Role of arginase in the male and female sexual arousal response

Expression of the Discoidin Domain Receptor Family Depended on Glucose and Their High Expression in Arterial Tissues in the Rat Model of Type 2 Diabetes

The active form of discoidin domain receptors (DDRs) is expressed in cell surface and regulated post-translationally by glucose. The DDR2 and DDR1 transfected in HEK293 cells were expressed mainly in their active forms with sizes of 130 and 120 kDa, respectively. DDRs were observed predominantly as 100 kDa proteins in glucose-depleted culture conditions. However, transfection of endothelial growth factor receptor (EGFR) in HEK293 cells resulted in the expression of only one form regardless of glucose concentration. Vascular smooth muscle cells, HT1080s, and MDA-MB-231 cancer cells expressed DDRs in their active forms in high glucose concentrations, which did not occur with EGFR. In diabetic rats, DDRs were expressed at high levels in arterial tissue but EGFR was not highly expressed. Taken together, these results suggest that DDRs expression depends on glucose concentration it may cooperate in the development of atherosclerosis and kidney fibroblasts, promoting nephropathy in diabetic rats.

An Update on Arginase Inhibitors and Inhibitory Assays

Arginase, which converts arginine into ornithine and urea, is a promising therapeutic target. Arginase is involved in cardiovascular diseases, parasitic infections and, through a critical role in immunity, in some cancers. There is a need to develop effective arginase inhibitors and therefore efforts to identify and optimize new inhibitors are increasing. Several methods of evaluating arginase activity are available, but few directly measure the product. Radiometric assays need to separate urea and dying reactions require acidic conditions and sometimes heating. Hence, there are a variety of different approaches available, and each approach has its own limits and benefits. In this review, we provide an update on arginase inhibitors, followed by a discussion on available arginase assays and alternative methods, with a focus on the intrinsic biases and parameters that are likely to impact results.

Diet Supplemented with Chrysophyllum albidum G. Don (Sapotaceae) Fruit Pulp Improves Reproductive Function in Hypertensive Male Rats

Hypertension has been implicated as a risk factor of reproductive disorders. High blood pressure may trigger impaired sperm quality and biomarkers of reproductive disorders. This study aims to investigate the effect of diet supplemented with Chrysophyllum albidum fruit pulp (FP) on sperm parameters, reproductive hormones, and antioxidant markers in testes and epididymis of hypertensive rats. Male Wistar rats were divided into seven groups (n = 10): normotensive control rats [NC], cyclosporine (25 mg/kg)-induced hypertensive rats [Hypert], hypertensive rats treated with captopril (10 mg/kg/day) [Hypert + Capt], hypertensive [Hypert + 2%FP and Hypert + 4%FP], and normotensive [2%FP and 4%FP] rats treated with 2% and 4% of diet supplemented with African star apple fruit's pulp [FP]. Hemodynamic parameters (arterial pressure, diastolic, and systolic pressure), sperm count, sperm motility, reproductive hormones, reactive oxygen species, and malondialdehyde levels were assessed. Diet supplemented with FP fed to hypertensive rats reduced mean arterial pressure, diastolic and systolic blood pressure, and heart rate. Furthermore, FP improved sperm quality in hypertensive rats by increasing sperm count, sperm motility with a concomitant reduction in sperm abnormality. FP also increased 3β and 17β-hydroxysteroid hydrogenase (3β-HSD and 17β -HSD) activities, as well as testosterone, luteinizing hormone, and follicle-stimulating hormone levels. Besides, FP triggered a significant increase in 3β-HSD, 17β -HSD, and STAR expression in rats' testicular tissues. Diet supplemented with FP also reduced ROS and malondialdehyde levels and triggered an increase in thiol levels, catalase, and glutathione-S-transferase activities. This study revealed that FP supplemented diet improved sexual function in cyclosporine-induced hypertensive rats by reducing blood pressure and modulation of sperm parameters, steroidogenic enzymes, and reproductive hormones.

