Gut Microbiota and Host Plasma Metabolites in Association with Blood Pressure in Chinese Adults.

Animal studies have revealed gut microbial and metabolic pathways of blood pressure (BP) regulation, yet few epidemiological studies have collected microbiota and metabolomics data in the same individuals. In a population-based, Chinese cohort who did not report antihypertension medication use (30-69 years, 54% women), thus minimizing BP treatment effects, we examined multivariable-adjusted (eg, diet, physical activity, smoking, kidney function), cross-sectional associations between measures of gut microbiota (16S rRNA [ribosomal ribonucleic acid], N=1003), and plasma metabolome (liquid chromatography-mass spectrometry, N=434) with systolic (SBP, mean [SD]=126.0 [17.4] mm Hg) and diastolic BP (DBP [80.7 (10.7) mm Hg]). We found that the overall microbial community assessed by principal coordinate analysis varied by SBP and DBP (permutational multivariate ANOVA P<0.05). To account for strong correlations across metabolites, we first examined metabolite patterns derived from principal component analysis and found that a lipid pattern was positively associated with SBP (linear regression coefficient [95% CI] per 1 SD pattern score: 2.23 [0.72-3.74] mm Hg) and DBP (1.72 [0.81-2.63] mm Hg). Among 1104 individual metabolites, 34 and 39 metabolites were positively associated with SBP and DBP (false discovery rate-adjusted linear model P<0.05), respectively, including linoleate, palmitate, dihomolinolenate, 8 sphingomyelins, 4 acyl-carnitines, and 2 phosphatidylinositols. Subsequent pathway analysis showed that metabolic pathways of long-chain saturated acylcarnitine, phosphatidylinositol, and sphingomyelins were associated with SBP and DBP (false discovery rate-adjusted Fisher exact test P<0.05). Our results suggest potential roles of microbiota and metabolites in BP regulation to be followed up in prospective and clinical studies.

Associations of sodium and potassium consumption with the gut microbiota and host metabolites in a population-based study in Chinese adults.

BACKGROUND: There is increasing evidence that sodium consumption alters the gut microbiota and host metabolome in murine models and small studies in humans. However, there is a lack of population-based studies that capture large variations in sodium consumption as well as potassium consumption. OBJECTIVE: We examined the associations of energy-adjusted dietary sodium (milligrams/kilocalorie), potassium, and sodium-to-potassium (Na/K) ratio with the microbiota and plasma metabolome in a well-characterized Chinese cohort with habitual excessive sodium and deficient potassium consumption. METHODS: We estimated dietary intakes from 3 consecutive validated 24-h recalls and household inventories. In 2833 adults (18-80 y old, 51.2% females), we analyzed microbial (genus-level 16S ribosomal RNA) between-person diversity, using distance-based redundancy analysis (dbRDA), and within-person diversity and taxa abundance using linear regression, accounting for geographic variation in both. In a subsample (n = 392), we analyzed the overall metabolome (dbRDA) and individual metabolites (linear regression). P values for specific taxa and metabolites were false discovery rate adjusted (q-value). RESULTS: Sodium, potassium, and Na/K ratio were associated with microbial between-person diversity (dbRDA P < 0.01) and several specific taxa with large geographic variation, including pathogenic Staphylococcus and Moraxellaceae, and SCFA-producing Phascolarctobacterium and Lachnospiraceae (q-value < 0.05). For example, sodium and Na/K ratio were positively associated with Staphylococcus and Moraxellaceae in Liaoning, whereas potassium was positively associated with 2 genera from Lachnospiraceae in Shanghai. Additionally, sodium, potassium, and Na/K ratio were associated with the overall metabolome (dbRDA P ≤ 0.01) and several individual metabolites, including butyrate/isobutyrate and gut-derived phenolics such as 1,2,3-benzenetriol sulfate, which was negatively associated with sodium in Guizhou (q-value < 0.05). CONCLUSIONS: Our findings suggest that sodium and potassium consumption is associated with taxa and metabolites that have been implicated in cardiometabolic health, providing insights into the potential roles of gut microbiota and host metabolites in the pathogenesis of sodium- and potassium-associated diseases. More studies are needed to confirm our results.

