Glucose homeostasis in the micropremie

This article evaluates the current knowledge of the kinetics of glucose homeostasis in the micropremie. Glucose production, glucose use, and glucose oxidation are reviewed in detail. This article also evaluates the developmental regulation of glucose homeostasis relative to some of the fundamental differences known to exist in the neonate compared to the adult.

Insulin resistance and glucose transporter expression during the euglycemic hyperinsulinemic clamp in the lamb

Three- to six-day-old lambs infused with 100 mU x kg(-1) x min(-1) insulin required greater amounts of glucose to maintain euglycemia during a euglycemic hyperinsulinemic clamp compared with 31- to 35-day-old insulin-infused lambs (15.87 +/- 3.47 vs. 4.30 +/- 1.11 mg x kg(-1) x min(-1), P < 0.05, respectively). Endogenous glucose production persisted in both groups; however, the percent decrease compared with age-matched lambs receiving no insulin was greater in the younger group compared with the older group (53%, P < 0.001, vs. 34%, P < 0.01). The younger animals showed greater glucose utilization compared with the older animals (215 vs. 96%, respectively, P < 0.01). No effect of insulin was noted on GLUT-4 protein expression in either group. GLUT-2 expression was increased in older vs. younger lambs. Older insulin-infused lambs showed lower GLUT-2 expression than older 0 insulin-infused lambs [0.94 +/- 0.07 vs. 1.64 +/- 0.10 (OD) units, P < 0.005]. Increased sensitivity to insulin in the younger animals was not related to acute changes in GLUT-4 expression. Increased GLUT-2 expression with age, as well as decreased expression with hyperinsulinemia, is consistent with the development of an insulin-resistant state in the adult.

Insulin counterregulatory hormones are ineffective in neonatal hyperinsulinemic hypoglycemia

Insulin counterregulatory hormones play a major role in the maintenance of glucose homeostasis. To evaluate the hypothesis that the reported imprecise control of glucose production by insulin is mirrored by a corresponding lack of response to the various insulin counterregulatory hormones, 30 spontaneously delivered mixed-breed term lambs weighing 4.9 +/- 0.5 kg (mean +/- SD) were studied at 5.0 +/- 0.7 days after birth following administration of 100 microCi D-[6-(3)H2]glucose in 0.9% NaCl by the primed-constant infusion technique to measure glucose kinetics. Infusion of 2.0 mU kg(-1) x min(-1) insulin produced hyperinsulinemic hypoglycemia and was combined with 1.0 mg x kg(-1) x min(-1) somatostatin (SRIF) to block insulin, glucagon, and growth hormone release. Infusion of 2 ng x mg(-1) x min(-1) glucagon or 10 microg x kg(-1) x h(-1) growth hormone with SRIF and insulin isolated the glucagon or growth hormone effect, respectively. The addition of metyrapone blocked cortisol release. Controls received only the isotope. In toto, the data can be interpreted to suggest that insulin has a greater effect on glucose uptake than on glucose production, and that neither glucagon, growth hormone, nor cortisol appreciably influenced the endogenous glucose production rate (Rp) during hyperinsulinemic hypoglycemia. The imprecise effect of these insulin counterregulatory hormones on neonatal glucose production mirrors the previously documented imprecise control by insulin.

The contribution of glucose to neonatal glucose homeostasis in the lamb

A multiplicity of substrates and hormones interact to influence neonatal glucose homeostasis. Based on prior studies in our laboratory, we hypothesized that glucose alone does not tightly control neonatal glucose homeostasis. Fifteen spontaneously delivered, mixed-breed term lambs, weighing 4.7 +/- 0.9 kg (mean +/- SD) were studied at 4.7 +/- 0.6 days after birth following administration of 100 microCi D[6,6-(3)H2] glucose in 0.9% NaCl by the prime plus constant infusion technique to measure glucose production. After a baseline period, five lambs received 8.5 mg x kg(-1) x min(-1) glucose in combination with the following to isolate the contribution of glucose: somatostatin to block insulin, glucagon, and growth hormone release; metyrapone to block cortisol release; phentolamine to block alpha-adrenergic release; and propranolol to block beta-adrenergic release (glucose + blockade). Five lambs received the above without the glucose infusion (blockade). Five lambs continued to receive 0.9% NaCl alone as the diluent for the isotopic tracer throughout the study (control). The glucose + blockade group had a significant increase in plasma glucose (P < .0001) and a significant increase in total glucose appearance (P < .0001) compared with both the blockade and control groups. Under conditions of glucose infusion at a rate 49% greater than the basal rate, the endogenous glucose production rate persisted such that there was only an evanescent decrease compared with that of the control group, which was not statistically different over time. As a substrate, glucose does not tightly control neonatal glucose homeostasis.

Red cell volume determination using a stable isotope of chromium

OBJECTIVE

To validate and improve a method of red cell volume determination by use of a stable isotope of chromium.

METHODS

Twelve subjects were sequentially injected with red blood cells labeled with a stable isotope of chromium (53Cr) and red blood cells labeled with radioisotopic chromium (51Cr). Measurement of 53Cr dilution was by gas chromatography/mass spectrometry. Measurement of 51Cr dilution was by gamma counter.

RESULTS

Comparison of the two methods led to results that differed on average by 34.5 +/- 45.0 mL (1.8 +/- 2.2%), 0.3 to 3.2%, 95% confidence interval.

CONCLUSION

Measurement of red cell volume by use of a stable isotope of chromium is accurate, with potential applications including measurement in pregnant women and children or other groups in whom exposure to radioisotopes is undesirable.