Diets supplemented with raw and roasted pumpkin (Cucurbita pepo L) seeds improved some biochemical parameters associated with erectile function in rats

This study investigated the effect of diet supplemented with raw and roasted pumpkin seeds on some key biochemical parameters relevant to erectile function in corpus cavernosal tissues of male rats. Rats were fed with basal diets (NC), diet supplemented with raw (5% and 10%) and roasted (5% and 10%) pumpkin seeds for the evaluation of adenosine deaminase (ADA), phosphodiesterase-5 (PDE-5), arginase, acetylcholinesterase (AChE) activities, including nitric oxide level and malondialdehyde (MDA) content. Diet supplemented with roasted pumpkin seeds showed better PDE-5, ADA, arginase activities, as well as NO and MDA levels. No significant difference was observed in AChE activities of rats treated with raw and roasted pumpkin seeds. The modulatory effects of raw and roasted pumpkin seeds on enzymes associated with erectile dysfunction suggest the biochemical rationale for its therapeutic role in enhancing erectile function. However, roasted pumpkin seeds (10%, w/w of diet) possess more beneficial effects than the raw seeds. PRACTICAL APPLICATIONS: Pumpkin is a nutritious vegetable used in folklore for the treatment of bladder, prostate, and kidney diseases. The seeds are known to contain phenolic compounds which exert different health benefits. Processing of foods has been shown to either improve the quality or reduce the bioactive components which affect its functionality. In this study, roasting improved the biochemical parameters associated with erectile function in male rats. Roasted pumpkin seeds also reduced the oxidative stress parameters in rats' penile tissues when compared to raw pumpkin seeds. This study revealed that thermal processing associated with roasting could improve the antioxidant activity of pumpkin seeds and crucial enzymes related to erectile function. Hence, consumption of roasted pumpkin seeds could be more beneficial compared to raw pumpkin seeds.

Pharmacokinetics and Pharmacodynamics of Promising Arginase Inhibitors

Up-regulation of arginase activity in several chronic disease conditions, including cancer and hypertension, may suggest new targets for treatment. Recently, the number of new arginase inhibitors with promising therapeutic effects for asthma, cancer, hypertension, diabetes mellitus, and erectile dysfunction has shown a remarkable increase. Arginase inhibitors may be chemical substances, such as boron-based amino acid derivatives, α-difluoromethylornithine (DMFO), and Nω-hydroxy-nor-L-arginine (nor-NOHA) or, of plant origin such as sauchinone, salvianolic acid B (SAB), piceatannol-3-O-β-D-glucopyranoside (PG) and obacunone. Despite their promising therapeutic potential, little is known about pharmacokinetics and pharmacodynamics of some of these agents. Several studies were conducted in different animal species and in vitro systems and reported significant differences in pharmacokinetics and pharmacodynamics of arginase inhibitors. Therefore, extra caution should be considered before extrapolating these studies to human. Physicochemical and pharmacokinetic profiles of some effective arginase inhibitors make it challenging to formulate stable and effective formulation. In this article, existing literature on the pharmacokinetics and pharmacodynamics of arginase inhibitors were reviewed and compared together with emphasis on possible drug interactions and solutions to overcome pharmacokinetics challenges and shortage of arginase inhibitors in clinical practice.

Deep sequencing of the transcriptome in the anterior pituitary of heifers before and after ovulation

We aimed to determine gene expression patterns in the anterior pituitary (AP) of heifers before and after ovulation via deep sequencing of the transcriptome (RNA-seq) to identify new genes and clarify important pathways. Heifers were slaughtered on the estrus day (pre-ovulation; n=5) or 3 days after ovulation (post-ovulation; n=5) for AP collection. We randomly selected 4 pre-ovulation and 4 post-ovulation APs, and the ribosomal RNA-depleted poly (A)+RNA were prepared to assemble next-generation sequencing libraries. The bovine APs expressed 12,769 annotated genes at pre- or post-ovulation. The sum of the reads per kilobase of exon model per million mapped reads (RPKM) values of all transcriptomes were 599,676 ± 38,913 and 668,209 ± 23,690, and 32.2 ± 2.6% and 44.0 ± 4.4% of these corresponded to the AP hormones in the APs of pre- and post-ovulation heifers, respectively. The bovine AP showed differential expression of 396 genes (P<0.05) in the pre- and post-ovulation APs. The 396 genes included two G-protein-coupled receptor (GPCR) genes (GPR61 and GPR153) and those encoding 13 binding proteins. The AP also expressed 259 receptor and other 364 binding proteins. Moreover, ingenuity pathway analysis for the 396 genes revealed (P=2.4 × 10⁻³) a canonical pathway linking GPCR to cytoskeleton reorganization, actin polymerization, microtubule growth, and gene expression. Thus, the present study clarified the novel genes found to be differentially expressed before and after ovulation and clarified an important pathway in the AP.

