Hormonal response to captopril pre-treatment during sodium nitroprusside-induced hypotension in man

To assess the hormonal response to captopril pre-treatment during sodium nitroprusside (SNP) -induced hypotension, 12 patients were studied during a spinal surgical procedure. Haemodynamic data, plasma-renin activity, aldosterone, adrenaline and noradrenaline levels were measured. Patients were randomly allocated to two groups: Group I, control patients; Group II, 3 mg kg-1 captopril pre-treated patients. SNP requirement for the same level (mean arterial pressure (MAP) = 55 mmHg) and duration of hypotension (88.5 +/- 28.7 vs. 95.2 +/- 22.5 min) was significantly lower in Group II than in Group I (16.5 +/- 14.2 mg vs. 39.3 +/- 16.7 mg; P less than 0.05) and a lower SNP infusion rate was required to induce and to maintain hypotension. In Group II patients, MAP remained significantly lower than the control and Group I values for 30 min after SNP withdrawal. Cardiac index (CI) remained stable in both groups. Heart rate was not modified in Group II during hypotension. Plasma-renin activity rose more dramatically in Group II patients than in Group I both during hypotension (13.9 +/- 7.5 vs. 2.8 +/- 0.9 ng ml-1 h-1; P less than 0.05) and after hypotension (23.4 +/- 15.4 vs. 2.2 +/- 0.8 ng ml-1 h-1; P less than 0.05). Plasma catecholamine levels increased in both groups during hypotension and remained raised in captopril patients after SNP withdrawal. It can be concluded that recovery from hypotension may be delayed when using captopril and that sympathoadrenal activity induced by hypotension is not substantially altered by captopril pre-treatment, suggesting that sympathetic blockade might not be the mechanism by which captopril reduces SNP requirement during controlled hypotension for surgical procedure in man.