Differential control of sympathetic outflow to kidney, heart, adrenal gland, and liver during systemic hypotension induced by cardiac tamponade in anesthetized dogs.

This study was designed to determine if cardiac tamponade-induced hypotension produces differential control in efferent sympathetic nerve activity to the kidney (RNA), heart (CNA), adrenal gland (AdNA), and liver (HNA) in pentobarbital-anesthetized dogs and to define whether systemic baroreceptors modify this response. We recorded RNA, CNA, AdNA, and HNA simultaneously during a 10 min period of sustained hypotension of 50 mm Hg, which was produced by intrapericardial saline infusion at 20 ml/min. When blood pressure reached 50 mm Hg, sympathetic nerve activity to all four organs increased significantly. Following this, RNA decreased significantly below the control (72 +/- 12%) at the end of experiment, while CNA, AdNA, and HNA remained elevated above control values throughout the experiment. Renal sympathoinhibition was reversed by cervical vagotomy, whereas this had no effect on CNA, AdNA, and HNA responses to hypotension. Additionally, the combined denervation of vagal, carotid sinus, and aortic nerves did not show any significant change in any variables. Thus these results indicate that hypotension due to cardiac tamponade in dogs produces an initial equivocal sympathoexcitation to the kidney, heart, adrenal gland, and liver followed by vagal afferent-mediated sympathoinhibition to the kidney but sustained excitation to the other three organs.