Effect of Systemic Hypothermia on Reactions of Pial Arteries to Acute Massive Blood Loss in Anesthetized Rats

Abstract

The effect of the lowering of body temperature on the responses of cerebral arteries was studied in anesthetized (urethane, 1000 mg/kg) male Wistar rats in conditions of hemodynamic stability and after pre-induced acute massive blood loss. Changes in the diameter of the pial arteries (initial diameter 10–40 µm) were evaluated via intravital microscopy in four experimental groups: without and with pre-induced blood loss (35% of the circulating blood volume), and in each group, at room temperature (22–23°C) and during gradually developing cold-water immersion hypothermia (12–13°C) until respiratory arrest. In the groups with pre-induced blood loss, respiratory arrest came about at room temperature after an average of 3 h with a decrease in body temperature to 32.4 ± 0.5°C, while during immersion cooling, it occurred after 2.5 h at 15.1 ± 0.8°C. In the groups without blood loss, respiratory arrest did not come about at room temperature for more than 3.5 h of observation, although rectal temperature decreased to 34.4 ± 0.2°C; during immersion cooling, respiratory arrest was observed after 3 h at a body temperature of 13.1 ± 0.3°C. During the lowering of body temperature, the rats of all experimental groups showed vasoconstriction. In the groups with blood loss, the reduction in the diameter of the pial vessels accounted for 10–15% of the initial immediately after blood withdrawal and more than 30% of that during subsequent immersion cooling. In rats without blood loss, the constriction of pial arteries during immersion cooling was significantly less. Thus, systemic hypothermia aggravates microcirculatory dysfunction induced by acute massive blood loss, suggesting an additive effect of hypothermia and hemorrhage on vasoconstrictor responses of the pial arteries in rats.