ROLE OF INTESTINAL FLUID IN RESTITUTION OF BLOOD-VOLUME AND PLASMA-PROTEIN AFTER HEMORRHAGE IN AWAKE RATS

To determine whether food and/or water in the gastrointestinal tract a ffects restitution of blood volume and plasma protein after hemorrhage , fed and 24-h-fasted awake rats received a 20 ml . kg(-1) . 3 min(-1) hemorrhage, and restitution of blood volume was measured by Evans blu e dye and dilution of hematocrit. Restitution of blood volume and plas ma protein in fed rats was complete by 2-4 h. In contrast, restitution was severely attenuated in fasted rats and was not complete by 24 h. Because initial blood volume was significantly lower in the fasted rat s (55.4 +/- 1.7 vs. 64.9 +/- 2.5 ml/kg in fed), the percent blood lost during hemorrhage was significantly greater (36 vs. 31%). However, th e attenuated restitution was not the result of the larger hemorrhage, as fed rats receiving a 36% hemorrhage also restored blood volume comp letely by 4 h. In fasted rats, complete restitution of blood volume di d occur when either water or food and water were given 4 h after hemor rhage. Gastrointestinal water content fell (from 65.5 +/- 4.8 to 47.9 +/- 1.6 ml/kg) 2 h after hemorrhage in fed but not in fasted rats (33. 5 +/- 2.4 to 30.6 +/- 2.5 ml/kg). These data suggest that gastrointest inal fluid is essential for complete restoration of blood volume in th e awake rat.