Hemodynamic Mechanisms Initiating Salt-Sensitive Hypertension in Rat Model of Primary Aldosteronism.

Few studies have investigated the hemodynamic mechanism whereby primary hyperaldosteronism causes hypertension. The traditional view holds that hyperaldosteronism initiates hypertension by amplifying salt-dependent increases in cardiac output (CO) by promoting increases in sodium retention and blood volume. Systemic vascular resistance (SVR) is said to increase only as a secondary consequence of the increased CO and blood pressure. Recently, we investigated the primary hemodynamic mechanism whereby hyperaldosteronism promotes salt sensitivity and initiation of salt-dependent hypertension. In unilaterally nephrectomized male Sprague-Dawley rats given infusions of aldosterone or vehicle, we found that aldosterone promoted salt sensitivity and initiation of salt-dependent hypertension by amplifying salt-induced increases in SVR while decreasing CO. In addition, we validated mathematical models of human integrative physiology, derived from Guyton's classic 1972 model - Quantitative Cardiovascular Physiology-2005 and HumMod-3.0.4. Neither model accurately predicted the usual changes in sodium balance, CO, and SVR that normally occur in response to clinically realistic increases in salt intake. These results demonstrate significant limitations with the hypotheses inherent in the Guyton models. Together these findings challenge the traditional view of the hemodynamic mechanisms that cause salt-sensitive hypertension in primary aldosteronism. Key words: Aldosterone, Blood pressure, Salt, Sodium, Rat.

High cysteine diet reduces insulin resistance in SHR-CRP rats.

Increased plasma total cysteine (tCys) has been associated with obesity and metabolic syndrome in human and some animal studies but the underlying mechanisms remain unclear. In this study, we aimed at evaluating the effects of high cysteine diet administered to SHR-CRP transgenic rats, a model of metabolic syndrome and inflammation. SHR-CRP rats were fed either standard (3.2 g cystine/kg diet) or high cysteine diet (HCD, enriched with additional 4 g L-cysteine/kg diet). After 4 weeks, urine, plasma and tissue samples were collected and parameters of metabolic syndrome, sulfur metabolites and hepatic gene expression were evaluated. Rats on HCD exhibited similar body weights and weights of fat depots, reduced levels of serum insulin, and reduced oxidative stress in the liver. The HCD did not change concentrations of tCys in tissues and body fluids while taurine in tissues and body fluids, and urinary sulfate were significantly increased. In contrast, betaine levels were significantly reduced possibly compensating for taurine elevation. In summary, increased Cys intake did not induce obesity while it ameliorated insulin resistance in the SHR-CRP rats, possibly due to beneficial effects of accumulating taurine.

Conplastic strains for identification of retrograde effects of mitochondrial dna variation on cardiometabolic traits in the spontaneously hypertensive rat.

Mitochondrial retrograde signaling is a pathway of communication from mitochondria to the nucleus. Recently, natural mitochondrial genome (mtDNA) polymorphisms (haplogroups) received increasing attention in the pathophysiology of human common diseases. However, retrograde effects of mtDNA variants on such traits are difficult to study in humans. The conplastic strains represent key animal models to elucidate regulatory roles of mtDNA haplogroups on defined nuclear genome background. To analyze the relationship between mtDNA variants and cardiometabolic traits, we derived a set of rat conplastic strains (SHR-mtBN, SHR-mtF344 and SHR-mtLEW), harboring all major mtDNA haplotypes present in common inbred strains on the nuclear background of the spontaneously hypertensive rat (SHR). The BN, F344 and LEW mtDNA differ from the SHR in multiple amino acid substitutions in protein coding genes and also in variants of tRNA and rRNA genes. Different mtDNA haplotypes were found to predispose to various sets of cardiometabolic phenotypes which provided evidence for significant retrograde effects of mtDNA in the SHR. In the future, these animals could be used to decipher individual biochemical components involved in the retrograde signaling.

Acute toxic effects of telmisartan in spontaneously hypertensive rats fed a high fructose diet.

