Abstract
Several studies have been reported on the occurrence of sperm motility inhibiting factors in the male reproductive fluids of different mammalian species, but these proteins have not been adequately purified and characterized. A novel sperm motility inhibiting factor (MIF-II) has been purified from caprine epididymal plasma (EP) by Hydroxylapatite gel adsorption chromatography, DEAE-Cellulose ion-exchange chromatography and chromatofocusing. The MIF-II has been purified to apparent homogeneity and the molecular weight estimated by Sephacryl S-300 gel filtration is 160 kDa. MIF-II is a dimeric protein, made up of two subunits each having a molecular mass of 80 kDa as shown by SDS-PAGE. The isoelectric point of MIF-II is 5.1 as determined by chromatofocusing and isoelectric focusing. It is a heat labile protein and maximal active at the pH 6.9 to 7.5. The sperm motility inhibiting protein factor at 2 µg/ml (12.5 nM) level showed maximal motility-inhibiting activity. The observation that the epididymal plasma factor lowered the intracellular cAMP level of spermatozoa in a concentration-dependent manner suggests that it may block the motility of caprine cauda spermatozoa by interfering the cAMP dependent motility function. The results revealed that the purified protein factor has the potential of sperm motility inhibition and may serve as a vaginal contraceptive. The antibody raised against the MIF-II has the potential for enhancement of forward motility of cauda-spermatozoa. This antibody may thus be useful for solving some of the problems of male infertility due to low sperm motility.
Highlights
Reproduction is a normal process of life
Occurrence of motility inhibiting protein factor has been reported in epididymal plasma of bovine [5], rat [6,7] and caprine [8]
Validity of the earliest reports on the occurrence of the motility inhibitor in different reproductive fluids remains to be proved in view of the observations that washed spermatozoa stick to the glass surface of hemocytometer which is widely used for sperm motility assays and this phenomenon of ‘‘cell- sticking’’ may give rise to artifact in motility estimations [25]
Summary
Reproduction is a normal process of life. Sperm maturity/ motility is essential to acquire fertilizing ability of male gamete. When mammalian sperm first enter the epididymis from the testis they are neither motile nor fertile. As they travel down the epididymis, they gradually acquire full capacity for progressive motility [1]. Spermatozoa are maintained in a quiescent state in the cauda epididymis until ejaculation. Several reports are there that mammalian reproductive fluids contain some factors, which cause quiescence of sperm. Studies on the bovine [5] reported clearly that its relatively low pH of about 5.5 acts in concert with some yet unidentified quiescence factor to maintain their immotile state. The quiescent state of rat spermatozoa in the distal epididymis may be dependent on a specific inhibitor protein, presumably acting at the sperm surface [6]. In our previous report we have discussed about the occurrence of motility inhibiting factor from caprine EP [8]
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