The Effect of Bromocriptine on the Secretion of Hypophysial Thyroidal Hormonal Axis

Thyrotropine secretion in human beings is under the influence of various factors. The effect of the hormones, triiodothyronine, thyroxine, somatostatin and thyroid-stimulating hormone has been well known. In this study the direct effect of stimulation of the dopaminergic system by bromocriptine on the thyrotropine secretion was investigated. In this study twenty women with hyperprolactinemia referred to the endocrine and metabolism research center of the Isfahan University of Medical Sciences were selected. For this purpose, only cases with prolactin levels greater than 20 nanogram were included in the study. The cases suspicious of systemic diseases and consumption of thyroid stimulatory drugs were excluded from the study. Five milliliter of blood was collected from each patient and then they were appropriately treated by bromocriptine. After 3 months their bloods were again collected. The levels of thyroxine, triiodothyronine, thyrotropine and prolactin were measured by the radioimmunoassay method. Thyrotropine levels showed a significant decrease (2.95 ± 0.89 mU/l before and 1.85 ± 1.08 mU/l after treatment) (P<0.001). In addition, the prolactin levels showed a significant decrease (30.08 ± 13.2 ng/ml before and 3.5 ± 2.2 ng/ml after treatment) (P<0.007). A significant relationship was found between decreases for TSH and triiodothyronine (r =+0.49, P<0.05) and between decreases for prolactin and TSH (r = +0.47, P<0.05). It can be concluded that the stimulatory effect of bromocriptine on the dopaminergic system can decrease the bodily levels of thyroid hormones through affecting the secretion rate of TSH.