Autoregulation in vasa recta of the rat kidney

Cohen, H. J.; Marsh, Donald J.; Kayser, B.

doi:10.1152/ajprenal.1983.245.1.f32

Cited by 31 publications

(25 citation statements)

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“…This hypothesis is supported by observations, particularly in volume-expanded rats, of poor autoregulation of medullary blood flow (MBF) (13,18,21,28,35,39,40). In contrast, however, other studies have demonstrated efficient autoregulation of MBF in rats and dogs (6,9,17,(23)(24)(25)(26)(27)29), even under conditions of volume expansion (24). These and other observations have led to an alternative hypothesis: that increased RAP increases the renal production of nitric oxide, which in turn mediates the increase in renal interstitial hydrostatic pressure (25).…”

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confidence: 83%

Autoregulation of renal medullary blood flow in rabbits

Eppel

Bergström

Anderson

et al. 2003

American Journal of Physiology-Regulatory, Integrative and Comp

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We examined the extent of renal medullary blood flow (MBF) autoregulation in pentobarbital-anesthetized rabbits. Two methods for altering renal arterial pressure (RAP) were compared: the conventional method of graded suprarenal aortic occlusion and an extracorporeal circuit that allows RAP to be increased above systemic arterial pressure. Changes in MBF were estimated by laser-Doppler flowmetry, which appears to predominantly reflect erythrocyte velocity, rather than flow, in the kidney. We compared responses using a dual-fiber needle probe held in place by a micromanipulator, with responses from a single-fiber probe anchored to the renal capsule, to test whether RAP-induced changes in kidney volume confound medullary laser-Doppler flux (MLDF) measurements. MLDF responses were similar for both probe types and both methods for altering RAP. MLDF changed little as RAP was altered from 50 to Ն170 mmHg (24 Ϯ 22% change). Within the same RAP range, RBF increased by 296 Ϯ 48%. Urine flow and sodium excretion also increased with increasing RAP. Thus pressure diuresis/natriuresis proceeds in the absence of measurable increases in medullary erythrocyte velocity estimated by laser-Doppler flowmetry. These data do not, however, exclude the possibility that MBF is increased with increasing RAP in this model, because vasa recta recruitment may occur.laser-Doppler flowmetry; pressure diuresis; renal blood flow; renal perfusion pressure; renal medulla PRESSURE DIURESIS/NATRIURESIS is a key mechanism in the long-term control of arterial pressure. There is strong evidence that this mechanism is mediated, at least in part, by a direct relationship between renal arterial pressure (RAP) and renal interstitial hydrostatic pressure, which in turn profoundly influences tubular sodium reabsorption (13,25,34,35). However, there is still much controversy as to the mechanism(s) by which increased RAP increases renal interstitial hydrostatic pressure, because total renal blood flow (RBF) and glomerular filtration rate are well autoregulated. One proposition is that increased RAP increases vasa recta capillary blood flow and pressure, which in turn increases renal interstitial hydrostatic pressure (8). This hypothesis is supported by observations, particularly in volume-expanded rats, of poor autoregulation of medullary blood flow (MBF) (13,18,21,28,35,39,40). In contrast, however, other studies have demonstrated efficient autoregulation of MBF in rats and dogs (6,9,17,(23)(24)(25)(26)(27)29), even under conditions of volume expansion (24). These and other observations have led to an alternative hypothesis: that increased RAP increases the renal production of nitric oxide, which in turn mediates the increase in renal interstitial hydrostatic pressure (25). Thus the issue of MBF autoregulation remains central to elucidating the precise mechanisms mediating pressure diuresis/natriuresis. Therefore, in this study, we used laser-Doppler flowmetry to examine the degree of MBF autoregulation in anesthetized rabbits. We paid particular attention t...

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confidence: 83%

Autoregulation of renal medullary blood flow in rabbits

Eppel

Bergström

Anderson

et al. 2003

American Journal of Physiology-Regulatory, Integrative and Comp

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“…The results of a recent study, however, cast doubt on this proposal. 16 The purpose of the present investigation was to determine if pressurenatriuresis is associated with changes in medullary hemodynamics or renal interstitial pressure (or both).…”

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confidence: 99%

“…Previous studies have examined the effects of reducing RPP after pressure was first increased by bilateral carotid occlusion. 10 - 16 Others have studied the effects of elevating RPP by infusion of catecholamines 9 -17 or by ligation of the carotid arteries.…”

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confidence: 99%

Pressure-diuresis in volume-expanded rats. Cortical and medullary hemodynamics.

