Acid Soluble Mononucleotides in Rat Diaphragm During Incubation

Inosine metabolism in the rat

1. Uptake and subsequent metabolism of purine and ribose moieties was monitored after intravenous administration of doubly labelled inosine. 2. More than 95% was cleared from the plasma within 5 min, and 99% within 20 min. 3. Approx. 50% of the 160 mumol total was rapidly incorporated into liver and kidney. Kidney removed the greatest amount (21 mumol/g wet wt.), about 10-fold more than heart, lung or liver. Lung and heart accounted for only 3%. These tissues then lost radioactivity during the remainder of the experiment. Radioactivity in the skeletal muscle, in contrast, increased from 8% of the injected dose at 5 min to 40% at 60 min. 4. In liver, kidney, heart and lung there was a significant difference in the fate of inosine. After initial incorporation of inosine, kidney predominantly lost inosine; heart preferentially lost purines; lung preferentially lost ribose radioactivity; and in liver the ribose radioactivity was rapidly lost, whereas purine was retained. Some of the ribose moiety was metabolized to glucose, presumably in the liver, and then released into the blood. Ribose radioactivity (probably as glucose) and radioactive hypoxanthine accumulated in skeletal muscle throughout the experiment. 5. Inosine caused a rapid and prolonged increase in the blood glucose content, from 6 to 15 mM in 60 min. This was accompanied by a small increase in plasma insulin. 6. It is concluded that the purine and ribose radioactivity lost from the kidney, liver and other tissues becomes incorporated into skeletal muscle.

Hypoxanthine levels in amniotic fluid: an indicator of fetal hypoxia?

During hypoxia there is an increased formation of hypoxanthine from the consumption of ATP; simultaneously the oxidation into uric acid is decreased. The purpose of this study was to determine possible correlations between hypoxanthine concentrations in the amniotic fluid and states of fetal hypoxia. We obtained 83 amniotic fluid samples from 68 patients during pregnancy or delivery. Hypoxanthine was assayed fluorimetrically according to GARDINER [4]. In the course of pregnancy, hypoxanthine levels in the amniotic fluid rise slightly. A marked increase occurs during delivery (without labor mean = 3.4 +/- 0.9 mumol/l, with labor mean = 7.0 +/- 5.4 mumol/l, p less than 0.02). There is no significant difference in the levels obtained from the first and second stages of labor. In intrauterine fetal death (Fig. 1) and in depressed newborns (Tab. I) there were increased hypoxanthine levels in the amniotic fluid, this was not seen in other complications of pregnancy. Independently from the fetal state increased hypoxanthine concentrations may occur in the amniotic fluid evidently as a consequence of labor activity. Thus the determination of hypoxanthine levels in the amniotic fluid cannot be used for the diagnosis of fetal hypoxia.