Uridine

The study was carried out on four experimental groups of animals (adult male Wistar rats weighing 220–250 g): 1st group (control) – non-treated rats; 2nd group (hypoxia) – rats exposed to 30 min acute hypoxic hypoxia (7% O₂); 3rd group (uridine + hypoxia) – rats injected i/v 30 min prior to hypoxic exposure with uridine (AppliChem, Germany) from which the mitoK_ATP activator uridine-5′-diphosphate (UDP) was formed in the tissue at a dose of 0.3 mg/100 g of body weight as described earlier^{14 (link)}; 4th group (uridine + 5-HD + hypoxia) – rats injected i/v 10 min after the administration of uridine (i.e., 20 min before hypoxia) with the selective inhibitor of mitoK_ATP 5-hydroxydecanoate (5-HD, Schering AG, USA) at a dose of 0.05 mg/100 g of body weight as described earlier^{14 (link)}. There were six rats in each group.
The study with laboratory animals was carried out in accordance with the European Convention for the Protection of Vertebrates used for experimental and other purposes (Strasbourg, 1986) and the principles of the Helsinki Declaration (2000). All the protocols were approved by the Institute of Theoretical and Experimental Biophysics Ethics Committee (Order No. 173/k of 03.10.2011, Protocol No. 02 of 01.03.2018).

All chromatographic analyses were performed using the Shimadzu Nexera UHPLC system (Kioto, Japan). This chromatograph is equipped with a binary solvent delivery system (LC-30AD), an autosampler with a 20 µL volume loop (SIL-20AC), a column thermostat (CTO20AC), and a diode-array UC-detector (SPD-M20A). LabSolution LC/GC 5.65 software (Shimadzu, Kioto, Japan) was used to collect and process data and control the apparatus. Acetonitrile (ACN) (HPLC Grade) and methanol (MeOH) (HPLC Grade) were purchased from Sigma–Aldrich (Steinheim, Germany). Packaging solvents, isopropanol, and methanol were purchased from J.T. Baker, Deventer, the Netherlands. Water was prepared with a Milli-Q Water Purification System (Millipore Corporation, Bedford, MA, USA). Standards of nucleosides—adenosine, guanosine, uridine—were obtained from Applichem (Darmstadt, Germany). Non-polar compounds—naphthalene, benzene, phenanthrene, caffeine, theophylline, and theobromine—were obtained from Sigma–Aldrich (St. Louis, MO, USA). For the synthesis of stationary phases (3-glycidoxypropyl) trimethoxysilane, decanol, octadecanol, cholesterol, benzyl alcohol, and phosphorus chloride were used, which were purchased from Alfa Aesar (Karlsruhe, Germany). Haskel (Burbank, CA, USA) laboratory equipment and packing pump were used to pack the stationary phases into 125 × 4.6 mm long empty columns.