Sex differences in control of renal outer medullary circulation in rats: role of prostaglandins.

A calibration technique was developed to quantify blood flow changes in the renal cortex and outer medulla in rats using platinum needle electrodes sensing partial pressure of locally generated hydrogen. Measurements were made in male and female rats to investigate sex differences in the humoral control and autoregulation of regional renal circulations. In males, both cortical and outer medullary blood flows were efficiently auto-regulated above an arterial pressure of 100 mmHg. The converting-enzyme inhibitor quinapril increased blood flow by 20% in both kidney zones, and inhibition of prostaglandin synthesis by indomethacin did not change the flow. In females, similar results were obtained only for the cortex; the medulla had a different response pattern. The blood flow was not autoregulated in the experimental pressure range up to 120 mmHg; quinapril did not change the flow, but indomethacin decreased the flow by 16% and at the same time restored its autoregulation capacity. We conclude that: 1) the medulla of female rats has a high basal level of vasodilator prostaglandins, which interferes with blood flow autoregulation in this kidney area, and 2) medullary flow in female rats is little affected by endogenous angiotensin.