Pressure-Dependent Renin Release: The Kidney Factor in Long-Term Control of Arterial Blood Pressure in Conscious Dogs

Abstract

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 (P_th), 2) a flat section above P_th (plateau-level), and 3) a steep slope below P_th. From dog to dog the slope varied from -0.20 to -0.54 ng AI/ml/h/mmHg and P_th from 78.4 to 107.1 mmHg. In every dog MAP was higher than P_th (MAP-P_th:12.8 ± 1.58 mmHg). Dogs with a higher P_th regularly showed a higher MAP (r = 0.76; P < 0.005). Due to its normal variability arterial pressure occasionally falls below P_th and thus causes renin release. Therefore MAP will stabilize at a level above P_th. The pressor effect (MAP-P_th) 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-P_th difference (r= 0.93; P < 0.0001). We conclude that in healthy dogs the level of long-term blood pressure can be explained almost completely by P_th and the slope of the pressure-dependent renin release. Our findings may offer new perspectives to the pathogenesis of hypertension.

Key Words:

• Renin Release
• Long-term Blood Pressure
• Threshold Pressure
• Hypertension
• Renal Baroreceptor