Several studies suggest that when manipulated experimentally in adulthood, the
lordosis response to
estrogen can be increased dramatically in male rats. Because adult-gonadectomized (Gx) animals were used in these studies, the lack of
testicular hormones in adulthood may have been
a factor. To examine this possibility, adult-Gx rats were implanted with blank (Bk)-,
testosterone (T)-, 5alpha-dihydrotestosterone (DHT)-, or
progesterone (P)-filled capsules, alone or in combination. We report a new finding, that a combined treatment of T plus P (T+P) at physiological doses for the male, but not T or P alone, reduced
lordosis significantly in males, with and without
estrogen priming. T+P did not inhibit
lordosis in females, nor did this specific treatment affect open field, aggressive, and male copulatory behaviors. In confirming studies done with much higher doses, DHT reduced
lordosis in both sexes. DHT and T+P also reduced
lordosis in adrenalectomized/Gx males. Mechanisms responsible for the T+P inhibition of
lordosis in males are not known, but they may include an upregulation of
androgen receptors by P, and this possibility is discussed.