EFFECTS OF SELECTIVE PHOSPHODIESTERASE INHIBITION ON CYCLIC-AMP HYDROLYSIS IN RAT CEREBRAL CORTICAL SLICES

The effects of selective inhibition of phosphodiesterase activities on the concentration and rate of hydrolysis of adenosine 3':5' cyclic-monophosphate (cyclic AMP) in rat cerebral cortical slices has been studied. Isoprenaline caused a rapid, concentration-dependent increase in cyclic AMP concentration to new steady-state levels (basal: 7.1 ± 0.7; 10 μM isoprenaline: 14.3 ± 1.4 pmol mg-1 protein). Addition of a β-adrenoceptor antagonist to isoprenaline-stimulated cerebral cortical slices caused a rapid decrease incyclic AMP concentration to basal levels (t( 1/2 ): 58 ± 18 s). Preincubation of slices for 30 min with the phosphodiesterase inhibitors 1-methyl-3-isobutylxanthine, denbufylline, rolipram or Ro20 1724 caused concentration-dependent increases in basal and isoprenaline-stimulated cyclic AMP concentrations and decreased the rate of cyclic AMP hydrolysis measured after addition of a β-adrenoceptor antagonist. However, SKF 94120 and zaprinast had none of these effects. The results are discussed with respect to previous studies of phosphodiesterase isozymic activities isolated from cerebrum and it is suggested that the Ca2+/calmodulin-independent, low K(m) cyclic AMP phosphodiesterase isozyme, which is selectively inhibited by denbufylline, rolipram and Ro20 1724, and is present in cerebrum is of critical importance to the regulation of cyclic AMP concentration in this tissue.