Effects of estrogen on nitric oxide synthase and histological composition in the rabbit clitoris and vagina

The Effect of Menopause on Vaginal Tissue Mechanics: A Brief Review

Often called "the change of life," menopause affects every part of a woman's body. As the sex hormones decrease, the reproductive organs experience the most remarkable changes, with the vagina becoming thinner, drier, and less elastic. Despite the important implications of these changes in genitourinary conditions, there are only a few experimental studies that focus on quantifying the effect of menopause on the mechanical properties of the vagina. These studies are mostly conducted using uniaxial tests on strips of vaginal tissues isolated from rats, rabbits, and sheep and, in only a few cases, from humans. The purpose of this article is to present a systematic review of experimental protocols, methods, and results that are currently published on how menopause alters the mechanical behavior of the vagina. This review will enable new investigators in the biomechanics field to identify important gaps and frame research questions that inform the design of new treatment options for menopausal symptoms.

Understanding sexual arousal and subjective-genital arousal desynchrony in women

Sexual arousal in women comprises two components: genital arousal and subjective arousal. Genital arousal is characterized by genital vasocongestion and other physiological changes that occur in response to sexual stimuli, whereas subjective arousal refers to mental engagement during sexual activity. For some women, genital arousal enhances subjective arousal; for others, the two types of arousal are desynchronous. However, the relationship between genital and subjective arousal might not be relevant to the diagnosis and treatment of sexual arousal dysfunction. Studies have shown that not all women who report sexual arousal problems have decreased genital arousal, and only some women with decreased genital arousal have low subjective arousal. To develop efficacious treatments for female sexual arousal dysfunction, researchers need to differentiate the women for whom genital sensations have a critical role in their subjective arousal from those who are not mentally aroused by genital cues. The mechanisms by which women become aroused and the inputs into arousal have considerable implications for treatment outcomes.

Effect of estrogen on molecular and functional characteristics of the rodent vaginal muscularis

INTRODUCTION

Vaginal atrophy is a consequence of menopause; however, little is known concerning the effect of a decrease in systemic estrogen on vaginal smooth muscle structure and function. As the incidence of pelvic floor disorders increases with age, it is important to determine if estrogen regulates the molecular composition and contractility of the vaginal muscularis.

AIM

The goal of this study was to determine the effect of estrogen on molecular and functional characteristics of the vaginal muscularis utilizing a rodent model of surgical menopause.

METHODS

Three- to 4-month old Sprague-Dawley rats underwent sham laparotomy (Sham, N = 18) or ovariectomy (Ovx, N = 39). Two weeks following surgery, animals received a subcutaneous osmotic pump containing vehicle (Sham, Ovx) or 17β-estradiol (Ovx). Animals were euthanized 1 week later, and the proximal vagina was collected for analysis of contractile protein expression and in vitro studies of contractility. Measurements were analyzed using a one-way analysis of variance followed by Tukey's post hoc analysis (α = 0.05).

MAIN OUTCOME MEASURES

Protein and mRNA transcript expression levels of contractile proteins, in vitro measurements of vaginal contractility.

RESULTS

Ovariectomy decreased the expression of carboxyl-terminal myosin heavy chain isoform (SM1) and h-caldesmon and reduced the amplitude of contraction of the vaginal muscularis in response to KCl. Estradiol replacement reversed these changes. No differences were detected in the % vaginal muscularis, mRNA transcript expression of amino-terminal MHC isoforms, l-caldesmon expression, and maximal velocity of shortening.

CONCLUSION

Systemic estrogen replacement restores functional and molecular characteristics of the vaginal muscularis of ovariectomized rats. Our results indicate that menopause is associated with changes in the vaginal muscularis, which may contribute to the increased incidence of pelvic floor disorders with age.

