Study On The Effects And Molecular Mechanism Of Beta3-adrenoceptor Subtypes Mediated Rat Detrusor Relaxation

Frequency, urgency and incontinence induced by detrusor dysfunction are the common problems, and detrusor instability (DI) is the main cause of detrusor dysfunction. The pathogenesis leading detrusor instability is still unclear. Many neurotransmitters, including acetycholine, noradrenaline, ATP, VIP and substance P commonly take part in accomplishing bladder delicate and complex function. Detrusor excitability, contractility and compliance are the main agents influencing bladder function. The cholinergic receptor is known to be the key receptor to the contraction of bladder, but the anticholinergic drugs in the treatment of DI is not satisfactory and the side effects is obvious. β-adrenoceptors (β-AR)is the most important agent contributing to bladder relaxation, and much evidence suggest that there were three β-AR subtypes-β1-AR, β2-AR andβ3-AR in detrusor cells. The distribution of the variousβ-AR subtypes is not homogeneous among the detrusor of different mammalian species. To our knowledge the major portion of the relaxation effects of β-adrenoceptors is mediated via β3-AR in human and rat detrusor. In the present, much study were performed at two aspects: First, by investigated the subtypes ofβ-AR mediated relaxation of detrusor based on pharmacological evaluations. Second, researching the expression ofβ-AR subtypes and its mRNA in the urinary bladder. Until now it is not clear that the distribution ofβ-AR subtypes in bladder of differently species, and because the different distribution and function amongβ-AR subtypes maybe attributed to their different molecular mechanism, we investigated the mechanism of β3-AR mediated detrusor relaxation must under subtypes level, but there seems to be no information on the mechanism of the relaxation effect mediated by β3-AR in bladder smooth muscle and the relationship between β3- adrenoceptors and detrusor instability.Object: aim at to comprehend the effects and mechanism of β3-adrenoceptor subtypes mediated rat detrusor relaxation, we would to study the following: 1. to observe the effects of β-AR subtypes on normal rat detrusor contractility and excitability. 2. to investigate the expression of β-adrenoceptor subtypes in rat dutrusor with RT-PCR and radioligand binding assay. 3. to observe the effect of detrusor instability secondary to bladder outflowobstruction(BOO) on the density and detrusor contractility, excitability and compliance ofβ3-adrenoceptors in the rat bladder. 4.we should discuss the molecule mechanism of beta3- adrenoceptor subtypes mediated rat detrusor relaxation, to provide theoretical and experimental evidences for clinical therapy.The main results and conclusions were as follows:1. The relaxation response produced by β-AR subtypes agonists or antagonists were examined by means of the in vitro detrusor strip study. The selectiveβ1,β2 and β3-AR agonist can caused concentration-dependent relaxations of the detrusor muscles. The relaxant response to isoproterenol were antagonized by the β1-,β2-AR antagonists (100μM) and theβ3-AR antagonists SR59230(1μM). It is indicated that all ofβ-AR subtypes mediate relaxation, and β3-AR is the main receptor mediating detrusor relaxation.2. Detrusor stripes could be contracted at definite tension, and there were no obviously changes while the detrusor stripes stimulated by differentβ-adrenoceptor subtypes antagonists, which means the excitability of detrusor is not the β-adrenoceptors. β- adrenoceptor subtypes agonists can decrease the contraction frequence of the isolated detrusor, and their effects were chiefly mediated via β3-adrenocepotrs. It is suggested that β3-adrenoceptors may play a role in detrusor instability.3. RT-PCR revealed all three subtypes of β-AR mRNA to be expressed in rat detrusor smooth muscles, the rate of β3-AR mRNA was 70%. The result confirmed thatβ3-AR is the main β-AR subtypes in rat bladder detrusor. 4. β3-AR subtypes density in bladder was firstly measured by radioligand binding assay. The result showed that th...