Metabolic effects of R-phenylisopropyladenosine during reversible forebrain ischemia studied by in vivo 31P nuclear magnetic resonance spectroscopy.

The metabolic effects of R-phenylisopropyladenosine (R-PIA), an agonist of adenosine A1 receptors, were studied by in vivo 31P NMR spectroscopy before, during, and after 30 min of reversible forebrain ischemia in the rat. R-PIA had no effect on cerebral metabolism before ischemia. During a 30-min ischemia, R-PIA reduced the decrease in phosphocreatine (43 +/- 11% of the control level at the end of ischemia vs. 27 +/- 9% in the reference group) and ATP (58 +/- 12% vs. 40 +/- 23%) and the increase in inorganic phosphate (672 +/- 210% vs. 905 +/- 229%). The intracellular acidosis elicited by ischemia was also less in the treated group (pH of 6.40 +/- 0.10 vs. 6.30 +/- 0.10). Recirculation was associated with a faster recovery of PCr, ATP, Pi, and pHi to control levels in the treated group than in the reference group. It is concluded that adenosine protects against ischemic injury by mechanisms that include metabolic protection.