Castrated Male Rats Research Articles

Transient reversal of olfactory preference following castration in male rats: Implication for estrogen receptor involvement

We examined the effects of the sex steroid milieu on sexual odor preference of sexually-experienced male rats using an alternate choice paradigm after endocrine manipulations. Gonadally intact (GI) males showed a male typical preference, i.e. spent longer time sniffing estrous females than males or ovariectomized females. At 1–2weeks after orchidectomy (ORx), the males exhibited a transient preference for sexually vigorous males, a female typical preference pattern, followed by a total loss of preference after 4weeks. Subcutaneous implantation of a Silastic capsule containing formestane (4-OHA), an aromatase inhibitor, had no effect on the preference of gonadally intact rats, but successfully prevented the emergence of the female typical preference after ORx. Capsules containing testosterone (T), dihydrotestosterone (DHT), or estradiol benzoate (EB), but not those with cholesterol (CH), restored masculine typical preference in ORx males at 2weeks after the placement. The feminine preference for males was observed at 2–3weeks after removal of T or EB capsules, but not by the removal of DHT and CH capsules. The results suggest that either exogenous androgen or estrogen maintains the masculine typical odor preference. Estrogen itself or produced through aromatization of circulating T, induces a transient feminine typical preference at a certain decreased titer during its disappearance from the circulation. Estrogen at different titers might determine appearance of masculine or feminine typical olfactory preference in adult ORx rats.

Estradiol enhances the acquisition of lithium chloride-induced conditioned taste aversion in castrated male rats.

The present study examined the effects of short-term treatment with ovarian hormones on the acquisition of conditioned taste aversion (CTA). Adult male rats were castrated and randomly divided into LiCl- and saline-treated groups. Nineteen days after castration, all of the animals were subjected to 23.5-h daily water deprivation for seven successive days (day 1 to day 7). On the conditioning day (day 8), the rats received either a 4 ml/kg of 0.15 M LiCl or the same dose of saline injection immediately after administration of a 2 % sucrose solution during the 30-min water session. Starting from day 6, rats in both groups received one of the following treatments: daily subcutaneous injection of (1) estradiol alone (30 μg/kg; estradiol benzoate (E) group), (2) estradiol plus progesterone (500 μg; E + progesterone (P) group), or (3) olive oil. From day 9 to day 11, all of the rats were given daily two-bottle preference tests during the 30-min fluid session. The estradiol and estradiol plus progesterone treatments in the LiCl groups resulted in significantly lower preference scores for the sucrose solution compared with the olive oil treatment groups, but no difference in preference score was seen between these two groups. These results indicate that both the estradiol and estradiol plus progesterone treatments in the LiCl groups enhanced the acquisition of CTA learning and suggest that estradiol affects the acquisition of CTA mediated by an activational effect in male rats, whereas progesterone treatment does not influence the effects of estradiol on the acquisition of CTA.

Two aromatase inhibitors inhibit the ability of a third to promote mating in male rats

Aromatase, the enzyme that aromatizes androstenedione (A) to estrone and testosterone (T) to estradiol (E), affects androgen control of male sex behavior in many vertebrates. In male monkeys, rats and quail, E mimics the ability of T to promote mating, and aromatase inhibitors block mating induced by T but not E. Aromatase inhibitors include androgens with different A-rings than T and A, e.g., 1,4,6-androstatriene-3,17-dione (ATD), azoles, e.g., fadrozole, and androgens α-halogenated at carbon 6, e.g., 6α-bromoA, 6α-fluoroA and 6α-fluoroT. 6α-FluoroT is the only 6α-halogenated androgen studied in regard to mating. It promotes mating in male rats and quail and was studied, before it was known to inhibit aromatase, because it cannot be aromatized yet has the same A-ring as T. 6α-FluoroT might promote mating by binding estrogen receptors (ER) directly, i.e., unassisted, or by metabolism to an androgen that binds ER. Since neither process would require aromatase, this study tested both hypotheses by determining how mating induced in castrated male rats by 6α-fluoroT is affected by ATD and fadrozole. Both aromatase inhibitors inhibited the effects of 6α-fluoroT on mating. Thus, 6α-fluoroT does not promote mating by direct ER binding or metabolism to another androgen. Since aromatase underlies a process in which 6α-fluoroT, unlike most nonaromatizable androgens, mimics T effects on male sex behavior, the process must involve a feature that 6α-fluoroT shares with T but not other nonaromatizable androgens. A-ring structure is a candidate. A hypothesis is also offered for how aromatase may participate without aromatizing the androgen.

