Modulation by endogenous opioid peptides of non-adrenergic neurotransmission in the guinea-pig taenia coli
Ishii, T.
Nihon Yakurigaku Zasshi. Folia Pharmacologica Japonica 78(4): 335-346
1981
ISSN/ISBN: 0015-5691 PMID: 6276276 Document Number: 175919
The effects of opioid peptides on the response to stimulation of adrenergic or non-adrenergic inhibitory nerve were investigated in the guinea-pig tenia coli. Leu-enkephalin, Met-enkephalin, (D-Ala2)-Met-enkephalin and .beta.-endorphin inhibited non-adrenergic inhibitory response, in a dose-dependent manner. (D-Ala2) Met-enkephalin and .beta.-endorphin were the most potent compounds inhibiting the elicited relaxation, having ID50 values of 1 .mu.M. The inhibitory actions of these opioid peptides were reversed by naloxone (1 .mu.M). Naloxone itself potentiated the non-adrenergic inhibitory response. The adrenergic inhibitory response was not affected by an application of Leu-enkephalin, .beta.-endorphin or naloxone. Using an immunohistochemical method, Met-enkephalin immunoreactive nerve fibers were observed in the longitudinal muscle layer, Auerbach plexus and circular muscle layer of the tenia. Endogenous opioid peptides may play a regulatory role in non-adrenergic inhibitory neurotransmission but not in adrenergic neurotransmission.