Activated whole-body arginine pathway in high-active mice

Abstract

Our previous studies suggest that physical activity (PA) levels are potentially regulated by endogenous metabolic mechanisms such as the vasodilatory roles of nitric oxide (NO) production via the precursor arginine (ARG) and ARG-related pathways. We assessed ARG metabolism and its precursors [citrulline (CIT), glutamine (GLN), glutamate (GLU), ornithine (ORN), and phenylalanine (PHE)] by measuring plasma concentration, whole-body production (WBP), de novo ARG and NO production, and clearance rates in previously classified low-active (LA) or high-active (HA) mice. We assessed LA (n = 23) and HA (n = 20) male mice by administering a stable isotope tracer pulse via jugular catheterization. We measured plasma enrichments via liquid chromatography tandem mass spectrometry (LC-MS/MS) and body compostion by echo-MRI. WBP, clearance rates, and de novo ARG and NO were calculated. Compared to LA mice, HA mice had lower plasma concentrations of GLU (71.1%; 36.8 ± 2.9 vs. 17.5 ± 1.7μM; p<0.0001), CIT (21%; 57.3 ± 2.3 vs. 46.4 ± 1.5μM; p = 0.0003), and ORN (40.1%; 55.4 ± 7.3 vs. 36.9 ± 2.6μM; p = 0.0241), but no differences for GLN, PHE, and ARG. However, HA mice had higher estimated NO production ratio (0.64 ± 0.08; p = 0.0197), higher WBP for CIT (21.8%, 8.6 ± 0.2 vs. 10.7 ± 0.3 nmol/g-lbm/min; p<0.0001), ARG (21.4%, 35.0 ± 0.6 vs. 43.4 ± 0.7 nmol/g-lbm/min; p<0.0001), PHE (7.6%, 23.8 ± 0.5 vs. 25.6 ± 0.5 nmol/g-lbm/min; p<0.0100), and lower GLU (78.5%; 9.4 ± 1.1 vs. 4.1 ± 1.6 nmol/g lbm/min; p = 0.0161). We observed no significant differences in WBP for GLN, ORN, PHE, or de novo ARG. We concluded that HA mice have an activated whole-body ARG pathway, which may be associated with regulating PA levels via increased NO production.

Protein fractional synthesis rates within tissues of high- and low-active mice

“…The mice used in this experiment were administered a pulse of stable isotope tracers an hour before tissue collection for analysis of amino acid whole body production and clearance as reported [ 17 ] and the mice underwent surgery with anesthesia. The anesthesia and surgical procedure would not make a large impact on the protein FSR as the incorporation of tracer from D 2 O has taken place over 24 hours.…”

“…Tissue collection and processing. Blood samples (0.05-0.1 ml per sample) were collected on two sampling time schedules (schedule 1: t = 3 and 30 minutes; schedule 2: t = 5 and 40 minutes) as previously described [17]. Blood samples were replaced with an equal volume of sterile normal saline.…”

“…al. [ 17 ]. Due to the additional measurements, surgery was necessary and blood samples were taken along the timeline of the greater study.…”

“…Plasma samples were chemically derivatized before liquid chromatography-tandem mass spectrometry (LC-MS/MS) by a modification for small plasma volumes of a method previously described [ 17 , 19 ]. In brief, deproteinized plasma supernatant was reacted at room temperature for 15 min in a mixture of 3 vol of 1 M sodium phosphate, pH 10, and 6 vol of a 5% (w/v) solution in acetonitrile of 9-fluorenylmethoxycarbonyl (Fmoc) chloride (Sigma Aldrich, St. Louis MO, USA).…”