Selective changes in the <i>α</i>-adrenoceptor-mediated contraction in the senescent rat urinary bladder

Abstract

The urinary bladder is innervated and functionally regulated by the autonomic nervous system. In order to elucidate the mechanism of functional changes in aged rat urinary bladder, we studied the influence of senescence on, 1) the α-adrenergic contractile response to phenylephrine in the urinary bladder body and trigone, 2) the muscarinic contractile response to carbachol in the body and trigone. The binding characteristics of [ 3 H]quinuclidinyl benzilate (QNB) to muscarinic cholinoceptors were compared in young and aged bladder. Bladders from young (2 -3 month-old) and aged (27 month-old) male Fischer 344 rats were isolated, cut into strips and mounted in the organ bath, then the developed tension was recorded. Histologically, the aged bladder did not show pathologic changes such as inflammation and hypertrophy. Carbachol-induced contraction in aged rat bladder was identical to that obtained in young rat. In the receptor binding assay, [ 3 H]QNB maximal binding capacity and Kd value were not significantly changed in aged bladder. In contrast, a selective α-adrenergic agonist phenylephrine, elicited greater contractions both in the aged body and trigone than those in young rats. The augmentation of α-adrenoceptor-mediated contractions in aged bladder may induce urinary dysfunction such as voiding difficulty.

Differences between young and aged rats in voiding frequency and detrusor muscle serotonergic contraction

“…The maximal urine flow rate and contraction of detrusor smooth muscle are decreased, while the voiding frequency and the residual volume are increased with aging (Homma et al, 2006;Pfisterer et al, 2006). A previous study reported an increase in smooth muscle cell hypertrophy and fibrosis in the bladder of aged rats (Aita et al, 2012). Consequently, hypertrophy and fibrosis of muscle cells by aging could be the reason why bladders of aged rats were heavier in our study.…”