Telmisartan is an angiotensin receptor blocker (ARB) and a selective peroxisome proliferator activated receptor gamma (PPARG) modulator. Recently, we tested metabolic effects of telmisartan (5 mg/kg body weight) in spontaneously hypertensive rats (SHR) fed a diet containing 60 % fructose, a widely used model of the metabolic syndrome. Surprisingly, we observed acute toxic effects of telmisartan. Rats lost body weight rapidly and died within 2 to 3 weeks due to bleeding into the upper gastrointestinal tract. SHR fed a high fructose diet and treated with telmisartan exhibited rapid decrease in blood pressure when compared to the SHR fed a high fructose diet and treated with valsartan. Concentrations of both unconjugated telmisartan and telmisartan glucuronide in the liver of SHR rats fed a high fructose diet were approximately 4 fold higher when compared to Brown Norway (BN) rats fed the same diet. Plasma concentrations of unconjugated telmisartan in the SHR were about 5 fold higher when compared to BN rats while plasma levels of telmisartan glucuronide were similar between the strains. Testing of other rat strains, diets, and the ARB valsartan showed that toxic effects of telmisartan in combination with high fructose diet are specific for the SHR. These results are consistent with the possibility that in some circumstances, SHR are predisposed to telmisartan toxicity possibly because of a genetically determined disturbance in telmisartan metabolism.

Dissecting the role of Folr1 and Folh1 genes in the pathogenesis of metabolic syndrome in spontaneously hypertensive rats.

Increased levels of plasma cysteine predispose to obesity and metabolic disturbances. Our recent genetic analyses in spontaneously hypertensive rats (SHR) revealed mutated Folr1 (folate receptor 1) on chromosome 1 as a quantitative trait gene associated with reduced folate levels, hypercysteinemia and metabolic disturbances. The Folr1 gene is closely linked to the Folh1 (folate hydrolase 1) gene which codes for an enzyme involved in the hydrolysis of dietary polyglutamyl folates in the intestine. In the current study, we obtained evidence that Folh1 mRNA of the BN (Brown Norway) origin is weakly but significantly expressed in the small intestine. Next we analyzed the effects of the Folh1 alleles on folate and sulfur amino acid levels and consecutively on glucose and lipid metabolism using SHR-1 congenic sublines harboring either Folr1 BN and Folh1 SHR alleles or Folr1 SHR and Folh1 BN alleles. Both congenic sublines when compared to SHR controls, exhibited significantly reduced folate clearance and lower plasma cysteine and homocysteine levels which was associated with significantly decreased serum glucose and insulin concentrations and reduced adiposity. These results strongly suggest that, in addition to Folr1, the Folh1 gene also plays an important role in folate and sulfur amino acid levels and affects glucose and lipid metabolism in the rat.

Genetically determined folate deficiency is associated with abnormal hepatic folate profiles in the spontaneously hypertensive rat.

Increased levels of plasma cysteine are associated with obesity and metabolic disturbances. Our recent genetic analyses in spontaneously hypertensive rats (SHR) revealed a mutated Folr1 (folate receptor 1) as the quantitative trait gene associated with diminished renal Folr1 expression, lower plasma folate levels, hypercysteinemia, hyperhomocysteinemia and metabolic disturbances. To further analyse the effects of the Folr1 gene expression on folate metabolism, we used mass spectrometry to quantify folate profiles in the plasma and liver of an SHR-1 congenic strain, with wild type Folr1 allele on the SHR genetic background, and compared them with the SHR strain. In the plasma, concentration of 5-methyltetrahydrofolate (5mTHF) was significantly higher in SHR-1 congenic rats compared to SHR (60+/-6 vs. 42+/-2 nmol/l, P<0.01) and 5mTHF monoglutamate was the predominant form in both strains (>99 % of total folate). In the liver, SHR-1 congenic rats showed a significantly increased level of 5mTHF and decreased concentrations of dihydrofolate (DHF), tetrahydrofolate (THF) and formyl-THF when compared to the SHR strain. We also analysed the extent of folate glutamylation in the liver. Compared with the SHR strain, congenic wild-type Folr1 rats had significantly higher levels of 5mTHF monoglutamate. On the other hand, 5mTHF penta- and hexaglutamates were significantly higher in SHR when compared to SHR-1 rats. This inverse relationship of rat hepatic folate polyglutamate chain length and folate sufficiency was also true for other folate species. These results strongly indicate that the whole body homeostasis of folates is substantially impaired in SHR rats compared to the SHR-1 congenic strain and might be contributing to the associated metabolic disturbances observed in our previous studies.

