[Effect of hypertonic NaCl solution on arterial pressure compensation after hemorrhage in rats]

Rats were bled within 5 min in lowering mean arterial pressure (MAP) to 25 mmHg and were subsequently infused intravenously with hypertonic (7.5% NaCl) or normal saline in a volume equal to 10% of the amount of the lost blood. Intravenous infusion of hypertonic saline significantly facilitated posthemorrhagic recovery of MAP, which was markedly attenuated by 6-hydroxydopamine or Captopril. When these two drugs were used together, the attenuation effect was complete. While hypertonic saline significantly increased plasma Na+ concentration, normal saline only gave rise to a decrease. Intracerebroventricular injection of hypertonic NaCl solution also facilitated the recovery of MAP significantly. These results suggest that after hemorrhage increased plasma Na+ concentration following i.v. of a small amount of hypertonic saline may act on the central nervous system and activate sympathetic nervous system and renin angiotensin system to facilitate a rapid recovery of MAP.