Pathological changes induced in the uterus of mice with the prolonged administration of progesterone and 19-nor-contraceptives

Murine Models and Research Progress on Dysmenorrhea

Dysmenorrhea is a prevalent gynecological disease among women at reproductive age. It is classified as the primary dysmenorrhea and the secondary dysmenorrhea according to the etiology. The primary dysmenorrhea is caused by uterine hypercontraction without any identifiable pelvic lesions, while the secondary dysmenorrhea is incurred by gynecological disorder with pelvic organic lesions. However, the underlying mechanism of dysmenorrhea is not completely clear. Animal models of dysmenorrhea, especially mouse and rat model, are helpful to explore the pathophysiological mechanism of dysmenorrhea, clarify the therapeutic effect of compounds, and guide clinical treatment. The murine model of primary dysmenorrhea is commonly induced by oxytocin or prostaglandin F_2α, while the secondary dysmenorrhea murine model was further created by injecting oxytocin on the basis of the established primary disease model. This review summarizes the current progress of dysmenorrhea models in rodent, including experimental methods, corresponding evaluation indexes, and the advantages and disadvantages of various murine dysmenorrhea models, in order to provide a reference for the selection of murine dysmenorrhea models and the further study of the pathophysiological mechanism of dysmenorrhea.

Establishment of a novel mouse model of adenomyosis suitable for longitudinal and quantitative analysis and perinatal outcome studies

The purpose of this study was to establish a novel mouse model of adenomyosis suitable for longitudinal and quantitative analyses and perinatal outcome studies. Using a 30 G needle, the entire uterine wall of one horn was mechanically punctured at a frequency of 100 times/1 cm (adenomyosis horn). The other horn was left unpunctured (control horn). Balb/c mice were sacrificed on day 14 (D14) or day 65 (D65) (n = 3 each). The uterus was fixed, paraffin-embedded, sliced, and stained. Lesions were detected and counted, and their volumes were measured. Cell proliferation and fibrosis were assessed by Ki67 and Masson's Trichrome staining, respectively. Blood vessels were detected using CD31 immunostaining. Some of the mice (n = 4), were mated and the date of delivery, litter size, number of implantations, and number and volume of postpartum lesions were measured. The number of lesions per horn did not differ between D14 and D65. The volume of the entire lesion was significantly greater on D65 than on D14 (p < 0.0001). The volume of the epithelial part of the lesion was significantly greater in D65 (p < 0.0001). The volume of the stromal part of the lesion was also greater on D65 (p < 0.0001). The percentage of Ki67 positive cells in the epithelial part of the lesion was significantly higher on D14 (p < 0.05). In contrast, the percentage of Ki67-positive cells in the stromal part was significantly higher on D65 (p < 0.01). Vascular density in the lesions was higher in on D65 (p < 0.05). The percentage of fibrotic area was significantly higher on D65 (p < 0.01). The date of delivery was slightly earlier than that reported for healthy mice of the same strain. The litter size was smaller than that reported in previous research. The number of implantation sites did not differ between the control and the adenomyosis horn. The number and volume of lesions did not differ between the non-pregnant and postpartum groups. This model can be applied to evaluate the pathogenesis of adenomyosis, validate the efficacy of therapeutic agents, and evaluate the effect of adenomyosis on pregnancy and vice versa.

Unveiling the Pathogenesis of Adenomyosis through Animal Models

Background: Adenomyosis is a common gynecological disorder traditionally viewed as “elusive”. Several excellent review papers have been published fairly recently on its pathogenesis, and several theories have been proposed. However, the falsifiability, explanatory power, and predictivity of these theories are often overlooked. Since adenomyosis can occur spontaneously in rodents and many other species, the animal models may help us unveil the pathogenesis of adenomyosis. This review critically tallies experimentally induced models published so far, with a particular focus on their relevance to epidemiological findings, their possible mechanisms of action, and their explanatory and predictive power. Methods: PubMed was exhaustively searched using the phrase “adenomyosis and animal model”, “adenomyosis and experimental model”, “adenomyosis and mouse”, and “adenomyosis and rat”, and the resultant papers were retrieved, carefully read, and the resultant information distilled. All the retrieved papers were then reviewed in a narrative manner. Results: Among all published animal models of adenomyosis, the mouse model of adenomyosis induced by endometrial–myometrial interface disruption (EMID) seems to satisfy the requirements of falsifiability and has the predictive capability and also Hill’s causality criteria. Other theories only partially satisfy Hill’s criteria of causality. In particular, animal models of adenomyosis induced by hyperestrogenism, hyperprolactinemia, or long-term exposure to progestogens without much epidemiological documentation and adenomyosis is usually not the exclusive uterine pathology consequent to those induction procedures. Regardless, uterine disruption appears to be a necessary but not sufficient condition for causing adenomyosis. Conclusions: EMID is, however, unlikely the sole cause for adenomyosis. Future studies, including animal studies, are warranted to understand how and why in utero and/or prenatal exposure to elevated levels of estrogen or estrogenic compounds increases the risk of developing adenomyosis in adulthood, to elucidate whether prolactin plays any role in its pathogenesis, and to identify sufficient condition(s) that cause adenomyosis.

