Anti-Mullerian hormone and cardiometabolic status: a systematic review.

BACKGROUND: To summarise the relationship between Anti-mullerian hormone (AMH) levels and cardiometabolic status in different populations. METHODS: PubMed, Scopus, and Embase were searched for retrieving observational studies published up to February 2022 investigating the relationship between AMH level and cardiometabolic status. RESULTS: Of 3,643 studies retrieved from databases, a total of 37 observational studies were included in this review. The majority of the included studies revealed an inverse association between AMH and lipid profiles, including triglycerides (TG), total cholesterol (TC), low-density lipoprotein (LDL), and a positive correlation with high-density lipoprotein (HDL). While some studies have revealed a significant inverse association between AMH and glycemic parameters, including fasting plasma glucose (FPG), fasting insulin, and HOMA-IR, others found no such relationships. There is also an inconsistency among studies regarding the association of AMH with adiposity indices and blood pressure. Evidence indicates a significant association between AMH and some vascular markers, such as intima-media thickness and coronary artery calcification. Of 3 studies evaluating the relationship between AMH and cardiovascular events, two studies showed an inverse relationship between AMH levels and cardiovascular (CVD), whereas another study showed no significant association. CONCLUSIONS: The results of this systematic review suggest that serum AMH levels can be associated with CVD risk. This may provide new insight into the use of AMH concentrations as a predictive marker for assessing the risk of cardiovascular disease, although more well-design longitudinal studies are still necessary for this area. Future studies on this topic will hopefully provide an opportunity to run a meta-analysis; it will increase the persuasiveness of this interpretation.

Is there any association between migraine headache and polycystic ovary syndrome (PCOS)? A review article.

BACKGROUND: Polycystic ovary syndrome (PCOS) and migraine headaches are considered to be common health problems that may share some risk factors. This study aimed to discuss the possible association between migraine headache and polycystic ovary syndrome. METHODS AND RESULTS: In this narrative review, PubMed, Scopus, Web of Science, and Google Scholar were systematically searched for retrieving and summarizing published studies up to January 2021 to explore the possible interplay between migraine headache and PCOS. We discuss the possible pathways that may explain the association between migraine headaches and PCOS signs/symptoms and complications. While genetic factors have profound effects on the pathogenesis of migraine headaches, sex hormones, including estrogen and progesterone may also play an important role in inducing migraine headaches. Some disorders, such as sleep apnea, amenorrhea, and vascular disease that are more likely to occur in women with PCOS, may cause or exacerbate migraine headaches in women with PCOS. CONCLUSIONS: Future comprehensive studies are needed to investigate the exact underlining mechanisms related to the association between PCOS and migraine headaches.

The effects of different physiologic concentrations of prolactin in association with reproductive hormones on the incidence of type 2 diabetes mellitus in men: Tehran Lipid and Glucose Study.

BACKGROUND: Data is inconsistent and, for the most part, not sufficient to demonstrate the association between serum Prolactin (PRL) concentration within the physiologic range and the incidence rate of type 2 Diabetes Mellitus (DM) among men. Moreover, since both PRL and type 2 DM are associated with reproductive hormones, investigating these hormones might improve our understanding of how PRL might impose its effect on the incidence rate of type 2 DM. METHODS: For the present study, 652 eligible men aged 29-70 with a normal baseline PRL concentration were selected from the Tehran Lipid and Glucose Study (TLGS). Participants were sub-classified into three groups (tertiles) according to the serum concentration of PRL and were followed for 15.8 years. The incidence of type 2 DM and PRL, LH, FSH, testosterone, and AMH concentrations were measured. The effect of hormonal variables on the incidence of type 2 DM was estimated using the log-binomial model, adjusted for major confounding factors. The correlations between PRL and the indicators of glucose and lipid metabolism and other hormonal variables were also explored. RESULTS: In the unadjusted model, PRL was not significantly associated with the incidence rate of type 2 DM (RR = 0.98, 95% CI: 0.94 - 1.03). After adjusting for potential confounders, the inverse effect of AMH on the incidence rate of type 2 DM was the only significant association. The analyses also indicated a significant positive association between PRL and LH/FSH ratio (r = 0.1, P = 0.01). CONCLUSION: No significant association was found between serum PRL concentrations within the physiologic range and the incidence rate of type 2 diabetes mellitus among middle-aged men. Men with higher concentrations of PRL within the physiologic range tended to show higher levels of LH and LH/FSH. AMH was the only variable significantly linked to the incidence rate of type 2 DM in men.