Mutant Wars2 gene in spontaneously hypertensive rats impairs brown adipose tissue function and predisposes to visceral obesity.

Brown adipose tissue (BAT) plays an important role in lipid and glucose metabolism in rodents and possibly also in humans. Identification of genes responsible for BAT function would shed light on underlying pathophysiological mechanisms of metabolic disturbances. Recent linkage analysis in the BXH/HXB recombinant inbred (RI) strains, derived from Brown Norway (BN) and spontaneously hypertensive rats (SHR), identified two closely linked quantitative trait loci (QTL) associated with glucose oxidation and glucose incorporation into BAT lipids in the vicinity of Wars2 (tryptophanyl tRNA synthetase 2 (mitochondrial)) gene on chromosome 2. The SHR harbors L53F WARS2 protein variant that was associated with reduced angiogenesis and Wars2 thus represents a prominent positional candidate gene. In the current study, we validated this candidate as a quantitative trait gene (QTG) using transgenic rescue experiment. SHR-Wars2 transgenic rats with wild type Wars2 gene when compared to SHR, showed more efficient mitochondrial proteosynthesis and increased mitochondrial respiration, which was associated with increased glucose oxidation and incorporation into BAT lipids, and with reduced weight of visceral fat. Correlation analyses in RI strains showed that increased activity of BAT was associated with amelioration of insulin resistance in muscle and white adipose tissue. In summary, these results demonstrate important role of Wars2 gene in regulating BAT function and consequently lipid and glucose metabolism.

Connexin 50 mutation lowers blood pressure in spontaneously hypertensive rat.

We assessed the effect of the previously uncovered gap junction protein alpha 8 (Gja8) mutation present in spontaneously hypertensive rat - dominant cataract (SHR-Dca) strain on blood pressure, metabolic profile, and heart and renal transcriptomes. Adult, standard chow-fed male rats of SHR and SHR-Dca strains were used. We found a significant, consistent 10-15 mmHg decrease in both systolic and diastolic blood pressures in SHR-Dca compared with SHR (P<0.01 and P<0.05, respectively; repeated measures analysis of variance (ANOVA)). With immunohistochemistry, we were able to localize Gja8 in heart, kidney, aorta, liver, and lungs, mostly in endothelium; with no differences in expression between strains. SHR-Dca rats showed decreased body weight, high-density lipoprotein cholesterol concentrations and basal insulin sensitivity in muscle. There were 21 transcripts common to the sets of 303 transcripts in kidney and 487 in heart showing >1.2-fold difference in expression between SHR and SHR-Dca. Tumor necrosis factor was the most significant upstream regulator and glial cell-derived neurotrophic factor family ligand-receptor interactions was the common enriched and downregulated canonical pathway both in heart and kidney of SHR-Dca. The connexin 50 mutation L7Q lowers blood pressure in the SHR-Dca strain, decreases high-density lipoprotein cholesterol, and leads to substantial transcriptome changes in heart and kidney.

Effects of transgenic expression of dopamine beta hydroxylase (Dbh) gene on blood pressure in spontaneously hypertensive rats.