Erectogenic and Aphrodisiac Property of Moringa oleifera: Involvement of Soluble Epoxide Hydrolase Enzyme

Soluble epoxide hydrolase (sEH) inhibitors have been reported to improve penile erection; therefore, sEH could be useful for management of erectile dysfunction. Methanolic and aqueous extracts of 30 Indian medicinal plants were screened for their sEH inhibition potential. Fifteen extracts showed >50% inhibition when screened at 50 µg/mL in sEH inhibition assay. Methanolic extract of Moringa oleifera Lam. (Moringaceae) seeds (MEMO) was most potent with IC50 1.7 ± 0.1 µg/mL and was selected for in vitro studies on isolated rat corpus cavernosum smooth muscle and in vivo sexual behaviour studies on healthy and diabetic rats. Rats were divided into five groups, each containing six animals and treated orally with either water, vehicle (1% Tween-20), MEMO (45 and 90 mg/kg/day for 21 days), and standard drug, sildenafil (5 mg/kg/day for 7 days). An equal number of female rats were used, and the effect of MEMO and sildenafil was compared with that of vehicle. MEMO significantly relaxed isolated rat corpus cavernosum smooth muscle at 0.1-100 µg/mL in vitro and significantly increased (p < 0.05) sexual activity, intracavernous pressure/mean arterial pressure in normal and diabetic rats. The increase in erectile function of rats by MEMO could be because of its sEH inhibitory activity. Copyright © 2016 John Wiley & Sons, Ltd.

Arginase as a Critical Prooxidant Mediator in the Binomial Endothelial Dysfunction-Atherosclerosis

Arginase is a metalloenzyme which hydrolyzes L-arginine to L-ornithine and urea. Since its discovery, in the early 1900s, this enzyme has gained increasing attention, as literature reports have progressively pointed to its critical participation in regulating nitric oxide bioavailability. Indeed, accumulating evidence in the following years would picture arginase as a key player in vascular health. Recent studies have highlighted the arginase regulatory role in the progression of atherosclerosis, the latter an essentially prooxidant state. Apart from the fact that arginase has been proven to impair different metabolic pathways, and also as a consequence of this, the repercussions of the actions of such enzyme go further than first thought. In fact, such metalloenzyme exhibits direct implications in multiple cardiometabolic diseases, among which are hypertension, type 2 diabetes, and hypercholesterolemia. Considering the epidemiological repercussions of these clinical conditions, arginase is currently seen under the spotlights of the search for developing specific inhibitors, in order to mitigate its deleterious effects. That said, the present review focuses on the role of arginase in endothelial function and its participation in the establishment of atherosclerotic lesions, discussing the main regulatory mechanisms of the enzyme, also highlighting the potential development of pharmacological strategies in related cardiovascular diseases.

Pro-sexual effects of Turnera diffusa Wild (Turneraceae) in male rats involves the nitric oxide pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Turnera diffusa Wild has been used in folk medicine by its aphrodisiac and tranquilizing properties. Previously we experimentally showed the aphrodisiac effect of a chemically characterized aqueous extract of Turnera diffusa in male rats. However, the mechanism of action underlying such effects has not been studied.

STUDY AIMS

As part of our systematic studies of pharmacological properties of Turnera diffusa, we aimed to analyze whether the increased sexual motivation and the augmented sexual performance of sexually sluggish (SL) male rats treated with Turnera diffusa involves the NO pathway. Additionally we analyzed whether such effects were exerted at the level of the brain or the spinal cord. Finally, anxiety levels and ambulatory activity were also evaluated.

