Spontaneous changes in arterial blood pressure and renal interstitial hydrostatic pressure in conscious rats.

Abstract

1. Previous work has demonstrated a positive relationship between experimentally induced changes in arterial pressure (AP) and renal interstitial hydrostatic pressure (RIHP). The purpose of the present study was to test the hypothesis that RIHP is positively correlated with the normal changes in AP that occur spontaneously in conscious rats. 2. Rats were chronically instrumented for the recording of AP (via an aortic catheter) and RIHP. RIHP was measured by implanting a Millar microtransducer, whose tip had been encapsulated in a 35 ,um pore polyethylene matrix (5 mm long, 2 mm o.d.), approximately 5 mm below the renal cortical surface. 3. A total of 56 h of simultaneous analog recording of AP and RIHP was obtained from ten rats. Each 1 h segment was digitized and evaluated at frequencies of 1, 0-1, 0-02 and 0O01 Hz. 4. In forty-nine out of fifty-six of these 1 h recordings taken at 1 Hz, there were significant positive linear correlations between AP and RIHP (mean r = 0 32) with a mean slope of 0-11 mmHg RIHP/1 mmHg AP. Low-pass filtering to 0 01 Hz significantly increased the r value to 0-48. 5. These results demonstrate that spontaneous changes in AP and RIHP are positively correlated. The spontaneous coupling of AP and RIHP may be of importance in the regulation of salt and water excretion by the pressure diuresis mechanism.Both theory and experimental evidence indicate that a close correspondence between arterial pressure (AP) and urinary excretion of salt and water (pressure diuresis) is

Moment-to-Moment Characteristics of the Relationship Between Arterial Pressure and Renal Interstitial Hydrostatic Pressure

“…However, the finding of a 1-second response lag makes single pulsation transmission unlikely and indicates that there is an inherent smoothing function linking pulsatile RAP with the relatively nonpulsatile RIHP. In addition, it is unknown whether anesthesia and surgery could affect the acute RAP-RIHP relationship; however, given that the overall slope of the present experiments is comparable with those performed previously in conscious animals, 8 the influence of these does not appear to be significant.…”

“…That is, moment-to-moment changes in RIHP may impact on urine formation, and the cumulative effect of these acute changes over time may account for the long-term aspect of pressure-natriuresis by inducing homeostatically appropriate changes in blood volume and thereby returning arterial pressure toward its operating point. 8,18 Similar to previous studies using conventional pressurenatriuresis methodology, 9 -17 the overall acute RAP-RIHP relationship was found to correlate linearly and to have a similar slope over a wide range of changes in RAP. However, despite the numerous studies describing the RAP-RIHP relationship as linear, none assessed whether there are differential regulations above and below the arterial pressure operating point.…”

“…Interestingly, only one study to date has described a statistically significant moment-tomoment correlation between spontaneous arterial pressure oscillations and RIHP within frequency windows of 1.00 to 0.01 Hz. 8 This same group also found that urine flow, a variable downstream from RIHP, responded to changes in arterial pressure within Ϸ6 seconds. 18 Because changes in RIHP are an intermediate step in pressure-natriuresis, there must be a shorter delay between arterial pressure and RIHP; however, the exact time course is yet to be elucidated.…”

“…9 -17 However, such assessments may not reflect true in vivo control of arterial pressure, because arterial pressure in conscious animals does not change from one steady-state to another but rather fluctuates spontaneously in varying degrees of magnitude around an operating point (baseline) and over a wide range of time frames (frequencies). 8 For example, oscillations in arterial pressure assessed over an acute time frame ( Figure 1A) tend to be more variable and of greater magnitude than fluctuations assessed over a prolonged timeframe ( Figure 1B). This suggests that kidneys are exposed to greater arterial pressure variations over a shorter time frame than have been examined using conventional pressurenatriuresis methodologies.…”

Long-Term Circulatory Consequences of Perinatal Iron Deficiency in Male Wistar Rats

“…11 Fluctuations in arterial pressure around the long-term level induce changes in perfusion of the poorly autoregulated medullary vessels and, consequently, cause changes in RIHP, which ultimately influence the set point of arterial pressure at which sodium and water balance occur. 26,27 That is, a decrease in the responsiveness and set point of the RAP-RIHP relationship can impact the pressure-natriuresis mechanism such that greater changes in arterial pressure are required to generate corresponding changes in RIHP to regain the sodium and water balance. 28 The blunting of the RAP-RIHP relationship may also explain, in part, the altered responsiveness in handling lowand high-sodium intake in the PID animals.…”