SYSTEMIC AND COLONIC VENOUS PLASMA EICOSANOID AND ENDOTOXIN CONCENTRATIONS, AND COLONIC VENOUS SERUM TUMOR-NECROSIS-FACTOR AND INTERLEUKIN-6 ACTIVITIES IN HORSES DURING LOW-FLOW ISCHEMIA AND REPERFUSION OF THELARGE COLON

Twenty-four horses were randomly allocated to 3 groups. Horses were an esthetized, subjected to a ventral midline celiotomy, and the large co lon was exteriorized and instrumented. Group-1 horses served as sham-o perated controls. Group-2 horses were subjected to 6 hours of low-now colonic arterial ischemia, and group-3 horses were subjected to 3 hour s of ischemia and 3 hours of reperfusion. Baseline (BL) samples were c ollected, then low-flow ischemia was induced by reducing ventral colon ic arterial blood now to 20% of BL. All horses were monitored for 6 ho urs after BL data were collected. Blood samples were collected from th e colonic vein and main pulmonary artery (systemic venous [SV]) for me asurement of plasma endotoxin, 6-keto prostaglandin F-1 alpha (6-kPG), thromboxane B-2 (TXB(2)), and prostaglandin E(2) (PGE(2)) concentrati ons. Tumor necrosis factor and interleukin-6 activities were measured in colonic venous (Cv) serum samples. Data were analyzed, using two-wa y ANOVA, and post-hoc comparisons were made, using Dunnett's and Tukey 's tests. Statistical significance was set at P < 0.05. Endotoxin was not detected in CV or SV plasma at any time. There was no detectable t umor necrosis factor or interleukin-6 activity in CV samples at any ti me. There were no differences at BL among groups for CV or SV 6-kPG, P GE(2), or TXB(2) concentrations, nor were there any changes across tim e in group-1 horses. Colonic venous 6-kPG concentration increased duri ng ischemia in horses of groups 2 and 3; CV 6-kPG concentration peaked at 3 hours in group-3 horses, then decreased during reperfusion, but remained increased through 6 hours in group-2 horses. Systemic venous 6-kPG concentration increased during reperfusion in group-3 horses, bu t there were no changes in group-2 horses. Colonic venous PGE(2) conce ntration increased during ischemia in horses of groups 2 and 3, and re mained increased for the first hour of reperfusion in group-3 horses a nd for the 6-hour duration of ischemia in group-2 horses. There were n o temporal alterations in SV PGE(2) concentration. There was no differ ence in CV or SV TXB(2) concentration among or within groups across ti me; however, there was a trend (P = 0.075) toward greater CV TXB(2) co ncentration at 3.25 hours, compared with BL, in group-3 horses. Eicosa noid concentrations were significantly lower in SV, compared with CV p lasma. Prostaglandin E(2) and 6-kPG concentrations were approximately 3 to 8 and 5 to 10 times greater, respectively, in CV than in SV plasm a. The increased concentrations of 6-kPG and PGE(2) in CV plasma were likely attributable to their accumulation secondary to colonic ischemi a. The increased values of these vasodilator eicosanoids may have a so le in the reactive hyperemia observed during reperfusion. The increase d 6-kPG concentration in SV plasma may represent spillover from the co lonic vasculature, but more likely reflects systemic production.