EFFECT OF ACUTE AND CHRONIC HYPONATREMIA ON BLOOD-BRAIN-BARRIER FUNCTION IN THE RAT

To study whether acute or chronic hyponatremia alters blood-brain barr ier (BBB) permeability, rats made hyponatremic by constant desmopressi n acetate infusion were studied by NMR spectroscopy and imaging. On co nstant volume ventilation and nitrous oxide, acute (1- and 2-day) and chronic (7- and 14-day) hyponatremic and normonatremic controls were i nfused with 0.25 M HCl. Despite reducing blood pH by at least 0.35 in < 50 min, brain pH, measured by P-31 NMR, was unaffected in any group. As a second test of BBB function, gadolinium-DTPA (Gd-DTPA) was injec ted intravenously in these five groups. Coronal slice H-1 NMR images o btained before and after Gd-DTPA showed image intensity changes in mul tiple areas outside brain, but neither control nor hyponatremic rats s howed any differences in cortex, white matter or cerebellum. To ascert ain whether the threshold for BBB disruption was altered, hypertonic m annitol (1.5, 2.0 or 3.0 mL) was injected rapidly into one internal ca rotid artery and pre- and post-Gd-DTPA images obtained. In both contro l and hyponatremic rats only the largest dose caused detectable Gd-DTP A leakage into brain. Thus, BBB function appears intact in both acute and chronic hyponatremia since neither H+ nor GD-DTPA penetrated the b arrier and resistance to mannitol disruption was unaffected by hyponat remia.