EFFECTS OF BROMOCRIPTINE ON SERUM PROLACTIN LEVELS, PITUITARY WEIGHT AND IMMUNOREACTIVE PROLACTIN CELLS IN ESTRADIOL-TREATED OVARIECTOMIZEDRATS - AN EXPERIMENTAL-MODEL OF ESTROGEN-DEPENDENT HYPERPROLACTINEMIA

The present study was designed to assess the effects of bromocriptine, a dopamine agonist, on pituitary wet weight, number of immunoreactive prolactin cells and serum prolactin concentrations in estradiol-treat ed rats. Ovariectomized Wistar rats were injected subcutaneously with sunflower oil vehicle or estradiol valerate (50 or 300 mu g rat(-1) we ek(-1)) for 2, 4 or 10 weeks, Bromocriptine (0.2 or 0.6 mg rat(-1) day (-1)) was injected daily during the last 5 or 12 days of estrogen trea tment. Data were compared with those obtained for intact control rats. Administration of both doses of estrogen increased serum prolactin le vels. No difference in the number of prolactin cells in rats treated w ith 50 mu g estradiol valerate was observed compared to intact adult a nimals. In contrast, rats treated with 300 mu g estradiol valerate sho wed a significant increase in the number of prolactin cells (P<0.05). Therefore, the increase in serum prolactin levels observed in rats tre ated with 50 mu g estradiol valerate, in the absence of morphological changes in the pituitary cells, suggests a ''functional'' estrogen-ind uced hyperprolactinemia. Bromocriptine decreased prolactin levels in a ll estrogen-treated rats. The administration of this drug to rats prev iously treated with 300 mu g estradiol valerate also resulted in a sig nificant decrease in pituitary weight and number of prolactin cells wh en compared to the group treated with estradiol alone. The general ant iprolactinemic and antiproliferative pituitary effects of bromocriptin e treatment reported here validate the experimental model of estrogen- induced hyperprolactinemic rats.