Age-specific cut-off levels of anti-Müllerian hormone can be used as diagnostic markers for polycystic ovary syndrome.

BACKGROUND: The majority of available studies on the AMH thresholds were not age-specific and performed the receiver operating characteristic curve (ROC) analysis, based on variations in sensitivity and specificity rather than positive and negative predictive values (PPV and NPV, respectively), which are more clinically applicable. Moreover, all of these studies used a pre-specified age categorization to report the age-specific cut-off values of AMH. METHODS: A total of 803 women, including 303 PCOS patients and 500 eumenorrheic non-hirsute control women, were enrolled in the present study. The PCOS group included PCOS women, aged 20-40 years, who were referred to the Reproductive Endocrinology Research Center, Tehran, Iran. The Rotterdam consensus criteria were used for diagnosis of PCOS. The control group was selected among women, aged 20-40 years, who participated in Tehran Lipid and Glucose cohort Study (TLGS). Generalized additive models (GAMs) were used to identify the optimal cut-off points for various age categories. The cut-off levels of AMH in different age categories were estimated, using the Bayesian method. MAIN RESULTS AND THE ROLE OF CHANCE: Two optimal cut-off levels of AMH (ng/ml) were identified at the age of 27 and 35 years, based on GAMs. The cut-off levels for the prediction of PCOS in the age categories of 20-27, 27-35, and 35-40 years were 5.7 (95 % CI: 5.48-6.19), 4.55 (95 % CI: 4.52-4.64), and 3.72 (95 % CI: 3.55-3.80), respectively. Based on the Bayesian method, the PPV and NPV of these cut-off levels were as follows: PPV = 0.98 (95 % CI: 0.96-0.99) and NPV = 0.40 (95 % CI: 0.30-0.51) for the age group of 20-27 years; PPV = 0.96 (95 % CI: 0.91-0.99) and NPV = 0.82 (95 % CI: 0.78-0.86) for the age group of 27-35 years; and PPV = 0.86 (95 % CI: 0.80-0.94) and NPV = 0.96 (95 % CI: 0.93-0.98) for the age group of 35-40 years. CONCLUSIONS: Application of age-specific cut-off levels of AMH, according to the GAMs and Bayesian method, could elegantly assess the value of AMH in discriminating PCOS patients in all age categories.

The role of ERα36 in cell type-specific functions of estrogen and cancer development.

Exploring the regulatory effects of estrogen on different body organs via its receptors is largely of interest. Recently, the expression, signaling and the clinical significance of ERα36, the newly identified isoform of ERα, mediating non-genomic signaling of estrogen, have been studied in a wide range of organs and tumors. ERα36 is expressed highly in the CNS and actively involved in neuroprotection. It is also suggested to be an important estrogen receptor involved in preserving bone in postmenopausal women. On the oncological side, although ERα36 has usually been considered to be an oncogenic molecule, results from some studies paradoxically imply its protective role in certain tumors. Collectively, it seems that ERα36 is highly involved in cell type-specific functions of estrogen through its MAPK/ERK signaling, which is dependent on ERα36 expression levels, ligand concentrations and disease stage. The response is also dependent on the levels of ERα66 and ERß. These factors influence the ERK kinetic and determine the ultimate mitogenic or antimitogenic signaling of estrogen, leading to cell survival or cell death. In this review, we summarize the recent organ-specific, cellular and molecular events and the mechanisms involved in estrogen effects mediated through the ERα36/ ERα66 with a particular focus on carcinomas where more clinical information has recently emerged.

Expression patterns of ERα66 and its novel variant isoform ERα36 in lactotroph pituitary adenomas and associations with clinicopathological characteristics.

