THE INFLUENCE OF ADRENAL-HORMONE STATUS ON NEUROENDOCRINE PEPTIDES IN THE RAT ANTERIOR-PITUITARY GLAND

Neuropeptide Y (NPY), neurotensin (NT), substance P (SP) and vasoactive intestinal peptide (VIP) are four structurally unrelated neuroendocrine peptides which affect anterior pituitary function. All four peptides appear to be locally synthesized in the anterior pituitary gland and have been shown to be regulated by thyroid and/or sex hormone status. We show here that NT, SP and VIP but not NPY are influenced by adrenal hormone status in the male rat pituitary gland. Adrenalectomy increased the content of VIP (35.4+/-4.0 (S.E.M.) vs control 11.9+/-1.1 pmol/g wet weight) but decreased that of SP (18.8+/-2.3 vs control 36.7+/-3.9 pmol/g wet weight). Adrenalectomy combined with castration decreased the content of SP (14.6+/-3.5 vs control 36.7+/-3.9 pmol/g wet weight) but had no effect on VIP content. Treatment with dexamethasone produced significant decreases in NT, SP and VIP contents (17.8+/-2.3 vs control 32.6+/-3.4 pmol/g wet weight, 5.5+/-0.9 vs control 36.7+/-3.9 pmol/g wet weight and 4.2+/-0.6 vs control 11.9+/-1.1 pmol/g wet weight respectively). The changes in pituitary peptide contents occurred in parallel with changes in mRNA levels, suggesting that alterations in glucocorticoid hormone status can alter the synthesis of these peptides. These results, together with the known effects of these neuroendocrine peptides suggest possible functions for locally produced SP and VIP in regulating the secretion of adrenocorticotrophin and/or other proopiomelanocortin-derived peptides. The differnetial effects of adrenalectomy and adrenalectomy combined with castration on VIP suggests that the regulation of this pituitary peptide is complex, and may be dependent, in part at least, on gonadal factors.