Increase of tubular secretion of creatinine by L-arginine: A mechanism of practical importance in the evaluation of renal function by means of creatinine clearance

Background. Tubular secretion of creatinine is increased by meat meals. Thi s increment has been attributed to the formation of new creatinine from cre atine contained in the cooked meals. However, no studies are available usin g amino acid infusions containing no creatine, which allow to further inves tigate the putative causes of increment in tubular creatinine secretion. Methods. We performed a prospective, interventional study involving 34 indi viduals with normal renal function participating in a protocol on arterial hypertension. A continuous infusion of L-arginine (6%, iv, in four 30 min p eriods at 50 100, 200 and 300 ml/h) was administered. Creatinine (CCr) and inulin (Cln) clearances were determined at baseline and during L-arginine i nfusion. We analyzed the effects of L-arginine on tubular secretion by comp aring CCr and Cln and calculated tubular secretion of creatinine (TSCr). Results. L-arginine infusion induced a significant increase in both CCr and Gin. CCr and Cln were respectively 117.9 +/- 22.7 and 107.5 +/- 23, before and 170.3 +/- 23 and 144.2 +/- 47.8 after the infusion of L-arginine (both p < 0.01). This increase was simultaneous with an increment in TSCr from 1 .12 +/- 0.4 to 1.43 +/- 0.6 (p < 0.01). CCr correlated significantly with C ln at baseline and at 60 min of infusion (r = 0.365, p = 0.031 and r = 0.36 8, p 0.038 respectively), but not at 120 min (r = 0.130 p = 0.412), a time corresponding to the maximum increase in Cln and TSCr. Conclusions. L-arginine induces a substantial increase of CCr, which exceed s that expected from the increase in glomerular filtration rate measured by Cln and corresponds to an increment in TSCr. This phenomenon adds a new in terpretation of the effect of amino acids on tubular handling of creatinine and has practical implications in the evaluation of renal function by mean s of creatinine clearance.