MATERIAL AND METHODS

Turnera diffusa (10-40 mg/kg) and sildenafil citrate (10 mg/kg) with or without a nonspecific inhibitor of NO synthase, Nω-nitro-L-arginine methyl esther (L-NAME, 12.5 mg/kg) were evaluated in SL rats, in a standard sexual behavior test and in the fictive ejaculation model in spinal cord transected and urethane-anaesthetized SL rats. Anxiety levels or ambulation were assessed in the burying behavior and open-field tests.

RESULTS

Turnera diffusa and sildenafil (both at 10 mg/kg) facilitated expression of male sexual behavior by shortening mainly ejaculation latency. Treatments also facilitated the number of discharges in the ejaculatory motor pattern as well as the number of ejaculatory motor patterns and its associated penile erections. L-NAME prevented the pro-sexual effects of treatments on both experimental models. Besides, the extract of Turnera diffusa (10 mg/kg) produced an anxiolytic-like effect in male rats without affecting ambulation.

CONCLUSIONS

Findings from the present work support the notion that pro-sexual effect of the aqueous extract of Turnera diffusa in rats involves the participation of NO pathway, mainly at central level. The anxiolytic-like effect of Turnera diffusa is an advantage to its use for improving sexual performance.

S-nitrosation of arginase 1 requires direct interaction with inducible nitric oxide synthase

Arginase constrains endothelial nitric oxide synthase activity by competing for the common substrate, L -Arginine. We have recently shown that inducible nitric oxide synthase (NOS2) S-nitrosates and activates arginase 1 (Arg1) leading to age-associated vascular dysfunction. Here, we demonstrate that a direct interaction of Arg1 with NOS2 is necessary for its S-nitrosation. The specific domain of NOS2 that mediates this interaction is identified. Disruption of this interaction in human aortic endothelial cells prevents Arg1 S-nitrosation and activation. Thus, disruption of NOS2-Arg1 interaction may represent a therapeutic strategy to attenuate age related vascular endothelial dysfunction.

Sonochemical stabilization of ultrafine colloidal biocompatible magnetite nanoparticles using amino acid, L-arginine, for possible bio applications

Materials obtained by the synergistic combination of nanotechnology and biomedicine are an important source of drug delivery and other health care related applications. The anchoring of amino acids onto the surface of nano-sized magnetite is one such example. Herein, we report on the binding of a semi-essential amino acid, L-arginine, onto the surface of nano magnetite, creating a stable aqueous suspension by an in situ one-step method using sonochemical synthesis. An ex situ two-step process was also attempted, but was soon discarded owing to the relative short duration of the suspension attributed to increase in particle size and lower extent of binding. The initial concentration of the amino acid was found to play an important role in controlling the particle size and also the binding motif. Lower concentrations of arginine were found to favor the formation of elongated tubular structures, while at higher concentrations, the elongated structures were less prominent and arginine was found to be adsorbed onto the surface of the magnetite. This surface-functionalized nanomagnetite with amino acids could become a promising vehicle for drug delivery.

Recent advances in arginine metabolism: roles and regulation of the arginases

As arginine can serve as precursor to a wide range of compounds, including nitric oxide, creatine, urea, polyamines, proline, glutamate and agmatine, there is considerable interest in elucidating mechanisms underlying regulation of its metabolism. It is now becoming apparent that the two isoforms of arginase in mammals play key roles in regulation of most aspects of arginine metabolism in health and disease. In particular, work over the past several years has focused on the roles and regulation of the arginases in vascular disease, pulmonary disease, infectious disease, immune cell function and cancer. As most of these topics have been considered in recent review articles, this review will focus more closely on results of recent studies on expression of the arginases in endothelial and vascular smooth muscle cells, post-translational modulation of arginase activity and applications of arginase inhibitors in vivo.

