Abstract
L-dopa, dopamine and norepinephrine (1mg/kg) caused a marked increase in palsma growth hormone (GH) when given i.v. to trained, unanesthetized, fasting dogs. Reduction of the dose to 100μg/kg eliminated the responses. On the other hand, the relatively small dose of epinephrine (10μg/kg) could increase plasma GH level. In this case a reduction of the dose to 1μg/kg also diminished the stimulatory effect. A significant increase in plasma glucose accompanied the rise in plasma GH with dopamine, norepinephrine and epinephrine but not with 1-dopa. Furthermore, in the case of dopamine and norepinephrine a concomitant increment of plasma cortisol was also found. Alpha adrenergic blockade with phentolamine suppressed the stimulatory effect of epinephrine and 1-dopa on GH release. These results suggest that GH release stimulated by catecholamines is mediated by alpha adrenergic receptor. An attempt to inhibit dopamine beta hydroxylase with fusaric acid did not alter the stimulatory effect of 1-dopa. This result suggests an important role for dopamine in GH secretion mechanisms.
