Effect of gastrin-releasing peptide (GRP) and GRP antagonists on TSH secretion from rat isolated pituitaries
C V Santos1, C C Pazos-Moura, E G Moura
1Department of Physiological Sciences, State University of Rio de Janeiro, Brazil.
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-Phe8-GRP and Gly6-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 (Ala6-GRP) did not change TSH secretion. This result suggests the existence of different subtypes of GRP receptors in the anterior pituitary gland.
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