Determination of Adenosine Effects and Adenosine Receptors in Murine Corpus Cavernosum

Abstract

This study tested the hypothesis that adenosine, in murine corpora cavernosa, produces direct relaxation of smooth muscle cells and inhibition of contractile responses mediated by sympathetic nerve stimulation. Penes were excised from anesthetized male C57BL/6 mice, dissected, and cavernosal strips were mounted to record isometric force. Adenosine, 2-chloroadenosine (stable analog of adenosine), and 2-phenylaminoadenosine (CV1808) (A2 A /A2 B agonist) produced concentrationdependent relaxations of phenylephrine-contracted tissues. Relaxation to 2-chloroadenosine was inhibited, in a concentrationdependent manner, by 2-(2-furanyl)-7-(2-phenylethyl)-7H-pyrazolo [4,3-e] Ϫ8-10 Ϫ6 M). The combination of both antagonists abrogated 2-chloroadenosine-induced relaxation. Electrical field stimulation (EFS; 1-32 Hz) of adrenergic nerves produced frequency-dependent contractions that were inhibited by compounds that increase adenosine levels, such as 5Ј-iodotubercidin (adenosine kinase inhibitor), erythro-9-(2-hydroxy-3-nonyl)adenine (adenosine deaminase inhibitor), and dipyridamole (inhibitor of adenosine transport). The adenosine A1 receptor agonist N 6 -cyclopentyladenosine (C8031) right-shifted contractile responses to EFS, with a significant inhibitory effect at 10 Ϫ6 M. Blockade of adenosine A1 receptors with 8-cyclopentyl-1,3-dipropylxanthine (C101) (10 Ϫ7 M) enhanced contractile responses to EFS and eliminated the inhibitory effects of 5Ј-iodotubercidin. Dipyridamole and 5Ј-iodotubercidin had no effect on adenosine-mediated relaxation. In summary, adenosine directly relaxes cavernosal smooth muscle cells, by the activation of A2 A / A2 B receptor subtypes. In addition, adenosine negatively modulates sympathetic neurotransmission, by A1 receptor subtype activation, in murine corpora cavernosa. Adenosine may subserve dual roles in modulating the physiological mechanisms of erection in mice.The balance between contracting and relaxing factors controls smooth muscle tone of both the penile vasculature and corpora cavernosa, and, therefore, it determines the functional state of the penis: flaccidity or erection (Andersson, 2001;Leite et al., 2007). Efferent autonomic sympathetic and parasympathetic nerves regulate penile function, via release of norepinephrine and acetylcholine, respectively. In addition, many investigators have provided evidence for functional roles of nonadrenergic-noncholinergic (NANC) inhibitory and excitatory nerves, which contain not only neuropeptides, such as neuropeptide Y, vasoactive intestinal polypeptide, substance P, and calcitonin gene-related polypeptide, but also transmitters such as nitric oxide (NO) and adenosine triphosphate (ATP) (Giuliano and Rampin,

Purinergic signalling in the reproductive system in health and disease

“…Experiments on isolated rabbit corpus cavernosum suggested that A 2B receptors were also involved in relaxation [189]. In another paper, it was claimed that adenosine directly relaxes cavernosal smooth muscle via both A 2A and A 2B receptor subtypes, while it modulates sympathetic neurotransmission via A 1 receptors [404]. Activation of A 1 receptors during penile erection results in reduced noradrenaline (NA) release and reduced cavernosal smooth muscle contraction, thereby facilitating penile erection [303].…”

Role of Adenosine Receptor(s) in the Control of Vascular Tone in the Mouse Pudendal Artery

“…Those factors, which regulate contraction and relaxation of vascular smooth muscle, determine the state of the penis (flaccidity versus erection) (Andersson, 2001;Tostes et al, 2007;Nunes et al, 2012). The flaccid state is mainly mediated by the release of norepinephrine from adrenergic nerve terminals and other vasoconstrictors, such as endothelin-1 and angiotensin II (Sáenz de Tejada et al, 1989, 2004.…”

“…The flaccid state is mainly mediated by the release of norepinephrine from adrenergic nerve terminals and other vasoconstrictors, such as endothelin-1 and angiotensin II (Sáenz de Tejada et al, 1989, 2004. The erection is mainly mediated by nitric oxide (NO) released from the endothelium and nonadrenergic-noncholinergic nerves in addition to other neurotransmitters and endothelium-derived hyperpolarizing factors (EDHFs), such as adenosine (Chiang et al, 1994;Tostes et al, 2007;Wen et al, 2011b).…”

“…at ASPET Journals on May 9, 2018 jpet.aspetjournals.org that may regulate penile erection in humans and animals (Takahashi et al, 1991(Takahashi et al, , 1992Chiang et al, 1994;Mantelli et al, 1995;Filippi et al, 2000;Noto et al, 2001;Tostes et al, 2007;Carneiro et al, 2008;Mi et al, 2008;Vallon and Osswald, 2009;Phatarpekar et al, 2010;Wen et al, 2010Wen et al, , 2011bWen et al, , 2012Ning et al, 2012;Headrick et al, 2013;Layland et al, 2014). Adenosine binds to a family of four P1 G proteincoupled AR subtypes: A 1 , A 2A , A 2B , and A 3 .…”

Mechanisms of Penile Erection and Basis for Pharmacological Treatment of Erectile Dysfunction

“…More recently, Tostes et al (2007) presented data suggesting that adenosine-induced relaxation in mouse CC is mediated through activation of both A 2A and A 2B adenosine receptors. Mice lacking adenosine deaminase (which is necessary for the breakdown of adenosine) showed priapic activity involving A 2B receptors (Mi et al, 2008).…”