003 1-3998{90/2805-0477$02 .00{0 PEDIATRIC RESEARCH Vol. 28, No.5, 1990 Copyright © 1990 International Pediatric Research Foundation, Inc. Printed in U.S. A. Hypoxanthine, Xanthine, and Uric Acid Concentrations in the Cerebrospinal Fluid, Plasma, and Urine of Hypoxemic Pigs JAN PETER POULSEN, STEPHAN IE 0YASJETER, JON SANDERUD, TORLEIV OLE ROGNUM, AND OLA DIDRI K SAUGSTAD Institutefor S urgical Research (J.P.P.. 1.S;. Institute fo r Pediatric Research [S.llJ.. O.D.S;. Institute ofForensic M edicine [T.O.R.;. and Department 0/Pediatrics [O.D.S},University a/Oslo. The National Hospital. N-0027 Oslo 1, Norway ABSTRACf. Th e concentrations of hypoxanthine, xan­ uate hypoxia , but to correlate a biochemically measured value thin e, and uric acid in plasma and cerebrospinal fluid with the outco me of hypoxia is difficult . Measurements of the (CSF), as well as the urinary output of hypoxanthine and purine metabolite hypoxanthine can be used as an indicator of xanthine, were measured in four groups of pigs (three hypoxia (I). Du ring tissue hypoxia, elevated hypoxanthine levels group s with differ ent degrees of hypoxemia and one control have been found in plasm a (2- 5), CSF (6, 7), and urine (8). group). During hypoxemia with arterial O, tension between However, no clear definition of clinical hypoxia is available, and 2.1 and 3.0 kPa [group 1, fractional inspired oxygen (FiOz) ma ny autho rs do not distinguish between the terms hypoxemia =0.081, hypoxanthine increased in CS F from a mean basal and hypoxia, which adds to the confusion. Our meaning of value of 18.1 to 39.3 umol /L at death ( p < 0.02 ), in plasma hypoxia has previously been described (I). In our study the pigs from 25.4 to 103.6 J.Lmol/L (p < 0.05 ), and in urine from were subjected to hypoxemia. We define hypoxe mia as deficient 21.3 to 87.1 nmol/kg/min (p < 0.02). Xanthine changed in oxygenation of the blood. Hypoxem ia may, however, not nec­ a similar way: in CSF from 4.0 to 10.6 umol /L (p < 0.02), essarily lead to tissue hypoxia. in plasma from 0.7 to 48.1 J.Lmol/L (p < 0.02), and in urine To further assess the usefulness of hypoxanthine as a biochem­ from 4.0 to 12.6 nmol/kg/min (p < 0.05). Uric acid in­ ical marker of hypoxia, we report how three degrees of hypox­ crea sed in CSF from 2.7 to 11.6 J.Lmol/L (p < 0.05), and emi a in young pigs influence the level ofhypoxanthine, xanthine, in plasma from 15.4 to 125.0 J.Lmol/L ( p < 0.02). During and uric acid in the CSF and plasma , as well as the pigs' urinary hypoxemia with arterial O 2 tension between 3.0 and 4.0 excretion of hypoxanthine and xanthine. kPa (group 2, Fi0 2 = 0.11), hypoxanthine increased in the CSF from 14.7 to 42.9 /-Lmol/L ( p < 0.02). Plasma hypo­ xanthine increased from 20.3 to a maximum of 44.1 J.Lmol/ MATER IALS AND METHODS L (p < 0.02), but decreased to initial values by the time of death. The urinary excretion of hypoxanthine increased Approval. The local hospital's ethical committee for animal from 13 to 54 nmol/kg /min (p < 0.02). Xanthine increased studies approved these experim ents. in the CS F from 3.9 to 13.3 J.L mol/L (p < 0.02), in plasma Animal model. The animal model was similar to that previ­ from 0.6 to 36.6 J.Lmol/L (p < 0.02 ), and in urine from 6 to ously described (9). Twent y-two young pigs of either sex (the 25 nmol/kg/min ( p < 0.02). Uric acid increa sed in CSF males had been castrated shortly after birth ) weighing 17-22 kg from 3.1 to 16.3 J.Lmol/L (p < 0.02), and in plasma from (mea n 18.1 kg) were used. They were anesthetized with an 15.3 to 208 J.Lmol/L (p < 0.02). During milder hypoxemia intraperitoneal injection of sodium pentobarbital (30 mg/kg). with arterial O. tension between 4.3 and 5.6 kPa (group 3, An i.v. line was established through an ear vein, and a contin uous Fi02 =0.14), or in the control group (group 4, Fi02 = infusion of Ringer acetate (10 mL/kg/h) was given during the 0.21), neither of the metabolites changed significantly. experiment. A further 100 mg of sodium pentobar bital was given (Pediatr Res 28: 477-481, 1990) i.v, if necessary every 30 min. A cuffed tube was placed in the trachea via a tracheostom y. Artificial ventilation was given by a Abbreviations ventilator (Servo-ventilator 900B, Elema-Schenander, Stoc k­ holm, Sweden). Ventilation