Physiological importance of dopamine as a noradrenaline precursor in the corpus luteum.

1. Both in vivo and in vitro studies have demonstrated that the adrenergic innervation of the ovary affects corpus luteum (CL) secretory function in many species. 2. In cattle, ovarian noradrenergic stimulation or the administration of noradrenaline (NA) to the ovary increases ovarian oxytocin (OT) secretion and post-translational processing of OT synthesis within a few minutes. Furthermore, NA affects both progesterone release and its synthesis by increasing cytochrome P450sec and 3 beta-hydroxysteroid dehydrogenase activity. This effect is mediated via luteal cell beta 1- and beta 2-adrenoceptors. 3. The total number of luteal beta-adrenoceptors correlates with peripheral progesterone concentrations during the luteal phase. Conversely, ovarian denervation causes a decrease of steroidogenic activity in the corpus luteum, an increase in beta-adrenoceptors on luteal cells, a delay in follicular development and the disruption of cyclicity, as well as other effects. Moreover, brief pharmacological blockade of ovarian beta-adrenoceptors in the mid-cycle of cattle decreases progesterone secretion by 20-40%. 4. We conclude that tonic beta-adrenoceptor stimulation of the CL ensures the basal secretion of progesterone, whereas acute noradrenergic activation supports the CL during stressful situations that could impair its function. Dopamine concentrations within the CL are highly correlated with those of NA during the oestrous cycle and are higher in the newly formed compared with the developed CL, the regressed CL or the CL of pregnant females.