Involvement of the adrenal medulla in ejaculatory reactions in the dog

To explore the peripheral signal controlling ejaculatory reactions, contraction of the seminal tract and seminal emission were monitored in the dog during electrical stimulation of the lumbar and greater splanchnic nerves in the presence or absence of sympathetic pathways connecting the lumbar sympathetic trunk to the seminal tract including the vas deferens, prostate and bladder neck. Electrical stimulation of the lumbar splanchnic nerve caused seminal emission, elevation of intraluminal pressure of the vas deferens and bladder neck, and contraction of the prostate without elevation of blood pressure. Transection of all peripheral sympathetic nerve pathways to the seminal tract completely blocked these responses. Electrical stimulation of the greater splanchnic nerve caused a marked elevation of blood pressure as well as the responses described above in both the presence and absence of peripheral sympathetic nerve pathways to the seminal tract. However, clamping the adrenal veins bilaterally blocked all of the above responses and declamping immediately reversed the block. Serum levels of epinephrine, norepinephrine and dopamine were significantly increased by electrical stimulation of the greater splanchnic nerve, while cortisol levels remained unchanged. Furthermore, intravenous administration of epinephrine (5 μg/kg) caused responses similar to those elicited by stimulating the greater splanchnic nerve. Dogs in which all sympathetic pathways to the seminal tract had been transected chronically showed retrograde ejaculation during manual penile stimulation. The above results indicate possible involvement of the greater splanchnic nerve and adrenal medulla in ejaculatory reactions in the dog.