Supersensitivity in the Isolated Urethra of the Rat Following “Chemical Sympathectomy”

The circular muscle activity of the urethra of the male rat was isometrically measured in vitro in response to noradrenaline, phenylephrine and isoprenaline. The urethra was found to be supplied with both alpha- and beta-adrenoceptors mediating contraction and relaxation, respectively. The substance 6-hydroxydopamine is known to cause a selective destruction of adrenergic nerves. In the present study 6-hydroxydopamine (100 mg/kg) was injected intravenously into a group of rats twice with a weekly interval. When the urethra was examined 2-3 weeks after the first injection a supersensitivity mediated both via alpha- and beta-adrenoceptors was found to have developed, suggesting that the urethra of the male rat normally is under the influence of adrenergic activity. The findings are discussed in relation to denervation supersensitivity of the neurogenic bladder in man.