Intrarenal Blood Oxygenation and Renal Function Measured by Magnetic Resonance Imaging During Long-Term Cyclosporine Treatment

Treatment with cyclosporine (CsA) markedly affects the renin-angiotensin-aldosterone system in parallel with an increase in the net tubular reabsorption or a decrease in secretion. Since tubular reabsorption is closely linked to medullary oxygen consumption, the aim of the present study was to investigate the intrarenal oxygenation and renal function in response to CsA. Six mini Göttingen pigs were treated with CsA (10 mg/kg/d) for 6 months. The intrarenal oxygenation was indirectly measured as R2* obtained with a multiecho gradient-echo magnetic resonance imaging (MRI) sequence. Single-kidney renal blood flow (skRBF) was measured by a velocity-sensitive gradient-echo MRI sequence. Relative single-kidney glomerular filtration rate (rskGFR) was derived from the MRI time-activity curve in response to an intravenous bolus of Gd-DTPA (0.05 mmol/kg). The present study showed that administration of CsA increased the medullary R2* (23.1 Hz vs 19.0 Hz, P = .002), whereas R2* was slightly increased in the renal cortex (13.3 Hz vs 12.3 Hz, P = .012). In parallel, rskGFR increased significantly (47.2 mL/min vs 19.8 mL/min, P = .005) but skRBF was unchanged (197.6 mL/min vs 202.5 mL/min, P > .05). The increased R2* in the renal medulla indicated that CsA augments the tubular reabsorption of water, leading to increased oxygen consumption. The supply of oxygen to the kidney was, however, maintained during treatment with CsA as suggested by an unchanged renal blood flow. The increased tubular reabsorption was compensated for by an elevated glomerular filtration rate.