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 baroreceptor nerve activity in spontaneously hypertensive rats (SHR) compared with Wistar Kyoto rats (WKY). Under urethane anesthesia (1.2 mg/Kg) the discharge of the recurrent laryngeal nerve was utilized as index of arterial baroreceptor activity (BNA) in rats with the ipslateral vagus cut at a proximal level. The ouabain (30 micrograms, i.v.) treatment produced an excitatory effect on BNA without changes in basal arterial pressure in both groups studied. This effect was larger in SHR (92 +/- 10%) than WKY (37 +/- 4%, P < 0.01). The arterial pressor 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) ouabain. The BNA under phenylephrine-induced peaks of high arterial pressure 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% P < 0.01). The inhibitory effects of sodium nitroprusside on arterial pressure and BNA were similar in SHR and WKY groups both before and after the ouabain treatment. These data indicate an excitatory effect of ouabain on baroreceptor nerve activity in normotensive and markedly in hypertensive rats which could contribute to the reflex arterial pressure regulation, besides the known inotropic action on the heart.