The structure of a hormone determines its function in target tissues. Recently, we have identified phosphorylated bovine prolactin (bPRL) and growth hormone (bGH). We have isolated and characterized the phosphorylated bPRL and have preliminary evidence that the structure of phosphorylated bPRL is different from nonphosphorylated bPRL. The hypothesis to be tested in this proposal will determine if in vivo posttranslational phosphorylation of either bPRL or bGH creates a hormone messenger with biological activities different from those of the native hormone. Posttranslational phosphorylation offers a mechanism by which the pituitary can specifically tailor several endocrine messages from a single gene product. These findings may have significant implications in our understanding of the physiology of the endocrine system. The bovine pituitary provides a system where isolation and characterization of PRL and GH are neither complicated by the structural and biological consequences of glycosylation nor limited by tissue availability. The specific objectives to test the hypothesis are: 1.Isolate and structurally characterize phosphorylated bPRL and bGH. 2. Determine the biological actions of phosphorylated bPRL and bGH in a series of bioassays and receptor assays and compare these activities with those induced by nonphosphorylated and reference preparations. If the hypothesis is correct then: 3.Determine the physiological agents that regulate the phosphorylation and secretion of bovine prolactin and growth hormone.