Brain stem auditory-evoked response in relation to neonatal glucose metabolism

Imprecise control of glucose homeostasis is a hallmark of neonatal glucose metabolism. A relatively wide range of glucose concentrations is considered 'euglycemic' (2.22-6.94 mmol/l, 40-125 mg/dl) in the neonatal period. We investigated the effects of a wide range of glucose concentrations on brain stem conduction time (BCT) I-V interpeak latency or prolonged wave V latency. Neonates were assessed by brain stem auditory-evoked response followed immediately by heelstick sampling to determine the blood glucose concentration. Twenty-seven appropriate for gestational age (AGA) term neonates (birth weight 3,245 +/- 766 g, mean +/- SD; gestational age 39 +/- 2 weeks) were studied 3.1 +/- 3.7 days after birth. Twenty-three AGA preterm neonates (birth weight 2,175 +/- 477 g; gestational age 35 +/- 1 weeks) were studied 6.0 +/- 7.2 days after birth. Brain stem conduction time wave I-V interpeak latency and wave V latency were determined in two trials using a Grason-Stadler ABR screener at a 60-decibel stimulation level in the right ear. Neonates were studied between 33 and 40 weeks gestational age. Although the blood glucose concentration ranged from 1.38 to 6.83 mmol/1 (25-123 mg/dl), there was no correlation between either brain stem conduction time wave I-V interpeak latency or wave V latency and blood glucose concentration. We conclude that alterations in glucose concentration within the generally accepted neonatal euglycemic range do not effect the functional status of the brain stem auditory pathway. We suggest that the data can be interpreted to affirm that tighter clinical control of glucose homeostasis is probably not required in the neonatal period.

Persistent glucose production and greater peripheral sensitivity to insulin in the neonate vs. the adult

Insulin resistance has been reported to partially explain the clinical appearance of neonatal hyperglycemia. To determine the relative resistance to insulin of glucose production vs. glucose utilization, the euglycemic hyperinsulinemic clamp technique was employed for the first time in the human neonate and was combined with stable isotopic determination of glucose production and glucose utilization. The basal rates of glucose production and glucose utilization were determined, after which each neonate was clamped at his or her own euglycemic glucose concentration while receiving regular human insulin at one rate of 0.2, 0.5, 1.0, 2.0, or 4.0 mU. kg-1.min-1. Persistent glucose production (> or = 1 mg.kg-1.min-1) during the clamp was recorded for all groups. A significant increase in the glucose infusion rate (P < 0.001) and in percent glucose utilization (P < 0.01) occurred in the 2.0 and 4.0 mU.kg-1.min-1 insulin groups. Metabolic clearance rate of insulin was significantly greater in the neonate compared with the adult at the 2.0 mU.kg-1.min-1 insulin infusion rate (P = 0.036). Our results indicate that, in contrast to the adult, the neonate has persistent glucose production (P = 0.001) and greater peripheral sensitivity to insulin (P = 0.015).

Glucose and lactate kinetics during a short exercise bout in pregnancy

Pregnancy is considered diabetogenic. Although exercise has been advocated to assist in metabolic control of the nonpregnant diabetic individual, there is a paucity of data about the metabolic effects of exercise during pregnancy. To examine whether moderate exertion may be beneficial in the maintenance of maternal carbohydrate homeostasis, glucose and lactate kinetics were measured in the third trimester in five pregnant nondiabetic women (gestational age, 34.2 +/- 0.1 weeks [mean +/- SE]) by infusion of 45 microg x kg(-1) x min(-1) [6,6-2H2]glucose and 70 microg x kg(-1) x min(-1) [U-13C]lactate tracers. Subjects were observed at rest for determination of baseline steady-state kinetics over a 30-minute period, and then they exercised for 30 minutes at 60% maximum oxygen consumption (VO2max) and were evaluated for 30 minutes postexercise. Glucose and lactate kinetics and lactate oxidation were measured throughout the exercise protocol. This study was repeated postpartum in all individuals at least 6 weeks after delivery. Compared with the steady-state preinfusion period, plasma glucose concentration was not elevated during exercise in either group, nor was plasma lactate concentration significantly different in either group. Glucose kinetics did not change during exercise, but lactate kinetics increased in both groups. V02 and percent of lactate C contribution to CO2, an indication of lactate oxidation, increased proportionally in both groups during exercise. Metabolic perturbations, as measured by glucose and lactate kinetics, do not appear to be different during the third trimester of pregnancy during a relatively short bout of exercise compared with the nonpregnant state.

Effect of intrauterine growth retardation on postnatal weight change in preterm infants

To investigate the cause or causes of early postnatal weight change, we measured total body water and fluid and energy balances in 14 preterm infants who were appropriate in size for gestational age (AGA) and in 5 weight-matched, preterm, small-for-gestational-age (SGA) infants. On the first day of life, AGA and SGA infants had the same weight and total body water content. At 6 +/- 2 days (mean +/- SD), AGA infants had had significant weight loss (94 +/- 45 gm) and body water loss (67 +/- 80 ml), whereas weight and total body water content in the SGA infants at the same age (5 +/- 1 days) did not differ from the values at birth. Loss of weight and total body water in AGA infants was accompanied by a greater diuresis than in SGA infants at the same amount of fluid intake. At the end of week 1, AGA and SGA infants had the same total energy expenditure (184 +/- 33 vs 171 +/- 17 kJ.kg-1 x day-1); energy intake, which had exceeded total energy expenditure from the third day of life and beyond, already provided 188 +/- 46 (AGA) or 209 +/- 109 kJ.kg-1 x day-1 (SGA), respectively, for energy storage. Nitrogen balance was positive. Subsequent weight gain occurred at the same rate in AGA and SGA infants; both total body water and solids increased. Energy intake, total energy expenditure, and the amount of energy stored (measured during stable weight gain on a regimen of full enteral feedings) had significantly increased compared with week 1, but both groups maintained similar energy storage.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid tolerance testing in pregnancy

OBJECTIVE

Macrosomia in the infant of the well-controlled diabetic mother suggests that a substrate other than glucose may influence fetal growth. We hypothesized that GDM alters lipid homeostasis during pregnancy. Our objective was to determine if an LTT could assist in identification of lipid abnormalities in the GDM individual.

