Hypertonic saline worsens infarct volume after transient focal ischemia in rats

Hypertonic saline (HS) has been advocated as a hyperosmolar agent for the treatment of cerebral edema, especially after traumatic brain injury. We tested the hypothesis that continuous intravenous HS administered during reperfusion from transient focal cerebral ischemia attenuates infarct volume.

Halothane-anesthetized male Wistar rats were subjected to 2 hours of middle cerebral artery occlusion (MCAO) by the intraluminal occlusion technique. At the onset of reperfusion, rats received a 10-mL/kg intravenous bolus of 0.9% saline (SAL, n=8) or 7.5% SAL (chloride:acetate 50:50, n=8) followed by a continuous infusion for 22 hours. In a second series of experiments, ischemic damage was determined in cohorts treated with equivolumetric 3% saline (n=8) or 20% mannitol (n=8). In a third series, regional cerebral blood flow was measured ([(14)C]iodoantipyrine autoradiography) at 6 hours of reperfusion in 7.5%-SAL-treated (n=5) or SAL-treated (n=5) animals.

In SAL rats, serum Na(+) was 137+/-3 and 138+/-2 mEq/L (mean+/-SEM) at baseline and 22 hours of reperfusion, respectively. In 7.5% SAL, serum Na(+) was 136+/-2 and 154+/-2 mEq/L at baseline and reperfusion, respectively. Physiological variables and reduction in laser-Doppler signal during MCAO and early reperfusion were not different between the 2 treatment groups. Cortical infarct volume was larger in 7.5%-SAL-treated rats (121+/-14 mm(3); 30+/-3% of contralateral cortex; P<0.05) than in SAL (64+/-15 mm(3); 16+/-4% of contralateral cortex). Striatal infarct volume was unchanged by HS therapy. Ipsilateral cortical tissue volume was increased relative to the contralateral side (by 26+/-5% with SAL; by 41+/-5% with 7.5% SAL). In contrast, ischemic damage was unaffected by 3%-SAL or 20%-mannitol treatment compared with SAL. Regional cerebral blood flow during reperfusion was heterogeneous in all animals, but there was no evidence of postischemic hypoperfusion or blood flow maldistribution in 7.5%-SAL-treated animals.

These data demonstrate that hypernatremia resulting from postischemic HS infusion worsens cortical infarct volume in transient focal cerebral ischemia. The deleterious effect is not linked to exacerbation of delayed hypoperfusion during early reperfusion (6 hours); however, blood flow defects at later recovery time points remain to be excluded. These results may have implications for HS therapy in clinical ischemic stroke.