Actions of pentagastrin on smooth muscle of isolated dog intestine.

Adult dogs were anesthetized and segments of small intestine were isolated and perfused via a mesenteric artery with Krebs-bicarbonate solution. Muscle responses were monitored with extraluminal force transducers implanted along the circular and longitudinal axes of the segments or by means of an intraluminal balloon. Agonists were administered as intra-arterial bolus injections in volumes not exceeding 0.1 ml. Antagonists were dissolved in the Krebs perfusion solution. Smooth muscle responses to pentagastrin (25 microgram), dimethyl-phenylpiperazinium (DMPP, 5 microgram), and bethanechol (BeCh, 5 microgram) were reduced during perfusion with atropine sulfate (25 ng/ml). Responses to DMPP (5 microgram) and pentagastrin (25 microgram) were diminished by perfusion with tetrodotoxin (20 ng/ml) and after depolarizing doses of nicotine (500 microgram), whereas responses to BeCh (5 microgram) were unaffected in both cases. Hexamethonium (10 microgram/ml) reduced responses to DMPP (5 microgram) but did not affect responses to BeCh (5 microgram) or pentagastrin (5 microgram). Responses to DMPP (5 microgram) were not reduced in segments desensitized to pentagastrin. The results suggest that the stimulatory effect of pentagastrin on isolated dog intestine results from an interaction of the peptide with nonnicotinic cholinergic receptors on postganglionic cholinergic nerves.