Effects of PGE1 and PGF2 alpha on the responses of gastrointestinal sphincters to field stimulation.

The study concerned the effects of PGE1 and PGF2 alpha on the spontaneous tone and the responses to field stimulation of isolated strips from: lower esophageal sphincter (LES), pyloric sphincter (PS) and ileocaecal sphincter (ICS) of cats. PGE1 and PGF2 alpha (0.3 microM) increased the LES tone and abolished the PS contractions. PGF2 alpha increased the tone of ICS while PGE1 had no effect at all. The effects of the prostaglandins (PG) were reduced when the preparations were pretreated with atropine, propranolol and phenoxybenzamine (1 microM). PGE1 and PGF2 alpha decreased the LES relaxation in response to field stimulation (0.5 msec, 2 Hz for 10 sec at supramaximal current). No responses of PS to field stimulation were observed after PG treatment. PGF2 alpha increased the amplitude of the relaxation response in the ICS to field stimulation. PGE1 did not change the effect of field stimulation in ICS. The effects of PGE1 and PGF2 alpha on the LES and ICS responses to field stimulation were not influenced by adrenergic and cholinergic blocking agents. The data suggest a PG effect on non-adrenergic, non-cholinergic (purinergic) transmission in the gastrointestinal sphincter smooth muscle on field stimulation. Due to the high concentration of PG used this effect was probably a pharmacological one.