Effect of gastrin-releasing peptide (GRP) and grp antagonists on TSH secretion from rat isolated pituitaries

Abstract

It has previously been demonstrated that gastrin releasing peptide (GRP), a bombesin-like peptide, inhibited TSH release “in vivo”. In this study, we have shown that GRP acts directly at the pituitary gland, inhibiting basal and TRH-stimulated TSH release from incubated rat anterior pituitary glands. This effect was observed at the highest GRP concentration (10 −5 M), but not at the lower concentrations (10 −7 and 10 −9 M). Incubation of the glands with two antagonists of GRP (d-Phe 8-GRP and Gly 6-GRP) induced an increase of basal TSH secretion. We suggest a physiological role of locally produced bombesin-like peptides in the control of TSH release. Another antagonist (Ala 6 — GRP) did not change TSH secretion. This result suggests the existence of different subtypes of GRP receptors in the anterior pituitary gland.