PURPOSE: The regulatory effects of estradiol on pituitary homeostasis have been well documented. However, the expression patterns of ERα66 and ERα36 and their correlations with the clinical course of postoperative prolactinoma tumors remain unclear. METHODS: The expression of ERα36, ERα66, Ki67, p53, and CD31 were determined by immunohistochemistry in 62 prolactinoma patients. Snap-frozen tumors and normal pituitaries were also examined by western blotting for estrogen receptor detection. RESULTS: A broad expression of ERα36 was identified in normal pituitaries. The median scores of ERα36 and ERα66 expression were 8 and 6 in normal pituitaries and 4 and 0 in tumors, respectively. Four phenotypes of ERα36 and ERα66 expression were explored in tumors with regard to sex, invasiveness, dopamine resistance, and recurrence. Low ERα36 expression was associated with tumor invasion and increased Ki67. Low ERα66 expression was associated with tumor invasion, dopamine-agonist resistance, and enhanced tumor size. Multivariable logistic regression analysis showed that low ERα36 expression is an independent risk factor for invasiveness. The significant inverse association of ERα66 with invasiveness, dopamine resistance, and tumor size remained significant after adjustment for sex as a potential confounder. After controlling for sex, the low ERα66/low ERα36 phenotype was 6.24 times more prevalent in invasive tumors than in noninvasive tumors. Although the decreasing trend of CD31 expression from surrounding nontumoral lactotroph adenomas to tumors was similar to that of the estrogen receptors, a significant correlation was not observed here. CONCLUSION: The decreasing trends of ERα36 and ERα66 expression from normal pituitaries to tumors are associated with aggressive clinical behavior.

Effects of Rosa damascena on reproductive improvement, metabolic parameters, liver function and insulin-like growth factor-1 gene expression in estradiol valerate induced polycystic ovarian syndrome in Wistar rats.

BACKGROUND: Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders in reproductive-age women. The present study aimed to evaluate the effects of Rosa damascena (RD) extract in estradiol valerate (EV) induced polycystic ovary syndrome rats. METHODS: Adult female Wistar rats were divided into control (n = 12) and PCOS groups (n = 36). The PCOS model was induced using EV (4 mg/kg/day), which was confirmed in 6 rats in each control and PCOS group by observation of irregular estrous cycles in vaginal smears and ovarian multiple cystic. Then, the rest of the control group (n = 6) and PCOS rats (n = 30 in 5 divided groups) were treated orally for 28 days with metformin (MET) as a positive control (200 mg/kg/day) and RD extract (400, 800, and 1200 mg/kg/day, respectively). Body and ovary weights, biochemical and histological parameters, and expression of the IGF-1 gene were measured. RESULTS: Compared to the PCOS group, metformin and higher doses of RD extract (800 and 1200 mg/kg/day) significantly reduced BW, HOMA-IR, FBS, FINS, TG, LDL, TT, E2, LH, TC, and liver enzymes, and increased HDL and FSH levels. In addition, ovarian weight and CFs decreased, and the findings showed an increment in PFs, CLs, PAFs, AFs, and GFs. IGF-1 gene expression levels were significantly decreased (p < 0.001). CONCLUSION: RD extract seems to have the potential therapeutic effect of alleviating PCOS complications, and IGF-1 signaling may be involved in the beneficial effects of RD on PCOS.

To what extent does polycystic ovary syndrome influence the cut-off value of prolactin? Findings of a community-based study.

PURPOSE: Polycystic ovary syndrome (PCOS) and hyperprolactinemia are the most frequent endocrine disorders in women which share several common features. There are inconsistent results regarding the existence of a possible pathophysiological interplay between these endocrinopathies and the elevation of prolactin (PRL) in PCOS. The purpose of this study was to explore the upper reference limit of PRL in PCOS women. PATIENTS AND METHODS: This study is a cross-sectional analysis using data collected from two population-based PCOS prevalence studies. After considering the exclusion criteria, 216 women with PCOS diagnosed based on the Rotterdam criteria and 702 eumenorrheic non-hirsute controls, were enrolled. The age distribution of PRL and the effect of PCOS on the percentiles of serum PRL were compared between the PCOS group and controls. The possible contributing factors for the elevation of PRL were evaluated. RESULTS: In the subgroup of women with PCOS, aged ≤35 years, the age-adjusted model of quantile regression revealed a significant elevation of PRL from the 60th percentile onwards, leading to an increase of nearly 10 â€‹ng/ml (p â€‹= â€‹0.023, 95% CI 1.3-17.62) of the 95th percentile of PRL. Hyperprolactinemic PCOS women had higher levels of luteinizing hormone (LH). CONCLUSIONS: In PCOS women, aged ≤35 years, the upper reference limit of serum PRL was approximately 1.5-fold higher than in controls. The pathway underlying PRL elevation in PCOS might be attributed to a decline in central dopaminergic tone associated with PCOS which leads to an increase in levels of both - PRL and LH.

Prevalence of idiopathic hirsutism: A systematic review and meta-analysis.

