Hypothyroidism induces uterine hyperplasia and inflammation related to sex hormone receptors expression in virgin rabbits

Diagnostic Imaging for Assessment of the Endocrine System in Exotic Animals

Diagnostic imaging can provide essential evidence supporting the diagnosis of endocrine diseases in exotic companion animals. The specific modality chosen depends on species, specific disease process/organ affected, equipment availability, and often, cost to the owner. While radiography is widely available in veterinary practices, the sensitivity for visualization of endocrine organs is low. Therefore, ultrasonography, computed tomography, or MRI may be preferred. Other specialized imaging modalities are useful for specific disease processes, such as nuclear scintigraphy and PET. This article compiles current evidence for diagnostic imaging of the endocrine system in exotic animals, organized by imaging modality, species, and disease process.

Thyroid Disease in Rabbits and Rodents

While thyroid disease is generally uncommon in rabbits and rodents, it is most frequently diagnosed in guinea pigs. Particularly, hyperthyroidism and thyroid neoplasms are diagnosed regularly in this species, while thyroid neoplasia is the most common thyroid disorder found in other rodents. Thyroid disease appears to be rare in rabbits, though modalities to reliably diagnose different disorders like hypothyroidism are currently lacking.

Modulatory effect of vitamin B6 on sex hormone receptors, thyroid, and kisspeptin/kiss1r system in the uterus of pseudopregnant bitches

This study evaluated whether the treatment of pseudopregnancy in bitches with vitamin B6 modulates uterine expression of receptors for progesterone (PR), oestrogen (ERα), androgen (AR), thyroid hormone (TRα) and the kisspeptin/Kiss1r system. Eighteen pseudopregnant bitches were treated for 20 days in groups receiving placebo (n = 6); cabergoline (5 μg/kg/day; n = 6); or vitamin B6 (50 mg/kg/day; n = 6). Blood was collected on the 1st day of drug administration and 120 h later to measure serum prolactin (PRL). After treatment, they were ovariohysterectomized and uterine fragments were collected for histomorphometry and immunohistochemical evaluation of PR, ERα, AR, TRα, Kiss1 and Kiss1r. After 120 h of cabergoline or vitamin B6 treatment, PRL levels were reduced in the bitches, confirming the antiprolactinemic effect of these drugs. Furthermore, regardless of treatment, the animals exhibited uterine histomorphometry consistent with dioestrus. The PR showed strong immunostaining in all regions and an increase in scores was observed for this receptor in animals treated with vitamin B6 in deep glands. In contrast, ERα and Kiss1R receptors showed weak to no immunostaining in all uterine regions and no changes between groups. Regarding AR, most animals treated with vitamin B6 showed increased trends in the deep gland and myometrium marking scores. In contrast, in both vitamin B6 and cabergoline treatments, a reduction in TRα marking scores was observed compared to the control group. In addition, on the endometrial surface, a reduction was observed in the marked area of Kiss1 after administration of cabergoline when compared to the pseudopregnant control group. These findings shed valuable insight into the use of vitamin B6 as a drug with actions similar to cabergoline in reducing PRL and uterine modulation in bitches.

The Thyroid Hormone Axis and Female Reproduction

Thyroid function affects multiple sites of the female hypothalamic-pituitary gonadal (HPG) axis. Disruption of thyroid function has been linked to reproductive dysfunction in women and is associated with menstrual irregularity, infertility, poor pregnancy outcomes, and gynecological conditions such as premature ovarian insufficiency and polycystic ovarian syndrome. Thus, the complex molecular interplay between hormones involved in thyroid and reproductive functions is further compounded by the association of certain common autoimmune states with disorders of the thyroid and the HPG axes. Furthermore, in prepartum and intrapartum states, even relatively minor disruptions have been shown to adversely impact maternal and fetal outcomes, with some differences of opinion in the management of these conditions. In this review, we provide readers with a foundational understanding of the physiology and pathophysiology of thyroid hormone interactions with the female HPG axis. We also share clinical insights into the management of thyroid dysfunction in reproductive-aged women.

