Effects of cold ischemia on the preserved rat kidney: Intrarenal distribution of perfusate

The intrarenal distribution of a modified Collins solution containing 5% of human albumin was investigated during the initial perfusion of rat kidneys and after 2, 12, and 16 hr of cold storage. Carbonized microspheres 9 μm in diameter were injected upstream into a mixing chamber and the change in regional renal resistance of three cortical zones was calculated. The resistance in the inner cortical zone increased to a significantly greater extent than that in the outer cortical zone. The prerequisites for a reduction of deep cortical and thus medullary blood flow after recirculation of the kidney seem to be already established during the hypothermic storage.     

Skin blood flow in sheep: comparison of xenon-133 washout and radioactive microsphere techniques

Blood flow was measured in leg and torso skin of conscious or anesthetized sheep by using 15-micron radioactive microspheres (Qm) and the 133Xe washout method (QXe). There was a good relationship between Qm in the cutaneous compartment and QXe calculated from the fast component of the biexponential washout curves (QXe = 0.40.Qm + 6.2, r = 0.90, P less than 0.001) with QXe values substantially below those determined with microspheres. Only at low blood flow levels was there a tendency for QXe to overestimate capillary blood flow as assessed with microspheres, but at higher blood flow levels the 133Xe washout method resulted in values substantially below those determined with microspheres. The slope of the slow component of the washout curves was inversely related to the tissue-blood partition coefficient in the subcutaneous tissue (r = 0.52, P less than 0.001), indicating an influence of the amount of subcutaneous fat on the washout rate. QXe calculated from the slow component of the washout curves was not significantly correlated with Qm in the subcutaneous compartment (r = 0.19, P greater than 0.10). In leg skin with dilated arteriovenous anastomoses, QXe was generally higher than in torso skin and leg skin with constricted arteriovenous anastomoses, indicating that shunt blood flow increases the washout of 133Xe.     

Intrarenal blood flow distribution: effect of carotid occlusion.

In this study we have examined the influence of bilateral carotid occlusion on intrarenal blood flow distribution. Using labeled microspheres to determine intrarenal hemodynamics, bilateral carotid ligation in mannitol or saline expanded dogs resulted in an increase in outer cortical blood flow and a decrease in inner cortical flow. Total renal blood flow and glomerular filtration rate did not change significantly during carotid occlusion whereas the average mean arterial blood pressure rose from 130 to 166 mmHg. Inner cortical flow resistance increased substantially after carotid occlusion; outer cortical resistance was unchanged. These results suggest that bilateral carotid occlusion selectively activates inner cortical renal sympathetic fibers.     

Intrarenal distribution of renal blood flow in the rat.

Intrarenal blood flow distribution was studied with the simultaneous use of the 99Tc labelled frog erythrocyte (microsphere) and the radioactive 86Rb fractionation method in the rat. The amount of blood entering the outer cortex (99Tc labelled erythrocytes method) proved to be higher than one perfusing the outer cortex (86Rb method), whereas the amount of blood entering the inner cortex (99Tc method) was less than the amount perfusing the inner cortex and medulla (86Rb method). Hence a group of the preglomerular arterioles in the outer cortex contributes to the blood supply of the inner cortex, on the other hand a group of preglomerular arteries in the inner cortex participates in the postglomerular blood supply of the medulla. Changes in the renal circulation are, however, associated with altered distribution of postglomerular vascular segments supplied by some groups of preglomerular arterioles. From this it is concluded that the postglomerular vessels of the deeper cortical layers constitute a system which is not parallelly coupled but comprises both series- and parallel-coupled sections. The contribution of these sections appears to vary depending on the actual haemodynamic conditions.     

Influence of antidiuretic hormone on intrarenal blood flow distribution in diabetes insipidus dogs and rats.

The distribution of labeled microspheres within the renal cortex was used to evaluate the influence of physiological amounts of antidiuretic hormone on intrarenal blood flow distribution in hypophysectomized dogs and in rats with hereditary diabetes insipidus. In both species, intravenous infusions of ADH caused a significant decrease in the ratio of inner to outer cortical blood flow. The change in blood flow distribution observed in the hypophysectomized dog with ADH was primarily a consequence of a decrease in inner cortical blood flow. No consistent changes in outer cortical blood flow were found. Also in the dog, glomerular filtration rates and electrolyte excretion rates (Na and K) increased following ADH. In contrast, ADH infusion into Brattleboro rats caused no change in glomerular filtration or excretion of Na and K.     

Renal blood flow distribution during steady-state exercise and exhaustion in conscious dogs.

