SPLANCHNIC AND RENAL SYMPATHETIC ACTIVITY IN RELATION TO HEMODYNAMICSDURING ISOFLURANE ADMINISTRATION IN PIGS

The aim of the present study was to investigate the impact of isoflura ne on regional neurogenic mechanisms in the control of vascular tone. Therefore, regional determinations of sympathetic activity and hemodyn amics were made in chloralose-anesthetized swine before and during adm inistration of 1.4% isoflurane. Sympathetic activity was examined from spillover of norepinephrine (NE) into the circulation using an isotop e dilution technique. Administration of isoflurane caused a marked dec rease in mesenteric (65 +/- 9 pmol.min(-1).100 g(-1); P < 0.05) NE spi llover. Renal NE spillover was moderately decreased (25 +/- 6 pmol.min (-1).100 g(-1); P < 0.05), whereas liver NE spillover did not change s ignificantly during isoflurane administration, suggesting that liver s ympathetic activity is maintained at this level of isoflurane anesthes ia. Total body NE spillover decreased (13 +/- 2 pmol.min(-1).100 g(-1) , P < 0.05). Thus, isoflurane affected sympathetic outflow in a region ally differentiated pattern. Significant correlations were found betwe en total body, mesenteric, and renal NE spillovers and vascular resist ances, supporting the concept that the observed reductions in vascular resistances in these circulations during isoflurane administration we re in part a consequence of reduced sympathetic outflow. In the liver circulation, no correlation was found between NE spillover and liver p ortal or liver arterial vascular resistances. Liver arterial resistanc e was significantly reduced during isoflurane administration while liv er portal resistance was unchanged. Administration of isoflurane cause d reductions in cardiac output, renal, portal, hepatic arterial, and t otal hepatic blood flows, whereas mesenteric blood flow was unchanged. To summarize, isoflurane decreased mesenteric and renal NE spillover with concomitant reductions in vascular resistances. Liver NE spillove r was, however, not changed, and no correlations to hepatic arterial a nd hepatic portal resistances were found. Thus, the effect of 1.4% iso flurane on sympathetic discharge and hemodynamics showed a differentia l pattern.