Sodium valproate effect on the structure of rat glandule thymus: Gender-related differences

Sodium valproate (VPA) was shown to inhibit cell growth mechanisms such as cell cycle arrest, proliferation suppression, increase of apoptosis. Many aspects of the contribution of the VPA pharmacological mechanisms and their significance in gender-related processes have not been investigated. In our study, we have tested hypothesis that the influence of VPA on thymus weight and structure might be gender-related. The thymus of Wistar rats of both genders aged 8 weeks was investigated in the following groups (n=6 each): controls, treated with VPA, castrated male and female treated with VPA, and the castrated control of both genders. The thymus weight, structural changes and area of cortical and medullar parts of the gland in slides stained with hematoxylin and eosin and immunohistochemically were assessed. A comparison of thymus weight of castrated male and of castrated VPA-treated male rats showed a significant thymus weight loss after VPA treatment (0.66±0.04g vs. 0.43±0.03g, p<0.05). The treatment with VPA caused an about 6-fold (0.39±0.12 vs. 0.07±0.03) increase of Hassall‘s corpuscles (HCs) numbers per 1mm2 in male and more than 4-fold increase (0.46±0.07 vs. 0.10±0.04) in female rats. In castrated males and females, the HCs number was also increased, but this increase was statistically significant only in male animals vs. controls (0.46±0.10 vs. 0.07±0.03, p<0.001 in males; 0.29±0.13 vs. 0.10±0.04, p>0.05 in females). When castrated male and female rats were treated with VPA, further increase of HC numbers was found. In our study, VPA has inhibited the proliferative capacity of thymocytes by diminishing the thymus weight and inducing a differentiation of thymic medullar epithelial cells into HCs. The diminishing of the gl. thymus weight under the influence of VPA was significant in castrated male rats. The number of HCs increased in animals of both genders under the influence of VPA. Gender differences in HCs development were noted in castrated animals.

Subcutaneous transplantation promotes organ formation of the fetal rat urogenital sinus

The aim of this study is to develop a novel experimental model of the subcutaneous transplantation of fetal urogenital sinus (UGS) into normal and castrated adult male rats for the pathophysiological investigation of the normal and developing prostate. Fetal UGS obtained from 20-day-old male rat embryos was subcutaneously transplanted into 7-week-old normal and castrated male rats. We observed the growth pattern, histopathological characteristics and immunohistochemical localization of cytokeratin 5 (CK 5), cytokeratin 8 (CK 8) and androgen receptor (AR) in the transplanted tissues. Almost all of the transplanted UGS organs gradually increased in weight over time in the non-castrated recipient animals, and the histopathological observations and immunohistochemical analysis of CK 5 and CK 8 revealed that the morphological changes in the tissues were in accordance with the features of normal prostate development. The histological characteristics included glandular epithelial dominant and stromal dominant area, with an increase in the glandular epithelial dominant areas over time and resemblance among a portion of the transplanted tissues within a certain period during the developmental course to the histopathology of human benign prostatic hyperplasia (BPH). The effects of androgens and resemblance in the immunohistochemical localization pattern changes in AR to that observed in the normal differentiating rat prostate were also noted. We conclude that the subcutaneous space provides an adequate microenvironment for UGS growth.

Effect of testosterone on Cisplatin-induced nephrotoxicity in surgically castrated rats.

