The present work was devoted to the study of certain aspects of the interaction of rat specific epididymal proteins (SEP) with spermatozoa.

No abstract

Previous investigations have established the production of specific epididymal proteins (SEP) in the rat which become attached to the sperm surface as these cells pass along the duct. The present study is concerned with the regulation of SEP synthesis by androgens. For this purpose, we determined the concentrations of SEP and protein DE, one of its main components (40%), during sexual maturation, after castration with and without androgen administration, and after ligation of the efferent ductuli in rats. SEP were first detectable at 25 days of age and attained adult values at 60-90 days of age. Protein DE behaved similarly. Castration of the adult rat led to a decrease in SEP and DE concentrations. The fall was more rapid and marked in the caput than in the caudal segments. SEP synthesis seemed to stop promptly after castration; the different rates of decrease of SEP in caput and cauda may reflect different rates of exit of spermatozoa from those segments. SEP and DE concentrations in castrated rats were increased by the administration of testosterone (100 micrograms/day). The SEP concentration was increased after 4 days and restored to control values after 11 days of treatment. Testosterone and 5 alpha-dihydrotestosterone were equipotent in inducing SEP and DE synthesis, while 5 alpha-androstandiols were less potent. The effects of androgens were significantly reduced by the simultaneous administration of cyproterone acetate. We propose that SEP is a suitable marker for following the action of androgens in the epididymis.

Androgenic stimulation (0.1 microM testosterone or 5 alpha-dihydrotestosterone in the medium) of cultured human epididymal tubules increased the synthesis of five proteins, identified by their mobility relative to albumin (Ra) in polyacrylamide gels as 0.31, 0.43, 0.67, 0.81 and 1.01. This effect was inhibited by the simultaneous presence of 10 microM cyproterone acetate in the medium. The caput epididymidis was the most active region in the production of these proteins and a gradient of decreasing activity was found in successive segments. The appearance of induced proteins in the culture medium suggests their secretory nature, while some data indicate that androgens may also affect the secretory process. Bands corresponding to Ra 0.31, 0.43, 0.68 and 1.01 were found in caput and cauda epididymidis fluids, while bands coincident with Ra 0.31 and 0.43 were consistently found in extracts (0.5 M NaCl) of caudal spermatozoa. Preliminary determinations of molecular weight and isoelectric point for the different bands yielded the following results: Ra 0.31, 38,000 and 5.8; Ra 0.43, 21,000 and 6.2; Ra 0.68, 69,000 and 5.1; Ra 0.81, 13,900 and 6.8; and Ra 1.01, 29,000 and 6.8.

Notwithstanding our improved descriptive knowledge of events occurring to mammalian sperm during epididymal maturation, the nature of the mechanisms involved in the development of such primary functions as forward motility (Bedford, 1975) and zona pellucida recognition (Saling, 1982) remain obscure.This review attempts to summarize the latest information produced by our laboratory in relation to the interaction of epididymal products with spermatozoa and the bearing that this interaction might have on sperm function.Our interest has been primarily focused on androgen-induced secretory epididymal proteins that associate to sperm during epididymal transit and that our group has described in rats (Cameo and Blaquier, 1976), hamsters (Gonzalez Echeverria, Cuasnic6 and Blaquier, 1982) and humans (Tezón et al., 1985b).Immature hamster sperm, obtained from the proximal segments of the epididymis, were used as a model to induce in vitro modifications of their functions (Cuasnicu et al., 1984a). Exposure of these spermatozoa to a preparation enriched with androgen-induced secretory proteins EP2-EP3 (Gonzalez Echeverria, was able to induce a significant increase in homologous zona pellucida binding (Cuasnicu et al., 1984b). Since zona binding seemed to be one of the functions developed by sperm during epididymal transit (Cuasnic6 et al., 1984a;Saling, 1982), our results were interpreted as reflecting the in vitro advancement of the maturational stage of these spermatozoa which was caused by the added epididymal preparation. Similarly, we were also able to show that immature sperm gained in fertilizing ability when pre-treated in vitro with the epididymal extract prior to in vivo or in vitro insemination (Gonzalez Echeverria et al., 1984).Our latest results confirm these preliminary findings and support the role of epididymal proteins in sperm maturation. Briefly, our studies show that the preparation of the epididymal proteins mentioned above, in which EP2-EP3 represented 16 % of the total protein, had a biological activity such that, on the average, treated sperm fertilized twice as many oocytes as their untreated controls (Gonzalez Echeverria et al., 1984 (Gwatkin, 1977)