Binding of Cytochalasin B to Hexose Transport Sites on Human Spermatozoa and Inhibition of Binding by Purines

Abstract

The action of prostaglandin E₂ (PGE₂) on the response of the circular muscle of the oviductal isthmus to stimulation of the perivascular, adrenergic nerves was compared in estrous and hCG treated rabbits. We measured latency from nerve stimulation to evoked potential discharge as well as the intramural pressure increase reflecting circular muscle contractions. We assume that these parameters are indirect estimates of the amount of norepinephrine (NE) released during nerve stimulation. In oviducts from estrous rabbits, PGE₂ (10^-13 M) increased the latency and decreased the magnitude of the contraction in response to nerve stimulation but had no effect on spontaneous myogenic activity or on the sensitivity of the muscle to exogenous NE. Therefore, the inhibitory actions of PGE₂ are probably on the adrenergic nerve terminals within the muscle, resulting in a decrease in the amount of transmitter released during nerve stimulation. On the other hand, PGE₂ (10^-13 M) had no effect on the neurogenic responses of oviducts from rabbits 72 h after injection of hCG. These results suggest that neurogenic contractions of the circular muscle of the isthmus may become insensitive to the inhibitory effects of endogenous prostaglandin soon after ovulation occurs. Thus, tonic neurogenic activity could reinforce the spontaneous contractions of the circular muscle of the isthmus which are believed to mediate ovum transport.