Effects of heat exposure and vitamin C intervention on oxidative stress and blood pressure changes in treadmill rats / 中华劳动卫生职业病杂志

Objective: To investigate the effect of oxidative stress caused by heat exposure on the blood pressure increase of treadmill rats and the intervention of antioxidants. Methods: In June 2021, Twenty-four healthy SD male rats were randomly divided into four groups: normal temperature feeding, normal temperature treadmill, high temperature treadmill and high temperature treadmill supplementation with vitamin C groups, 6 rats in each group. The rats run on the platform in normal temperature or heat exposure environment for 30 min in the morning and in the afternoon daily, 6 days per week. The daily vitamin C supplement dose of high temperature treadmill supplementation with vitamin C group was 10 mg/kg. BP recordings were done at the end of the week. The rat vascular lipofuscin (LF) was detected by ELISA, the rat serum nitric oxide (NO) was detected by nitrate reductase method, the serum malondialdehyde (MDA) was detected by thibabituric acid method, the serum glutathione peroxidase (GPx) and superoxide dismutase (SOD) were detected by chemiluminescence method, and the serum catalase (CAT) was detected by ammonium molybdate method. The total antioxidant capacity (T-AOC) of serum was measured by iron reduction/antioxidant capacity method, and the content of nuclear erythroid 2-related factor 2 (Nrf2) in vascular tissue was measured by Western blot. The intra-group mean was compared by repeated measurement analysis of variance, and the inter-group mean was compared by single-factor analysis of variance and post-event LSD-t test. Results: Compared with the previous time point, the systolic BP and diastolic BP of the high temperature treadmill group were significantly increased at 7, 14 and 21 d, and decreased at 28 d which were higher than the initial level (P<0.05), and the systolic BP and diastolic BP values at each experimental time point were significantly higher than those of normal temperature treadmill group (P<0.001). The changes of thickening of the artery wall, no smoothing of the endodermis and irregular arrangement of muscle cells in high temperature treadmill group were observed. Compared with the normal temperature treadmill group, the content of MDA in serum, and LF in vascular tissue were significantly increased, the activities of SOD, CAT, T-AOC, the content of NO in serum, and the expression of Nrf2 in vascular tissue were significantly decreased in high temperature treadmill group (P<0.05). Compared with the high temperature treadmill group, the systolic BP and diastolic BP values at 7, 14, 21 and 28 d, the content of serum MDA and LF in vascular tissue were significantly decreased, the activities of CAT and T-AOC, and the expression of Nrf2 in vascular tissue significantly increased (P<0.05), the histopathological changes of the artery wall improved in high temperature treadmill supplementation with vitamin C group. Conclusion: Heat exposure has effect on oxidative stress, which may be related to the increase of BP. Vitamin C as an anti-oxidative enhancer can prevent those negative effects, which could alleviate the pathological changes of vessel intima in heat-exposed rats. And the Nrf2 may be a regulated factor to vascular protection.

Intermittent heat exposure induces thoracic aorta injury in spontaneously hypertensive rats by activating the AMPK/mTOR/ULK1 pathway / 南方医科大学学报

OBJECTIVE@#To investigate the effects of different manners of heat exposure on thoracic aorta injury in spontaneously hypertensive rats (SHRs) and explore the underlying mechanism.@*METHODS@#Normal 6 to 7-week-old male SHRs were randomized into control group (cage at room temperature), intermittent heat exposure group (SHR-8 group, exposed to 32 ℃ for 8 h daily for 7 days) and SHR-24 group (with continuous exposure to 32 ℃ for 7 days). After the treatments, the pathologies of the thoracic aorta of the rats were observed with HE staining, and the expressions of Beclin1, LC3B and p62 were detected with Western blotting and immunofluorescence assay; TUNEL staining was used to observe cell apoptosis in the thoracic aorta, and the expressions of caspase-3, Bax, and Bcl-2 were detected using Western blotting. The effects of intraperitoneal injections of 3-MA (an autophagy agonist), rapamycin (an autophagy inhibitor) or compound C 30 min before intermittent heat exposure on the expressions of proteins associated with autophagy, apoptosis and the AMPK/mTOR/ULK1 pathway in the aorta were examined with immunohistochemistry.@*RESULTS@#In SHR-8 group, the rats showed incomplete aortic intima with disordered cell distribution and significantly increased expressions of Beclin1, LC3II/LC3I and Bax, lowered expressions of p62 and Bcl-2, and increased apoptotic cells in the thoracic aorta (P < 0.05). Pretreatment with 3-MA obviously inhibited the expressions of autophagy- and apoptosis-related proteins, whereas rapamycin promoted their expressions. Compared with the control group, the rats in SHR-8 group had significantly down-regulated p-mTOR and up-regulated p-AMPK and p-ULK1 expression of in the aorta; Treatment with compound C obviously lowered the expressions of p-AMPK and p-ULK1 and those of LC3B and Beclin1 as well.@*CONCLUSION@#In SHRs, intermittent heat exposure causes significant pathologies and promotes autophagy and apoptosis in the thoracic aorta possibly by activating the AMPK/mTOR/ULK1 pathway.

