ECHISTATIN, A DISINTEGRIN, INHIBITS SPERM-OOLEMMAL ADHESION BUT NOT OOCYTE PENETRATION

Objective: To study the effects of echistatin, a disintegrin known to block the binding of fibronectin (FN) and vitronectin to their respect ive integrin receptors, alpha 5 beta 1 and alpha v beta 3, on the adhe sion of human spermatozoa to the oolemma of zona-free hamster eggs and their subsequent penetration. Design: Motile capacitated human sperma tozoa and zona-free hamster eggs were coincubated in the presence of e chistatin or in its absence and observed at short serial intervals. Wh ole mounts of these eggs, washed out of sperm suspension and stained w ith acridine orange, were scored for numbers of oolemmal adherent and penetrating sperm. Setting: University Hospital laboratories. Patients : Known fertile semen donors. Main Outcome Measures: Numbers of sperma tozoa adherent to the oolemma and those penetrating the oocyte. Result : Sperm adherence to the oolemma was reduced significantly at micromol ar concentrations of echistatin, in a concentration-dependent manner. In contrast, echistatin did not inhibit the penetration of oocytes by sperm that had become adherent to the oolemma despite the presence of echistatin. Conclusions: We propose that two processes occur in the bi nding of sperm to the oolemma, one that is echistatin sensitive and po ssibly involving the integrin receptors that recognize FN and vitronec tin, and a second process, resistant to echistatin, that leads to game te membrane fusion.