Retinoic acid exerts sexually dimorphic effects on muscle energy metabolism and function

The retinol dehydrogenase Rdh10 catalyzes the rate-limiting reaction that converts retinol into retinoic acid (RA), an autacoid that regulates energy balance and reduces adiposity. Skeletal muscle contributes to preventing adiposity, by consuming nearly half the energy of a typical human. We report sexually dimorphic differences in energy metabolism and muscle function in Rdh10+/− mice. Relative to wild-type (WT) controls, Rdh10+/− males fed a high-fat diet decrease reliance on fatty-acid oxidation and experience glucose intolerance and insulin resistance. Running endurance decreases 40%. Rdh10+/− females fed this diet increase fatty acid oxidation and experience neither glucose intolerance nor insulin resistance. Running endurance increases 220%. We therefore assessed RA function in the mixed-fiber type gastrocnemius muscles (GM), which contribute to running, rather than standing, and are similar to human GM. RA levels in Rdh10+/− male GM decrease 38% relative to WT. Rdh10+/− male GM increase expression of Myog and reduce Eif6 mRNAs, which reduce and enhance running endurance, respectively. Cox5A, complex IV activity, and ATP decrease. Increased centralized nuclei reveal existence of muscle malady and/or repair in GM fibers. Comparatively, RA in Rdh10+/− female GM decreases by less than half the male decrease, from a more modest decrease in Rdh10 and an increase in the estrogen-induced retinol dehydrogenase Dhrs9. Myog mRNA decreases. Cox5A, complex IV activity, and ATP increase. Centralized GM nuclei do not increase. We conclude that Rdh10/RA affects whole body energy use and insulin resistance partially through sexual dimorphic effects on skeletal muscle gene expression, structure, and mitochondria activity.     

有机磷阻燃剂TDCIPP对雌性大鼠甲状腺的潜在毒性作用

目的: 研究磷酸三(1, 3-二氯-2-丙基)酯(TDCIPP)对雌性大鼠甲状腺系统的潜在毒性作用及机制。方法: 将32只离乳3周的雌性SD大鼠随机分为对照组(玉米油灌胃)及TDCIPP低、中、高剂量组(50、100、250 mg/kg·d,溶于玉米油)(n=8),灌胃给药21 d,每天1次。于末次给药后处死动物,取血和甲状腺、肝脏,检测血清中促甲状腺激素(TSH)、三碘甲腺原氨酸(T3), 甲状腺素(T4)和游离甲状腺素(FT4)水平变化;组织切片(HE染色)用于检测甲状腺形态学病变;RT-PCR技术与Western blot技术检测与甲状腺功能相关的基因和蛋白表达的变化。结果: 与对照组比较,TDCIPP染毒后大鼠甲状腺出现滤泡排列不规则、胶质变少、滤泡增生、肥大等现象,TDCIPP低剂量组的血清TSH水平和高剂量组的T3水平均显著升高(P＜0.05),低剂量组促甲状腺激素受体(TSHR)mRNA表达和中、高剂量组甲状腺激素受体β(TRβ)蛋白表达均显著降低(P＜0.05,P＜0.01),中、高剂量组甲状腺过氧化物酶(TPO)mRNA表达显著增高(P＜0.05,P＜0.01),三个剂量组尿苷二磷酸葡萄糖醛酸转移酶(UGTs)、细胞色素氧化酶-3A1(CYP3A1)蛋白表达水平显著上调(P＜0.05)。结论: 大鼠暴露在50 mg/(kg·d)以上剂量的TDCIPP,即可以刺激甲状腺组织的增生,改变血清中甲状腺素的水平,干扰甲状腺的功能,表现出对甲状腺的毒性作用。     

Gender-specific effects of thyroid hormones on cardiopulmonary function in SHHF rats.

