AJP - Gastrointestinal and Liver Physiology, Vol 255, Issue 3 352-G360, Copyright © 1988 by American Physiological Society
Inhibitory opioid receptors in canine pylorus
H. D. Allescher, S. Ahmad, E. E. Daniel, J. Dent, F. Kostolanska and J. E. Fox
Department of Neurosciences, McMaster University, Hamilton, Ontario, Canada.
In 18 anesthetized dogs, antroduodenal and pyloric motility was monitored
in vivo by a sleeve and perfused side-hole manometric assembly and by
antral and duodenal serosal strain gauges. Close intra-arterial injection
to the pylorus of dynorphin-(1-13) (Dyn) for kappa-receptors,
[D-Pen2,5]enkephalin (DPen2,5-Enk) for delta-receptors, and
[N-Me-Phe3-D-Pro4]morphiceptin (PL017) and
[D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAGO) for mu-receptors showed no
excitatory effect in the pylorus. When pyloric motor activity was increased
by duodenal field stimulation 3-5 cm aboaad from the pylorus, Dyn greater
than DPen2,5-Enk greater than DAGO produced a dose-dependent inhibition of
the pyloric motor activity. Naloxone (200 micrograms/kg iv and 20
micrograms ia) had no effect on the pyloric excitation due to duodenal
field stimulation, but it reduced the inhibitory response of
intra-arterially injected opioids. In addition, opioid binding
([3H]diprenorphine) in microsomal and mitochondrial fractions from the
inner circular muscle ring of the pylorus showed a distribution similar to
the neuronal marker [3H]saxitoxin but no correlation to the plasma membrane
marker 5'-nucleotidase. These results suggest the existence of inhibitory
opioid receptors (kappa- and delta-receptors) on excitatory neurons in the
intestinal neuronal pathway, which activates the canine pylorus.
