Metabolism and uptake of adenosine in rat isolated lung and its inhibition

Abstract

1 The metabolism of adenosine perfused through the pulmonary circulation of isolated lungs from rats was investigated radiochemically. 2 Following a lOs infusion of radioactive ['4C]-or [3H]-adenosine, the recovery of radioactivity in effluent from the lung after 1 min increased from 30% at 0.5 JAM to 80% at 1 mM adenosine. 3 Unchanged adenosine comprised the major radioactive species in effluent, being about a third of the total up to 100 IAM. 4 Uptake of radioactivity was saturable at high concentrations with an apparent Km of 215 AM. 5Radioactivity retained in lung comprised over 80% as ATP and about 2% as adenosine at all concentrations. 6 Perfusion of lungs with Krebs solution containing dipyridamole (1-100 MM) or adenine (10 JM) increased the rate of radioactive efflux, decreased uptake of radioactivity by lung and decreased metabolites of adenosine (inosine and hypoxanthine) in the effluent.7 Dipyridamole (10 ltM) was more potent in decreasing uptake in guinea-pig lungs than in rat lungs. 8 From these results we conclude that the pulmonary circulation in rat lung exhibits a significant inactivation process for adenosine. The isolated lung provides a convenient preparation for studying in situ pharmacological or pathological modifications of this vascular inactivation process.

Effect of infused adenosine on cardiac output and systemic resistance in normal subjects.

“…Adenosine has been shown to relax human pulmonary arteries in vitro (McCormack et al, 1987). In addition, it is catabolised by pulmonary endothelial cells (Bakhle & Chelliah, 1983;Hellewell & Pearson, 1983), and it is possible that adenosine in doses of 0.03 mg kg-1 min-1 might act as a selective pulmonary vasodilator. We have shown that when this dose is given into a peripheral vein, it is devoid of any systemic cardiovascular effects, at least in subjects with a normal pulmonary circulation, presumably because this dose does not saturate the pulmonary vascular clearance pathways.…”

A comparison of nucleoside transport and metabolism in hypertensive and normotensive rats.

“…We chose 100 fiM cold adenosine since this is less than the K m for adenosine that has previously been reported in rat lung. 3 Effluent was collected in 15-second fractions for a total of 3 minutes, after which perfusion and ventilation were terminated and the lungs were rapidly dissected free of remaining heart and trachea, frozen at -70 °C in liquid N 2 , and weighed. Both effluent fractions and lung were stored at -70 °C until analyzed.…”

Effects of pulmonary oedema on pharmacokinetics of adenosine in rat isolated lungs

“…Further 30 gl aliquots of lung effluent were applied to plastic-backed fluorescent silica gel thin layer chromatography (t.l.c.) plates to separate the metabolites ofadenosine, as described by Bakhle & Chelliah (1983), using the solvent system n-butanol: ethyl acetate:methanol:ammonia, 7:4:3:7 (Shimizu et al, 1970). On average, 72% of the radioactivity was recovered from the t.l.c.…”

“…If these catabolic enzymes were inhibited but adenosine uptake was unchaiged then we might expect the same efflux rate with dereased metabolites. If the kinases, which normally phosphorylate most of the adenosine taken up (Bakhle & Chelliah, 1983;Hellewell & Pearson, 1983), were inhibited, then the prediction would be for a greater proportion ofmetabolites and a normal efflux rate. What we observed was none of these possibilities.…”

“…One of the features of ANTU-induced pulmonary oedema is damage to the endothelium of the pulmonary capillaries (Cunningham & Hurley, 1972;Meyrick et al, 1972). Adenosine is extensively metabolized on passage through the pulmonary circulation of rat isolated lung (Bakhle & Chelliah, 1983) most probably by the endothelial cells (Dieterle et al, 1978;Pearson et al, 1978). It was therefore reasonable to assume that ANTU-induced injury would affect adenosine metabolism in rat lung.…”