Urodynamic analysis of age-related changes of alpha 1-adrenoceptor responsiveness in female beagle dogs.
OBJECTIVE
We have evaluated age-related changes of alpha 1-adrenoceptor responsiveness in the lower urinary tract of female beagle dogs by urodynamic analyses.


METHODS
Six aged parous and 6 young nonparous female beagle dogs were studied. Mean ages (+/- standard error of the mean) of the 2 groups were 68.3 +/- 2.3 and 12.4 +/- 0.08 months. Before and after 4 administrations of alpha 1-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 < 0.05). After the minimum dose administration (0.03 mg./kg.), the urethral closing pressure in both groups increased significantly (p < 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% of the initial values (p < 0.01), which was significantly greater than that in the young dogs (p < 0.05).


CONCLUSIONS
These findings suggest that 1) age-related increase of alpha 1-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.
Takahashi
S
S
Department of Urology, Faculty of Medicine, University of Tokyo, Japan.
Moriyama
N
N
Yamazaki
R
R
Kawabe
K
K
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000375:Aging / Q000502:physiology*; D000818:Animals; D004285:Dogs; D005260:Female; D008879:Midodrine / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000502:physiology*; D014521:Urethra / Q000502:physiology; D001743:Urinary Bladder / Q000502:physiology; D014563:Urodynamics / Q000502:physiology*
D000316:Adrenergic alpha-Agonists; D011942:Receptors, Adrenergic, alpha; D008879:Midodrine