Involvement of Я3-Adrenergic Receptor Activation Via Cyclic

Involvement of ␤3-adrenergic receptor activation via cyclic GMP- but not NO-dependent mechanisms in human corpus cavernosum function Giuseppe Cirino*†, Raffaella Sorrentino*†, Roberta d’Emmanuele di Villa Bianca*, Ada Popolo‡, Alessandro Palmieri§, Ciro Imbimbo§, Ferdinando Fusco§, Nicola Longo§, Gianfranco Tajana‡, Louis J. Ignarro¶ʈ, and Vincenzo Mirone§ Dipartimentos di *Farmacologia Sperimentale e §Urologia, Facolta`di Medicina Universita`di Napoli-Federico II, 80131 Naples, Italy; ‡Dipartimento di Scienze Farmaceutiche, Universita`di Salerno, 84100 Fisciano-Salerno, Italy; and ¶Department of Molecular and Medical Pharmacology, University of California School of Medicine, Los Angeles, CA 90095-1735 Contributed by Louis J. Ignarro, March 7, 2003 ␤ ␤ The 3-adrenoreceptor plays a major role in lipolysis but the role and possess 3-receptors that share most of the characteristic prop- distribution of ␤3-receptors in other specific sites have not been erties, although some species-specific differences have been ␤ ␤ extensively studied. 3-adrenergic receptors are present not only in identified. The 3-receptor plays a major role in lipolysis but the ␤ adipose tissue but also in human gall bladder, colon, prostate, and role and distribution of 3-receptors in other specific sites have skeletal muscle. Recently, ␤3-adrenergic receptor stimulation was not been extensively studied. Tissue distribution studies have ␤ shown to elicit vasorelaxation of rat aorta through the NO–cGMP demonstrated the presence of 3-receptors not only in adipose signal transduction pathway. Here we show that ␤3-receptors are tissues but also in human gall bladder and more recently in colon, ␤ present in human corpus cavernosum and are localized mainly in prostate, and skeletal muscle (9–11). In addition, 3-receptor smooth muscle cells. After activation by a selective ␤3-adrenergic stimulation has been recently demonstrated to elicit vasorelax- receptor agonist, BRL 37344, there was a cGMP-dependent but NO- ation of rat aorta through activation of NO synthase and the independent vasorelaxation that was selectively blocked by a specific subsequent increase in tissue levels of cGMP (12). Here we show ␤ ␤3-receptor antagonist. In addition, we report that the human corpus that 3-receptors are present in human corpus cavernosum cavernosum exhibits basal ␤3-receptor-mediated vasorelaxant tone (HCC) and that their activation causes a cGMP-dependent but and that ␤3-receptor activity is linked to inhibition of the RhoA͞ NO-independent vasorelaxation that involves the Rho-kinase Rho-kinase pathway. These observations indicate that ␤3-receptors pathway. may play a physiological role in mediating penile erection and, therefore, could represent a therapeutic target for treatment of Materials and Methods erectile dysfunction. Human Tissues. In male-to-female transsexual surgical procedures, the penis and testicles are amputated and a neovagina is erectile dysfunction ͉ Rho kinase ͉ endothelin created to simulate female external genitalia by using techniques that have been described (13). Patients underwent appropriate rectile dysfunction (ED) is defined as the inability to achieve hormonal pretreatment with antiandrogens and estrogens to Eand maintain an erection sufficient to permit satisfactory adapt to female appearance, and the therapy was discontinued sexual intercourse. ED is the result of psychological, neurologic, 2 months before surgery. The corpora cavernosa were carefully hormonal, arterial, or cavernosal impairment or a combination excised from the amputated penis and placed in ice-cold oxy- of two or more of these factors. After sexual stimulation, nerve genated Krebs solution and washed extensively with heparinized impulses cause the release of neurotransmitters, including nitric Krebs solution. After the lavage, the corpora cavernosa were oxide (NO), from the cavernous nerve terminal, resulting in the placed in ice-cold Krebs solution and kept on ice until the relaxation of arteries and arterioles with a consequent increase experiments were conducted, within 2 h. All patients were informed of all procedures and gave their written consent. The in penile blood flow. NO is also generated by vascular endothe- protocol was approved by the Ethics Committee of the Medical lial cells in the corpus cavernosum in response to increased School of the University of Naples. penile blood flow. This process, together with relaxation of the trabecular smooth muscle leading to an increase in the compli- HCC Strips. Longitudinal strips (2 cm) were dissected after the ance of sinusoids, results in the filling and expansion of the trabecular structure of the penis (5, 13). Isolated HCC strips sinusoidal system (1). were immediately placed in Krebs solution