Effects of two different patterns of estradiol replacement on the sexual behavior of rhesus monkeys

Seven pairs of rhesus monkeys consisting of adult males and adult, ovariectomized females were tested for sexual behavior. Behavioral tests were conducted under two patterns of estradiol treatment of the females. Under the "constant estrogen" condition, females were given SC injections of 10 micrograms estradiol benzoate on 28 consecutive days. Under the "cyclic estrogen" condition, females were given 28 days of estradiol treatment at varying doses based upon the artificial menstrual cycle devised by Michael, Zumpe and Bonsall (6). Rates of male mounting, hip-touch (incomplete mounts), and male threaten-away behavior (redirected aggression) increased during estradiol administration. Mounting peaked at the time of the highest estrogen dosage in the cyclic treatment condition, but was highest during the first portion of the period of constant treatment. Hip-touch and threaten-away behaviors were more frequent in the constant condition than during cyclic treatment. The high levels of these behaviors during the constant treatment suggest a lack of coordination between male and female motivation which is overcome by providing estradiol stimulation in a pattern which mimics the menstrual cycle.