Chemical Characterization of Neuroendocrine Targets for Progesterone in the Female Rat Brain and Pituitary

The secretory products of some of the cell types which respond directly to actions of progesterone in the female rat brain and pituitary were determined by combining immunocytochemistry with autoradiography following systemic administration of the synthetic progestin ligand 3H-R5020. Four major findings are reported: (1) Approximately 90% of the tyrosine hydroxylase (TH)-immunoreactive neurons in the hypothalamic arcuate nucleus have progesterone receptors, while TH-immunoreactive neurons in other portions of the hypothalamus (e.g. the periventricular region and the zona incerta) do not. (2) Approximately 30% of the beta-endorphin neurons in the hypothalamus have progesterone receptors. (3) None of the luteinizing hormone-releasing hormone neurons examined have progesterone receptors. (4) Approximately 98% of the cells in the anterior pituitary that have progesterone receptors contain luteinizing hormone. Lactotrophs do not contain progesterone receptors. Many progestin targets in the brain remain to be characterized chemically. The implications for progesterone-inducible genes and neuroendocrine control systems are discussed.