Urodynamic action of clonidine in the chronic spinal cat

Abstract

AbstractSpinalization produces a central micturition dysreflexia characterized by weak vesical contraction reflexes and by an exaggerated urethro‐urethral contraction reflex, causing the peripheral syndromes of underactive detrusor and detrusor‐sphincter dys‐synergia. We explored the action of catecholaminergic drugs of central action on these micturitional dysfunctions.Twenty‐four male cats were spinalized by transection of the spinal cord at C5–C6 level and studied 1–18 weeks later. Cystosphincterograms were performed without using anesthetic drugs. Pves, Pura, the EMG of the external sphincter, the EMG of the extensor hindleg muscles, and urine emission were studied. The responses of the spinal vesicovesical contraction, urethro‐vesical contraction, and urethro‐urethral contraction reflexes were explored. Clonidine (0.02–0.06 mg/kg intravenously [IV], intraperitoneally [IP], or per os), phentolamine (0.7–1 mg/kg, IV), and yohimbine (0.4–1 mg/kg, IV) were administered.Clonidine, at doses of 0.02 mg/kg, IV or IP, or higher, produced the following effects: (1) it significantly increased the intensity and duration of Pves waves; (2) it inhibited the spasms of the external sphincter; (3) it induced voiding; (4) it reduced spasticity; (5) it reinforced the vesico‐vesical contraction reflex; (6) it antagonized the exaggeration of the urethro‐urethral contraction reflex; (7) it corrected totally or partially the underactive detrusor and detrusor‐sphincter dys‐synergia. Taken orally (0.02–0.03 mg/kg) the urodynamic effect of clonidine was not significant; higher doses produced vomiting and other adverse effects. The action of clonidine was blocked by yohimbine but not by phentolamine.These results suggest that the absence of the descending noradrenergic pathways plays a role in the physiopathology of neurogenic bladder dysfunctions in chronic spinalized cats.