Effects of footshock stress on the sensitivity of the isolated rat pacemaker to catecholamines.

The effect of repeated footshock on the sensitivity of the isolated rat pacemaker to the chronotropic effect of catecholamines was studied. Footshock stress caused subsensitivity to noradrenaline and supersensitivity to isoprenaline. The subsensitivity to the neurotransmitter was abolished by cocaine, whereas supersensitivity to isoprenaline was unchanged after blockade of the extraneuronal uptake. The pA2 value of metoprolol was increased by repeated footshock. Butoxamine reversed the supersensitivity to isoprenaline and the alteration of the pA2 value. Repeated footshock stress appears to cause prejunctional subsensitivity to noradrenaline and to increase the function of postjunctional beta 2-adrenoceptors.