The Effect of Partial Clamping of the Renal Artery on Pressures in the Proximal and Distal Tubules and Peritubular Capillaries of the Rat Kidney

Abstract

The purpose of this study was to measure the intratubular and peritubular capillary hydrostatic pressures in acute experiments of partial clamping of the renal artery to such a degree that a significant reduction of the filtration pressure was ascertained. The renal artery of rats weighing about 250 grams were clipped with a 0.20 mm silver clamp, which reduced the urine flow and the glomerular filtration rate to below the range of spontaneous variations and caused occlusion of minor or major parts of the nephron population. Intratubular and peritubular capillary pressures were measured directly by the micropuncture technique. The results demonstrated that proximal intratubular as well as peritubular capillary pressures in partially clamped kidneys were not measurably different from those of normal, control kidneys (12–13 mm Hg), whereas distal intratubular pressures were significantly reduced (from 6.7 mm Hg in normal to 3.9 mm Hg) in clamped kidneys. The results are discussed in relation to previous and recent findings and interpretations. The hypothesis a proposed that the physiological function of the juxtaglomerular apparatus is to serve as a feed‐back mechanism whereby changes being a function of the proximal intratubular pressure via the release of angiotensin adjusts the proximal reabsorption and the intrarenal vascular resistance in such a way that proximal intratubular hydrostatic pressures are maintained.

The effects of combined renal vasodilatation and pressor agents on renal hemodynamics and the tubular reabsorption of sodium.

“…These observations strengthen the concept that it is the vasodilatation which results in diminished reabsorption of sodium and not some more direct effect of the infused agent on tubular transport (14). We have suggested previously that increased renal medullary blood flow may diminish the absolute reabsorption of sodium by the ascending limb of Henle's loop (4,5), and Leyssac has suggested that angiotensin may diminish proximal tubular reabsorption of sodium (15). Although the effects have not been entirely predictable, angiotensin does produce natriuresis under some conditions (16)(17)(18)(19).…”

“…Furthermore, natriuresis in the absence of salt loading accompanies increased renal blood flow when local vasodilatation is produced by a variety of agents (7)(8)(9)(10)(11)(12)(13), and we have observed that the unilateral natriuresis accompanying increased renal blood flow during the renal arterial infusion of acetylcholine is due in part to diminished net tubular reab-sorption of sodium (14). Leyssac has suggested that angiotensin may depress proximal tubular reabsorption (15), and it has been demonstrated that under certain conditions angiotensin may produce natriuresis (16)(17)(18)(19). If the reabsorption of sodium distally to the proximal convolution relates in part in some inverse manner to blood flow, then the vasoconstrictor effects of angiotensin could limit the natriuretic effect that the agent could exert by way of depressing proximal tubular reabsorption.…”

Studies on Glomerulotubular Balance During Aortic Constriction, Ureteral Obstruction and Venous Occlusion in Hydropenic and Saline-Loaded Rats

“…Although the results of the present experiments may in part be explained by this model, it is clear that the changes in reab sorption cannot be explained by changes in the absolute values for the capillary hydrostatic and oncotic pressures. Aortic constriction, ureteral obstruction and venous occlusion during hydropenia all produce renal vasodilation [16,22,29]; however, the effects on capil lary hydrostatic pressure are different: peritubular capillary pressure is unchanged by aortic constriction [17], but rises with ureteral obstruc tion and venous occlusion [10,16]. The effects on filtration fraction, and thus peritubular oncotic pressure, are also different: filtration fraction is usually unchanged by aortic constriction [15], but is reduced by ureteral pressure [29] and venous occlusion [16].…”

A Micropuncture Study of Glomerular Filtration and Tubular Reabsorption of Endogenous Renin in the Rat

“…The rats were prepar ed for micropuncture and clearance measurements as previously described [8]. Polyethylene catheters were inserted into the left jugular vein for infusions and into the right carotid artery for blood sampling and continuous recording of systemic arterial pres sure with a capacitance pressure transducer (Han sen, S&W, Copenhagen).…”