Animal Models of Adenomyosis

Adenomyosis is a nonmalignant uterine disorder in which endometrial tissue exists within and grows into the myometrium. Animal models have generated limited insight into the still-unclear pathogenesis of adenomyosis, provided a platform for preclinical screening of many drugs and compounds with potential as therapeutics, and elucidated mechanisms underlying the pain and fertility issues that occur in many women with the disease. Spontaneous adenomyosis has been studied in nonhuman primates, primarily in the form of case reports. Adenomyosis is routinely experimentally induced in mice through methods such as neonatal tamoxifen exposure, pituitary engraftment, and human tissue xenotransplantation. Several studies have also reported hormonal or environmental toxicant exposures that give rise to murine adenomyosis, and genetically engineered models have been created that recapitulate the human-like condition, most notably involving alteration of β-catenin expression. This review describes the animal models for adenomyosis and their contributions to our understanding of the factors underpinning the development of symptoms. Animal models represent a unique opportunity for understanding the molecular basis of adenomyosis and developing efficacious treatment options for affected women. Herein, we assess their different potentials and limitations with regard to identification of new therapeutic interventions and reflect on future directions for research and drug validation.

The Pathogenesis of Adenomyosis vis-à-vis Endometriosis

Adenomyosis is used to be called endometriosis interna, and deep endometriosis is now called adenomyosis externa. Thus, there is a question as to whether adenomyosis is simply endometriosis of the uterus, either from the perspective of pathogenesis or pathophysiology. In this manuscript, a comprehensive review was performed with a literature search using PubMed for all publications in English, related to adenomyosis and endometriosis, from inception to June 20, 2019. In addition, two prevailing theories, i.e., invagination—based on tissue injury and repair (TIAR) hypothesis—and metaplasia, on adenomyosis pathogenesis, are briefly overviewed and then critically scrutinized. Both theories have apparent limitations, i.e., difficulty in falsification, explaining existing data, and making useful predictions. Based on the current understanding of wound healing, a new hypothesis, called endometrial-myometrial interface disruption (EMID), is proposed to account for adenomyosis resulting from iatrogenic trauma to EMI. The EMID hypothesis not only highlights the more salient feature, i.e., hypoxia, at the wounding site, but also incorporates epithelial mesenchymal transition, recruitment of bone-marrow-derived stem cells, and enhanced survival and dissemination of endometrial cells dispersed and displaced due to iatrogenic procedures. More importantly, the EMID hypothesis predicts that the risk of adenomyosis can be reduced if certain perioperative interventions are performed. Consequently, from a pathogenic standpoint, adenomyosis is not simply endometriosis of the uterus, and, as such, may call for interventional procedures that are somewhat different from those for endometriosis to achieve the best results.

Naturally Occurring and Melengestrol Acetate-associated Reproductive Tract Lesions in Zoo Canids

As husbandry practices have improved, safe and effective contraception for captive wildlife management has become a necessity. Melengestrol acetate (MGA), a synthetic progestin, is highly effective and has been used in many zoo species. Long-term use of MGA has been associated with uterine lesions in zoo felids, but effects in zoo canids have not been evaluated. This retrospective study documented spontaneously occurring lesions and investigated the impact of MGA on the reproductive health of zoo canids. Reproductive tracts from adult females were submitted by US zoos to the Association of Zoos & Aquariums' Wildlife Contraception Center Health Surveillance Program. Reproductive tracts were sampled and processed for histopathologic examination following standard protocols. Microscopic evaluations were performed without prior knowledge of MGA treatment status. Prevalence of uterine lesions was evaluated and compared between MGA-treated animals (n = 20) and control (untreated) animals (n = 61). Common lesions within the study population as a whole included endometrial hyperplasia (predominantly cystic) (53%), hydrometra (33%), and adenomyosis (25%). Treatment with MGA was a risk factor for endometrial hyperplasia, hydrometra, fibrosis, and adenomyosis. Uterine mineralization occurred exclusively in MGA-treated animals. Results indicate that MGA contraception can lead to lesions that may permanently impair the fertility of females. Therefore, if long-term contraception of zoo canids is necessary, the use of alternate methods of reproductive control such as gonadotropin-releasing hormone (GnRH) analogs or GnRH vaccines that reduce gonadal hormone exposure should be pursued.

