When ovariectomized Fischer female rats are hormonally primed with 10 μg
estradiol benzoate, a 5 min restraint experience rapidly inhibits
lordosis behavior. Addition of
progesterone to the hormonal priming prevents this restraint-induced inhibition. In prior work, we reported evidence that
progesterone receptors (PR) may contribute to this protective effect of
progesterone. In the current manuscript, we provide evidence that
progesterone metabolites may also contribute to
progesterone's ability to reduce the effects of restraint. Ovariectomized female rats were hormonally primed with 10 μg
estradiol benzoate followed 2 days later with 4.0 mg/kg of the
progesterone metabolite,
allopregnanolone.
Allopregnanolone, administered either 4 h or 2 h before the restraint experience, was as effective as
progesterone in reducing the
lordosis-inhibitory effects of restraint. In the second experiment,
progesterone metabolism was blocked with 50 mg/kg of the 5α-reductase inhibitor,
finasteride. Surprisingly,
finasteride did not prevent
progesterone from reducing the effects of restraint. In a third experiment, we tested the possibility that
allopregnanolone acted through metabolism to
dihydroprogesterone. Rats were treated with
allopregnanolone or with
allopregnanolone plus the 3α-hydroxysteroid
dehydrogenase inhibitor,
indomethacin.
Indomethacin did not prevent
allopregnanolone from reducing the effects of restraint. Mechanisms are discussed whereby cross-talk between PR-mediated and metabolite-mediated events may converge in producing
progesterone's attenuation of the effect of restraint.