Gender Differences in Renal Functioning and Disease

Chronic kidney disease (CKD) affects about 10% of the adult population in Switzerland. Despite decades of research, the mechanisms involved in the development and progression of CKD remain unclear, and there is a lack of preventative therapies. Women are relatively protected against CKD, but this topic has been little studied. The kidney is very sensitive to hypoxia and its chronic oxygen depravation is the final step in the pathogenesis of CKD. A special MRI application, called BOLD-MRI, has the ability to measure renal tissue oxygenation in humans. In a recent BOLD-MRI study, the investigators demonstrated that cortical oxygenation is significantly higher in women than in men, which may explain women's lower susceptibility to declining renal function. However, whether this is true under different dietary conditions (high salt-low salt), and whether renal oxygenation changes throughout the menstrual cycle is unknown and will be assessed in this study. Renal oxygenation depends on its perfusion. Renal micro-perfusion can be measured with contrast-enhanced ultrasound (CEUS) and is expressed as PI (perfusion index). CEUS is a recent imaging technique that combines conventional ultrasound with the administration of a microbubble contrast agent (a lipid or albumin-enveloped gas compound). The microbubbles are inert and eliminated by pulmonary and hepatic systems within one hour of administration. They are not nephrotoxic and have no major side effects. Whether there are differences in renal perfusion as measured with CEUS between men and women with and without CKD will be also assessed in this study. Oxygenation of the kidneys does not only depend on their perfusion, but also on their consumption, mainly related to tubular active sodium transport. Thus, their oxygenation is lower in the case of a high salt diet compared to a low salt diet. This has been proven in men, but not in women. Recently, another MRI technique called 23Na MRI was used to measure the amount of salt stored in the skin and muscles. It is possible that the cutaneous and muscular capacity of storing salt according to dietary salt intake is lower in men, but this has not, at present, been examined.