AJP - Gastrointestinal and Liver Physiology, Vol 248, Issue 3 307-G312, Copyright © 1985 by American Physiological Society
Opiate nerves mediate feline pyloric response to intraduodenal amino acids
J. C. Reynolds, A. Ouyang and S. Cohen
Intraluminal pressures and myoelectric activity were recorded from the
feline antrum, pylorus, and duodenum in response to intraduodenal amino
acid solutions. Mixed amino acids (0.02 mg/ml, 3.0 ml) increased the
amplitude of pyloric contractions (59.7 +/- 7.9 mmHg) and pyloric spike
activity (73.7 +/- 6.8% of slow waves with spike activity) compared with a
saline control (P less than 0.001). The selectivity of these responses was
determined with specific amino acids. L-Tryptophan (10 or 40 mM) produced a
response similar to the mixed amino acid response, while L-phenylalanine or
L-glycine (10 or 40 mM) had no effect. Intra-arterial tetrodotoxin,
intraluminal ethyl aminobenzoate, or intravenous naloxone (1.0 mg/kg)
abolished the pyloric responses to amino acids (P less than 0.02).
Bilateral cervical vagotomy had no effect. Cholecystokinin octapeptide
(CCK-OP) produced dose-dependent increases in the amplitude of pyloric
contractions and in pyloric spike activity. The ED50 dose of CCK-OP (1.0
microgram/kg iv) gave an increase in pyloric pressure of 155.6 +/- 49.9
mmHg and in spike activity of 77.7 +/- 9.4%, similar to mixed amino acids
or tryptophan. These effects of CCK-OP were not antagonized, however, by a
dose of naloxone (1.0 mg/kg) that blocked the maximal pyloric response to
leucine-enkephalin. We concluded intraduodenal mixed amino acids or
tryptophan increase phasic, spike-dependent pyloric contractions in the cat
via nonvagal, naloxone-sensitive neural pathways, phenylalanine, a
structurally similar essential amino acid, had no effect on the feline
gastroduodenal junction, and the pyloric responses to exogenous CCK-OP are
mediated by pathways distinct from the responses to tryptophan or mixed
amino acids.
