Pressure-dependent renin release: the kidney factor in long-term control of arterial blood pressure in conscious dogs.

In 12 conscious dogs on a normal sodium diet the renal venous-arterial plasma renin activity-difference as a function of mean renal artery pressure (renin stimulus-response curve; RSRC) as well as long-term mean arterial blood pressure (MAP; pressure-histograms) were measured repeatedly. The RSRC has 1) a threshold pressure (Pth), 2) a flat section above Pth (plateau-level), and 3) a steep slope below Pth. From dog to dog the slope varied from -0.20 to -0.54 ng AI/ml/h/mmHg and Pth from 78.4 to 107.1 mmHg. In every dog MAP was higher than Pth (MAP-Pth:12.8 +/- 1.58 mmHg). Dogs with a higher Pth regularly showed a higher MAP (r = 0.76; P less than 0.005). Due to its normal variability arterial pressure occasionally falls below Pth and thus causes renin release. Therefore MAP will stabilize at a level above Pth. The pressor effect (MAP-Pth) of this feedback system should depend on the sensitivity of the pressure-dependent renin release mechanism (slope of RSRC). Accordingly we observed a close correlation between the slope of the RSRC and the MAP-Pth difference (r = 0.93; P less than 0.0001). We conclude that in healthy dogs the level of long-term blood pressure can be explained almost completely by Pth and the slope of the pressure-dependent renin release. Our findings may offer new perspectives to the pathogenesis of hypertension.