The role of peripheral catecholamines in oxotremorine tremor in the rat and its antagonism by beta adrenoceptor blocking agents.

Oxotremorine, 0.25 mg/kg, produces marked tremor in the rat, which is abolished by scopolamine, 0.5 mg/kg, and is substantially reduced in intensity and duration both by adrenalmedullectomy and by chemical sympathectomy with 6-hydroxydopamine. Oxotremorine increases plasma norepinephrine from 0.62 +/- 0.07 to 3.01 +/- 0.47 ng/ml and plasma epinephrine, from 0.82 +/- 0.14 to 3.42 +/- 0.48 ng/ml, in conscious unrestrained rats. l-Propranolol (0.5-2.5 mg/kg) reduces tremor, and at 2.5 mg/kg is more effective than either chemical sympathectomy or adrenal demedullation. d-Propranolol and sotalol are also active at 4 and 10 times the dose of l-propranolol, respectively. l-Propranolol does not prevent the rise in catecholamines induced by oxotremorine. It is suggested that stimulation of central muscarinic receptors causes tremor by a combination of two effects. There is an increase in cholinergic influence to motor efferents accompanied by an activation of the sympathoadrenal system to release catecholamines which augment tremor by stimulation of beta2 adrenoceptors.