Sympathetic reflex responses during treatment of essential hypertension with hydrallazine and oxprenolol.

1. The short term effects of hydrallazine, oxprenolol and oxprenolol plus hydrallazine were studied in five patients with essential hypertension. 2. The increase in pulse rate caused by hydrallazine was prevented by combined treatment with oxprenolol, which also lowered the high plasma noradrenaline levels, associated with the use of hydrallazine. 3. Plasma renin activity was higher in the supine and standing positions with hydrallazine than with oxprenolol alone and with the patients standing this high renin level was prevented by simultaneous treatment with oxprenolol. With the patients supine, combination of oxprenolol with hydrallazine resulted in a mean plasma renin activity which was less than half that with hydrallazine alone, although this difference was not statistically significant. 4. The combination of oxprenolol with hydrallazine did not lower the blood pressure further, but reduced the increased sympathetic activity which occurred with hydrallazine alone.