Background: Cortisol is known to increase blood pressure. One possible mechanism is the reported increase in renal vascular resistance (RVR). It is unknown whether this is due to a direct effect of cortisol on the kidneys.
Objective: To study the effect of infusion of cortisol directly into the renal artery on renal blood flow (RBF) and on renal 11beta-hydroxysteroid dehydrogenase (11beta-HSD)-mediated conversion of cortisol to cortisone in patients with primary hypertension.
Design and methods: Twenty-seven patients with primary hypertension participated in this study. Fifteen received placebo and 12 received glycyrrhetinic acid (GRA; 500 mg) orally 2.5 h before the study. After a 10 min infusion of 5% glucose, cortisol was infused in stepwise increasing doses (0.625, 1.25 and 2.5 microg/kg per min), for 10 min each dose. At the end of each infusion step, RBF was measured using the xenon-133 washout technique. Plasma samples from the femoral artery and renal vein were taken for measurement of cortisol and cortisone. Urine was collected for measurement of steroid concentrations for 6 h on the day before the infusion and for 6 h after the infusion.
Results: After placebo or GRA, cortisol infusion did not change RVR, RBF or blood pressure. RVR values were 0.72 (0.45-0.89) mmHg/ml per min per 100 ml tissue [median (first and third quartiles)] and 0.71 (0.64-0.91) mmHg/ml per min per 100 ml tissue during infusion of 5% glucose and infusion of the highest dose of cortisol, respectively ( P= NS). Cortisol infusion increased the venous-arterial difference in plasma cortisone concentration across the kidney from 76 (40-115) nmol/l to 138 (100-186) nmol/l (P< 0.05) and increased the cortisol : cortisone ratios in the renal vein and in urine (both P< 0.05). As compared with placebo, administration of GRA increased the cortisol : cortisone ratios in peripheral and renal veins and in the urine.
Conclusion: Acute infusion of cortisol in high doses directly into the renal artery in patients with primary hypertension did not affect RBF or RVR. Infusion of cortisol resulted in increased cortisol-cortisone conversion by renal 11beta-HSD2, but the concurrent increase in renal and urinary cortisol : cortisone ratio suggests a relative insufficiency of renal 11beta-HSD2 activity as a result of enzyme saturation. This may enhance mineralocorticoid receptor stimulation by cortisol.