Adrenal vein catecholamines and met-enkephalin during staged hemorrhage and naltrexone administration in cats

Concurrent levels of catecholamines and met-enkephalin in adrenal vein, femoral vein, and femoral artery were measured under baseline conditions and during staged hemorrhage in halothane (1 MAC)-anesthetized cats (Group II, n = 8) and compared to a nonbled control group (Group I, n = 5). In Group III (n = 14) an i.v. bolus of naltrexone in a range of different dosages (0.01 mg/kg to 10 mg/kg) followed by a continuous infusion was administered prior to induction of hemorrhage. In Group II, the loss of 25% of estimated total blood volume led to a significant decrease (-40 +/- 11 mmHg) in mean arterial blood pressure (MABP) without evoking adrenal stimulation. Hemorrhage to 50% of total blood volume was without a further significant fall in MABP, but led to a significant increase in catecholamine and met-enkephalin levels in the adrenal vein. Naltrexone-treated cats in Group III were not different from Group II in regard to hemodynamic and sympathoadrenal response during staged hemorrhage. We conclude that prophylactic administration of naltrexone has no effect on hemodynamic parameters during staged hemorrhage and that the concurrent adrenal secretion of catecholamines and met-enkephalin is not modulated by actions on opiate receptors in the halothane-anesthetized cat.