Probing the specificity determinants of amino acid recognition by arginase

Arginase is a binuclear manganese metalloenzyme that serves as a therapeutic target for the treatment of asthma, erectile dysfunction, and atherosclerosis. In order to better understand the molecular basis of inhibitor affinity, we have employed site-directed mutagenesis, enzyme kinetics, and X-ray crystallography to probe the molecular recognition of the amino acid moiety (i.e., the alpha-amino and alpha-carboxylate groups) of substrate l-arginine and inhibitors in the active site of arginase I. Specifically, we focus on (1) a water-mediated hydrogen bond between the substrate alpha-carboxylate and T135, (2) a direct hydrogen bond between the substrate alpha-carboxylate and N130, and (3) a direct charged hydrogen bond between the substrate alpha-amino group and D183. Amino acid substitutions for T135, N130, and D183 generally compromise substrate affinity as reflected by increased K(M) values but have less pronounced effects on catalytic function as reflected by minimal variations of k(cat). As with substrate K(M) values, inhibitor K(d) values increase for binding to enzyme mutants and suggest that the relative contribution of intermolecular interactions to amino acid affinity in the arginase active site is water-mediated hydrogen bond < direct hydrogen bond < direct charged hydrogen bond. Structural comparisons of arginase with the related binuclear manganese metalloenzymes agmatinase and proclavaminic acid amidinohydrolase suggest that the evolution of substrate recognition in the arginase fold occurs by mutation of residues contained in specificity loops flanking the mouth of the active site (especially loops 4 and 5), thereby allowing diverse guanidinium substrates to be accommodated for catalysis.

Inhibition of arginase activity enhances inflammation in mice with allergic airway disease, in association with increases in protein S-nitrosylation and tyrosine nitration

Pulmonary inflammation in asthma is orchestrated by the activity of NF-kappaB. NO and NO synthase (NOS) activity are important modulators of inflammation. The availability of the NOS substrate, l-arginine, is one of the mechanisms that controls the activity of NOS. Arginase also uses l-arginine as its substrate, and arginase-1 expression is highly induced in a murine model of asthma. Because we have previously described that arginase affects NOx content and interferes with the activation of NF-kappaB in lung epithelial cells, the goal of this study was to investigate the impact of arginase inhibition on the bioavailability of NO and the implications for NF-kappaB activation and inflammation in a mouse model of allergic airway disease. Administration of the arginase inhibitor BEC (S-(2-boronoethyl)-l-cysteine) decreased arginase activity and caused alterations in NO homeostasis, which were reflected by increases in S-nitrosylated and nitrated proteins in the lungs from inflamed mice. In contrast to our expectations, BEC enhanced perivascular and peribronchiolar lung inflammation, mucus metaplasia, NF-kappaB DNA binding, and mRNA expression of the NF-kappaB-driven chemokine genes CCL20 and KC, and lead to further increases in airways hyperresponsiveness. These results suggest that inhibition of arginase activity enhanced a variety of parameters relevant to allergic airways disease, possibly by altering NO homeostasis.

Zaprinast, a phosphodiesterase type-5 inhibitor, alters paced mating behavior in female rats

Nitric oxide (NO) is the primary mediator of blood flow in female genital tissues and drugs that enhance the activity of nitric oxide, such as phosphodiesterase type-5 (PDE-5) inhibitors, increase vaginal blood flow in anesthetized rats. The goal of the present study was to test the effects of one PDE-5 inhibitor, zaprinast, on the display of sexual behaviors in gonadectomized, estrogen- and progesterone-treated female rats. Experiment 1 demonstrates that zaprinast alters paced mating behavior by lengthening the contact-return latency to ejaculation; there is a significant relationship between dose of zaprinast (range 1.5-6 mg/kg) and contact-return latency to ejaculation. Experiment 2 illustrates that zaprinast has no effect on preference for an intact male as measured in a No Contact partner preference test. Rats receiving zaprinast tend to exhibit reduced locomotor activity in both experiments. Collectively, these findings demonstrate that modulation of the NO-cGMP pathway using a PDE-5 inhibitor alters the display of paced mating behaviors in rats.