Post-translational regulation of endothelial nitric oxide synthase (eNOS) by estrogens in the rat vagina

INTRODUCTION

Estrogens control vaginal blood flow during female sexual arousal mostly through nitric oxide (NO). Although vascular effects of estrogens are attributed to an increase in endothelial NO production, the mechanisms of endothelial NO synthase (eNOS) regulation by estrogens in the vagina are largely unknown.

AIMS

Our hypothesis was that estrogens regulate eNOS post-translationally in the vagina, providing a mechanism to affect NO bioavailability without changes in eNOS protein expression.

METHODS

We measured eNOS phosphorylation and eNOS interaction with caveolin-1 and heat shock protein 90 (HSP90) in the distal and proximal vagina of female rats at diestrus, 7 days after ovariectomy and 2 days after replacement of ovariectomized rats with estradiol-17beta (15 microg).

MAIN OUTCOME MEASURES

Molecular mechanisms of eNOS regulation by estrogen in the rat vagina.

RESULTS

We localized phospho-eNOS (Ser-1177) immunohistochemically to the endothelium lining blood vessels and vaginal sinusoids. Estrogen withdrawal decreased phosphorylation of eNOS on its positive regulatory site (Ser-1177) and increased eNOS binding to its negative regulator caveolin-1 (without affecting eNOS/HSP90 interaction), and they were both normalized by estradiol replacement. Protein expressions of phosphorylated Akt (protein kinase B) and extracellular signal-regulated protein kinase 1/2 (ERK1/2) were not affected by estrogen status, suggesting that the effect of estrogens on eNOS (Ser-1177) phosphorylation was not mediated by activated AKT or ERK1/2. eNOS phosphorylation on its negative regulatory site (Ser-114) was increased in the vagina by estrogen withdrawal and normalized by estradiol replacement, implying that the maintenance of low phosphorylation of eNOS on this site by estradiol may limit eNOS interaction with caveolin-1 and preserve the enzyme's activity. Total eNOS, inducible NOS, caveolin-1, and HSP90 protein expressions were not affected by ovariectomy or estradiol replacement in the distal or proximal vagina.

CONCLUSIONS

These results define novel estrogen signaling mechanisms in the vagina which involve eNOS phosphorylation and eNOS-caveolin-1 interaction.

Endothelial nitric oxide synthase regulation in female genital tract structures

INTRODUCTION

Female sexual arousal disorder (FSAD) is a major component of female sexual dysfunctions, affecting 25-70% of women. The mechanisms of FSAD are poorly understood. Estrogen contributes to the control of genital blood flow during the sexual response. Vascular effects of estrogen are mostly attributed to its regulation of endothelial nitric oxide (NO) production. However, the role of endothelial NO synthase (eNOS) and the mechanisms that regulate eNOS in female genital tract structures are largely unknown.

AIM

To review available evidence of the mechanisms of eNOS regulation in female genital tract structures.

METHODS

This article reviews the literature that relates to the role of NO and eNOS in female sexual arousal and its modulation by estrogen.

MAIN OUTCOME MEASURES

Association between female sexual arousal, NO, and eNOS.

RESULTS

The NO/cyclic guanosine monophosphate pathway is believed to have a primary role in the regulation of clitoral and vaginal blood flow, and smooth muscle relaxation during sexual arousal. Estrogen is critical for maintaining vaginal and clitoral blood flow and vaginal transudate production. Estrogen regulates eNOS by genomic mechanisms, involving augmented mRNA transcription and protein synthesis, and by non-genomic mechanisms, which occur without alterations in gene expression. However, limited studies have evaluated the physiological role of endothelial NO and the molecular mechanisms of eNOS regulation in the female genital tract.

CONCLUSIONS

The effects of estrogen on increasing genital blood flow and smooth muscle relaxation have been attributed mostly to regulation of eNOS. However, the exact mechanisms of eNOS regulation in female genital tract structures and the molecular basis for the eNOS defect with aging and vascular diseases warrant further investigation.

