Neuromedin-B shows a widespread distribution throughout mammalian neural and peripheral tissues and may be involved in the modulation of a variety of physiological processes. The highest concentrations of neuromedin-B are found in the anterior pituitary gland, suggesting that it may be of physiological importance within this tissue. To examine this hypothesis, we have used Northern blotting to demonstrate that neuromedin-B is present in the anterior pituitary as a result of local synthesis and have examined the effects of endocrine manipulations on its mRNA and immunoreactive peptide content. In thyroidectomized male rats, neuromedin-B content was decreased (104.1 +/- 5.8 vs. control, 390.9 +/- 23.3 fmol/gland; P less than 0.01) as was its mRNA (7 +/- 1.3% vs. 100%; P less than 0.014), while treatment of intact animals with T4 produced no effect on either peptide content or mRNA. Adrenalectomized male rats showed a significant increase in both neuromedin-B content (313.8 +/- 11.8 vs. control, 233.7 +/- 16.9 fmol/gland; P less than 0.05) and mRNA (377 +/- 27% vs. 100%; P less than 0.014), while dexamethasone treatment increased peptide content (347.8 +/- 32 vs. control, 233.7 +/- 16.9 fmol/gland; P less than 0.01) without any effect on mRNA levels. In female rats, ovariectomy decreased neuromedin-B content (132.4 +/- 13.3 vs. control, 335.0 +/- 37.2 fmol/gland; P less than 0.01) and mRNA levels (6 +/- 2% vs. 100%; P less than 0.014) while estrogen treatment of both ovariectomized and intact rats produced large increases in neuromedin-B (887.8 +/- 114.4 and 1328 +/- 175 fmol/gland, respectively, vs. control, 335.0 +/- 37.2 fmol/gland; both P less than 0.01) and its mRNA (246 +/- 18% and 378 +/- 31%, respectively, vs. 100%; both P less than 0.014). In castrated male rats, no significant alteration in peptide content was observed, and treatment of both castrated and intact male rats with testosterone was similarly without effect. These results demonstrate that 1) neuromedin-B is locally synthesized within the rat anterior pituitary gland; and 2) the local production of neuromedin-B is influenced by endocrine status, which is consistent with an autocrine/paracrine role for this peptide in this tissue.