Uptake of [6,7- 3H]Estradiol-17β in ovariectomized rats, guinea pigs, and hamsters: Correlation with species differences in behavioral responsiveness to estradiol

Abstract

Activation of female copulatory behavior requires a far lower dose of esterified estradiol in rats and guinea pigs than in hamsters. Thus, rats and guinea pigs can be said to be behaviorally more responsive to estradiol than hamsters. In the current experiment, the time-course of uptake and metabolism of [6,7- 3H]estradiol-17β was studied in ovariectomized rats, guinea pigs, and hamsters in an attempt to correlate possible species differences in these measures to the afore-mentioned species differences in behavioral responsiveness to estradiol. It was found that rats and guinea pigs had a much higher affinity for [6,7- 3H]estradiol-17β (as indicated by tissue/plasma concentration ratios) than hamsters in uterus, anterior pituitary, and hypothalamus. These results suggest that one factor involved in species differences in response to a hormone is differential target tissue affinity for the hormone. Some species differences in metabolism of [6,7- 3H]estradiol-17β were also noted, but estrone appeared to be the principal metabolite in all three species.