Renal cortical and papillary blood flow in spontaneously hypertensive rats.

Abstract

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 ...

Enhanced vascular tone in the renal vasculature of spontaneously hypertensive rats.

“…The recent finding that papillary blood flow is reduced in SHR before the development of hypertension suggests that an elevation in renal medullary vascular resistance may participate in the development of this disease. 10 The present study examined whether structural changes or alterations in the vascular tone of the preglomerular vasculature of juxtamedullary nephrons could explain the decrements in renal medullary hemodynamics 11 and the pressure-natriuretic response in the kidney of SHR. 9 The results of the present study indicate that there are significant differences in the pressure-diameter relations in the preglomerular vasculature of juxtamedullary nephrons in SHR and WKY rats.…”

“…11 Furthermore, studies on the mechanism of pressurenatriuresis indicated that it is associated with changes in renal medullary hemodynamics, renal interstitial pressure, and inhibition of tubular reabsorption in deep nephrons. 1819 The present finding suggests that an elevated vascular tone in the preglomerular vasculature of juxtamedullary nephrons of SHR may account for the elevated renal medullary vascular resistance in this model of hypertension.…”

“…910 In the SHR, the abnormality in the pressure-natriuretic response is associated with a reduction in papillary blood flow 11 and renal interstitial hydrostatic pressure. 12 These observations suggest that an elevation in renal medullary vascular resistance may participate in the resetting of the renal function toward higher pressures in SHR.…”

“…12 These observations suggest that an elevation in renal medullary vascular resistance may participate in the resetting of the renal function toward higher pressures in SHR. 11 The factors responsible for reducing papillary blood flow in SHR are unknown. Medullary blood flow is derived exclusively from the perfusion of deep nephrons.…”

Elevated renovascular tone in young spontaneously hypertensive rats. Role of cytochrome P-450.

“…1 ' 2 In the SHR, the blunted pressure-natriuretic response is associated with a reduction in papillary blood flow 3 and renal interstitial hydrostatic pressure. 4 Recent studies by Gebremedhin et al 5 suggest that the decline in papillary blood flow in adult SHR is due to an enhanced vascular tone rather than structural changes in the preglomerular vasculature of the deep nephrons.…”