Effects of salt loading on sympathetic activity and blood pressure in anesthetized two-kidney, one clip hypertensive rats

Besim Özaykan,Ayşe Doğan

doi:10.17305/bjbms.2011.2555

Besim Özaykan, Ayşe Doğan

Open Access

https://doi.org/10.17305/bjbms.2011.2555

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Abstract

In this study, we investigated the effects of salt loading on sympathetic pressor activity, cardiac autonomic activity, mean arterial pressure (MAP), heart rate (HR) and on the relations between them in anesthetized two-kidney, one clip (2K1C) hypertensive rats. We submitted rats to either renal artery clipping or sham operation. Distilled water or 0.5 % NaCl was given orally to the clipped and sham-operated control rats for 4 weeks. Then, MAP and HR differences between pre- and post- autonomic blockade were evaluated as indexes of sympathetic pressor and cardiac autonomic activity, respectively. The autonomic blockade decreased MAP to the similar levels in all groups (between 81.7±7.6 -87.3±7.1 mmHg). Sympathetic pressor activity was greater in the clipped rats than in its sham-operated controls only under salt loading (55.3±6.2 vs. 37.0±4.1 mmHg, p<0.05). Cardiac autonomic activity was, predominantly, sympathetic and more in the clipped group than in the sham-operated rats under distilled water (48.3±8.6 vs. 19.7±7.0 beats/min, p<0.05) but not under salt loading. Salt loading inverted the relationship between HR and cardiac autonomic activity in 2K1C hypertensive rats (r=-0.76, p=0.046 vs. r=0.89, p=0.019). These results suggest that salt loading may have augmented the effect of renovascular constriction on MAP by affecting the sympathetic pressor activity and the relation between cardiac autonomic activity and HR in 2K1C hypertensive rats.

Highlights

Two-kidney, one clip hypertension (2K1C) is primarily caused by high levels of angiotensin II (ANG II) [1, 2] and sympathetic activity [3]
We aimed to investigate the influence of salt loading on sympathetic pressor activity, cardiac autonomic activity, mean arterial blood pressure (MAP), heart rate (HR) and on the relations between them in anesthetized 2K1C hypertensive rats
Basal BP and HR There were no significant differences between the two clipped groups with regard to basal diastolic (DBP), mean and systolic (SBP) arterial blood pressures (Figure 1)

Summary

Introduction

Two-kidney, one clip hypertension (2K1C) is primarily caused by high levels of angiotensin II (ANG II) [1, 2] and sympathetic activity [3]. Salt intake has the effects on sympathetic activity [4] beside renin angiotensin system [5]. Salt intake condition may affect sympathetic activity as a result of an interaction between ANG II and baroreflex [7]. When salt intake is low, high ANG II may reset the arterial baroreflex to higher operating pressures. This resetting is likely an important factor in the changes of sympathetic outflow [8]. Due to the interaction between ANG II and baroreflex, a high salt diet can affect sympathetic activity both directly and indirectly. The relationship between salt intake and sympathetic activity in this form of hypertension remains unclear. We aimed to investigate the influence of salt loading on sympathetic pressor activity, cardiac autonomic activity, mean arterial blood pressure (MAP), heart rate (HR) and on the relations between them in anesthetized 2K1C hypertensive rats

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