The inhibitory effect of furosemide on the contractile response of equine trachealis to cholinergic nerve stimulation.

The effects of furosemide on the responses of equine trachealis muscle with and without epithelium to electrical field stimulation (EFS) and exogenous acetylcholine (ACh) were investigated in organ baths. Tissues were pretreated with guanethidine and the parameters used for EFS were those previously demonstrated to activate postganglionic cholinergic neurons. In tissues with intact epithelium, furosemide (100 microM) shifted the frequency-response curve to the right. In the preparations without epithelium, furosemide did not affect the response to EFS. Neither in epithelium-on nor in epithelium-off tissues was the ACh dose-response curve affected by the administration of furosemide. We conclude that furosemide (100 microM) decreases the equine tracheal smooth muscle responses to EFS through inhibition of cholinergic neurotransmission, and that this effect is dependent on epithelium.