General tissue characteristics of the lower urethral and vaginal walls in the domestic rabbit

In European rabbits, the distal urethra (DU) opens into the anterior pelvic vagina forming a single canal by which females copulate, give birth, and urinate. We investigated whether the histological characteristics of the DU and the pelvic and perineal vagina are different. The DU and vagina of rabbits (Oryctolagus cuniculus) were cut and stained with hematoxylin-eosin and Masson's trichrome (n = 3). Data were compared by using Friedman's ANOVA for repeated measures. The walls of the DU and vagina are composed of mucosa, submucosa, smooth muscle, and an external layer. Differences in tissue characteristics of the mucosa, orientation of the smooth muscle fibers, components of the external layer (connective tissue, blood vessels, and striated musculature), and thickness of the tissue layers were found among regions. The lack of histological homogeneity along the urethra and vagina possibly reflects differences in the functions of each segment.

Increased vaginal oxidative stress, apoptosis, and inducible nitric oxide synthase in a diabetic rat model: implications for vaginal fibrosis

OBJECTIVE

To determine whether vaginal fibrosis occurs in diabetic animals and is associated with oxidative stress and cell death and with the expression of inducible nitric oxide synthase (iNOS), as a putative antifibrotic mechanism.

DESIGN

Research experimental project.

SETTING

University research laboratory.

ANIMAL(S)

Female Wistar rats.

INTERVENTION(S)

Female rats were injected with streptozotocin or saline and killed at 3 months. The vaginas were excised and processed for paraffin-embedded sections (n = 6 per group) or were frozen for biochemical and molecular biology procedures.

MAIN OUTCOME MEASURE(S)

Immunohistochemistry and quantitative image analysis were applied to tissue sections to measure alpha-smooth muscle actin, transforming growth factor beta1, plasminogen activator inhibitor, NOS isoforms, Cu/Zn superoxide dismutase, apoptotic index, and nitrotyrosine. Xanthine dehydrogenase, reactive oxygen species (ROS), and hydroxyproline were measured in fresh vaginal tissue (n = 5 per group). Reactive oxygen species also were determined in blood.

RESULT(S)

Diabetes was associated with vaginal fibrosis, as evidenced by increased collagen, transforming growth factor beta1, plasminogen activator inhibitor, and apoptosis, and by decreased alpha-smooth muscle actin. The increment of ROS and the reduction of superoxide dismutase indicated oxidative stress in diabetic tissue, accompanied by iNOS induction and increased nitric oxide-ROS reaction.

CONCLUSION(S)

Diabetes in the rat causes oxidative stress and fibrosis in the vagina, which may be compensated partially by iNOS induction to reduce ROS.

Streptozotocin-induced diabetes in the rat is associated with changes in vaginal hemodynamics, morphology and biochemical markers

Background

Diabetes is associated with declining sexual function in women. However, the effects of diabetes on genital tissue structure, innervation and function remains poorly characterized. In control and streptozotocin-treated female rats, we investigated the effects of diabetes on vaginal blood flow, tissue morphology, and expression of arginase I, endothelial nitric oxide synthase (eNOS) and cGMP-dependent protein kinase (PKG), key enzymes that regulate smooth muscle relaxation. We further related these changes with estrogen receptor alpha (ERα) and androgen receptor (AR) expression.

Results

In addition to significantly elevated blood glucose levels, diabetic rats had decreased mean body weight, lower levels of plasma estradiol, and higher plasma testosterone concentration, compared to age-matched controls. Eight weeks after administration of buffer (control) or 65 mg/kg of streptozotocin (diabetic), the vaginal blood flow response to pelvic nerve stimulation was significantly reduced in diabetic rats. Histological examination of vaginal tissue from diabetic animals showed reduced epithelial thickness and atrophy of the muscularis layer. Diabetic animals also had reduced vaginal levels of eNOS and arginase I, but elevated levels of PKG, as assessed by Western blot analyses. These alterations were accompanied by a reduction in both ERα and AR in nuclear extracts of vaginal tissue from diabetic animals.

