AJP - Gastrointestinal and Liver Physiology, Vol 241, Issue 2 122-G128, Copyright © 1981 by American Physiological Society
Effect of histamine on motor function of opossum sphincter of Oddi
J. Toouli, W. J. Dodds, R. Honda and W. J. Hogan
In this study, we evaluated the effect of histamine on phasic contractile
activity in the opossum sphincter of Oddi (SO). SO manometry was done in 35
animals, using an infused catheter system with minimal compliance. In
anesthetized animals, phasic SO contractions occurred at a frequency of 7.3
+/- 0.3 (SE) contractions/min with an amplitude of 83 +/- 4 mmHg.
Intravenous histamine (5-80 micrograms/kg) invariably inhibited the
frequency and amplitude of SO phasic contractions. At larger doses, the SO
contractions were abolished for several minutes. The SO inhibitory effect
of histamine was duplicated by the selective H1-agonist,
2-pyridylethylamine, and abolished by H1-blockade with pyrilamine or neural
blockade with tetrodotoxin. After tetrodotoxin, histamine and
2-pyridylethylamine caused an increased frequency and amplitude of SO
contractions. This excitatory effect was blocked by pyrilamine. The
histamine effects on SO phasic contractions were not altered by metiamide,
atropine, phentolamine, propranolol, hexamethonium, or a large dose of
nicotine. We conclude that 1) histamine depresses phasic SO contractions in
the opossum; 2) histamine's depressant SO effect is mediated by H1
stimulation of noncholinergic, nonadrenergic SO inhibitory nerves,
overriding an H1 stimulatory effect on SO smooth muscle; and 3) histamine
has no H2-mediated effect on the opossum SO.
