Avaliação in vitro do efeito relaxante de inibidores de fosfodiesterases e agonista beta-adrenérgico em bexiga de camundongos utilizando modelo experimental de hiperatividade detrusora.

Abstract

Overactivity bladder syndrome has classically been treated with antimuscarinics. However, frequent adverse systemic effects have led to the search for new therapeutic options. β3- adrenoceptor (β3-AR) agonists relax the detrusor smooth muscle (DSM) by the adenylyl cyclase pathway, increasing cyclic adenosine monophosphate (cAMP). Rolipram, a selective type 4 phosphodiesterase inhibitor (IPDE4), elevates intracelular cAMP levels by supressing hydrolysis. Phosphodiesterase type 5 inhibitors (IPDE5), such as tadalafil, relax DSM by the nitric oxide/cyclic guanosine monophosphate pathway (NO/cGMP). It has been hypothesized that the inhibition of phophodiesterases could potentiate the relaxing effect of β3-AR agonists. The main objective of this study is to evaluate in vitro the effects of the combination of a β3-AR agonist with two different phosphodiesterase inhibitors (IPDE4 and IPDE5) in a experimental model of detrusor overactivity. The experiments were performed on bladder strips of mice and divided in two phases. The following drugs were used: BRL 37344 (β3-AR agonist), tadalafil (IPDE5) and rolipram (IPDE4). In the first phase, after potassium-induced contraction, strips isolated from naive mice were exposed to increasing concentrations of each study drug. In another series of experiments, prior to contraction, strips were incubated with either tadalafil or rolipram and then increasing concentrations of BRL 37344 were added. In the second phase, the same protocol was performed with animals treated with L-NAME for 30 days. Chronic L-NAME administration leads to detrusor overactivity by NO deprivation. Cumulative concentration-response curves were constructed. In the first phase, preincubation with tadalafil increased the relaxing response of BRL 37344 in two concentrations. Pretreatment with rolipram had no effect on the relaxation obtained with BRL 37344. In LNAME- treated mice, rolipram showed the best relaxation when compared to the other drugs. In these animals, rolipram increased the relaxing response of BRL 37344 in almost all concentrations, but no synergistic effect with tadalafil was observed. Phosphodiesterase inhibitors associated with the already proven effective β3-AR agonists may represent a new approach for patients with storage symptons. In our experimental model, the relaxing effect of the β3-AR agonist was potentiated by IPDE4 but not by IPDE5, suggesting cAMP plays an important role in DSM relaxation. Keywords: Detrusor smooth muscle. β3-adrenoceptor agonist. Phosphodiesterase inhibitors.