Background:Cisplatin (CP) is an important antitumor drug with serious side effects such as nephrotoxicity. Estrogens can affect CP-induced nephrotoxicity; however, the role of testosterone (TS), the main male sex hormone, is not clear.Objectives:This study aimed to investigate the effect of TS on CP-induced nephrotoxicity in castrated male rats.Materials and Methods:A total of 54 male Wistar rats were castrated and allocated into eight groups. Groups 1 through 3 respectively received 10, 50, and 100 mg/kg/wk of TS and group 4 received sesame oil for four weeks; then all four groups received 2.5 mg/kg/d CP for one week. Groups 5 through 8 received the same treatment regimen as groups 1 through 4 during first four weeks but instead of CP, they received saline for one week. Then the animals were sacrificed for biochemical and histopathologic studies.Results:CP increased the serum levels of blood urea nitrogen (BUN), creatinine (Cr), and malondialdehyde (SMDA) as well as kidney weight (KW), bodyweight (BW) loss, and kidney tissue damage score (KTDS). It significantly decreased the serum and kidney levels of nitrite and serum level of TS in comparison with the control group (P < 0.05). However, coadministration of CP and low dose of TS significantly decreased the serum levels of BUN as well as Cr and KTDS (P < 0.05). Administration of high-dose TS alone increased the SMDA level, KTDS, and KW while decreased the BW significantly (P < 0.05).Conclusions:It seems that testosterone in low dose, i.e. physiologic dose, protects kidneys against CP-induced nephrotoxicity; however, special care is needed in CP therapy of patients with high levels of TS.

Novel molecular events associated with altered steroidogenesis induced by exposure to atrazine in the intact and castrate male rat

Toxicology is increasingly focused on molecular events comprising adverse outcome pathways. Atrazine activates the hypothalamic-pituitary adrenal axis, but relationships to gonadal alterations are unknown. We characterized hormone profiles and adrenal (intact and castrate) and testis (intact) proteomes in rats after 3 days of exposure. The adrenal accounted for most of the serum progesterone and all of the corticosterone increases in intact and castrated males. Serum luteinizing hormone, androstenedione, and testosterone in intact males shared a non-monotonic response suggesting transition from an acute stimulatory to a latent inhibitory response to exposure. Eight adrenal proteins were significantly altered with dose. There were unique proteomic changes between the adrenals of intact and castrated males. Six testis proteins in intact males had non-monotonic responses that significantly correlated with serum testosterone. Different dose–response curves for steroids and proteins in the adrenal and testis reveal novel adverse outcome pathways in intact and castrated male rats.

Testosterone enhances functional recovery after stroke through promotion of antioxidant defenses, BDNF levels and neurogenesis in male rats

It is reported that circulating testosterone levels decrease after cerebral ischemia. The aim of this study was to evaluate the effects of testosterone on oxidative stress, brain-derived neurotrophic factor (BDNF) levels, neurogenesis, histological damage and sensorimotor recovery in a castrated male rat model of focal cerebral ischemia. Animals were divided into four groups. For all animals, castrations were conducted 7 days before transient middle cerebral artery occlusion (MCAO) was done and cerebral ischemia was induced. The first group served as sham. Second was MCAO group and received vehicle only, third was MCAO group that was post-treated with testosterone and the fourth was MCAO group post-treated with testosterone and flutamide. Treatment only with testosterone significantly weakened oxidative stress and increased BDNF levels and sensorimotor recovery during a 10 days period. Rats receiving testosterone demonstrated a significant reduction in infarct volume and a significant increase in neurogenesis on 10th day after focal cerebral ischemia. Our results for the first time showed a potential advantageous effect of testosterone after cerebral ischemia in male rats, which was probably mediated by promoting antioxidant defenses, BDNF levels and neurogenesis.

Time-dependent effects of castration on the bladder function and histological changes in the bladder and blood vessels

We examined the effect of androgens on bladder blood flow (BBF), bladder function and histological changes in castrated male rats. Male Wistar rats were classified into unoperated group (control group), groups castrated at the age of 8 weeks (group 8wPC) and groups castrated at the age of 4 weeks (group 4wPC). Each rat was used at the age of 20 weeks. BBF was measured using fluorescent microspheres. Bladder cystometry was performed without anesthesia or restraint; the bladder was first irrigated with saline and then with 0.25% acetic acid (AA) solution. Maximum voiding pressure and voiding interval were measured. The bladder and iliac artery were histologically examined for differences in smooth muscle and quantity of collagen fiber to analyze the effect of castration on the smooth muscle content. No differences were noted in BBF following castration. The voiding intervals for all groups were shortened (P < 0.001) following AA irrigation. No significant difference was noted in the maximum voiding pressure. Histological changes were observed in bladder and iliac artery. Smooth muscle/collagen ratio at the bladder was lower in groups 8wPC and 4wPC compared to the control group (P< 0.01), while that at the iliac artery was decreased in group 4wPC compared to the control group (P< 0.001). In conclusion, our findings indicate that castration does not alter BBF, but leads to histological changes in the bladder as well as its associated blood vessels.

