Inhibitory Action of Propranolol on the Contractions Induced by Nerve Stimulations or Calcium in the Smooth Muscle of Rat Vas Deferens

Inhibitory effects of propranolol on the contractions to various treatments were investigated in the epididymal half of the rat vas deferens. Reportedly, 10-5 ?? 3×10-4 M propranolol inhibited 150 mM K-induced contractions dose-dependently; 3×10-4 M propranolol abolished the contractions. The present results showed that propranolol at concentrations up to 10-4 M did not inhibit the maximal contractions to 10-3 M norepinephrine (NE) or 10-2 M methacholine (MCh). Propranolol at 3×10-4 M slightly inhibited contractions to NE and MCh by 11% and 12%, respectively. In contrast, propranolol inhibited twitch components of the contractions induced by nerve stimulations at similar doses to those reported for high K contractions. Propranolol also inhibited contractions to Ca in high K-containing solution and shifted the dose-response curve to the right. Propranolol did not affect the depolarizations by high K measured by microelectrodes. Propranolol at concentrations of 10-5 ?? 3×10-5 M diminished the magnitude of spikes dose-dependently. Spikes were rarely observed in the presence of 10-4 M propranolol in spite of generation of e.j.p.s with amplitudes that would be sufficient to induce spikes in the absence of propranolol. These results suggest that propranolol inhibits contractions by decreasing Ca-influx through the potential-operated Ca-channels in the smooth muscle cells of rat vas deferens.