Conclusion

In ovariectomized (estrogen deficient) animals, previous reports from our lab and others have documented changes in blood flow, tissue structure, ERα, arginase I and eNOS that parallel those observed in diabetic rats. We hypothesize that diabetes may lead to multiple disruptions in sex steroid hormone synthesis, metabolism and action. These pathological events may cause dramatic changes in tissue structure and key enzymes that regulate cell growth and smooth muscle contractility, ultimately affecting the genital response during sexual arousal.

Physiology of female sexual function: animal models

INTRODUCTION

Data concerning the physiology of desire, arousal, and orgasm in women are limited because of ethical constraints. Aim. To gain knowledge of physiology of female sexual function through animal models.

METHODS

To provide state-of-the-art knowledge concerning female sexual function in animal models, representing the opinions of seven experts from five countries developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURE

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Sexual desire may be considered as the presence of desire for, and fantasy about, sexual activity. Desire in animals can be inferred from certain appetitive behaviors that occur during copulation and from certain unconditioned copulatory measures. Proceptive behaviors are dependent in part on estrogen, progesterone, and drugs that bind to D1 dopamine receptors, adrenergic receptors, oxytocin receptors, opioid receptors, or gamma-amino butyric acid receptors. Peripheral arousal states are dependent on regulation of genital smooth muscle tone. Multiple neurotransmitters/mediators are involved including adrenergic, and nonadrenergic, noncholinergic agents such as vasoactive intestinal polypeptide, nitric oxide, neuropeptide Y, calcitonin gene-related peptide, and substance P. Sex steroid hormones, estrogens and androgens, are critical for structure and function of genital tissues including modulation of genital blood flow, lubrication, neurotransmitter function, smooth muscle contractility, mucification, and sex steroid receptor expression in genital tissues. Orgasm may be investigated by urethrogenital (UG) reflex, in which genital stimulation results in rhythmic contractions of striated perineal muscles and contractions of vagina, anus, and uterine smooth muscle. The UG reflex is generated by a multisegmental spinal pattern generator involving the coordination of sympathetic, parasympathetic, and somatic efferents innervating the genital organs. Serotonin and dopamine may modulate UG reflex activity.

CONCLUSIONS

More research is needed in animal models in the physiology of female sexual function.

Ovariectomy alters the structural and biomechanical properties of ovine femoro-tibial articular cartilage and increases cartilage iNOS

OBJECTIVE

To examine the effect of oestrogen depletion produced by surgical ovariectomy on the structural and biomechanical properties of ovine femoro-tibial articular cartilage (AC), and the production of inducible nitric oxide synthase (iNOS) and nitrotyrosine by these tissues.

METHODS

Six aged ewes were surgically ovariectomised (OVX), while six were used as unoperated controls. Dynamic biomechanical indentation testing of tibial plateau AC was performed at 26 weeks post-op. Histological sections of medial tibial plateau and lateral tibial plateau (LTP), medial and lateral femoral condyles (MFC, LFC) and patellar AC were examined for histopathology, toluidine blue staining intensity, and patterns of collagen birefringence intensity. Immunoreactivity for iNOS and nitrotyrosine was assessed in full-thickness biopsy plugs of LFC and patellar AC, and patellar AC explants were cultured to determine in vitro NO release.

RESULTS

Phase lag was reduced overall in LTP-AC of OVX sheep (10.9+/-2.2 degrees vs 12.1+/-2.3 degrees ; P<0.0001). Cartilage thickness was reduced in the LTP of OVX sheep (P=0.0002), in association with localised changes in dynamic shear modulus. Toluidine blue staining intensity was reduced in the patella, LFC, and MFC. Histological examination revealed greater histopathology scores in the MFC of OVX animals, and altered collagen birefringence intensity plots in the LTP. Immunostaining for iNOS was increased in patella AC (P=0.008), whilst nitrotyrosine immunoreactivity was increased in patella (P=0.03) and LFC (P<0.0001) AC. NO release by patellar AC explants was also elevated.

