Evidence that central epinephrine neurons participate in the control and regulation of neuroendocrine events during the estrous cycle.

Although evidence has shown that central epinephrine (E) neurons play an essential role in the control of preovulatory gonadotropoin surge in rats, their function and site(s) of action are unknown. These experiments were performed in an attempt to identify any changes in E concentration or activity that might take place in areas of the brain known to receive adrenergic axon terminals and to be associated with increased output of gonadotropins (LH, FSH, and PRL) during the estrous cycle. E concentrations were measured by radioenzymatic assay, and E activity was assessed by the linear rate of decline of E (RDE) which occurs 2 h after administration of the centrally active E synthesis inhibitor, SKF 64139. During the proestrous critical period (1500-1700 h), significant increases in both concentration and RDE occurred in the medial preoptic area (mPOA) accompanied by a smaller but significant increase in the RDE in the mediobasal hypothalamus (MBH); 4 h later (2100-2300 h), significant increases in both concentration and RDE were seen in the MBH. At estrus, although E concentrations were generally higher in both the mPOA and MBH than on other days of the cycle, the concentration and RDE in the MBH increased significantly between 1500-1700 h, while RDE in the mPOA increased again between 1700-1900 h. There were no significant changes in either E concentration or RDE in the mPOA or MBH at metestrus or diestrus or in the perifornical area at any of the times studied. Thus, these findings may be associated with the output of gonadotropins over the periovulatory period.