Specific changes in the cholinergic system in guinea-pig vas deferens after denervation.

A small rapid phase (1st phase) was distinguished from a concomitant phase (2nd phase) in contraction of guinea-pig vas deferens. The vas deferens 4 days after denervtion exhibited supersensitivity to stimulants. The supersensitivity in the 2nd phase of contraction was nonspecific, but that in the 1st phase was specific to muscarinic cholinergic agonists. The increase in sensitivity resulted in a shift of the dose-response curve to lower concentrations without significant change in the maximal response. Muscarinic cholinergic receptors in the vas deferens, determined by measuring binding of [3H]quinuclidinyl benzilate, changed after denervation. The maximal binding sites increased from 115 to 165 fmol/mg of protein with no significant change in the dissociation constant. The affinity of the receptor for agonist also did not change significantly. Studies on [3H]WB4101 binding indicated no significant change in alpha adrenergic receptors after denervation. Thus, specific supersensitivity of the cholinergic mechanism mediated by muscarinic acetylcholine receptors occurred after denervation of guinea-pig vas deferens. This increased sensitivity is discussed in relation to the amount of receptor.