The spontaneously hypertensive rat (SHR) is the most widely used animal model of essential hypertension and left ventricular hypertrophy. Catecholamines play an important role in the pathogenesis of both essential hypertension in humans and in the SHR. Recently, we obtained evidence that the SHR harbors a variant in the gene for dopamine beta hydroxylase (Dbh) that is associated with reduced adrenal expression of Dbh mRNA and reduced DBH enzymatic activity which correlated negatively with blood pressure. In the current study, we used a transgenic experiment to test the hypothesis that reduced Dbh expression predisposes the SHR to hypertension and that augmentation of Dbh expression would reduce blood pressure. We derived 2 new transgenic SHR-Dbh lines expressing Dbh cDNA under control of the Brown Norway (BN) wild type promoter. We found modestly increased adrenal expression of Dbh in transgenic rats versus SHR non-transgenic controls that was associated with reduced adrenal levels of dopamine and increased plasma levels of norepinephrine and epinephrine. The observed changes in catecholamine metabolism were associated with increased blood pressure and left ventricular mass in both transgenic lines. We did not observe any consistent changes in brainstem levels of catecholamines or of mRNA levels of Dbh in the transgenic strains. Contrary to our initial expections, these findings are consistent with the possibility that genetically determined decreases in adrenal expression and activity of DBH do not represent primary determinants of increased blood pressure in the SHR model.

Hepatotoxic effects of fenofibrate in spontaneously hypertensive rats expressing human C-reactive protein.

Dyslipidemia and inflammation play an important role in the pathogenesis of cardiovascular and liver disease. Fenofibrate has a well-known efficacy to reduce cholesterol and triglycerides. Combination with statins can ameliorate hypolipidemic and anti-inflammatory effects of fibrates. In the current study, we tested the anti-inflammatory and metabolic effects of fenofibrate alone and in combination with rosuvastatin in a model of inflammation and metabolic syndrome, using spontaneously hypertensive rats expressing the human C-reactive protein transgene (SHR-CRP transgenic rats). SHR-CRP rats treated with fenofibrate alone (100 mg/kg body weight) or in combination with rosuvastatin (20 mg/kg body weight) vs. SHR-CRP untreated controls showed increased levels of proinflammatory marker IL6, increased concentrations of ALT, AST and ALP, increased oxidative stress in the liver and necrotic changes of the liver. In addition, SHR-CRP rats treated with fenofibrate, or with fenofibrate combined with rosuvastatin vs. untreated controls, exhibited increased serum triglycerides and reduced HDL cholesterol, as well as reduced hepatic triglyceride, cholesterol and glycogen concentrations. These findings suggest that in the presence of high levels of human CRP, fenofibrate can induce liver damage even in combination with rosuvastatin. Accordingly, these results caution against the possible hepatotoxic effects of fenofibrate in patients with high levels of CRP.

Gender-related effects on substrate utilization and metabolic adaptation in hairless spontaneously hypertensive rat.

Cold exposure of rats leads to ameliorated glucose and triglyceride utilization with females displaying better adaptation to a cold environment. In the current study, we used hairless rats as a model of increased thermogenesis and analyzed gender-related effects on parameters of lipid and glucose metabolism in the spontaneously hypertensive (SHR) rats. Specifically, we compared hairless coisogenic SHR-Dsg4 males and females harboring mutant Dsg4 (desmoglein 4) gene versus their SHR wild type controls. Two way ANOVA showed significant Dsg4 genotype (hairless or wild type) x gender interaction effects on palmitate oxidation in brown adipose tissue (BAT), glucose incorporation into BAT determined by microPET, and glucose oxidation in skeletal muscles. In addition, we observed significant interaction effects on sensitivity of muscle tissue to insulin action when Dsg4 genotype affected these metabolic traits in males, but had little or no effects in females. Both wild type and hairless females and hairless males showed increased glucose incorporation and palmitate oxidation in BAT and higher tissue insulin sensitivity when compared to wild type males. These findings provide evidence for gender-related differences in metabolic adaptation required for increased thermogenesis. They are consistent with the hypothesis that increased glucose and palmitate utilization in BAT and muscle is associated with higher sensitivity of adipose and muscle tissues to insulin action.

Rosuvastatin ameliorates inflammation, renal fat accumulation, and kidney injury in transgenic spontaneously hypertensive rats expressing human C-reactive protein.

