The role of the muscarinic system in regulating estradiol secretion varies during the estrous cycle: the hemiovariectomized rat model.

There is evidence that one gonad has functional predominance. The present study analyzed the acute effects of unilateral ovariectomy (ULO) and blocking the cholinergic system, by injecting atropine sulfate (ATR), on estradiol (E2) serum concentrations during the estrous cycle. The results indicate that ULO effects on E2 concentrations are asymmetric, vary during the estrous cycle, and partially depend on the cholinergic innervation. Perforation of the left peritoneum resulted in lower E2 serum concentrations in the three stages of the estrous cycle. At proestrus, unilateral or bilateral perforation of the peritoneum resulted in lower E2 serum concentrations.ULO of the right ovary (left ovary in situ) resulted in significantly higher E2 concentrations than animals with ULO of the left ovary (right ovary in situ). ATR treatment to ULO rats on D1 resulted in a significant drop of E2 serum concentrations. ULO rats treated with ATR on D2 or P, resulted in an asymmetrical E2 secretion response; when the right ovary remained in situ an increase in E2 was observed, and a decrease when the left ovary remained in situ. The results obtained in the present study suggest that each ovary's ability to compensate the secretion of E2 from the missing ovary is different and varies during the estrous cycle. The results also suggest that the cholinergic system participates in regulating ovarian E2 secretion. Such participation varies according to the ovary remaining in situ and the stage of the estrous cycle of the animal. The results agree with previously stated hypothesis of a neural pathway arising from the peritoneum that participates in regulating E2 secretion, and also supports the idea of cross-talk between the ovaries, via a neural communication, that modulates E2 secretion.

The acute asymmetric effects of hemiovariectomy on testosterone secretion vary along the estrous cycle. The participation of the cholinergic system.

The presence of asymmetry in the capacity of the left and right ovaries to secrete testosterone was analyzed by studying the effects of hemiovariectomy along the estrus cycle one hour after surgery. The effects of ether anesthesia on hormone serum levels were also analyzed. Bilateral ovariectomy and the extirpation of the left ovary performed on the day of proestrus resulted in significantly lower testosterone levels. Compared to the anesthetized group, the effects of perforating the peritoneum unilaterally varied according to the day of the estrous cycle and the side of the peritoneum surgery was performed on. Injecting atropine sulfate (ATR) to control or anesthetized rats on D1 resulted in a significant increase of testosterone serum levels. The effects of perforating the peritoneum on testosterone levels depended on the cholinergic innervation and varied along the estrous cycle. Blocking the cholinergic system before performing unilateral or bilateral ovariectomy had different effects depending on the day of the estrous cycle. Testosterone plasma levels increased significantly when surgery was performed on the day of diestrus and dropped when surgery was performed on proestrus. Similar effects were observed when the left adrenal was extirpated from animals with the cholinergic system blocked. The results presented herein support the hypothesis of asymmetry in the ovaries' abilities to secrete steroid hormones, and that the capacity to secrete testosterone varies along the estrous cycle.

The participation of the cholinergic system in regulating progesterone secretion through the ovarian-adrenal crosstalk varies along the estrous cycle.

This study was designed to analyze the acute effects of unilateral or bilateral ovariectomy or adrenalectomy, performed on different days of the estrous cycle, on progesterone (P4) serum levels 1 h after surgery. The effects of blocking the cholinergic system by injecting atropine sulfate were also analyzed. Ether anesthesia treatment on diestrus 1 (D1) increased P4 serum levels. Compared to right sham-operated animals, right ovariectomy (left ovary in situ) performed on diestrus 2 (D2) or proestrus (P), resulted in P4 serum levels increase. Compared to animals with left sham surgery, left adrenalectomy (right adrenal in situ) performed on P day resulted in significantly lower P4 concentrations. Bilateral adrenalectomy resulted in a significant drop of P4 serum levels; the most remarkable drop was observed in animals treated on D2. Bilateral ovariectomy performed on D1 resulted in lower P4 serum levels, and the same treatment performed on P resulted in a significant rise of P4 serum levels. Injecting atropine sulfate to untouched (control group) rats resulted in significantly higher P4 concentrations. Blocking the cholinergic sys-tem on D1 or P to rats with the right adrenal removed resulted in lower P4 serum levels; while, in contrast, atropine sulfate treatment performed on D2 resulted in P4 serum levels increase. The results support the hypothesis of asymmetry in the ovaries' and adrenals' capacities to secrete P4; that this capacity varies along the estrous cycle; and that P4 secretion by the ovaries and adrenals is regulated by the cholinergic system.