BRAIN OUABAIN IN THE MEDIAN PREOPTIC NUCLEUS MEDIATES SODIUM-SENSITIVE HYPERTENSION IN SPONTANEOUSLY HYPERTENSIVE RATS

Presser responses to an acute increase in cerebrospinal fluid sodium a nd exaggeration of the hypertension and sympathetic hyperreactivity in spontaneously hypertensive rats (SI-IR) by high sodium diet involve r elease of brain ''ouabain'' and subsequent activation of the brain ren in-angiotensin system. Tn the present study, we determined whether rel ease of ''ouabain'' in the median preoptic nucleus participates in the se responses. In conscious Wistar rats, the presser and heart rate res ponses to central hypertonic saline (0.3 mol/L NaCl, 3.8 mu L/min over 10 minutes) and ouabain (0.6 mu g) were compared after median preopti c nucleus injection of either gamma-globulins or Fab fragments binding ouabain and brain ''ouabain'' with high affinity. Microinjection of F ab fragments into the median preoptic nucleus abolished the presser an d tachycardic responses to central hypertonic saline and significantly reduced the presser response to central ouabain. In SHR on high sodiu m, microinjection of Fab fragments into the median preoptic nucleus si gnificantly decreased baseline blood pressure to a level not different from that in SHR on regular sodium (149+/-7 Versus 145+/-5 mm Tig), w hereas the enhanced responses to air stress were not affected. Our res ults support the concept that blood pressure responses to central hype rtonic saline and exaggeration of the hypertension in SHR by high sodi um diet depend on release of brain ''ouabain'' in the median preoptic nucleus.