Recently, we derived "humanized" spontaneously hypertensive rats (SHR-CRP) in which transgenic expression of human CRP induces inflammation, oxidative stress, several features of metabolic syndrome and target organ injury. In addition, we found that rosuvastatin treatment of SHR-CRP transgenic rats can protect against pro-inflammatory effects of human CRP and also reduce cardiac inflammation and oxidative damage. In the current study, we tested the effects of rosuvastatin (5 mg/kg) on kidney injury in SHR-CRP males versus untreated SHR-CRP and SHR controls. All rats were fed a high sucrose diet. In SHR-CRP transgenic rats, treatment with rosuvastatin for 10 weeks, compared to untreated transgenic rats and SHR controls, was associated with significantly reduced systemic inflammation which was accompanied with activation of antioxidative enzymes in the kidney, lower renal fat accumulation, and with amelioration of histopathological changes in the kidney. These findings provide evidence that, in the presence of high CRP levels, rosuvastatin exhibits significant anti-inflammatory, anti-oxidative, and renoprotective effects.

Sterol regulatory element binding protein 2 overexpression is associated with reduced adipogenesis and ectopic fat accumulation in transgenic spontaneously hypertensive rats.

It has been reported that the major function of the sterol regulatory element binding protein 2 (SREBP-2) is to activate preferentially cholesterol biosynthesis in liver and adipose tissue rather than fatty acid synthesis. In the current study, we analyzed the effects of overexpression of human dominant-positive SREBP-2 transgene under control of PEPCK promoter in the spontaneously hypertensive rat (SHR) on lipid and glucose metabolism. Transgenic overexpression of SREBP-2 was associated with significantly higher hepatic triglycerides (20.4+/-0.9 vs. 17.0+/-0.05 micromol/g, P<0.05) but not cholesterol (10.6+/-0.4 vs. 10.9+/-0.4 micromol/g) and decreased relative weight of epididymal fat pad (0.73+/-0.03 vs. 0.83+/-0.03, P<0.05). In addition, muscle triglyceride (15.8+/-3.7 vs. 8.5+/-1.2 micromol/g, P<0.001) and cholesterol (3.6+/-0.5 vs. 2.1+/-0.1 micromol/g, P<0.05) concentrations were significantly increased in transgenic rats when compared to SHR controls. Ectopic fat accumulation was associated with significantly increased serum glucose levels (6.4+/-0.1 vs. 5.9+/-0.1 mmol/l, P<0.005) and reduced insulin levels (1.78+/-0.33 vs. 2.73+/-0.37 nmol/l, P<0.05) in transgenic rats. These results provide evidence for important role of SREBP-2 in regulation of lipid and glucose metabolism.

Pharmacogenetic analysis of captopril effects on blood pressure: possible role of the Ednrb (endothelin receptor type B) candidate gene.

The objective of the current study was to search for genetic determinants associated with antihypertensive effects of angiotensin-converting enzyme (ACE) inhibitor captopril. Linkage and correlation analyses of captopril-induced effects on blood pressure (BP) with renal transcriptome were performed in the BXH/HXB recombinant inbred (RI) strains derived from spontaneously hypertensive rat (SHR) and Brown Norway (BN-Lx) progenitors. Variability of blood pressure lowering effects of captopril among RI strains was continuous suggesting a polygenic mode of inheritance. Linkage analysis of captopril-induced BP effects revealed a significant quantitative trait locus (QTL) on chromosome 15. This QTL colocalized with cis regulated expression QTL (eQTL) for the Ednrb (endothelin receptor type B) gene in the kidney (SHR allele was associated with increased renal expression) and renal expression of Ednrb correlated with captopril-induced BP effects. These results suggest that blood pressure lowering effects of ACE inhibitor captopril may be modulated by the variants at the Ednrb locus.

Recent progress in the genetics of spontaneously hypertensive rats.

