Interactions of exercise training and ACE inhibition on insulin action in obese Zucker rats.

Exercise training or chronic treatment with angiotensin-converting enzyme (ACE) inhibitors can ameliorate glucose intolerance, insulin resistance of muscle glucose metabolism, and dyslipidemia associated with the obese Zucker rat. The purpose of the present study was to determine the interactions of exercise training and ACE inhibition (trandolapril) on these parameters in the obese Zucker rat. Animals were assigned to a sedentary control, a trandolapril-treated (1 mg. kg-1. day-1 for 6 wk), an exercise-trained (treadmill running for 6 wk), or a combined trandolapril-treated and exercise-trained group. Exercise training, alone or with trandolapril, significantly (P < 0. 05) increased peak O2 consumption by 31-34%. Similar decreases in fasting plasma insulin (34%) and free fatty acids (31%) occurred with exercise training alone or in combination with trandolapril. Compared with control, exercise training or trandolapril alone caused smaller areas under the curve (AUC) for glucose (12-14%) and insulin (28-33%) during an oral glucose tolerance test. The largest decreases in the glucose AUC (40%) and insulin AUC (53%) were observed in the combined group. Similarly, whereas exercise training or trandolapril alone improved maximally activated insulin-stimulated glucose transport in isolated epitrochlearis (26-34%) or soleus (39-41%) muscles, the greatest improvements in insulin action (67 and 107%, respectively) were seen in the combined group and were associated with similarly enhanced muscle GLUT-4 protein and total hexokinase levels. In conclusion, these results indicate combined exercise training and ACE inhibition improve oral glucose tolerance and insulin-stimulated muscle glucose transport to a greater extent than does either intervention alone.     

Influences of AT1 receptor blockade on tissue metabolism in obese men

ANG II applied to the interstitial space influences carbohydrate and lipid metabolism in a tissue-specific fashion. Thus endogenous ANG II may have a tonic effect on tissue metabolism that could be reversed with ANG II type 1 (AT1) receptor blockade, particularly during adrenergic stimulation. We studied 14 obese men. They were treated for 10 days with the AT1 receptor blocker irbesartan or with placebo in a double-blind and crossover fashion. At the end of each treatment period, we assessed skeletal muscle and adipose tissue metabolism using the microdialysis technique. The ethanol dilution technique was applied to follow changes in tissue blood flow. Measurements were obtained at baseline and during application of incremental isoproterenol concentrations through the microdialysis catheter. Blood pressure decreased from 133 +/- 3/84 +/- 3 to 128 +/- 3/79 +/- 2 mmHg for systolic and diastolic blood, respectively (P = 0.02 and 0.006, respectively) with AT1 receptor blockade. Isoproterenol perfusion caused a dose-dependent increase in dialysate glycerol in adipose tissue and in skeletal muscle. Irbesartan slightly reduced the isoproterenol-induced glycerol response in adipose tissue (P < 0.05 by ANOVA). Ethanol ratio, interstitial glucose supply, and lactate production in adipose tissue and skeletal muscle were similar with placebo and irbesartan. We conclude that AT1 receptor blockade in obese men does not reveal a major tonic ANG II effect on interstitial glucose supply, lipolysis, or glycolysis in skeletal muscle, either at rest or during beta-adrenergic stimulation. Endogeneous ANG II may slightly increase adipose tissue lipolysis. The mechanism may promote the redistribution of triglycerides from adipose tissue toward other organs.     

Cardiovascular dysfunction in Zucker obese and Zucker diabetic fatty rats: role of hydronephrosis

Recent studies in our laboratory using the Zucker obese (ZO) and Zucker diabetic fatty (ZDF) rat models resulted in unexpectedly high mortality rates in all genotypes including healthy homozygous lean Zucker rats, possibly because of renal dysfunction. Therefore, we evaluated left ventricular (LV) and kidney morphology and function in young ZO, Zucker diabetic fatty obese (ZDFO), homozygous Zucker/ZDF lean (ZL), and Sprague-Dawley (SD) rats. Hydronephrosis was evident in ZL, ZO, and ZDFO but not SD kidneys. ZDFO rats exhibited impaired LV shortening and relaxation with increased arterial stiffness. LV wall thickness was lower and LV end-systolic wall stress was higher in ZDFO compared with SD rats. Plasma ANG II was lower in ZO and ZDFO rats, which may be a result of reduced renal parenchyma with hydronephrosis; norepinephrine was higher in ZDFO rats than SD controls. Covariate analysis indicated that LV end-systolic wall stress was associated with renal dysfunction. The presence of hydronephrosis and its association with LV dysfunction potentially limits the ZDF model for study of the effects of diabetes on renal and cardiovascular function.     

