OUABAIN PRODUCES DIVERSE EXCITATORY EFFECTS ON AFFERENT BARORECEPTOR NERVE ACTIVITY IN SHR AND WKY ANIMALS

The effect of acute ouabain treatment was evaluated on afferent barore ceptor nerve activity in spontaneously hypertensive rats (SHR) compare d with Wistar Kyoto rats (WKY). Under urethane anesthesia (1.2 mg/Kg) the discharge of the recurrent laryngeal nerve was utilized as index o f arterial baroreceptor activity (BNA) in rats with the ipslateral vag us cut at a proximal level. The ouabain (30 mu g, i.v.) treatment prod uced an excitatory effect on BNA without changes in basal arterial pre ssure in both groups studied. This effect was larger in SHR (92 +/- 10 %) than WKY (37 +/- 4 %, P < 0.01). The arterial presser response to phenylephrine was similar in both SHR and WKY before (20 +/- 1 and 22 +/- 1.2 mmHg) and after (18 +/- 1.4 and 20 +/- 2 mmHg, respectively) o uabain. The BNA under phenylephrine-induced peaks of high arterial pre ssure was significantly higher in SHR (61 +/- 15 %) than in WKY (41 +/ - 5 % P < 0.01) but after ouabain treatment the opposite was observed (31 +/- 5 vs. 61 +/- 4 % Pi 0.01). The inhibitory effects of sodium ni troprusside on arterial pressure and BNA were similar in SHR and WKY g roups both before and after the ouabain treatment. These data indicate an excitatory effect of ouabain on baroreceptor nerve activity in nor motensive and markedly in hypertensive rats which could contribute to the reflex arterial pressure regulation, besides the known inotropic a ction on the heart.