Mediating role of sleep in association between maternal heat exposure during early pregnancy and risk of preterm birth / 环境与职业医学

Background Preterm birth-related complications are the leading cause of death in newborns and children under the age of 5 years. Maternal heat exposure has been associated with both sleep status during pregnancy and the increased risk of preterm birth. However, whether sleep status could mediate the association between heat exposure and preterm birth remains unclear. Objective To evaluate the association between maternal heat exposure in early pregnancy and preterm birth, and to further explore potential mediation effect of sleep status on the association between heat exposure and preterm birth. Methods A birth cohort was established in Guangzhou Panyu Maternal Child Health Hospital (Guangzhou Panyu District He Xian Memorial Hospital) from 2017 until now. Pregnant women (with gestational age between 8 and 13 weeks) were included in this study when they presented to the hospital for their first prenatal care visit and signed an informed consent. Then they were followed up until delivery. A total of 3 268 pregnant women were included for the final analysis. Questionnaires were distributed to collect the demographic characteristics, lifestyles, and sleep status of pregnant women. Daily meteorological data during the study period were collected from meteorological monitoring stations in Guangzhou and the average ambient mean temperature of four weeks before the survey was calculated and assigned for each pregnancy. The 75th, 80th, 85th, 90th, and 95th percentiles (P75, P80, P85, P90, and P95) of the average ambient temperature of all pregnant women were used as the thresholds to define heat exposure. Logistic regression was used to evaluate the effects of heat exposure in different definitions on preterm birth and sleep status (sleep duration, night sleep timing, and wake up timing). The mediation effects of sleep status on the relationship between heat exposure and preterm birth were also analyzed. Results Among all the included participants, 165 newborns were preterm births with an incidence rate of 5.0%. Heat exposures with thresholds of P90 and P95 increased the risk of preterm birth, with ORs (95%CIs) of 1.66 (1.04-2.57) and 1.90 (1.03-3.33), respectively (P<0.05). Heat exposures with thresholds of P75, P80, P85, P90, and P95 decreased the sleep duration (<9 h vs. ≥9 h, control group: ≥9 h), and the ORs (95%CIs) were 1.51 (1.25-1.83), 1.44 (1.17-1.77), 1.35 (1.08-1.70), 1.43 (1.09-1.87), and 1.45 (1.00-2.13), respectively. Heat exposures with P75 and P80 thresholds resulted in earlier wake up timing (<8: 00 vs. ≥8: 00, control group: <8: 00), with ORs (95%CIs) of 0.77 (0.63-0.93) and 0.76(0.61-0.93), respectively. No significant association was observed between heat exposure and night sleep timing. The mediation analyses showed that under heat exposure with P90 threshold, a statistically significant mediation effect was observed for sleep duration, and the proportion mediated was 6.07% (95%CI: 0.17%-25.00%) (P<0.05). No significant mediation effect was observed for night sleep timing and wake up timing. Conclusion An elevated risk of preterm birth after heat exposure in early pregnancy may be partly mediated through reducing sleep duration.

A study of regenerative ability of liver after repetitive heat stress induced liver injury.

Background: It is well known that heat stress produces liver injury. It is also known that liver regenerate after injury. This way, there should be almost no or minimal alteration in the size of the liver after regeneration. Aims & Objective: In the present study, after heat induced liver injury, the ability of liver to regenerate itself was assessed. Liver injury was assessed by biochemical [Serum Glutamic Pyruvate Transaminase (SGPT); Serum Glutamic Oxaloacetic Transaminase (SGOT); and Alkaline Phosphatase (ALKP)], morphological, and morphometric changes. On the other hand, Liver regeneration was evaluated by morphological and morphometric observations of male adult albino rats (Wistar strain). Material and Methods: The experimental animals were subjected to repetitive heat stress for 4 hours daily, at 37 ± 0.5 ˚C in a Biological Oxygen Demand (BOD) incubator (relative humidity 65 - 82%) for 2 and 5 consecutive days. Biochemical assessment was done on blood collected from left ventricle of beating heart of rats. Morphometric and morphological studies were conducted under light microscope on paraffin sections (H&E) of liver from control and experimental animals. The morphometric analysis was done by intersection – point counting method, using simple square lattice test system. Relative Liver Wet Weight of all animals was calculated. Results: Progressively degenerative changes in morphological observations (disruption of cell plates in liver lobules and Kupffer cell hyperplasia), progressively increased statistical significance of morphometric (numerical density of Kupffer cells on area - Nak), and biochemical parameters informed that increasing liver damage was present with increased repetition of heat exposures in 2 and 5 days heat exposed experimental albino rats. With this liver degeneration, Relative Liver Wet Weight of all the experimental animals should have been decreased but it was not, reiterating about well-known fact of regenerative ability of liver. Along with progressive changes of heat induced liver injury, progressively increasing regenerative changes were also evident on morphological (binucleate cells and anisocytosis) observations supported by statistically significant morphometric (volume density of hepatocytes – Vvh and numerical density of hepatocytes - Nvh) parameters in experimental animals. Conclusion: The above findings suggested that the regenerative ability of liver progressively increased with progressively increasing liver injury.