The effects of tamoxifen and estradiol on myometrial differentiation and organization during early uterine development in the CD1 mouse

We used a neonatal mouse model to examine the histogenesis of uterine adenomyosis, and to test whether adenomyosis is due to an abnormality in myometrial differentiation, or in extracellular matrix proteins expression. We also studied the effects of tamoxifen and estradiol on uterine development, myometrial differentiation, and organization. Female CD1 pups were treated with oral tamoxifen (1 mg/kg) (n=27) or estradiol (0.1 mg/kg) (n=24) from age 1 to 5 days. Uteri from control (n=27) and treated mice were obtained on days 2, 5, 10, 15, and 42 of age. We examined the sections histologically, using image analysis and immunohistochemistry for alpha-smooth muscle actin (alpha-SMA), desmin, vimentin, laminin, fibronectin, and estrogen receptor-alpha. Following tamoxifen exposure, all uteri showed adenomyosis by 6 weeks of age (seen as early as day 10). The inner myometrium showed thinning, lack of continuity, disorganization, and bundling. alpha-SMA expression was normal. Desmin expression normally showed a wave of maturation that was absent in tamoxifen-treated mice. In the estradiol group, adenomyosis was not observed. All uterine layers were normally developed, but hypertrophied. The inner myometrium retained its circular arrangement. There was no difference in the localization of laminin or fibronectin between groups (laminin expression was reduced in the tamoxifen treated uteri). Vimentin could not be detected in all groups. Our results suggest that the development of the inner myometrium is particularly sensitive to estrogen antagonism, and can be affected by steroid receptors modulation. Disruption of the inner myometrium may play a role in the development of uterine adenomyosis.

Development of leiomyosarcoma of the uterus in MMTV-CR-1 transgenic mice

Overexpression of Cripto-1 (CR-1) in FVB/N mice using the MMTV-LTR promoter results in increased mammary tumourigenesis in these female transgenic mice (MMTV-CR-1). Here, we characterize uterine tumours that developed in 15/76 (19.7%) of MMTV-CR-1 female nulliparous or multiparous mice during 24 months of observation compared with 0/33 (0%) of FVB/N normal control mice observed during the same time period (p < 0.01). The uterine tumours collected from the MMTV-CR-1 mice were classified as leiomyosarcomas and found to express the CR-1 transgene by polymerase chain reaction analysis and immunohistochemistry. Detection by western blot analysis showed higher levels of phosphorylated (P) forms of c-src, Akt, GSK-3beta, and dephosphorylated (DP)-beta-catenin in lysates from MMTV-CR-1 uterine leiomyosarcomas in comparison with lysates from normal control FVB/N uteri. Immunostaining showed increased nuclear localization of beta-catenin in the MMTV-CR-1 uterine leiomyosarcomas. Increased immunostaining for CR-1 was detected in 9/13 (69.2%) cases of human leiomyosarcoma compared with staining in 3/15 (20%) human leiomyoma sections. Stronger immunostaining for P-src, P-Akt, P-GSK-3beta and increased nuclear localization of beta-catenin was also seen in human leiomyosarcomas in comparison with leiomyomas. Normal human uterine smooth muscle (UtSM) cells treated with exogenous soluble rhCR-1 showed increased levels of P-src, P-Akt, P-GSK-3beta and dephosphorylated (DP)-beta-catenin and increased proliferation (p < 0.05) and migration (p < 0.01) in comparison with untreated control UtSM cells. Inhibitors against c-src, Akt or beta-catenin, individually or in combination, significantly reduced CR-1-induced migration. These results suggest a role for CR-1 during uterine tumourigenesis either directly by activating c-src and Akt and/or via cross-talk with the canonical Wnt signalling pathway, as suggested by the increased expression of P-GSK-3beta, DP-beta-catenin, and increased nuclear localization of beta-catenin in human and MMTV-CR-1 mice leiomyosarcomas.

Experimental adenomyosis

Adenomyosis has been reported in a number of different animal species, whereas endometriosis appears limited to humans and non-human primates. This suggests a different aetiology of the two conditions. Adenomyosis develops spontaneously in certain strains of laboratory mice. Its incidence in mice can be markedly enhanced by systemic exposure to various hormonal agents, including prolactin, progesterone, synthetic progestins, certain oestrogenic agents, as well as tamoxifen and toremifene. The precise hormonal changes necessary remain unclear, although the evidence suggests that adenomyosis in this model is not due to a simple oestrogenic effect. Study of the pathological and molecular alterations in this model indicates that disturbances to the uterine stroma, blood vessels and myometrium are also important factors in the development of adenomyosis.

