Localisation of corticosteroids in male mouse kidney by mass spectrometry imaging

Renal sodium balance is important for blood pressure homeostasis and is regulated by corticosteroids, chiefly aldosterone but also glucocorticoids. Abundance of these hormones in functional subregions of the kidney is unknown, previous work being limited to measurements in plasma and urine, and in microdialysate from kidney medulla. Here mass spectrometry imaging (MSI) was applied to map corticosteroids in kidney to understand how their distribution overlays with functional targets. Male C57BL6 mice, aged 10 weeks, were fed diets containing 0.03%, 0.3% or 3% w:w sodium for two weeks and kidneys harvested at cull. Steroids were localised as Girard T derivatives on cryosections using Matrix assisted laser desorption ionisation Fourier transform ion cyclotron MSI, with confirmation by liquid extraction surface analysis. Co-registration was performed on sections stained with hematoxylin and eosin. Corticosterone localised along the papilla, medulla and inner cortex, whereas 11-dehydrocorticosterone was concentrated in the medulla. Higher amounts of aldosterone were present in medulla and outer cortex. Distribution patterns were unchanged by dietary salt, but amounts of corticosterone were elevated, particularly in outer cortex with low salt diet. MSI holds great promise to dissect corticosteroid signalling in functional zones of the kidney.