Overflow of endogenous norepinephrine from PVH nucleus of DOCA-salt hypertensive rats

Previous studies from this laboratory demonstrated that there was enhanced basal and evoked (K+ depolarization) overflow of endogenous norepinephrine (NE) into the perfusate of a push-pull cannula placed in the paraventricular nucleus of the hypothalamus (PVH) of conscious freely moving spontaneously hypertensive rat (SHR) compared with Wistar-Kyoto (WKY) or Sprague-Dawley (SD) rats. The present study was carried out to determine whether results obtained with SHR were specific to this genetic model of hypertension by examining NE release in deoxycorticosterone acetate (DOCA)-salt hypertension. DOCA-salt hypertension was produced in 8-wk-old uninephrectomized SD rats by administering a 50-mg DOCA Silastic pellet subcutaneously 7 days postnephrectomy and providing 0.9% NaCl + 0.2% KCl drinking solution at libitum for 3 wk. Sham-implanted animals received normal tap water. Blood pressure was similar to that of 8- to 10-wk-old SHR. Basal release of NE as well as release after K+ added to the push-pull cannula or sodium nitroprusside or phenylphrine administered intravenously was determined. It was observed that there was no difference in basal overflow or after K+ administration in DOCA-salt hypertensive rats compared with sham animals. Similarly, the increase in NE overflow due to sodium nitroprusside or the decrease due to phenylphrine was similar between DOCA-salt rats or sham controls. This was in sharp contrast to what was observed in SHR: basal or K(+)-evoked release was significantly greater in SHR than WKY, SD, DOCA-salt, or DOCA-sham controls. It is concluded that central noradrenergic activity involving the PVH is not altered in DOCA-salt hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)