Role of alpha-adrenergic receptor mechanism in closure of the internal urethral orifice during ejaculation.

The effects of autonomic drugs on closure of the internal urethral orifice during ejaculation were investigated in dogs. The closure of the internal urethral orifice was induced by the electric stimulation of the lateral fibers of the lower mesenteric plexus. The closing state of the orifice was measured with a latex balloon inserted into the orifice. The autonomic drugs were given into the aorta just above its bifurcation. From the results obtained in this study it was concluded that the closure of the internal urethral orifice during ejaculation is predominantly under the influence of the adrenergic nervous system, particularly through an alpha-adrenergic receptor mechanism.