1. The effect on plasma renin activity (PRA) of dopamine and noradrenaline infusions was studied in three patients with Shy—Drager syndrome, three patients with Parkinson's disease and normal autonomic reflexes, and three healthy volunteers. The patients with the Shy—Drager syndrome had functional evidence of a peripheral lesion of the sympathetic nervous system and subnormal PRA on a controlled sodium intake.

2. In all subjects catecholamines were infused step-wise for 4 min until a 30% rise in systolic blood pressure occurred.

3. In each subject, PRA fell after noradrenaline but rose after dopamine. The mean fractional increase in PRA after dopamine was no less in the Shy—Drager patients than in the control groups.

4. The results suggest, first, that stimulation of dopamine receptors can release renin, and secondly, that inadequate renin stores cannot explain the low PRA found in our patients with autonomic failure.

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