To determine whether renal blood flow is reduced or redistributed during exercise, we measured total renal flow (TRF) and intrarenal flow distribution (IRFD) in nine dogs. They ran on a motor-driven treadmill at 3-8 mph at grades of 8-15% for an average of 35 min. We measured aortic pressure, heart rate, stroke volume, and cardiac output (CO) via chronically implanted catheters and an electromagnetic flow probe. We injected 15-mum radiolabeled microspheres (85Sr, 141Ce, and 51Cr) via a left atrial catheter during resting control, steady state (SS) and exhaustive (EE) exercise; measured their distribution by gamma spectrometry; and determined TRF as % CO and as ml/100 g per min. We determined IRFD for the outer and inner cortex and the outer medulla. TRF as %CO dropped (P less than 0.05) during both levels of exercise: from 10.2 +/- 0.7% to 3.9 +/- 0.4% (SS) and 3.4 +/- 0.6% (EE). TRF in ml/100 g per min did not change significantly from control (228 +/- 30 ml/100 g per min). IRFD was unchanged with exercise, remaining at about 80, 20, and 3% of TRF for the outer and inner cortex and outer medulla, respectively. We conclude that blood flow is not diverted from the kidneys during severe exercise in the dog.     

Cardiac output distribution and intrarenal haemodynamics: role of thromboxanes.

The effects of imidazole, an inhibitor of thromboxane synthesis, were studied on the distribution of cardiac output and on the intrarenal haemodynamics in anaesthetized, furthermore on the salt and water excretion in conscious rats. Imidazole treatment (10 mg/100 g b.m., intraperitoneally, twice a day for two days) failed to influence the arterial blood pressure, the cardiac output and its distribution in organs investigated (heart, muscle, lung [bronchial fraction], skin, liver, spleen, small intestine, adrenal gland and kidneys). The medullary blood flow increased, while cortical blood flow remained unchanged, but the intrarenal percentile blood flow shifted towards the medulla. Imidazole elevated the water turnover in the animals, but no change in sodium and potassium excretion occurred. It is supposed that thromboxanes may affect the renal medullary vascular tone without altering the vascular smooth muscle activity in other organs.     

Is the renin-angiotensin system involved in urinary concentration mechanisms?

Renin release elicited by i.v. injection of loop-diuretics was used to study the effects of angiotensin II (AII) on intrarenal hemodynamics. The vasoconstrictive action of intrarenally synthesized AII predominates in the efferent glomerular arteriole. Such a vasoconstrictive effect could affect blood flow in the vasa recta which stem from efferent arterioles of juxtamedullary glomeruli. Renin secretion and renal inner medullary blood flow (tissue clearance of 133Xe) were simultaneously measured before and after frusemide-induced renin release. The relationship between renin secretion and renal inner medullary blood flow was inverse. Changes in renal medullary blood flow may be physiological determinants of medullary osmolality and renal concentration ability. The intrarenal role of AII in urinary concentration recovery after frusemide was examined. Inhibition of renin release by propranolol or AII-blockade (by saralasin or Hoe 409) delayed recovery of urinary osmolality. In the conscious rat, propranolol slowed down recovery of the cortico-papillary gradient for sodium. Its vasoconstrictive action on the efferent glomerular arteriole might enable the renin-angiotensin system to participate in the control of renal excretion of salt and water.     

Angiotensin II receptors in the kidney

Angiotensin II (AngII) receptors have been localized in rat kidney by using the high-affinity agonist analog 125I-labeled [Sar1]AngII as a probe for in vitro autoradiography. Receptors were associated with four morphologically distinct patterns of distribution. First, a high density of receptors occurs in glomeruli. These are diffusely distributed, consistent with a mesangial localization. AngII receptor density shows a cortical gradient, which is highest in superficial and midcortical glomeruli and lowest in juxtamedullary glomeruli. Receptors associated with both superficial and deep glomeruli show down-regulation during low-sodium intake. Second, low levels of tubular AngII binding were seen in the outer cortex. Third, a very high density of AngII receptors occurs in longitudinal bands in the inner zone of the outer medulla in association with vasa recta bundles. Receptors in this site also show down-regulation during low dietary sodium intake. Fourth, a moderate density of receptors occurs diffusely throughout the inner zone of the outer medulla in the interbundle areas. These results suggest that AngII exerts a number of different intrarenal regulatory actions. In addition to the known vascular, glomerular, and proximal tubular effects of AngII, these findings focus attention on possible actions of AngII in the renal medulla where it could regulate medullary blood flow and thereby modify the function of the countercurrent concentrating system.     

