Rhythms in second messenger mechanisms

Abstract

In this chapter circadian rhythms in the beta-adrenoceptor/adenylate cyclase/phosphodiesterase system are presented and discussed. Daily variation in total number and affinity of beta-adrenoceptors in rat forebrain and rat heart ventricles seem to be of minor importance in the circadian regulation of the cAMP concentration in these tissues. Pronounced and significant circadian rhythms in cAMP formation by the adenylate cyclase and cAMP degradation by the phosphodiesterases could be demonstrated in either rat forebrain or heart ventricles. Also the accessibility of cardiac adenylate cyclase to different stimuli was circadian-phase-dependent. Furthermore, data are presented which indicate that the catalytic unit of the adenylate cyclase must undergo qualitative changes with age.