S141 The effect of losartan on fibrosis occurred in an castrated male rats model of veno-occlusive erectile dysfunction

S141 The effect of losartan on fibrosis occurred in an castrated male rats model of veno-occlusive erectile dysfunction

Denervation and Castration Effects on the Cross‐Sectional Area of Pubococcygeus Muscle Fibers in Male Rats

The number of fibers in skeletal muscles changes little through life; however, the cross-sectional area of its fibers is modified as result of denervation and in some muscles by castration. The pubococcygeus muscle (Pcm) participates in micturition and ejaculatory processes and its fibers cross-sectional area is reduced in castrated rats, but denervation effects remained unknown. Here, we used a model in which unilateral denervation of this muscle in gonadally intact and castrated male rats, allowed us to explore the neural and gonadal hormone effects on the cross-sectional area of its fibers. Denervation significantly reduced the mean cross-sectional area values; likewise, the percentage distribution of its fibers. We found that castration had a greater effect than denervation. Castration resulted in a lack of fibers from 2,000 to 3,999 μm(2) , while in denervation it was from 2,500 to 3,999 μm(2) . It was interpreted that the castration effect was due to a lack of the direct gonadal hormone effect on muscle fibers, and to a reduction of the indirect hormonal action in its neuromuscular complex. In denervated Pcm of gonadally intact animals these effects were present; however, in denervated but castrated animals these were absent. Thus, combined surgeries resulted in the lowest mean cross-sectional area values with a restricted fiber distribution from 500 to 1,499 μm(2) . In conclusion, the study in this important muscle showed that cross-sectional area of its fibers depends on neural and direct/indirect gonadal hormone effects.

Uterotrophic and Hershberger Assays for Endocrine Disruption Properties of Plastic Food Contact Materials Polypropylene (PP) and Polyethylene Terephthalate (PET)

Plasticizers or plastic materials such as phthalates, bisphenol-A (BPA), and styrene are widely used in the plastic industry and are suspected endocrine-disrupting chemicals (EDC). Although plastic materials such as polypropylene (PP) and polyethylene terephthalate (PET) are not EDC and are considered to be safe, their potential properties as EDC have not been fully investigated. In this study, plastic samples eluted from plastic food containers (PP or PET) were investigated in Sprague-Dawley rats using Hershberger and uterotrophic assays. In the Hershberger assay, 6-wk-old castrated male rats were orally treated for 10 consecutive days with plastic effluent at 3 different doses (5 ml/kg) or vehicle control (corn oil, 1 ml/100 g) to determine the presence of both anti-androgenic and androgenic effects. Testosterone (0.4 mg/ml/kg) was subcutaneously administered for androgenic evaluation as a positive control, whereas testosterone (0.4 mg/ml/kg) and flutamide (3 mg/kg/day) were administered to a positive control group for anti-androgenic evaluation. The presence of any anti-androgenic or androgenic activities of plastic effluent was not detected. Sex accessory tissues such as ventral prostate or seminal vesicle showed no significant differences in weight between treated and control groups. For the uterotrophic assay, immature female rats were treated with plastic effluent at three different doses (5 ml/kg), with vehicle control (corn oil, 1 ml/100 g), or with ethinyl estradiol (3 μg/kg/d) for 3 d. There were no significant differences between test and control groups in vagina or uterine weight. Data suggest that effluents from plastic food containers do not appear to produce significant adverse effects according to Hershberger and uterotrophic assays.

