射精の研究

第6報 射精時における内尿道口の閉鎖の末梢機構について

抄録

The effects of autonomic drugs on closure of the internal urethral orifice during ejaculation were investigated in dogs.
Methods and materials. The closure of the internal urethral orifice was measured with latex balloon inserted into the orifice. Seminal emission and ejaculation were measured with posterior urethrogram. In this study the nerve fibers descending on the anterior wall of the aorta into the plexus were tentatively named as the central branch of the lower mesenteric. plexus and fibers entering from the lateral portion into the plexus as the lateral branch of the plexus. These two groups of the fibers were cut and the peripheral end of the cut fibers were electrically stimulated with square waves of 2 msec, 10Hz and 2V. To cause closure of the internal urethral orifice, the lateral branch was stimulated with above-mentioned condition for 3sec in every 20sec. And to cause seminal emission and ejaculation the central branch was stimulated continuously.
The autonomic drugs were given into the aorta just above its bifurcation.
The results obtained are as follows:
1) Effect of α-adrenergic drugs. Administration of phenylephrine (α-stimulant), 10-100μg, caused closure of the internal urethral orifice and phentolamine (α-blocker), 1-10mg, suppressed the closure. Seminal emission was suppressed completely by phentolamine, and rhythmic alterations of posterior urethral pressure, which is considered as ejaculation, were also abolished. With α-stimulant the rhythmic alterations were induced.
2) Effects of β-adrenergic drugs.
Isoproterenol (β-stimulant), 10-30μg, depressed the closure of the internal urethral orifice and propranolol (β-blocker), 1-10mg strengthened it. But these depressing and strengthening effects are thought to be pretencious phenomena.
Seminal emission and the rhythmic alterations of the posterior urethral pressure did not show any significant change after administration of the β-stimulant and β-blocker.
3) Effects of cholinergic and anticholinergic drugs.
Acetylcholine (1-10μg) and atropine (1-10μg) did not show any significant effect on closure of the internal urethral orifice as well as seminal emission and rhythmic alteration of the posterior urethral pressure.
4) Effects of ganglion stimulant and blocker.
Closure of the internal urethral orifice was strengthened by DMPP (10-30μg), and was suppressed by hexamethonium (100-500μg). No significant effect on seminal emission or the rhythmic alterations were observed.
From these results it is concluded that the internal urethral orifice during ejaculation as well as seminal emission and ejaculation is predominantly under the control of α-adrenergic receptor mechanism.