Suppression of renin secretion by propranolol in salt-depleted dogs

d, 1-propranolol was infused into salt-depleted, conscious dogs at two dosages: 1 mg/kg followed by 0.60 ? 0.67 mg/kg/hr, and 5 mg/kg followed by 1.57 ? 1.76 mg/kg/hr. At both dosages, propranolol decreased plasma renin activity (PRA), plasma aldosterone concentration, and heart rate significantly. Renin substrate concentration remained unchanged. PRA was suppressed with the higher dosage but not with the lower dosage, to values found with dietary salt loading. Mean arterial blood pressure (MABP) remained unchanged with the low-dose infusions, but decreased significantly with the high-dose infusions. The data suggest that the mechanism(s) for the increase in PRA with low-salt diets is sensitive to propranolol and that the effect of propranolol on MABP is dependent on the salt intake and on the dose administered.