Sympathetic transduction of cardiac sympathetic nerve activity in healthy, conscious sheep

Sympathetic transduction is the study of how impulses of sympathetic nerve activity (SNA) affect end‐organ function. Recently, the transduction of resting bursts of muscle SNA (MSNA) has been investigated and shown to have a role in the maintenance of blood pressure through changes in vascular tone in humans. In the present study, we investigate whether directly recorded resting cardiac SNA (CSNA) regulates heart rate (HR), coronary blood flow (CoBF), coronary vascular conductance (CVC), cardiac output (CO) and mean arterial pressure. Instrumentation was undertaken to record CSNA and relevant vascular variables in conscious sheep. Recordings were performed at baseline, as well as after the infusion of a β‐adrenoceptor blocker (propranolol) to determine the role of β‐adrenergic signalling in sympathetic transduction in the heart. The results show that after every burst of CSNA, there was a significant effect of time on HR (n = 10, ∆: +2.1 ± 1.4 beats min^–1, P = 0.002) and CO (n = 8, ∆: +100 ± 150 mL min^–1, P = 0.002) was elevated, followed by an increase in CoBF (n = 9, ∆: +0.76 mL min^–1, P = 0.001) and CVC (n = 8, ∆: +0.0038 mL min^–1 mmHg^–1, P = 0.0028). The changes in HR were graded depending on the size and pattern of CSNA bursts. The HR response was significantly attenuated after the infusion of propranolol. Our study is the first to explore resting sympathetic transduction in the heart, suggesting that CSNA can dynamically change HR mediated by an action on β‐adrenoceptors. image

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