Spontaneously hypertensive heart failure (SHHF) rats develop hypertension and heart failure. We hypothesized that induction of hyperthyroidism should accelerate development of heart failure in male SHHF rats. Male and female SHHF rats received diets containing desiccated thyroid glands (DTG) or a control diet for 8 wk. Male and female Wistar-Kyoto rats were used as normotensive controls. DTG treatment reduced body weight in male, but not female, SHHF rats but increased body temperature and heart weight-to-body weight ratio in both genders. In DTG-treated male SHHF rats, serum triiodothyronine levels doubled relative to SHHF controls, whereas O2 consumption increased in DTG-treated SHHF rats. Frequency of breathing in air increased in DTG-treated female rats, and ventilation increased in DTG-treated male rats. Ventilatory equivalents exhibited gender differences in SHHF rats, were decreased in both genders by DTG treatment, and reached levels similar to those of Wistar-Kyoto rats. DTG increased heart rate, right ventricular pressure, and contractility in both genders and increased left ventricular pressure in SHHF male rats. These results refute our hypothesis and suggest that cardiopulmonary function of SHHF male rats may be improved by DTG treatment.     

The effects of synthetic salmon calcitonin on thyroid C and follicular cells in adult female rats

Structural and morphometric features of thyroid C and follicular cells were studied in adult rat females after treatment with synthetic salmon calcitonin (CT). The animals were chronically treated with either a low (10 IU/kg b.w) or a high (100 IU/kg b.w) dose of CT. A stereological method was applied to determine the volume density and the number of immunoreactive C cells. The height and volume density of follicular epithelium, colloid, interstitium and the follicles (epithelium plus colloid), as well as the index of activation rate were calculated. A significant decrease in body weight, as well as the volume density of immunoreactive C cells and the number of C cells per mm2, was observed in rats treated with both doses of CT. The height and volume density of follicular epithelium and follicles, as well as the index of activation rate were significantly increased in the animals given the high CT dose, while the volume densities of colloid and interstitium were reduced. No significant changes in the examined morphometric parameters were detected after treatment with the low CT dose. According to these results it can be concluded that the structural features of thyroid C and follicular cells were affected by the high dose CT treatment in the opposite manner, while the low dose CT treatment influenced only C cells.     

Retinoic acid can enhance the stimulation by thyroid hormone of heme oxygenase activity in the liver of thyroidectomized rats

The effects of retinoic acid (RA) (50 μg/100 g body wt. per day) on hepativ heme oxygenase activty, δ-aminolevulinate synthase (ALAS) activity and on cytochrome P-450 content were determined in thyroidectomized rats treated with T₃ (10 μg/100 g body wt. per day) or diluent. RA, when administered for 3 days, failed to influence significantly the activity of either heme oxygenase or ALAS, however, the retinoid depleted hepatic cytochrome P-450 content by 17% (P < 0.01) and microsomal heme content by 47% (P < 0.001). T₃ administration enhanced heme oxygenase activity by 72% (P < 0.001) and ALAS activity by 251% (P < 0.001) above levels in diluent treated controls and depleted cytochrome P-450 levels by 55% (P < 0.001) and heme levels by 75% (P < 0.001). When RA and T₃ were administered together, the retinoid markedly enhanced the T₃ stimulation of heme oxygenase activity; 173% above controls (P < 0.001), and 61% above T₃ alone (P < 0.001). However, RA failed to influence the effect of T₃ on ALAS activity or cytochrome P-450 depletion. The results indicate that RA can influence the levels of hepatic cytochrome P-450 and can modulate the stimulation of heme oxygenase activity by thyroid hormone in vivo.     

Adrenal function in female rats before puberty: the effects of gonadectomy

The following study was designed to test whether the change in the amplitude of the adrenal rhythm and the response to stress seen at puberty in female rats is dependent upon stimulation of the adrenal system by gonadal steroids. Rats were gonadectomized either at two days of age or at 21 days of age and periodic blood samples were taken by cardiac puncture and assayed for corticosterone (B) by a fluorometric procedure. Ovariectomy at weaning age (21 days) had no effect on adrenal function until the time of normal puberty onset. In intact animals, a rise in resting levels of corticosterone and an increase in the incremental response to ether stress was noted at 35 days of age. (Puberty in females was 35.3 ± 1.2 days as indicated by vaginal opening). Ovulation occurred the following day in 9/10 rats. Gonadectomy at two days of age had essentially the same effect as later gonadectomy in females. By 70 days of age, resting corticosterone values and stress responses in gonadectomized females reached levels similar to intact females. It is concluded that an independent adrenarche can occur in females but that gonadal steroids present at the time of puberty modulate the timing of this process.     

