Recent progress in our understanding of the structure and function of gonadotropins has led to the development of hormone analogs that can be tailored to have desirable levels of LH and/or FSH activities. It is now possible to design analogs of human chorionic gonadotropin (hCG) that retain virtually the entire structure of hCG but that function more like FSH. Indeed, some are even more potent than FSH in vivo. Other analogs of hCG have been developed that bind to both LH and FSH receptors. The abilities of these analogs to mimic LH or FSH in vivo are unknown. Studies proposed in Aim 1 are designed to develop a long-acting bifunctional gonadotropin agonist. This will be accomplished in part by attaching the C-terminus of the hCG Beta-subunit to an analog known to have dual LH and FSH activity. Studies in Aim 1 will also determine if creating additional glycosylation signals in the alpha and Beta-subunits will prolong the half-life of this hCG analog. The studies in Aims 2 and 3 are a prelude to the development of a potent bi-functional LH/FSH antagonist that will have a long plasma half-life. In Aim 2 we will determine the effects of removing the N- and O-linked oligosaccharides from hCG on its clearance. While it is well known that chemical or enzymatic deglycosylation reduces the half-life of gonadotropins, the effects of genetic deglycosylation are unknown. In Aim 3 we will determine if specific amino acids in the Beta-subunits of hCG, FSH, and bovine LH are responsible for their different turnover rates. In Aim 3 we will also study the effects of inserting an inter-subunit disulfide bond on hormone activity and clearance. The hypothesis to be tested is that gonadotropin clearance is partly a consequence of subunit dissociation. The presence of an inter-subunit disulfide may slow subunit dissociation and substantially reduce clearance. In Aim 4 we will prepare and test a deglycosylated analog of hCG that binds to both LH and FSH receptors to learn if it blocks the actions of both LH and FSH. The final design of this analog will depend on what is learned about prolonging the half-lives of deglycosylated gonadotropins in Aims 2 and 3.