Urbanization in China is associated with pronounced perturbation of plasma metabolites.

INTRODUCTION: Urbanization is associated with major changes in environmental and lifestyle exposures that may influence metabolic signatures. OBJECTIVES: We investigated cross-sectional urban and rural differences in plasma metabolome analyzed by liquid chromatography/mass spectrometry platform in 500 Chinese adults aged 25-68 years from two neighboring southern Chinese provinces. METHODS: We first examined the overall metabolome differences by urban and rural residential location, using Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) and random forest classification. We then tested the association between urbanization status and individual metabolites using a linear regression adjusting for age, sex, and province and conducted pathway analysis (Fisher's exact test) to identify metabolic pathways differed by urbanization status. RESULTS: We observed distinct overall metabolome by urbanization status in OPLS-DA and random forest classification. Using linear regression, out of a total of 1108 unique metabolite features identified in this sample, we found that 266 metabolites were differed by urbanization status (positive false discovery rate-adjusted p-value, q-value < 0.05). For example, the following metabolites were positively associated with urbanization status: caffeine metabolites from xanthine metabolism, hazardous pollutants like 4-hydroxychlorothalonil and perfluorooctanesulfonate, and metabolites implicated in cardiometabolic diseases, such as branched-chain amino acids. In pathway analysis, we found that xanthine metabolism pathways differed by urbanization status (q-value = 1.64E-04). CONCLUSION: We detected profound differences in host metabolites by urbanization status. Urban residents were characterized by metabolites signaling caffeine metabolism and toxic pollutants and metabolites on known pathways to cardiometabolic disease risks, compared to their rural counterparts. Our findings highlight the importance of considering urbanization in metabolomics analysis.

Circulating Short-Chain Fatty Acids Are Positively Associated with Adiposity Measures in Chinese Adults.

Epidemiological studies suggest a positive association between obesity and fecal short-chain fatty acids (SCFAs) produced by microbial fermentation of dietary carbohydrates, while animal models suggest increased energy harvest through colonic SCFA production in obesity. However, there is a lack of human population-based studies with dietary intake data, plasma SCFAs, gut microbial, and anthropometric data. In 490 Chinese adults aged 30-68 years, we examined the associations between key plasma SCFAs (butyrate/isobutyrate, isovalerate, and valerate measured by non-targeted plasma metabolomics) with body mass index (BMI) using multivariable-adjusted linear regression. We then assessed whether overweight (BMI ≥ 24 kg/m2) modified the association between dietary-precursors of SCFAs (insoluble fiber, total carbohydrates, and high-fiber foods) with plasma SCFAs. In a sub-sample (n = 209) with gut metagenome data, we examined the association between gut microbial SCFA-producers with BMI. We found positive associations between butyrate/isobutyrate and BMI (p-value < 0.05). The associations between insoluble fiber and butyrate/isobutyrate differed by overweight (p-value < 0.10). There was no statistical evidence for an association between microbial SCFA-producers and BMI. In sum, plasma SCFAs were positively associated with BMI and that the colonic fermentation of fiber may differ for adults with versus without overweight.

Sequence variant analysis reveals poor correlations in microbial taxonomic abundance between humans and mice after gnotobiotic transfer.

Transplanting human gut microbiotas into germ-free (GF) mice is a popular approach to disentangle cause-and-effect relationships between enteric microbes and disease. Algorithm development has enabled sequence variant (SV) identification from 16S rRNA gene sequence data. SV analyses can identify which donor taxa colonize recipient GF mice, and how SV abundance in humans is replicated in these mice. Fecal microbiotas from 8 human subjects were used to generate 77 slurries, which were transplanted into 153 GF mice. Strong correlations between fecal and slurry microbial communities were observed; however, only 42.15 ± 9.95% of SVs successfully transferred from the donor to the corresponding recipient mouse. Firmicutes had a particularly low transfer rate and SV abundance was poorly correlated between donor and recipient pairs. Our study confirms human fecal microbiotas colonize formerly GF mice, but the engrafted community only partially resembles the input human communities. Our findings emphasize the importance of reporting a standardized transfer rate and merit the exploration of other animal models or in silico tools to understand the relationships between human gut microbiotas and disease.

