Flow resistance of the interlobular artery in the rat kidney

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 two aspects: 1) 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; 2) A mathematical model was constructed, assuming that the diameter of the interlobular artery decreased stepwise from 60 to 10 micrometers. The artery was divided into 20 segments, each segment containing one afferent arteriole. The flow in the afferent arterioles increased linearly from 100 nl . min-1 in the first segment to 130 nl . min-1 in the last segment. When the pressure in the first segment was 120 mmHg, it was calculated that 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. We conclude that the afferent arteriole of the most superficial nephron is nearly maximally dilated and that the juxtamedullary nephron is able to either dilate or constrict its arteriole in normotensive and normohydrated rats.