Release of ovarian progesterone during the rat oestrous cycle by ganglionic cholinergic influence: the role of norepinephrine

The coeliac ganglion neurons, whose axons constitute the superior ovarian nerve (SON), contain cholinergic receptors. The aim of this work was to study the effect of cholinergic agents added to the coeliac ganglion on the release of ovarian progesterone in the coeliac ganglion-SON-ovary in vitro system. We also analyzed the release of norepinephrine in the ovarian compartment and its possible relationship with the release of progesterone. After the addition of cholinergic agents in the ganglion compartment, progesterone release was determined by radioimmuneassay (RIA) and norepinephrine by catecholamine assay (HPLC). The release of progesterone and norepinephrine in the ovary compartment was studied during period of 180 min in pre-oestrus (PE), oestrus (E), dioestrus day 1 (D1) and dioestrus day 2 (D2) rats. The most relevant results concerning the action of acetylcholine were found on PE and dioestrus. On PE, the pre-ovulatory peak of progesterone, which is known to respond to the endocrine action, was not modified by neural effect of acetylcholine in our scheme. On the other hand, the progesterone peak occurs in the afternoon of D1, which has been described as independent of the gonadotrophic action but was inhibited by neural effect of acetylcholine in our experimental scheme. This action on D1 was accompanied by a decrease of norepinephrine release in the ovary compartment. We conclude that the action of cholinergic agents varies according to the oestrous cycle stage and constitutes one of the factors governing the secretory activity of the ovarian steroids, in this case, progesterone.