The role of the urothelium in mediating bladder responses to isoprenaline.
OBJECTIVE
To investigate whether the responses of the pig bladder to isoprenaline (a nonselective beta-adrenoceptor agonist) are influenced by the presence of an intact urothelium and whether any influence might be attributed to the release of nitric oxide (NO), since stimulation of beta-adrenoceptors induces a direct relaxation of detrusor smooth muscle and beta-adrenoceptors are also present on the urothelium.


METHODS
Paired (in the presence or absence of urothelium) longitudinal strips of pig bladder dome were set up in tissue baths and the developed tension recorded. Relaxation responses to isoprenaline were examined after pre-contraction with carbachol. The inhibitory effects of isoprenaline were examined by comparing responses to carbachol in the absence and presence of isoprenaline. To examine a possible role for NO, similar experiments were performed in the presence of the NO synthase inhibitor N(G)-nitro-L-arginine (L-NNA).


RESULTS
In the presence of the urothelium, both the potency (pEC(50)) and the maximum contractile responses to carbachol were depressed. In relaxation experiments, isoprenaline relaxed carbachol pre-contracted tissues by approximately 75%, and the potency and maximum relaxation were similar in the absence and presence of the urothelium. In the inhibition experiments, the presence of isoprenaline caused rightward parallel shifts of the concentration-response curves to carbachol, but isoprenaline did not influence the maximum contractions. In the presence of the urothelium there was a greater shift with 0.1 microm isoprenaline than in denuded tissues. Incubation with L-NNA did not affect the influence of the urothelium on responses to isoprenaline in any experimental group.


CONCLUSIONS
The relaxation responses of the bladder to isoprenaline do not appear to involve the urothelium or NO release in vitro. However, contractile responses to carbachol were inhibited in the presence of an intact urothelium, and this might reflect the release of an inhibitory factor other than NO.
Murakami
Shigetaka
S
Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield, UK.
Chapple
Christopher R
CR
Akino
Hironobu
H
Sellers
Donna J
DJ
Chess-Williams
Russell
R
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D007545:Isoproterenol / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism*; D013552:Swine; D001743:Urinary Bladder / Q000187:drug effects* / Q000502:physiology; D019459:Urothelium / Q000187:drug effects* / Q000502:physiology
D000318:Adrenergic beta-Agonists; D009569:Nitric Oxide; D007545:Isoproterenol