rate and tidal volume were adjusted CSF, cerebrospinal fluid until Paco, ranged between 4 and 5.3 kPa (30-40 mm Hg). No FiO z, fractional inspired oxygen further adjustme nts of the ventilato r .were done du ring the hy­ Pao-, arterial O 2 tension poxemic period. Paco-, arterial CO 2 tension A midline suprapubic laparotomy was performed and a uri­ nary catheter was placed in the bladder for measuring diuresis and urinary hypoxanthine and xanthine. Hypoxia is a common insult during the perinatal and neonatal Polyethylene catheters were inserted into a femoral artery and period. Several biochemical measurements can be done to eval- a femoral vein. The arterial catheter was used for taking blood samples and for measuring blood pressure continuously with a Received Janu ary 15. 1990: accepted June 5, 1990. strai n gauge tra nsducer, Go uld recorde r 2600S (Gould Inc. Re­ Correspondence and reprint requests: Dr. Jan Peter Poulsen, Institute for Sur­ cording Systems, Cleveland, OH). Th e venous catheter was used gical Research, University of Oslo, The Nationa l Hospital, N-0027 Oslo 1, Norway. for giving Ringer acetate plus additional sodium pentobarbital. Supported by the Norwegian Wom en's Public Health Association, the Norwe­ Th e pigs were divided into three hypoxemic and one contro l gian Research Coun cil for Science and the Humanities, The Lrerdal Foundation for Acute Medicine. and Odd Fellow Medical Research Foundation. J.P.P. is a group. Seven animals were made hypoxemic by art ificial venti­ Research Fellow with The Norwegian Cancer Society. lation with 8% oxygen in nitrogen (FiOz = 0.08) (group 1). Seven 477 478 POULSEN ET AL. animals were ventilated with II % oxygen (Fi0 2 = 0.11) (group were checked by coelution with known pure standards. This was 2). Five animals were ventilated with 14% oxygen (Fi02 = 0.14) especi ally necess ary at low xanthine con centrations. (group 3), and three anima ls were ventilated with room air (Fi02 Quantificati on of peaks was done by peak height ratios. All = 0.2 1), servi ng as norm oxemic contro ls (group 4). The oxygen pure stan dards used for the HPLC were obtain ed from Sigm a conce ntratio ns were measured continuo usly in all pigs during Chemical Co., St. Lou is, MO. th e experime nts with a Dameca OM 83 1 oxygen m onitor (Da­ Uric acid was measured on an RA-I OOO(Tec hnicon In stru­ meca Inc., Copen hagen, Denmark). ments, Tarrytown , N Y), auto ma tic blood analyzer. During hyp oxemia with Fi02 = 0.08, the Pao, remained Statistics. Results are given as mean ± SO. Wilcoxon's two­ between 2.1 and 3.0 kPa (15. 8-22.5 m m Hg). This degree of tailed rank test was applied for testing th e significance of differ­ hypoxemia lasted until the animals died after a mean of 170 min ences between comparable groups. A p value <0.05 was consid­ (range 120-240 min). During hypoxemia with Fi02 = 0.11, the ered statistically significant. Pao, rem ain ed between 3.0 an d 4.0 kPa (22.5-30 mm Hg), and these pigs died after a mean of 283 min (ra nge 165-445 min ). RESULTS During the mildest hypoxemia (Fi0 2 = 0. 14), the Pa02 remained between 4.3 and 5.6 kPa (32.5-42 mm Hg). All anima ls tolerated Blood gases and mean arterial pressure. Tab le I shows th e th is degree of hypoxem ia for 480 m in, after which th ey were arterial Pao-, O2 sat uratio n, and mean arterial blood pressure in killed with an i.v. overdose of sodium pentobarbital. The pigs in the four groups of pigs. There were no differen ces between the the control group were observed from 185 to 480 m in and then groups before th e start of hypoxemia. In the animals with the killed. During artificial ventilatio n, I mL of pancuron ium bro­ two most severe degrees of hypoxemia, the re was an initial m ide (Pavu lon 2 mg/rnl., Organ on Tekn ika, Boxtel, Nether­ increase in blood pressure at the start of the hypoxemia, lasting lands) was given i.v. every 30 min to prevent muscular contrac­ for abou t I h. The blood pressure in both th ese gro ups th en tions, which may lead to artificially high hypox anthine levels gradually declined toward zero in th e term inal phase, as previ­ ( 10). ously described (13). No significan t cha nges in the mean Paco, Blood samples. Arteria l blood samples were taken after a were found in any gro up.