Temporal and other effects of catechol estrogens on prolactin secretion in the rat

Temporal alterations in plasma prolactin levels caused by the administration of 2-hydroxyestradiol and 2-hydroxyestrone (100 microgram/kg) into the right atrium of freely-moving conscious male rats were examined. The catechol estrogens were given in a single bolus via an indwelling cannula and plasma prolactin concentration was monitored by taking blood samples every 2 min. A pulsatile elevation of plasma prolactin occurred approximately 4 h after the injection of 2-hydroxyestradiol and a small increase was also observed when it was administered to rats bearing a Silastic capsule containing estradiol. 2-Hydroxyestrone had no effect in untreated male rats but produced a 5- to 6-fold elevation in plasma prolactin level 4 h after its administration to rats implanted with estradiol. It is proposed that 2-hydroxyestrone suppresses the action of estradiol on prolactin secretion from the pituitary and that the accumulated hormone is released when the concentration of this catechol estrogen falls below a critical level. A longer latent period was required to produce an elevation in plasma prolactin levels by 2-hydroxyestradiol than by estradiol.