HEPATIC BLOOD-FLOW IN HOUSES DURING THE RECUPERATIVE PERIOD FROM MAXIMAL EXERCISE

Objective-To determine effects of walking or standing on hepatic blood flow of horses after brief, intense exercise. Animals-6 adult Thoroug hbreds (4 mares, 2 geldings). Procedure-Horses were preconditioned on a treadmill to establish uniform level of fitness. Once fit, treadmill speed causing each horse to exercise at 120% of maximal oxygen consum ption was determined and used in simulated races at 14-day intervals. In a three-way crossover study, horses were exercised at a speed induc ing 120% of maximal oxygen consumption until fatigued or for a maximum of 2 minutes. Three interventions were studied: resting on the treadm ill (REST), exercised then standing on the treadmill for 30 minutes (M S), and exercised then walking at 2 mis for 30 minutes (MW). At 60 sec onds after completion of exercise, bromsulphalein (BSP) was infused IV , and blood samples were collected every 2 minutes for 30 minutes for analysis of BSP concentration. Hematocrit and plasma total solids conc entration were measured. Pharmacokinetic parameters were derived, usin g nonlinear regression, and were compared, using Friedman's repeated m easures analysis on ranks. Results-Plasma BSP concentration was higher after exercise. Median hepatic blood flow (BSP clearance) decreased s ignificantly from 23.8 (REST) to 20.7 (MS) and 18.7 (MW) ml/min/kg. Me dian steady-stale volume of distribution of BSP decreased from 47.6 (R EST) to 42.7 (MW) and 40.2 (MS) ml/kg. Differences among trials were n ot significant when horses walked or stood after exercise. Conclusions -Hepatic blood flow and pharmacokinetics of BSP are markedly altered i mmediately after exercise. Limiting movement of horses during this per iod did not affect hepatic blood flow.