Effect of the Diet on Urinary Excretion of Alpha-ketoglutarate

Acid Base Disorder

G protein-coupled receptor 99, 2-oxoglutarate receptor 1, alpha-ketoglutarate, urine, pH, acidosis, alkalosis, Healthy volunteers

* The G coupled-protein receptors 99 (GPR99) was discovered in 2002 by Wittenberg et al. and is involved as a metabolic receptor. It has been shown that the natural ligand of GPR99 is an intermediate in the Krebs cycle, alpha-ketoglutarate (aKG). Studies done on rats have shown that aKG is measurable in the blood, freely filtered by the glomerulus and highly reabsorbed in the proximal tubule in metabolic acidosis, while it is not reabsorbed in metabolic alkalosis. No absorption or secretion of aKG intervene between the end of the proximal tubule and the final urine. Thus, having a receptor aKG in the distal tubule creates a paracrine communication with the proximal tubule, informing about the acid-base status of the body and allows adjustment of the urinary excretion of acid or base. * The hypothesis is that GPR99 is aKG sensor in the distal tubules and allow to report the acid-base status (determined by the metabolic activity of the proximal tubule) of the body to the distal tubule. This can then adapt the urinary excretion of acid or base in the final urine. Acidifying the body by a high meat consumption associated with a test of acidification, the kidney should reduce its aKG excretion and the concentration of this metabolite should be even lower in the urine. And vice versa in the case of alkalizing the body through a vegetarian diet associated with an alkalizing test. * Twelve healthy omnivorous volunteers will be selected. First inclusion visit includes verification of inclusion/exclusion criteria and signed informed consent. Urine and plasma baseline measurements will be performed and volunteers will meet a dietician. This person will tell them concerning meat and vegetarian diet as well as how to have a diet with 6g of salt per day.Volunteers are then randomized in order to determine which diet they will start first.The first phase will last during 4 days. The diet is followed during 3 days, and a 24-hour urine collection will begin on the third day at 7: 00 am. The fourth day, volunteers will have an investigational's day at the investigation's center after completing their urine collection at home (7:00 am). During the day of investigation, volunteers will give their urine (8: 00 am, corresponding to the baseline urine), and then the meat arm will receive a tablet of 50meq of NH4Cl and the vegetarian arm will receive a tablet of 1g of NaHC03. Volunteers will stay in the investigation center for 6h. Each hour since 8:00am, a urine sample will be taken, and at 3 hours and 6 hours post-tablet, a blood sample will also be made.This investigational's day will be followed by one to two weeks of treatment washing out. After that, the second phase will begin and will as the first phase excepted that the diet will be inversed. 5 other healthy vegetarian or vegan volunteers are recruited. Inclusion visit is the same as omnivorous volunteers. Only investigational's day at the investigation's center will be performed (no diet, no urine collection).

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