Effects of substance P on intestinal circulation and oxygen consumption

The effects of intra-arterial administration of substance P upon intestinal blood flow, oxygen consumption, intestinal motor activity, and distribution of blood flow to the compartments of the gut wall were measured in anesthetized dogs. Blood flow to the segment of distal ileum was measured with an electromagnetic blood flow meter and A-VO2 was measured spectrophotometrically. Oxygen uptake was calculated as the product of A-VO2 and total blood flow. The clearance of 86Rb was measured to estimate the density of the perfused intestinal capillaries. Changes in blood flow distribution were estimated from the distribution of radiolabeled microspheres. Motor activity was monitored from changes in intraluminal pressure. Substance P induced a dose-related increase in intestinal blood flow, oxygen consumption, and intestinal motor activity. A significant increase in 86Rb clearance and increase in blood flow to the muscles was also observed. The results of these studies indicate that substance P relaxes intestinal arterioles and precapillary sphincters thereby inducing intestinal hyperemia and increased oxygen consumption. These changes, at least in part, might be due to the increased intestinal motility with enhanced metabolic demands of the muscularis for oxygen.     

Aortic blood flow subtraction: an alternative method for measuring total renal blood flow in conscious dogs

We have measured total renal blood flow (TRBF) as the difference between signals from ultrasound flow probes implanted around the aorta above and below the renal arteries. The repeatability of the method was investigated by repeated, continuous infusions of angiotensin II and endothelin-1 seven times over 8 wk in the same dog. Angiotensin II decreased TRBF (350 +/- 16 to 299 +/- 15 ml/min), an effect completely blocked by candesartan (TRBF 377 +/- 17 ml/min). Subsequent endothelin-1 infusion reduced TRBF to 268 +/- 20 ml/min. Bilateral carotid occlusion (8 sessions in 3 dogs) increased arterial blood pressure by 49% and decreased TRBF by 12%, providing an increase in renal vascular resistance of 69%. Dynamic analysis showed autoregulation of renal blood flow in the frequency range <0.06-0.07 Hz, with a peak in the transfer function at 0.03 Hz. It is concluded that continuous measurement of TRBF by aortic blood flow subtraction is a practical and reliable method that allows direct comparison of excretory function and renal blood flow from two kidneys. The method also allows direct comparison between TRBF and flow in the caudal aorta.     

Effects of cardiac oscillations and lung volume on acinar gas mixing during apnea

We evaluated the importance of cardiogenic gas mixing in the acini of 13 dogs during 2 min of apnea. 133Xe (1-2 mCi in 4 ml of saline) was injected into an alveolar region through an occluded pulmonary artery branch, and washout was measured by gamma scintillation scanning during continued occlusion or with blood flow reinstated. The monoexponential rate constant for Xe washout (XeW) was -0.4 +/- 0.08 (SE) min-1 at functional residual capacity (FRC) with no blood flow in the injected region. It decreased by more than half at lung volumes 500 ml above and 392 ml below FRC. With intact pulmonary blood flow, XeW was -1.0 +/- 0.08 (SE) min-1 at FRC, and it increased with decreasing lung volume. However, if calculated Xe uptake by the blood was subtracted from the XeW measured with blood flow intact, resulting values at FRC and at FRC + 500 ml were not different from XeW with no blood flow. Reasonable calculation of Xe blood uptake at 392 ml below FRC was not possible because airway closure, increased shunt, and other factors affect XeW. After death, no significant XeW could be measured, which suggests that XeW caused by molecular diffusion was small. We conclude that 1) the effect of heart motion on the lung parenchyma increases acinar gas mixing during apnea, 2) this effect diminishes above or below FRC, and 3) there is probably no direct effect of pulmonary vascular pulsatility on acinar gas mixing.     

Nitric oxide synthase inhibitor L-NAME has no effect on 86Rb accumulation in rat renal cortical slices

The aim of present study was to investigate the effect of the nitric oxide synthase inhibitor L-NAME on the 86Rb uptake in rat renal cortical slices. Rats were divided into three groups: 1. Control. 2. Acute: L-NAME (10 mg/kg i.v.) as a bolus 15 min before the excision of the kidneys. 3. Sub-chronic: L-NAME (10 mg/kg/day) per os for 4 days. Renal cortical slices were incubated for 10, 20, 30, 60, 90, 180 seconds in Krebs-Ringer solution containing 50 kBq 86Rb/100 ml (T = 37 degrees C, PO2 approximately 159 mm Hg). 56Rb accumulation (S/M) was calculated as the ratio of the radioactivity of the cortical slices (S) and the radioactivity of the incubating medium (M). The S/M ratio can be described as a function of time by the following equations. Control: y = 0.265 ln(x) - 0.220, r(xy) = 0.886; acute L-NAME: y = 0.224 ln(x) - 0.171, r(xy) = 0.921; sub-chronic L-NAME: y = 0.331 ln(x) - 0.496, r(xy) = 0.942. (y = S/M, x = t). p < 0.001 in all of the groups, but there is no difference between the groups. In conclusion, L-NAME administered in vivo failed to influence the in vitro 86Rb accumulation in rat renal cortical slices.     

