Intrarenal blood flow distribution during adenosine-mediated vasoconstriction

Intrarenal infusion of adenosine induces an initial vasoconstriction followed by a subsequent vasodilation. The intrarenal distribution of blood flow in the vasoconstriction phase is unknown. The present study was undertaken to assess the effect of intrarenal infusion of adenosine on intracortical distribution of renal blood flow during both the vasoconstriction and vasodilation phases. Renal blood flow distribution was measured with radiolabeled microspheres in anesthetized sodium-depleted dogs before and during the early vasoconstriction phase and the late vasodilation phase of intrarenal infusion of adenosine. During the vasoconstriction phase, there was a uniform decrease in blood flow in each renal cortical zone. In the late phase of adenosine infusion, there was a significant increase in deep cortical flow without significant changes in superficial cortical flow compared with control. The effects of adenosine were also compared with those exerted by norepinephrine in which decreased blood flow was demonstrated in all zones. We conclude that the vasoconstrictor phase of adenosine infusion is characterized by a uniform reduction of renal blood flow to all cortical zones, whereas the vasodilator phase is characterized by a selective deep cortical vasodilation.

Left ventricular cannulation for microsphere estimation of rabbit renal blood flow

When cannulation of the left ventricle and the left atrium were compared as methods for measuring for measuring renal blood flow distribution with radioactive microspheres in 9 conscious and 6 anesthetized rabbits, there were no differences between the two injection routes. Left ventricular cannulation per se did not affect cardiac output, nor the percentage of the cardiac output supplying the kidneys; but cardiac outputs estimated by thermodilution by injections via this route were up to 10% greater than those from left atrial injection. The advantages of left ventricular cannulation for experiments on regional blood flow distribution in conscious animals are discussed.

Renal blood flow distribution measured by microspheres during isovolemic hematocrit alteration in rats

The distribution of 15-μm microspheres was measured in rat kidneys before and after the animals had undergone either isovolemic hematocrit increase or isovolemic hematocrit decrease. Raising the systemic arterial hematocrit from 46 ± 1% (mean ± SEM) to 59 ± 1% caused a significant decrease in the rates of urinary sodium and potassium excretion [Formula: see text], but no significant changes in total renal blood flow (RBF), filtration fraction (FF), outer cortical flow, inner cortical flow, or rate of urinary volume excretion [Formula: see text]. Fractional sodium excretion was also unchanged suggesting that the decreased [Formula: see text] was the result of a decreased glomerular filtration rate (GFR). The measured decrease in GFR was not statistically significant. Lowering the systemic hematocrit from 45 ± 1% to 33 ± 1% caused a significant fall in FF as well as significant increases in the rate of urine volume excretion [Formula: see text], [Formula: see text], and GFR. There was a significant increase in RBF but again no change in the flow distribution between inner and outer cortex. The findings show that hematocrit alterations alone do not immediately lead to a redistribution of blood flow between inner and outer cortex of the rat kidney.