Role of the noradrenergic system in the secretory function of the corpus luteum.

The importance of sympathetic innervation changed significantly during sexual maturation and in the course of the oestrous cycle in females. Basal secretion of progesterone is partly dependent on constant beta-adrenergic stimulation since local infusion of propranolol (beta-blocker) into the ovary decreased progesterone secretion by 20-30% of pre-treatment value. Noradrenaline given into the abdominal aorta in the moderate doses affected very quickly and dramatically the secretory function of the corpus luteum during the luteal phase in cattle and also in other species. Thus short-lasting mobilization stress protects and even supports corpus luteum function. This effect is exerted through the stimulation of beta-adrenoceptors which then activates specific intracellular enzymes. Additionally noradrenaline acts upon vascular alpha-receptors and increase ovarian blood flow allowing utilization of serum-derived lipoprotein as a source of cholesterol for steroidogenesis. The highest amount of specific beta-receptors in luteal membranes was found in the newly-formed corpus luteum which does appear to require noradrenergic support especially at that stage of its development. The mechanism of noradrenaline influence upon luteal cells resulting concomitant progesterone and ovarian oxytocin secretion is, however, obscure. It is suggested that intracellular second messengers (cAMP, Ca2+) involved in noradrenaline action can simultaneously affect the secretion of both these hormones and this indicates some functional relationship between them. The presented results are focused mainly upon cattle due to the importance of this species among other domestic animals. Nevertheless for comparison data from other species are also quoted.