CONCLUSIONS

Oestrogen depletion induced by OVX caused regional thinning of femoro-tibial cartilage, with biomechanical and histological changes suggestive of a disturbance in the content and/or structural organisation of the proteoglycan and collagen macromolecular assembly. The observed up-regulation of cartilage iNOS suggests a possible mechanism for these matrix changes.

ANATOMY OF THE CLITORIS

PURPOSE

We present a comprehensive account of clitoral anatomy, including its component structures, neurovascular supply, relationship to adjacent structures (the urethra, vagina and vestibular glands, and connective tissue supports), histology and immunohistochemistry. We related recent anatomical findings to the historical literature to determine when data on accurate anatomy became available.

MATERIALS AND METHODS

An extensive review of the current and historical literature was done. The studies reviewed included dissection and microdissection, magnetic resonance imaging (MRI), 3-dimensional sectional anatomy reconstruction, histology and immunohistochemical studies.

RESULTS

The clitoris is a multiplanar structure with a broad attachment to the pubic arch and via extensive supporting tissue to the mons pubis and labia. Centrally it is attached to the urethra and vagina. Its components include the erectile bodies (paired bulbs and paired corpora, which are continuous with the crura) and the glans clitoris. The glans is a midline, densely neural, non-erectile structure that is the only external manifestation of the clitoris. All other components are composed of erectile tissue with the composition of the bulbar erectile tissue differing from that of the corpora. The clitoral and perineal neurovascular bundles are large, paired terminations of the pudendal neurovascular bundles. The clitoral neurovascular bundles ascend along the ischiopubic rami to meet each other and pass along the superior surface of the clitoral body supplying the clitoris. The neural trunks pass largely intact into the glans. These nerves are at least 2 mm in diameter even in infancy. The cavernous or autonomic neural anatomy is microscopic and difficult to define consistently. MRI complements dissection studies and clarifies the anatomy. Clitoral pharmacology and histology appears to parallel those of penile tissue, although the clinical impact is vastly different.

CONCLUSIONS

Typical textbook descriptions of the clitoris lack detail and include inaccuracies. It is impossible to convey clitoral anatomy in a single diagram showing only 1 plane, as is typically provided in textbooks, which reveal it as a flat structure. MRI provides a multiplanar representation of clitoral anatomy in the live state, which is a major advantage, and complements dissection materials. The work of Kobelt in the early 19th century provides a most comprehensive and accurate description of clitoral anatomy, and modern study provides objective images and few novel findings. The bulbs appear to be part of the clitoris. They are spongy in character and in continuity with the other parts of the clitoris. The distal urethra and vagina are intimately related structures, although they are not erectile in character. They form a tissue cluster with the clitoris. This cluster appears to be the locus of female sexual function and orgasm.

Estrogen modulates endothelial and neuronal nitric oxide synthase expression via an estrogen receptor beta-dependent mechanism in hypothalamic slice cultures

Although it is evident that estrogen has important physiological effects in the brain, the signaling mechanisms mediating these effects remain unclear. We recently showed that estrogen mediates attenuated blood pressure responses to psychological stress in ovariectomized female rats through brain nitric oxide (NO). An area likely to mediate these effects is the hypothalamic paraventricular nucleus (PVN), because here NO exerts inhibitory effects on autonomic output to the periphery. Because little is known about how estrogen acts on the NO system in the PVN, our aim was to study the effects of estrogen on the NO system in the PVN of hypothalamic slices cultures. We show that 17beta-estradiol (E2; 1 nm) increases endothelial NO synthase (eNOS) protein expression and decreases the numbers of neuronal NOS (nNOS)-positive neurons in the PVN after 8 and 24 h, respectively. Using the nonselective estrogen receptor (ER) antagonist, ICI 182,780 (10 nm), we determined that E2-induced changes in NOS expression in the PVN are ER dependent. Using the ERbeta agonist, genistein (0.1 microm), we determined that activation of ERbeta induces increased eNOS expression and a decreased number of nNOS-positive neurons. We used the selective ERalpha agonist, propyl-pyrazole-triol (10 nm), and antagonist, methyl-piperidino-pyrazole (1 microm), to exclude the possibility that ERalpha is involved in the E2-induced increase in eNOS and nNOS in the PVN. These results demonstrate that E2 induces changes in NOS expression in the PVN and that these effects are ERbeta dependent.

