Interaction between the thyrotrophin-releasing hormone-induced growth hormone rise and dopaminergic drugs: studies in pathologic conditions of the animal and man.

A rise in plasma growth hormone (GH) after thyrotrophin-releasing hormone (TRH) and a striking reduction after dopaminergic drugs is present in acromegalic ('responder') patients. We have investigated the GH response to dopaminergic stimuli in two 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. In addition, we have studied the TRH-induced GH rise 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 five out of six cirrhotic patients oral administration of L-Dopa was followed by the usual rise in plasma GH. infusion of DA increased plasma GH levels in three out of seven cirrhotic patients and in four out of five subjects an earlier GH rise after TRH was seen. However, in the 'responder' acromegalics, the infusion of DA, besides lowering baseline plasma GH, was capable of reducing the TRH-induced GH rise. Collectively these data indicate that the TRH-induced GH rise emphasizes defects in the neurohormonal links between the central nervous system and the anterior pituitary. Instead, the paradoxical fall of GH after dopaminergic drugs appears to be a prerequisite of acromegaly and may be attributable to receptors for DA located on the tumorous tissue.