Aging and rat pacemaker sensitivity to beta-adrenoceptor agonists.

Sympathetic control of cardiac function is known to decrease with age. This report deals with the sensitivity of pacemakers isolated from young, adult and senescent rats to isoprenaline and noradrenaline. Pacemaker sensitivity to the catecholamines decreases from young to adult rats, the effect remaining unaltered after in vitro denervation and inhibition of the catecholamine dissipating mechanisms. Pacemakers isolated from senescent rats showed subsensitivity to the chronotropic effect of isoprenaline and noradrenaline after in vitro inhibition of the catecholamine dissipating mechanisms. This suggests that the efficiency of the extraneuronal uptake process may be physiologically reduced in the pacemaker of senescent rats.