Differences among ovariectomized female rhesus macaques in the display of sexual behavior without and with estradiol treatment.
Ovariectomized, estrogen-primed, adult female rhesus macaques were preselected for the display of high (HLP) and low (LLP) levels of sexual performance. Eight sexually vigorous adult males were selected as partners. For 13 consecutive days each month, females received 0, 2.5, 5.0, and 10.0 micrograms of estradiol benzoate (EB) and were tested on Days 12 and 13 of injection. Blood samples were taken before and on the last day of each of the four injection series, and serum levels of estradiol, progesterone, and testosterone were determined with a radioimmunoassay. The HLP females (n = 5) displayed higher levels of receptivity and proceptivity and received more mounts, intromissions, and ejaculations when tested without EB treatment than LLP females (n = 5) did when they were tested with 10.0 micrograms of EB. Female receptivity, proceptivity, and attractiveness cannot be explained by estrogen action alone. The effectiveness of estrogen is limited by the somatic characteristics of the individual on which it acts.