in insulin occurred in all subjects (P < 0.001). With the nearly identical plasma insulin levels during the two studies (30-60 min levels: GLP-1 study, 151 +/- 48; insulin study, 146 +/- 31 pmol/L), the rate of disappearance of glucose progressively increased in response to both GLP-1 and insulin infusions, but was not significantly different between the studies. The design of the study necessitated conducting the GLP-1 study first, which may have been accompanied by a greater stress than the second study. We, therefore, measured cortisol levels. Basal cortisol (and ACTH) levels were not different. However, cortisol levels significantly increased during the GLP-1 infusions, and this was preceded by an increase in ACTH levels. Somatostatin levels were not different either basally or during the clamps. We conclude that in the euglycemic state, an acute infusion of GLP-1 does not have insulin-like effects in lean nondiabetic men. Intravenous administration of GLP-1 activates hypothalamic neuroendocrine neurons.

Resistive training maintains bone mineral density in postmenopausal women

We examined the effects of a total body resistive training program (RT) on total and regional bone mineral density (BMD) in older women. Twenty-seven healthy postmenopausal women (mean age 62 +/- 1 years) participated in a strength training program three times/week for 16 weeks. Strength was assessed before and after training by either one or three repetition maximum (1RM and 3RM) tests. Both upper and lower body strength significantly increased by 36-65% and 32-98%, respectively, after training. There was a small but significant decrease in body weight and body mass index after training (P < 0. 05), with no change in the waist-to-hip ratio. BMD, assessed by dual-energy X-ray absorptiometry, did not change over the duration of the training period in the anterioposterior spine (L2-L4), femoral neck, Ward's triangle, and greater trochanter. BMD of the total body, lateral spine (B2-B4), and the regions of the radius (1/3 radius and ultradistal radius) also did not fall in subsets of these women. Muscular strength of both the leg and chest press were significantly associated with L2-L4, femoral neck, Ward's triangle, and greater trochanter BMD (range r = 0.57-0.84, all P < 0.005). Markers of bone turnover, namely, bone-specific alkaline phosphatase, osteocalcin, and urinary aminoterminal cross-linked telopeptide of type I collagen did not change significantly. In conclusion, a resistive training program maintains BMD and improves muscular strength in healthy, older women. This may be important in preventing the negative health outcomes associated with the age-related loss of bone density.

Effects of hypertonicity on water intake in the elderly: an age-related failure

Dehydration is a common clinical syndrome associated with many illnesses and treatments in the elderly. Prior studies have shown diminished sensation of thirst during water deprivation. It is currently unclear whether age-related decreases in thirst perception impair the defense against a hyperosmolar challenge. To examine the impact of water ingestion during hyperosmolality, young and old subjects were allowed free access to water during and after an intravenous infusion of 5% hypertonic saline. Cumulative water intake and serum osmolality were compared between seven healthy young (20-28 yrs) and seven healthy old (72-89 yrs) volunteers during and following a two hour hypertonic saline infusion at a rate of 0.06 mlxkg(-1) min(-1). Serum osmolality and water intake were markedly different between the two groups. In the old group, serum osmolality increased by 17 mosmol/kg above baseline despite free access to water. In contrast, serum osmolality increased to only 7 mosmol/kg above baseline in the young group and did not rise further. By ingesting water, the young were able to defend against an additional increase in serum osmolality. The young drank approximately twice that of the old during the infusion period. Healthy older individuals drink less than young despite a significantly increased serum osmolality. This hypodipsia in old individuals increases their susceptibility to hypertonicity.

Increased disorderliness of basal insulin release, attenuated insulin secretory burst mass, and reduced ultradian rhythmicity of insulin secretion in older individuals

Insulin is secreted in a pulsatile fashion. Rapid pulses are considered to be important for inhibiting hepatic glucose output, and ultradian pulses for stimulating peripheral glucose disposal. Aging is characterized by a progressive impairment in carbohydrate tolerance. We undertook the current studies to determine whether alterations in pulsatile insulin release accompany the age-related changes in carbohydrate metabolism. Healthy young (n = 8; body mass index, 21 +/- 1 kg/m2; age, 24 +/- 1 yr) and old (n = 9; body mass index, 24 +/- 1 kg/m2; age, 77 +/- 2 yr) volunteers underwent two studies. In the first study, insulin was sampled every 1 min for 150 min, and pulse analysis was conducted using a recently validated multiparameter deconvolution technique. In the second study, insulin was sampled every 10 min for 600 min, and insulin release was evaluated by Cluster analysis. In the 150-min studies, insulin secretory burst mass (P < 0.05) and amplitude (P < 0.01) were reduced in the elderly. In addition, approximate entropy, a measure of irregularity or disorderliness of insulin release, was increased in the aged (P < 0.01). In the 600-min studies, interpulse interval was greater in the aged (P < 0.05), and burst number was less (P < 0.05). We conclude that normal aging is characterized by more disorderly insulin release, a reduction in the amplitude and mass of rapid insulin pulses, and a decreased frequency of ultradian pulses. Whether these alterations in insulin pulsatility contribute directly to the age-related changes in carbohydrate metabolism will require further study.

