Synthetic seminal plasma peptide inhibits testosterone production in frog testis in vitro.

The role of synthetic seminal plasma peptide, designed using biochemical and mass spectroscopy analyses of native peptides extracted from seminal plasma, was studied in amphibian (Rana esculenta) testicular steroidogenesis. Production of testosterone and prostaglandin F(2alpha) was determined by incubating frog testes with synthetic peptide in vitro. Analysis of the data showed a dose-dependent inhibition of testosterone production (43% at 10(-5) M concentration) without prostaglandin F(2alpha) synthesis being affected. Determination of the peptide activity during the annual R. esculenta reproductive cycle showed inhibition of testosterone production in post-reproductive and recovery periods, suggesting a possible involvement of peptide in gonad steroidogenesis.