Impact of photoperiod on uterine redox/inflammatory and metabolic status of golden hamster, Mesocricetus auratus

Photoperiod modulates reproductive physiology at multiple levels in seasonally breeding animals. Golden hamsters are long-day breeders that diminish their fertility during the short days. Photoperiod is known to regulate hormonal milieu and uterus is a hormone-sensitive dynamic tissue. However, there is lack of molecular insight regarding the impact of photoperiod on uterine physiology with respect to redox and metabolic status in Mesocricetus auratus. We evaluated the impact of photoperiod on circulatory hormonal parameters (triiodothyronine [T3], thyroxin [T4], estradiol [E2], progesterone [P4], melatonin, and insulin), their receptor expressions and key markers associated with redox (SIRT-1/FOXO-1), inflammatory (NFĸB/COX-2) and metabolic (IR/GLUT4) status in uterus. Adult female golden hamsters were exposed to different photoperiodic regimes, that is, short photoperiod (SP; 8L:16D) and long photoperiod (LP; 16L:8D) for 12 weeks. SP drastically decreased peripheral hormone profiles (T3, T4, E2, and P4) and compromised uterine histoarchitecture when compared with LP-exposed hamsters. Further, SP markedly decreased thyroid hormone receptor-α (TRα), insulin receptor, and glucose uptake transporter-4 (GLUT-4) expressions in uterus. We noted enhanced uterine oxidative (increased MDA and decreased SOD/CAT levels), SIRT-1/FOXO-1 expression and inflammatory (NFĸB/COX-2) load in SP condition. Further, elevated levels of circulatory insulin, melatonin, and its receptor (MT-1) expression in uterus was noted under SP condition. Thus, we may suggest that photoperiod might regulate uterine seasonality through modulation of local hormonal and redox/metabolic homeostasis thereby may restrict offspring bearing capacity under short days.

Effects of hypothyroidism on the female pancreas involve the regulation of estrogen receptors

This study aimed to investigate the impact of short-time hypothyroidism on the expression of aromatase, estrogen receptors (ERα, β), and GPR30 in the pancreas of female rabbits. The formation of new islets and the expression of insulin, GLUT4, and lactate dehydrogenase (LDH) were also analyzed. This purpose is based on actions that thyroid hormones and estrogens have on β-cells differentiation, acinar cell function, and insulin secretion. Twelve Chinchilla-breed adult virgin female rabbits were divided into control (n = 6) and hypothyroid (n = 6; methimazole 10 mg/kg for 30 days) groups. In the complete pancreas, expressions of aromatase and estrogen receptors, as well as proinsulin, GLUT4, and LDH were determined by western blot. Characteristics of islets were measured in slices of the pancreas with immunohistochemistry for insulin. Islet and acinar cells express aromatase, ERα, ERβ, and GPR30. Hypothyroidism increased the expression of ERα and diminished that for aromatase, ERβ, and GPR30 in the pancreas. It also promoted a high number of extra small islets (new islets) and increased the expression of proinsulin and GLUT4 in the pancreas. Our results show that actions of thyroid hormones and estrogens on β-cells neogenesis, acinar cell function, and synthesis and secretion of insulin are linked. Thus, the effects of hypothyroidism on the pancreas could include summatory actions of thyroid hormones plus estrogens. Our findings indicate the importance of monitoring estrogen levels and actions on the pancreas of hypothyroid women, particularly when serum estrogen concentrations are affected such as menopausal, pregnant, and those with contraceptive use.

A New Perspective on Thyroid Hormones: Crosstalk with Reproductive Hormones in Females

Accumulating evidence has shown that thyroid hormones (THs) are vital for female reproductive system homeostasis. THs regulate the reproductive functions through thyroid hormone receptors (THRs)-mediated genomic- and integrin-receptor-associated nongenomic mechanisms, depending on TH ligand status and DNA level, as well as transcription and extra-nuclear signaling transduction activities. These processes involve the binding of THs to intracellular THRs and steroid hormone receptors or membrane receptors and the recruitment of hormone-response elements. In addition, THs and other reproductive hormones can activate common signaling pathways due to their structural similarity and shared DNA consensus sequences among thyroid, peptide, and protein hormones and their receptors, thus constituting a complex and reciprocal interaction network. Moreover, THs not only indirectly affect the synthesis, secretion, and action of reproductive hormones, but are also regulated by these hormones at the same time. This crosstalk may be one of the pivotal factors regulating female reproductive behavior and hormone-related diseases, including tumors. Elucidating the interaction mechanism among the aforementioned hormones will contribute to apprehending the etiology of female reproductive diseases, shedding new light on the treatment of gynecological disorders.