Effects of dehydroepiandrosterone, Premarin and Acolbifene on histomorphology and sex steroid receptors in the rat vagina

To assess the specific estrogenic and/or androgenic effects of a potential novel hormone replacement therapy, we have examined the morphology of the rat vagina 9 months after ovariectomy (OVX) and treatment of OVX animals with dehydroepiandrosterone (DHEA), conjugated estrogens Premarin and the selective estrogen receptor modulator Acolbifene. OVX led to atrophy and inflammatory changes while Acolbifene reduced the inflammation incidence and induced mucification of the vaginal epithelium. Premarin induced a typical keratinized stratified squamous epithelium while DHEA induced stimulation of the vaginal epithelium, with mucous cells typical of an androgenic effect, combined with increased collagen fiber compactness of the lamina propria. On the other hand, after OVX, the vaginal muscle layer decreased by 46%, an effect which was 41 and 100% reversed by DHEA and Premarin, respectively. The present data show particularly interesting effects of DHEA on the three layers of the vaginal wall, namely a highly mucified epithelium, an increased muscularis thickness and increased collagen fiber compactness in the lamina propria. DHEA exerts both androgenic and estrogenic effects on the vaginal mucosa, thus providing a more physiological replacement therapy.

A Double‐Blind Randomized Placebo Control Study Comparing the Objective and Subjective Changes in Female Sexual Response Using Sublingual Apomorphine

INTRODUCTION

Female sexual dysfunction and its therapeutic approach is a growing area.

AIM

We aimed to assess the subjective and objective changes of the female sexual response, in patients with orgasmic sexual dysfunction using 3 mg SL Apomorphine (APO).

METHODS

Twenty-four patients (mean age 32 years old, SD: 9.69) were included in a prospective randomized cross-over protocol. Sexual response was evaluated objectively (duplex ultrasound) and subjectively (self-reported questionnaire) following vibrator stimuli with the addition of 3 mg SL APO or placebo.

MAIN OUTCOME MEASURE

Sexual response objective (PSV, EDV, RI) and subjective (arousal and lubrication degree and orgasm achievement). Adverse events were also recorded.

RESULTS

Clitoral hemodynamical changes, particularly peak systolic velocity (PSV), were significantly higher with APO (P = 0.003), mean increase of PSV poststimulus was 72.50% with placebo (from 9.7 cm/second to 17.0 cm/second) and 139.14% with APO (from 9.7 cm/second to 21.4 cm/second). SUBJECTIVE CHANGES (AROUSAL AND LUBRICATION) WERE ALSO SIGNIFICATIVE WITH APO (P < 0.05).

CONCLUSION

According to our observations, APO seemed to produce more subjective and objective changes in the sexual arousal phase of women with orgasmic sexual dysfunction than placebo. Future research is needed to evaluate the place of this drug in the treatment of the female sexual dysfunction.

Sex steroid hormones differentially regulate nitric oxide synthase and arginase activities in the proximal and distal rabbit vagina

