Blood pressure response to chronic episodic hypoxia: role of the sympathetic nervous system

Previous studies in several strains of rats have demonstrated that 35 consecutive days of recurrent episodic hypoxia (7 h/day) cause an 8- to 13-mmHg persistent increase in diurnal systemic blood pressure (BP). Carotid chemoreceptors and the sympathetic nervous system have been shown to be necessary for development of this BP increase. The present study was undertaken to further define the role of renal artery sympathetic nerves and the adrenal medulla in this BP increase. Male Sprague-Dawley rats had either adrenal medullectomy, bilateral renal artery denervation, or sham surgery. Rats from each of these groups were subjected to episodic hypoxia for 35 days. Control groups received either compressed air or were left unhandled. Adrenal demedullation or renal artery denervation eliminated the chronic diurnal mean BP response (measured intra-arterially) to episodic hypoxia, whereas sham-operated controls continued to showed persistent elevation of systemic BP. Plasma and renal tissue catecholamine levels at the end of the experiment confirmed successful adrenal demedullation or renal denervation in the respective animals. The chronic episodic hypoxia-mediated increase in diurnal BP requires both intact renal artery nerves as well as an intact adrenal medulla.