Glucagon-like peptide-1 can reverse the age-related decline in glucose tolerance in rats

Wistar rats develop glucose intolerance and have a diminished insulin response to glucose with age. The aim of this study was to investigate if these changes were reversible with glucagon-like peptide-1 (GLP-1), a peptide that we have previously shown could increase insulin mRNA and total insulin content in insulinoma cells. We infused 1.5 pmol/ kg-1.min-1 GLP-1 subcutaneously using ALZET microosmotic pumps into 22-mo-old Wistar rats for 48 h. Rat infused with either GLP-1 or saline were then subjected to an intraperitoneal glucose (1 g/kg body weight) tolerance test, 2 h after removing the pump. 15 min after the intraperitoneal glucose, GLP-1-treated animals had lower plasma glucose levels (9.04+/-0.92 mmol/liter, P < 0.01) than saline-treated animals (11.61+/-0.23 mmol/liter). At 30 min the plasma glucose was still lower in the GLP-1-treated animals (8.61+/-0.39 mmol/liter, P < 0.05) than saline-treated animals (10.36+/-0.43 mmol/liter). This decrease in glucose levels was reflected in the higher insulin levels attained in the GLP-1-treated animals (936+/-163 pmol/liter vs. 395+/-51 pmol/liter, GLP-1 vs. saline, respectively, P < 0.01), detected 15 min after glucose injection. GLP-1 treatment also increased pancreatic insulin, GLUT2, and glucokinase mRNA in the old rats. The effects of GLP-1 were abolished by simultaneous infusion of exendin [9-39], a specific antagonist of GLP-1. GLP-1 is therefore able to reverse some of the known defects that arise in the beta cell of the pancreas of Wistar rats, not only by increasing insulin secretion but also by inducing significant changes at the molecular level.

Metabolic correlates of obesity and radiographic features of knee osteoarthritis: data from the Baltimore Longitudinal Study of Aging

OBJECTIVE

To examine the relationship between metabolic correlates of obesity and radiographic knee osteoarthritis (OA).

METHODS

We included 464 Caucasian men and 275 Caucasian women aged 40 years and above who were participants in the Baltimore Longitudinal Study of Aging. Subjects had bilateral anteroposterior standing knee radiographs read for features of OA using Kellgren-Lawrence scales. Resting blood pressure, fasting lipids, 2 h oral glucose tolerance test, and anthropometric measurements were obtained at the same visit as the knee radiograph. Metabolic correlates of obesity were compared between subjects with Kellgren-Lawrence grade > or = 2 (definite knee OA) and grade 0 (normal radiograph) by sex.

RESULTS

Both men and women with knee OA had higher unadjusted systolic blood pressure than those with normal knee radiographs; unadjusted measures of glucose metabolism and lipids did not vary by presence of knee OA in men or women. After adjustment for age and obesity, systolic blood pressure did not vary by presence of knee OA in men. While women with knee OA did have higher adjusted mean systolic blood pressure than women with normal radiographs (127 +/- 2.4 vs 120 +/- 2.2 mm Hg; p = 0.04), both values were within normal range. Unexpectedly, men with knee OA had lower adjusted mean 2 h glucose levels compared to men without OA (7.5 +/- 0.2 vs 8.4 +/- 0.2 mmol/l; p = 0.01). Other adjusted variables did not differ by presence of knee OA.

CONCLUSION

These data do not support the hypothesis that metabolic correlates of obesity are independently associated with radiographic knee OA after adjustment for age and obesity.

The effects of acute hyperglycemia and hyperinsulinemia on plasma leptin levels: its relationships with body fat, visceral adiposity, and age in women

The acute effects of hyperglycemia and hyperinsulinemia on plasma leptin levels were determined in 42 highly trained women athletes (18-69 yr) and 14 sedentary control women (18-50 yr, body mass index < 25 kg/m2), using the glucose clamp technique. The relationships of body composition, physical fitness, age, and plasma leptin levels were examined in all participants. In addition, the effect of weight loss and aerobic exercise and plasma leptin levels were examined in 4 Newly diagnosed untreated noninsulin-dependent diabetes mellitus patients. The time course of plasma leptin levels changed little from basal during hyperglycemic (approximately 10 mmol/L) or hyperinsulinemic-euglycemic (400-3000 pmol/L) clamp studies in either athletes, controls, or noninsulin-dependent diabetes mellitus patients. A strong correlation between plasma leptin levels and fasting insulin was present (r = 0.60, P < 0.001). Plasma leptin and percent fat were higher in controls than athletes (12.6 vs. 4.0 ng/mL and 33.2 vs. 20.8%; both P < 0.001). The relationships between percent fat (dual-energy x-ray absorptiometry) or intraabdominal adipose tissue (computed tomography) and leptin for the entire group were highly significant (r = 0.70, r = 0.52; P < 0.001). When percent fat was controlled, the relationship between fasting insulin and leptin remained (P < 0.002). There was not a significant association between age and plasma leptin levels in a univariate analysis in this population. However, after adjustment for percent fat, a significant inverse relationship between age and leptin appeared (P < 0.05). The weight loss and aerobic exercise program resulted in an average 6 +/- 0.8 kg wt loss. Leptin levels decreased > 28% in each patient (P < 0.01). In conclusion, neither acute hyperglycemia or hyperinsulinemia affects plasma leptin levels. Percent fat is the strongest predictor of leptin levels, even in lean, highly trained women athletes.

A cross-sectional study on body composition and energy expenditure in women athletes during aging

The relationships between total and regional body composition, intra-abdominal adipose tissue (IAAT), resting metabolic rate (RMR), and substrate oxidation were examined in 43 highly trained women athletes and 14 sedentary women aged 18-69 yr. Athletes were divided into four groups (18-29, 30-39, 40-49, and 50-69 yr) and controls into two groups (18-29 and 40-50 yr). Maximal oxygen consumption declined with age (r = -0.52, P < 0.0005) in the athletes and was higher in all groups of athletes than in controls (P < 0.0001). No differences in percent fat and fat-free mass (FFM) were found between the youngest and oldest athletes. Although body mass index was < 25 kg/m2 in all subjects, percent body fat and total fat mass were higher in controls than in athletes for both young and older women (all P < 0.05). FFM was higher in young athletes than in young controls (P < 0.0001). Despite similar percent fat among athletes, IAAT increased with age (r = 0.75, P < 0.0001), but subcutaneous abdominal fat and sagittal diameter did not. IAAT and subcutaneous abdominal fat were also higher in young controls than in young athletes and in older controls than in older athletes (all P < 0.005). Age and FFM were independent predictors of the decline in RMR in the athletes. Fat oxidation (g/day) was highest in the youngest athletes and declined with age (r = -0.47, P < 0.005). We conclude that intense chronic exercise in women athletes prevented the decline in FFM with age. Endurance-trained women have low IAAT stores, which may potentially reduce subsequent risk associated with the metabolic syndrome.

