Reciprocal pattern of the TSH and PRL responses to dopamine receptor blockade in women with physiological or pathological hyperprolactinaemia.

The TSH and PRL responses to administration of the two dopamine (DA) receptor antagonists sulpiride and domperidone, were studied in fifteen normoprolactinaemic subjects, twenty-two post-partum women and sixteen subjects with presumptive evidence of (six subjects) or surgically confirmed (ten subjects) prolactinomas. Sulpiride (100 mg i.m.) or domperidone (10 mg i.v.) elicited a slight increase in basal TSH levels in both normoprolactinaemic and post-partum women, but induced a clear-cut TSH rise in subjects with a tumour. Conversely, sulpiride and domperidone strikingly stimulated PRL secretion in normoprolactinaemic and post-partum women, but only slightly enhanced base-line PRL levels in women with prolactinomas. The reason for the reciprocal pattern of TSH and PRL responsiveness to DA receptor blockade of post-partum women and subjects with prolactinomas is presently obscure. Since baseline PRL levels in the two hyperprolactinaemic states overlapped widely, it would appear that hyperprolactinaemia per se is not responsible for such behaviour.