Correction: The Gut-Brain Axis in Healthy Females: Lack of Significant Association between Microbial Composition and Diversity with Psychiatric Measures.

[This corrects the article DOI: 10.1371/journal.pone.0170208.].

The Role of the Gut Microbiota in Sustained Weight Loss Following Roux-en-Y Gastric Bypass Surgery.

BACKGROUND: The aim of the study was to investigate the role of the gut microbiota in weight regain or suboptimal weight loss following Roux-en-Y gastric bypass (RYGB). MATERIALS AND METHODS: The gut microbiota composition in post-RYGB patients who experienced successful weight loss (SWL, n = 6), post-RYGB patients who experienced poor weight loss (PWL, n = 6), and non-surgical controls (NSC, n = 6) who were age- and BMI-matched to the SWL group (NSC, n = 6) were characterized through 16S rRNA gene sequencing. To further investigate the impact of the gut microbiota on weight profile, human fecal samples were transplanted into antibiotic-treated mice. RESULTS: Orders of Micrococcales and Lactobacillales were enriched in SWL and PWL groups compared to the NSC group. No significant difference was observed in the gut microbiota composition between PWL and SWL patients. However, transfer of the gut microbiota from human patients into antibiotic-treated mice resulted in significantly greater weight gain in PWL recipient mice compared to SWL recipient mice. A few genera that were effectively transferred from humans to mice were associated with weight gain in mice. Among them, Barnesiella was significantly higher in PWL recipient mice compared to SWL and NSC recipient mice. CONCLUSION: These results indicate that the gut microbiota are at least functionally, if not compositionally, different between PWL and SWL patients. Some taxa may contribute to weight gain after surgery. Future studies will need to determine the molecular mechanisms behind the effects of the gut bacteria on weight regain after RYGB.

Greater Microbial Translocation and Vulnerability to Metabolic Disease in Healthy Aged Female Monkeys.

Monkeys demonstrate gastrointestinal barrier dysfunction (leaky gut) as evidenced by higher biomarkers of microbial translocation (MT) and inflammation with ageing despite equivalent health status, and lifelong diet and environmental conditions. We evaluated colonic structural, microbiomic and functional changes in old female vervet monkeys (Chlorocebus aethiops sabeus) and how age-related leaky gut alters responses to Western diet. We additionally assessed serum bovine immunoglobulin therapy to lower MT burden. MT was increased in old monkeys despite comparable histological appearance of the ascending colon. Microbiome profiles from 16S sequencing did not show large differences by age grouping, but there was evidence for higher mucosal bacterial loads using qPCR. Innate immune responses were increased in old monkeys consistent with higher MT burdens. Western diet challenge led to elevations in glycemic and hepatic biochemistry values only in old monkeys, and immunoglobulin therapy was not effective in reducing MT markers or improving metabolic health. We interpret these findings to suggest that ageing may lead to lower control over colonization at the mucosal surface, and reduced clearance of pathogens resulting in MT and inflammation. Leaky gut in ageing, which is not readily rescued by innate immune support with immunoglobulin, primes the liver for negative consequences of high fat, high sugar diets.

An Aberrant Microbiota is not Strongly Associated with Incidental Colonic Diverticulosis.

