Peripheral catecholamines mediate certain responses to central cholinergic receptor stimulation by oxotremorine

The role of peripheral catecholamines in mediating the pressor and tremorigenic effects of oxotremorine were investigated in conscious rats. At time of peak tremor intensity induced by oxotremorine, plasma adrenaline and noradrenaline were increased 3--4-fold. Tremor intensity was substantially reduced by either adrenal medullectomy, chemical sympathectomy with 6-hydroxydopamine, or injection of 2.5 mg/kg L-propranolol. The pressor response to oxotremorine was not reduced by adrenal denervation, which however prevented the usual rise in plasma adrenaline but not that of noradrenaline. It is concluded that central cholinergic receptor stimulation activates the sympatho-adrenal system. While both adrenaline and intact sympathetic nerves are necessary for the mediation of the full tremorigenic effect, the pressor response to oxotremorine is mainly due to the effect of noradrenaline on vascular alpha-receptors.