Dual effects of clonidine on micturition reflex in urethane anesthetized rats.

The effects of clonidine (CLO) on reflexly activated bladder motility have been examined in urethane-anesthetized rats and compared to its effects on field stimulation-induced contractions of isolated urinary bladder. Intravenous CLO suppressed micturition reflex transiently in a yohimbine-sensitive manner. The suppressive effect of i.v. CLO was greater after surgical sympathectomy (bilateral section of the hypogastric nerves). Intracisternal CLO was more effective than topical (on the bladder dome) or intracerebroventricular CLO in suppressing micturition. When tested in experimental conditions involving activation of both excitatory and inhibitory reflexes to the bladder CLO produced either inhibitory and/or excitatory effects on bladder motility in dependence of factors such as dose, route of administration and integrity of the sympathetic (inhibitory) innervation to the bladder. CLO suppressed bladder contractions produced by dimethylphenilpiperazinium, a ganglionic stimulant, and reduced those produced by postganglionic nerve stimulation. CLO inhibited, in a yohimbine-sensitive manner, amplitude of field stimulation-induced contractions of isolated rat bladder, and its effectiveness was inversely related to the frequency of stimulation. Our findings are suggestive that the inhibitory action of CLO on micturition reflex is counteracted, in normal animals, by a negative feedback on sympathetic inhibitory influences carried out through the hypogastric nerves.