Contribution of angiotensin to the control of medullary hemodynamics

The unique architecture and organization of medullary vasculature permit regional regulation of medullary hemodynamics by vasoactive hormones and are conducive to the operation of the countercurrent multiplication system. Recent studies suggest that an increase in inner medullary blood flow causes medullary solute washout, which in turn decreases passive sodium transport in the thin ascending limb of Henle's loop. In canine models of chronic sodium retention accompanied by activation of the renin-angiotensin system, glomerular filtration rate (GFR), renal blood flow (RBF), and intracortical blood flow distribution were similar to those in normal dogs; however, papillary plasma flow (PPF) was markedly reduced and papillary tissue solute content was increased significantly both during hydropenia and after saline loading. During euvolemic diuresis with loop diuretics, there was an increased renin release associated with a marked reduction in PPF, despite an increase in total RBF. Direct intrarenal infusion of angiotensin II (AngII) (at a dose not affecting GFR and RBF) induced ipsilateral sodium retention, conservation of urinary concentration, and papillary ischemia. These studies provide evidence for regional regulation of medullary hemodynamics by AngII, possibly contributing to sodium retention in chronic salt-retaining states.     

Role of prostaglandins in the cortical distribution of renal blood flow following reductions in renal perfusion pressure

The purpose of this study was to examine the role of prostaglandins in the redistribution of renal cortical blood flow that occurs following reductions in renal perfusion pressure. The distribution of blood flow to the renal cortex was examined using radio-labeled microspheres (15 +/- 1 micron). It was found that in animals not treated with a prostaglandin synthesis inhibitor a decrease in renal perfusion pressure to the limit of renal blood flow autoregulation was associated with a decrease in fractional flow to the outer cortex (Zone I) and an increase in fractional flow to the inner cortex (Zones III and IV). A further decrease in renal perfusion pressure below the limit of autoregulation produced a further decrease in the fractional flow to Zone I and a further increase in fractional flow to Zones III and IV. In contrast, in animals treated with the prostaglandin synthesis inhibitor meclofenamate (5 mg/kg, i.v. bolus) a reduction in renal perfusion pressure to the limit of renal blood flow autoregulation produced no change in fractional blood flow to any of the 4 cortical zones. A further decrease in renal perfusion pressure, however, did produce a fall in fractional blood flow to Zone I and an increase in fractional flow to Zones III and IV. In conclusion, the results of this study indicate that within, but not below, the limit of renal blood flow autoregulation prostaglandin synthesis is an important factor in the regulation of renal cortical blood flow distribution.     

Prostaglandin D2, another renal prostaglandin?

Prostaglandin (PG) D₂ was biosynthesized by rabbit renal papillae incubates in vitro. Quantification of the renal prostaglandins by gas chromatography-mass spectroscopy demonstrated that the concentration of PGD₂ generated by renal papillae was to the amount of PGE₂ or about 1 μg/g tissue/30 min. Infusion of the sodium salt of PGD₂ into the renal artery of the dog produced a dose related increase in renal blood flow and urine flow, free water clearance, sodium excretion and potassium excretion without changes in systemic hemodynamics. At low doses PGD₂ increased renal blood flow to all cortical zones. Higher concentrations of PGD₂ produced a shift in the intrarenal distribution of blood flow toward the juxtamedullary nephrons.     

Role of prostagalandins in the cortical distribution of renal blood flow following reductions in renal perfusion pressure

The purpose of this study was to examine the role of prostaglandins in the redistribution of renal cortical blood flow that occurs following reductions in renal perfusion pressure. The distribution of blood flow to the renal cortex was examined using radio-labeled microspheres (15 ± 1 μm). It was found that in animals not treated with a prostaglandin synthesis inhibition a decrease in renal perfusion pressure to the limit of renal blood flow autoregulation was associated with a decrease in fractional flow to the outer cortex (Zone I) and an increase in fractional flow to the inner cortex (Zones III and IV). A further decrease in renal perfusion pressure below the limit of autoregulation produced a further decrease in the fractional flow to Zone I and a further increase in fractional flow to Zones III and IV. In contrast, in animals treated with the prostaglandin synthesis inhibitor meclofenamate (5 mg/kg, i.v. bolus) a reduction in renal perfusion pressure to the limit of renal blood flow autoregulation produced no change in fractional blood flow to any of the 4 cortical zones. A further decrease in renal perfusion pressure, however, did produce a fall in fractional blood flow to Zone I and an increase in fractional flow to Zones III and IV. In conclusion, the results of this study indicate that within, but not below, the limit of renal blood flow autoregulation prostaglandin synthesis is an important factor in the regulation of renal cortical blood flow distribution.     

