The effects of morphine and methionine-enkephalin on the release of purines from cerebral cortex slices of rats and mice.

1 Slices of cerebral cortex from Wistar rats, TO mice or C57 mice were preincubated with [3H]-adenosine, and labelled purines were subsequently releases by electrical stimulation or by perfusing with ouabain, 100 micro M. 2 Electrically-evoked purine release was substantially reduced when the Ca2+ concentration in the medium was lowered from 2.4 to 0.1 mM. In both rats and mice, the electrically-evoked release was increased by morphine and methionine-enkephalin (Met-enkephalin), 10 micro M, and in rats and TO mice by morphine 1 micro M, both drug effects being prevented by naloxone. 3 Purine release evoked by ouabain was also increased by morphine 1 and 10 micro M, though not by Met-enkephalin, from slices of rat cortex. Ouabain-induced release from TO mice was reduced by morphine, and from C57 mice was unchanged. 4 The enhancement by morphine of electrically-evoked purine release may indicate that purines mediate some effects of morphine in the CNS.