Progression of coronary and mesenteric vascular dysfunction in Zucker obese and Zucker diabetic fatty rats

We investigated the progression of vascular dysfunction associated with the metabolic syndrome with and without hyperglycemia in lean, Zucker obese, and Zucker diabetic fatty (ZDF) rats. Responses of aorta and small coronary and mesenteric arteries were measured to endothelium-dependent and -independent vasodilators. Indices of oxidative stress were increased in serum from ZDF rats throughout the study, whereas values were increased in Zucker obese rats later in the study [thiobarbituric acid reactive substances: 0.45 +/- 0.02, 0.59 +/- 0.03 (P < 0.05), and 0.58 +/- 0.03 (P < 0.05) mug/ml in serum from 28- to 40-wk-old lean, Zucker obese, and ZDF rats, respectively]. Acetylcholine (ACh)-induced relaxation was not altered in vessels from lean animals from 8-40 wk. ACh-induced relaxation was nearly abolished in coronary arteries from 28- to 36-wk-old Zucker obese rats and by 16-36 wk in ZDF rats and was attenuated in aorta and mesenteric vessels from ZDF rats [%relaxation to 10 muM ACh: 72.2 +/- 7.1, 17.9 +/- 5.9 (P < 0.05), and 23.0 +/- 4.5 (P < 0.05) in coronary vessels; and 67.9 +/- 9.2, 50.1 +/- 5.5, and 42.3 +/- 4.7 (P < 0.05) in mesenteric vessels from 28- to 40-wk-old lean, Zucker obese, and ZDF rats, respectively]. The attenuated ACh-induced relaxation was improved when vessels were incubated with tiron, suggesting superoxide as a mechanism of endothelial dysfunction. Sodium nitroprusside-induced relaxation was not altered in aorta or coronary arteries and was potentiated in mesenteric arteries from Zucker obese rats. Our data suggest that diabetes enhances the progression of vascular dysfunction. Increases in indices of oxidative stress precede the development of dysfunction and may serve as a marker of endothelial damage.     

Differential adipose tissue inflammatory state in obese nondiabetic Zucker fatty rats compared to obese diabetic zucker diabetic fatty rats

Adipose tissue (AT) inflammation is linked to the pathogenesis of diabetes in obesity. Here, we compare the AT inflammatory state of 2 animal models of obesity and obesity plus diabetes, respectively. Obese nondiabetic ZF rats exhibited a trend towards increased proportions of CD11b positive cells in the adipose tissue stroma vascular fraction suggesting a state of increased AT inflammation compared to their lean littermates, but no alterations in systemic inflammatory parameters. In contrast, obese diabetic ZDF rats exhibited systemic as well as local AT inflammation with elevated levels of circulating Regulated upon Activation, Normal T-cell Expressed and Secreted Protein (Rantes), interleukin 1β (IL-1β) and monocyte chemotactic protein 1 (MCP-1), and an increased infiltration of adipose tissue CD11b positive cells. Our data provide a novel phenotypic characterisation of 2 common metabolic animal models and suggest an association of obesity with local inflammation in adipose tissue, and an association of diabetes with local inflammation in adipose tissue plus systemic inflammation. AT inflammation in obesity might therefore initiate a process that above a certain limits finally results in systemic inflammation and diabetes.     

Study of some factors controlling fatty acid oxidation in liver mitochondria of obese Zucker rats.