Subclinical Hypothyroidism in Patients with Diabetic Retinopathy: Role of Vascular Endothelial Growth Factor

BACKGROUND

Considering the vital role of vascular endothelial growth factor (VEGF) in the development of diabetic retinopathy (DR) in one hand and the frequent association between subclinical hypothyroidism (SCH) and DR on the other hand.

OBJECTIVE

The present study was proposed to explore the possible role of VEGF in the relation between SCH and DR, thus we investigated the relation between SCH and VEGF levels in patients with DR.

METHODS

Two hundred patients with DR were recruited in this study [100 patients with proliferative diabetic retinopathy (PDR) and 100 patients with non-proliferative diabetic retinopathy (NPDR)]. Patients with DR were divided into 2 groups according to thyroid function: patients with SCH or those with euthyroidism. Patients were subjected to careful history taking, and underwent clinical and ophthalmological examination. Fasting blood glucose, glycosylated hemoglobin, fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), TSH, FT4, FT3, VEGF and thyroid volume were assessed Results: Among all the studied patients, 21.5% (43/200) had SCH. DR patients with SCH had higher age, diabetes duration, HbA1c, HOMA-IR and VEGF than those with euthyroidism. The frequency of PDR in patients with SCH was 72.1% (31/43) and 43.9% (69/157) in those with euthyroidism, whereas the frequency of NPDR in patients with SCH was 27.9 (12/43) and 56.1% (88/157) in those with euthyroidism (P < 0.003). In multivariate analysis, PDR, HOMA-IR and VEGF levels were the significant predictor variables of SCH.

CONCLUSIONS

Increased VEGF levels may be implicated in the relationship between SCH and DR.

Is There an Association Between Hypothyroidism and Sexual Dysfunction: A Systematic Review and Cumulative Analysis

INTRODUCTION

Many investigators have found a detrimental effect on sexual functioning developed by hypothyroidism in both sexes, but a cumulative analysis has not been conducted.

AIM

This study aims to summarize and quantify the association between overt or subclinical hypothyroidism and the risk of sexual dysfunction (SD) through a meta-analysis.

METHODS

4 electronic databases were systematically searched. The quality of evidence was rated by the GRADE approach. This meta-analysis was registered on the PROSPERO (ID: CRD42020186967).

MAIN OUTCOME MEASURE

The strength of the relationship between overt/subclinical hypothyroidism and SD was quantified by presenting the relative risk (RR) with its 95% confidence interval (CI).

RESULTS

7 studies involving 460 patients with hypothyroidism and 2,143 healthy controls were included in this meta-analysis. Among the 7 included studies, 2 studies were provided the data of both overt and subclinical hypothyroidism. Pooled results from 4 included studies investigating overt hypothyroidism indicated that overt hypothyroidism led to significant SD in both sexes (RR = 2.26, 95% CI: 1.42 to 3.62, P = 0.001), while synthetic RR of 5 eligible studies reporting subclinical hypothyroidism failed to find a positive association between subclinical hypothyroidism and SD (RR = 1.3, 95% CI: 0.85 to 1.99, P = 0.229), irrespective of gender (all P > 0.05). Subgroup analyses revealed that women with overt hypothyroidism rather than men with overt hypothyroidism were correlated with a significant higher risk of SD. The quality of evidence in the study of overt hypothyroidism and subclinical hypothyroidism was considered low and moderate, respectively.

CONCLUSION

SD is a devastating problem in female patients with clinical hypothyroidism but insusceptible in either women or men with subclinical hypothyroidism. Clinicians should be aware of these phenomena and manage the sufferers accordingly in clinical practice. More rigorous studies are still needed to validate this evidence. Shen M, Li X, Wu W, et al. Is There an Association Between Hypothyroidism and Sexual Dysfunction: A Systematic Review and Cumulative Analysis. Sex Med 2021;9:100345.

