P. Chamouard et al., DELTA-OPIOID RECEPTOR AGONISTS INHIBIT NEUROMUSCULAR-TRANSMISSION IN HUMAN COLON, European journal of pharmacology, 262(1-2), 1994, pp. 33-39
The present study was undertaken to investigate the possible role of d
elta-opioid receptors in the neuroregulation of human colonic motility
by using a superfusion model. Spontaneous mechanical activity and res
ponses to electrical transmural nerve stimulation of both longitudinal
and circular muscle strips from the human sigmoid colon were studied.
Exogenously added delta-opioid receptor agonists did not modify spont
aneous contractile activities of either type of strip. Nerve stimulati
on induced a triphasic response composed of an initial contraction fol
lowed by a relaxation and an off-contraction. This response was mediat
ed by cholinergic excitatory nerves and non-adrenergic, non-cholinergi
c excitatory and inhibitory nerves. [Met(5)]Enkephalin and the synthet
ic delta-opioid receptor agonist [D-Pen(2),D-Pen(5)]enkephalin (DPDPE)
significantly decreased the amplitude of the initial contraction and
of the off-contraction. The effects of both delta-opioid receptor agon
ists were reduced in the presence of either the delta-opioid receptor
antagonist, ICI 174864, or another delta-opioid receptor antagonist, n
altrindole. ICI 174864 prevented neither the effects of a natural kapp
a-opioid receptor agonist, dynorphin-(1-13), nor those of the mu-opioi
d receptor agonist, PL017. Therefore, these data suggest that delta-op
ioid receptors might be involved in the neuroregulation of smooth musc
le of human colon and may mediate inhibition of cholinergic and non-ch
olinergic excitatory transmission within the myenteric plexus.