Prejunctional inhibition of non-adrenergic non-cholinergic transmission in the rat anococcygeus muscle.

The muscarinic agonist McN-A-343 did not affect the tone or nitroprusside-induced relaxations of the rat anococcygeus, but inhibited non-adrenergic non-cholinergic (NANC) relaxations. Atropine, pirenzepine and gallamine blocked the McN-A-343 inhibition of NANC relaxations. Agonists of alpha 1-(methoxamine) or alpha 2-adrenoceptors (clonidine, rilmenidine) increased tone and reduced NANC relaxations. Carbachol also increased tone but produced a greater reduction of NANC relaxations. The findings suggest that activation of prejunctional muscarinic receptors on NANC terminals inhibits transmitter release, but there is no evidence for prejunctional alpha-adrenoceptors.