BACKGROUND: Although the negative impacts of idiopathic hirsutism (IH) on psychological aspects are well-documented, there is no enough study estimating the prevalence of this endocrine disorder. OBJECTIVE: This meta-analysis was conducted to estimate the pooled prevalence of IH in the women population. METHODS: PubMed, Scopus, and Web of Science databases were explored to obtain papers published from inception to September 2020 investigating the prevalence of IH in women. A meta-regression was conducted to assess the impact of polycystic ovary syndrome (PCOS) diagnostic criteria, and ethnicity on the pooled prevalence of IH. RESULTS: Of 8346 records retrieved through searching databases and other sources, eight studies were selected for the final analyses. The pooled prevalence of idiopathic hirsutism among women, regardless of PCOS diagnostic criteria, and the race was 7.74% (95% CI: 4.10, 14.14). The meta-regression analysis showed that the pooled prevalence of idiopathic hirsutism did not significantly differ based on the PCOS diagnostic criteria and ethnicity. A subgroup analysis based on the PCOS criteria showed the pooled prevalence of 7.24% (95% CI: 2.84, 17.24), 13.05% (95% CI: 10.02, 16.81), and 3.12% (95% CI: 2.16, 4.48) for NIH (National Institutes of Health), Rotterdam, and not reported PCOS diagnostic criteria groups, respectively. The subgroup analysis based on the ethnicity estimated a pooled prevalence of 6.01% (95% CI: 1.87, 17.69) and 9.36% (4.07, 16.63) for European and Asian groups, respectively. CONCLUSION: The meta-analysis demonstrated that the pooled prevalence of IH was 7.74% and there was no difference between PCOS criteria and ethnicity subgroups.

Estrogen as a key regulator of energy homeostasis and metabolic health.

Over the last two decades, it has become evident that estrogens preserve the integrity of energy homeostasis at central and peripheral levels. Estrogen deficiency, such as that caused by menopause or ovariectomy, has been linked to obesity and metabolic disorders that can be resolved or reversed by estrogen therapy. 17ß-estradiol (E2), as the major estrogen in the body, primarily regulates energy balance via estrogen receptor alpha (ERα). At the central level, E2 plays its catabolic role predominantly by interacting with hypothalamic arcuate neurons and sending signals via ventromedial hypothalamic neurons to control brown adipose tissue-mediated thermogenesis. In peripheral tissues, several organs, particularly the liver, brown and white adipose tissues, and pancreatic ß cells, have attracted considerable attention. In this review, we focused on the current state of knowledge of "central and peripheral" estrogen signaling in regulating energy balance via "nuclear and extranuclear pathways" in both "females and males". In this context, according to an exploratory approach, we tried to determine the principal estrogen receptor subtype/isoform in each section, the importance of extranuclear-initiated estrogen signaling on metabolic functions, and how sex differences related to ER signaling affect the prevalence of some of the metabolic disorders. Moreover, we discussed the data from a third viewpoint, understanding the clinical significance of estrogen signaling in abnormal metabolic conditions such as obesity or being on a high-fat diet. Collectively, this review exposes novel and important research gaps in our current understanding of dysmetabolic diseases and can facilitate finding more effective treatment options for these disorders.

Impact of Polycystic Ovary Syndrome on Silent Coronary Artery Disease and Cardiovascular Events; A Long-term Population-based Cohort Study.

BACKGROUND: The existing data regarding the impact of Polycystic Ovary Syndrome (PCOS) on the risk of developing cardiovascular disease (CVD) are conflicting. AIM: To explore the effect of PCOS status on the occurrence of silent coronary artery disease (CAD)/CVD. METHODS: A total of 1591 women without CVD at baseline, aged 18-45 years, including 356 PCOS patients (defined by the Rotterdam criteria) and 1235 eumenorrheic non-hirsute women without polycystic ovarian morphology (controls), were selected from the Tehran Lipid and Glucose Study (TLGS). The median follow-up was 15.4 years, and most participants were in their late reproductive years at the end of the study. Silent CAD and CVD outcomes in PCOS and control groups were compared according to the multivariable-adjusted hazard ratios (HRs) and cumulative hazard functions. RESULTS: There was no difference in CVD risk factors between the PCOS and control groups. After controlling for confounders, PCOS status did not increase the risk of silent CAD (HR: 0.96, 95% CI 0.86-1.08). Regardless of PCOS status, women with a history of silent CAD showed 2.25 times higher CVD events than those without this history (95% CI 1.63-3.10). PCOS status reduced the CVD incidence by 42%, independently of silent CAD or traditional risk factors (HR: 0.58, 95% CI 0.35-0.98). CONCLUSIONS: Whereas silent CAD, regardless of PCOS, accelerated CVD, PCOS preserved it, most likely due to a combination of protective factors, including the endocrine pattern in the late reproductive period, environmental/social elements, and recruiting additional counseling and lifestyle modifications.