Pancreatic polypeptide administration improves abnormal glucose metabolism in patients with chronic pancreatitis

Chronic pancreatitis (CP) is associated with lowered plasma levels and a blunted nutrient-induced release of pancreatic polypeptide (PP). To investigate the possible role of PP on glucose metabolism, we studied male patients with documented CP (n = 5) and obesity-matched control subjects (NL) (n = 6). Hepatic glucose production (HGP) and overall glucose disposal rates were determined by [3-3H]glucose infusion during a hyperinsulinemic-euglycemic clamp during three separate admissions. Basal rates of HGP were higher in CP patients. In response to an infusion of insulin (60 pmol.m-2.min-1), HGP fell 91 +/- 5% in NL subjects but only 68 +/- 8% in CP subjects (P < 0.05). One month later, the clamp was repeated during the final 2 h of an 8-h infusion of bovine PP (2 pmol.kg-1.min-1). HGP before the insulin infusion and its subsequent suppression (NL: 83 +/- 5%; CP: 86 +/- 15%) were nearly identical between groups. In follow-up studies 1 month after the PP infusion, HGP both basally and in response to insulin alone were similar to the first study. During oral glucose tolerance tests (OGTT) performed 18 h after the PP infusion, subjects with normal (n = 7) baseline OGTT responses showed no effect. All patients with diabetic (n = 3) or nondiagnostic (n = 1) OGTT responses, however, demonstrated lowered mean plasma glucose levels (approximately -2.3 mmol/L; range: -0.6 to -7.2 mmol/L). OGTTs repeated 1 month after the PP treatment showed a return to pretreatment responses. We conclude that chronic pancreatitis accompanied by PP deficiency is associated with partial hepatic resistance both in the basal state and in response to hyperinsulinemia. This impairment is reversed after iv PP administration. PP deficiency may therefore play a role in the development of pancreatogenic diabetes caused by pancreatic injury.

Resistive training increases insulin action in postmenopausal women

BACKGROUND

This study examined the effects of 4 months of resistive training in postmenopausal women on glucose metabolism and peripheral tissue sensitivity to endogenously released insulin.

METHODS

Thirteen moderately obese (30-49% body fat) postmenopausal women (50-65 years) participated in the study. The six more obese women were enrolled in the resistive training with weight loss (RT & WL) program, while the remainder participated in resistive training alone (RT). beta-cell sensitivity to glucose and peripheral tissue sensitivity to endogenously released insulin were examined during hyperglycemic clamps (7.9 mmol/L above basal) before and after the intervention(s).

RESULTS

The RT program resulted in a significant improvement in upper and lower body strength (p < .01) in all subjects. Body weight, fat mass, and percent body fat decreased with RT & WL (p < .001), but did not change with RT alone. There was no change in fat-free mass or maximal oxygen consumption after the intervention(s). Insulin response during the last 20 min of the 2 hr hyperglycemic clamps (7.9 mmol/L above basal plasma glucose levels) decreased after the intervention(s) in the entire group by 29% (p < .01), but decreased more in the group that lost weight (43%, p < .05) than in women who remained weight stable (16%, p = .05). Glucose utilization did not change.

CONCLUSION

RT alone, or in combination with WL, increases insulin action and reduces hyperinsulinemia in postmenopausal women. This suggests that RT has the potential to ameliorate and perhaps prevent the development of insulin resistance and may reduce the risk for glucose intolerance and non-insulin-dependent diabetes mellitus (NIDDM) in postmenopausal women.

The effect of age on insulin resistance and secretion: a review

Aging is associated with an increased incidence of hypertension, noninsulin-dependent diabetes mellitus, and coronary heart disease. Because these conditions often cluster in the same individuals, there has been speculation that a common mechanism is responsible for all of these pathological states. Both epidemiological and clinical research has shown that insulin resistance and/or hyperinsulinemia are associated with glucose intolerance, dyslipidemia (high plasma triglyceride and low high-density lipoprotein-cholesterol levels), and higher systolic and diastolic blood pressures. Therefore, insulin resistance and hyperinsulinemia have been proposed as the causal link among the elements of the cluster mentioned above, now most commonly referred to as the insulin resistance syndrome, syndrome X, or the metabolic syndrome. The elderly are more glucose intolerant and insulin-resistant, but it remains controversial whether this decrease in function is an inevitable consequence of "biological aging" or the result of what might be referred to as environmental or lifestyle variables: increased obesity, a detrimental pattern of fat distribution, or physical inactivity that usually accompany age. All of these modifiable environmental factors have also been shown to result in increases in insulin resistance and hyperinsulinemia and are risk factors for the development of the diseases of the metabolic syndrome. Recent interventional studies that have attempted to reverse these conditions in the elderly have shown improved insulin sensitivity, and glucose tolerance. Insulin secretion, on the other hand, seems to decrease with age even after adjustments for differences in adiposity, fat distribution, and physical activity. This may be responsible for the glucose intolerance in the very old even after improvements have been made in their lifestyle variables.

Atrial natriuretic peptide levels in the elderly: differentiating normal aging changes from disease

BACKGROUND

Atrial natriuretic peptide (ANP) levels increase with advancing age and in patients with cardiac dysfunction. Previous studies have failed to differentiate the elevated ANP levels of normal aging from those of cardiac disease.

METHODS

To differentiate the increased ANP levels seen in normal aging from that of disease, fasting supine ANP was measured in healthy young (n = 24), healthy old (n = 90), and clinically stable but cardiovascularly diseased old (n = 269) residents of a life care facility. ANP levels were correlated with physical exam findings, blood chemistries, measures of physical and cognitive function, and medications.

