Effect of progesterone on the hypothalamic cAMP concentration in estradiol-primed rats.

The effect of progesterone on the concentration of adenosine 3',5' cyclic monophosphate (cAMP) in the hypothalamus of ovariectomized estradiol primed rats was studied. Progesterone (2 mg/rat), injected 3 days after the priming dose of estradiol benzoate into ovariectomized rats, produced 4 h later an increase in the hypothalamic nucleotide content; whereas the lowest levels of cAMP were found 24 h after progesterone injection suggesting a biphasic response. The increase of hypothalamic cAMP observed at 4h of progesterone injection was blocked by the administration of an alpha(phenoxybenzamine) or a beta-adrenoblocker (propranolol) suggesting the participation of both, alpha and beta adrenergic receptors. Nevertheless, the administration of diethyldithiocarbamate, a blocker of norepinephrine synthesis has no effect to prevent the increase of hypothalamic cAMP induced by progesterone. Since no changes were observed in the hypothalamic cAMP concentration in the animals killed by afternoon, it may be inferred that the effects of progesterone on this parameter may depended on the time of the day at which it was administered.