Updates on Thyroid Disease in Rabbits and Guinea Pigs

Hyperthyroidism seems to be a rare, but likely underdiagnosed disease of guinea pigs (Cavia porcellus) and rabbits (Oryctolagus cuniculus). Diagnosis is confounded by nonspecific clinical signs, lack of validated assays, and species-specific reference intervals. With increasing English-language publications on the topic, naturally occurring thyroid disease is likely to be increasingly diagnosed in exotic small mammals. The most consistently observed clinical signs include weight loss with or without a change in appetite and a palpable cervical mass. Diagnosis is supported by elevated blood thyroxine concentrations. Treatment may include thyreostatic agents, radioactive iodine, or surgical thyroidectomy.

Hypothyroidism modifies differentially the content of lipids and glycogen, lipid receptors, and intraepithelial lymphocytes among oviductal regions of rabbits

Hypothyroidism affects the content of triacylglycerol (TAG), total cholesterol (TC), oxidized lipids, glycogen, and infiltration of immune cells into the ovary and uterus. This study aimed to analyze the impact of hypothyroidism on the lipid content of different regions of the oviduct. Control (n = 6) and hypothyroid (n = 6; 10 mg/kg/day of methimazole in the drinking water for 30 days) adult rabbits were used. In the fimbriae/infundibulum (FIM/INF), ampulla, (AMP), isthmus (IST), and utero-tubal junction (UTJ), the TAG and TC concentrations, presence of oxidized lipid, relative expressions of perilipin A (PLIN A), peroxisome proliferator-activated receptor γ (PPARγ), CAAT/enhancer-binding protein α (C/EBPα), and farnesoid X receptor (FXRα) were analyzed. The content of glycogen and glycans, as well as the infiltration of lymphocytes, were also quantified. In the FIM/INF, hypothyroidism reduced the content of TC, expression of C/EBPα, and presence of glycans while increased the number of intraepithelial lymphocytes. In the AMP and IST-UTJ regions, hypothyroidism increased the content of TAG, oxidized lipids, expression of PPARγ, and glycogen content but decreased the expression of PLIN-A. The FXRα expression in secretory cells of IST-UTJ was higher in the hypothyroid rabbits compared to controls. Additionally, hypothyroidism reduced the C/EBPα expression and the number of intraepithelial lymphocytes in the AMP and IST-UTJ regions, respectively. We demonstrated that the effect of hypothyroidism depends on the oviductal region, possibly associated with different physiological functions specific to each region. These alterations may be related to infertility, tubal disturbances, and ectopic pregnancy observed in hypothyroid women.

Inferring lanosterol functions in the female rabbit reproductive tract based on the immunolocalization of lanosterol 14-demethylase and farnesoid beta-receptor

Female reproductive organs have de novo synthesis of cholesterol. Some sterol molecules, intermediaries in the cholesterol synthesis, have important paracrine/autocrine actions. Lanosterol binds to the farnesoid beta-receptor (FXRβ), a molecule widely expressed in the ovaries, suggesting that it may play a role in reproduction. Up to date, we know little about lanosterol functions across female reproductive organs. We described immunolocalized lanosterol 14-demethylase (LDM or CYP51A1), responsible for catalyzing the conversion of lanosterol in cholesterol, and FXRβ in the ovary, oviduct, uterus, and vagina of virgin and pregnant rabbits. In virgin rats, we found CYP51A1 and FXRβ immunoreactivity was found in all ovarian follicles, epithelial cells, stroma, and Graafian follicles. Also, the epithelium and stroma, as well as the smooth muscle of the oviduct, vagina, and uterus showed CYP51A1 and FXRβ immunoreactivity. In pregnant dams, we observed the presence of CYP51A1 and FXRβ immunoreactivity in the corpora lutea, giant uterine cells, and trophoblastic cells. The presence of CYP51A1 and FXRβ support that lanosterol participates in diverse reproductive processes, including follicular maturation, transport of gametes and zygote, implantation of blastocyst, lubrication, and contraction of the vagina, secretion of female prostate, and control of delivery mediated by pelvic muscles contraction.