Livers of genetically obese Zucker rats showed, compared with lean controls, hypertrophy and enrichment in triacylglycerols, indicating that fatty acid metabolism was directed towards lipogenesis and esterification rather than towards fatty acid oxidation. Mitochondrial activities of cytochrome c oxidase and monoamine oxidase were significantly lower when expressed per g wet wt. of liver, whereas peroxisomal activities of urate oxidase and palmitoyl-CoA-dependent NAD+ reduction were unchanged. Liver mitochondria were able to oxidize oleic acid at the same rate in both obese and lean rats. For reactions occurring inside the mitochondria, e.g. octanoate oxidation and palmitoyl-CoA dehydrogenase, no difference was found between both phenotypes. Total carnitine palmitoyl-, octanoyl- and acetyl-transferase activities were slightly higher in mitochondria from obese rats, whereas the carnitine content of both liver tissue and mitochondria was significantly lower in obese rats compared with their lean littermates. The carnitine palmitoyltransferase I activity was slightly higher in liver mitochondria from obese rats, but this enzyme was more sensitive to malonyl-CoA inhibition in obese than in lean rats. The above results strongly suggest that the impaired fatty acid oxidation observed in the whole liver of obese rats is due to the diminished transport of fatty acids across the mitochondrial inner membrane via the carnitine palmitoyltransferase I. This effect could be reinforced by the decreased mitochondrial content per g wet wt. of liver. The depressed fatty acid oxidation may explain in part the lipid infiltration of liver observed in obese Zucker rats.     

Increased rates of fatty acid uptake and plasmalemmal fatty acid transporters in obese Zucker rats

Giant vesicles were used to study the rates of uptake of long-chain fatty acids by heart, skeletal muscle, and adipose tissue of obese and lean Zucker rats. With obesity there was an increase in vesicular fatty acid uptake of 1.8-fold in heart, muscle and adipose tissue. In some tissues only fatty acid translocase (FAT) mRNA (heart, +37%; adipose, +80%) and fatty acid-binding protein (FABPpm) mRNA (heart, +148%; adipose, +196%) were increased. At the protein level FABPpm expression was not changed in any tissues except muscle (+14%), and FAT/CD36 protein content was altered slightly in adipose tissue (+26%). In marked contrast, the plasma membrane FAT/CD36 protein was increased in heart (+60%), muscle (+80%), and adipose tissue (+50%). The plasma membrane FABPpm was altered only in heart (+50%) and adipose tissues (+70%). Thus, in obesity, alterations in fatty acid transport in metabolically important tissues are not associated with changes in fatty acid transporter mRNAs or altered fatty acid transport protein expression but with their increased abundance at the plasma membrane. We speculate that in obesity fatty acid transporters are relocated from an intracellular pool to the plasma membrane in heart, muscle, and adipose tissues.     

Angiotensin II type 1 receptor blocker ameliorates overproduction and accumulation of triglyceride in the liver of Zucker fatty rats

The effects of angiotensin II type 1 receptor blocker (ARB) on triglyceride (TG) metabolism associated with insulin resistance were explored in Zucker fatty (ZF) rats. Olmesartan medoxomil, a newly developed ARB, was given as a 0.01% drinking solution ad libitum to ZF and Zucker lean (ZL) rats for 4 wk. Olmesartan lowered blood pressure in both strains to the same extent. ZF rats had a markedly low insulin sensitivity index (SI) and glucose effectiveness (SG), together with significantly increased glucose levels. Olmesartan treatment substantially elevated both SI and SG. The ZF rats were hyperlipidemic, with plasma TG levels sixfold higher than those of the ZL rats. Olmesartan remarkably decreased the plasma free fatty acid level in the ZF rats, but it did not exert a significant effect on the plasma TG level. The TG secretion rate assessed by the Triton WR-1339 technique was almost six times higher in the ZF than in the ZL rats, and olmesartan treatment suppressed this TG overproduction by one-half. The TG content in the liver was ten times higher in the ZF than in the ZL rats, and olmesartan halved this high hepatic TG content without affecting the cholesterol content. The fatty liver developed in the ZF rats was ameliorated by olmesartan treatment. Olmesartan treatment had no significant effects on TG metabolism or insulin sensitivity in the ZL rats. Taken in sum, ARB improves the overproduction and accumulation of TG in the liver associated with insulin resistance, and it does so through mechanisms independent of its hypotensive action.     

