Increased numbers of sperm in the oviducts and improved fertilization rates in rabbits after administration of phenylephrine or ergonovine near the time of insemination.

Phenylephrine, an alpha-adrenoceptor agonist, was administered im to does near the time of mating or insemination. The treatment increased sperm numbers in the oviducts by about 50-fold and in the uterus by about 10-fold at 2 or 2.5 h after insemination. Methoxamine, another alpha-adrenoceptor agonist that was given im, did not increase sperm numbers, although both phenylephrine' and methoxamine significantly increased the number and amplitude of uterine contractions when contractions were measured by strain gauge force transducers attached to the uterus of conscious does. Ergonovine, an ergot derivative given im, increased sperm numbers more than 10-fold in the oviducts and five to 10-fold in the uterus at 2 or 2.5 h after insemination. Ergonovine increased the frequency and amplitude of uterine contractions when given iv but not when given im. In tests with a range of doses of phenylephrine and ergonovine, 5 mg of phenylephrine and .6 mg of ergonovine appeared to be near optimal for maximizing the number of sperm in the uterus and oviducts at 2.5 h after insemination. Phenoxybenzamine, an alpha-adrenoceptor blocking agent, prevented the phenylephrine-induced increases in both uterine contractions and sperm numbers in the oviducts and uterus. Phenoxybenzamine also prevented the effect of ergonovine on sperm numbers. In does inseminated with low numbers of sperm (92,000; an inseminate selected to result in a low fertilization rate in control does), the administration of phenylephrine or ergonovine significantly increased ovum fertilization rates (16% for control does, 52 and 63%, respectively, for phenylephrine- and ergonovine-treated does).