CHANGES IN THE CONCENTRATIONS OF GLUCAGON-LIKE PEPTIDE-1(7-36)AMIDE AND GASTRIC-INHIBITORY POLYPEPTIDE DURING THE LACTATION CYCLE IN GOATS

Plasma concentrations of glucagon-like peptide-1 (7-36)amide (GLP) and gastric inhibitory polypeptide (GIP) were determined at fortnightly i ntervals for over a year throughout the pregnancy-lactation cycle of g oats. Both GIP and GLP concentrations were elevated during lactation a nd f'ell rapidly when milk secretion was terminated. At the onset of l actation GLP concentrations rose rapidly whereas GIP concentrations sh owed a delayed response. GLP concentrations remained high throughout l actation but those of GIP declined linearly as milk yields fell. Serum insulin concentrations correlated positively with plasma glucose conc entrations but not with either GIP or G-LP concentrations. Negative co rrelations were found between serum insulin concentrations and milk yi eld and plasma non-esterified fatty acid concentrations. The results a re consistent with plasma GIP and GLP concentrations being: determined by other factors in addition to nutrient intake and absorption. Chang es in GIP concentrations mirrored reported changes in the hypertrophy and atrophy of the intestine in ruminants while GLP concentrations may be more dependent on the neural and endocrine factors associated with lactation. The elevated concentrations of both peptides indicated a s pecific role in lactation independent of their normal anabolic and ins ulinotropic effects.