Effect of experimental diabetes on cholinergic, purinergic and peptidergic motor responses of the isolated rat bladder to electrical field stimulation or capsaicin

Abstract

An attempt has been made to pharmacologically isolate cholinergic, P 2 purinoceptor-mediated and peptidergic (capsaicin-sensitive, tachykinin-mediated) contraction of the guanethidine-treated rat bladder detrusor preparation, in vitro. The effect of experimental diabetes was assessed on these types of contraction. Responses were evoked by electrical field stimulation (single shocks or 1 Hz for 30 s or 10 Hz for 40 s). Single shocks and 1-Hz stimulation were applied in the presence of (a) atropine (1 μM) or (b) P 2 purinoceptor antagonists (50 μM pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid) [PPADS] plus 100 μM suramin. Long-term electrical field stimulation (10 Hz for 40 s) (c) was applied with both atropine and the P 2 purinoceptor antagonists present in the organ bath. The effects of capsaicin (d) and ATP (e) were also studied. Three groups of experimental animals were used: streptozotocin-treated (50 mg·kg −1 i.p., 8 weeks before the experiment), parallel solvent-treated and untreated rats. (a) Responses to electrical field stimulation in the presence of atropine were reduced by half by PPADS plus suramin, but were resistant to capsaicin tachyphylaxis. They were enhanced in preparations taken from diabetic rats. (b) Contractions to electrical field stimulation in the presence of PPADS plus suramin were reduced by 2/3 by atropine, but were left unchanged by capsaicin or diabetes. (c) Contractions to long-term stimulation had a quick and a sustained phase. Especially the latter was inhibited by capsaicin tachypyhlaxis; it was also strongly reduced in preparations taken from diabetic rats. (d) Contractions to capsaicin (30 nM and 1 μM) were resistant to tetrodotoxin, strongly reduced by a combination of tachykinin NK 1 and NK 2 receptor antagonists, and slightly reduced in preparations from diabetic animals. Capsaicin (1 μM) had no acute inhibitory action on cholinergic or purinergic responses, nor did it cause relaxation in precontracted preparations treated with tachykinin receptor antagonists. (e) ATP-induced contractions were strongly reduced by PPADS plus suramin (50 plus 100 μM) and to a similar degree by 100 plus 200 μM, respectively. It is concluded that experimental diabetes selectively impairs peptidergic, capsaicin-sensitive responses (especially those that involve impulse conduction) in the rat detrusor preparation. The contractile response to electrical field stimulation that remains after atropine plus the P 2 purinoceptor antagonists has a yet unknown transmitter background.