Colonic diverticula are protrusions of the mucosa through weak areas of the colonic musculature. The etiology of diverticulosis is poorly understood, but could be related to gut bacteria. Using mucosal biopsies from the sigmoid colon of 226 subjects with and 309 subjects without diverticula during first-time screening colonoscopy, we assessed whether individuals with incidental colonic diverticulosis have alternations in the adherent bacterial communities in the sigmoid colon. We found little evidence of substantial associations between the microbial community and diverticulosis among cases and controls. Comparisons of bacterial abundances across all taxonomic levels showed differences for phylum Proteobacteria (p = 0.038) and family Comamonadaceae (p = 0.035). The r-squared values measuring the strength of these associations were very weak, however, with values ~2%. There was a similarly small association between the abundance of each taxa and total diverticula counts. Cases with proximal only diverticula and distal only diverticula likewise showed little difference in overall microbiota profiles. This large study suggests little association between diverticula and the mucosal microbiota overall, or by diverticula number and location. We conclude that the mucosal adherent microbiota community composition is unlikely to play a substantial role in development of diverticulosis.

Interactions Between Stress and Sex in Microbial Responses Within the Microbiota-Gut-Brain Axis in a Mouse Model.

OBJECTIVE: Animal models are frequently used to examine stress response, but experiments seldom include females. The connection between the microbiota-gut-brain axis and behavioral stress response is investigated here using a mixed-sex mouse cohort. METHODS: CF-1 mice underwent alternating days of restraint and forced swim for 19 days (male n = 8, female n = 8) with matching numbers of control animals at which point the 16S rRNA genes of gut microbiota were sequenced. Mixed linear models accounting for stress status and sex with individuals nested in cage to control for cage effects evaluated these data. Murine behaviors in elevated plus-maze, open-field, and light/dark box were investigated. RESULTS: Community-level associations with sex, stress, and their interaction were significant. Males had higher microbial diversity than females (p = .025). Of the 638 operational taxonomic units detected in at least 25% of samples, 94 operational taxonomic units were significant: 31 (stress), 61 (sex), and 34 (sex-stress interaction). Twenty of the 39 behavioral measures were significant for stress, 3 for sex, and 6 for sex-stress. However, no significant associations between behavioral measures and specific microbes were detected. CONCLUSIONS: These data suggest sex influences stress response and the microbiota-gut-brain axis and that studies of behavior and the microbiome therefore benefit from consideration of how sex differences drive behavior and microbial community structure. Host stress resilience and absence of associations between stress-induced behaviors with specific microbes suggests that hypothalamic-pituitary-adrenal axis activation represents a threshold for microbial influence on host behavior. Future studies are needed in examining the intersection of sex, stress response, and the microbiota-gut-brain axis.

Daily Changes in Composition and Diversity of the Intestinal Microbiota in Patients with Anorexia Nervosa: A Series of Three Cases.

Anorexia nervosa, a severe psychiatric illness, is associated with an intestinal microbial dysbiosis. Individual microbial signatures dominate in healthy samples, even over time and under controlled conditions, but whether microbial markers of the disorder overcome inter-individual variation during the acute stage of illness or renourishment is unknown. We characterized daily changes in the intestinal microbiota in three acutely ill patients with anorexia nervosa over the entire course of hospital-based renourishment and found significant, patient-specific changes in microbial composition and diversity. This preliminary case series suggests that even in a state of pathology, individual microbial signatures persist in accounting for the majority of intestinal microbial variation. Copyright © 2017 John Wiley & Sons, Ltd and Eating Disorders Association.

Carcinogenesis and therapeutics: the microbiota perspective.

Cancer arises from the acquisition of multiple genetic and epigenetic changes in host cells over the span of many years, promoting oncogenic traits and carcinogenesis. Most cancers develop following random somatic alterations of key oncogenic genes, which are favoured by a number of risk factors, including lifestyle, diet and inflammation. Importantly, the environment where tumours evolve provides a unique source of signalling cues that affects cancer cell growth, survival, movement and metastasis. Recently, there has been increased interest in how the microbiota, the collection of microorganisms inhabiting the host body surface and cavities, shapes a micro-environment for host cells that can either promote or prevent cancer formation. The microbiota, particularly the intestinal biota, plays a central role in host physiology, and the composition and activity of this consortium of microorganisms is directly influenced by known cancer risk factors such as lifestyle, diet and inflammation. In this REVIEW, we discuss the pro- and anticarcinogenic role of the microbiota, as well as highlighting the therapeutic potential of microorganisms in tumourigenesis. The broad impacts, and, at times, opposing roles of the microbiota in carcinogenesis serve to illustrate the complex and sometimes conflicted relationship between microorganisms and the host-a relationship that could potentially be harnessed for therapeutic benefits.

