Changes on erectile function induced by surgical castration in C57bl/6 mice: evaluation of nitric oxide-cGMP-phosphodiesterase 5 and Rho-kinase pathways

Author(s)

Rodrigo de Oliveira Capel Martins

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Ciências Médicas
• Defense date: 2011-10-19

Examining board members

Gilberto De Nucci; Gabriel Forato Anhê; Kleber Gomes Franchini; Rita de Cassia Aleixo Tostes Passaglia; Sidney Glina

• Advisor: Gilberto De Nucci

Abstract

Penile erection is a vascular phenomenon under psychological control, modulated by androgens where the erection or flacid penile state is determined by the momentary condition of either contraction or relaxation of the arterial system and the cavernous trabecular smooth muscle. Since erectile dysfunction is defined as the inability to achieve or maintain a penile erection for satisfactory sexual intercourse and may be due to psychological or organic causes, which may be, vascular, neurological, surgical or drug induced and affects about 50% of men older than 40 years old and a growing number of men aged 20 years or more. The phosphodiesterase type 5 inhibitors are orally, the best treatment option although there are other alternatives such as intracavernous injection of papaverine, phentolamine, or alprostadil, and in severe cases, the penile prosthesis. However there are cases of people who do not respond satisfactorily to these drugs and, cause(s) remain unknown. In order to investigate whether the proposed model of erectile dysfunction caused by orchiectomy in vivo also changes the response of corpus cavernosum in vitro contractile and relaxing stimulation, as well as morphological changes in the corpus cavernosum of C57BL / 6 adults males mice (25-30g) surgically castrated. We evaluated the contractile response to phenylephrine (alpha1 agonist) in the presence or absence of L-NAME (NO-inhibitor) and fasudil (HA1077, Rho-kinase inhibitor), electrical stimulation (EFS: 4, 8, 16Hz, 50V, 10 seconds), as well as the relaxation response to acetylcholine (ACh) in the presence or absence of L-NAME, HA 1077, Bay 41-2272 (guanylyl cyclase activator) in the absence or presence of ODQ (guanylyl cyclase inhibitor) and sodium nitroprusside (SNP, NO donor) in the absence or presence of ODQ. The morphological parameters evaluated were length, cross-sectional area and volume of the penis, transversal sectional area of corpora cavernosa, fraction of smooth muscle, collagen xxx and sinusoidal lumen and quantitative smooth muscle / collagen tissue as well as the immunoexpression of guanylyl cyclase, phosphodiesterase 5 type and endothelial NOS. Two segments of the corpus cavernosum were obtained from each animal. Tissues were mounted in organ baths with Krebs-Henseleit and after stabilization, concentration curves were performed. Our results showed that castration increased the potency and maximal response of phenylephrine (pEC50 = 5.452 ± 0.100, Emax = 0.117 ± 0.005) compared to controls (pEC50 = 6.138 ± 0.110; Emax = ± 0.005 and 0.086) and HA1077 reverses this effect causing any alterations in the response of the animal control, electrical field stimulation was significantly higher in castrated animals (p <0.001) at all frequencies tested. We observed that the relaxation of ACh is diminished in the castrated animals, and higher doses caused contraction, Bay 41-2272 had reduced potency and maximum response in the castrated group, while SNP had no difference between groups. HA1077 was significantly higher in both potency and maximum response in castrated animals (pEC50 = 5.863 ± 0.060; Emax = 0.141 ± 0.005) compared to controls (pEC50 = 6.867 ± 0.070; Emax = 0.058 ± 0.001). Macroscopic analysis showed that, between the first and eighth weeks after castration, castrated animals showed hypoplasia and atrophy thereafter. Microscopic parameters: castrated animals lost 7% of the corpus cavernosum and 30% of the fraction of smooth muscle. The nNOS immunoreactivity was similar in both groups as eNOS, guanylyl cyclase and PDE5 are reduced in castrated animals, and data of guanyl cilcase and PDE5 were also confirmed by western blot. We demonstrated that surgical castration: increases the sensitivity of the cavernous smooth muscle contraction mechanisms, either by adrenergic stimulation or by the mechanism of calcium sensitization mediated by Rho-kinase, and reduces the relaxing response to mechanisms mediated by nitric oxide-cGMP-PDE5; causes loss of striated and smooth muscle, increased fat and decreased expression of proteins essential for maintaining the function of the erection mechanism (AU)

• FAPESP's process: 07/06605-0 - Erectile dysfunction by surgical/chemical castration in mice: evaluation of the NO/cGMP-PDE5 and Rho-kinase pathway
• Grantee: Rodrigo de Oliveira Capel Martins
• Support Opportunities: Scholarships in Brazil - Doctorate