SPONTANEOUS CHANGES IN ARTERIAL BLOOD-PRESSURE AND RENAL INTERSTITIALHYDROSTATIC-PRESSURE IN CONSCIOUS RATS

1. Previous work has demonstrated a positive relationship between expe rimentally induced changes in arterial pressure (AP) and renal interst itial hydrostatic pressure (RIHP). The purpose of the present study wa s to test the hypothesis that RIHP is positively correlated with the n ormal changes in AP that occur spontaneously in conscious rats. 2. Rat s were chronically instrumented for the recording of AP (via an aortic catheter) and RIHP. RIHP was measured by implanting a Millar microtra nsducer, whose tip had been encapsulated in a 35 mu m pore polyethylen e matrix (5 mm long, 2 mm o.d.), approximately 5 mm below the renal co rtical surface. 3. A total of 56 h of simultaneous analog recording of AP and RIHP was obtained from ten rats. Each lh segment was digitized and evaluated at frequencies of 1, 0.1, 0.02 and 0.01 Hz. 4. In forty -nine out of fifty-six of these 1 h recordings taken at 1 Hz, there we re significant positive linear correlations between AP and RIHP (mean r = 0.32) With it mean slope of 0.11 mmHg RIHP/1 mmHg AP. Low-pass fil tering to 0.01. Hz significantly increased the r value to 0.48. 5. The se results demonstrate that spontaneous changes in AP and RIHP are pos itively correlated. The spontaneous coupling of AP and RIHP may be of importance in the regulation of salt and water excretion by the pressu re diuresis mechanism.