Salacia oblonga improves cardiac fibrosis and inhibits postprandial hyperglycemia in obese Zucker rats

Diabetes has a markedly greater incidence of cardiovascular disease than the non-diabetic population. The heart shows a slowly developing increase in fibrosis in diabetes. Extended cardiac fibrosis results in increased myocardial stiffness, causing ventricular dysfunction and, ultimately, heart failure. Reversal of fibrosis may improve organ function survival. Postprandial hyperglycemia plays an important role in the development of type 2 diabetes and cardiovascular complications, and has been proposed as an independent risk factor for cardiovascular diseases. Salacia oblonga (S.O.) is traditionally used in the prevention and treatment of diabetes. We investigated the effects of its water extract on cardiac fibrosis and hyperglycemia in a genetic model of type 2 diabetes, the obese Zucker rat (OZR). Chronic administration of the extract markedly improved interstitial and perivascular fibrosis in the hearts of the OZR. It also reduced plasma glucose levels in non-fasted OZR, whereas it had little effect in the fasted animals, suggesting inhibition of postprandial hyperglycemia in type 2 diabetic animals, which might play a role in improvement of the cardiac complications of OZR. Furthermore, S.O. markedly suppressed the overexpression of mRNAs encoding transforming growth factor betas 1 and 3 in the OZR heart, which may be an important part of the overall molecular mechanisms. S.O. dose-dependently inhibited the increase of plasma glucose in sucrose-, but not in glucose-loaded mice. S.O. demonstrated a strong inhibition of alpha-glucosidase activity in vitro, which is suggested to contribute to the improvement of postprandial hyperglycemia.     

Enhanced AT1 receptor-mediated vasocontractile response to ANG II in endothelium-denuded aorta of obese Zucker rats

In the present study, we tested the hypothesis that ANG II causes a greater vasoconstriction in obese Zucker rats, a model of type 2 diabetes, with mild hypertension. Measurement of isometric tension in isolated aortic rings with intact endothelium revealed a modest but not significantly greater ANG II-induced contraction in obese than lean rats. Removal of endothelium or inhibition of nitric oxide (NO) synthase by N(G)-nitro-L-arginine methyl ester (L-NAME) enhanced 1) ANG II-induced contraction in both lean and obese rats, being significantly greater in obese rats (E(max) g/g tissue, denuded: lean 572 +/- 40 vs. obese 664 +/- 16; L-NAME: lean 535 +/- 14 vs. obese 818 +/- 23) and 2) ANG II sensitivity in obese compared with lean rats, as revealed by the pD(2) values. Endothelin-1 and KCl elicited similar contractions in the aortic rings of lean and obese rats. ACh, a NO-dependent relaxing hormone, produced greater relaxation in the aortic rings of obese than lean rats, whereas sodium nitroprusside, an NO donor, elicited similar relaxations in both rat strains. The expression of the ANG type 1 (AT(1)) receptor protein and mRNA in the endothelium-intact aorta was significantly greater in obese than lean rats, whereas the endothelium-denuded rings expressed modest but not significantly greater levels of AT(1) receptors in obese than lean rats. The endothelial NO synthase protein and mRNA expression levels were higher in the aorta of obese than lean animals. We conclude that, although ANG II produces greater vasoconstriction in obese rat aortic rings, enhanced endothelial AT(1) receptor-mediated NO production appears to counteract the increased ANG II-induced vasoconstriction, suggesting that arterial AT(1) receptor may not be a contributing factor to hypertension in this model of obesity.     

Gastrin release in obese Zucker rats

In this study, gastrin release in the obese Zucker rat was investigated by in vivo and in vitro experiments. Obese rats exhibited normal plasma gastrin levels at 3 weeks (preobese), were moderately hypergastrinemic at 3 months and severely hypergastrinemic at 5 months, compared to lean littermates. Following oral peptone, plasma gastrin levels doubled in both lean and obese rats. Basal and vagally stimulated gastrin release from perfused stomachs was greater in obese compared to lean rats and atropine had no effect on basal gastrin release in either group. Basal somatostatin release from the perfused stomach was found not to differ in both groups of animals. Morphological studies revealed an increase in the number of gastrin-containing G-cells in adult obese rats compared to lean littermates, but not in 3-week-old pups compared to lean littermates, indicating a strong correlation between cell number and plasma gastrin levels. These data indicate that the obese Zucker rat exhibits fasting hypergastrinemia in vivo, a condition which appears after weaning and increases in severity with age. Gastrin hypersecretion persists from the vascularly perfused stomach preparation. The basal hypergastrinemia of the obese Zucker rat is independent of a hyperactive postganglionic cholinergic drive but is associated with and probably causally related to an increase in antral G-cell numbers.     

