[Roles of sacral spinal alpha-adrenoceptive mechanism in micturition reflex in the decerebrate dog].

Roles of sacral spinal alpha-adrenoceptive mechanism in micturition reflex were examined in 19 decerebrate dogs. Alpha 1- and alpha 2-adrenergic agents were injected into the sacral subarachnoidal space. Micturition reflex was evoked by filling the bladder before and after the drug injection. The intravesical pressure (IVP), the intraurethral pressure (IUP) and the electromyogram (EMG) of the external urethral sphincter muscle (EUS) were recorded simultaneously. The bladder volume, the IVP at the threshold of micturition reflex, the minimum IUP, the maximum IUP and the mean IUP were measured during collecting phase. The maximum IVP and the minimum IUP were measured during contraction phase. The effects of adrenergic agents on these measured parameters were analyzed using Wilcoxon's test. The changes of the EUS-EMG were also studied. Intrathecal injection of phenylephrine, an alpha 1-agonist, significantly increased the bladder volume and the mean IUP during the collecting phase, and tended to enhance the EUS-EMG during both phases. Intrathecal injection of prazosin, an alpha 1-antagonist, tended to diminish the EUS-EMG during both phases. Intrathecal injection of clonidine, an alpha 2-agonist, significantly decreased the minimum IUP, the maximum IUP and the mean IUP during the collecting phase, and tended to diminish the EUS-EMG during both phases. Intrathecal injection of yohimbine, an alpha 2-antagonist, decreased the maximum IVP during the collecting phase significantly. These results suggest that the sacral alpha-adrenoceptive mechanism mediates elevation of the threshold of micturition reflex and facilitation of the EUS activity via alpha 1-receptor, while facilitation of the bladder contractility and inhibition of the EUS activity via alpha 2-receptor.