Insulin and gastric inhibitory polypeptide secretion in young milk-fed and adult goats.

Plasma concentrations of glucose, immunoreactive insulin (IRI), and immunoreactive gastric inhibitory polypeptide (IR-GIP) were studied in six adult and five young milk-fed goats after intravenous or intraduodenal infusions of glucose. Glucose concentrations after intraduodenal infusions were elevated from 3.5 to 4.7 mmol/liter on the average in adult and from 4 to 7 mmol/liter in young goats. Intravenous infusions were given at rates adjusted to mimic very closely the plasma glucose curves after intraduodenal infusions. Plasma IRI increased from 250 to 600 pmol/liter in adult and from 180 to 500-600 pmol/liter in young goats, but no significant differences were observed between intravenous and intraduodenal infusions. Duodenal infusions of glucose did not stimulate the release of IR-GIP in adult or young goats. It is concluded that the goat is lacking the incretin system for rapid disposal of oral glucose loads and that IR-GIP does not participate in regulation of glucose-stimulated insulin release in this species.