Retinoic acid can enhance the stimulation by thyroid hormone of heme oxygenase activity in the liver of thyroidectomized rats.

The effects of retinoic acid (RA) (50 micrograms/100 g body wt. per day) on hepatic heme oxygenase activity, delta-aminolevulinate synthase (ALAS) activity and on cytochrome P-450 content were determined in thyroidectomized rats treated with T3 (10 micrograms/100 g body wt. per day) or diluent. RA, when administered for 3 days, failed to influence significantly the activity of either heme oxygenase or ALAS, however, the retinoid depleted hepatic cytochrome P-450 content by 17% (P less than 0.01) and microsomal heme content by 47% (P less than 0.001). T3 administration enhanced heme oxygenase activity by 72% (P less than 0.001) and ALAS activity by 251% (P less than 0.001) above levels in diluent treated controls and depleted cytochrome P-450 levels by 55% (P less than 0.001) and heme levels by 75% (P less than 0.001). When RA and T3 were administered together, the retinoid markedly enhanced the T3 stimulation of heme oxygenase activity; 173% above controls (P less than 0.001), and 61% above T3 alone (P less than 0.001). However, RA failed to influence the effect of T3 on ALAS activity or cytochrome P-450 depletion. The results indicate that RA can influence the levels of hepatic cytochrome P-450 and can modulate the stimulation of heme oxygenase activity by thyroid hormone in vivo.     

Retinoic acid signaling reduction recapitulates the effects of alcohol on embryo size

Intrauterine growth restriction (IUGR) is commonly observed in human pregnancies and can result in severe clinical outcomes. IUGR is observed in Fetal Alcohol Syndrome (FAS) fetuses as a result of alcohol (ethanol) exposure during pregnancy. To further understand FAS, the severe form of Fetal Alcohol Spectrum Disorder, we performed an extensive quantitative analysis of the effects of ethanol on embryo size utilizing our Xenopus model. Ethanol‐treated embryos exhibited size reduction along the anterior–posterior axis. This effect was evident primarily from the hindbrain caudally, while rostral regions appeared refractive to ethanol‐induced size changes, also known as asymmetric IUGR. Interestingly, some embryo batches in addition to shortening from the hindbrain caudally also exhibited an alcohol‐dependent reduction of the anterior head domain, known as symmetric IUGR. To study the connection between ethanol exposure and reduced retinoic acid levels we treated embryos with the retinaldehyde dehydrogenase inhibitors, DEAB and citral. Inhibition of retinoic acid biosynthesis recapitulated the growth defects induced by ethanol affecting mainly axial elongation from the hindbrain caudally. To study the competition between ethanol clearance and retinoic acid biosynthesis we demonstrated that, co‐exposure to alcohol reduces the teratogenic effects of treatment with retinol (vitamin A), the retinoic acid precursor. These results further support the role of retinoic acid in the regulation of axial elongation.     

Thiocyanate effects on thyroid function of weaned mice

The aim of this study was to determine the effects of thiocyanate on thyroid function in weaned mice. At this developmental period, induction and reversibility of thiocyanate effects have not yet been studied. In the present work, adult female mice were given thiocyanate [SCN(-) (1 g L(-1))] in their drinking water from the 15(th) day of pregnancy until either the 25(th) (group B) or the 15(th) day (group C) after parturition. During five days after weaning, water and food consumptions of treated mice (group B) were 42.2+/-1.2% and 56.4+/-0.9%, respectively, less than those of the controls (group A). On the sacrifice day (the 25(th) day after birth), body weight, thyroid iodine content and thyroid hormone levels (FT(4) and FT(3)) decreased by 10.4+/-3.0%, 40.6+/-2.3%; 18.7+/-2.3% and 18.1+/-1.3%, respectively. Plasma TSH increased by 30.6+/-1.7% along with the hypertrophy of thyroid glands (52.6+/-3.1%). We have observed a hypertrophy of follicle cells and a decrease in colloid volume within histological slides. After SCN(-) withdrawal (group C), partial or total recovery were noted in all parameters studied. We concluded that hypothyroidism effects added to the weaning event affected greatly thyroid function and behaviour of mice; these would be largely reversed by withdrawing thiocyanate treatment for a period of ten days.     