Nitric oxide synthase (NOS) and arginase have been shown to regulate nitric oxide (NO) production reciprocally in genital tissues. In animal models, NO is an important regulator of vaginal blood flow and vaginal wall contractility. In this study, we investigated the modulation of NOS and arginase activities by estrogens and androgens in the proximal and distal rabbit vagina. In intact control animals, total NOS activity was higher in the proximal (528+/-78 pmol/mg protein) than the distal (391+/-44 pmol/mg protein) vagina. However, arginase activity was higher in the distal (206+/-8 nmol/mg protein) than the proximal (64+/-5 nmol/mg protein) vagina. Ovariectomy enhanced NOS activity in the proximal but not distal vagina with concomitant decrease in arginase activity in both the proximal and distal vagina. In ovariectomized rabbits, replacement with 5alpha-dihydrotestosterone (DHT) or Delta5-androstenediol (Adiol) increased NOS activity beyond that observed in ovariectomized rabbits receiving vehicle. In contrast, DHT and Adiol treatment reduced arginase activity more than that of the ovariectomized rabbits receiving vehicle. Testosterone exhibited inconsistent effects on NOS and arginase activity in the distal and proximal vagina. Estradiol replacement in ovariectomized animals reduced NOS activity in the proximal vagina down to levels that were comparable to intact control animals. However, estradiol positively modulated arginase activity in the distal vagina. Western blot analyses indicated that in the proximal vagina, neural NOS protein levels paralleled the changes observed in enzyme activity. These observations suggest that steroid hormones differentially regulate NOS and arginase activities of the proximal and distal regions of the vagina. Although estrogen treatment reduced total NOS activity in proximal vagina, estrogens are known to enhance vaginal blood flow. This paradoxical observation may be explained by differential regulation of n-NOS and e-NOS in the proximal and distal vagina. We suggest that changes in vaginal blood flow and compliance may depend on the endocrine status and the levels of circulating androgens and estrogens.

Topical administration of the nitric oxide donor glyceryl trinitrate modifies the structural and biomechanical properties of ovine articular cartilage

OBJECTIVE

To examine the effect of topical administration of glyceryl trinitrate (GTN), an exogenous nitric oxide (NO) donor, on the structural and biomechanical properties of uncalcified articular cartilage (UCC) in aged ewes.

DESIGN

Twelve ewes were used for this study. Six of these were treated with 2% GTN ointment (0.7 mg/kg) twice per week (GTN), and the remaining six were used as normal controls (NOC). After sacrifice at 26 weeks, dynamic biomechanical indentation testing and thickness determination (by needle penetration) were performed on tibial plateau articular cartilage at 18 locations. Using histological sections prepared from the lateral and medial femoral condyles (LFC, MFC) and tibial plateau (LTP, MTP), the thickness of UCC, cartilage proteoglycan content (intensity of toluidine blue staining; LFC, MFC only), and collagen birefringence (LTP, MTP, LFC only) were quantified by computer-assisted image analysis.

RESULTS

Phase lag of tibial plateau cartilage was reduced in GTN sheep relative to NOC (mean of all testing locations 11.0+/-1.9 degrees vs 12.1+/-2.3 degrees; P=0.0001). GTN treatment also globally reduced UCC thickness across the joint (ANOVA for all measured zones, P<0.0001). UCC thinning was most pronounced in the MFC (P=0.025) and LTP (P=0.0002). Proteoglycan content was reduced in the MFC(P=0.019), while collagen birefringence was increased in superficial cartilage zones of the LTP.

CONCLUSIONS

NO donation via topical administration of GTN to normal ewes reduced the thickness and phase lag of femoro-tibial articular cartilage, suggesting a disturbance in chondrocyte metabolism. Regional alterations of collagen organisation and proteoglycan content were consistent with this interpretation.

A review of the physiology and pharmacology of peripheral (vaginal and clitoral) female genital arousal in the animal model

PURPOSE

We review contemporary scientific data concerning the physiology and pharmacology of peripheral female genital arousal responses in the animal (rabbit and rat) model.

MATERIALS AND METHODS

We reviewed the contemporary literature and our research studies concerning physiology and pharmacology of peripheral genital arousal from 3 experimental animal models, including genital smooth muscle cell culture, genital strip organ bath and in vivo animal model studies.