RESULTS

ANP levels were almost fourfold higher in the healthy elderly than in the young (11.4 +/- 1.1 (SEM) vs 3 +/- 0.3 pmol/L, p < .01), and two-and-one-half times higher in the cardiovascular-diseased elderly than the healthy elderly (29 +/- 1.9 vs 11.4 +/- 1.1 pmol/L, p < .01). An ANP value of 21 pmol/L has a sensitivity of 83% and specificity of 52% in distinguishing those elders classified as healthy from those classified as having chronic cardiovascular disease. ANP levels had positive univariate correlation with age (even from 70 to 102 years) and systolic blood pressure. ANP rose progressively with increasing numbers of markers of cardiovascular comorbidity. ANP was higher in subjects with jugular venous pressure > 10 cm, presence of a third heart sound, peripheral edema, artificial cardiac pacemaker, atrial arrhythmias, and in those taking digoxin, diuretics, or nitrates. On multivariate analysis independent predictors of ANP levels were, in descending order, nitrates, age, diuretics, and atrial arrhythmias.

CONCLUSION

These data suggest that ANP levels greater than 21 pmol/L are associated with cardiovascular comorbidity in a clinically stable elderly cohort.

In praise of the hyperglycemic clamp. A method for assessment of beta-cell sensitivity and insulin resistance

The most widely used methods for the assessment of beta-cell response and peripheral tissue sensitivity to insulin include the oral glucose tolerance test (OGTT), the frequently sampled intravenous glucose tolerance test, and the hyperinsulinemiceuglycemic clamp technique. During an OGTT, glucose levels increase after a variable lag period, then reach a peak and fall variably among individuals. The response even varies in the same subject upon repeat testing. A more reproducible glucose curve is achieved with an intravenous glucose tolerance test in which the plasma glucose levels rise rapidly to a very high level and fall exponentially. In neither of the two methods is a steady-state glucose level achieved. In the hyperinsulinemic-euglycemic clamp technique, a steady-state glucose level can be maintained at any level of hyperinsulinemia. However, an assessment of beta-cell sensitivity is not obtained. The less used hyperglycemic clamp technique can assess beta-cell sensitivity as well as peripheral tissue sensitivity. Moreover, a measure of glucose effectiveness or non-insulin-mediated glucose uptake can also be determined. With this technique the beta-cells of all subjects are stimulated with the same arterial glucose concentration, thus enabling assessment of beta-cell response to identical plasma glucose levels. Comparison of responses to stable hyperglycemic stimuli can be made in glucose-tolerant and -intolerant states with the addition of various substances, either alone or in combination. The use of the hyperglycemic clamp and several of its variant forms is reviewed as an alternative method for assessment of glucose homeostasis.

Insulin response during the oral glucose tolerance test: the role of age, sex, body fat and the pattern of fat distribution

To clarify their primary roles on insulin response to oral glucose, age and sex differences in body composition should be taken into account. Oral glucose tolerance tests were performed on 472 men and 299 women of the Baltimore Longitudinal Study of Aging, ranging in age from 20 to 96 years. Subjects who were taking medications or had any diseases which could affect glucose tolerance were excluded. In addition to insulin and glucose values for the glucose tolerance test, we calculated body mass index (BMI), percentage body fat from skinfolds (% Body Fat), waist hip ratio (WHR), mean glucose level over the 2-hour test (GM), the basal insulin (IO), and the mean insulin response over the 2-hour test (IM). There was no significant sex difference in mean age, but men had significantly higher BMI (25.6 vs 24.0 kg/m2), WHR (0.93 vs 0.76), and GM (8.5 vs 7.7 mM), while % Body Fat was lower (25% vs 33%). Unadjusted IO and IM levels were significantly higher in men than in women (51 vs 44 and 303 vs 231 pM--antilogs of log-normalized values). Insulin levels, adjusted for differences in age, % Body Fat, WHR, and GM by analysis of covariance, however, showed no sex differences (49 vs 46 and 282 vs 257 pM). Adjusted insulin levels declined significantly with age; IM fell progressively from 323 pM in 20 to 39-year olds, 267 pM in 40 to 59-year, 253 pM in 60 to 79-year, and 228 pM in 80 to 96-year olds (p < 0.01). We conclude that the sex differences in insulin levels are explained by differences in body habitus and post-load glucose levels, but that insulin levels decline with age per se.

Resistive training increases fat-free mass and maintains RMR despite weight loss in postmenopausal women

Percent body fat increases with age and is often accompanied by a loss in muscle mass, strength, and energy expenditure. The effects of 16 wk of resistive training (RT) alone or with weight loss (RTWL) on strength (isokinetic dynamometer), body composition (dual-energy X-ray absorptiometry), resting metabolic rate (RMR) (indirect calorimetry), and sympathetic nervous system activity (catecholamines) were examined in 15 postmenopausal women (50-69 yr). RT resulted in significant improvements in upper and lower body strength in both groups (P < 0.01). The nonobese women in the RT group (n = 8) did not change their body weight or fat mass with training. In the obese RTWL group (n = 7), body weight, fat mass, and percent body fat were significantly decreased (P < 0.001). Fat-free mass and RMR significantly increased with training in both groups combined (P < 0.05). There were no significant changes in resting arterialized plasma norepinephrine or epinephrine levels in either group with training. RT increases strength with and without weight loss. Furthermore, RT and RTWL increase fat-free mass and RMR and decrease percent fat in postmenopausal women. Thus, RT may be a valuable component of an integrated weight management program in postmenopausal women.