A Meta-Analysis of Observational Studies on Prolactin Levels in Women with Polycystic Ovary Syndrome.

Women with polycystic ovary syndrome (PCOS) are reported to have different levels of prolactin (PRL) compared to women without PCOS. This study aimed to evaluate the PRL levels in women with PCOS, compared to the control group, before and after adjustment for potential confounders. Using a logical combination of keywords, a comprehensive search was carried out in PubMed and Web of Science, from inception to 30 August 2022. Weighted mean differences (WMDs) with corresponding 95% CIs in PRL levels were employed with a random-effects model. I2 was applied to evaluate heterogeneity among studies. A meta-regression analysis and subgroup analysis were conducted to explore heterogeneity sources. Publication bias was assessed by the Egger test. Thirty-two studies, measuring PRL levels in 8551 PCOS patients according to the Rotterdam criteria and 13,737 controls, were included in the meta-analysis. Pooled effect size suggested that the overall weighted mean difference (WMD) of PRL level was significantly higher in women with PCOS, compared to controls (WMD = 1.01, 95% CI: 0.04-1.98, p = 0.040). The result of meta-regression adjusted for age, BMI, and the continent of origin, revealed no confounding effect on results. Sub-group analysis of PRL levels according to the continent of origin showed significantly higher PRL levels among Eurasian PCOS patients compared to the control; this difference was not statistically significant in the subgroups of women from Asia, Europe, and South America. In conclusion, PRL levels in patients who were diagnosed according to the Rotterdam criteria were significantly higher than non-PCOS participants. Slightly higher levels of PRL could be presented as a diagnostic feature of PCOS.

The Prevalence of Polycystic Ovary Syndrome, Its Phenotypes and Cardio-Metabolic Features in a Community Sample of Iranian Population: Tehran Lipid and Glucose Study.

Objectives: The aim of the present study was to evaluate the prevalence of polycystic ovary syndrome (PCOS), its phenotypical and cardio-metabolic features in a community sample of the Iranian population in comparison to healthy eumenorrheic, non-hirsute women without polycystic ovaries. The second aim was to assess the cardio-metabolic characteristics of women who suffered from one criteria of PCOS compared to those healthy eumenorrheic, non-hirsute women. Methods: In this cross-sectional population-based study, a total of 1,960 eligible women, aged (18-45 years) were recruited from the Tehran-Lipid and Glucose-Study participants and were classified as the three groups of (i) women with PCOS by the Rotterdam criteria, (ii) non-PCOS women with one criteria of PCOS and (iii) healthy eumenorrheic, non-hirsute women without polycystic ovaries morphology (PCOM) as the control group. Further PCOS women were extended to four phenotypes of hyperandrogenism, oligo-anovulation, polycystic ovaries (phenotype A), hyperandrogenism, oligo/anovulation (phenotype B), hyperandrogenism, polycystic ovaries (phenotype C) and oligo-anovulation, polycystic ovaries (phenotype D). Cardio-metabolic profiles and the prevalence of comorbidities of metabolic syndrome (MetS) and lipid abnormalities were compared among these groups linear, and the median regression models adjusted for age and body mass index. Results: The prevalence of PCOS according to the diagnostic criteria of the NIH, Rotterdam and AE-PCOS Society were 13.6, 19.4, and 17.8, respectively. Among those who met the Rotterdam criteria, 23.9, 46.3, 21.6, and 8.2% had phenotypes A, B, C, and D, respectively. Among the remaining 1,580 women who did not fulfil the PCOS criteria, 108 (6.8%) suffered from only oligo/anovulation, 332 (21%) only hyperandrogenism/hyperandrogenemia, 159 (16.2%) only PCOM in ultrasound and 981 (62%) were healthy eumenorrheic, non-hirsute women without PCOM. The study revealed that some adiposity indices and lipid abnormalities in PCOS phenotypes with hyperandrogenism (A, B, and C) were worse than in healthy women. By contrast, women with phenotype D did not differ from the healthy ones in terms of adiposity and lipid abnormalities. However, the respective values for other cardio-metabolic profiles and MetS rates in different phenotypes of PCOS were similar to the healthy women. Only the prevalence of MetS in phenotype A was significantly higher than in the healthy women. There were no statistically significant differences between participants with one criteria of PCOS and healthy counterparts in terms of most adiposity indexes, cardio-metabolic factors, and comorbidity of MetS and its components. However, women with hyperandrogenism had a significantly higher level of the waist to height ratio (WHtR) and hypertriglyceridemia than their healthy counterparts. Conclusion: PCOS, mainly classical phenotypes A and B, are common among Iranian women of reproductive age. Women with PCOS who had androgen excess exhibited the worst lipid profile, and those who had full three criteria of the syndrome exhibited the higher rate of MetS. However, women with only ovulatory dysfunction and only PCOM had similar cardio-metabolic characteristics, compared to healthy subjects. These data suggest that routine screening for metabolic disturbances may be needed in the prevention of cardio-metabolic disorders in patients with more serious phenotypes of PCOS.

