The proposed study is designed to characterize the mechanisms of action of the physiological and pharmacological agents which govern the secretion of prolactin by the pituitary gland. These mechanisms will be compared with those involved in the synthesis and secretion of prolactin by pituitary tumors. A dispersed pituitary cell technique will be developed and these cells will be packed in a chromotographic column and perfused with median containing dopamine agonists and antagonists. A comparison of the response of normal pituitary cells with those pituitary tumors will be studied. The opposing effects of dopamine and estradiol will be studied in vivo and in vitro. The generation of pituitary tumors in rats fed potassium thiocyanate will be attempted and, the response of this tumor to dopamine agonists will be compared with those produced in pituitary tumors MtTW15 and 7315a. Preliminary data suggest that some pituitary tumors are devoid of dopaminergic receptors and that pituitary glands loose their sensitivity to dopamine agonists after prolonged incubation. The possible relation between these phenomena will be studied. Finally the possibility that dopamine catalyzes the generation of a substance within the pituitary gland which is the direction inhibitor of prolactin secretion is proposed. Studies to identify the substance are described.