The smooth-muscle adrenoreceptors of rat and guinea pig tracheas

Effects of adrenaline and noradrenaline upon the smooth muscle contractile activity were shown to have a biphasic character. In low concentrations the effects coincide with that of phenylephrine, in high concentrations--with that of isadrine. The alpha-adrenoreceptors seem to be located at the metasympathetic neurons of the intramural ganglia and at postganglionic cholinergic nervous fibers, whereas the beta-adrenoreceptors at the smooth muscle cells.