INFLUENCE OF HALOTHANE AND ISOFLURANE ON THE CONTRACTILE RESPONSES TOPOTASSIUM AND PROSTAGLANDIN-F2-ALPHA IN ISOLATED HUMAN PIAL-ARTERIES

Volatile anaesthetics may modulate cerebrovascular resistance, but the ir direct actions on human cerebral arteries are unknown. in the prese nt study, we have evaluated the effects of halothane and isoflurane at different MAC (0.4, 1.0 and 2.0) on contractions induced by depolariz ation (potassium) or receptor stimulation (prostaglandin F-2 alpha) in isolated ring segments of human pial arteries. Neither halothane nor isoflurane had significant effects on potency (unaffected EC, value) o r the maximum response (Emax) in potassium-contracted arteries, even t hough there was a general tendency to attenuation of Emax. Similarly, the potency of prostaglandin F-2 alpha was unchanged (unaffected EC(50 ) value). However, the Emax value for prostaglandin F-2 alpha at normo capnia (mean Pco(2) 4.3 (SEM 0.1) kPa, pH 7.41 (0.01)) and addition of halothane (0.4, 1.0 and 2.0 MAC) was significantly attenuated to 96 ( 2)%, 91 (3)% and 84 (4)% at the respective MAC concentrations. Isoflur ane at 2 MAC and normocapnia also reduced Emax to 94 (3)%. During hypo capnia (Pco(2) 2.7 (0.1) kPa, pH 7.64 (0.01)), the vasodilator effect of halothane was reduced, whereas isoflurane at 0.4 and 1.0 MAC enhanc ed the contraction induced by prostaglandin F-2 alpha.