[Suppression by dopamine of GH release induced by GRF in a case of acromegaly]

Inhibition of plasma GH by dopaminergic agonists is one of the characteristics of the GH secretion in acromegaly. GRF is known to stimulate GH secretion in most patients with acromegaly. In order to elucidate the relationship between GRF and dopamine in regulating the secretion of GH in this disease, we examined plasma GH responses to dopamine (DA) infusion (4 micrograms/kg/min), GRF injection (100 micrograms i.v.), sulpiride (SP) injection (200 mg i.v.), a DA blocker, DA plus GRF and SP plus GRF in a 51-year-old male patient with acromegaly. Plasma GH was reduced to 14% of the initial level by iv infusion of DA, and was elevated to 158% by iv injection of GRF. No considerable change was observed in plasma GH by iv infusion of SP (114% of the initial level). GH release induced by GRF was remarkably reduced by simultaneous administration of DA (28% of the initial level), whereas SP administration did not affect GRF-induced GH release (154%). The marked reduction of GH release after DA plus GRF seems to suggest that the effect of DA on the GH regulation is stronger than that of GRF in this acromegalic patient. It is suggested also that endogenous DA may not play an inhibitory role in GH secretion in this case since DA blockade by SP did not raise basal GH levels and the GH response to GRF.