Galanin is widely distributed throughout the rat neural and endocrine system. The highest concentrations are found in the anterior pituitary, and it can influence classical pituitary hormone secretion. The effects of endocrine manipulation on pituitary galanin content, mRNA, and immunostaining have been investigated in the rat. In females, medical (39 +/- 4 fmol/gland), surgical (33 +/- 2), or combined (28 +/- 6) castration resulted in a highly significant decrease in galanin content (control, 223 +/- 14; P less than 0.0001). Estrogen in physiological and pharmacological doses produced a significant increase in galanin content (368 +/- 14 and 373 +/- 13, respectively; P less than 0.01) associated with an increase in galanin mRNA content. In the male, high dose dexamethasone and thyroidectomy caused a fall in galanin content, while galanin mRNA levels showed a rise and fall, respectively. Adrenalectomy caused a rise in galanin content, while adrenalectomy and castration produced a dramatic decrease in tissue galanin content. No change in galanin mRNA was observed in these groups. Galanin immunostaining paralleled the results of tissue content in all groups examined, except in the medically castrated group, in which there was some intragroup variation in staining patterns. In normal and high-dose estrogen-treated females, galanin expression was seen mainly in lactotrophs, with a small number of somatotrophs and thyrotrophs staining. In the male, galanin expression was confined to somatotrophs and thyrotrophs. Galanin mRNA was localized at the cellular level by in situ hybridization. In the normal pituitary only scattered lactotrophs contained message, while in high-dose estrogen-treated animals the number of positive cells, mostly lactotrophs, was vastly increased. Thus, the cellular localization of galanin immunostaining varies between the sexes. Galanin peptide and mRNA levels in the pituitary are powerfully influenced by endocrine status.