Histochemical localization of cyclic 3',5'-AMP phosphodiesterase in rat pineal gland.

Female Wistar rats maintained in a light:dark 12:12 photoperiod cycle were used to investigate the histochemical localization of the cAMP phosphodiesterase activity in the pineal gland of rats killed in the light period or in the dark period of the diurnal lighting regimen. Enzyme activity was identified along the plasma membrane of pinealocytes. The distribution of phosphodiesterase activity for cyclic guanosine monophosphate was similar to that found for cyclic adenosine monophosphate, suggesting that the same enzyme hydrolyzes both nucleotides. In the theophylline control, the reaction product along the plasma membrane of pinealocytes disappeared almost totally. In control sections without substrate, no reaction product was found. The animals decapitated in the dark period of the diurnal cycle showed a distribution of phosphodiesterase activity similar to that found in animals killed in the light period.