Effect of ischemia and infarction on regional content of adenine nucleotides and derivatives in canine left ventricle

Intestinal formation of hypoxanthine and uric acid during endotoxemia

The objective of this study was to examine the intestinal metabolism of high-energy purine compounds as sensitive indicators of tissue ischemia during endotoxemia. Arterial (art) and portal venous (PV) concentrations as well as the intestinal net concentration changes of adenosine (ADO), hypoxanthine (Hypo), and uric acid (UA) were measured at baseline and after 60 and 120 min in rats that were subjected to a 1-hr continuous infusion of endotoxin (1.5 mg/kg; group E), and in control animals (group C). Furthermore, the arterial (SaO2) and portal venous oxygen saturation (S(PV)O2) was determined at the same time points. Animals in both groups remained normotensive throughout the study period and no differences in mean arterial blood pressure were observed. In both groups, adenosine concentrations remained constant throughout the study and no changes in the net concentration difference (NCD) of adenosine between arterial and portal venous blood were observed [ADO(NCD); baseline: group E, -23 +/- 46 nmole/L; group C, 17 +/- 84 nmole/L; 120 min: group E, 14 +/- 38 nmole/L; group C, 5 +/- 40 nmole/L]. In contrast to control animals, hypoxanthine and uric acid concentrations increased in arterial and portal venous blood in endotoxemic rats after 120 min. This was accompanied with an increase in the intestinal net concentration differences of both hypoxanthine and uric acid, indicating the gut as the predominant source of these two compounds during endotoxemia [Hypo(NCD); baseline: group E, -36 +/- 53 nmole/L; group C, -53 +/- 185 nmole/L; 120 min: group E, 538 +/- 211 nmole/L; group C, 99 +/- 100 nmole/L] [UA(NCD); baseline: group E, 2.04 +/- 1.62 micromole/L; group C, -0.04 +/- 1.11 micromole/L; 120 min: group E, 9.58 +/- 3.04 micromole/L; group C, 0.35 +/- 1.34 micromole/L]. Furthermore, in endotoxemic rats the portal venous oxygen saturation decreased despite unaltered arterial oxygen saturation [SaO2; baseline: group E, 95.2 +/- 0.9%; group C, 94.2 +/- 0.9%; 120 min: group E, 95.4 +/- 0.7%; group C, 96.4 +/- 0.9%] [S(PV)O2; baseline: group E, 86.2 +/- 3.1%; group C, 85.7 +/- 1.4%; 120 min: group E, 69.1 +/- 4.5%; group C, 82.3 +/- 1.9%]. These results indicate the presence of tissue ischemia in the intestinal tract during early, normotensive endotoxemia. Furthermore, because of the direct toxic damage mediated by oxygen radicals that are generated during the production of uric acid, intestinal mucosal injury observed during endotoxemia may be related to an enhancement of the ATP-degradation pathway.

Evidence for adenosine triphosphate degradation in critically-ill patients

Alterations of cellular energy metabolism may provide important markers during the clinical course of critically ill patients. To determine whether adenosine triphosphate (ATP) degradation occurs in critically ill patients, we measured levels of adenosine, inosine, hypoxanthine, and xanthine in 18 patients and seven control subjects. The mean concentration of hypoxanthine (3.8 microM) in the critically ill patients was elevated (p less than 0.01) compared to that of our control population (0.1 microM). A subgroup of seven critically ill patients had levels of hypoxanthine, xanthine, or inosine higher than those of any member of the control group. This subgroup was characterized by a lower systolic blood pressure, an increased requirement for vasopressors, and a markedly decreased survival rate when compared to the other critically ill patients. Arterial and mixed venous blood gas values were not helpful in predicting survival and did not correlate with levels of ATP degradation products. In two patients who showed subsequent clinical improvement, the initially elevated levels of hypoxanthine and xanthine returned to normal. This study indicates that critically ill patients have elevated levels of ATP degradation products. These increased levels may indicate cellular hypoxia.

Metabolic basis for disorders of purine nucleotide degradation

Purine nucleotide degradation refers to a regulated series of reactions by which human purine ribonucleotides and deoxyribonucleotides are degraded to uric acid in humans. Two major types of disorders occur in this pathway. A block of degradation occurs with syndromes involving immune deficiency, myopathy or renal calculi. Increased degradation of nucleotides occurs with syndromes characterized by hyperuricemia and gout, renal calculi, anemia or acute hypoxia. Management of disorders of purine nucleotide degradation is dependent upon modifying the specific molecular pathology underlying each disease state.