The role of alpha-adrenergic receptors in the vasoconstrictor response induced by indomethacin in the kidney.

The effect of indomethacin, an inhibitor of prostaglandin (PG) synthesis, was studied on the renal circulation, Na+ and water excretion in anaesthesized dogs during alpha-receptor inhibition. Indomethacin decreased cortical blood flow (CBFcontr, 454 +/- 142; CBFindo, 332 +/- 51 ml per min per 100 g; p less than 0.02) as well as medullary blood flow (OMBFcontr, 339 +/- 95; OMBFindo, 183 +/- 46 ml per min per 100 g; p less than 0.001), salt and water excretion, further it caused a shift in the intrarenal blood flow distribution toward the cortex. Alpha-blockade prevented the indomethacin-induced vasoconstriction in the cortex (CBF alpha inhibition + indo, 455 +/- 76 ml per min per 100 g) but not in the medullar (OMBF alpha inhibition + indo, 259 +/- 102 ml per min per 100 g, p less than 0.05). Alpha-blockade failed to prevent the indomethacin-induced antidiuresis, antinatriuresis and the intrarenal blood flow redistribution. GFR remained unaffected in all three series of studies. Our experimental findings are in line with the presumption that alpha-receptors are involved in the renal circulatory changes caused by indomethacin, probably as a result of an enhanced NE release during the inhibition of PG production. A NE--PG feed back mechanism is suggested in the regulation of renal circulation. The reduction of salt and water output induced by indomethacin appears to be independent of the alterations in renal haemodynamics, and seems rather to be the result of enhanced Na+ reabsorption, predominantly at the distal segment of the nephron, in the absence of PG, and/or a direct action of indomethacin.     

Effects of induced hypothermia on organ blood flow in a hibernator and a nonhibernator

Regional blood flow and hemodynamic variables during induced hypothermia were compared in six guinea pigs and four hedgehogs. Tracer microspheres were used for blood flow measurements, since this technique is more accurate than the earlier method (86Rb+ distribution) used for cardiac output distribution measurements in hibernators. Heart rate and blood pressure decreased with reduced temperature in a comparable fashion in the two species, while cardiac output was less affected in the hedgehogs than in the guinea pigs. Total peripheral resistance increased in both species. At 34 degrees C the hedgehogs had a higher myocardial blood flow per gram tissue than the guinea pigs and it was not reduced in the hedgehogs when the body temperature was lowered to 22 degrees C, whereas in the guinea pigs it was markedly reduced. The brown adipose tissue of the hedgehogs showed a fourfold increase in blood perfusion at 22 degrees C when compared with 34 degrees C. In the hedgehogs the fractional distribution of cardiac output to the myocardium increased with decreasing body temperature, while the renal fraction decreased. In the guinea pigs, on the other hand, the fractional distribution of cardiac output to the myocardium remained unchanged but increased to the kidneys.     

Neuropeptide Y reduces ovarian blood flow in the rabbit

Neuropeptide Y-containing nerve fibers have previously been demonstrated to innervate the mammalian ovary. These nerve fibers innervate primarily the vasculature. In this study we have developed a method for in vivo measurement of the ovary blood flow rate by means of the 133Xe method. Using this technique we measured the ovary blood flow rate and investigated the dose-response relationship between close intraarterial-injected NPY and the ovary blood flow rate. A monoexponential washout curve for 133Xe was found for the whole washout process, ensuring that the blood flow rate at any time could be calculated from the curve. We found a mean blood flow rate in the nonpregnant rabbit ovary at 43.6 +/- 4.4 ml.(100 g)-1.min-1 (mean +/- SEM). Injection of NPY (20, 200, 2000 pM) in the aorta close to a. ovarica resulted in a dose-dependent decrease in the ovarian blood flow rate with a maximum reduction to 40.7 +/- 6.3% (mean +/- SEM) of the control blood flow rate. These findings make it likely that receptors able to interact with NPY are present in the vasculature of the rabbit ovary.