INHIBITION BY ENFLURANE OF BAROREFLEX MEDIATED MESENTERIC VENOCONSTRICTION IN THE RABBIT ILEUM

Background: Halothane and isoflurane are known to attenuate neurally m ediated regulation of mesenteric vein diameter. The current study eval uated the effects of enflurane on baroreflex control of small mesenter ic veins. Methods. Changes in mesenteric vein diameter, intravenous pr essure, mean arterial pressure, and heart rate in response to bilatera l carotid occlusion, aortic nerve stimulation, and celiac ganglion sti mulation were measured in 23 chloralose-anesthetized rabbits before, d uring, and after 1% and 2% inhaled enflurane administration. In six ot her rabbits, sympathetic efferent nerve activity was recorded directly from a postganglionic splanchnic nerve, also during bilateral carotid occlusion and aortic nerve stimulation, before, during, and after inh alation of 1% and 2% enflurane. Results. Baseline mean arterial pressu re and heart rate decreased, and mesenteric vein diameter increased, i n response to inhaled enflurane. Reflex venoconstriction and the incre ases in mean arterial pressure, intravenous pressure, and heart rate, in response to bilateral carotid occlusion, were significantly inhibit ed at both levels of inhaled enflurane. Decreases in mean arterial pre ssure and heart rate, and reflex venodilation in response to aortic ne rve stimulation, were attenuated by 2%, but not 1%, enflurane. Mesente ric venoconstriction, blood pressure increase, and bradycardia in resp onse to celiac ganglion stimulation were unaffected by 2% inhaled and 5% superfused enflurane. Both 1% and 2% inhaled enflurane attenuated r esting and carotid sinus-mediated increases in sympathetic efferent ne rve activity. Conclusions. These results indicate that enflurane alter s splanchnic venous reflexes in large part via the inhibition of sympa thetic efferent activity.