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 (0.4ug/kg × min) or glucose. Twelve normal
women served as controls. In normal women the mean thyrotrophin (TSH) concentration
declined significantly (P < 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 < 0.001) and normal women (P < 0.02), but the PRL
suppression was significantly (P < 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.
Dopamine - TSH - Hyperprolactinaemia