et al. 1988

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SUMMARY This study evaluated whether pressure-diuretic and pressure-natriuretlc responses are associated with alterations in vasa recta hemodynamics. Autoregulation of cortical and papillary blood flow was studied using a laser-DoppIer flowmeter in volume-expanded and hydropenk rats. Superficial cortical flow and whole kidney renal blood flow were antoregulated in volume-expanded rats and decreased by less than 10% after renal perfusion pressure was lowered from 150 to 100 mm Hg. In contrast, papillary blood flow was not autoregulated and fell by 24 ± 2%. The failure of papillary blood flow to autoregulate was due to changes in the number of perfused vessels as well as to alterations In blood flow in individual ascending and descending vasa recta. Pressure hi vasa recta capillaries increased from 6.8 ± 0.8 to 13.8 ± 1.2 mm Hg after renal perfusion pressure was elevated from 100 to 150 mm Hg, and renal Interstitial pressure rose from 7.4 ± 0.8 to 12.3 ± 1.4 mm Hg. In hydropenic rats, papillary blood flow was autoregulated to a significant extent, but it still decreased by 19% after renal perfusion pressure was lowered from 150 to 100 mm Hg. The pressure-diuretic and presure-natriuretic responses in hydropenic rats were blunted in comparison to those observed in volume-expanded rats.

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“…32 The reason for the discrepant results is unknown. Papillary blood flow could be altered in the absence of changes in red blood cell velocity if the number of perfused vasa recta capillaries is altered by changes in RPP.…”

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Renal cortical and papillary blood flow in spontaneously hypertensive rats.

Roman

Kaldunski

1988

Hypertension

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SUMMARY The present study examined whether an alteration in renal medullary hemodynamics is associated with the development of hypertension in the spontaneously hypertensive rat (SHR). The relationships between whole kidney, cortical and papillary blood flows, and renal perfusion pressure were compared in 3-to 5-, 6-to 9-, and 12-to 16-week-old SHR and Wistar-Kyoto rats (WKY). Cortical and papillary blood flows were measured using a laser-Doppler flowmeter. Whole kidney and superficial cortical blood flows were similar in the different age groups of SHR and WKY over most of the range of perfusion pressure studied. Control papillary blood flows, determined at a renal perfusion pressure equal to the mean arterial pressure of each animal, were not significantly different in the 3-to 5-and 12->to 16-week-old SHR in comparison to values observed in age-matched WKY. In contrast, the control papillary blood flow was 30% lower in 6-to 9-week-old SHR in comparison to the value observed in WKY. Papillary blood flows were significantly less in all age groups of SHR than the corresponding flows measured in WKY when they were compared at equivalent renal perfusion pressures. These findings indicate that medullary vascular resistance is elevated even in very young SHR and suggest that alterations in vasa recta hemodynamics may participate in the development of hypertension by shifting the pressure-natriuresis relationship toward higher pressures. 1 -2 The kidneys of hypertensive patients 3 and genetically hypertensive rats 4 " 6 require an elevated renal perfusion pressure (RPP) to excrete sodium and water normally. We have demonstrated that the pressure-natriuresis relationship is shifted toward higher pressures even in very young, 3-to 5-week-old SHR. 6 The factors responsible for resetting the pressure-natriuresis relationship in this model of hypertension are unknown.Recent studies have indicated that elevations in RPP increase the delivery of sodium to the tip of the loop of Henle 7 and that chemical papillectomy blunts the pres- sure-natriuretic response. 8 These findings indicate that inhibition of tubular reabsorption in the deep nephrons contributes to the pressure-natriuretic response. Moreover, our studies indicating that elevations in RPP increase pressure and flow in the renal vasa recta circulation suggest that changes in medullary hemodynamics may signal the pressure-natriuresis response.9 "" The present study examined whether an alteration in renal medullary hemodynamics is associated with the development of hypertension in the SHR. The relationships between renal blood flow (RBF), cortical and papillary blood flows, and RPP were compared in 3-to 5-, 6-to 9-, and 12-to 16-week-old SHR and WistarKyoto rats (WKY). The results indicate that renal medullary vascular resistance is elevated early in the development of hypertension and suggest that changes in medullary hemodynamics may participate in the resetting of the pressure-natriuresis relationship in the SHR. Materials and MethodsExperiments were performed on ...

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Autoregulation in vasa recta of the rat kidney

Cited by 31 publications

References 0 publications

Autoregulation of renal medullary blood flow in rabbits

Autoregulation of renal medullary blood flow in rabbits

Pressure-diuresis in volume-expanded rats. Cortical and medullary hemodynamics.

Renal cortical and papillary blood flow in spontaneously hypertensive rats.

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