Fertilization promoting peptide, a tripeptide similar to thyrotrophin-releasing hormone, stimulates the capacitation and fertilizing ability of human spermatozoa in vitro.

Recent studies have demonstrated that a prostatic tripeptide similar in structure to thyrotrophin-releasing hormone (TRH) can stimulate the in-vitro capacitation and fertilizing ability of epididymal mouse spermatozoa. Therefore we have proposed that this tripeptide be referred to as fertilization promoting peptide (FPP). Using chlortetracycline fluorescence analysis and the hamster oocyte penetration test (HOPT), we have obtained evidence that FPP can also promote the capacitation and fertilizing ability of ejaculated human spermatozoa in vitro. FPP (25-200 nM) caused a significant increase in the proportion of B-pattern uncapacitated cells, with no significant stimulation of acrosomal exocytosis. Comparison of FPP with two structurally similar tripeptides, TRH and pyroglutamyl phenylalanylprolineamide, at 50 nM revealed that only FPP could significantly promote capacitation. Finally, after a brief exposure to progesterone to induce acrosomal exocytosis in capacitated cells, FPP-treated suspensions penetrated a significantly higher proportion of oocytes than the untreated controls when assessed in the HOPT. The presence of FPP in human seminal plasma at concentrations similar to those used here suggests that, in vivo, FPP may play a positive role in promoting human sperm function.