Identification of bombesin-immunoreactive cells in rat, human, and other mammalian pituitaries, their ontogeny and the effect of endocrine manipulations in the rat.

Bombesin and gastrin-releasing peptide are homologous peptides which have biological activity in mammals. The distribution of bombesin immunoreactivity in rat, guinea pig, cat, dog, pig, cow, monkey, and human pituitaries was investigated using immunocytochemistry with various different antisera. Polyclonal antisera identified bombesin-immunoreactive (IR) cells in the anterior pituitaries of all species except monkey and human, although positive nerves were present in the human posterior lobe. In contrast, a monoclonal antibody demonstrated bombesin-IR cells in anterior and intermediate lobe (or equivalent) of all species. Both types of antibodies identified the anterior pituitary cells as somatotrophs, which may be significant because bombesin and related peptides influence pituitary growth hormone secretion. Differences in bombesin immunoreactivity were seen in male and female rats, with males having more positive cells, and females showing more intense immunoreactivity in those cells which were positive. Ontogenetic studies in rats revealed that bombesin-IR cells were first seen at birth. The effect of estrogen on bombesin-IR cells was studied using ovariectomized and estrogen-treated female rats. Estrogen treatment decreased very significantly the number of bombesin-IR cells, compared with controls, whereas ovariectomy increased significantly the frequency of bombesin-IR cells, so that the staining pattern began to resemble that seen in normal male rats. No bombesin-IR cells were detected in pituitaries from thyroidectomized rats. These results suggest that immunoreactive bombesin/gastrin-releasing peptide in the pituitary is modulated by endocrine status and this peptide may be involved in paracrine interactions in this tissue.