Effects of Aging on Urethral Function in the Male Rat

Kwon, Sung Dae; Lee, Jeong Gu

Abstract

Many symptoms of age related bladder dysfunction may be associated with urethral dysfunction. We compared the contractile responsiveness of urethral strips from young adults (6-9 months) and old (24-27 months) male Fisher 344 rats. Circularly and longitudinally oriented urethral strips from proximal (bladder neck) and distal urethra were obtained and suspended in organ baths containing Tyrodes buffer. Contractile responses to field stimulation (FS), phenylephrine, bethanechol and KC1 were recorded. Results were as followed: 1. Contractile responses of proximal urethral strips from old rats to FS, bethanechol, phenylephrine, KCI were greater than those of young rats. In young rats, general order of responsiveness was FS >KC1 = phenylephrine >bethanechol. In old rats, it became FS >bethanechol >KCI = phenylephrine. 2. Magnitude of the contractile responses for distal urethral strips were significantly lower than for proximal urethra and there were no significant differences of the responses between two age group. 3. For the circularly oriented strips, responses of old rats to FS, bethanechol, phenylephrine and KC1 also were greater than those of young rats. In young rats, general order of responsiveness was FS>KCl =phenylephrine =bethanechol. In old rats, it became FS>bethanechol >KC1 >phenylephrine. 4. For the longitudinally oriented strips, responsiveness to FS and bethanechol was similar between younger and old rats. However, responses to phenylephrine were greater for young rats than for old ones. For both young and old rats, general order of contractile responsiveness was FS>phenylephrine=KCl>bethanechol, In old rats contractile responses of proximal, circular urethral strips to various stimulation were greater than those in young ones. 5. Degree of field stimulated relaxant responses of the urethra precontracted by phenylephrine were similar between two age groups at higher frequencies(16-64 Hz.): whereas higher degrees of relaxation were observed in young rats at lower frequencies(1-8 Hz.). Circularly oriented urethral strips showed better relaxation with FS than did longitudinal ones. Relaxant responses were only partially (50%) blocked by preincubation of L-NAME. These results suggest that as male became older, their urethra responds to various stimulation with obstructive pattern than did the younger ones and also, lesser degree of urethral relaxation may causes obstructive voiding due to poor Opening of bladder outlet. Also it can be said that the ratio of the receptor density of cholinergic and adrenergic nerves varies as one become old.