Contractile responses of longitudinal and circular smooth muscle of the canine stomach to prostaglandins E and F2alpha.

Muscle strips were excised from the circular and longitudinal layers of the fundus, corpus and antrum, and from the inner portion of the pyloric ring. In general prostaglandin (PG)F2 alpha as well a PGE1 and PGE2 stimulated the longitudinal muscle. However, there were remarkable regional differences. The sensitivity to PGs was greatest in the fundus and corpus (threshold near 10(-10) mol/l) and only weak in antrum (threshold 5.10(-8) to 10(-7) mol/l). In longitudinal antrum strips acetylcholine induced a combined phasic-tonic response, whereas PGs produced purely phasic response. The effects of PGF2alpha and PGE on the circular layer were complex. PGF2 alpha produced excitatory responses in circular fundus and corpus similar to those in the longitudinal layer of the same regions. PGE produced dual responses in circular fundus (excitation at low concentration and strong inhibition at concentration of 10(-7) mol/l). In circular corpus PGE induced pure inhibition (threshold near 10(-9) mol/l for inner pylorus). These effects of PGs appeared in the presence of adrenergic and cholinergic blocking agent as well as of tetrodotoxin and were, therefore, direct effects on smooth muscle. Indomethacin (10(-7)-10(-6) mol/l) suppressed spontaneous tone of the fundus and corpus and increased phasic activity of inner pylorus. This indicates that endogenous PG synthesis may be involved in the control of spontaneous activity in gastric muscle.