The development and regression of deciduosarcomas and other lesions caused by estrogens and progestins in rabbits

A series of experiments were conducted to study the histopathological effects of a combination of exogenous estrogens and progestins in mature rabbits. Estradiol (14-45 microg/day) and levonorgestrel (30-233 microg/day) were administered by intravaginal or subdermal Silastic devices for various time intervals to study the development of lesions with time and to determine if lesions regressed following withdrawal of the steroids. The origin of splenic decidual tumors (primary or metastasis from the uterus) was determined by administering the same steroid combination to castrated male rabbits. It was determined that uterine decidualization is present after 7 days of steroid treatment and that neoplasms of decidual cells may appear in the uterus after only 30 days of steroid administration. Decidual changes were observed frequently in uterine arteries, often concurrent with infarct-like areas of necrosis of the uterine wall. Withdrawal of contraceptive steroids for 14-120 days after 60 days' administration resulted in atrophy and disappearance of decidual cells and decidual tumors. Decidual neoplasms developed in the spleen of all castrated male rabbits given subdermal steroids, demonstrating that these tumors can arise as primary neoplasms of the spleen. The foregoing lesions appear to be peculiar to the rabbit and, together with previous data, suggest the rabbit to be a poor model for evaluating the effects of contraceptive steroids in other species.

Induction of endometriosis and adenomyosis by transvaginal pituitary transplantation in mice with and without natural killer cell activity

PROBLEM

The aims of this study were to establish a mouse model of endometriosis and adenomyosis and to elucidate the necessity of reduced natural killer (NK)-cell and T-cell activities in the establishment of endometriosis and adenomyosis.

METHOD OF STUDY

Pituitary glands, submandibular glands, a hypothalami were transvaginally inoculated into the uteri of syngeneic female mice. Twenty weeks later, the recipient mice were sacrificed and examined.

RESULTS

Cysts, adhesion of the uteri to surrounding tissues, and adenomyosis had formed in the uteri of 7 (29.2%), 14 (58.3%), and 22 (91.7%) mice, respectively, out of 24 BALB/c mice after the transplantation of pituitary glands. Similar findings were obtained by experiments with C3H/He and C57BL/6 mice. In NK-cell-deficient C57BL/6-bgJ and T-cell-deficient BALB/c nu/nu mice, an increase in the formation of cysts, adhesion, and adenomyosis was not observed.

CONCLUSIONS

These findings indicate that transvaginal pituitary transplantation specifically induces cysts, adhesion, and adenomyosis. Reduced NK-cell activities may not be necessary in the primary development of endometriosis and adenomyosis.

Animal model of uterine adenomyosis: is prolactin a potent inducer of adenomyosis in mice?

Uterine adenomyosis is a benign lesion but a serious disease for women, because the symptoms are characterized by abnormal bleeding, pain, cramps, and sterility. Thus elucidation of the mechanisms involved in the development of the disease would contribute to improved management and treatment and prophylaxis of this lesion. A mouse model, in which ectopic pituitary isografting is associated with an increase in the plasma level of prolactin, is useful for a rapid and frequent induction of uterine adenomyosis and can be used to study the origin of this lesion.

Studies of the components of an oral contraceptive agent in albino rats. II. Progestogenic component and comparison of effects of the components and the combined agent

Albino rats were fed norethindrone acetate in the diet for 2 yr at dosage levels (0.3--0.4 mg/kg) of about 10 and 100 times the recommended human dose as used in a combination estrogen-progestogen oral contraceptive. The treated rats had dose-related growth retardation and alopecia, but an enhanced survival rate. Dose-related changes in the male rats included testicular and accessory gonadal atrophy, and in the females, uterine changes. In animals of both sexes at the high dose level, there was liver enlargement with increased foci of cell alterations and cystic mastopathy. Females had increased adrenal gland weights, decreased ovarian weights, and ovarian atrophy. Females at both dose levels had an increased incidence of uterine polyps, and rats of either sex in the high-dose group had an increased incidence of liver neoplastic nodules. However, there were no significant differences with respect to tumor incidence, probability of tumor development, or number of tumors developing in treated compared to untreated rats. In fact, in the females there was a delayed onset of tumor formation.

[Chlormadinone-induced changes in the proliferative activity of Ehrlich ascites tumor]

The effect of Chlormadinone on the proliferation of Ehrlich ascites tumour was studied by employing the stathmokinetic method. In a high percentage of female mice carrying the tumour and treated by Chlormadinone an increase in tumour cell proliferation was observed, while in a few animals the proliferative activity was decreased.

No significant changes were observed in tumour cell proliferation in the male mice.