Carbachol effect on kinetics of the alpha1-adrenergic contractile response of the rat vas deferens

摘要

Analysis of the control kinetics of the rat vas deferens contractile response to phenylephrine showed that alpha 1-adrenoceptors mediating the contraction could be in different functional states. In some organs these receptors represented a single pool with Hill coefficient n = 1 (the linear mode of the Scatchard plot), in others--not a single pool, n > 1 (not linear mode of the Scatchard plot). Activation of muscarinic cholinergic receptors by carbachol exerted a stimulating effect on the alpha 1-adrenergic contractile response especially to low adrenomimetic concentrations and the maximum response was increased. The action of cholinomimetic was accompanied by a decrease of Hill coefficient. When the control represented a single pool of alpha 1-adrenoceptors in the presence of carbachol Scatchard plot became biphasic with Hill coefficient n < 1, in addition to the low affinity pool the high affinity appeared. In case of not homogeneous control pool, in the presence of carbachol a single pool was revealed and n was close to 1. These findings suggest that the stimulatory effect of carbachol is caused by its modulator action on the alpha 1-adrenoceptors states and activating influence on the intracellular effector's system.