Endocrine Abstracts

Blood pressure homeostasis is regulated via renal sodium reabsorption by aldosterone and glucocorticoids, although the role of glucocorticoids is less clear. High-salt diets lead to suppression of aldosterone in plasma, but changes in available ligands for the mineralocorticoid and glucocorticoid receptors in kidney subregions are unknown. Hypothetically, high-salt intake modifies aldosterone and corticosterone amounts in specific kidney subregions. Kidney cryosections from male C57BL6/J mice (age=2 weeks, n=6) receiving different dietary salt (low=0.03% vs normal=0.3% vs high=3%), under Home office guidance, were subject to mass spectrometry imaging analysis following derivatisation with Girard T. Steroid derivatives were detected in renal sections as ions with m/z 474.2957 (Δppm=1.05), 460.3166 (Δppm=0.65) and 458.3010 (Δppm=0.65), in tissue sections, using matrix assisted laser desorption/ionisation (MALDI) coupled to Fourier Transform Ion cyclotron mass spectrometry. These represented aldosterone, corticosterone (active glucocorticoid) and 11-dehydrocorticosterone (inert glucocorticoid metabolite formed by 11β-hydroxysteroid dehydrogenase type 2) derivatives respectively. Steroids were quantified in plasma by liquid chromatography tandem mass spectrometry. Data are mean±SEM compared by one way ANOVA with Dunnett’s post-hoc test. * P<0.05 vs normal-salt. Plasma concentrations of corticosterone (228±58 vs 251±66 vs 312±45nM; low-, normal-, high-salt respectively) were unaffected by dietary salt. 11-Dehydrocorticosterone was lower with low-salt (0.94*±0.13 vs 2.31±0.55 vs 0.72*±0.14nM) and aldosterone lower with high-salt (0.91±0.21 vs 0.41±0.14 vs 0.01*±0.002nM). Within kidney tissue, under normal dietary conditions, corticosterone signal intensity was higher in inner cortex than the rest of the kidney. The highest levels of 11-dehydrocorticosterone were in the medulla. Aldosterone signal was similar in medulla and outer cortex. Corticosterone signal intensity increased in mice outer cortex on high-salt, while 11-dehydrocorticosterone and aldosterone were unaffected. The use of MSI highlights regions of the kidney susceptible to changes in mineralocorticoid and glucocorticoid signalling following changes in dietary salt.