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
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Neonatal
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A Cell
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Arginine
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Hypoglycemia
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Somatostatin