RESEARCH DESIGNS AND METHODS

The LTT consisted of bolus infusion of 1.0 mg/kg 10% Intralipid (Cutter Vitrum, Berkeley, CA) followed by measurements of plasma glucose, insulin, glycerol, total triglycerides, and triglyceride fatty acids (18:1 and 18:2), total FFAs, and total phospholipids for 30 min before and 90 min after the bolus. The study groups were composed of 8 nonpregnant, nondiabetic subjects, 8 pregnant, nondiabetic subjects, 8 GDM patients receiving insulin, and 8 GDM patients who were diet controlled.

RESULTS

Plasma glucose and plasma insulin concentrations did not change significantly after the bolus. No significant difference was noted in the K2 for glycerol of the nonpregnant, nondiabetic group compared with the pregnant groups. The K2 for total triglycerides, plasma triglyceride 18:1, and plasma triglyceride 18:2 indicated increased rates of disappearance of these substrates for the nonpregnant nondiabetic group compared with all pregnant groups. No significant differences were observed among the pregnant groups for any of these parameters.

CONCLUSIONS

Pregnancy may be associated with a decreased rate of triglyceride lipolysis compared with nonpregnancy. No differences in lipid metabolism were noted among normal pregnant and relatively well-controlled GDM patients.

Glucose kinetics following administration of an intravenous fat emulsion to low-birth-weight neonates

To evaluate the mechanism(s) of the observed increase in plasma glucose concentration following the administration of an intravenous fat emulsion to the neonate, we measured glucose kinetics in eight low-birth-weight neonates by the prime constant rate infusion technique with D-[6,6-2H2]glucose at a rate of 0.22 +/- 0.01 mumol.kg-1 x min-1 (39.4 +/- 1.3 micrograms.kg-1 x min-1) while the neonates received 32 +/- 5 mumol.kg-1 x min-1 glucose (6.3 +/- 1.1 mg.kg-1 x min-1) plus an amino acid mixture (parenteral alimentation) alone and in combination with an intravenous fat emulsion (Intralipid). Following the latter combination, there were significant increases in plasma glucose concentration [4.07 +/- 0.11 (73 +/- 2 mg/dl) to 5.00 +/- 0.22 mmol/l (90 +/- 4 mg/dl); P < 0.01] and in plasma insulin concentration [72 +/- 14 (10 +/- 2 microU/ml) to 172 +/- 36 pmol/l (24 +/- 5 microU/ml); P < 0.05]. The parenteral alimentation and intravenous fat effusion combination did not affect the glucose production rate: 0.15 +/- 0.05 mumol.kg-1 x min-1 (0.03 +/- 0.01 mg.kg-1 x min-1) during the parenteral alimentation alone and 0.16 +/- 0.05 mumol.kg-1 x min-1 (0.03 +/- 0.01 mg.kg-1 x min-1) when parenteral alimentation was combined with an intravenous fat emulsion. We conclude that the increased plasma glucose concentration seen in association with administration of parenteral alimentation combined with an intravenous fat emulsion to the premature neonate is not due to enhanced glucose production but could be the result of alterations in glucose utilization.

Hypertrophic cardiomyopathy associated with dexamethasone therapy for bronchopulmonary dysplasia

The potential induction of cardiac effects by high-dose dexamethasone therapy was evaluated prospectively in 13 respirator-dependent infants with bronchopulmonary dysplasia by means of two-dimensional and M-mode echocardiography. The initial divided dose of dexamethasone was 500 micrograms/kg per day, tapered progressively for as long as 6 weeks. Evaluations were made before treatment and at 3, 7, 14, 21, 28, 35, and 42 days after the start of dexamethasone therapy. This regimen was associated with a significant (p less than 0.01) increase in thickness of the interventricular septum (2.60 +/- 0.09 to 4.00 +/- 0.16 mm), diastolic left ventricular free wall (2.80 +/- 0.13 to 4.06 +/- 0.20 mm), and diastolic right ventricular free wall (1.55 +/- 0.08 to 2.02 +/- 0.12 mm). In addition, seven dexamethasone-treated infants but no control infants had systolic anterior motion of the mitral valve (p less than 0.001). These effects were transient, reached their maximal degree by the third week of treatment, and approached pretreatment conditions by the sixth week of treatment. Ejection fraction was not affected; heart rate and mean arterial pressure were transiently increased during dexamethasone therapy. We conclude that a transient absolute myocardial hypertrophy is associated with dexamethasone therapy in infants with bronchopulmonary dysplasia. The mechanism or mechanisms through which this hypertrophy arises and the cardiopulmonary implications are unclear.

Capillary (heelstick) versus venous blood sampling for the determination of glucose concentration in the neonate

Various sites may be used to obtain blood (plasma) for the determination of the glucose concentration in the neonate. Because multiple sites may be sampled in the same neonate, it is important to determine the variability in blood glucose concentration which may result from such sampling. Since pain and mechanical forces may be different because of the method used to obtain the capillary (heelstick) blood compared to the venous specimen, the two sites were sampled, and the blood glucose concentration was determined simultaneously in 25 asymptomatic well neonates whose mean birth weight was 2,562 +/- 152 g and whose gestational age was 35.5 +/- 1.5 weeks. There was a significant (p less than 0.0001), but relatively weak correlation (r2 = 0.64) between capillary (heelstick) blood and venous blood relative to blood glucose concentration. When the capillary (heelstick)-venous glucose concentration difference was compared to the mean of the capillary (heelstick) and venous glucose concentrations, a difference of +/- 0.5 mM (9 mg/dl) was noted in 3 of 25 neonates. Appropriately obtained capillary (heelstick) blood samples provide measurement of blood glucose concentration which are variable compared to venous samples, but which are probably not significant physiologically.

