RESUMO
PURPOSE: Recently, dietary supplementation with inorganic nitrate (NO3) has been proposed to endurance athletes to increase their performance. However, it has been suggested that an excess of NO3 might be harmful. The present study analyzed the effect of NO3 supplementation on kidney function. METHODS: Thirteen young male subjects performed a 20-min cycling exercise at 85% of the maximal oxygen capacity. Seven days before exercise, the subjects ingested either a placebo (Pl) or 450 mg of potassium nitrate (PN) per day. Venous blood samples and urine collections were collected before and immediately after exercise and after 60 min of recovery. Glomerular filtration rates (GFR) and clearances (Cl) were calculated from serum content and urine output for creatinine (Crn), albumin (Alb), and urea. RESULTS: Under resting conditions, GFR and all clearance measures did not differ between Pl and PN. Immediately after exercise, GFR remained stable in both Pl and PN, whereas Cl-urea decreased significantly (P < 0.05) in Pl (-44%) and PN (-49%). Alb urine outputs were enhanced by 18- to 20-fold in Pl and PN, respectively (P < 0.05). After the recovery period, GFR remained enhanced under Pl conditions, whereas Cl-urea returned to initial values in placebo and nitrate supplementation. Alb output and Cl-Alb remained enhanced under PN conditions. CONCLUSION: These results mainly indicate that dietary nitrate supplementation over a week does not induce any specific kidney function modifications either at rest or during sustained submaximal exercise as compared with Pl.
