ROLE OF ANGIOTENSIN-II AND CATECHOLAMINES IN BLOOD-PRESSURE VARIABILITY RESPONSES TO STRESS IN SHR

dThe contribution of the renin-angiotensin system (RAS) and the sympat hetic nervous system (SNS) to blood pressure (BP) and heart rate (HR) variability responses to air-jet stress was assessed in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Activity of the endoge nous RAS was suppressed by chronic treatment by a nonpeptide angiotens in II receptor antagonist (losartan). The role of alpha(1)-adrenocepto r activity was evaluated in rats by acute administration of prazosin. In untreated animals, an air jet induced an increase in systolic BP (S BP; 9 +/- 2 mmHg for WKY and 8 +/- 2 mmHg for SHR) and in HR (56 +/- 1 9 beats/min for WKY and 76 +/- 8 beats/min for SHR), followed by an in crease of the midfrequency (MF; 0.2-0.6 Hz) component of HR in WKY (18 3%) and by an increase of the MF component of SBP and diastolic BP in SHR (65%). Prazosin prevented BP rises as well as the MF component of BP and HR increases associated with air-jet stress. Chronic suppressio n of the RAS by losartan did not alter the BP response to the air jet in WKY and slightly reduced it in SHR but abolished all the BP and HR variability changes in both strains. These results indicate that the S NS but not RAS is essential for the BP rise induced by stress and demo nstrate that RAS in conjunction with SNS is involved in BP and HR vari ability changes associated with stress.