Acta ilnaesthesiol Scand zyxwvutsrqp 1985: 29: 287-293 Vasodilator Responses to Enflurane in the Small Intestine B.-A. HENRIKSSON, B. BIBER, D. LUNDBERG, J. MARTNER, H. NILSSON and J. PONTPN Departments of Anaesthesia and Intensive Care, Sahlgrenska Hospital and t)stra Hospital, Department of Physiology, University of Goteborg, Gothenburg and University of Lund, Lund, Sweden Local effects of enflurane on intestinal vascular resistance were studied zyxwv in viva in cats. Ajejunal segment was prepared and perfused at constant flow with blood from the femoral arteries. The intestine was either: (1) left with intact sympathetic innervation, (2) denervated and exposed to electrical post-ganglionic vasoron- strictor nerve stimulation, or (3) excluded from neurogenic remote control by post-ganglionic denervation. Enflurane dissolved in lipid and intra-arterially administered to the jejunal segment in doses comparable to those clinically encountered, decreased intestinal vascular resistance in relation to the intra-arterial concen- tration of the drug. The vasodilator response was, at the highest enflurane doses studied (blood concentration: 400 and 800 mg. 1-I), most pronounced in the intestine with intact sympathetic innervation. Otherwise, no differences were observed in vasodilator responses between the three different investigated modes of neuro- genic influence on the intestine. In vitro enflurane (-in-lipid) did not affect the vasoconstrictor response to electrical field stimulation in the rat mesenteric arterioles. Enflurane, however, dose-dependently reduced spontaneous contractile activity in the rat portal veins. Received 27 April, accepted for publication 20 August 1984 Key words: Autonomic nervous system; cat; enflurane; intestine, small; isolated vessels; regional blood flow; vascular resistance. Enflurane anaesthesia is associated with a dose-depen- dent reduction in arterial pressure explained both by a depressed cardiac performance (1) and a decreased peripheral vascular resistance (2). The change in vas- cular resistance may partly be explained by a de- creased sympathetic vasoconstrictor tone (3), but a peripheral interaction with vascular tone is also quite possible. In a previous experimental study we have investigated the decrease in intestinal vascular tone elicited by enflurane (4). Although suppression of cen- tral sympathetic outflow seemed to contribute to this response, a peripheral interaction with intestinal vas- cular tone was also indicated. However, it is not evi- dent whether this effect of enflurane is exerted on the peripheral nervous pathways, at the neuroeffector junctions, on local regulatory mechanisms within the intestinal wall or directly on the vascular smooth mus- cles. The aim of the present study was therefore to investigate further the background of the peripheral interaction by enflurane on the intestinal vascular tone. Experiments were performed zyxwvut in vivo by local administration of enflurane to the feline small intestine during different modes of neurogenic control. In vitro, the properties of rat mesenteric arterioles and portal veins exposed to enflurane were studied. MATERIAL AND METHODS In viva experiments This part of the study was performed on ten cats of mean weight 5.0 kg (range 4.5-5.2 kg). The animals had been deprived of food zy ftrr 12 h but had free access to water. Anaesthesia, surgical procedures, recordings and calculatiom were the same as those described in a previous investigation (4). To summarize, anaesthesia was induced with enflurane and continued with chlora- lose (50 mg.kg-'). The animals were ventilated with air at a set volume and with 20 breaths.min-' (Harvard 661 small animals venti- lator) through a tracheal cannula. End-tidal enflurane concen- trations were measured with a coated quartz crystal detector (5). Hydration and compensation for metabolic acidosis were ac- complished by a continuous infusion (5-10 ml.kg- '.h zyx I) ofa solution containing glucose, sodium chloride and sodium bicarbonatr. Core temperature was kept at 37-38°C. The abdomen was opened in the midline and a 15-20-cm length of the jejunal segment with adherent mesenteric lymphatic nodes was isolated with intact vascular and nervous supply. The remaining part of the intestinal tract from the duodenum to the distal colon, the great omentum and the spleen were extirpated. The experimental set-up is illustrated in Figure zyx 1. After heparin administration (5000 IE i.v.), both femoral arteries were cannulated in order to supply blood to the cannulated superior mesenteric artery via a silicone tubing by-pass circuit, also incorporating an injection site for local intra-arterial (La.) administration of drugs to the intes- tine. Mesenteric venous outflow from the jejunal segment was di-