AJP - Gastrointestinal and Liver Physiology, Vol 256, Issue 1 100-G106, Copyright © 1989 by American Physiological Society
Prostaglandins augment muscarinic responses in the rabbit cecum
K. Nakao, K. Kitamura and H. Kuriyama
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Effects of prostaglandin E2, F2 alpha, and synthetic thromboxane A2 (PGE2,
PGF2 alpha, and STA2, respectively) on electrical and mechanical responses
of the rabbit cecum were investigated. Transmural electrical stimulation
evoked an excitatory junction potential (EJP) and contraction, events that
were inhibited by 1 microM atropine or 0.3 microM tetrodotoxin.
Indomethacin (up to 30 microM) modified neither the membrane potential nor
the muscle tone but did inhibit amplitudes of the EJP and the twitch
contraction. In the presence of 30 microM indomethacin, PGE2 (below 1 nM)
had no effect on the membrane potential or muscle tone, while PGE2 (above
10 nM) contracted the cecal tissues, without depolarization. PGE2 enhanced
the twitch contraction and restored the EJP in the presence of 30 microM
indomethacin. Acetylcholine (0.1-3 microM) depolarized the membrane, but in
the presence of 30 microM indomethacin, this depolarization was inhibited.
PGE2 (0.1-100 nM) prevented these inhibitory actions of indomethacin. PGF2
alpha (0.1-100 nM) had weaker actions than PGE2 while STA2 (0.1-100 nM) had
no effect on muscarinic responses. Thus muscarinic responses are augmented
by primary prostaglandins.
