Ranitidine inhibits adrenergic transmission in the rat isolated anococcygeus muscle

Abstract

1. The effects of ranitidine on adrenergic transmission in the rat isolated anococcygeus muscle were investigated. 2. Cumulative doses (2-8 mmol/L) of ranitidine produced a concentration-dependent inhibition of motor responses of the rat isolated anococcygeus muscle evoked by field stimulation (20-25 V, 10 Hz for 10 s, 1 ms pulse width) every 2 min, but also potentiated the contractile response to exogenous noradrenaline (5 μmol/L). The inhibited motor responses recovered rapidly and completely after washing out ranitidine. 3. 4-Aminopyridine (100 μmol/L) effectively reversed the partially inhibited (55% or greater) motor responses. 4. The results strongly suggest that ranitidine can inhibit adrenergic transmission in the anococcygeus muscle by a prejunctional mechanism with, presumably, consequent development of supersensitivity of the effector cells to noradrenaline.