Title: An investigation of the mechanism of lead-induced relaxation of pigeon crop smooth muscle.

Authors: Boyer, I J; DiStefano, V

Published In J Pharmacol Exp Ther, (1985 Sep)

Abstract: Lead-induced crop dysfunction is probably due to a direct action on the smooth muscle or the neural elements in crop tissue. Strips of crop tissue relax when exposed to lead chloride in vitro. We found that tetrodotoxin and the neurotransmitter antagonists propranolol, sotalol and apamin failed to alter lead-induced relaxation, suggesting that the effect is not neurally mediated. Lead, manganese, cadmium and theophylline inhibited calcium-induced contractions in depolarized crop tissue. However, lead, like the phosphodiesterase inhibitor theophylline and unlike the calcium-influx blocker verapamil, did not inhibit bethanechol- or potassium-stimulated contractions and calcium influx into crop tissue. This suggests that lead does not act by blockade of calcium influx. Lead stimulated cyclic AMP production in cell-free crop membrane preparations. Lead also enhanced manganese stimulation of cyclic AMP production. The results suggest that lead-induced relaxation may be due to stimulation of adenylate cyclase activity resulting in increased intracellular cyclic AMP levels.

PubMed ID: 2863369

MeSH Terms: Adenylate Cyclase/analysis; Animals; Bethanechol; Bethanechol Compounds/pharmacology; Calcium/metabolism; Calcium/pharmacology; Columbidae; Crop, Avian/drug effects*; Lead/toxicity*; Male; Manganese/pharmacology; Muscle Relaxation/drug effects; Muscle, Smooth/drug effects*; Potassium/pharmacology; Tetrodotoxin/pharmacology