Differential effects of high consumption of fructose or glucose on mesenteric arterial function in female rats

We have recently shown that type of supplemented simple sugar, not merely calorie intake, determines adverse effects on metabolism and aortic endothelial function in female rats. The aim of the current study was to investigate and compare the effects of high consumption of glucose or fructose on mesenteric arterial reactivity and systolic blood pressure (SBP). Sprague–Dawley female rats were supplemented with 20% w/v glucose or fructose in drinking water for 8 weeks. Here, we show that both sugars alter insulin signaling in mesenteric arteries (MA), assessed by a reduction in phosphorylated Akt, and increase in SBP. Furthermore, ingestion of glucose or fructose enhances inducible nitric oxide synthase (iNOS) expression and contractile responses to endothelin and phenylephrine in MA of rats. The endothelium-dependent vasodilation to acetylcholine and bradykinin as well as the relaxation responses to the nitric oxide donor sodium nitroprusside are impaired in MA of fructose- but not glucose-supplemented rats. In contrast, only glucose supplementation increases the expression of phosphorylated endothelial NOS (eNOS) in MA of rats. In conclusion, this study reveals that supplementation with fructose or glucose in liquid form enhances vasocontractile responses and increases iNOS expression in MA, effects which are accompanied by increased SBP in those groups. On the other hand, the preserved vasodilatory responses in MA from glucose-supplemented rats could be attributed to the enhanced level of phosphorylated eNOS expression in this group.     

Temperature and photoperiod effects on thyroid function and metabolism in cotton rats (Sigmodon hispidus)

This study investigates the environmental cue(s) used by cotton rats to mediate seasonal shifts in thyroid function and metabolism. Summer-caught and winter-caught animals were exposed to combinations of five photoperiods and two temperatures for 60 days. Oxygen consumption and several parameters of thyroxine (T₄) and triiodothyronine (T₃) dynamics were then measured. Photoperiod had a significant effect only on serum T₃ concentration: an inverse relationship with length of day. Cold exposure also increased serum T₃, as well as the T₃ pool and T₃ utilization (i.e., disappearance) rate. In addition, cold increased metabolic rate, T₄ clearance, and T₄ volume of distribution, while it decreased serum T₄ concentration. For a few parameters, season of capture also had a significant effect. Because many of the observed changes could result from a seasonal or temperature-induced shift in T₄ to T₃ deiodination, it is suggested that one important effect of these environmental cues is the regulation of this enzyme(s). Since T₃ utilization increases over 12-fold in winter-caught cotton rats maintained at 5°C (over summer-caught animals maintained at 30°C), but metabolic rate only increased about 25% in these same animals, the roles/fates of this additional T₃ remains to be determined.     

Retinoic acid elicits cytostatic,cytotoxic and immunomodulatory effects on uveal melanoma cells

The current therapy of uveal melanoma (UM) metastases remains inefficient, which warrants the development of new treatment modalities. For the first time we investigated the effects of retinoic acid (RA) on a panel of UM cell lines and found that RA induces morphological changes compatible with differentiation, suppresses proliferation and causes apoptosis in these cells. RA treatment resulted in an increase of p21, p27 and p53 protein levels and G1 arrest in UM cells, which correlated with significant down-modulation of surface Her2/neu proto-oncogene expression. In addition, RA-treated UM cells exhibited increased sensitivity to both MHC class I-restricted killing by cytotoxic T lymphocytes and NK cell-mediated lysis that were accompanied by more efficient conjugate formation between UM cells and killer lymphocytes. Taken together, our results implicate UM as a new target for treatment with retinoids and suggest that retinoids and T- or NK-cell based immunotherapy can have mutually enhancing effects in UM patients.