This award from the U.S.-Argentina Cooperative Science Program supports research in biology to be conducted by Dr. Jose R. Lemos of the Worcester Foundation for Experimental Biology, Dr. Roger Y. Tsien of the University of California, San Diego and Dr. Ernesto J. Podesta of the University of Buenos Aires, Argentina. The project focuses on the fact that the interaction of a peptide with the appropriate receptors on a cell surface, and the subsequent signal transduction are some of the most important steps in the mechanism of peptide hormone action. The approach will allow study of the mechanism of peptide hormone stimulation of steroid secretion. The aim of the project is to understand stimulus- secretion coupling. Using state-of-the-art techniques, the investigators will examine the compartmentalization of the cAMP-mediated response of individual Leydig cells to hormonal stimulation. The award will allow continuation of a productive U.S.-Argentina collaboration.