Role of glucagon in perinatal glucose homeostasis

The role of pancreatic insulin secretion in neonatal glucoregulation. I. Healthy term and preterm infants

The glucoregulatory role of insulin in adult subjects is undisputed. However, less is known about the secretion of insulin and its actions in the neonatal period, either for healthy subjects, or for those at risk of disordered blood glucose homoeostasis. The relationships between blood glucose and plasma immunoreactive insulin concentrations were therefore examined in 52 healthy children (aged 1 month-10 years), 67 appropriate birth weight for gestational age (AGA) term infants, and 39 AGA preterm neonates. In children and AGA neonates, plasma immunoreactive insulin concentration was positively related to blood glucose concentration. However, although both groups of neonates had significantly lower blood glucose concentrations than children, plasma immunoreactive insulin concentrations were significantly higher in both term and preterm neonates, when compared with children. The variation in plasma immunoreactive insulin concentrations was greater for neonates than for children. These data suggest, that compared with older subjects, plasma immunoreactive insulin concentrations are high in newborn babies and that neonatal pancreatic insulin secretion is less closely linked to circulating blood glucose concentrations. There are important implications for the interpretation of studies in hypoglycaemic and hyperglycaemic neonates.

Metabolic events in infants of diabetic mothers during first 24 hours after birth. I. Changes in plasma glucose, insulin and glucagon

Changes in plasma glucose, nonantibody-bound insulin and glucagon concentrations were studied in 32 newborn infants of diabetic mothers (IDM) during the first 24 hours after birth. Ten infants were born to White class A mothers and 22 to class B-F mothers. The infants were kept fasting during the investigative period and blood was sampled from an umbilical artery catheter. At birth, plasma glucose and glucagon levels were similar in the class A and B-F infants, whereas nonantibody-bound insulin levels were approximately 15-fold higher in the class B-F infants than in the class A infants (p less than 0.001). After birth, plasma glucose fell in all infants, the nadir being reached at two hours (p less than 0.01). Plasma glucose fell by approximately 35% in the class A infants and 63% in the class B-F infants (p less than 0.01). Eight IDM had asymptomatic hypoglycemia (plasma glucose less than 1.9 mmol/l) and four of these infants had glucose levels below 1.7 mmol/l and were withdrawn from further study. In the remaining four hypoglycemic IDM, plasma glucose was about 1.6-fold higher (p less than 0.01) and insulin about 11-fold higher (p less than 0.001) at birth compared to the 24 normoglycemic IDM. The hypoglycemia was attended by unchanged insulin levels in the class A infants, whereas insulin fell in the class B-F infants (p less than 0.01). However, during the whole investigative period, plasma insulin of the class B-F infants was higher than that of the class A infants (p less than 0.01). After birth, plasma glucagon increased slowly in all IDM and peak values were reached after 12 hours in the class A infants (p less than 0.05) and 24 hours in the class B-F infants (p less than 0.01). Only those infants who became hypoglycemic after birth exhibited a significant increment in plasma glucagon from 0.2 hours (p less than 0.05). These results suggest that neonatal hypoglycemia of IDM results from high plasma levels of nonantibody-bound insulin together with a very retarded increment in plasma glucagon levels. The degree of neonatal hypoglycemia and hyperinsulinemia of an individual IDM seems to be positively correlated to the severity of the diabetes of the mother.

Pancreatic endocrine response to the first feed in term newborn infants

Blood glucose, insulin, C-peptide and glucagon were evaluated in 36 newborn term infants at birth, and before and 60 min after the first feed during the first day of life. Under basal conditions glycaemia diminished during the first day of life and glucagon increased, while insulin and C-peptide did not show any variation. The C-peptide: insulin molar ratio was higher in the newborn than in adults because of the longer half-life of C-peptide, probably due to reduced renal function in the neonatal period. The subjects were divided into two groups: 18 newborn infants were given a feed of commercially available milk powder reconstituted in water at 10% (5 ml/kg); the other 18 were given a feed of 5 ml/kg 10% glucose solution. In each group 6 were given the first feed after a fast of 6 h, 6 after a fast of 12 h and 6 after a fast of 24 h from birth. After the first feed with milk, the average increase of glycaemia was 19.83 mg%, of insulin 6.06 muU/ml, and of C-peptide 1.88 ng/ml. After the first feed with glucose the average increase of glycaemia was 13.59 mg%, of insulin 2.46 muU/ml, and of C-peptide 0.59 ng/ml. Glucagon did not show significant changes after the first feed.

Interrelation of maternal and foetal glucose and free fatty acids. The role of insulin and glucagon

At birth there is a statistically significant correlation between the maternal blood sugar and the umbilical venous and arterial blood glucose. The glucose concentration in the mother is higher than in the umbilical vein, and in the latter higher than in the umbilical artery. The free fatty acids also show a falling gradient from the mother to the umbilical vein and artery. This supports the assumption that glucose and FFA pass the placenta from the mother to the foetus. Insulin concentration is significantly higher in the mother than in the cord blood. There is however no difference between umbilical venous and arterial plasma insulin. A statistically significant correlation between glucose and insulin is only demonstrable in the maternal blood. Glucagon levels are about the same in maternal and umbilical arterial blood, but are significantly higher in umbilical venous blood. These results are consistent with the supposition that insulin and glucagon do not cross the placenta to a significant extent and can be synthesised by the foetus. In the first few hours after birth, a fall of glucose and a rise in FFA occur at the same time. Insulin tends to be lower than at birth and glucagon rises.

Effect of intravenous L-alanine administration on plasma glucose, insulin and glucagon, blood pyruvate, lactate and beta-hydroxybutyrate concentrations in newborn infants. Study in term and preterm newborn infants

Ten term and eleven preterm newborn infants with appropriate weights for their gestational age were infused for one minute with L-alanine (150 mg/kg) at the age of 29 to 76 hours (mean 48 hours) and circulating levels of glucose, lactate, pyruvate, D-betahydroxybutyrate (D-BOHB), insulin and glucagon were monitored. Plasma glucose concentrations increased from 2.7 +/- 0.16 (mean +/- S.E.M.) to 3.7 +/- 0.2 mmol/l after 50 min (p less than 0.01) in term infants. In preterm infants, after an initial decrease of the glucose level from 3.1 +/- 0.16 to 2.6 +/- 0.16 mmol/l (p less than 0.05), it returned to the baseline level at 50 min: 3.0 +/- 0.2 mmol/l. The blood concentration of D-BOHB decreased in term infants from 192 +/- 37 to 112 + 6 micrometer/l (p less than 0.01) after 40 min. In preterms, its decrease was not significant (p greater than 0.05). Plasma glucagon level rose from 53 +/- 5 to 70 +/- 8 pmol/l after ten minutes (p less than 0.01) in terms infants and from 61 +/- 6 to 75 +/- 9 after 20 min (p less than 0.01) in preterm infants. There were no significant changes in plasma insulin concentrations in either group. Forty minutes after L-alanine infusion, I/G ratios were lower in preterm infants (1.26 +/- 0.14) than in term infants (1.71 +/- 0.25) (p less than 0.01). There was no relationship between the glycemic responses to L-alanine and the basal levels of D-BOHB. The data suggest that the glycemic effect of L-alanine infusion and circulating glucagon depends upon a specific stage in maturation. The antiketogenic effect of L-alanine infusion is observed in term infants as in adults.