Relationship between fasting plasma insulin and ambulatory blood pressure in young, non-obese normotensive subjects

Insulin resistance, hyperinsulinemia, and hypertension: an epidemiologic approach

During the past 2 decades, numerous experimental studies have provided solid evidence for the existence of several mechanisms connecting insulin resistance and hyperinsulinemia with blood pressure elevation, within the context of the cardiometabolic syndrome. In parallel, several groups have attempted to examine these associations from an epidemiologic perspective, but relevant findings were less consistent and not extensively discussed. Hyperinsulinemia has been associated with high blood pressure levels and hypertension development in cross-sectional, case-control, and prospective cohort studies. An association between insulin resistance and hypertension is also evident in existing studies, but prospective data on this relation are limited. Moreover, most of the evidence supporting close associations between these factors derives from Caucasian and Japanese populations, whereas data in other populations are not in agreement. This review summarizes and evaluates the relevant epidemiologic evidence to elucidate an important aspect of the relationship between hypertension and the cardiometabolic syndrome.

Diurnal variations in cardiovascular function and glucose regulation in normotensive humans

To define the physiological relationships between cardiovascular function, glucose regulation, and insulin secretion, we submitted nine young normotensive subjects to ambulatory blood pressure monitoring and blood sampling at 20-minute intervals for 24 hours to measure glucose, insulin, C peptide, cortisol, and growth hormone. Subjects ingested three identical carbohydrate-rich meals in the morning (8:30 AM), early afternoon (2 PM), and evening (8 PM). On the following day, they underwent an intravenous glucose tolerance test for quantification of insulin sensitivity. Significant postmeal increases in systolic pressure averaging 18 +/- 10 mm Hg in the morning, 18 +/- 8 mm Hg in the early afternoon, and 26 +/- 19 mm Hg in the evening were observed. Postprandial variations in diastolic pressure and heart rate were significant only for the morning meal. The magnitude of the postprandial increases in systolic pressure was correlated with the amount of insulin secreted in the morning but not later in the day. Pulses of growth hormone consistently occurred 3 to 4 hours after the morning and midday meals, as well as after the onset of sleep. Our findings indicate that under normal conditions, there is a quantitative relationship between postprandial insulin secretion and blood pressure.

Independent association between fasting plasma insulin and ambulatory blood pressure in 50-year-old women

The aim of the present study was to investigate correlations between fasting insulin and ambulatory blood pressure in healthy 50-year-old women. Sixty-five women without anti-hypertensive medication were investigated at a Primary Health Care Centre in Enköping, Sweden. Fasting plasma insulin, office blood pressure and heart rate were measured as well as ambulatory blood pressure and heart rate (Spacelab 90202). Log-transformed insulin correlated with all blood pressure recordings (r = 0.3-0.5; p < 0.05) but only with night-time heart rate (r = 0.3; p < 0.05). In multiple regression analyses log-insulin still correlated with night-time systolic blood pressure and heart rate, but not with the other blood pressure variables, after elimination of the influence of body mass index. We conclude that fasting plasma insulin shows an obesity-independent correlation with night-time systolic blood pressure and heart rate in healthy women, possible indicators of a "basic" sympathetic nervous outflow in muscle tissue during sleep.

The relationship of fasting insulin levels to vascular risk factors in a general practice in Northern Ireland

OBJECTIVE

To investigate the relationship between insulin and vascular risk factors in a healthy male population at high risk of ischaemic heart disease.

DESIGN

Computer-generated random number selection of subjects.

SETTING

A suburban general practice population (total practice population 4500) in Northern Ireland.

SUBJECTS

Four hundred male subjects, aged 35-65 years, were randomly selected with 273 responding.

INTERVENTION

At interview, each subject completed a questionnaire, had blood pressure measured and a 12-lead ECG recorded. The next morning, fasting blood samples were taken and a timed overnight urine collection for the albumin excretion rate was returned.

RESULTS

To exclude the confounding effects of other variables on insulin concentrations, a healthy nonobese, nondiabetic, normotensive group with no history of ischaemic heart disease, no family history of diabetes and not taking drugs was identified (n = 120). Within this group there was a significant correlation between insulin and triglyceride (r = 0.30; P < 0.05), high-density lipoprotein (HDL) cholesterol (r = 0.24; P < 0.05) and glucose (r = 0.30; P < 0.05). A group with higher insulin levels (n = 22) were compared to a group with lower insulin levels (n = 22). Serum triglyceride was higher (1.29 +/- 0.1 vs. 1.00 +/- 0.08 mmol L-1; P < 0.05), HDL cholesterol was lower (1.26 +/- 0.06 vs. 1.50 +/- 0.09 mmol L-1; P < 0.05) and plasma glucose higher (5.2 +/- 0.1 vs. 4.9 +/- 0.1 mmol L-1; P < 0.05) in the group with higher insulin levels.

CONCLUSIONS

There is a relationship between insulin and triglyceride, HDL cholesterol and glucose but not blood pressure, cholesterol or low-density-lipoprotein (LDL) cholesterol in a healthy population at high risk of ischaemic heart disease.

