Ovarian Asymmetry

Abstract

Ovarian asymmetry reaches its maximum expression in birds, where only the left ovary develops. In mammals, differences in ovarian performance can be seen in the bat Taphozous melanopogon melanopogon, where ovulation occurs only in the right ovary; or in the white-toothed shrews, Crocidura russula monacha, where the left ovary plays a dominant role over the right one. In humans, the right ovary receives more innervation than the left. This review evaluates established concepts on ovarian asymmetry, and presents evidence that ovarian innervation plays a role in the differentiation between right and left ovaries. Analyses of the effects of surgical denervation, and on the effects of systemic or local injection of neurotoxins, or drugs, affecting neuronal transmission, have shown that the ovarian innervation arriving through the superior ovarian nerve plays a direct role in regulating ovarian follicle responses to the effects of gonadotropins. The ovary sends neural information of its activities to the central nervous system via the vagus nerve. The response to the neural signal arising from the ovary can be ipsilateral or contralateral. Therefore, the regulation of ovarian functions depends not only on the effects of gonadotropins, but also, on the modulating effects of the ovarian innervation on gonadotropin actions and the specific ovary under study.