Glucose and lactate kinetics in the neonate

To evaluate the ontogeny of neonatal glucose homeostasis, glucose production and lactate production have been measured in nine prematurely born appropriate for gestational age neonates [birth weight 1985 +/- 100 g, (SEM) gestational age 33.6 +/- 0.7 weeks] and five full term appropriate for gestational age neonates [birth weight 3254 +/- 111 g, gestational age 40.8 +/- 0.4 wks] and compared to six non pregnant, nondiabetic adults [weight of 57.7 +/- 2.2 kg, age 32 +/- 2 years]. Ra glucose (preterm) averaged 27.7 +/- 2.8 mumol.kg-1 min-1 (5.0 +/- 0.5 mg.kg-1 min-1) and Ra glucose (term) averaged 28.9 +/- 3.9 mumol.kg-1 min-1 (5.2 +/- 0.7 mg.kg-1 min-1); both were higher than the Ra glucose of the adult controls (16.1 +/- 2.8 mumol.kg-1 min-1 (2.9 +/- 0.5 mg.kg-1 min-1) (P less than 0.05 vs preterm and P less than 0.05 vs. term). Ra lactate (preterm) averaged 100 +/- 11.9 mumol.kg-1 min-1 (9.1 +/- 1.1 mg.kg-1 min-1) and Ra lactate (term) average 77.2 +/- 13.0 mumol.kg-1 min-1 (7.1 +/- 1.2 mg.kg-1 min-1); both were higher than the Ra lactate of the adult controls 35.9 +/- 6.5 mumol.kg-1 min-1 (3.3 +/- 0.6 mg.kg-1 min-1) (P less than 0.01 vs preterm and P less than 0.05 vs. term). The potential for gluconeogenesis from lactate was estimated by determining the ratio of [Ra Lactate/Ra Glucose]. The [Ra Lactate/Ra Glucose] (preterm) (187 +/- 12 (x10(-2)) was similar to that of the [Ra Lactate/Ra Glucose] (term) (136 +/- 16) (x10(-2)).(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha-adrenergic agonists stimulate neonatal glucose production less than beta-adrenergic agonists in the lamb

Epinephrine, a catecholamine with both alpha (alpha)- and beta (beta)-adrenergic agonist effects, may produce clinical hyperglycemia in the adult by increasing glucose production and decreasing glucose clearance. However, the relative contribution of alpha v beta adrenergic agonists in control of neonatal glucose kinetics has not been defined. Twenty-three term lambs (weighing 4.4 +/- 0.2 kg, mean +/- SEM, and aged 3.8 +/- 0.4 days) were infused with 0.9% NaCl at 0.6 mL.kg-1 min-1 + 100 microCi/kg D[6-3H]-glucose by prime plus constant infusion for 210 minutes. Ra (rate of production) was measured during infusion of variable doses of epinephrine with or without variable doses of propranolol, a competitive beta-adrenergic antagonist to isolate the alpha-adrenergic agonist effects. All basal kinetic data were comparable. Under conditions of epinephrine infusion, the plasma glucose concentration increased from 95 +/- 10 mg/dL to 129 +/- 18 mg/dL (50 ng.kg-1 min-1 epinephrine; P less than .0001) and from 85 +/- 6 mg/dL to 253 +/- 8 mg/dL (500 ng.kg-1 min-1 epinephrine; P less than .00001) compared with controls (96 +/- 7 mg/dL to 95 +/- 8 mg/dL). When epinephrine and propranolol were infused simultaneously, plasma glucose concentration increased from 95 +/- 10 mg/dL to 122 +/- 12 mg/dL (50 ng.kg-1 min-1 epinephrine + 1.1 micrograms.kg-1 min-1; P less than .0001) and from 78 +/- 9 mg/dL to 134 +/- 12 mg/dL (500 ng.kg-1 min-1 epinephrine + 11 micrograms.kg-1 min-1; P less than .0001) compared with controls (no epinephrine, no propranolol).(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased response to catecholamines in the newborn: effect on glucose kinetics in the lamb

Epinephrine, a catecholamine with both alpha (alpha) and beta (beta) adrenergic effects, may produce hyperglycemia in adults by increasing glucose production and decreasing glucose clearance. To document the degree of sensitivity and characterize maturation of neonatal glucose control, glucose kinetics were measured in 14 term newborn lambs (weight 4.5 +/- 0.3 kg [mean +/- SEM] and aged 4.1 +/- 0.4 days). Following infusion of 0.9% NaCl at 0.06 mg.kg-1 min-1 plus 100 microCi/kg D[6-3H] glucose by prime plus constant infusion, rate of production (Ra) and glucose clearance were measured during administration of epinephrine. The responses in the newborns were compared with those in six adult sheep. Under conditions of epinephrine infusion, the plasma glucose concentration in the newborn lambs increased to 129 +/- 18 mg/dL (50 ng.kg-1 min-1 epinephrine), P less than .0001, and 253 +/- 8 mg/dL (500 ng.kg-1 min-1 epinephrine), P less than .0001, compared with 95 +/- 8 mg/dL (controls, no epinephrine). Comparable values for Ra were 6.5 +/- 1.6 mg.kg-1 min-1 (50 ng.kg-1 min-1 epinephrine), P = NS, and 18.5 +/- 3.0 mg.kg-1 min-1 (500 ng.kg-1 min-1 epinephrine), P less than .0001, compared with 5.3 +/- 0.5 mg.kg-1 min-1 (controls, no epinephrine).(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of glucose homeostasis in low birth weight infants

