Autoradiographic demonstration of 125I-Tyr4-bombesin binding sites on rat anterior pituitary cells.

Because several direct effects of bombesin related peptides on pituitary hormone release have been demonstrated, we chose to study the presence of bombesin binding sites in the adult male rat anterior pituitary in aggregate cell culture by autoradiographic localization of 125I-tyrosine4-bombesin (125I-Tyr4-BBN) binding and immunocytochemical localization of the anterior pituitary hormones. When aggregates were cultured in medium without hormonal supplements, the number of cells with detectable 125I-Tyr4-BBN binding was below 1%. In cell aggregates cultured in the presence of 1 nM estradiol (E2) 125I-Tyr4-BBN binding was detected on 5.4 +/- 0.8% of the cells after redispersion and on 5.8 +/- 1.1% of the cells in sections of paraffin embedded aggregates. The binding cell types were mainly lactotrophs and somatotrophs. The binding of 125I-Tyr4-BBN (3 or 5 nM) was specific because it was inhibited by the addition of an excess of unlabelled Tyr4-BBN or the bombesin receptor antagonist L686,095. In aggregates cultured in the presence of 1 nM E2 and 4 nM dex, the percentage of cells with detectable 125I-Tyr4-BBN binding was significantly lower than that in aggregates cultured in the presence of 1 nM E2 alone. Binding on somatotrophes almost completely disappeared. The present data show that specific 125I-Tyr4-BBN binding sites are present on anterior pituitary cells, are detectable mainly on a small subpopulation of lactotrophs and somatotrophs, and are affected by hormonal conditions.(ABSTRACT TRUNCATED AT 250 WORDS)