Some pharmacological properties of the circular smooth muscle layer of the rat vas deferens

Vas deferens preparations were perfused in-vitro through the lumen and externally with a modified Tyrode solution alone or containing drugs. Contractions of the circular (internal) smooth muscle layer were recorded as changes in the pressure of internal perfusion. Contractions of the longitudinal (external) layer were simultaneously recorded through a tension transducer. When the organ was perfused through the lumen, the circular layer contracted after addition of methacholine (pD2 = 4.13), and noradrenaline (pD2 = 5.00), and relaxed after addition of isoprenaline (pD2 = 5.22). These effects were also observed when the drugs were perfused externally, although with lower values of pD2 for noradrenaline and methacholine. The circular fibres were less sensitive when compared with the longitudinal fibres perfused externally with the above agonists. Methacholine-induced contractions of the circular layer were competitively antagonized by atropine (pA2 = 8.53), indicating the presence of muscarinic receptors. The effects induced by noradrenaline and isoprenaline were antagonized by indoramin (pA2 = 7.78), and timolol (pA2 = 8.68), respectively, indicating the presence of alpha- and beta-adrenoceptors. The effect of noradrenaline was potentiated by cocaine and denervation, indicating the presence of neuronal uptake, and by corticosterone, indicating the presence of extraneuronal uptake in the circular layer.