Effects of compartmental fluid repletion on heat-induced limb vasodilation in dehydrated baboons

Dehydration attenuates the increase in hindlimb blood flow produced by environmental heating (EH) in baboons. This study explored whether intravascular volume repletion alone was sufficient to remove this dehydration-induced attenuation. In six unanesthetized, chronically instrumented baboons, the increases in hindlimb blood flow during EH were measured under these conditions: euhydrated, dehydrated (64-68 h of water deprivation) without fluid replenishment, and dehydrated with intravenous fluid replenishment by either 6% high-molecular-weight dextran solution (to replenish vascular volume) or hyperosmotic saline (to replenish vascular and interstitial fluid volumes). EH consisted of acute exposure to ambient temperatures of 38-42 degrees C until core temperature (Tc) reached 39.5 degrees C. During dehydration without fluid replenishment the increments in mean iliac artery blood flow (MIBF) and iliac vascular conductance (IVC) produced by EH (i.e., value at Tc = 39.5 degrees C - pre-EH value) were reduced by 39 and 44%, respectively. After infusion of a volume of dextran solution equal to blood volume lost during dehydration, the increment in MIBF during EH was partially restored to the euhydrated level, but the increment in IVC remained at the dehydrated level. Infusion of hyperosmotic saline during dehydration completely restored the increases in MIBF and IVC during EH to euhydrated levels. Thus restoration of normal blood volume alone in dehydrated baboons does not completely restore normal hindlimb vasodilation during EH.