Possible thyrotrophs insensitivity to dopamine in hyperprolactinaemic amenorrhoeic patients

The study assessed the sensitivity of the thyrotrophs of hyperprolactinaemic patients to a physiological dose of dopamine (DA). Eight hyperprolactinaemic amenorrhoeic patients received 4-hour infusions of either DA (0.4 micrograms/kg x min) or glucose. Twelve normal women served as controls. In normal women the mean thyrotrophin (TSH) concentration declined significantly (P less than 0.05) from 81 +/- 6.6% of basal levels during glucose infusion to 59 +/- 5.8% of basal levels during DA infusion. In contrast DA infusion to hyperprolactinaemic patients caused no significant reduction in TSH levels compared to glucose infusion (DA infusion 68 +/- 4.7% of basal levels; glucose infusion 73 +/- 4.9% of basal levels). DA infusion caused a significant reduction in serum prolactin (PRL) levels both in hyperprolactinaemic patients (P less than 0.001) and normal women (P less than 0.02), but the PRL suppression was significantly (P less than 0.05) less pronounced in the hyperprolactinaemic patients, compared to normal women. We propose that the abnormal PRL as well as TSH secretion in hyperprolactinaemic amenorrhoeic patients may be due to a common defect. Both the lactotrophs and the thyrotrophs may be relatively insensitive to dopaminergic inhibition.