1. The time-course of the rise in plasma renin activity (PRA) in response to an acute postural stimulus was demonstrated in four normal subjects over 90 min.

2. The ability of racemic propranolol to inhibit this rise was confirmed.

3. This inhibition is shown to be due to antagonism of beta-adrenergic receptors rather than to the membrane-stabilizing properties of racemic propranolol.

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