Chronic Treatment with NaF Promotes Dyslipidemia in Rats

The present study aimed to evaluate the chronic effect of NaF on: 1) inhibitory pathway of insulin signal transduction in liver (L) and muscle (M); 2) plasma concentration (PC) of triglycerides (TGL); 3) total cholesterol (TC); 3) high‐density lipoprotein cholesterol (HDL‐C); 4) low‐density lipoprotein cholesterol (LDL‐C); 5) very low‐density lipoprotein cholesterol (VLDL‐C). Seven‐week‐old castrated male Wistar rats were randomly divided into two groups: 1) control group (CN); 2) fluoride group (FN), which was treated with NaF in drinking water and F in food pellets (4.0 mgF/kg bw/day). After 42 days, PC of TGL, TC, HDL‐C, LDL‐C and VLDL‐C quantification analysis, and insulin receptor substrate‐1 (IRS‐1) serine phosphorylation status tests in L and M were performed by Western Blotting method. The FN group showed a significant increase (p&lt;0.05) in PC of TGL (CN: 30.7 + 3.6 vs FN: 46.9 + 2.7), TC (CN: 76.1 + 2.1 vs FN: 87.0 + 4.2), and VLDL‐C (CN: 6.1 + 0.7 vs FN: 9.4 + 0.5), in comparison with the CN group. However, the treatment with NaF didn't promote alteration in PC of HDL‐C or LDL‐C, or in IRS‐1 serine phosphorylation status in L or in M. The chronic treatment with F promoted: 1) increase in PC of TGL, TC, and VLDL‐C; 2) no alteration in PC of HDL‐C or LDL‐C; 3) no alteration in inhibitory pathway of insulin signal in L or in M. Financial support: FAPESP (2010/10664–5).

Rapid effects of 17β-estradiol on male copulatory behaviors are not elicited by the novel membrane active estrogenic compound STX.

Estrogens have been shown to rapidly promote male copulatory behaviors with a time-course that suggests rapid signaling events are involved. The present study tested the hypothesis that estrogen acts through a novel Gq protein-coupled membrane estrogen receptor (ER). Thus, either estradiol (E2), STX (a diphenylacrylamide compound that selectively activates a membrane ER pathway), or vehicle were administered acutely to castrated male rats that bore subcutaneous (sc) dihydrotestosterone implants to maintain genital sensitivity. Appetitive (level changes, genital investigation) and consummatory (mounts, intromissions, ejaculations) components of male sexual behavior were measured in a bilevel testing apparatus. Testing showed that E2 treatment promoted olfactory and mounting behaviors, but had no effect on motivation as measured by anticipatory level changes. STX treatment showed no effect on either component of male sexual behavior. These results support previous results that showed that E2 can rapidly affect male sexual behaviors but fail to support a role for the specific membrane-initiated pathway activated by STX.

Does the timing of estrogen administration after castration affect its ability to preserve sexual interest in male rats? — Exploring the critical period hypothesis

Loss of libido is a major side effect that reduces the quality of life of prostate cancer patients on androgen-deprivation therapy. Estrogen restores sexual interest to some extent in castrated male mammals; however, the beneficial effects of estrogen vary greatly among different studies. We investigated whether the timing of estrogen treatment after castration affected its ability to restore sexual interest in male rats.For each rat, sexual behavior was tested with receptive female rats before castration, and after 2weeks of either oil alone (as a control) or oil plus estradiol (E2) treatment administered via Silastic tubes implanted immediately, at 1month (Short-Term), or at 3months (Long-Term) after castration.Intromission frequency decreased and genital sniffing frequency increased significantly after castration compared to pre-castration levels, regardless of the testing time post-castration. E2 treatment at any time point did not reverse these changes. However, more E2-treated than control rats exhibited mounting behavior, with a significant difference between the Long-Term groups. Mounting frequency did not differ from pre-castration levels for either E2 or control rats under the Immediate condition, but declined significantly in rats treated with oil only under both the Short- and Long-Term conditions. In contrast, E2 treatment elevated mounting frequency above the castrate levels to a similar extent in both the Short and Long-term groups.In conclusion, E2 administration partially restores sexual interest in castrated male rats, and the length of post-castration delay in E2 administration does not affect the ability of E2 to restore mounting behavior.

The effect of testosterone administration on motor nucleus of the trigeminal nerve in immature of castrated male rat

The effect of testosterone administration on motor nucleus of the trigeminal nerve in immature of castrated male rat

English

In this study, the effects of edible bird&rsquo;s nest on sexual function of male castrated rats were investigated for the first time. The testosterone (T), luteinizing hormone (LH) and estradiol (E2) levels, the penis and prostate and seminal vesicle indexes, and the protein expression of endothelial nitric oxide synthase (eNOS) were estimated. The prostate and seminal vesicle index and the expression of eNOS increased significantly in groups treated with edible bird&rsquo;s nest in comparison to the control group. The results demonstrated that the edible bird&rsquo;s nest may promote the sexual function of male castrated rats and T was supposed to be responsible for this function. Edible bird&rsquo;s nest may serve as an effective medicine for erectile dysfunction (ED) treatment. &nbsp; Key words:&nbsp;Edible bird&rsquo;s nest, sexual function, castrated rats, erectile dysfunction, hormones, nitric oxide synthase.