Long-term effects of a high-carbohydrate diet and exercise on insulin action in older subjects with impaired glucose tolerance

Carbohydrate metabolism was assessed in 20 glucose-intolerant subjects before and after 12 wk on a high-carbohydrate diet (HC) or the diet combined with exercise training (HC-EX). The diet provided 60% of energy as carbohydrate and 20% as fat. Neither treatment altered fasting glucose or insulin concentrations or their response to a meal. During a glucose clamp (216 pmol insulin/L) glucose disposal increased from 13.2 +/- 0.83 to 14.6 +/- 0.83 mumol.kg fat-free mass-1.min-1 (P < 0.05) in both groups. During more pronounced hyperinsulinemia (654 pmol/L) glucose disposal did not change significantly (49.9 +/- 3.8 to 50.7 +/- 3.8 mumol.kg fat-free mass-1.min-1). Muscle glycogen increased in the HC-EX group (78.5 +/- 8.1 to 161.1 +/- 15.7 mmol glucose/kg muscle), with no changes in the HC group. These results do not support the recommendation to increase the dietary carbohydrate content for improving postprandial glucose metabolism or insulin action in glucose-intolerant adults unless combined with exercise training, which promotes muscle glycogen storage.

Hypotensive response to atrial natriuretic peptide administration is enhanced with age

BACKGROUND

Plasma levels of atrial natriuretic peptide (ANP) increase with age. To test the hypothesis that the cardiovascular response to ANP is age dependent and to examine the role of the increased levels of ANP in the hypotensive response to orthostatic challenge, we compared the hemodynamic response of young and elderly subjects to ANP infusion and orthostatic challenge.

METHODS

Blood pressure, heart rate, forearm cutaneous resistance, plasma ANP, and plasma norepinephrine were measured in the supine position and following upright tilt before and after a 60-minute infusion of atrial natriuretic peptide (0.05 microgram/kg/min) in 7 young (27 +/- 4 years) and 5 elderly (74 +/- 4 years) normotensive, healthy subjects.

RESULTS

Prior to ANP infusion, the response to upright tilt was similar in both groups. Infusion of ANP produced similar steady state plasma levels of ANP in both groups (young: 435 +/- 49 pg/ml; elderly: 429 +/- 32 pg/ml). Supine systolic blood pressure decreased by 4 +/- 2 mmHg in the young subjects and by 18 +/- 8 mmHg in the elderly subjects after infusion (p < .08). In contrast, changes in supine heart rate, forearm cutaneous resistance, and plasma norepinephrine were similar in both groups (delta heart rate: young +5 +/- 3 beats/min, elderly +4 +/- 2 beats/min; delta forearm cutaneous resistance: young -38 +/- 9%, elderly -40 +/- 6%; delta norepinephrine: young +55 +/- 11%, elderly: +43 +/- 13%). ANP infusion abolished the vasoconstrictor response normally associated with orthostatic challenge in both groups, despite a significant release of catecholemines and an enhanced heart rate response. This resulted in significant systolic blood pressure reduction in both young (-7 +/- 2 mmHg, p < .05) and elderly subjects (-16 +/- 4 mmHg, p < .05). The drop in systolic blood pressure in response to upright tilt and ANP infusion was four times larger in the elderly subjects (change from pre-ANP level: young -8 +/- 3 mmHg, elderly -32 +/- 5 mmHg, p < .005).

The insulinotropic actions of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (7-37) in normal and diabetic subjects

Despite similar glycemic profiles, higher insulin levels are achieved following oral versus intravenous administration of glucose. This discrepancy is due to the incretin effect and is believed to be mediated via stimulation of beta-cells by hormone(s) released from the gut. The leading gut hormone candidates are glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide (GLP-1). To determine the relative insulinotropic activity of these peptides, we infused GLP-1(7-37) and GIP into normal subjects and patients with non-insulin dependent diabetes mellitus (NIDDM). In normal subjects during euglycemia, GLP-1(7-37) stimulated insulin release, whereas GIP did not. Using the Andres clamp technique, we established stable hyperglycemia for 2 h (5.4 mmol/l above the basal level). During the second hour, either GIP, GLP-1(7-37), or both were infused in normal healthy volunteers and in patients with NIDDM. In normal subjects, at a glucose level of 10.4 mmol/l, the 90-120 min insulin response was 279 pmol/l. GIP at a dose of 1, 2 or 4 pmol/kg/min augmented the 90-120 min insulin response by 69, 841 and 920 pmol/l, while GLP-1(7-37), at a dose of 1.5 pmol/kg/min augmented the insulin response by 2106 pmol/l. When both hormones were administered simultaneously, the augmentation was additive--2813 pmol/l. In the diabetic subjects, GIP had no effect, while GLP-1(7-37) augmented the insulin response by 929 pmol/l. We conclude that in normal healthy subjects, GLP-1(7-37), on a molar basis, is several times more potent than GIP at equivalent glycemic conditions. The additive insulinotropic effect suggests that more than one incretin may be responsible for the greater insulin levels observed following oral administration of glucose compared to the intravenous route. In NIDDM, GIP had no insulinotropic effect, while GLP-1(7-37) had a marked effect. This suggests that GLP-1(7-37) may have therapeutic potential as a hypoglycemic agent in NIDDM patients.

Splanchnic neural regulation of somatostatin secretion in the isolated perfused human pancreas

OBJECTIVE

The somatostatin-secreting delta cells in the islets of Langerhans appear to be regulated by neural mechanisms that have not been defined clearly. In this study, the celiac neural bundle of the human pancreas was electrically stimulated in the presence and absence of selective neural antagonists.

SUMMARY BACKGROUND DATA

The authors previously reported on studies of the splanchnic neural regulation of insulin, glucagon, and pancreatic polypeptide secretion. In these studies, alpha-adrenergic fibers appeared to have a predominant effect, strongly inhibiting the secretion of insulin, glucagon, and pancreatic polypeptide secretion. Cholinergic fibers appeared to stimulate strongly, although beta-adrenergic fibers weakly stimulated, the secretion of these hormones. Investigations of neural regulatory mechanisms governing human somatostatin release in vitro have not been previously reported.

METHODS

Pancreata were obtained from eight cadaveric organ donors. The isolated perfused human pancreas technique was used to assess the regulation of somatostatin secretion by the various neural fibers contained within the celiac plexus. The secretory response of somatostatin was examined in the presence of 16.7 mmol/L glucose, with and without neural stimulation, and specific neural antagonists.

