Possible Thyrotrophs Insensitivity to Dopamine in Hyperprolactinaemic Amenorrhoeic Patients

Summary

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.

Key words

Dopamine - TSH - Hyperprolactinaemia