Plasma catecholamines, plasma renin activity and haemodynamics during sodium nitroprusside-induced hypotension and additional beta-blockage with bunitrolol.

The effects of beta-blockade on certain physiological and haemodynamic responses to sodium nitroprusside-induced hypotension have been studied in 5 patients, aged 18--54 years, undergoing inner ear surgery. Samples of blood were collected under premedication, following induction of anaesthesia, during neuroleptanalgesia, during a sodium nitroprusside infusion adjusted to produce a 40% fall in blood pressure, during superimposed beta-blockage with bunitrolol and under stable haemodynamic conditions after discontinuation of sodium nitroprusside. The sodium nitroprusside-induced reduction in blood pressure led to a massive increase in plasma noradrenaline and adrenaline and in plasma renin activity. beta-blockade with bunitrolol did not affect the increased catecholamine concentrations, the increase in plasma renin activity was significantly reduced, the increase in heart rate was reversed, and total peripheral resistance and diastolic blood pressure were further reduced. These changes can be attributed to the intrinsic beta-synmpathomimetic activity of bunitrolol in addition to its beta-blocking effect. Since no adverse effect was observed in this study, combined therapy with sodium nitroprusside and beta-receptor blockade should be employed if the effects of increased sympathetic tone are considered to be undesirable.