Influence of Age on the Rhythm in Basal and Forskolin-Stimulated Adenylate Cyclase Activity of the Rat Heart

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Abstract
In male rats of three different ages (Group I: 7 weeks, Group II: 4 months, Group III: > 10 months) basal and forskolin-stimulated adenylate cyclase (AC) activity were investigated in rat heart ventricles of animals sacrificed at 8 time points within 24 hours of a day. Maximum (Emax) and half-maximum (EC50) stimulation by a water-soluble forskolin (FOR; 0.1-100 .mu.mol/l) were determined from dose-response curves. In young rats (Group I) significant rhythmicity was found in basal and FOR-stimulated AC activity, which was successfully reduced or abolished with age by a reduction in amplitude. Mean basal AC activity increased about 2-fold from Group I to Group II/III. Mean maximum in FOR stimulation was about 12-fold in Group I and about 7-fold in Group II and III. EC50-values displayed neither a significant rhythmicity in either group nor an age-dependency. It is concluded that the stimulatory potency of the catalytic subunit of the AC is reduced with age.