Bilateral ovariectomy or adrenalectomy are experimental tools used to understand the mechanisms regulating the hypothalamus-pituitary-ovarian and the hypothalamus-pituitary-adrenal axis. There is evidence that acute unilateral perforation of the dorsal peritoneum in rats results in significant changes in progesterone, testosterone and estradiol serum concentrations. Because different surgical approaches for unilateral or bilateral ovariectomy or adrenalectomy, sectioning the superior ovarian nerve or the vagus nerve are used, we compare the acute effects on hormone serum concentrations resulting from the unilateral or bilateral dorsal approach to performing bilateral ovariectomy or adrenalectomy with those obtained when an unilateral incision is performed in the ventral abdomen. In general, the progesterone, testosterone and estradiol serum concentrations were higher in animals with ventral approach than in those with dorsal surgery, the effects varying depending on the day of the estrous cycle when surgery was performed. The results suggest that the neural signals arising from different zones of the peritoneum and/or the abdominal wall play different roles in the mechanisms regulating steroid hormones concentrations.

The present study analyzed the participation of the left and right superior ovarian nerves (SON) in regulating progesterone, testosterone, and estradiol serum levels in unilaterally ovariectomized rats on each day of the estrous cycle. For this purpose, ovarian hormone concentrations in serum were measured in animals with either sham-surgery, unilateral ovariectomy (ULO), unilateral sectioning of the SON, or sectioning of the SON innervation of the in situ ovary in rats with ULO. This investigation results show that the right and left ovaries have different capacities to maintain normal hormone levels, that such capacity varies during the estrous cycle, and that it depends on the integrity of the SON innervation. In rats with only one ovary, the effects of ovarian denervation on hormone levels varied according to which ovary remained in situ, the specific hormone, and the day of the estrous cycle when treatment was performed. Present results support the idea that the ovaries send and receive neural information that is processed in the central nervous system and we propose that this information participates in controlling the secretion of gonadotropins related to the regulation of ovarian functions.

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 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.