The effect of furosemide on the intrarenal blood flow distribution in the dog

Furosemide (40 μg/min) was perfused directly into the renal artery of dogs in whom the femoral blood pressure was reduced (80 mm Hg) by aortic clamping above the renal arteries. This maneuver, which does not influence the intrarenal blood flow distribution, produced significant decreases of the urine volume, natriuresis, Ccreat, and CPAH, and prevented the marked diuresis normally produced by furosemide. Therefore the chances that systemic physiological changes occurred, secondary to large fluid movements, were minimized. In those conditions, however, furosemide produced a significant increase of the urine output and sodium excretion in the experimental kidney whereas Ccreat and CPAH were not affected. The outer cortical blood flow rate (ml/100 g-min) was modified neither by aortic constriction (562 ± 68 versus 569 ± 83) nor by the subsequent administration of furosemide (424 ± 70). The blood flow rate of the outer medulla in these three conditions remained unchanged (147 ± 52 versus 171 ± 44 versus 159 ± 54). The initial distribution of the radioactivity in each compartment remained comparable in the three conditions. In parallel with the results from the krypton-85 disappearance curves, the autoradiograms, silicone rubber casts, and EPAH did not suggest any change in the renal blood flow distribution secondary to furosemide administration.

A comparison of the disappearance curves of 133X3 and 85Kr for the measurement of the intrarenal distribution of blood flow

Krypton-85 and xenon-133 disappearance curves which are used to measure the intrarenal distribution of blood flow have been compared in two groups of animals under normal conditions. The blood flow rates (ml/100 g per min), percentage of initial radioactivity, and regional blood flow (ml/100 g kidney tissue) of the cortex calculated from the krypton-85 decay curves were found to be more elevated than those obtained from the xenon-133 curves. The same conclusions can be drawn from the results obtained for the outer medulla with the exception that the percentage of initial radioactivity was not different when calculated with either method. Among other considerations, the fact that the tissue to blood partition coefficient of krypton is not influenced by the hematocrit and that this radioisotope may be used for the preparation of the autoradiograms leads to the conclusion that it is preferable to use krypton-85 rather than xenon-133 for the measurement of intrarenal distribution of blood flow in animal experimentation.

Effect of retransfusion after hemorrhagic hypotension on intrarenal distribution of blood flow in dogs

Hemorrhagic hypotension in anesthetized dogs produces a marked decrease of the cortical blood flow, whereas the medullary blood flow is well preserved. These animals were maintained at blood pressures of 50 mm Hg during a 3 hr period after which their blood pressures were restored by the reinfusion of blood or dextran, or both. In the first group of animals, the reinfusion of blood reestablished the blood pressure to control values, but the cortical blood flow was still nonuniformly decreased whereas the medullary blood flow appeared to be increased. In the second group of animals, phenoxybenzamine failed to protect the kidney completely since after blood reinfusion, the same anomalies described for the preceding group were found in 7 out of 10 dogs. The animals of the third group were reinfused with 50% of the shed blood and 10 ml/kg of a 10 g/100 ml solution of low molecular weight dextran. The modifications of the intrarenal distribution of the blood flow were less marked in this group although the blood flow rate of the inner cortex and the outer medulla was always elevated under these conditions. The reinfusion of low molecular weight dextran alone (20 ml/kg of a 10 g/100 ml solution) restored the blood pressure to levels slightly lower than those observed under control conditions but reestablished a normal pattern of intrarenal blood flow. The reinfusion of high molecular weight dextran was inefficient in correcting completely the anomalies of the renal blood flow. Mechanisms such as the increased sympathetic tone, the liberation of angiotensin, and the intravascular cellular aggregation could possibly account for the persisting anomalies of the renal circulation after reinfusion and are discussed.

Effect of norepinephrine, isoproterenol, and adrenergic blockers upon the intrarenal distribution of blood flow

The effect of intrarenal administration of norepinephrine, isoproterenol, and adrenergic blockers upon the intrarenal distribution of blood flow has been studied with the 85Kr method. Norepinephrine produces marked vasoconstriction of the outer cortex while it increases the medullary blood flow rate. Isoproterenol had no effect of its own and antagonized the norepinephrine effect. Phenoxybenzamine produced no particular effect and prevented the hemodynamic modifications produced by norepinephrine. Phenoxybenzamine also unmasked the cortical vasodilating effect of isoproterenol. Propranolol was found to have an adrenergic-like effect on the cortical and medullary circulations which was inhibited by phenoxybenzamine. It is concluded that the cortical circulation is very reactive to vasoactive stimuli whereas the outer medulla seems to present a rather passive vascular bed.