Pharmacological developments in male contraception

Characterization of the proteomes associating with three distinct membrane raft sub-types in murine sperm

Mammalian sperm are transcriptionally and translationally inactive. To meet changing needs in the epididymis and female tract, they rely heavily on post-translational modifications and protein acquisition/degradation. Membrane rafts are sterol and sphingolipid-enriched micro-domains that organize and regulate various pathways. Rafts have significance in sperm by transducing the stimulus of sterol efflux into changes in intracellular signaling that confer fertilization competence. We recently characterized three biochemically distinct sub-types of sperm rafts, and now present profiles for proteins targeting to and associating with these sub-types, along with a fraction largely comprised of "non-raft" domains. Proteomics analysis using a gel-based LC-MS/MS approach identified 190 strictly validated proteins in the raft sub-types. Interestingly, many of these are known to be expressed in the epididymis, where sperm membrane composition matures. To investigate potential roles for rafts in epididymal protein acquisition, we compared the expression and localization of two different sterol-interacting proteins, apolipoprotein-A1 (apoA1) and prominin-1 (prom1) in sperm from different zones. We found that apoA1 was gradually added to the plasma membrane overlying the acrosome, whereas prom1 was not, suggesting different mechanisms for raft protein acquisition. Our results define raft-associating proteins, demonstrate functional similarities and differences among raft sub-types, and provide insights into raft-mediated epididymal protein acquisition.

The effects of oxytocin and arginine vasopressin in vitro on epididymal contractility in the rat

Oxytocin (OT) and arginine vasopressin (AVP) have been found to be present in the reproductive system of the mammalian male, but their function in this system is unclear. This study examined the effects of these two hormones on contractions of the rat caput epididymis, as well as the hormones' effects on epididymal diameter during contractions. The initial segments of caput epididymides were observed in vitro in a solution of modified Tyrode's solution, with a test solution containing a concentration of either OT or AVP being added after a 5-min period. The frequency and diameter of the epididymal contractions were measured before and after addition of each test solution. Also observed was the effect of magnesium concentrations on the ability of OT to induce changes in epididymal contractility. This study found that the frequency of epididymal contractions increase and that the diameter of the epididymal tubules decrease proportionally during contractions with the addition of either OT or AVP. Furthermore, we noted that Mg++ has an inverse correlation with the frequency of contractions of the caput epididymis both in the presence and absence of OT. These findings suggest that both OT and AVP may have a role in regulating epididymal contractility and thus, perhaps, sperm transport through that organ.