RESULTS

The basal somatostatin secretion was 88 +/- 26 fmol/g/min and increased 131 +/- 23% (n = 8, p < 0.01) in response to 16.7 mmol/L glucose. The augmentation seen with glucose was inhibited 66 +/- 22% (n = 8, p < 0.05) during celiac neural bundle stimulation. Alpha-adrenergic blockade resulted in a 90 +/- 30% (n = 6, p < 0.01) augmentation of somatostatin release. Beta-adrenergic blockade caused a 13 +/- 2% (n = 6, p < 0.05) suppression of somatostatin release. Complete adrenergic blockade resulted in a 25 +/- 23% (n = 5, p = not significant) inhibition of somatostatin release. Cholinergic blockade resulted in a 40 +/- 10% (n = 6, p < 0.02) suppression of somatostatin release.

CONCLUSIONS

The predominant effect of celiac neural bundle stimulation was inhibition of somatostatin secretion through an alpha-adrenergic effect. Beta-adrenergic fibers stimulate somatostatin secretion; cholinergic fibers have a negligible effect on somatostatin secretion. These data suggest that the splanchnic innervation of the pancreas has a potent regulatory role in somatostatin release in this in vitro human model.

Effects of recombinant human IGF-I on glucose and leucine kinetics in men

To examine the effects of recombinant human (rh) insulin-like growth factor I (IGF-I), insulin, and saline on metabolic parameters, we studied 20 young nonobese healthy men. Euglycemic clamps with 240-min IGF-I infusions at two doses (49 and 33 pmol.kg-1 x min-1, n = 8 and 12 subjects) were performed and compared with hyperinsulinemic-euglycemic clamps (2.25 pmol.kg-1 x min-1, n = 9). Leucine and glucose kinetics were examined with L-[1-13C]leucine and [3-3H]glucose. Glucose rate of appearance (Ra) declined equivalently in the 49 pmol.kg-1.min-1 IGF-I and insulin clamps but remained at basal levels during the 33 pmol.kg-1 x min-1 IGF-I infusions. In contrast, Rd of glucose was increased by 176% in the 49 pmol.kg-1 x min-1 IGF-I and 78% in the 33 pmol.kg-1 x min-1 IGF-I infusions. Furthermore, to prevent hypoglycemia after the termination of both rhIGF-I infusions, it was necessary to infuse glucose for an additional 2-20 h. Ra of leucine was suppressed significantly by both IGF-I and insulin, whereas leucine oxidation was not affected by either hormone. Therefore, the rate of disappearance of leucine expressed as the difference between Ra and oxidation rates was significantly reduced in all clamps. In addition, IGF-I significantly suppressed beta-cell secretion without affecting the other glucoregulatory hormones. In contrast to insulin, IGF-I had no apparent effect on lipolysis, as measured by changes in nonesterified fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperinsulinemia after pancreatic transplantation. Prediction by a novel computer model and in vivo verification

OBJECTIVE

The authors evaluated systemic venous insulin release as a cause of the hyperinsulinemia (HNS) associated with pancreatic transplantation (PTX) with respect to the mechanism and metabolic consequences.

SUMMARY BACKGROUND DATA

Many investigators believe the postoperative anatomy associated with common PTX techniques to be the sole cause of the two- to threefold posttransplantation HINS. However, this concept remains to be conclusively proved and characterized quantitatively.

METHODS

The authors used three approaches to achieve their objectives. First, a computer model was generated based on established data concerning blood flow and tissue insulin extraction to determine whether it was mathematically possible for HINS to be caused by systemic insulin release. Second, HINS clamps were applied to normal dogs using the Andres clamp technique to quantify the in vivo differences in peripheral insulin levels and the metabolic consequences of systemic versus portal insulin infusion. Third, prolonged insulin half-life was evaluated as a possible mechanism of HINS from systemic insulin release by determination of biexponential rates of plasma disappearance from an endogenous pulse of insulin in surgically induced dog models of systemic and portal insulin release.

RESULTS

First, the computer model calculated a 1.4- to 2.9-fold increase in peripheral venous insulin levels with systemic versus portal insulin release, verifying mathematically the concept of HINS resulting from systemic insulin release. Second, the actual systemic insulin infusion produced a 1.3- to 1.4-fold increase in peripheral venous insulin levels compared with portal infusion (p < 0.05). No significant differences in hepatic glucose output, total glucose disposal, or glucose infusion requirements were seen. Third, although the basal insulin level was twofold higher in the surgically induced animal models with systemic insulin release (p < 0.003), there were no differences in biexponential insulin clearance parameters.

CONCLUSIONS

The HINS produced by systemic insulin release did not significantly alter glucose metabolism and was not the result of altered peripheral insulin clearance parameters. In vivo systemic venous insulin infusion studies produce HINS, but not to the degree calculated by mathematic modeling or that occurs after clinical PTX, making it likely that other factors also play a role in the HINS after PTX.

The effect of age on insulin response and glucose utilization during four hyperglycemic plateaus

In order to evaluate the potential role of insulin insensitivity as a cause of the glucose (G) intolerance of aging, we performed 230 hyperglycemic clamps, 85 on young (Y, 24 to 39 years), 47 on middle age (M, 40 to 59 years), and 98 on old (O, 60 to 90 years) carefully screened subjects of the Baltimore Longitudinal Study of Aging. The 2-h plasma G levels on an oral glucose tolerance test (OGTT) were < 7.8 mmol/l in Y and M and < 10 mmol/l in old; the latter group was further dichotomized at 7.8 mmol/l into a "normal" group, ON, and an impaired group, OI. Four hyperglycemic plateaus were created: 3.0, 5.4, 7.9, and 12.8 mmol/l above basal. Three measures of glucose tolerance--1) G at 2 h after glucose ingestion, 2) glucose utilization, M, at each hyperglycemic plateau, and 3) glucose decay constant, K, obtained at the conclusion of each clamp--showed the best performance in the young group (Y > M = ON > OI). Despite these differences in glucose tolerance, plasma insulin responses (I) during the clamp were not significantly different except that ON < Y at the basal + 12.8 plateau (300 +/- 42 vs. 456 +/- 48 pmol/l, p < 0.01). Insulin-dependent glucose uptake, a measure of tissue sensitivity to insulin, was decreased in the old-impaired group at every plateau except the highest. We conclude that healthy, active older subjects showed moderate intolerance to oral and IV glucose and that the mechanism of this physiological aging process is most likely decreased insulin sensitivity.

