INTERACTION BETWEEN THE THYROTROPHIN-RELEASING HORMONE-INDUCED GROWTH HORMONE RISE AND DOPAMINERGIC DRUGS: STUDIES IN PATHOLOGIC CONDITIONS OF THE ANIMAL AND MAN

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Abstract
A rise in plasma growth hormone (GH) after thyrotropin-releasing hormone (TRH, thyroliberin) and a striking reduction after dopaminergic drugs [including bromocriptine] is present in acromegalic (responder) patients. The GH response to dopaminergic stimuli was studied in 2 conditions of animals and man, which, like acromegaly, are characterized by a TRH-induced GH rise, i.e., rats with electrolytic lesions of the median eminence (ME) and patients with hepatic cirrhosis. The TRH-induced GH rise was studied in rats with ME lesions in the cirrhotic patients and in a group of responder acromegalics before and after administration of dopaminergic drugs. In rats with ME lesions an infusion of dopamine (DA) neither modified baseline GH levels nor the TRH-induced GH rise. In 5 of 6 cirrhotic patients oral L-dopa administration was followed by the usual rise in plasma GH. Infusion of DA increased plasma GH levels in 3 of 7 cirrhotic patients and in 4 of 5 subjects an earlier GH rise after TRH was seen. In the responder acromegalics, the infusion of DA, besides lowering baseline plasma GH, was capable of reducing the TRH-induced GH rise. The TRH-induced GH rise evidently emphasizes defects in the neurohormonal links between the CNS and the anterior pituitary. The paradoxical fall of GH after dopaminergic drugs appears to be a prerequisite of acromegaly and may be attributable to DA receptors located on the tumorous tissue.

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