The effects of gastric inhibitory polypeptide (GIP) on the release of anterior pituitary hormones.

Several members of the secretin family of hormones have been demonstrated to alter anterior pituitary hormone secretion. Here we report the action of gastric inhibitory polypeptide (GIP) on gonadotropin and somatotropin release. Intraventricular injection of 1 microgram (0.2 nmole) GIP (2.5 microliters) produced a significant decrease in plasma FSH at 30 (p less than 0.02) and 60 min after its injection (p less than 0.01). The FSH-lowering effect of a higher dose of 5 micrograms (1 nmole) of GIP was already developed at 15 min (p less than 0.01) and was prolonged until the end of the experiment (60 min, p less than 0.05). No change in plasma LH was detected at any time during the experimental period. If 5 micrograms of estradiol-benzoate were given SC 48 hr prior to experiment, the initial values of FSH and LH were markedly decreased. In these animals GIP failed to influence plasma FSH and LH. When dispersed anterior pituitary cells from OVX rats were cultured overnight and incubated in vitro with GIP, the peptide was found to induce both FSH and LH release. Highly significant release occurred with the lowest dose tested of 10(-7) M and there was a dose-response effect for both hormones. The slope of the dose-response curve was similar for both FSH and LH release. GIP was less potent than LHRH which produced a greater stimulation of both FSH and LH release at a dose of 10(-9) M than did 10(-7) M GIP. The two peptides had an additive effect on the release of both FSH and LH.(ABSTRACT TRUNCATED AT 250 WORDS)