Cerebral hypoperfusion as a stimulus for growth hormone release in man.

In healthy male volunteers the effect of a short-term cerebral ischemia due to an acute orthostatic hypotension, on the release of growth hormone (HGH) was studied. Peroral administration of guanethidine 12.5 mg t.i.d. for 3 days plus 25 mg before the experiment was used to block peripheral vascular reflexes and thus to provoke orthostatic intolerance. An extreme increase of HGH serum levels (on average from 0.8 to 13.6 ng/ml; p < 0.001) was found in subjects who developed clinical signs of syncope after assuming upright posture. The possible mechanisms of this finding are discussed.