Platelet-Activating Factor (PAF) Induces Strong Mechanical Activities Accompanied by Basal Tension Increases in Esophageal and Gastric Fundus Smooth Muscles from Rat

In rats, platelet-activating factor (PAF) has been reported to increase mechanical activity in various gastrointestinal smooth muscles (SMs) except for esophagus SM. The aim of this study was to examine whether PAF increases mechanical activity in rat esophagus longitudinal SM (LSM) and to compare PAF actions in esophagus LSM with those in other gastrointestinal LSMs. PAF (10^-9-10^-6 M) increased esophagus LSM mechanical activities in a concentration-dependent manner; PAF mainly elicited basal tension increases that were almost eliminated by a PAF receptor antagonist CV-6209 (10^-5 M; against 10^-6 M PAF). In the LSM of the gastric fundus, which is similar to esophagus LSM in that it is derived from the foregut during development, PAF (10^-6 M) increased basal tension to a comparable, albeit significantly different, magnitude as in esophagus LSM. In contrast, in LSMs of the duodenum-jejunum, ileum, and ascending colon, which are derived from the midgut, and the descending colon, which is derived from the hindgut, the ability of PAF (10^-6 M) to increase basal tension was less than that in esophagus and gastric fundus LSMs. Interestingly, in ascending colon LSMs, PAF (10^-6 M) induced oscillatory contractions with a small increase in basal tension. PAF-induced contractions were positively correlated with the mRNA expression levels of the PAF-degrading enzymes Pafah2 (R = 0.82) and Pafah1b3 (R = 0.51). These results suggest that PAF strongly stimulates mechanical activities that are mainly accompanied by basal tension increases in rat LSMs of the gastrointestinal tracts that are derived from the foregut during embryogenesis.