The Gut-Brain Axis in Healthy Females: Lack of Significant Association between Microbial Composition and Diversity with Psychiatric Measures.

OBJECTIVE: This study examined associations between the composition and diversity of the intestinal microbiota and measures of depression, anxiety, eating disorder psychopathology, stress, and personality in a group of healthy adult females. METHODS: Female participants (n = 91) ages 19-50 years with BMI 18.5-25 kg/m2 were recruited from central North Carolina between July 2014 and March 2015. Participants provided a single fecal sample and completed an online psychiatric questionnaire that included five measures: (i) Beck Anxiety Inventory; (ii) Beck Depression Inventory-II; (iii) Eating Disorder Examination-Questionnaire; (iv) Perceived Stress Scale; and (v) Mini International Personality Item Pool. Bacterial composition and diversity were characterized by Illumina sequencing of the 16S rRNA gene, and associations were examined using Kendall's tau-b correlation coefficient, in conjunction with Benjamini and Hochberg's False Discovery Rate procedure. RESULTS: We found no significant associations between microbial markers of gut composition and diversity and scores on psychiatric measures of anxiety, depression, eating-related thoughts and behaviors, stress, or personality in a large cohort of healthy adult females. DISCUSSION: This study was the first specifically to examine associations between the intestinal microbiota and psychiatric measures in healthy females, and based on 16S rRNA taxonomic abundances and diversity measures, our results do not suggest a strong role for the enteric microbe-gut-brain axis in normal variation on responses to psychiatric measures in this population. However, the role of the intestinal microbiota in the pathophysiology of psychiatric illness may be limited to more severe psychopathology.

Statistical Measures to Quantify Similarity between Molecular Dynamics Simulation Trajectories.

Molecular dynamics simulation is commonly employed to explore protein dynamics. Despite the disparate timescales between functional mechanisms and molecular dynamics (MD) trajectories, functional differences are often inferred from differences in conformational ensembles between two proteins in structure-function studies that investigate the effect of mutations. A common measure to quantify differences in dynamics is the root mean square fluctuation (RMSF) about the average position of residues defined by Cα-atoms. Using six MD trajectories describing three native/mutant pairs of beta-lactamase, we make comparisons with additional measures that include Jensen-Shannon, modifications of Kullback-Leibler divergence, and local p-values from 1-sample Kolmogorov-Smirnov tests. These additional measures require knowing a probability density function, which we estimate by using a nonparametric maximum entropy method that quantifies rare events well. The same measures are applied to distance fluctuations between Cα-atom pairs. Results from several implementations for quantitative comparison of a pair of MD trajectories are made based on fluctuations for on-residue and residue-residue local dynamics. We conclude that there is almost always a statistically significant difference between pairs of 100 ns all-atom simulations on moderate-sized proteins as evident from extraordinarily low p-values.

Compositional data analysis of the microbiome: fundamentals, tools, and challenges.

PURPOSE: Human microbiome studies are within the realm of compositional data with the absolute abundances of microbes not recoverable from sequence data alone. In compositional data analysis, each sample consists of proportions of various organisms with a sum constrained to a constant. This simple feature can lead traditional statistical treatments when naively applied to produce errant results and spurious correlations. METHODS: We review the origins of compositionality in microbiome data, the theory and usage of compositional data analysis in this setting and some recent attempts at solutions to these problems. RESULTS: Microbiome sequence data sets are typically high dimensional, with the number of taxa much greater than the number of samples, and sparse as most taxa are only observed in a small number of samples. These features of microbiome sequence data interact with compositionality to produce additional challenges in analysis. CONCLUSIONS: Despite sophisticated approaches to statistical transformation, the analysis of compositional data may remain a partially intractable problem, limiting inference. We suggest that current research needs include better generation of simulated data and further study of how the severity of compositional effects changes when sampling microbial communities of widely differing diversity.

