EFFECTS OF ENFLURANE ON ADRENERGIC-FUNCTION IN CANINE MESENTERIC-ARTERY AND VEIN

We examined the pre- and postsynaptic effects of enflurane on the supe rior mesenteric artery and vein. We measured the release of norepineph rine (NE) from sympathetic nerve terminals caused by electrical stimul ation (ES) or potassium and changes in vascular smooth muscle tension. The effect of enflurane was also examined in the presence of alpha(1) - and alpha(2)-adrenoceptor antagonists. Enflurane (1.4 to 1.6 minimum alveolar anesthetic concentration [MAC] in the dog) did not alter bas al tension, but it significantly inhibited tension development caused by 40 mM KCl and ES in the canine mesenteric artery and vein. Enfluran e inhibited the KCl- and ES-induced release of NE from sympathetic ner ve terminals in the canine mesenteric vein. The alpha(1)- and alpha(2) -adrenoceptor antagonists, corynanthine or yohimbine, did not modify t he effect of enflurane on the ES-induced frequency response curve of t he mesenteric artery and vein. These data suggest that enflurane has a t least two sites of action in mesenteric vascular beds. One site is p resynaptic where it inhibits NE release, and the other is a postsynapt ic site distal to the adrenergic receptor where it inhibits the smooth muscle contraction process.