An alteration in sensitivity to cholinergic agents on guinea-pig ilea and atria after repeated administration of an organophosphate and an antagonism by a carbamate

Yamada, S.; Okudaira, H.; Hayashi, E.

Archives Internationales de Pharmacodynamie et de Therapie 241(1): 32-44


ISSN/ISBN: 0003-9780
PMID: 526070
Accession: 004715251

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The effect of 4-methylthiophenyl dipropylphosphate (propaphos, organophosphorus insecticide) and 2-sec-butylphenyl-N-methylcarbamate (BPMC, carbamate insecticide) on the sensitivity to the effects of acetylcholine (ACh), carbachol (CCH) and nicotine was studied on guinea pig isolated ilea and atria. The response of the tissues to ACh was significantly enhanced in the presence of propaphos (3.3 .times. 10-7 M) or BPMC (4.8 .times. 10-6 M), while that to CCH was unaffected. The repeated administration of propaphos (5 mg/kg per day, p.o. for their responses were significantly decreased. The response to CCH was decreased as seen by a significant increase in these values. Pretreatment with BPMC (25 mg/kg per day p.o., 7 days) significantly reduced the change in the responsiveness of the tissues to ACh, CCH and nicotine produced by the propaphos administration. The activity of cholinesterase (ChE) declined by 50-70% in blood and tissues from propaphos-treated animals, and its inhibition was significantly reduced by the pretreatment with BPMC to 30-40%. Apparently changes in synaptic ChE activity, as reflected by the changes in ChE activity of blood and tissues, may be responsible for the change in sensitivity of ilea and atria to cholinergic agents produced by the repeated administration of propaphos and for the antagonism by BPMC. The toxic effect of the ChE inhibitors may be due to ACh activation.