Heart rate variability and electrocardiogram waveform as predictors of morbidity during hypothermia and rewarming in rats.

This study examined electrocardiogram (ECG) waveform, heart rate (HR), mean blood pressure (BP), and HR variability as potential autonomic signatures of hypothermia and rewarming. Adult male Sprague-Dawley rats had telemetry transmitters surgically implanted, and 2 weeks were allowed for recovery prior to induction of hypothermia. Rats were lightly anesthetized (sodium pentobarbital, 35 mg/kg i.p.) and placed in a coil of copper tubing through which temperature-controlled water was circulated. Animals were cooled to a core temperature (Tc) of 20 degrees C, maintained there for 30 min, and then rewarmed. Data (Tc, BP, HR from ECG, and 10-s strips of ECG waveforms) were collected every 5 min throughout hypothermia and rewarming. Both HR and BP declined after initial increases with the drop in HR starting at a higher Tc than the drop in BP (29.6 +/- 2.4 degrees C vs. 27.1 +/- 3.3 degrees C, p < 0.05). Animals that were not successfully rewarmed exhibited a significant (p < 0.05) increase in the normalized standard deviation of interbeat intervals (IBI) throughout cooling compared with animals that were successfully rewarmed. The T wave of the ECG increased in amplitude and area with decreasing Tc. T-wave amplitude and IBI variability show potential as predictors of survival in hypothermic victims.

Comparison of oxygenated perfluorocarbon and humidified oxygen for rewarming hypothermic miniswine.

This study examines a method to rapidly rewarm the core using total liquid ventilation with warmed, oxygenated perfluorocarbon. Yucatan miniswine were splenectomized and surgically implanted with telemetry devices to transmit electrocardiographic response, arterial pressure, and core temperature. Hypothermia (core temperature = 25.9 +/- 1.3 degrees C) was induced by placing cold-water circulating blankets over the animals. Control animals (N = 7) were rewarmed using warm (37.8 degrees C), humidified oxygen. Experimental animals (N = 6) were rewarmed with oxygenated perfluorocarbon liquid (37.3 degrees C). The time to rewarm was significantly shorter in experimental animals (1.98 +/- 0.5 vs. 8.61 +/- 1.6 hours, p < 0.0001), with almost no afterdrop in the experimental group. Lactate dehydrogenase and aspartate aminotransferase were significantly increased in the control animals compared with the experimental animals. All animals that survived being chilled to 25 degrees C survived rewarming. This method may provide a means of more rapidly rewarming profoundly hypothermic victims while reducing the risks associated with current methods.

Treatment of hyperthermia-induced extravasation with hypertonic saline (7.5%) in 6% dextran 70 (HSD) in Wistar/Furth rats.

This study determined the effectiveness of hypertonic saline (7.5%) in 6% Dextran 70 (HSD) in reducing hyperthermia-induced extravasation in Wistar/Furth (WF) rats and compared this extravasation with that previously reported in Sprague-Dawley (SD) rats. Wistar/Furth rats (male, n = 12/group, 300-325 g) were placed unrestrained in a chamber (41.5 degrees C) until a core temperature (Tc) of 42.6 degrees C was attained. Immediately following heat exposure, HSD or normal saline (4 mL/kg) was administered via jugular catheter, followed 15 min later by Evan's blue (Eb, 25 mg/kg) in normal saline. After another 15-min interval, animals were anesthetized, exsanguinated, tissues removed and washed in normal saline, and Eb was extracted with formamide. Another group of normothermic WF rats were also given Eb and had tissues harvested. Comparisons were made to extravasation in normothermic and hyperthermic SD rats. In hyperthermic SD rats, Eb content increased significantly in liver, kidney, and intestinal tissues. In hyperthermic WF rats compared to normothermic WF rats, Eb content of kidney and spleen was increased; however, Eb content of heart, skeletal muscle, and intestine was significantly decreased. HSD-treated WF rats had increased extravasation in intestinal tissue compared to that of saline-treated rats. However, HSD treatment resulted in significant decreases in wet weight/dry weight ratios of heart (4.34 +/- 0.10 versus 4.51 +/- 0.11) and skeletal muscle tissue (3.78 +/- 0.08 versus 3.91 +/- 0.08). Findings of this study indicate that HSD did not prevent the hyperthermia-induced extravasation of Eb in kidney and spleen; that the increase in plasma volume following HSD administration is most likely due to the movement of fluid into the vasculature from the skeletal muscle mass; and that the WF strain may have limited value for the study of extravasation.

