Knut Aukland

In vivo measurements of local metabolic rate in the dog kidney. Effect of mersalyl, chlorothiazide, ethacrynic acid and furosemide.

The initial rate of temperature rise during arterial occlusion was measured with fine thermocouples placed in the kidney of anesthetized dogs for estimation of local metabolic rate. Experimental evaluation of the necessary assumptions indicated the method to be applicable in the cortex and outer medulla. Since renal metabolism seems mainly determined by tubular reabsorption of sodium, the method can be used to localize the natriuretic action of diuretics. Mersalyl reduced metabolic rate per unit tissue volume of the outer medulla to 65% of control without significant reduction in the cortex, indicating inhibition of sodium transport in the loops of Henle. Chlorothiazide lowered cortical metabolic rate to 76% of control, with no change in outer medulla, indicating an action in the convoluted tubules. Ethacrynic acid and furosemide acted mainly in the loops of Henle, as indicated by reduction of outer medullary metabolic rate to 21 and 32% of control values respectively. Cortical metabolic rate fell to 78 a...

Oxygen Cost of Sodium Reabsorption in Proximal and Distal Parts of the Nephron

The relationship between changes in tubular sodium reabsorption and changes in renal oxygen consumption (Na/O2) was determined in dogs made anemic, as the arteriovenous difference in oxygen saturation was more than doubled by antecedent bleeding. Tubular sodium reabsorption was reduced by 45 ± 3%, and oxygen consumption by 36 ± 4% after blocking distal sodium transport with ethacrynic acid and chlorothiazide. On the basis of these data it could be calculated that 34 ± 5 Eq Na+ were transported in the distal nephron per/mol O2 consumed. Similar Na/O2 ratios were obtained by reducing proximal sodium reabsorption by lowering glomerular filtration rate after blocking distal sodium reabsorption. During infusion of chlorothiazide and ethacrynic acid, oxygen consumption was not further decreased by reduction of net proximal sodium reabsorption with mannitol infusion. This observation supports the hypothesis that energy-dependent sodium reabsorption in the proximal tubules is not reduced during mannitol diuresis....

Renal Medullary Heat Clearance in the Dog

Renal medullary heat clearance was investigated in anesthetized dogs to evaluate countercurrent exchange of heat. Sudden changes in the temperature of renal arterial blood were induced by infusion of 3 to 7 ml/min of saline at room temperature. The resulting changes in medullary temperature, measured with fine thermocouples, started with increasing delay from cortex towards the papilla. Average rate constant for heat uptake in the inner medulla was 0.61 min−1. In the outer medulla, rate constants from 0.6 to 5.0 min−1 were observed, with the higher values in the subcortical zone. Inner medullary clearance rose during diuresis, but was practically uninfluenced by lowering perfusion pressure to 35 mm Hg. Calculated heat conduction (diffusion) from cortex into medulla was close to observed clearances, which are thus mainly determined by heat conduction. Clearance due to flow in vasa recta and loops of Henle was small, presumably due to efficient countercurrent heat exchange, whereas urine flow in collecting ducts is not subject to this effect. Formulas for countercurrent exchange not taking into account length diffusion (parallel to the vasa recta) are not valid for medullary heat exchange. The present heat clearance technique cannot be used for estimating medullary blood flow.

MEASUREMENT OF HUMAN UTERINE CERVICAL BLOOD FLOW BY LOCAL HYDROGEN GAS CLEARANCE

Present knowledge of local blood flow in the human myometrium is based on relatively few observations. Total uterine blood flow has been measured by electromagnetic flowmeter (Assali et al., 1960) and by NzO-technique (Assali et al., 1953; Metcalfe et al., 1955), but no information on local blood flow in the myometrium can be obtained by these methods. A relative measure of local myometrial blood flow may be obtained by heat conductivity (Prill, 1959) or local clearance of Na24 (McCall and Sopp, 1951), but neither method gives an absolute flow measurement. Theoretically, local clearance of Xenon133 injected into the myometrium can be interpreted in terms of absolute flow per gram of tissue, and measurements have been described both for isthmus and cervix in pregnant and non pregnant women (Munck et al., 1964; Lysgaard and LefBvre, 1965). This article presents data on local blood flow in the fibromuscular tissue of the cervix in humans measured by the hydrogen desaturation technique (Aukland et al., 1964). The criteria for acceptable measurements are discussed on the basis of studies on the reproducibility of subsequent measurements in a given area, and on comparison of simultaneous measurements in different areas of the cervix.

Countercurrent Exchange of Heat in the Dog Kidney

The mechanisms of renal heat clearance were studied in anesthetized dogs by recording renal venous and cortical temperatures during step changes of arterial blood temperature induced by infusion of 0.9% saline of room temperature into the renal artery. The venous thermodilution curves were well described by a three-exponential function with average rate constants: k1 = 10.4 min-1, k2 = 2.2 min-1, and k3 = 0.59 min-1, and intercepts at 34%, 44%, and 22%, respectively. The various components were interpreted as follows: The slow component mainly represents heat conduction from inner medullary and perirenal tissue as shown by extrarenal temperature recording and by calculating the heat distribution volume. Local cortical recordings showed that cortex is not a homogeneous compartment, and k2 reflects an average cortical heat clearance, k1 is much higher than blood flow per gram of tissue in any kidney region and results from heat exchange between intrarenal arteries and veins. The arteriovenous diffusion of heat explains the higher temperatures observed in the cortex and the renal medulla than in renal venous blood. The arteriovenous thermodilution technique is unsuited for local and total renal blood flow measurements, because of countercurrent diffusion and heat exchange witli perirenal tissue.