[Alpha adrenergic mechanism on the reflex micturition in the male decerebrate dog]

We investigated the alterations of urodynamic parameters of reflex micturition evoked by filling the bladder with physiological saline prior to and after the administration of midodrine (alpha 1 agonist), terazosin (alpha 1 antagonist), clonidine (alpha 2 agonist) and yohimbine (alpha 2 antagonist) in 28 male decerebrate dogs. The significant finding produced by midodrine was an increase in contraction pressure, while terazosin produced a significant decrease in threshold pressure, contraction pressure and urethral pressure. Clonidine produced a decrease in threshold pressure, urethral pressure and external urethral sphincter activity, while yohimbine produced a significant increase in bladder volume and urethral pressure. It seems that alpha 1 adrenergic activity modulates urethral closing pressure via postsynaptic alpha 1 receptors, and that alpha 2 adrenergic activity mainly modulates urethral closing pressure via presynaptic alpha 2 receptors in the lower urinary tract function.