Exercise increases muscle GLUT-4 levels and insulin action in subjects with impaired glucose tolerance

A decline in insulin sensitivity is associated with aging, inactivity, and obesity. The effects of exercise training on glucose homeostasis independent of weight loss in older glucose-intolerant individuals are not well established. We examined the effects of exercise training on oral glucose tolerance, insulin action, and concentration of the GLUT-4 glucose transporters in skeletal muscle. Exercise training at 50 and 75% of heart rate reserve was performed for 12 wk in 18 individuals (age = 64 +/- 2, body fat = 37.0 +/- 1.5%). Peripheral insulin action was determined 96 h after the last exercise bout using a two-step hyperinsulinemic-euglycemic glucose clamp (insulin = 192 and 708 pmol/l). Percent body fat and fat-free mass (FFM) were unchanged with training. Diet composition, assessed by diet record, did not change over the 12 wk. Improved oral glucose tolerance was observed, as exhibited by lower plasma glucose concentrations after training (P < 0.05), whereas plasma insulin response remained unchanged. The rate of glucose disposal was unchanged during the low insulin concentration but increased 11.0% at the high insulin concentration (P < 0.05) after training (54.4 +/- 4.4 vs. 60.4 +/- 5.5 mumol.kg FFM-1.min-1). Skeletal muscle glycogen and GLUT-4 concentration increased 24 and 60%, respectively, with training. There was no direct relationship between the change in GLUT-4 protein and the change in glucose disposal rate. These findings demonstrate that chronic exercise training without changes in body composition improves peripheral insulin action in subjects with impaired glucose tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-mediated pseudoacromegaly: clinical and biochemical characterization of a syndrome of selective insulin resistance

We have performed clinical, physiological, in vitro biochemical and genetic studies of a patient with severe insulin resistance associated with the phenotype of "pseudoacromegaly," defined as the presence of acromegaloid features in the absence of elevated levels of GH or insulin-like growth factor-I (IGF-I). Despite marked hyperinsulinemia, insulin and IGF-I binding to circulating blood cells and cultured skin fibroblasts was normal. Insulin and IGF-I-stimulated autophosphorylation of their respective receptors in cultured skin fibroblasts was also normal. However, neither insulin nor IGF-I were able to stimulate 2-deoxy D-glucose uptake by cultured skin fibroblasts. In contrast, the ability of insulin and IGF-I (or IGF-II) to stimulate amino acid uptake and thymidine incorporation into DNA was not impaired. This unique discordant signaling defect through both insulin and IGF-I receptors appeared not to be the consequence of altered expression or primary structure of the insulin receptor or the GLUT-4 glucose transporter, as assessed by several genetic and biochemical techniques. GLUT-4 expression in muscle was normal on Western blots, and SSCP screening of all 11 exons of the gene for nucleotide variation revealed no variations from normal. DNA sequencing and SSCP screening of exons 2-22 of the insulin receptor gene revealed only one variation predicted to alter the amino acid sequence (Val985-->Met). No functional differences between Met985 and wild-type human insulin receptors were evident in studies performed with Chinese hamster ovary cell transfectants that overexpress either receptor. This data combined with our previously published epidemiological data concerning the frequency of the Met985 allele, indicate that this variant insulin receptor is not responsible for the insulin resistant glucose uptake or the clinical syndrome of pseudoacromegaly. We conclude that: 1) The molecular lesion responsible for the selective biochemical defect in this individual appears to involve a signaling intermediate required for insulin and IGF-I regulation of glucose transport, and/or an effector mechanism operative in this process. 2) Cells derived from this patient may be a valuable tool in the search for such molecular mechanisms. 3) The Met985 allele is a relatively common variant which has no demonstrable adverse consequences for insulin receptor function. 4) Pseudoacromegaly can be viewed as the expected result of hyperinsulinemia driving the unopposed mitogenic and anabolic actions of insulin.

The pituitary-adrenal glucocorticoid response is altered by gender and disease

BACKGROUND

This study examined the role of age, gender, and disease in the regulation of the pituitary-adrenal axis.

METHODS

Serum cortisol and immunoreactive corticotropin (ACTH) were measured for five hours after a bolus administration of ovine corticotropin releasing hormone (oCRH, 1 microgram/kg) during three separate investigations: 1) age: comparison was made between young men (26 +/- 3 years [means +/- SE]) vs old men (73 +/- 2 years); 2) gender: comparison between old men (73 +/- 2 years) vs old women (68 +/- 3 years); and 3) disease: comparison was made between healthy subjects (no disease, 44 +/- 6 years) vs subjects with a chronic stable disease (diabetes mellitus [DM] or hypertension [HBP], 48 +/- 5 years).