Increases in brain and cardiac AT1 receptor and ACE densities after myocardial infarct in rats

In the brain, ouabain-like compounds (OLC) and the reninangiotensin system (RAS) contribute to sympathetic hyperactivity in rats after myocardial infarction (MI). This study aimed to evaluate changes in components of the central vs. the peripheral RAS. Angiotensin-converting enzyme (ACE) and angiotensin type 1 (AT1) receptor binding densities were determined by measuring 125I-labeled 351A and 125I-labeled ANG II binding 4 and 8 wk after MI. In the brain, ACE and AT1 receptor binding increased 8-15% in the subfornical organ, 14-22% in the organum vasculosum laminae terminalis, 20-34% in the paraventricular nucleus, and 13-15% in the median preoptic nucleus. In the heart, the greatest increase in ACE and AT1 receptor binding occurred at the infarct scar (approximately 10-fold) and the least in the right ventricle (2-fold). In kidneys, ACE and AT1 receptor binding decreased 10-15%. After intracerebroventricular infusion of Fab fragments to block brain OLC from 0.5 to 4 wk after MI, increases in ACE and AT1 receptors in the subfornical organ, organum vasculosum laminae terminalis, paraventricular nucleus, and medial preoptic nucleus were markedly inhibited, and ACE and AT1 receptor densities in the heart increased less (6-fold in the infarct scar). In kidneys, decreases in ACE and AT1 receptor binding were absent after treatment with Fab fragments. These results demonstrate that ACE and AT1 receptor binding densities increase not only in the heart but also in relevant areas of the brain of rats after MI. Brain OLC appears to play a major role in activation of brain RAS in rats after MI and, to a modest degree, in activation of the cardiac RAS.     

Increased growth hormone binding to liver membranes of obese Zucker rats

Developmental changes in hepatic growth hormone binding sites were examined in the genetically obese male fa/fa rats and in the lean littermates. At 16 days, fa/fa pups are normoinsulinemic; the specific binding of 125I-hGH to liver membranes is comparable in the two genotypes. At 4 weeks and later on, plasma membranes and Golgi fractions of male obese Zucker rats have more GH binding sites than lean littermates. The GH pituitary content is comparable in the two genotypes from 2 to 8 weeks and in 14-week-old fa/fa rats it is half that in lean animals. In the two genotypes plasma IGFI dramatically increases during puberty. At 4 weeks, plasma IGFI level is significantly higher in fa/fa rats than in lean littermates. In this model of genetic obesity, an increased GH binding to liver membranes is observed after the third week of life, shortly after the onset of hyperinsulinemia in the fa/fa rat.     

Role of the angiotensin II AT2 receptor in inflammation and oxidative stress: opposing effects in lean and obese Zucker rats

Inflammation and oxidative stress are believed to contribute to hypertension in obesity/diabetes. Recently, we reported a role for the AT(2) receptor in blood pressure control in obese Zucker rats. However, the role of AT(2) receptors in inflammation and oxidative stress in obesity is not known. Therefore, in the present study, we tested the effects of the AT(2) receptor agonist CGP-42112A on inflammation and oxidative stress in obese Zucker rats and compared them in their lean counterparts. Rats were systemically treated with either vehicle (control) or CGP-42112A (1 μg·kg(-1)·min(-1); osmotic pump) for 2 wk. Markers of inflammation (CRP, MCP-1, TNF-α, and IL-6) and oxidative stress (HO-1, gp-91(phox)) as well as an antioxidant (SOD) were determined. Control obese rats had higher plasma levels of CRP, MCP-1, TNF-α, IL-6, and HO-1 compared with control lean rats. Conversely, plasma SOD activity was lower in control obese than in control lean rats. Furthermore, the protein levels of TNF-α and gp-91(phox) were higher in the kidney cortex of control obese rats. Interestingly, CGP-42112A treatment in obese rats reduced the plasma and kidney cortex inflammatory (TNF-α, IL-6) and oxidative stress (gp-91(phox)) markers and increased plasma SOD activity to the levels seen in lean control rats. However, CGP-42112A treatment in lean rats increased inflammatory (TNF-α, IL-6) and oxidative stress (gp-91(phox)) markers in the plasma and kidney cortex. Our present studies suggest anti-inflammatory and antioxidative functions of AT(2) receptor in obese Zucker rats but proinflammatory and prooxidative functions in lean Zucker rats.     