and kept at 4°C until NO seems to be the principal mediator released both by nerves use. Krebs solution had the following composition (mM): 115.3 and endothelial cells after sexual stimulation. The vascular NaCl͞4.9 KCl͞1.46 CaCl ͞1.2 MgSO ͞1.2 KH PO ͞25.0 smooth muscle relaxant effect of NO is mediated by cGMP, and 2 4 2 4 NaHCO ͞11.1 glucose. HCC strips were mounted in a 2-ml the tissue levels of cGMP in the corpus cavernosum are regulated 3 organ bath containing oxygenated (95% O ͞5% CO ) Krebs by phosphodiesterase-5 (2, 3). The pathophysiology of ED was 2 2 solution at 37°C. HCC strips were connected to isometric force not well understood until the discovery was made that NO is the transducers (Model 7002, Ugo Basile, Comerio, Italy) and principal neurotransmitter of the nonadrenergic͞noncholinergic changes in tension were recorded continuously by using a nerves that innervate the corpus cavernosum, and that the polygraph linearcorder (WR3310, Graphtec, Yokohama, Ja- PHARMACOLOGY NO–cGMP signal transduction pathway is the main effector of pan). Tissues were preloaded with2goftension and allowed to penile erection (4–6). These findings were followed by the equilibrate for 90 min in Krebs solution that was changed at availability of sildenafil for the oral treatment of ED. Despite the clinical success of sildenafil, the physiology of the corpus cavernosum and the pathophysiology of ED are still incompletely Abbreviations: HCC, human corpus cavernosum; ED, erectile dysfunction; PE, phenyleph- understood (3). rine; ACh, acetylcholine; hET-1, human endothelin-1; L-NAME, L-NG-nitroarginine- ␤ methylester; IBMX, 1-methyl-3-isobutylxanthine; SNP, sodium nitroprusside. The 3-adrenergic receptor subtype of sympathetic nervous system has been extensively characterized at the structural level †G.C. and R.S. contributed equally to this work. (7, 8). Humans, other large mammalian species, and rodents ʈTo whom correspondence should be addressed. E-mail: [email protected]. www.pnas.org͞cgi͞doi͞10.1073͞pnas.0931347100 PNAS ͉ April 29, 2003 ͉ vol. 100 ͉ no. 9 ͉ 5531–5536 Downloaded by guest on October 2, 2021 Fig. 1. Relaxant effects of BRL 37344 on HCC strips. (a) BRL 37344 (BRL) relaxed HCC strips in the presence (ϩ end) and absence (Ϫ end) of endothelium. (b) L-NAME (100 ␮M) did not inhibit BRL 37344-induced vasorelaxation of HCC. (c) 1-H-[1,2,4]oxadiazolo [4,3a]quinoxalin-1-one (10 ␮M) did not inhibit BRL 37344-induced vasorelaxation. (d) Methylene blue (MB; 10 ␮M) inhibited BRL 37344-induced vasorelaxation. Data were analyzed by using ANOVA. **, P Ͻ 0.01, significantly different from corresponding control values. The data represent the mean Ϯ SEM from eight separate experiments (eight strips per experiment). 15-min intervals. After equilibration, tissues were standard- antagonists or inhibitors were added 5 min before the addition ized by using repeated phenylephrine (PE; 1 ␮M)-elicited of BRL 37344. ACh (1 ␮M) and SNP (1 ␮M) were also tested contractile responses until equal responses were obtained. as positive controls. After a 30-min incubation time, the strips After standardization, endothelial integrity was assessed by were rapidly blotted and quick-frozen in liquid nitrogen. One testing relaxant responses to 1 ␮M acetylcholine (ACh; Sigma). milliliter of buffer (containing 5% trichloroacetic acid and 10 Strips that did not attain a relaxation of at least 70% were ␮M IBMX) per gram of tissue was added to each sample. discarded. To evaluate tissue relaxant responsiveness, HCC Samples were homogenized and the precipitate was sedi- ␮ strips were precontracted with 1 M PE or human endothe- mented by centrifugation at 1,500 ϫ g for 10 min. The lin-1 (hET-1; 10 and 30 nM, respectively; Tocris Neuramin, supernatant was carefully removed and used in the next step Bristol, U.K.), and once a stable contraction was achieved (sediment was discarded). Residual trichloroacetic acid was (about 15 min), cumulative concentration responses to ACh ␮ ␤ removed by extraction into 5 vol of water-saturated diethyl (0.01–3 M), the 3-receptor selective agonist BRL 37344 ether (repeated twice for a total of 3 extractions). Any residual (10–300 ␮M; Tocris Neuramin), and sodium nitroprusside ␮ ether was removed by warming the samples at 50°C for 5 min. (SNP; 0.01–3 M) were obtained. To assess the functional role The samples were then processed according to the instructions of the vascular endothelium in relaxation of HCC strips, provided with the kit (Cayman Chemical, Ann Arbor, MI) for endothelium-denuded strips were tested. HCC strips were determination of cAMP and cGMP levels. Data are expressed denuded of functional endothelium by incubating strips with as pmol͞g of wet weight tissue and each sample was run in distilled water for 15 sec.

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