The spontaneously hypertensive rat (SHR) is the most widely used animal model of essential hypertension and accompanying metabolic disturbances. Recent advances in sequencing of genomes of BN-Lx and SHR progenitors of the BXH/HXB recombinant inbred (RI) strains as well as accumulation of multiple data sets of intermediary phenotypes in the RI strains, including mRNA and microRNA abundance, quantitative metabolomics, proteomics, methylomics or histone modifications, will make it possible to systematically search for genetic variants involved in regulation of gene expression and in the etiology of complex pathophysiological traits. New advances in manipulation of the rat genome, including efficient transgenesis and gene targeting, will enable in vivo functional analyses of selected candidate genes to identify QTL at the molecular level or to provide insight into mechanisms whereby targeted genes affect pathophysiological traits in the SHR.

Genetic regulation of catecholamine synthesis, storage and secretion in the spontaneously hypertensive rat.

Understanding catecholamine metabolism is crucial for elucidating the pathogenesis of hereditary hypertension. Here we integrated transcriptional and biochemical profiling with physiologic quantitative trait locus (eQTL and pQTL) mapping in adrenal glands of the HXB/BXH recombinant inbred (RI) strains, derived from the spontaneously hypertensive rat (SHR) and normotensive Brown Norway (BN.Lx). We found simultaneous down-regulation of five heritable transcripts in the catecholaminergic pathway in young (6 weeks) SHRs. We identified cis-acting eQTLs for Dbh, Pnmt (catecholamine biosynthesis) and Vamp1 (catecholamine secretion); enzymatic activities of Dbh and Pnmt paralleled transcripts, with pQTLs for activities mirroring eQTLs. We also detected trans-regulated expression of Vmat1 and Chga (both involved in catecholamine storage), with co-localization of these trans-eQTLs to the Pnmt locus. Pnmt re-sequencing revealed promoter polymorphisms that result in decreased response of the transfected SHR promoter to glucocorticoid, compared with BN.Lx. Of physiological pertinence, Dbh activity negatively correlated with systolic blood pressure in RI strains, whereas Pnmt activity was negatively correlated with heart rate. The finding of such cis- and trans-QTLs at an age before the onset of frank hypertension suggests that these heritable changes in biosynthetic enzyme expression represent primary genetic mechanisms for regulation of catecholamine action and blood pressure control in this widely studied model of hypertension.

Long-term pioglitazone treatment augments insulin sensitivity and PKC-epsilon and PKC-theta activation in skeletal muscles in sucrose fed rats.

It has been suggested that thiazolidinediones (TZDs) ameliorate insulin resistance in muscle tissue by suppressing muscle lipid storage and the activity of novel protein kinase C (nPKC) isoforms. To test this hypothesis, we analyzed long-term metabolic effects of pioglitazone and the activation of nPKC-epsilon and -theta isoforms in an animal model of the metabolic syndrome, the spontaneously hypertensive rat (a congenic SHR strain with wild type Cd36 gene) fed a diet with 60 % sucrose from the age of 4 to 8 months. Compared to untreated controls, pioglitazone treatment was associated with significantly increased basal (809+/-36 vs 527+/-47 nmol glucose/g/2h, P<0.005) and insulin-stimulated glycogenesis (1321+/-62 vs 749+/-60 nmol glucose/g/2h, P<0.0001) in isolated gastrocnemius muscles despite increased concentrations of muscle triglycerides (3.83+/-0.33 vs 2.25+/-0.12 micromol/g, P<0.005). Pioglitazone-treated rats exhibited significantly increased membrane/total (cytosolic plus membrane) ratio of both PKC-epsilon and PKC-theta isoforms compared to untreated controls. These results suggest that amelioration of insulin resistance after long-term pioglitazone treatment is associated with increased activation of PKC-epsilon and -theta isoforms in spite of increased lipid concentration in skeletal muscles.

Autocrine effects of visfatin on hepatocyte sensitivity to insulin action.

