Effects of sympathectomy on blood pressure and its variability in conscious rats

To further assess the role of the sympathetic nervous system (SNS) in the control of blood pressure (BP), continuous recordings of BP were performed in conscious freely moving rats that had received daily injections of guanethidine or saline from 7 to 90 days of age. Guanethidine extensively destroyed the peripheral sympathetic fibers as indicated by marked decreases in the norepinephrine content of the heart and kidneys and the absence of pressor response to tyramine injection. Such a chronic sympathectomy did not alter the BP and heart rate (HR) levels but markedly enhanced the BP variability while the HR variability and the sensitivity of the cardiac baroreceptor reflex were not altered. Angiotensin-converting enzyme inhibition with perindopril induced a rapid fall in BP and normalized the BP variability in sympathectomized animals. It is concluded that in rats, the SNS is not necessary for the full development of the BP level but is essential to buffer the spontaneous variability of BP. After sympathectomy, BP is maintained at nearly normal levels mainly through activation of the renin angiotensin system.