GLP-compliant evaluation and standardization of the peripubertal castrate male rat Hershberger assay for oral exposure of test agents

Since oral exposure is more relevant than the sc route for human exposure to environmental substances, studies to evaluate and standardize this route in the Hershberger assay were conducted in 2001–2003. Interest in environmental androgen agonists is increasing, so the oral route of the Hershberger assay may be useful to quantify agonist activity of these substances. Castrated Sprague–Dawley rats were dosed (PND 60–69) with androgen receptor agonists and/or antagonists, terminated on PND 70, and body, liver, and accessory sex organs (ASOs) weighed. Methyltestosterone (MT) po, at 0.1–50mg/kg/day, resulted in dose-dependent increases in ASO weights at 5–50mg/kg; 0.1mg/kg/day was without statistically significant effect. Testosterone propionate (TP) (sc) at 0.1–1.6mg/kg/day also resulted in dose-dependent increases in ASO weights, at all doses. Detection of putative androgen antagonists by the oral route was confirmed with dose–response curves of antagonism from flutamide (FLU) po at 1, 5, or 10mg/kg/day, with MT at 5 or 10mg/kg/day (po, 4h later). These results extend the OECD Hershberger assay evaluation and standardization to the oral route and identify and discuss challenges of the assay to detect (anti)androgen-active compounds.

Discovery of Diarylhydantoins as New Selective Androgen Receptor Modulators

A novel selective androgen receptor modulator scaffold has been discovered through structural modifications of hydantoin antiandrogens. Several 4-(4-hydroxyphenyl)-N-arylhydantoins displayed partial agonism with nanomolar in vitro potency in transactivation experiments using androgen receptor (AR) transfected cells. In a standard castrated male rat model, several compounds showed good anabolic activity on levator ani muscle, dissociated from the androgenic activity on ventral prostate, after oral dosing at 30 mg/kg. (+)-4-[3,4-Dimethyl-2,5-dioxo-4-(4-hydroxyphenyl)imidazolidin-1-yl]-2-(trifluoromethyl)benzonitrile ((+)-11b) displayed anabolic potency with a strong dissociation between levator ani muscle and ventral prostate (A(50) = 0.5 mg/kg vs 70 mg/kg). The binding modes of two compounds, including (+)-11b, within the AR ligand-binding domain have been studied by cocrystallization experiments using a coactivator-like peptide. Both compounds bound to the same site, and the overall structures of the AR were very similar.

Mild exercise increases dihydrotestosterone in hippocampus providing evidence for androgenic mediation of neurogenesis

Mild exercise activates hippocampal neurons through the glutamatergic pathway and also promotes adult hippocampal neurogenesis (AHN). We hypothesized that such exercise could enhance local androgen synthesis and cause AHN because hippocampal steroid synthesis is facilitated by activated neurons via N-methyl-D-aspartate receptors. Here we addressed this question using a mild-intense treadmill running model that has been shown to be a potent AHN stimulator. A mass-spectrometric analysis demonstrated that hippocampal dihydrotestosterone increased significantly, whereas testosterone levels did not increase significantly after 2 wk of treadmill running in both orchidectomized (ORX) and sham castrated (Sham) male rats. Furthermore, analysis of mRNA expression for the two isoforms of 5α-reductases (srd5a1, srd5a2) and for androgen receptor (AR) revealed that both increased in the hippocampus after exercise, even in ORX rats. All rats were injected twice with 5'-bromo-2'deoxyuridine (50 mg/kg body weight, i.p.) on the day before training. Mild exercise significantly increased AHN in both ORX and Sham rats. Moreover, the increase of doublecortin or 5'-bromo-2'deoxyuridine/NeuN-positive cells in ORX rats was blocked by s.c. flutamide, an AR antagonist. It was also found that application of an estrogen receptor antagonist, tamoxifen, did not suppress exercise-induced AHN. These results support the hypothesis that, in male animals, mild exercise enhances hippocampal synthesis of dihydrotestosterone and increases AHN via androgenenic mediation.