Absence of beta-adrenergic receptor involvement in cerebrovascular dilation by halothane in monkeys

We determined, in monkeys, whether halothane-induced cerebrovascular dilation is mediated by beta-adrenergic receptors and whether cerebrovascular tone progressively returns to baseline values during prolonged halothane anesthesia. Total cerebral blood flow (CBF), cerebral perfusion pressure, plasma halothane concentration, and arterial blood gas tensions and pH were measured in 14 rhesus monkeys mechanically ventilated with 0.5% (inspired) halothane, 33% O2 and balance N2O. Halothane was increased to 2.0% and the measurements repeated 30 and 60 min later. Then either 0.9% NaCl (controls n = 6) or propranolol (n = 8), 1.0 mg/kg was infused intravenously over 10 min, and the measurements repeated at 70, 90, 120, and 150 min. After 30 min at 2.0% halothane, CBF increased in the controls by 50% (P less than 0.05) from 92 +/- 8 (mean +/- SD) to 137 +/- 39 ml X 100 g-1 X min-1 and in the propranolol group by 30% (P less than 0.05) from 106 +/- 33 to 137 +/- 28 ml X 100 g-1 X min-1. After 2.5 hr of 2.0% halothane anesthesia, CBF remained elevated above baseline levels, but by only 28 and 23% in the control and propranolol groups, respectively. Cerebrovascular resistance was identical in both groups (0.55 +/- 0.33 vs 0.53 +/- 0.13 mm Hg X ml-1 X 100 g 1 X min 1). The results show that there is only a 10-20% return of CBF toward baseline levels after up to 2.5 hr of 2% halothane anesthesia. The results also indicate that halothane-induced cerebrovascular dilation is not mediated by beta-adrenergic receptors.