Endocrinologic basis of electrochemical vaginal potential in estrous cycle of rats

This sequel to an earlier report on the correlation of vagino-oral voltage measurements in rats with their estrous cycles deals with the endocrinologic activation of these voltages. The normally sinusoidal voltages, positive during estrus and negative during diestrus, were absent in spayed rats but were restored with a single intraperitoneal injection of 5 microgram or more of 17beta-estradiol or with 0.1 mg of adrenaline injected subcutaneously every 12 hours. Estrogen antagonists, drugs that inhibit catecholamine synthesis or adrenergic beta blockers, totally inhibit the negative potential recorded during estrus. Vaginal estrous potentials in the rat reflect an important reproductive state possibly linked to sexual behavior (heat) or to ovulation. Triggering of the cyclic potential by adrenaline without estrogenic medication suggests that adrenaline belongs to the group of sexual-specific hormones.