Recent cloning of cDNAs for LH, FSH and TSH receptors indicated these proteins belong to a sub-family of G-protein-coupled receptors with seven transmembrane regions and a large extracellular domain. We have recently isolated cDNAs for both human LH and FSH receptors and expressed the functional proteins capable of signal transduction in transfected cells. Binding studies indicated that the human receptors, unlike their rodent counterparts, have unique species-specific ligand recognition properties, underlying the importance of using the human receptors to study human physiology and pathophysiology. Because truncated rat LH receptor with only the extracellular region retains full ligand binding, we propose to study the ligand binding and signal transduction of human LH and FSH receptors with altered N-linked carbohydrates and peptide backbone in the extracellular region. Using a recently adapted RNA virus expression system, we will express large amounts of the extracellular region of recombinant human LH and FSH receptors with full ligand binding ability for testing as receptor antagonists in vitro and in vivo. Using the human LH receptor and a reporter gene driven by a gonadotropinresponsive promoter, we have developed a luminescence bioassay for human LH and CG. We will use this bioassay to screen for defective hCG molecules during spontaneous abortion. Because auto-antibodies to TSH receptors have been shown to be involved in different thyroid diseases, we propose to use recombinant human gonadotropin receptors to screen for inhibitory and stimulatory receptor autoantibodies in sera of patients with premature ovarian failure and testotoxicosis, respectively. The present proposal should yield truncated human receptors capable of selectively antagonizing the actions of human LH and FSH in patients,, as well as further our understanding of diseases with defects of gonadotropins and their receptors.