Suppression of the endogenous glucose production rate (Ra) is the adult response to glucose infusion. Persistent Ra (greater than or equal to 1 mg.kg-1min-1 or less than 80% decrease in basal Ra) in response to glucose infusion is evidence of a transitional homeostatic state in the neonate during the first days after birth. To determine whether postnatal development produces an adultlike response, Ra was measured in 11 infants (birth weight 1716 +/- 48 g, gestational age 33 +/- 0.3 weeks) at 2 to 5 weeks of age. In these paired studies, 4 micrograms.kg-1min-1 D-(U-13C)glucose tracer was infused by prime constant infusion to determine Ra, during infusion of either saline solution or glucose, the latter at a rate of 5.3 +/- 0.2 mg.kg-1min-1 (mean +/- SEM). When the results of the saline infusion turnover period were compared with those of the glucose infusion turnover period, plasma glucose concentration increased significantly, from 88 +/- 3 mg/dL to 101 +/- 4 mg/dL (P less than 0.001). Plasma insulin concentration remained unchanged (12 +/- 5 microU/mL vs 8 +/- 3 microU/mL). Ra was heterogenous during glucose infusion, and persistent Ra was present in six of 11 infants. Of the five infants who had decreased Ra during glucose infusion, three received glucose at a rate exceeding basal Ra. Of the remaining six infants who evidenced persistent Ra during glucose infusion, three received glucose at a rate equal to or in excess of basal Ra. We conclude that glucose homeostasis in low birth weight infants is transitional throughout the neonatal period.

Hepatic response to insulin in control of glucose kinetics in the neonatal lamb

Imprecise control of neonatal glucose homeostasis may be partially due to decreased hepatic response to insulin. In prior kinetic studies the effect of that response could not be determined because the hormonal effects of insulin could not be separated from those of glucagon. Somatostatin (SRIF) suppresses secretion of both and has been used to differentiate the hormonal effects. Eighteen term lambs (age 4.2 +/- 0.3 days and birth weight 4.0 +/- 0.2 kg (M +/- SEM] were infused with 0.9% NaCl at 0.06 mL.kg-1 min-1 plus 100 microCi/kg D[6-3H] glucose by prime plus constant infusion. Ra (production) and Rd (utilization) were measured during infusion of SRIF or SRIF plus replacement insulin (0.2 mU.kg-1 min-1). There was a rise in pl. glucose (98 +/- 10 to 119 +/- 10 mg/dL (P less than .0001)); a fall (46.2%) in pl insulin [13 +/- 2 to 7 +/- 1 microU/mL (P less than .0004); a rise in Ra (7.8 +/- 1.5 to 13.2 +/- 4.1 mg.kg-1 min-1 P less than .047); and a rise in Rd (7.7 +/- 1.4 to 11.3 +/- 3.0 mg.kg-1 min-1 (P less than .047)) in SRIF treated animals compared to nontreated controls. There was no change in plasma glucagon (454 +/- 182 to 255 +/- 141 pg/mL) in SRIF treated animals compared to nontreated controls. All perturbations were eliminated when SRIF plus replacement insulin produced control insulin levels. Insulin suppression in the neonatal period resulted in glucagon being unopposed which produced an elevated rate of glucose production and elevated plasma glucose concentration.

Effects of maternal transport on admission patterns at a tertiary care center

Major changes have occurred in the delivery of perinatal care during the last two decades. Documentation of perinatal regionalization statistics at Women and Infants Hospital of Rhode Island in Providence support the increasing proportion of low birth weight infants in the region being born at the tertiary care center, the decreasing number of neonatal transports in concert with an increasing number of maternal transports, and the increasing proportion of neonatal transports with birth weights greater than or equal to 2500 gm. Patterns of modern perinatal care are materially changing the delivery of health care at tertiary care facilities.

Hepatic and peripheral responsiveness to a glucose infusion in pregnancy

To enhance glucose transfer to the fetus, the pregnant woman may evidence hyperglycemia after feeding. In order to evaluate whether hepatic responsiveness, in contrast to peripheral uptake, contributes to this response, the glucose production rate was measured in 15 pregnant nondiabetic patients, in 12 pregnant insulin-dependent diabetic patients, and in 12 nonpregnant nondiabetic patients (controls). Seventeen of the women were infused with 3.2 mg X kg-1 min-1 of glucose. All glucose-infused groups had an elevated plasma glucose concentration compared to their saline solution-infused counterparts. The glucose production rate was suppressed in the nondiabetic glucose-infused groups. The glucose production rate of the pregnant nondiabetic patients was similar to that of the pregnant insulin-dependent diabetic patients, but the glucose production rate of the latter group was more variable than that of nonpregnant nondiabetic controls (p less than 0.05). We conclude that in third trimester, pregnant nondiabetic and insulin-dependent diabetic subjects have parallel hepatic and peripheral responsiveness to glucose and insulin compared to their nonpregnant counterparts. Although the pregnant patient may exhibit relative insulin insensitivity, hepatic or peripheral responsiveness to insulin would not explain the persistence of the relative hyperglycemia noted clinically.

Mechanisms of beta sympathomimetic action on neonatal glucose homeostasis in the lamb

Beta sympathomimetic drugs are used clinically to inhibit premature labor. Significant alterations in glucose homeostasis have been documented in both mother and offspring. To determine the mechanism(s) of beta sympathomimetic drugs on neonatal glucose homeostasis, ritodrine hydrochloride was infused in a newborn term lamb model of glucose kinetics by a crossover design. There was a progressive rise in plasma glucose concentration and plasma insulin concentration during ritodrine hydrochloride infusion compared with the control (saline) infusion. The rise in plasma glucose concentration was associated with a progressive rise in Ra (rate of appearance, production) and Rd (rate of disappearance, utilization). The ritodrine hydrochloride-infused animals had a progressive rise in [insulin/glucose] compared with our prior studies in the newborn lamb, suggesting direct stimulation of pancreatic beta cell secretion. In the neonatal lamb, beta sympathomimetic drugs directly stimulate both hepatic glucose production and pancreatic beta cell secretion. These effects explain, in part, why infants of mothers infused with ritodrine hydrochloride may evidence alterations in neonatal glucose homeostasis.

