Role of catecholamine and adenosine in the ischemic response following release of a renal artery occlusion

Hypothesis: adenosine mediates hemodynamic changes in renal failure

The decreased filtration fraction and glomerular filtration rate characteristic of renal failure could be produced, at least in part, by increased concentration of an endogenous substance which constricts afferent and dilates efferent arterioles. Adenosine satisfies several criteria: (a) exogenous adenosine and its precursors decrease filtration fraction and glomerular filtration rate; (b) the kidneys produce and release adenosine, and production and release are augmented during conditions associated with the induction of renal failure--hypoxia, ischemia, and renal vasoconstriction; (c) several substances known to antagonize adenosine-uptake processes in some cells, which could thereby increase extracellular adenosine concentration, not only have "adenosine-like" effects on the kidney but also induce and/or potentiate existing renal failure. A corollary of this hypothesis is that adenosine-receptor antagonists, such as the methylxanthines, should counteract the hemodynamic changes characteristic of renal failure. It has been known for several years that aminophylline (1,3-dimethylxanthine ethylenediamine) increases the filtration fraction and the glomerular filtration rate.

A possible purinergic mechanism for reactive ischemia in isolated, cross-circulated rat kidney

The isolated kidney of the recipient rat was perfused at a fixed flow rate with blood from a donor by a cross-circulation technique. The renal vasculature responded to the release of arterial occlusion with vasoconstriction, the magnitude of which was increased with increase in the duration of occlusion. ATP, ADP, AMP, adenosine, noradrenaline and 5-HT injected into the renal artery induced a prominent vasoconstriction; IMP and inosine had only a weak vasoconstrictor effect even in large doses. Theophylline reduced the vasoconstriction in response to arterial occlusion and to ATP and adenosine but did not affect that produced by noradrenaline or 5-HT. This suggests that adenine compounds, particularly adenosine, may play a role in the genesis of reactive vasoconstriction after arterial occlusion in the isolated rat kidney.

Femoral vascular responses to purine and pyrimidine derivatives: release of 5-hydroxytryptamine by purine derivatives in isolated, cross-circulated rat hindlimb

The mode of actions of the purines, adenosine, adenosine-5'-triphosphate (ATP), guanosine and guanosine-5'-triphosphate (GTP), and the pyrimidines, cytidine, cytidine-5'-triphosphate (CTP), thymidine, thymidine-5'-triphosphate (TTP), uridine and uridine-5'-triphosphate (UTP) was investigated in the isolated hindlimb preparation of the rat. A single injection of adenosine, ATP, GTP or UTP into the femoral artery induced a biphasic response, a prominent vasoconstriction preceded by a transient vasodilatation, whereas guanosine and uridine caused only a vasoconstriction. Cytidine, CTP, thymidine and TTP were almost ineffective on the vascular bed. The vasoconstrictor responses to adenosine, ATP, guanosine and GTP were effectively antagonized by either methysergide or reserpine, whereas those to uridine and UTP were not modified by either methysergide or phentolamine. Adenine, D-(-)-ribose and hypoxanthine had no effect on the vascular bed. The 5-hydroxytryptamine (5-HT) release from the hindlimb was fluorometrically determined. The present results provide direct evidence that the vasoconstriction caused by ATP, adenosine, GTP and guanosine is attributed to the release of 5-HT from their stores and that purine nucleotides and nucleosides are capable of releasing 5-HT.

Adenosine production in the ischemic kidney

We conducted experiments to determine (1) tissue, blood, and urine levels of adenosine produced by the ischemic kidney under conditions of renal artery occlusion, and (2) the site(s) of production and release of adenosine by the kidney. Concentrations of adenosine, inosine, and hypoxanthine in the dog urine were found to increase after 2 minutes of renal artery occlusion as were concentrations of these metabolites in renal tissue after 10 minutes of renal artery occlusion. Renal venous plasma levels of inosine and hypoxanthine also were elevated after 3 minutes of arterial occlusion. In modified stop-flow experiments, adenosine appeared in the urine in a peak that corresponded most closely with proximal tubule fluid. 5'-Nucleotidase, the enzyme which catalyzes the dephosphorylation of 5'-AMP or 5'-IMP to adenosine or inosine, respectively, was found to be located primarily on the external membranes and mitochondria of proximal tubule cells, but not in distal tubule or collecting duct cells. Since adenosine has been demonstrated to elicit renal vasoconstriction and is produced by the ischemic kidney, it is suggested that adenosine may be involved in the mediation of postocclusion renal ischemia.

Enhancement of the post-occlusive oscillation in the splenic circulation by adenosine

1. The blood flow to the splenic artery of dogs anaesthetized with sodium pentobarbitone was measured under constant pressure perfusion with the animal's own blood led from the femoral artery.2. Immediately after release of occlusion there was a rapid increase of inflow rate above the pre-occlusion level which then oscillated up and down. In a majority of cases such oscillatory responses continued for a while but progressively diminished during a period of about 6 min.3. This post-occlusive oscillatory response was not modified by either neural or autonomic receptor blocking agents such as tetrodotoxin, guanethidine, phentolamine, propranolol, atropine and methysergide.4. In the cases with a relatively short-lasting response, the selective administration of adenosine into the splenic artery caused a distinct enhancement of the oscillation.5. These results suggest that adenosine may play an important role in the post-occlusive oscillatory response of the splenic circulation.