Urodynamic Analysis of Age-Related Changes of alpha sub 1 -Adrenoceptor Responsiveness in Female Beagle Dogs

Purpose

We have evaluated age-related changes of alpha₁-adrenoceptor responsiveness in the lower urinary tract of female beagle dogs by urodynamic analyses.

Materials and Methods

Six aged parous and 6 young nonparous female beagle dogs were studied. Mean ages (plus/minus standard error of the mean) of the 2 groups were 68.3 plus/minus 2.3 and 12.4 plus/minus 0.08 months. Before and after 4 administrations of alpha₁-adrenoceptor agonist (midodrine hydrochloride 0.03, 0.1, 0.3 and 1.0 mg./kg. intravenously), cystometry, urethral pressure profilometry and external urethral sphincter electromyography were performed.

Results

After 0.3 mg./kg. midodrine administration, mean bladder capacity in the aged dogs significantly decreased, compared with that in the young dogs (p less than 0.05). After the minimum dose administration (0.03 mg./kg.), the urethral closing pressure in both groups increased significantly (p less than 0.05) with no changes in bladder capacity or arterial blood pressure. The proximal urethral closing pressure in the aged dogs increased dose dependently. After administration of 1.0 mg./kg. drug it reached 257 percent of the initial values (p less than 0.01), which was significantly greater than that in the young dogs (p less than 0.05).

Conclusions

These findings suggest that 1) age-related increase of alpha₁-adrenoceptor responsiveness occurs in the bladder and in the proximal urethra. The former may be one of the etiologies of detrusor instability in the elderly. 2) A lower dose of midodrine hydrochloride may be useful for the treatment of stress incontinence, independent of age.