Influence of macrophage migration inhibitory factor (MIF) on the zinc content and redox state of protein-bound sulphydryl groups in rat sperm: indications for a new role of MIF in sperm maturation

The function of macrophage migration inhibitory factor(MIF) in spermmaturation was studied by investigating its role in the biochemical maturation of the outer dense fibres. Rat spermobtained from the caput and cauda epididymiswere stimulated overnight with either recombinant MIF or MIF-containing vesicles originating from epididymalfluid at various concentrations. The zinc content of both the spermand the medium was determined by means of atomic absorption spectrometry. Incubation in both recombinant MIF and vesicular MIF resulted in a statistically significant decrease of the zinc content in stimulated caput spermof , 50%. In parallel, the conditioned media showed a clear increase in the concentration of this trace metal. The effect of MIF was less marked in cauda sperm. In addition, we demonstrated a statistically significant increase of detectable free thiol groups in the spermmid- and principle piece in isolated rat spermafter stimulation with MIF at concentrations of 25 and 50 ng/ml. Our data suggest that MIF plays an important role in the maturation process of rat spermduring epididymaltransit by inducing the elimination of zinc and affecting the amount of free sulphydryl groups in the spermflagella.