Role of L-arginine/NO/cGMP/KATP channel signaling pathway in the central and peripheral antinociceptive effect of thymoquinone in rats.

OBJECTIVES: Growing evidence demonstrates that L-arginine/NO/cGMP/KATP channel pathway has a modulatory role in pain perception. Previous studies have shown that thymoquinone exerts antinociceptive effects; however, the mechanisms underlying antinociception induced by thymoquinone have not been fully clarified. The aim of the present study was to evaluate the role of L-arginine/NO/cGMP/KATP channel pathway in the central and peripheral antinociceptive effect of thymoquinone in rats. MATERIALS AND METHODS: Rats were pretreated intraplantarly (IPL) or intracerebroventricularly (ICV) with L-arginine (the NO precursor), l-NAME (an NO synthase inhibitor), SNAP (an NO donor), methylene blue (a guanylyl cyclase inhibitor), glibenclamide (the blocker of KATP channel), and tetraethylammonium (TEA, a Kv channel blocker) before the injection of thymoquinone. RESULTS: Local ipsilateral (20 and 40 µg, IPL) but not contralateral and ICV (4 and 8 µg) administration of thymoquinone caused a dose-dependent and significant antinociception in both early and late phases of the formalin test. Pretreatment of rats with L-arginine (100 µg, IPL or ICV) and SNAP (200 µg, IPL or ICV) increased while l-NAME (100 µg, IPL or 1 µg, ICV) and methylene blue (400 µg, IPL or ICV) decreased the antinociceptive effects of thymoquinone in the formalin test. The administration of TEA (IPL or ICV) did not modify but glibenclamide (50 µg, IPL or ICV) significantly abolished the peripheral and central antinociceptive effects of thymoquinone in both phases of the formalin test. CONCLUSION: The results of the present study indicate that L-arginine/NO/cGMP/KATP channel pathway participates in the central and peripheral antinociceptive effect of thymoquinone.

Attenuation of morphine tolerance and dependence by thymoquinone in mice.

OBJECTIVE: Dependence and tolerance are major restricting factors in the clinical use of opioid analgesics. In the present study, the effects of thymoquinone, the major constituent of Nigella sativa seeds, on morphine dependence and tolerance were investigated in mice. MATERIALS AND METHODS: Male adult NMRI mice were made tolerant and dependent by repeated injections of morphine (50, 50, and 75 mg/kg, i.p. on 9 a.m., 1 p.m., and 5 p.m., respectively) during a 3-day administration schedule. The hot-plate test was used to assess tolerance to the analgesic effects of morphine. Naloxone (2 mg/kg, i.p.) was injected to precipitate withdrawal syndrome in order to assess the morphine dependence. To evaluate the effects of thymoquinone on tolerance and dependence to morphine, different single or repeated doses of thymoquinone were administered in mice. Rotarod was used to assess the motor coordination. RESULTS: Administration of single or repeated doses of thymoquinone (20 and 40 mg/kg, i.p.) significantly decreased the number of jumps in morphine dependent animals. Repeated administration of thymoquinone (20 and 40 mg/kg, for 3 days) and also single injection of thymoquinone (40 mg/kg, on the fourth day) attenuated tolerance to the analgesic effect of morphine. None of the thymoquinone doses (10, 20, and 40 mg/kg) produced any antinociceptive effects on their own. Motor coordination of animals was impaired by the high dose of thymoquinone (40 mg/kg). CONCLUSION: Based on these results, it can be concluded that thymoquinone prevents the development of tolerance and dependence to morphine.