Involvement of Catecholestrogens in the release of pituitary hormones

Catecholestrogens (CE), natural metabolic products of 17ß-estradiol and estrone, were assayed in anterior and posterior pituitary lobes and in the median eminence of the rat. The highest CE values were found in the median eminence and the lowest in the anterior pituitary. The CE concentrations in pars nervosa and pars intermedia of the posterior pituitary were quite similar. No sexual difference in the CE content was found in median eminence, anterior and posterior pituitary lobes. The highest CE concentrations were found in the median eminence and pars intermedia of lactating rats. During the estrous cycle median eminence CE showed maximal values in the morning of the proestrus, while anterior pituitary CE showed a decrease in the afternoon of the proestrus. Posterior pituitary lobe CE content did not change throughout the stages of the estrous cycle. Ovariectomy decreased CE content in the anterior pituitary but did not change the CE content in pars nervosa and pars intermedia of the posterior pituitary lobe. Estrogen therapy in ovariectomized animals increased CE content in pars nervosa. In the lactating rats, the separation of mothers from their pups for 4 h increased CE content in the posterior lobe and showed no variations in the anterior lobe. When pups were replaced and allowed to suckle for 5 and 30 min, CE content decreased in both the anterior and posterior pituitary lobes. Pars nervosa CE varied with suckling in the same way as the whole posterior lobe did. Pars intermedia and median eminence, both of which exhibited high CE values in the lactating rats, showed no CE variations in the model of separation/suckling. Parallel studies of COMT activity showed no variations in any model and in any pituitary lobe except anterior pituitary during the estrous cycle: COMT activity at Diestrus 2 was significantly low. The results obtained suggest that the CE are involved in the hormonal changes taking place in rat sexual cycle and lactation.