Effect of the organophosphate iso-OMPA on amylase release by pancreatic lobules of dog, guinea pig, and cat.

Organophosphates (OPs) cause irreversible inhibition of cholinesterases (ChEs) and profound cholinergic stimulation. There are major differences in the response of the dog and cat pancreas to the in vivo administration of Diazinon (O,O-diethyl O-2-isopropyl-4-methyl-6-pyrimidyl phosphothioate), a butyrylcholinesterase (BuChE) inhibitor. Acute edematous pancreatitis is found in the dog but not in the cat. The present experiments were designed to see what effect OP had in vitro on pancreatic exocrine function of dog, cat, and guinea pig, and whether the effects were consistent with an anti-ChE activity. A water-soluble OP agent, tetraisopropyl pyrophosphoramide (iso-OMPA) at 10(-3) M, which like Diazinon inhibits BuChE, was used. Minced pieces of fresh whole pancreata 3 mm in size were taken from 3 dogs, 4 guinea pigs, and 2 cats. The tissues were placed in flasks containing Eagle's solution and gassed with 100% O2. Cumulative amylase release was measured by Phadebas method up to 3 h. At half-maximal acetylcholine (ACH) concentration (10(-5) M), the canine pancreas pretreated with iso-OMPA (10(-3) M) showed a 42-87% greater release of amylase than tissues receiving ACH alone (p less than 0.001). The same potentiated response to ACH was seen in guinea pig pancreas pretreated with iso-OMPA (p less than 0.001), but iso-OMPA pretreatment did not augment the ACH response in the cat. Atropine pretreatment effectively blocked all ACH responses, and there was no effect seen with iso-OMPA alone. In the dog, iso-OMPA in combination with half-maximal carbachol (10(-6) M), or in combination with half-maximal cholecystokinin (CCK-8) stimulation (10(-9) M), provided no potentiated amylase release.(ABSTRACT TRUNCATED AT 250 WORDS)