Effects of α-Adrenergic Activation on the Shift of Electrolytes and Fluid after Hemorrhage in Rats

To assess the effects of α-adrenergic activation on hemorrhage-induced shifts of K⁺, Na⁺ and fluid between the intravascular and extravascular spaces, we continuously measured changes in plasma concentrations of K⁺ and Na⁺ (Δ[K⁺]p, Δ[Na⁺]p) and blood volume (ΔBV) over 60min after hemorrhage in nephrectomized rats. Hemorrhage was conducted over 5 min at the level of 0.5, 1.0 and 1.5% of body weight (H_0.5, H_1.0, H_1.5), and the result was compared with hemorrhage of 1.0% body weight after administration of α-adrenoreceptor antagonist prazosin (0.2mg/kg, H_1.0p). Δ[K⁺]p increased significantly (p<0.05) after hemorrhage, and the peak value was proportional to the level of hemorrhage (0.18±0.08, 0.62±0.22 and 1.64±0.19 meq/l in H_0.5, H_1.0 and H_1.5, respectively). Δ[Na⁺]p decreased significantly (pÅ0.05) after hemorrhage, and the decrease was sustained until the end of the experiment (-0.8±0.6, -1.0±0.5and -2.2±0.5 meq/l in H_0.5, H_1.0 and H_1.5, respectively). In H_1.0P, the increase in Δ[K⁺]p (0.25±0.09 meq/l at the peak) and the decrease in Δ[Na⁺]p (- 0.2±0.1 meq/l at the bottom) were suppressed significantly (p Å 0.05) compared to H_1.0. Although ΔBV was greater in H_1.0P than H_1.0, plasma K⁺ content was not different between the groups. In H^1.0, the calculated concentrations of K⁺ and Na⁺ in the fluid which shifted into the intravascular space ([K⁺]sf, [Na⁺]sf) in the first 30min after hemorrhage were higher in [K⁺]sf (6.25±0.70 meq/l) and lower in [Na⁺]sf (128.0±3.2meq/l) than the pre-hemorrhage plasmalevel. With regard to H_1.0P, [K⁺]sf and [Na⁺]sf were not different from the pre-hemorrhage level of plasma. These results suggest that α-adrenergic activation after hemorrhage induces K⁺ movement into plasma to increase [K⁺]p, which might be related to the fluid shift from the intracellular to the extracellular space.