Hormonal correlates of sexual behavior in the female musk shrew: the role of estradiol.

Plasma levels of several steroid hormones in the female musk shrew, (Suncus murinus), are reported along with experiments on the causational role steroids play in female sexual behavior. Gonadally intact females sampled directly after a brief (about 7 minutes on average) sexual interaction with a male had equivalent plasma levels of estradiol (E2) but significantly higher plasma progesterone (P4) levels than resting females. In Experiment 2, females that engaged in nonsexual activities with conspecifics other than gonadally intact males had plasma levels of E2 and P4 equivalent to those of females that engaged in sexual behavior with males. Taken together, the results of these two experiments suggest that the relatively higher levels of plasma P4 noted in active musk shrews is not a response specific to sexual interactions with males. In Experiment 3, ovariectomized musk shrews were treated with E2 implants. These tonically administered physiological doses of E2 were not able to activate sexual behavior. However, two steroid-sensitive reproductive target tissues, the cervix and flank pad, were responsive to E2 treatment. Supplemental injections of P4 given to E2 treated ovariectomized females were also ineffective in restoring sexual behavior. These results suggest that physiological doses of E2 do not have direct effects on the expression of female sexual behavior in this mammalian species.