Influence of ephedrine and syrosingopine on sympathetic ganglia in the dog and rabbit

Depressor responses to i.v. injection of hexamethonium (0.5 ?? 3 mg/kg) and tetraethylammonium (5 mg/kg) were attenuated by repeated administrations of ephedrine in the dog and rabbit. Those to hexamethonium were also reduced by repeated administrations of tyramine in the dog. Cardiovascular responses to nicotine (0.1 ?? 1 mg/kg), dimethylphenylpiperazinium (0.01 ?? 0.1 mg/kg) and tetramethylammonium (0.1 ?? 1 mg/kg) were modified by ephedrine (total, 35 ?? 80 mg/kg) in the dog and rabbit, i.e., the initial transient negative chronotropic and depressor actions were reduced, the subsequent marked pressor actions were attenuated while those durations were prolonged, and the late long lasting hypotensive actions were abolished. Pressor responses to carotid occlusion and splanchnic stimulation in the dog were reduced by repeated administrations of ephedrine (total, 35 mg/kg) or by pretreatment with syrosingopoine (0.05 ?? 1 mg/kg), although the reduction in the latter responses were not significant. Positive chronotropic responses to pre and post-ganglionic stimulation of the stellate ganglion were reduced by the same treatment, and the reductions in the former responses were more prominent than those in the latter. The decreases in caudal mesenteric blood flow response to pre- and post-ganglionic stimulation of the caudal mesenteric ganglion were attenuated by the treatment, though the attenuation in the former responses was not significant. From the results, it is suggested that ganglionic function may be altered by repeated administration of ephedrine or by pretreatment with syrosingopine.