Prostaglandin E2 modulates neurally induced nonadrenergic, noncholinergic gastric relaxations in the rabbit in vivo

Prostaglandin (PG) E2 has been shown to modulate adrenergic and cholinergic neurotransmission in the gut. This study investigated PGE2 influence on vagally induced, nonadrenergic, noncholinergic (NANC) gastric relaxations. Mechanical activity of the stomach was recorded in anesthetized rabbits.In atropine-treated animals, electrical vagal stimulation or arterial bolus injection of the ganglion stimulant dimethyl phenylpiperazinium iodide (DMPP) evoked inhibitory responses that varied from a brisk relaxation, interrupted by a poststimulus excitatory motility (biphasic response), to a long-lasting relaxation (monophasic response). PGE2 reduced and, at the highest doses, abolished the neurally induced relaxant responses elicited either by vagal stimulation or DMPP administration but did not affect the gastric relaxation caused by adenosine triphosphate (ATP), sodium nitroprusside (SNP), or vasoactive intestinal polypeptide (VIP). ATP or 2-methylthioadenosine triphosphate (2-MeSATP) reduced and then suppressed vagally induced inhibitory motility; the relaxant responses elicited by SNP, VIP, and ATP itself were not influenced. After administration of the prostaglandin synthesis inhibitor suprofen, ATP and 2-MeSATP failed to block vagally induced inhibitory responses. Arterial infusion of adenosine at the highest rates did not influence the amplitude of the vagally induced relaxant responses. Following theophylline administration, ATP still blocked the relaxation elicited by vagal stimulation. PGE2 may modulate NANC inhibitory neurotransmission in the stomach. The effects of ATP on the neurally induced NANC gastric relaxation may be caused by PGE2.