Ranitidine inhibits adrenergic transmission in the rat isolated anococcygeus muscle.
1. The effects of ranitidine on adrenergic transmission in the rat isolated anococcygeus muscle were investigated. 2. Cumulative doses (2-8 mmol/L) or 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 mumol/L). The inhibited motor responses recovered rapidly and completely after washing out ranitidine. 3. 4-Aminopyridine (100 mumol/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.
Gwee
M C
MC
Department of Pharmacology, Faculty of Medicine, National University of Singapore, Lower Kent Ridge.
Cheah
L S
LS
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D003864:Depression, Chemical; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000294:innervation*; D009638:Norepinephrine / Q000494:pharmacology; D011899:Ranitidine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013564:Sympathetic Nervous System / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*
D011899:Ranitidine; D015761:4-Aminopyridine; D009638:Norepinephrine