Sympathetic and parasympathetic components of reflex tachycardia induced by hypotension in conscious dogs with and without heart failure

The autonomic components of the reflex tachycardia following nitroglycerin and inferior vena caval occlusion (IVCO) were analysed in conscious, unsedated normal dogs and in dogs with congestive heart failure (CHF) before and after selective and combined beta-adrenergic and cholinergic blockades. In normal dogs nitroglycerin and IVCO decreased mean arterial pressure from 98 ± 1 to 69 ± 1 mmHg and 73 ± 2 mm Hg, respectively, while heart rate increased from 77 ± 3 to 176 ± 4 and 154 ± 6 beats/min (bpm), respectively. Selective beta-adrenergic or cholinergic blockades partially prevented the reflex tachycardia, while combined blockades abolished the reflex tachycardia. Thus, the reflex tachycardia following hypotension induced by either nitroglycerin or IVCO is mediated by a combination of sympathetic and parasympathetic influences.