Comparative effects of tamoxifen and bromocriptine on prolactin and pituitary weight in estradiol-treated male rats

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Abstract
Male ACI rats were treated with estradiol to induce hyperprolactinemia and pituitary hypertrophy and hyperplasia. Animals received estradiol alone or with tamoxifen or bromocriptine for 4, 8, or 12 weeks. Estradiol treatment resulted in time‐dependent increases in pituitary wet weight and serum prolactin concentrations. Tamoxifen completely blocked the increase in both variables; bromocriptine decreased but did not prevent time‐dependent increases. Animals were also treated for 8 weeks with estradiol alone, followed by 4 weeks with estradiol and tamoxifen or bromocriptine. Neither compound reversed the hyperprolactinemia, although the pituitary wet weight of animals treated with bromocriptine was slightly but significantly reduced. These findings suggest that in this model if treatment is initiated simultaneously with estrogen stimulation, tamoxifen is more effective than bromocriptine at the doses studied; and, if therapy is initiated subsequent to the establishment of estrogen‐induced hyperprolactinemia and pituitary hyperplasia, bromocriptine is more effective than tamoxifen at the doses studied.