RESULTS

Nitric oxide (NO) appears to be a key pathway mediating clitoral smooth muscle relaxation. In the vagina NO appeared to have a more controversial role in mediating vaginal muscularis smooth muscle relaxation. Vasoactive intestinal polypeptide induced vaginal smooth muscle relaxation. Functional alpha-adrenergic receptors were expressed in the clitoris and vagina, and mediated norepinephrine induced genital smooth muscle contraction. Androgens and estrogens modulated distinct physiological responses in vagina, and androgens facilitated vaginal smooth muscle relaxation. Papaverine hydrochloride, a smooth muscle relaxant, and phentolamine mesylate, an alpha-blocker, administered into the vaginal spongy muscularis layer increased vaginal wall pressure and vaginal blood flow. Sildenafil caused significant increases in genital (clitoral and vaginal) blood flow and vaginal lubrication in intact and ovariectomized animals. This response was more pronounced in animals treated with estradiol, suggesting that the NO cyclic guanosine monophosphate pathway is involved in the physiological mechanism of female genital arousal and that sildenafil facilitates this response in an in vivo animal model.

CONCLUSIONS

To achieve improved understanding of the biological aspects of female sexual function, further research is needed in the physiology and pharmacology of peripheral (clitoral and vaginal) genital arousal in the animal model.

Morphological modifications in clitoris and vagina in spontaneously hypertensive rats

We evaluated possible morphological alteration in clitoris and vagina from spontaneous hypertensive rats (SHR) and normotensive WKY rats. Clitoris and vagina were processed by Masson's trichrome, anti-alpha-smooth-muscle actin, anticollagen type I (COL I) and type III (COL III), and anti-TGFbeta(1). SHR presented higher amount of clitoral cavernous smooth muscle (CSM), vascular smooth muscle; TGFbeta(1) in clitoral vessel wall; higher wall/lumen ratio in both vaginal and clitoral vessels; and remarkable interstitial fibrosis, expressed by a higher amount in interstitial COL I and III in both clitoris and vagina, compared to WKY rats. Nerve fibers from clitoral and vaginal tissue in SHR showed important fibrosis at perineurium. SHR showed positive correlation between systolic blood pressure (SBP) and clitoral CSM; SBP and fibrosis in clitoris; and SBP and COL I and III in clitoris, respectively. Similar findings were observed between SBP and COL I and III in vagina. In conclusion, SHR present morphologic changes in clitoral vessels as well as in clitoral cavernous space, which have a high positive correlation with the high blood pressure level. Moreover, the increase in extracellular matrix affects not only the clitoral and vaginal interstitium but also the nerve structures from both clitoris and vagina.

Nitric oxide-cyclic GMP signaling pathway in the regulation of rabbit clitoral cavernosum tone

We investigated the role of nitric oxide (NO)-guanosine 3',5'-cyclic monophosphate (cGMP) signaling in the regulation of rabbit clitoral cavernosum (CC) tone. Tension measurements, reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and NADPH-diaphorase staining were performed in CC. In the precontracted CC strips with phenylephrine (10(-5) M), acetylcholine (ACh) relaxed, dependent on dosage. Pretreatment with atropine, N(omega) nitro-L-arginine-methyl ester (NAME) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), guanylate cyclase inhibitor abolished the ACh-induced relaxations, but tetrodotoxin (TTX) did not. Sodium nitroprusside relaxed the strips in the presence of atropine and NAME, but not in the presence of ODQ. Electrical field stimulation (EFS) relaxed the strips dependent on stimulus strength. Pretreatment with TTX, NAME, or ODQ abolished the EFS-induced relaxation, but atropine did not. L-Arginine partially restored the inhibited response to ACh and EFS. The inducible NO synthase (iNOS) and neuronal NOS (nNOS) mRNAs and iNOS and endothelial NOS (eNOS) proteins were identified in the CC. NADPH-diaphorase staining revealed the positivity on the nerve trunks and fine nerve fibers in the CC. Finally, results demonstrate that the nNOS, ENOS, and the NO-cGMP signaling pathway are involved in the regulation of clitoral tumescence.