Increased alpha1D adrenergic receptor activity and protein expression in the urinary bladder of aged rats.
A possibility that aging affects (a) expression of the alpha1D-adrenergic receptor (AR1D), (b) AR1D-mediated contractions and (c) sympathetic innervation in the urinary bladder in rats was studied. Contraction produced by phenylephrine and inhibition of these contractions by a non-selective alpha1-adrenergic antagonist prazosin and a selective AR1D antagonist BMY7378 were compared between 6- and 24-month-old Fisher rats. Expressions of VMAT and AR1D in the bladder were assessed by immunofluorescence and Western blot. Phenylephrine-induced contractions were larger and inhibition of these contractions by BMY7378 was significantly greater in 24-month-old rats. Aging increased expression of AR1D in the bladder. Density of VMAT-immunoreactive neurites was decreased in smooth muscle but elevated in the suburothelial region of 24-month-old rats. The results suggest that influence of adrenergic activity on bladder contractility increases with aging is due to overexpression of the AR1D. Influence of adrenergic activity on the urothelial function may also be enhanced with aging.