Flow resistance of the interlobular artery in the rat kidney

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Abstract
The afferent and efferent arterioles are considered to be the most important resistance vessels within the renal vasculature, but there are indications that a pressure drop occurs along the interlobular artery. This pressure drop was investigated from 2 aspects. In rat kidneys the stop-flow pressure in the efferent arterioles was measured with the micropuncture technique. At arterial pressures between 100 and 130 mmHg the stop-flow pressure did not exceed 85 mmHg, which means that the highest pressure at the end of the interlobular artery was 85 mmHg. A mathematical model was constructed, assuming that the diameter of the interlobular artery decreased stepwise from 60-10 .mu.m. The artery was divided into 20 segments, each segment containing 1 afferent arteriole. The flow in the afferent arterioles increased linearly from 100 nl.cntdot.min-1 in the first segment to 130 nl.cntdot.min-1 in the last segment. When the pressure in the 1st segment was 120 mmHg, the pressure in the last segment was 85 mmHg. These findings strengthen the theory that the interlobular artery may participate in the regulation of the intracortical blood flow in the rat kidney. The afferent arteriole of the most superficial nephron is nearly maximally dilated and the juxtamedullary nephron is able to either dilate or constrict its arteriole in normotensive and normohydrated rats.