Pressure-dependent renin release and arterial pressure maintenance in conscious rats

The relationship between pressure-dependent renin release and mean arterial pressure (MAP) level was assessed in normotensive intact (n = 10), sympathectomized (guanethidine at 1-13 wk of age; n = 8), and renal-denervated (1 wk before the study; n = 6) rats under normal-salt diet. MAP was recorded beat-to-beat for 2 h in conscious animals. Then plasma renin concentration (PRC) responses to graded reductions of MAP were determined using an aortic inflatable cuff. Neither sympathectomy nor renal denervation altered baseline MAP level and PRC. Lowering MAP below a threshold pressure induced large increases in PRC. Threshold pressure did not differ between intact (87 +/- 1 mmHg), sympathectomized (88 +/- 2 mmHg), and renal-denervated (83 +/- 2 mmHg) rats. MAP frequently fell below threshold pressure in sympathectomized but not in intact and renal-denervated rats. We conclude that in conscious normotensive quiet rats under normal-salt diet the pressure-dependent renin release is not activated spontaneously and is therefore unlikely to play a role in MAP maintenance. This regulatory mechanism develops and operates normally in the absence of sympathetic nerves.