Adult male Sprague-Dawley rats rarely exhibit
progesterone-facilitated
lordosis following
steroid treatments which are effective in females. In contrast,
progesterone-facilitated
lordosis has been observed following priming with
estradiol pulses in another strain. The aim of this study was to compare
progesterone-facilitated feminine sexual behavior in adult male and female Sprague-Dawley rats following priming with
estradiol benzoate (EB) or
estradiol pulses. Female sexual behavior was measured in adult, gonadectomized males and females treated as follows: Two pulses of
estradiol followed by
progesterone or oil the next day; EB (two doses) for 3 days, and
progesterone or oil the next day. These protocols were repeated at 4- or 6-day intervals, respectively.
Progesterone-facilitated
lordosis was observed consistently in both sexes treated with
estradiol pulses. By the fifth test,
lordosis quotients did not differ between the sexes, but the
lordosis ratings in
progesterone-treated males remained lower than those observed in females. Proceptivity (hop-darting) was facilitated by
progesterone in females, but was never observed in males.
Lordosis was induced in both sexes by 15 micrograms EB, but was not reliably facilitated by
progesterone. Treatment with the lower dose of EB (1.5 micrograms) induced high levels of receptivity in females (occasionally facilitated by
progesterone), but not in males regardless of subsequent treatment (i.e,
progesterone or oil). These data suggest that
progesterone-facilitated
lordosis can be induced in male Sprague-Dawley rats, if a regimen of
estradiol pulses is used. Thus, the brain of the adult male is not inflexibly differentiated with regard to
progesterone facilitation of feminine receptive behavior.