Behavioral changes in albino rats due to repetitive heat stress of moderate level.

Background: There are a number of studies showing the effect of severe heat stress on behaviour. Severe heat stress has been well reported to cause changes in activity level, attitude/mood, and behaviour. But, the effect of repetitive heat stress of moderate level on all these parameters has not been studied extensively. Aims & Objective: In the present study, the effect of repetitive heat stress of moderate level was assessed on activity level, attitude / mood, and behaviour (spontaneous and provoked) of adult albino male rats (wistar strain). Material and Methods: The experimental animals were subjected to repetitive heat stress for 4 hours daily, at 37±0.5ºC in a Biological Oxygen Demand (BOD) incubator (relative humidity 65-82%) for five consecutive days. Daily changes were assessed in activity level during and after heat exposure and in attitude / mood along with behaviour (both spontaneous and provoked) after heat exposure in experimental animals and compared with control animals. Results: There was increased restlessness during heat exposure and decreased level of activity after heat exposure in experimental animals. The mood of the experimental animals was depressed and the experimental animals kept them isolated and did not respond on provoking after heat stress. Conclusion: All the above observations confirmed that exposure to repetitive heat stress, even of moderate level, causes significant change in behaviour of male albino rats.

Effects of Acute Exhausted Exercise on the Myocardial HSP70 and Plasma ANP of Rats in a High Temperature Environment / 中国运动医学杂志

Objective To investigate the effect of acute exhausted exercise in high temperature environment on the expression of myocardial HSP70 and plasma ANP level of in rats. Methods Forty eight male Sprague-Dawley rats was randomly and equally assigned to the following six groups:control group(C),exercise group(E),one-hour heat exposure group (H), heat exposure and exercise group (HE), exercise and 24 hours after exercise group(E'),heat exposure and 24 hours after exercise(HE'). Each group consisted of 8 rats. Rats in E,HE,E' and HE' ran on a treadmill until exhaustion, while rats in H and H' were exposed in a high temperature environment (33℃ ,50%RH) for one hour. Rats in C,E,HE and H were killed immediately after exercise or heat exposure. Rats in HE' and E' were killed 24 hours after exercise. Samples from myocardium and serum were collected for determining HSP70,ANP and CK-MB. Results(1) HSP70 levels in groups E and E' are significantly higher than that in group C(P<0.05 and P<0.01,respectively),and the level in group HE' is significantly higher than that in groups H and E'(P<0.01 );The HSP70 level in group H is significantly higher than that in group C. (2) The ANP and CK-MB levels in group E are Significantly higher than that in group C.and in group HE is higher than in group H (P<0.05);The HSP70 levels in group E' and HE' significantly decrease comparing to that in groups E and HE (P<0.01). Conclusions(1)Both heat exposure and exercise can induce the increased expression of myocardial HSP70 in rats and the peak expression is seen 24 hours after exercise. The increased expression of HSP70 may have protective effects on the heat-induced myocardial injury. (2) The increased ANP levels in plasma immediately after exhausted exercise improves the blood circulation in myocardium and hints the potential possibility of myocardial damage. However,the high temperature environment does not strengthen the increase of plasma ANP level that caused by exhaustive exercise.

Protective effects and mechanism of heat shock response on cardiovascular system in rats after heat exposure / 中国病理生理杂志

AIM: To study protective effects and mechanism of heat shock response (HSR) on cardiovascular system in rats after heat exposure. METHODS: The study was divided into 2 experiments: ① Protective effects of HSR on cardiovascular system in rats after heat exposure. SD rats randomly allocated into 2 groups: heat shock group (HS group), sham control group (SC group). HS group were treated with heat shock, but SC group weren't. After recovering for 20 h at room temperature, two groups exposed to death in thermal environment, and blood pressure and electrocardiogram were measured continuously. Through Chart software mean arterial pressure(MAP), existent time etc were acquired. ② SD male rats randomly allocated into 3 groups: HS group, SC group and normal temperature control group (NC group). NC group weren't treated. The treatment in HS and SC group was identical with in the first experiment, but it would be terminated at 73 min after heat exposure, meanwhile content of MDA of myocardium were measured. RESULTS: ① Existent time in HS group was longer than that in SC group and shock arrived later; ② During earlier period after heat exposure MAP had no significant changes between HS and SC group, but after 60 mins MAP in HS group were higher than that in SC group; ③ Compared with NC group, content of MDA in myocardium in SC group was higher significantly at 73 min after heat exposure. Howerer, content of MDA in HS group was lower than in SC group, and had no significant changes with NC group. CONCLUSION:Through decreasing production of MDA in myocardium, HSR has a protective effect on cardiovascular system in rats after heat exposure.