Aging effects on contractility of longitudinal and circular detrusor and trigone of rat bladder.
OBJECTIVE
Aging is associated with bladder dysfunction, including difficult voiding and urinary leakage. Voiding involves reduction in the bladder lumen in all dimensions brought about by contraction of the meshwork of longitudinal, circular and oblique layers of detrusor smooth muscles. Most in vitro physiological studies of the effects of aging on bladder function used the longitudinal detrusor. To understand the region specific effects of aging on bladder function the contractile responses of longitudinal and circular detrusor, and trigone segments of the bladder from young and old rats were monitored.


METHODS
These studies were performed using male Fisher 344 rats 6 months (young) and 27 months (old) old obtained through the National Institute on Aging. Each rat was anesthetized and the bladder was isolated. From each bladder a strip of longitudinal detrusor, circular detrusor and trigone was isolated and mounted in an in vitro multi-muscle chamber containing normal physiological solution at 37C. Isometric contractions of the 3 bladder strips were monitored after electrical field stimulation, 120 mM. potassium and 1 to 1,000 microM. bethanechol using a digital oscilloscope.


RESULTS
In longitudinal detrusor from old rats there was no significant difference in the contractions evoked by electrical stimulation or high potassium but there was a significant reduction in contractions evoked by bethanechol compared with the responses of longitudinal detrusor from young rats. In circular detrusor from old rats there was a significant increase in contractions evoked by electrical stimulation and a slight increase in contractions produced by high potassium but no significant change in contractions evoked by bethanechol compared with the responses of circular detrusor from young rats. In trigone from old rats there was a significant decrease in contractions evoked by electrical stimulation, high potassium and bethanechol compared with young trigone.


CONCLUSIONS
The reduction in contractions evoked by bethanechol suggests an age related reduction in muscarinic receptors in the longitudinal detrusor of aged rats. An increase in contractions evoked by electrical stimulation without a change in contractions evoked by bethanechol suggests a decrease in compliance caused by an increase in collagen in the circular detrusor of aged rats. A general decline in all contractile responses, including those evoked by high potassium, suggests reduced membrane depolarization in the trigone of aged rats. The effect of aging is specific to different regions and functional components of the bladder, probably due to changes in muscarinic receptors, collagen and depolarization.
Pagala
M K
MK
Neuromuscular Research Laboratory, Division of Urology, Department of Surgery, Maimonides Medical Center, Brooklyn, New York 11219, USA.
Tetsoti
L
L
Nagpal
D
D
Wise
G J
GJ
D000375:Aging / Q000502:physiology*; D000818:Animals; D018723:Bethanechol / Q000494:pharmacology; D003094:Collagen / Q000032:analysis; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000503:physiopathology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344; D011976:Receptors, Muscarinic / Q000187:drug effects; D001743:Urinary Bladder / Q000187:drug effects / Q000503:physiopathology*
D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D018723:Bethanechol; D003094:Collagen; D011188:Potassium