Sample processing and analyses
All blood samples were centrifuged at 1500 g for 5 min at 4 °C. The plasma was separated and stored at −80 °C for later determination of concentrations of the amino acids, L-citrulline (μmol/L) and L-arginine (μmol/L). All amino acid analyses were performed by ARUP Laboratories (Salt Lake City, UT) via Liquid Chromatograph-Tandem Mass Spectrometry (LC-MS/MS) using the Sciex aTRAQEach urine sample was aliquoted into two separate tubes (minimum 0.5 ml urine per tube), then stored at −80 °C. One of the aliquoted urine samples was used to determine urine creatinine (Cr). Urine Cr analysis was performed by either ARUP Laboratories (Salt Lake City, UT) or the Central Laboratory at the University of Utah Health Hospital (Salt Lake City, UT).The second aliquoted urine sample was used to determine urine nitric oxide metabolites, nitrites/nitrates (NOx). For urine NOx analysis, using methods as previously described [