Abstract
Action of prostaglandin (PG) on gastrointestinal motility was studied in vivo and in vitro.
PG-E1, E2 and F2α (10-7-10-6M) contracted the isolated longitudinal muscle strips of guinea-pig stomach and colon. However, in contrast to PG-F2α, PG-1 and E2 relaxed the isolated circular muscle strips.
Ca uptake of the circular muscle strip of dog ileum, relaxed in Ca free.KCl solution, was increased with the additon of increasing amount of Ca++. At 0.05 mM Ca++, Ca-net uptake was 3.13×10-6 moles/kg wet wt. in the absence of PG-E1 (10-5M), but 4.16×10-6 moles/kg wet wt. in the presence of it. At 0.5 mM Ca++, this uptake was 2.89×10-5 moles/kg wet wt. in control and was 2.49×10-5 moles/kg wet wt., 1.81×10-5 moles/kg wet wt. in the presence of PG-E1 and La+++ (10-5M), respectively, at which concentrations Ca contractures were inhibited by 70%.
Propulsive activity of the isolated segmental preparation from guinea-pig colon was increased by the serosal applications of PG-E1 and F2α (10-6M). This increase of the action, however, was abolished in the presence of atropine (5×10-7g/ml) and tetrodotoxin (10-7g/ml).
The action of PG-E1 on gastrointestinal motility in man was investigated roentgenologically. When this decylester (4mg) was orally administered with a barium meal (200ml), intestinal motility was stimulated within 60 min after the meal. However, gastric motility was not.
From these results observed, it was considered that the mechanism of PG-E1 induced relaxation in circular muscle might depend on the decrease of Ca++ influx by a formation of PG-Ca complex within the cell membrane, and that the stimulating action of PGs on intestinal motility in man and the isolated guinea-pig colon might at least exert an indirect effect via the intrinsic nerves within the intestinal wall.
