Relaxations mediated by adrenergic and non-adrenergic nerves in human isolated taenia coli

In human taenia coli electrical field stimulation after cholinergic blockade excited mainly non-adrenergic inhibitory nerves. Adrenergic relaxations during stimulation were demonstrated only with short electrical pulses at high frequencies or with ganglion stimulants. Reduction by tetrodotoxin of relaxations to indirectly acting sympathomimetics supports the histochemical finding that colonic adrenergic nerves are mainly preganglionic, and possibly synapse with non-adrenergic inhibitory nerves. When the latter undergo direct maximal stimulation, responses to adrenergic nerve excitation are masked.