Neonatal morbidities in infants of mothers with glucose intolerance in pregnancy

Of 1839 pregnant women screened prospectively, 52 were identified to have glucose intolerance. Ten additional pregnant women identified as having glucose intolerance before the universal screening were also included in the study cohort. These 62 patients were followed in a perinatal high-risk clinic with weekly plasma glucose determinations. The patients were treated with diet and, in addition, 21 of 62 were treated with insulin therapeutically. By observational cohort design, the infants and a comparable number of matched controls were evaluated for evidence of neonatal morbidities and classified into percentile for birth weight. Compared with the control group, the operative mode of delivery, the mean birth weight, the birth-weight percentile, the male/female ratio, the frequency of low Apgar score (less than or equal to 6 at 1 min), and the number of infants with congenital anomalies were significantly higher in the infants born to the glucose-intolerant mothers. Although the mean maternal blood sugar was maintained within a reasonably euglycemic range, the usual neonatal morbidities were not eliminated entirely. Further understanding and management of glucose intolerance in pregnancy is necessary to further diminish or eliminate neonatal morbidities.

Pathophysiology, diagnosis, and management of glucose homeostasis in the neonate

The neonate appears to be in a transitional stage of glucose homeostasis. Maturation of neonatal glucose homeostasis requires coordination of opposing hormonal, neural, and enzymatic controls. The vulnerability of the neonate to carbohydrate disequilibrium has been described by tracing the maturation of carbohydrate homeostasis physiologically. The many examples of neonatal hypoglycemia and hyperglycemia have been enumerated. Much information in recent years has increased our understanding of the mechanism of these conditions in the newborn. Continued research of the biochemical and physiologic bases for alterations of carbohydrate metabolism should further enhance our ability to diagnose and treat the neonate effectively.

The effects of arterial glucose infusion above the celiac axis in the neonatal lamb

Refractory hypoglycemia has been reported in an infant receiving glucose infusion via an umbilical artery catheter (UAC) above the celiac axis. To prove the hypothesis that hypoglycemia resulted from direct glucose infusion to the pancreas, 15 term spontaneously delivered lambs were infused with 5.3 +/- 0.1 mg X kg-1 min-1 of glucose via an arterial catheter. In 9 glucose was infused below the celiac, and the glucose production rate (GPR) was derived. After a recovery period, the study was repeated with glucose infused above the celiac. During glucose infusion above the celiac, the plasma glucose concentration was lower than when the infusion was given below the celiac (140 +/- 6 vs. 175 +/- 11 mg/dl, p less than 0.01). There was also a fall in the average GPR (3.7 +/- 0.5 vs. 5.5 +/- 0.8 mg X kg-1 min-1, p less than 0.05). In 6 lambs the study was performed in the reverse sequence (high then low infusion) and no differences were noted in the parameters measured. However, there was a marked heterogeneity in the paired GPR in these lambs. We conclude that direct glucose infusion above the celiac increases glucose delivery to the pancreas. This produces increased insulin delivery to the portal system resulting in suppressed GPR and reduction in plasma glucose concentration. These changes may account for refractory hypoglycemia in infants clinically when glucose is infused above the celiac through a UAC.

Glucose kinetics in glucose-infused small for gestational age infants

To evaluate the maturation of glucose homeostasis in the small for gestational age (SGA) neonate, glucose kinetics were measured with 78% enriched D-[U-13C]glucose by the prime plus constant infusion technique in nine SGA infants and compared with the rate obtained in seven term appropriate for gestational age infants and 13 preterm appropriate for gestational age infants. All of the infants had received glucose intravenously from birth and continued to receive the glucose infusion throughout the study. Fasting plasma glucose and plasma insulin concentrations and plasma [13/12C]ratios were measured during the steady state turnover period. From this data, the glucose production rate was derived. During the turnover period, the SGA and both groups of appropriate for gestational age infants had similar average plasma glucose, plasma insulin, plasma glucagon concentrations, and similar persistent rates of glucose production during glucose infusion. We conclude that under stimulation of glucose infusion, the SGA infant and his AGA counterpart have similar hormonal regulatory responses as well as functional integrity in handling glucose during the second day after birth.

Post-hepatic insulin secretion in the fetal lamb

Post-hepatic insulin secretion was measured in six chronically catheterized fetal lambs (fetal weight 2.8 +/- 0.3 kg, mean +/- S.E.M.) and the results were compared with those obtained in nine prematurely delivered newborn lambs (birth weight 3.1 +/- 0.3 kg and postnatal age 1.3 +/- 0.2 days). The fetal and neonatal lambs received either a 0.45% saline or a glucose infusion respectively, which resulted in a 2-fold increase in the plasma glucose concentration. [131I]insulin was infused for 110 min to determine the rate of insulin secretion during a steady state of plasma glucose concentration. Post-hepatic insulin secretion and the metabolic clearance rate were calculated. With the 2-fold rise in plasma glucose concentration, the post-hepatic insulin secretion rate increased significantly in the newborn lamb and in three out of four fetuses. The plasma insulin concentration increased significantly in the fetus (11 +/- 4.0 to 35 +/- 8 microU/ml, P less than 0.05) during glucose stimulation as a result of decreased metabolic clearance rate of insulin (10.6 +/- 1.9 to 6.3 +/- 1.8 ml . kg-1 . min-1) and an increase in post-hepatic insulin secretion rate. In spite of an increase in post-hepatic insulin secretion rate, the increase in plasma insulin concentration in the newborn lamb was not significant because of large variation in the values obtained. The data suggest that pancreatic beta-cells in the newborn and in the fetal lamb are equally responsive to a 2-fold increase in plasma glucose concentration.

