The process of secretion of adenohypophysial hormones will be analyzed in vivo and in vitro. Emphasis will be placed on two hormones, prolactin and growth hormone. Changes in hormone levels in pituitary tissue and in blood or incubation medium will be followed by three assay methods: bioassay, radioimmunoassay and electrophoretic assay. The objective of these studies is to evaluate changes in form of the hormone in the gland and after secretion. The secretory process will also be studied in two model systems that provide homogeneous populations of secretory cells: the pars intermedia of the anuran pituitary and the rostral parsdistalis of the teleost adenohypophysis. The effects of chemical modifications of purified rat prolactin and growth hormone on their activity in the three assay methods will be analyzed to determine the kinds of alterations that can produce differential detectability. Attempts will be made to purify the hypothalamic factors that regulate prolactin and growth hormone secretion and their mechanisms of action will be analyzed. Radioimmunoassays for prolactin and growth hormone that are more meaningful, physiologically, than those currently available will be developed, by using the secreted forms of these hormones for immunization, for labeling with I125 and as standards.