1. α1-Adrenoceptor-mediated vasoconstriction was studied before and during propranolol therapy in eight normal renin essential hypertensive patients; four were known ‘responders’ and four, age-matched ‘non-responders’ to previous β-receptor blocker monotherapy. Plasma renin activity, plasma adrenaline and noradrenaline concentrations as well as forearm blood flow were measured before and during regional postjunctional α1-adrenoceptor blockade with prazosin. All measurements were done on placebo and again after 6 weeks’ propranolol monotherapy (320 mg/day).

2. Propranolol reduced heart rate and plasma renin activity to the same extent in ‘responders’ and ‘non-responders’. Resting plasma adrenaline concentrations tended to be higher in ‘responders’ before propranolol; they remained unchanged in both groups on propranolol. Plasma noradrenaline concentrations were similar in both groups before and on propranolol.

3. Before propranolol forearm flow was not different in ‘responders’ and ‘non-responders’. Non-specific vasodilatation with sodium nitroprusside produced a similar increase in forearm flow before and after propranolol in both groups.

4. Prazosin-induced increments in forearm flow tended to be higher in ‘responders’ before propranolol. After propranolol the vasodilator effect of prazosin was attenuated in ‘responders’ but it remained unchanged in ‘non-responders’ (P < 0.01).

5. In patients with normal renin essential hypertension the antihypertensive response to propranolol monotherapy is paralleled by a decrease in postjunctional α1-adrenoceptor-mediated vasoconstriction.

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