Glucose kinetics in nondiabetic and diabetic women during the third trimester of pregnancy

Glucose kinetics were measured with 78% enriched D-[U-13C] glucose by the prime constant infusion technique during the third trimester of pregnancy in nine nondiabetic women, nine insulin-dependent diabetic women, six gestational diabetic women, and five control women (nonpregnant, nondiabetic) after an overnight fast. The patients not dependent on insulin were diagnosed as diabetic by oral glucose tolerance tests with the use of O'Sullivan and Mahan's criteria as modified by Carpenter and Coustan during the third trimester. The turnover studies were repeated post partum (6 weeks to 5 months after delivery) in 14 of the 24 pregnant subjects. All pregnant groups had a progressive fall in plasma glucose concentration during the study, but there was a steady state of plasma glucose concentration during the turnover period. In comparison to the control subjects, both the pregnant nondiabetic and pregnant insulin-dependent diabetic women had significantly higher plasma insulin concentrations throughout the study (p less than 0.05). There were no differences in the glucose turnover rate between any of the pregnant groups (1.7 +/- 0.2 mg . kg-1 min-1 in pregnant nondiabetic women; 1.5 +/- 0.2 mg . kg-1 min-1 in pregnant insulin-dependent diabetic women; and 2.1 +/- 0.4 mg . kg-1 min-1 in gestational diabetic women) and the control group of women (1.8 +/- 0.2 mg . kg-1 min-1) (mean +/- SEM). When the pregnant patients were studied post partum, the glucose turnover rate was similar when referenced to body weight; however, because of a 9.6% to 14.5% fall in weight post partum, the absolute values were higher in the pregnant women. We conclude that, in the basal state after an overnight fast, (1) both nondiabetic and diabetic patients accelerated their glucose turnover rate during pregnancy to provide for increased maternal and fetoplacental metabolic requirements, and (2) in the diabetic subjects the nearly normal plasma glucose and insulin concentrations and other metabolic parameters, as well as the glucose turnover rate, suggested good metabolic control during pregnancy in most of the insulin-dependent and in all of the gestational diabetic patients.

Glucose kinetics in infants of diabetic mothers

Glucose kinetic studies were performed to define the glucose turnover rate with 78% enriched D-[U-13C] glucose by the prime constant infusion technique at less than or equal to 6 hours of age in nine infants of diabetic mothers (four insulin-dependent and five chemical diabetic patients) at term. Five normal infants were studied as control subjects. All infants received 0.9% saline intravenously during the study with the tracer. Fasting plasma glucose, insulin, and glucose13/12C ratios were measured during the steady state, and the glucose turnover rate was derived. The average plasma glucose concentration was similar during the steady state in the infants of the diabetic mothers and in the control infants, and the glucose turnover rate was not significantly different among the groups: 2.3 +/- 0.6 mg . kg-1 min-1 in infants of insulin-dependent diabetic patients; 2.4 +/- 0.4 mg . kg-1 min-1 in infants of chemical diabetic patients; and 3.2 +/- 0.3 mg . kg-1 min-1 in the control subjects. Good control of maternal diabetes evidenced by the normal maternal hemoglobin A1c and plasma glucose concentration at delivery and cord plasma glucose concentration resulted in glucose kinetic values in the infants of diabetic mothers that were indistinguishable from those of control subjects. The data further support the importance of good control of the diabetic state in the pregnant woman to minimize or prevent neonatal hypoglycemia.

Persistent glucose production during glucose infusion in the neonate

In adults, glucose infusion results in a decreased glucose production rate (GPR) as a mechanism for maintaining euglycemia. To document the development of glucose homeostasis, we derived the GPR in 23 preterm appropriate for gestational age infants, 14 term appropriate for gestational age infants, and in 6 adults. After a 3-h fast, the average plasma glucose and insulin concentration was measured and the GPR was derived. During glucose infusion (5.6 +/- 0.3 mg X kg-1 min-1), compared with saline controls, the preterms had a rise in plasma glucose and plasma insulin, and the GPR was 1.4 mg X kg-1 min-1 (range, 0-4.4) vs. 3.0 mg X kg-1 min-1 (range, 1.8-4.1) (saline controls). In the term infants, only the plasma insulin concentration was elevated when the glucose infused (5.7 +/- 0.3 mg X kg-1 min-1) infants were compared with the saline controls and GPR was 0.4 X kg-1 min-1 (range, 0-2.6) vs. 3.4 mg X kg-1 min-1 (range, 2.8-5.7) (saline controls). In comparison to saline infused adults, glucose infusion (3.2 +/- 0.1 mg X kg-1 min-1) resulted in a significant rise in plasma glucose and in plasma insulin; and the GPR was reduced to 0.1 mg X kg-1 min-1 (range, 0-0.3) from 2.0 mg X kg-1 min-1 (range, 1.5-2.4). 5 of 13 preterms and 2 of 7 term infants had persistent GPR during glucose infusion; in contrast, the GPR in all adults was unmeasurable. There was no correlation between the plasma glucose concentration and the GPR in the newborn or in the adult. Both newborns and adults did have a correlation between plasma insulin concentration and the GPR; however, there was considerable variability in the neonate. We conclude that there are significant developmental differences in neonatal glucose homeostasis and that insulin is important in neonatal hormonal control of glucose production.

Glycemic response to lipid infusion in the premature neonate

The effect of lipid infusion on glucose homeostasis in the preterm newborn infant was evaluated. Seven infants were given a test dose of 0.25 gm/kg/hour of lipid emulsion. Their response was characterized by :(1) a two fold increase in serum free fatty acid concentrations, (2) a small, transient rise in insulin values, and (3) a sustained increase in serum glucose concentration (mean increment in serum glucose was 24% over baseline). Nine infants received a test dose of 0.5 gm/kg/hr of lipid. Their response was similar to that in the lower infusion group, but of a greater magnitude: an eightfold increase in free fatty acids, sustained increase in serum insulin concentration, and a mean increment in serum glucose values of 65% over baseline. Increased lipid availability in the low-birth-weight newborn infant plays a significant role in promoting an increase in serum glucose concentrations.