Flunarizine pretreatment attenuates hyperthermia-induced extravasation in rats.

Previous work has established that there is an increase in endothelial permeability in hyperthermic rats. This work assessed the potential of the calcium channel blocker (E)-1-bis(4-fluorophenyl)methyl-4-(3-phenyl-2-propenyl)piperazine dihydrochloride (flunarizine) as a pretreatment to ameliorate this extravasation. Five groups of male rats (n=12 rats per group, 400-500 g) were given 0, 0.3, 1, 2, or 3 mg/kg flunarizine (FL0, FL0.3, FL1, FL2, and FL3, respectively) by gavage 30 min prior to induction of hyperthermia. Hyperthermia was achieved by placing unrestrained animals in their own cages in a chamber maintained at 41.5 degrees C until a core temperature (Tc) of 42.6 degrees C was attained. Then, 25 mg/kg of Evans blue in saline was administered via a jugular cannula. After 15 min the animals were anesthetized, exsanguinated, tissues removed and washed in saline, and Evans blue extracted with formamide. As the dose of flunarizine was increased, there was a significant (P<0.05) reduction of Evans blue recovered from the liver, kidney, lung, spleen, and intestinal tissue. Endurance time in the heat to reach a Tc of 42.6 degrees C increased significantly from 194+/-39 min (mean+/-SD) with FL0 to 275+/-33 min with FL1, but decreased again with FL2 (206+/-42) and FL3 (199+/-60). Thus, flunarizine pretreatment attenuated hyperthermia-induced extravasation, and 1 mg/kg flunarizine markedly increased the tolerance time to heat exposure.

Telemetry augments the validity of the rat as a model for heat acclimation.

Repeated exposure to heat stress results in physiological adaptations which increase tolerance to heat stress. Core temperature (Tc) and heart rate (HR), two indices of successful heat acclimation, are both increased by the handling and restraint usually required to measure these variables in the rat. This study compares measurement of these variables in telemetry- and nontelemetry-equipped heat-acclimated rats. Four groups of male Sprague-Dawley rats were used: CAC (24, control for acclimated), HAC (24, heat acclimated), TCAC (3, telemetry implanted control for acclimation), and THAC (3, telemetry implanted, heat acclimated). The CAC and TCAC rats were maintained at 26 degrees C for 2 weeks; HAC and THAC groups were maintained at 32-33 degrees C for 2 weeks. The telemetry rats were surgically implanted with transmitters which measured activity, temperature, blood pressure (BP), and ECG. Following acclimation, the rats were subjected to a heat-stress test as follows: animals were placed in a chamber maintained at 41.5 degrees C until a Tc of 41.5 degrees C was reached, when the animals were removed to a 26 degrees C chamber to recover. The Tc of the CAC and HAC rats was manually measured with a rectal probe every 15 min. The TCAC and THAC rats had Tc, HR, and BP monitored electronically every 2.5 min from 30 min prior to heat stress through 30 min after heat. The THAC rats maintained lower Tc, HR, and BP than the TCAC rats throughout the heat stress. The CAC and HAC rats had higher Tc and slower rates of cooling after heat than either of the telemetry groups. Simultaneous measurement of HR, BP, and Tc has not previously been reported in unrestrained heat-acclimated rats. Measurement of these variables without the confounding effects of restraint or handling has increased the validity of the rat as a model for human heat acclimation.