Plasma volumes and hematocrits in rats with chronic sinoaortic denervation hypertension

Plasma volume changes were assessed in female Wistar rats with neurogenic hypertension induced by sinoaortic denervation, SAD. Tail veins of conscious, restrained rats were used for injection of Evans blue dye and for sampling into microhematocrit tubes. Only at 3 days did total plasma volume of SAD rats show a modest reduction of about 16% (P less than 0.05 vs. sham-operated plus unoperated controls). At 3, 6, and 13 wk, SAD mean body weight, plasma volume, and sodium concentration were similar to sham values. SAD hematocrits, however, like arterial pressures, were elevated at all postoperative times studied. In anesthetized SAD and sham rats, red blood cell (51Cr method) and plasma volumes were the same and so were hematocrits. The latter was unlike the finding in unanesthetized groups. Hematocrits from the same SAD rats were lower after induction of anesthesia than before (P less than 0.025). Thus, elevated hematocrits apparently resulted from the release of sequestered red blood cells into the circulation by unanesthetized SAD rats. In conclusion, plasma volume is within the normal range in SAD rats except for the first few postoperative days. Factors affecting volume regulation at that time are discussed.