RESULTS

Basal concentrations of cortisol were significantly higher in younger men (127 +/- 17 vs 74 +/- 11 nmol/L, p < .03), as were peak cortisol levels (499 +/- 30 vs 397 +/- 36 nmol/L, p < .05, ANOVA). However, the 5-hour nadir of cortisol, area under the curve, delta area under the curve, time to peak, and variability of the responses during three separate admissions were similar in young and old. When the responses to oCRH in old men and old women were compared, old women had significantly higher basal values of cortisol (163 +/- 30 vs 75 +/- 11 nmol/L, p < .02), peak levels of cortisol (p < .0001) and the 5-hour nadir of cortisol was 124% higher in older women (657 +/- 61 vs 298 +/- 50 nmol/L, p < .0006). When the response to oCRH was examined in healthy subjects and subjects with disease (DM and HBP), men with disease had a peak cortisol response 40% higher (p < .003) than healthy men and the level remained 85% higher (p < .0005) at 5 hours. The responses of ACTH to oCRH were not different in the groups being compared for any study. The variation of cortisol response could be explained by the peak cortisol levels (R2 = .718, p < .0001), with a small significant contribution from disease (R2 = .013, p < .002). In summary, the adrenal response to oCRH remained elevated throughout the period of study in elderly women. In addition, subjects with a chronic disease (DM and HBP) had a greater response of cortisol to oCRH compared with healthy subjects.

CONCLUSION

This study demonstrated that the pituitary-adrenal response to oCRH in the elderly is gender specific and chronic stable disease (DM and HBP) is associated with altered regulation of the adrenal glucocorticoid response.

An epidemiological test of the hyperinsulinemia-hypertension hypothesis

The association between hyperinsulinemia and hypertension was tested in a population of 421 men and 228 women from the Baltimore Longitudinal Study of Aging. Subjects are white, middle-class, generally healthy, community-dwelling volunteers who ranged in age from 17-95 yr. Those with disease or medications known to influence any of the studied variables were excluded from the analysis. Twenty-five percent of the subjects were borderline or hypertensive [systolic blood pressure (BP) > or = 140 or diastolic BP > or = 90 mm Hg]. Standard oral glucose tolerance tests were performed; the logarithms of the fasting insulin level and insulin area were used in the analyses. In addition, body mass index and percent body fat (from age and skinfold thickness equations) and waist hip ratio were computed. In simple correlations, systolic BP and diastolic BP were statistically significantly related to insulin levels (only 1-4% of the variance was explained). Since age, body fat, fat distribution, insulin levels, and BP were highly intercorrelated, insulin and blood pressure correlations were examined after controlling for the confounding variables. Correlations of BP and insulin levels adjusted for age, body fat, and fat distribution were entirely nonsignificant. In this large noninterventive population study, the hyperinsulinemia-hypertension hypothesis is not confirmed.

Effect of glucose, insulin, and hypertonicity on atrial natriuretic peptide levels in man

To determine the effects of hyperglycemia and hyperinsulinemia on atrial natriuretic peptide (ANP) levels in man, we studied normotensive nondiabetic volunteers (aged 25 to 63 years) during infusion of insulin and/or 20% dextrose (glucose clamp technique) to achieve three different states of "glycemia/hyperinsulinemia," as follows: (1) euglycemia for 2 hours during infusion of insulin (80 mU.m-2.min-1), resulting in plasma insulin levels of approximately 1,200 pmol/L (n = 9); (2) moderate stable hyperglycemia at a level of 11 mmol/L (198 mg/dL) for 2 hours, with infusion of glucagon-like peptide-1 (7-37) amide (GLP-1) during the second hour, which increased endogenous insulin responses to approximately 2,100 pmol/L (n = 9); and (3) marked stable hyperglycemia at a level of 18.5 mmol/L (330 mg/dL) for 2 hours, with endogenous insulin responses of approximately 720 pmol/L (n = 9). In addition, six patients with non-insulin-dependent diabetes mellitus were studied with the GLP-1 protocol at a hyperglycemic level of 14.5 mmol/L (261 mg/dL). In normal subjects, plasma ANP levels increased significantly from 3.0 +/- 0.4 to 4.6 +/- 0.8 pmol/L during marked hyperglycemia, but did not change during euglycemia or moderate hyperglycemia despite higher insulin levels (P < .01, ANOVA). Sodium excretion rates were also highest during the marked hyperglycemic study (125 +/- 14 v 91 +/- 7 v 74 +/- 10 mumol/min, P < .05, marked v moderate hyperglycemia v euglycemia). In diabetic subjects, ANP levels increased significantly from 12.5 +/- 4.1 to 21.1 +/- 5.0 pmol/L during hyperglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of glyburide on beta-cell sensitivity to glucose-dependent insulinotropic polypeptide

OBJECTIVE

To assess whether treatment with glyburide alters beta-cell sensitivity to GIP in NIDDM patients.

RESEARCH DESIGN AND METHODS

We studied 5 untreated NIDDM patients in a meal study (Ensure, 240 ml/M2) and a 2-h hyperglycemic glucose clamp study (glucose 5.4 mM above fasting). From 60 to 120 min of the clamp, GIP was infused in a primed continuous manner at a rate of 2 pmol.kg-1 x min-1. Subjects then were treated with glyburide. After they had been on a stable dose of medication for 1 mo, the meal study and glucose clamp studies were repeated.

RESULTS

In response to treatment, a decrease in fasting glucose and an increase in weight was observed (12.8 +/- 1.8 vs. 8.5 +/- 0.8 mM and 74.3 +/- 6.3 vs. 76.1 +/- 6.3 kg, respectively, P < 0.05). In response to the meal study, the AUC for glucose was less, for insulin was increased, and for GIP was unchanged after treatment (16.9 +/- 2.1 vs. 12.6 +/- 6.9 mM, P < 0.05; 161 +/- 47 vs. 242 +/- 60 pM, P < 0.05; and 199 +/- 22 vs. 219 +/- 18 pM, respectively). During the hyperglycemic clamp, steady-state glucose and 90- to 120-min GIP values were equivalent before and after treatment (18.0 +/- 1.3 vs. 18.3 +/- 1.3 mM and 302 +/- 59 vs. 298 +/- 37 pM, respectively). The 90-120 min insulin responses to the hyperglycemic clamp were greater after therapy (123 +/- 37 vs. 283 +/- 80 pM, P < 0.05) reflecting increased beta-cell responses to GIP.

CONCLUSIONS

We conclude that glyburide enhances beta-cell sensitivity to GIP.