Mirabegron relaxes urethral smooth muscle by a dual mechanism involving ß3 -adrenoceptor activation and α1 -adrenoceptor blockade.

LINKED ARTICLE: This article is commented on by Michel, M. C., pp. 429-430 of this issue. To view this commentary visit http://dx.doi.org/10.1111/bph.13379. BACKGROUND AND PURPOSE: Mirabegron is the first ß3 -adrenoceptor agonist approved for treatment of overactive bladder syndrome. This study aimed to investigate the effects of ß3 -adrenoceptor agonist mirabegron in mouse urethra. The possibility that mirabegron also exerts α1 -adrenoceptor antagonism was also tested in rat smooth muscle preparations presenting α1A - (vas deferens and prostate), α1D - (aorta) and α1B -adrenoceptors (spleen). EXPERIMENTAL APPROACH: Functional assays were carried out in mouse and rat isolated tissues. Competition assays for the specific binding of [(3) H]prazosin to membrane preparations of HEK-293 cells expressing each of the human α1 -adrenoceptors, as well as ß-adrenoceptor mRNA expression and cyclic AMP measurements in mouse urethra, were performed. KEY RESULTS: Mirabegron produced concentration-dependent urethral relaxations that were shifted to the right by the selective ß3 -adrenoceptor antagonist L-748,337 but unaffected by ß1 - and ß2 -adrenoceptor antagonists (atenolol and ICI-118,551 respectively). Mirabegron-induced relaxations were enhanced by the PDE4 inhibitor rolipram, and the agonist stimulated cAMP synthesis. Mirabegron also produced rightward shifts in urethral contractions induced by the α1 -adrenoceptor agonist phenylephrine. Schild regression analysis revealed that mirabegron behaves as a competitive antagonist of α1 -adrenoceptors in urethra, vas deferens and prostate (α1A -adrenoceptor, pA2  â‰… 5.6) and aorta (α1D -adrenoceptor, pA2  â‰… 5.4) but not in spleen (α1B -adrenoceptor). The affinities estimated for mirabegron in functional assays were consistent with those estimated in radioligand binding with human recombinant α1A - and α1D -adrenoceptors (pKi  â‰… 6.0). CONCLUSION AND IMPLICATIONS: The effects of mirabegron in urethral smooth muscle are the result of ß3 -adrenoceptor agonism together with α1A and α1D -adrenoceptor antagonism.

17-Beta-estradiol directly regulates the expression of adrenergic receptors and kisspeptin/GPR54 system in GT1-7 GnRH neurons.

Estradiol plays a critical role in the feedback regulation of reproduction, in part by modulating the neurosecretory activity of gonadotropin-releasing hormone (GnRH) neurons. While indirect effects of estradiol on GnRH neurons have been clearly demonstrated, direct actions are still controversial. In the current study, we examined direct effects of 17beta-estradiol upon the expression of receptors for afferent signals at the level of the GnRH neuron, using immortalized GT1-7 cells. Using RT-PCR, we confirmed the expression of mRNA for the adrenergic receptors (AR) alpha(1)A-, alpha(1)B-, alpha(1)D-, alpha(2)A-, alpha(2)C-, and beta(1)-AR, and showed for the first time that mRNAs for alpha(2)B-, beta(2)- and beta(3)-AR, for kisspeptin and its receptor GPR54 and for the novel estrogenic receptor GPR30 are expressed in GT1-7 cells. After treatment with 10 nM 17beta-estradiol, alpha(1)B-AR mRNA was significantly increased (14-fold) after 6 h as determined by real-time PCR, while alpha(1)B- and alpha(1)D-AR mRNA were significantly increased (19- and 23-fold, respectively) after 24 h. The expression of KiSS-1 and GPR54 mRNAs were also significantly increased (8- and 6-fold, respectively) after 24 h treatment of GT1-7 cells with estradiol. GPR30 mRNA expression was not affected by estradiol. Our data also showed that kisspeptin-10 (1-10 nM) can significantly stimulate GnRH release and GnRH mRNA expression in GT1-7 cells. These results suggest that the complex physiologic effects of estradiol on the function of the reproductive axis could be mediated partly through direct modulation of the expression of receptors for afferent signals in GnRH neurons.

The role of adrenergic receptor polymorphisms in heart failure.

The main function of the cardiac adrenergic system is to regulate cardiac work both in physiologic and pathologic states. A better understanding of this system has permitted the elucidation of its role in the development and progression of heart failure. Regardless of the initial insult, depressed cardiac output results in sympathetic activation. Adrenergic receptors provide a limiting step to this activation and their sustained recruitment in chronic heart failure has proven to be deleterious to the failing heart. This concept has been confirmed by examining the effect of beta-blockers on the progression of heart failure. Studies of adrenergic receptor polymorphisms have recently focused on their impact on the adrenergic system regarding its adaptive mechanisms, susceptibilities and pharmacological responses. In this article, we review the function of the adrenergic system and its maladaptive responses in heart failure. Next, we discuss major adrenergic receptor polymorphisms and their consequences for heart failure risk, progression and prognosis. Finally, we discuss possible therapeutic implications resulting from the understanding of polymorphisms and the identification of individual genetic characteristics.

The role of adrenergic receptor polymorphisms in heart failure

The main function of the cardiac adrenergic system is to regulate cardiac work both in physiologic and pathologic states. A better understanding of this system has permitted the elucidation of its role in the development and progression of heart failure. Regardless of the initial insult, depressed cardiac output results in sympathetic activation. Adrenergic receptors provide a limiting step to this activation and their sustained recruitment in chronic heart failure has proven to be deleterious to the failing heart. This concept has been confirmed by examining the effect of ß-blockers on the progression of heart failure. Studies of adrenergic receptor polymorphisms have recently focused on their impact on the adrenergic system regarding its adaptive mechanisms, susceptibilities and pharmacological responses. In this article, we review the function of the adrenergic system and its maladaptive responses in heart failure. Next, we discuss major adrenergic receptor polymorphisms and their consequences for heart failure risk, progression and prognosis. Finally, we discuss possible therapeutic implications resulting from the understanding of polymorphisms and the identification of individual genetic characteristics.

Variantes genéticas de los receptores adrenérgicos y enfermedades cardiovasculares / Genetic variants of the adrenergic receptors and cardiovascular diseases

El proyecto Genoma Humano ha logrado descifrar la secuencia completa del genoma, aportando una herramienta única para el estudio de la genética humana. Sin embargo, se ha observado cada vez más frecuentemente la aparición de variantes genéticas, o polimorfismos, en cada uno de los genes estudiados. Como reguladores claves de diversos sistemas, los receptores adrenérgicos proveen un sistema único para explorar una posible relación entre los polimorfismos del receptor y la respuesta a fármacos y susceptibilidad o progresión de las enfermedades cardiovasculares. Los adrenoreceptores pertenecen la superfamilia de los receptores con siete dominios de transmembrana que producen su efecto a través del acoplamiento con distintas proteínas G. Hasta la fecha se han identificado varios subtipos de adrenoreceptores alfa sub 1A, alfa sub 1B, alfa sub 1D, alfa sub 2A, alfa sub 2B, alfa sub 2C ß1, ß2, ß3 y ß4. Este artículo provee una visión general de los polimorfismos existentes en los receptores adrenérgicos y su relación con las enfermedades cardiovasculares