Visfatin was originally described as an adipokine with insulin mimetic effects. Recently, it was found that visfatin is identical with the Nampt (nicotinamide phosphoribosyltransferase) gene that codes for an intra- and extracellular NAD biosynthetic enzyme and is predominantly expressed outside the adipose tissue. In the current study, we found strong protein and mRNA expression of visfatin in rat heart, liver, kidney, and muscle, while the expression of visfatin in visceral fat was significantly lower and undetectable in subcutaneous fat. The insulin-mimetic effects of visfatin (extracellular form of Nampt or eNampt) are controversial and even less is known about autocrine effects of visfatin (intracellular form of Nampt or iNampt). Since liver plays a major role in glucose metabolism, we studied visfatin effects on insulin-stimulated cellular glucose uptake in Fao rat hepatocytes using RNA interference (RNAi). RNAi-mediated downregulation of visfatin expression in Fao cells was associated with significantly reduced NAD biosynthesis (0.3+/-0.01 vs. 0.5+/-0.01 mmol/h/g, P<0.05) and with significantly decreased incremental glucose uptake after stimulation with insulin when compared to controls with normal expression of visfatin (0.6+/-0.2 vs. 2.2+/-0.5 nnmol/g/2 h, P=0.02). These results provide evidence that visfatin exhibits important autocrine effects on sensitivity of liver cells to insulin action possibly through its effects on NAD biosynthesis.

Selected adipokines - plasma concentrations and adipose tissue expressions during 24-hour lipid infusion in healthy men.

Our aim was to assess the reaction of TNFalpha, resistin, leptin and adiponectin to lipid infusion. Eight healthy subjects underwent a 24-hour lasting infusion of lipid emulsion. Plasma concentrations and expressions of selected cytokines in subcutaneous fat were measured. TNFalpha plasma concentration did not change during the first 4 hours of hypertriglyceridemia, but a significant increase after 24 hours was detected (p<0.001 for 0; 30; 240 min vs. 24 h). Plasma concentration of resistin significantly increased at 30 min of infusion and remained elevated (p<0.01 for 0 min vs. 30; 240 min; p<0.001 for 0 min vs. 24 h). Plasma concentrations of leptin and adiponectin did not show any significant changes. Although the expression of resistin in the subcutaneous adipose tissue tended to increase, the change was not significant. Expressions of TNFalpha, leptin and adiponectin were unaffected. In conclusions, our results indicate that acutely induced hyperlipidemia could influence the secretion of TNFalpha and resistin.

Long-term pioglitazone treatment enhances lipolysis in rat adipose tissue.

OBJECTIVES: The insulin-sensitizing effects of thiazolidinediones are believed to depend at least in part on reductions in circulating levels of nonesterified fatty acids (NEFA). The mechanisms that mediate the reductions in NEFA are not fully understood and could involve reductions in adipose tissue lipolysis, increases in glyceroneogenesis and NEFA reesterification in triglycerides in adipose tissue and increases in NEFA metabolism by oxidative tissues. METHODS: In a congenic strain of spontaneously hypertensive rats that fed a high-sucrose diet to promote features of the metabolic syndrome, we studied the effects of chronic pioglitazone treatment over 4 months on adipose tissue lipolysis and NEFA metabolism. RESULTS: We observed significant increases in basal and adrenaline-stimulated NEFA and glycerol release, and near-total suppression of NEFA reesterification in epididymal adipose tissue isolated from rats chronically treated with pioglitazone. However, pioglitazone-treated rats also exhibited significant increases in mitochondrial DNA levels in adipose tissue (3.2-fold increase, P=0.001) and potentially greater sensitivity to the antilipolytic effects of insulin than untreated controls. In addition, chronic pioglitazone treatment was associated with increased palmitate oxidation in soleus muscle, reduced fasting levels of serum NEFA and triglycerides, as well as reduced serum levels of insulin and increased serum levels of adiponectin. CONCLUSIONS: Despite suppressing NEFA reesterification and increasing basal and adrenaline-stimulated lipolysis, chronic pioglitazone treatment may decrease circulating NEFA levels in part by increasing adipose tissue sensitivity to the antilipolytic effects of insulin and by enhancing NEFA oxidation in skeletal muscle.