STIMULATING EFFECT OF PYROGLUTAMYLGLUTAMYLPROLINE-AMIDE, A PROSTATIC,TRH-RELATED TRIPEPTIDE, ON MOUSE SPERM CAPACITATION AND FERTILIZING ABILITY IN-VITRO

Pyroglutamylglutamylprolineamide, a prostatic tripeptide with structur al similarities to thyrotrophin-releasing hormone (TRH), has been foun d in the seminal plasma of several mammalian species, suggestive of a biological function relating to spermatozoa. Using chlortetracycline ( CTC) fluorescence analysis and in vitro fertilization, we have obtaine d evidence that the tripeptide stimulates mouse sperm capacitation and fertilizing ability in vitro. The tripeptide at concentrations from 5 -500 nM was added to sperm suspensions and cells were assessed with CT C after 40 min, insufficient time for complete capacitation by a major ity of spermatozoa under standard conditions of incubation. Concentrat ions of 25 nM and higher significantly promoted capacitation, as evide nced by a decrease in the proportion of acrosome-intact F pattern sper matozoa, characteristic of uncapacitated cells, and an increase in the proportion of acrosome-intact B pattern spermatozoa, characteristic o f capacitated cells. However, there was no significant stimulation of acrosomal exocytosis. These results suggested that peptide-treated cel ls would be more fertile than their untreated counterparts. This was c onfirmed using in vitro fertilization, where the presence of 100 nM pe ptide during sperm preincubation and gamete coincubation significantly stimulated fertilizing ability (peptide, 56.5% of oocytes fertilized; controls, 26.5%). Comparison of the prostatic tripeptide and TRH effe cts on capacitation revealed that TRH at a concentration of 250 nM was as effective as the prostatic tripeptide in promoting the F double ri ght arrow B transition but was less effective or ineffective at lower concentrations. In vitro fertilization assessment of the two peptides, at 100 nM, revealed that only the prostatic tripeptide significantly stimulated fertility. Again, this was consistent with the CTC analyses . Because the prostatic tripeptide can stimulate sperm function in vit ro, it is possible that it plays a similar role in vivo and promotes f ertilizing ability of ejaculated spermatozoa. We therefore propose tha t this tripeptide be referred to as fertilization promoting peptide (F PP). (C) 1994 Wiley-Liss, Inc.