Angiotensin n (Au) may be involved in long term blood pressure (BP) regulation in part by increasing sympathetic outflow. To test this hypothesis, rats were placed on either a low salt (LS; <0.01% NaCl) diet, to increase All levels, or a high salt (HS, 8% NaCl) diet, for 2 to 3 weeks. It was then determined if losartan (10 mg/kg, I.V.), an All type 1 receptor antagonist, suppresses lumbar sympathetic nerve activity (LSNA) and heart rate (HR) more in LS compared to HS conscious rats. The experiment consisted of three recording periods: 30 min control, 40 min after losartan injection and 30 min after BP was restored near to but not above control values by methoxamine infusion. In LS rats (n=6), 5 min after losartan, BP decreased from 114±5 to 92±6 mm Hg, LSNA increased from 99±3 to 143±5 %, and HR increased from 467±12 to 530±7 b/min (all p<0.05). Despite a further fall in BP by 40 min after losartan (to 81±6 mm Hg), LSNA returned towards control (119±4 %), although HR remained elevated (524±8 b/min). Thirty min after BP was restored to pre-losartan values (112±5 mm Hg), both LSNA and HR were suppressed below control (49±11%, 343±14 b/min; p<0.05). In contrast, there were no significant changes in BP (110±6 to 108±6 mm Hg), HR (469±13 to 476±13 b/min) and LSNA (101±4 to 103±9%) after losartan in HS rats (n=5). We conclude that endogenous All supports LSNA and HR in conscious sodium deprived rats and that this action can only be revealed when BP is maintained at basal levels. These results suggest that AH plays an important role in long-term regulation of BP in part by enhancing sympathetic activity.
|Original language||English (US)|
|State||Published - 1996|
ASJC Scopus subject areas
- Molecular Biology