Abstract
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-treated rats. Ovariectomized Wistar rats were injected subcutaneously with sunflower oil vehicle or estradiol valerate (50 or 300 micrograms/rat(-1) week (-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 treatment. Data were compared with those obtained for intact control rats. Administration of both doses of estrogen increased serum prolactin levels. No difference in the number of prolactin cells in rats treated with 50 micrograms estradiol valerate was observed compared to intact adult animals. In contrast, rats treated with 300 micrograms estradiol valerate showed a significant increase in the number of prolactin cells (P < 0.05). Therefore, the increase inn serum prolactin levels observed in rats treated with 50 micrograms estradiol valerate, in the absence of morphological changes in the pituitary cells, suggests a "functional" estrogen-induced hyperprolactinemia. Bromocriptine decreased prolactin levels in all estrogen-treated rats. The administration of this drug to rats previously treated with 300 micrograms estradiol valerate also resulted in a significant decrease in pituitary weight and number of prolactin cells when compared to the group treated with estradiol alone. The general antiprolactinemic and antiproliferative pituitary effects of bromocriptine treatment reported here validate the experimental model of estrogen-induced hyperprolactinemic rats.
Highlights
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 estradioltreated rats
There are only a few animal models available which are sensitive to dopamine agonists, such as the SMtTW tumor, a spontaneous prolactin-secreting transplantable tumor [4], and some studies using estrogen-induced hyperprolactinemia and pituitary enlargement [3,11,12,13,14,15]. These studies did not report which doses and duration of in vivo estrogen administration are required to promote prolactin hypersecretion without pituitary enlargement or if bromocriptine effects on prolactin levels and lactotroph proliferation may vary with different schedules of estrogen treatment
The present study was designed to assess the effects of bromocriptine on pituitary wet weight, number of prolactin cells and serum prolactin levels in ovariectomized animals subacutely or chronically stimulated with estrogen, in order to validate an experimental model for the study of the interaction between estrogen and dopamine in controlling prolactin secretion and lactotroph proliferation in vivo
Summary
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 estradioltreated rats. The present study was designed to assess the effects of bromocriptine on pituitary wet weight, number of prolactin cells and serum prolactin levels in ovariectomized animals subacutely or chronically stimulated with estrogen, in order to validate an experimental model for the study of the interaction between estrogen and dopamine in controlling prolactin secretion and lactotroph proliferation in vivo.
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