Activation of spermatozoan adenylate cyclase by a low molecular weight factor in porcine seminal plasma.

The ejaculated porcine spermatozoa were fractionated into the cytosol, membrane, midpiece plus tail (flagella) and head fractions, and their adenylate cyclase activities were measured. About 65% of the total activity was located in the flagella fraction. For all the fractions, Mn2+-dependent adenylate cyclase activity was about 20 times higher than Mg2+-dependent activity, and guanine nucleotides, fluoride, and other reagents tested did not activate adenylate cyclase. The results suggest that the GTP-dependent regulatory subunit is absent in porcine spermatozoa. The porcine seminal plasma was found to stimulate the adenylate cyclase activity in spermatozoa. The stimulating factor in porcine seminal plasma was partially purified by gel filtration and the molecular weight of the factor appeared to be between 200 and 300. The partially purified factor is heat stable and is not inactivated by treatment with Pronase, trypsin, phospholipase A2 or D but is inactivated by acid hydrolysis. It is easily soluble in water, partially soluble in methanol, and insoluble in ethanol, ethyl ether, chloroform, or acetone. The activation of sperm adenylate cyclase by the factor occurred without a time lag. The activating effect was dose-dependent, saturated at high dose, and ascribed to the increase of the maximal velocity (Vmax). The effect of the factor appears to be limited to adenylate cyclase in spermatozoa; the factor activated adenylate cyclase both in porcine and bovine spermatozoa but failed to activate those in other porcine tissues. The factor was shown to activate the enzyme not only in the ejaculated spermatozoa but also in the epididymal sperm. The factor was also found to elevate the cAMP level in the intact porcine spermatozoa. The factor enhanced the motility of corpus and cauda epididymal spermatozoa. These findings indicate the possibility that this factor initiates the spermatozoan motility upon ejaculation through directly activating adenylate cyclase.