Serum insulin level versus blood pressure: a cross-sectional, case-controlled study in non-obese, middle-aged Japanese subjects with normal glucose tolerance

To assess the relationship between blood pressure (BP) and serum insulin level in non-obese (body mass index (BMI) < or = 27 kg m-2), middle-aged (40-64 years of age) Japanese subjects with normal glucose tolerance, a three-phase study protocol was designed. First, the responses of plasma glucose and serum insulin to an oral glucose load were compared between 40 patients with untreated essential hypertension and 40 age-, sex- and BMI-matched normotensive control subjects. Second, the glucose and insulin responses to an i.v. glucose load were evaluated in 7 non-obese hypertensive, 7 non-obese normotensive and 7 obese hypertensive subjects. Third, BP and serum lipid profile were compared between 21 hyperinsulinaemic (serum insulin level (while fasting, after glucose loading, or both) > 2 SDs higher than the mean) and 21 age-, sex- and BMI-matched normoinsulinaemic subjects (serum insulin level within 1 SD of the mean). The glucose and insulin responses to the oral glucose load were comparable between the hypertensive and normotensive groups. Similarly, the glucose and insulin responses to the i.v. glucose load were comparable between the non-obese hypertensive and normotensive groups, whereas the mean AUCinsulin in the obese hypertensive group was significantly greater (p < 0.01) than that in either of the non-obese groups. The respective mean values for systolic and diastolic BPs did not differ between the hyperinsulinaemic and normoinsulinaemic groups. The mean serum triglyceride and HDL cholesterol concentrations were significantly higher (p < 0.01) and lower (p < 0.05), respectively, in the hyperinsuslinaemic than in the normoinsulinaemic group.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased urinary C-peptide and albumin excretion in juvenile borderline hypertensives

The study was designed to evaluate the urinary excretion of C-peptide and albumin, and urinary N-acetyl-beta-D-glucosaminidase (NAG) activity in juvenile borderline hypertensives. The second aim was to examine the relationship between these variables and ambulatory blood pressure level and variability. The study group consisted of 21 non-obese males consecutively chosen from patients with borderline hypertension, defined by sphygmanometer readings, examined in our outpatient clinic. All subjects collected separately their day-time and night-time urines during the period of ambulatory blood pressure monitoring. In 16 patients, who were considered to have "sustained" borderline hypertension, both 24-h urinary C-peptide excretion and 24-h UAE were significantly increased in comparison to those of the controls, while NAG activity did not differ significantly between the two groups. UAE was significantly lower at night than during the day in both borderline hypertensives and controls. Twenty-four-hour UAE in borderline hypertensives correlated significantly with the ambulatory blood pressure variability, but not with the average blood pressure level. These results suggest that the 24-h insulin secretion rate estimated by means of urinary C-peptide excretion is significantly increased in "sustained" borderline hypertensives. Elevated UAE in juvenile borderline hypertensives can be explained by a possible direct effect of systemic blood pressure variability on albuminuria.

Insulin and hypertension: are they related?

It has been postulated that insulin resistance and the concomitant compensatory hyperinsulinemia contribute to the pathogenesis of hypertension, possibly by stimulating the sympathetic nervous system, promoting renal sodium reabsorption, modulating cation transport, and/or stimulating vascular smooth muscle hypertrophy. The purpose of this article is to present a comprehensive up-to-date review of the literature and critically examine the insulin resistance-hyperinsulinemia-hypertension hypothesis.

Early nocturnal blood pressure changes in diabetic autonomic neuropathy assessed by Fourier series

The 24 h periodic pattern of blood pressure was studied in 44 patients with diabetes mellitus (14 type 1, 30 type 2; mean duration of disease 6.5 +/- 1.8 years) in good metabolic control but with abnormal cardiovascular reflex responses; of these 21 were normotensive and 23 hypertensive. All had abnormal responses to at least two out of four tests: deep breathing, lying to standing, Valsalva manoeuvre and postural hypotension. Two sex- and age-matched groups, consisting of 20 normotensive and 20 hypertensive diabetic patients without dysautonomia, were studied as controls. Each patient underwent ambulatory blood pressure monitoring for at least 24 h, using an auscultatory automatic device. Data were analysed using the sum of three periodic functions (Fourier partial sum). In the diabetic normotensive groups, the absolute blood pressure fell to its night-time minimum more rapidly, and increased to its morning maximum more slowly, in those with abnormal cardiovascular reflexes than in the controls (nightly blood pressure decrease -5.8/-4.7 vs. -3.8/-4.0 mmHg/h; increase 4.7/3.6 vs. 5.9/6.1 mmHg/h). The same behaviour was found in both hypertensive groups but the amplitude of the differences was more marked (blood pressure nocturnal decrease -7.7/-7.1 vs. -4.3/-3.9 mmHg/h; increase 3.2/2.1 vs. 5.8/4.3 mmHg/h). This analysis of 24 h ambulatory blood pressure data may be of value in diagnosis and evaluation of autonomic deficits.

Effect of chronic treatment with enalapril on glucose tolerance and serum insulin in non-insulin-resistant Japanese patients with essential hypertension

The effect of enalapril, an angiotensin converting enzyme inhibitor, on glucose tolerance and serum insulin response to a glucose load has been evaluated in 8 non-obese patients (3 women and 5 men) with untreated essential hypertension (WHO Stage I or II) and without insulin resistance. Following a 2-month run-in control period, each patient received oral enalapril 10 mg once daily for 6 months, and an intravenous glucose tolerance test (IVGTT) was performed at the end of the run-in control and active treatment periods. Treatment with enalapril significantly lowered both the systolic and diastolic blood pressures. The response of plasma glucose to the IVGTT, glucose disappearance rate (k-value) and area under the serum insulin concentration time curve were comparable between the two phases. The results suggest that long-term treatment with enalapril has no effect on glucose tolerance in non-obese, non-insulin-resistant patients with mild-to-moderate essential hypertension.