Role of norepinephrine in the release of prolactin induced by suckling and estrogen.

Release of prolactin from the anterior pituitary can be induced by a variety of neuronal and hormonal stimuli, including suckling and estrogen. To determine whether noradrenergic neurons in the central nervous system mediate the response to either of these stimuli, norepinephrine synthesis was inhibited by diethyldithiocarbamate (DDC; 50 mg/kg). When administered to suckled, lactating rats, DDC had no effect on suckling-induced increase in plasma prolactin. The drug also had no effect on prolactin levels in ovariectomized rats. However, when DDC was administered to ovariectomized rats treated with estrogen to increase plasma prolactin levels, there was a fall in plasma prolactin levels which correlated with a decrease in hypothalamic norepinephrine synthesis. It is proposed that estrogen increases noradrenergic neuron activity which in turn increases prolactin release from the pituitary.