Intrinsic heart rate after infusion of angiotensin II in rats with sino-aortic deafferentation.

We investigated the effect of the infusion of angiotensin II on intrinsic heart rate in rats with sino-aortic deafferentation. Sino-aortic deafferentated (SAD) rats studied 48 h after surgery presented significant tachycardia when compared with sham-operated rats (426 +/- 16 vs 338 +/- 6 bpm), but no change in intrinsic heart rate (369 +/- 9 vs 369 +/- 11 bpm). Infusion of angiotensin II into the SAD group 48 h after deafferentation did not produce an additional increase in heart rate (423 +/- 16 vs 426 +/- 16 bpm) or a change in intrinsic heart rate (369 +/- 11 vs 369 +/- 9 bpm) when compared with sham-operated rats submitted to saline infusion. Intravenous (iv) infusion of angiotensin II into sham-operated rats produced a significant increase in both heart rate (381 +/- 12 vs 338 +/- 6 bpm) and intrinsic heart rate (427 +/- 9 vs 369 +/- 11 bpm). These data indicate that a) tachycardia after SAD is not associated with an increase in intrinsic heart rate, b) in sham-operated rats, the tachycardia occurring after angiotensin II infusion is associated with an increase in intrinsic heart rate, and c) angiotensin II infusion does not alter the intrinsic heart rate of rats tested 48 h after sino-aortic deafferentation. We conclude that the increase in intrinsic heart rate caused by angiotensin II in conscious rats depends on the integrity of the baroreceptor reflex.