Hyperviscosity in the newborn lamb produces pertubation in glucose homeostasis

We studied the effect of hyperviscosity on plasma glucose concentration, endogenous glucose production, and plasma insulin concentration in 12 term mixed breed newborn lambs. After a 7-hr fast, 0.45% saline was infused at a constant rate for 6 hr during which time hourly plasma glucose and 3-hourly plasma insulin concentrations were determined. A glucose turnover determination by the prime-constant infusion technique using 3H6 radiolabeled glucose was performed at a steady state. An exchange transfusion was then carried out using maternal packed red blood cells in six lambs to produce hyperviscosity and using maternal whole blood in six other lambs to maintain normoviscosity. After the exchange transfusion, a second study identical to that in the pre-exchange period was carried out. There was no significant difference in the mean plasma glucose concentration (mg/dl; mean +/- S.E.) between groups during the first turnover period (pre-exchange transfusion) [103 +/- 4.9 (normoviscous) versus 96 +/- 4.8 (Hyperviscous)], but during the postexchange transfusion turnover period, the plasma glucose concentration was lower in the hyperviscous than in the normoviscous group [89 +/- 4.3 (Normoviscous) versus 76 +/- 4.0 (Hyperviscous)] (P less than 0.05.) Endogenous glucose production declined from the first to the second glucose turnover determination in both groups, but there was no significant difference between the normoviscous and hyperviscous groups. Plasma insulin concentrations were similarly low in both groups suggesting suppression in the fasted state. The data suggest that the hyperviscosity acts as an independent variable to depress plasma glucose concentration, the mechanism of which is still undefined.

Endogenous posthepatic insulin secretion and metabolic clearance rates in the neonatal lamb

Posthepatic insulin availability has been evaluated by steady-state insulin turnover studies with 131I-insulin. Spontaneously delivered term (age 3.3 +/- 0.8 days) (mean +/- S.E.) and prematurely delivered lambs (betamathasone treated at 132 days) (age, 1.1 +/- 0.2 days) were compared with 4- to 5-month-old sheep. After a 7-hr fast, animals received 0.45% saline or 5.7 mg/kg/min glucose (0.06 ml/kg/min) for 6-hr followed by the tracer insulin infusion for 110 min. Plasma glucose, insulin, and immunoprecipitable insulin were measured sequentially during the steady state. Endogenous posthepatic insulin secretion and metabolic clearance rates were derived. Neither endogenous posthepatic insulin secretion rates nor metabolic clearance rates were different among the three groups of animals when either 0.45% saline or 5.7 mg/kg/min exogenous glucose infusions were compared. Secretory response of the pancreatic beta cell to continuous glucose infusion seems similar for the term and preterm lamb when compared to adult sheep.

The role of hepatic control of glucose homeostasis in the etiology of neonatal hypo- and hyperglycemia

Precise control of glucose homeostasis is well recognized in the adult. Going from a period of complete dependence on the maternal organism for delivery of substrate, the fetus is born not only with a need to furnish himself with glucose for energy and rapid growth but also with the need to maintain a balance between glucose deficiency and excess. This is especially difficult because of the intermittent nature of exogenous oral intake in the neonatal period. Development of glucose homeostasis requires a balance between substrate availability (both absolute and relative) and coordination of hormonal, neural and enzymatic systems. The large number of conditions producing or associated with both hypo- and hyperglycemia in the newborn, especially the low birth weight or sick neonate, emphasizes this vulnerability. Newer techniques including stable isotope methodology, now being employed with increasing frequency, will help define maturation of neonatal carbohydrate homeostasis and further clarify nutritional requirements in this transitional period.

The preterm small-for-gestational age infant: a two-year follow-up study

Previous investigators have reported unfavorable neurologic and developmental outcome of small-for-gestational age (SGA) infants (birth weight less than 1,500 grams born at term or at less than 30 weeks. of gestation. Since obstetrical considerations for the delivery of a SGA fetus often arise between 30 and 38 weeks, the outcome of these survivors becomes a relevant issue. In 1975 and 1976, twenty-eight of 47 such infants survived and 21 were followed sequentially during the first two years. Their birth weight was 1,220 +/- 195 grams (mean +/- S.D.) and the gestation 33.4 +/- 2 weeks. Each SGA infant was paired with a birth weight-matched appropriate-for-gestation (AGA) infant whose birth weight was 1,195 +/- 190 grams and gestation 29 +/- 2 weeks. The weight, length, and head circumference of the SGA infants attained the tenth percentile by 6 to 8 months and were similar to the AGA group. Quarterly neurologic examinations showed similar findings during the first year in the two groups. At 2 years, two SGA (diplegia) and one AGA (hemiplegia) infants were abnormal. The quarterly Bayley scores of the SGA infants were lower during the first 18 months but at 24 months, the two groups had similar scores. The favorable outcome in preterm SGA infants weighing less than 1,500 grams may serve as useful information in making clinical decisions for the management of mothers with suspected intrauterine growth retardation.

Renal functions of low birth weight infants during the first two months of life

A postnatal contraction of extracellular fluid occurs in low birth weight infants. Patterns of postnatal renal maturation were assessed with the assumption that changes in body composition were mediated in part by the developing kidney. Twenty-two appropriate for gestational age, low birth weight infants (birth weight mean = 1380 g, gestational age mean 31 weeks) were studied between 12 hr and 61 days of age to evaluate simultaneously glomerular and tubular functional maturation. Since most low birth weight infants have respiratory morbidities (respiratory distress followed by chronic lung disease), the infants were grouped into: group I (13 infants), transient or absent respiratory morbidities; and group II (9 infants), persistent and severe respiratory morbidites. Sodium excretion decreased with postnatal age in both groups. Sodium intake did not vary with postnatal age. The percentage of fractional sodium excretion was inversely related to postnatal age. Creatinine clearance correlated directly with postnatal age in both groups. Increased sodium excretion and percentage of fractional sodium excretion in the first 10 days of life may reflect extracellular fluid solute losses through the kidney. The premature kidney matured in a balanced fashion and persistent respiratory morbidities did not alter this pattern.