Inducible NO synthase dependent S-nitrosylation and activation of arginase1 contribute to age-related endothelial dysfunction

Endothelial function is impaired in aging because of a decrease in NO bioavailability. This may be, in part, attributable to increased arginase activity, which reciprocally regulates NO synthase (NOS) by competing for the common substrate, L-arginine. However, the high Km of arginase (>1 mmol/L) compared with NOS (2 to 20 micromol/L) seemingly makes direct competition for substrate unlikely. One of the mechanisms by which NO exerts its effects is by posttranslational modification through S-nitrosylation of protein cysteines. We tested the hypothesis that arginase1 activity is modulated by this mechanism, which serves to alter its substrate affinity, allowing competition with NOS for L-arginine. We demonstrate that arginase1 activity is altered by S-nitrosylation, both in vitro and ex vivo. Furthermore, using site-directed mutagenesis we demonstrate that 2 cysteine residues (C168 and C303) are able to undergo nitrosylation. S-Nitrosylation of C303 stabilizes the arginase1 trimer and reduces its Km value 6-fold. Finally, arginase1 nitrosylation is increased (and thus its Km decreased) in blood vessels from aging rats, likely contributing to impaired NO bioavailability and endothelial dysfunction. This is mediated by inducible NOS, which is expressed in the aging endothelium. These findings suggest that S-nitrosylated arginase1 can compete with NOS for L-arginine and contribute to endothelial dysfunction in the aging cardiovascular system.

Chronic foot shock induces hyperactive behaviors and accompanying pro- and anti-inflammatory responses in mice

Behavioral and accompanying physiological and immunological changes were investigated at various times during chronic irregular mild foot shock (CMFS) in adult male BALB/c mice. CMFS induced a significant hyperlocomotor activity in a familiar environment as well as increased consumption of chocolate milk (a favored drink) throughout the 5-week stress period. Unlike other chronic stress models, CMFS did not induce depressive-like behaviors. Hyperactivity was associated with transient elevations of pro-inflammatory cytokines (TNFalpha and IL-1beta) and IL-2 and more sustained (IL-10) or later (arginase activity) elevations in anti-inflammatory mediators in the spleen (serum levels below levels of detection) suggesting a transition from a pro-inflammatory state to an anti-inflammatory state during CMFS. Similar increases in brain levels of IL-2 and arginase activity were also detected and may contribute to CMFS-induced hyperactivity as both of these mediators have been shown to induce hyperactivity. To our knowledge, this is the first time that increased arginase activity has been documented during a stress paradigm. Altogether, the data indicate that CMFS induces behavioral changes distinct from other chronic stress models. CMFS is associated with multiple dynamic immunological changes, suggesting involvement of multiple factors in chronic stress-induced behavioral changes.

Effects of tamoxifen on vaginal blood flow and epithelial morphology in the rat

Background

Tamoxifen, a selective estrogen receptor modulator with both estrogenic and anti-estrogenic activity, is widely used as adjuvant therapy in breast cancer patients. Treatment with tamoxifen is associated with sexual side effects, such as increased vaginal dryness and pain/discomfort during sexual activity. There have been limited investigations of the effect of tamoxifen on estrogen-dependent peripheral genital arousal responses. The objective of this study was to investigate the effects of tamoxifen on vaginal physiology in the rat.

Methods

Female Sprague-Dawley rats were subjected to sham surgery or bilateral ovariectomy. After 2 weeks, sham-operated rats were implanted with subcutaneous osmotic infusion pumps containing vehicle (control) or tamoxifen (150 μg/day). Ovariectomized rats were similarly infused with vehicle. After an additional 2 weeks, vaginal blood flow responses to pelvic nerve stimulation were measured by laser Doppler flowmetry and vaginal tissue was collected for histological and biochemical assay.

Results

Tamoxifen treatment did not change plasma estradiol concentrations relative to control animals, while ovariectomized rats exhibited a 60% decrease in plasma estradiol. Tamoxifen treatment caused a significant decrease in mean uterine weight, but did not alter mean vaginal weight. Vaginal blood flow was significantly decreased in tamoxifen-infused rats compared to controls. Similar to ovariectomized animals, estrogen receptor binding was increased and arginase enzyme activity was decreased in tamoxifen-infused rats. However, different from control and ovariectomized animals, the vaginal epithelium in tamoxifen-infused rats appeared highly mucified. Periodic acid-Schiff staining confirmed a greater production of carbohydrate-rich compounds (e.g. mucin, glycogen) by the vaginal epithelium of tamoxifen-infused rats.

Conclusion

The observations suggest that tamoxifen exerts both anti-estrogenic and pro-estrogenic effects in the vagina. These physiological alterations may eventually lead to vaginal atrophy and compromise sexual function.

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.