PROSTAGLANDINS AND MODULATION OF SMALL-BOWEL MYOELECTRIC ACTIVITY

We explored the effects of prostaglandins (PG) F2-alpha and E2 on the motor and myoelectric activity of the small intestine using closed intra-arterial injections in conscious chronically instrumented dogs. PGF2-alpha (0.125-5-mu-g) and PGE2 (1-10-mu-g) were injected via a T tube into a branch of the superior mesenteric artery perfusing a 15-cm segment of jejunum. Experiments were performed on four dogs in which the recording devices had been implanted above, below, and within the perfused segment. PGF2-alpha given during phase I of the migrating myoelectric complex cycle induced phasic contractions in the perfused segment of intestine in a dose-dependent manner. Atropine (50-100-mu-g), hexamethonium (15 mg), or TTX (10-15-mu-g) administered before the injection of PGF2-alpha failed to inhibit the effects of PGF2-alpha. In contrast pretreatment of the perfused segment with verapamil (2.5 mg) or PGE2 (1-5-mu-g) abolished the effects of PGF2-alpha. Moreover, PGE2 injected 5 min after the administration of PGF2-alpha inhibited the PGF2-alpha-induced contractions. Administration of PGE2 alone (3-10-mu-g) before the arrival of phase III activity in the perfused segment abolished phase III from this segment of intestine. Our studies indicate opposing effects of PGF2-alpha and PGE2 on small intestinal myoelectric and contractile activities. PGF2-alpha has a direct excitatory effect on the intestinal smooth muscle, which is calcium channel dependent but independent of intrinsic nerves. PGE2 has an inhibitory effect both on the spontaneous and PGF2-alpha-induced small intestinal myoelectric and contractile activity.