Plasma Glucagon-Immunoreactive Components in Early Life in Dogs

Summary

High plasma concentrations of C-terminal immunoreactive glucagon (IRG) have been found during early life in several mammalian species. We have analyzed the plasma IRG of 12 h to 60 day-old dogs in terms of the 4 peaks (IRG ^> 20,000, IRG⁹⁰⁰⁰, IRG³⁵⁰⁰ and IRG ²⁰⁰⁰) obtained by gel filtration on Bio-Gel P-30. Significant changes with age and in response to administered agents were confined to IRG⁹⁰⁰⁰ and IRG³⁵⁰⁰. IRG⁹⁰⁰⁰ was 9-fold higher in 12-36 h old dogs than in adults (108 ± 24 pg/ml pancreatic glucagon equivalents v. 12 ± 3 pg/ml, mean ± SEM) and showed a decline to 2-fold higher (27 ± 5 pg/ml) at 31-60 days. IRG³⁵⁰⁰ was higher than in the adult only during the first 36 h of life (36 ± 5 pg/ml v. 15±3 pg/ml). Arginine infusion (0.5 g/kg over 15 min) caused an increase in plasma levels of both IRG⁹⁰⁰⁰ and IRG³⁵⁰⁰ in the newborn, whereas in adult dogs only IRG³⁵⁰⁰ was increased. Insulin injection (0.2 U/kg intravenously) causing a marked hypoglycemia had no significant effect on the plasma level of any IRG component in newborn dogs. Dihydrosomatostatin infusion (10 μg/kg bolus ± 90 μg/kg over 30 min) caused a decrease in both IRG⁹⁰⁰⁰ and IRG³⁵⁰⁰. The increased basal level and secretory response to arginine of IRG⁹⁰⁰⁰ in newborn dogs may reflect an immaturity of the A cells, whereby more of this component, which may represent a precursor of pancreatic glucagon, is secreted than in the adult. The immature A cells also appear to have an impaired secretory response to hypoglycemia.

Key-Words:

Immunoreactive Glucagon Components - Neonatal - A Cell - Arginine - Hypoglycemia - Somatostatin