Long-term AT1 receptor blockade improves metabolic function and provides renoprotection in Fischer-344 rats

Fischer-344 (F344) rats exhibit proteinuria and insulin resistance in the absence of hypertension as they age. We determined the effects of long-term (1 yr) treatment with the angiotensin (ANG) II type 1 (AT(1)) receptor blocker L-158,809 on plasma and urinary ANG peptide levels, systolic blood pressure (SBP), and indexes of glucose metabolism in 15-mo-old male F344 rats. Young rats at 3 mo of age (n = 8) were compared with two separate groups of older rats: one control group (n = 7) and one group treated with L-158,809 (n = 6) orally (20 mg/l) for 1 yr. SBP was not different between control and treated rats but was higher in young rats. Serum leptin, insulin, and glucose levels were comparable between treated and young rats, whereas controls had higher glucose and leptin with a similar trend for insulin. Plasma ANG I and ANG II were higher in treated than untreated young or older rats, as evidence of effective AT(1) receptor blockade. Urinary ANG II and ANG-(1-7) were higher in controls compared with young animals, and treated rats failed to show age-related increases. Protein excretion was markedly lower in treated and young rats compared with control rats (young: 8 +/- 2 mg/day vs. control: 129 +/- 51 mg/day vs. treated: 9 +/- 3 mg/day, P < 0.05). Long-term AT(1) receptor blockade improves metabolic parameters and provides renoprotection. Differential regulation of systemic and intrarenal (urinary) ANG systems occurs during blockade, and suppression of the intrarenal system may contribute to reduced proteinuria. Thus, insulin resistance, renal injury, and activation of the intrarenal ANG system during early aging in normotensive animals can be averted by renin-ANG system blockade.     

CCK-resistance in Zucker obese versus lean rats

Obese Zucker rats are less sensitive to the satiety effect of CCK than lean litter mates. The present studies further characterised this CCK resistance. Subcutaneous injection of the CCK agonist caerulein dose-dependently decreased food intake in Zucker obese and lean rats whereas the CCK-B agonist gastrin-17 did not. Caerulein at 4 μg/kg, which resulted in CCK plasma bioactivity slightly above postprandial levels, decreased food intake in lean rats but not in obese rats. The decrease in food intake was also more marked at higher caerulein doses (20–100 μg/kg) in lean versus obese rats. In lean animals the satiety effects of the “near physiological” 4 μg/kg caerulein dose was abolished after blockade of vagal afferents with capsaicin, whereas the effects of higher caerulein doses were not. CCK-stimulated amylase secretion from pancreatic acini and binding capacity of ¹²⁵I- labelled CCK-8 were decreased in obese versus lean rats. The CCK-A antagonist loxiglumide at 20 mg/kg, a dose which abolished the action of all caerulein doses on food intake, failed to alter the food intake either in obese or in lean rats when given without an agonist. The results suggest that the satiety effects of “near physiological” doses of caerulein in lean rats are mediated by vagal afferents whereas pharmacological doses act via non-vagal mechanisms. The differences in CCK's satiety effect between lean and obese rats may be due to differences in CCK-receptor binding and action at peripheral vagal sites. However, the failure of the CCK-A antagonist to increase food intake questions whether any of the effects of exogenous CCK are of physiological relevance.     

Dephosphorylation increases insulin-stimulated receptor kinase activity in skeletal muscle of obese Zucker rats

Serine/threonine phosphorylation of insulin receptor has been implicated in the development of insulin resistance. To investigate whether dephosphorylation of serine/threonine residues of the insulin receptor may restore the decreased insulin-stimulated receptor tyrosine kinase activity in skeletal muscle of obese Zucker rats, insulin receptor tyrosine kinase activity was measured before and after alkaline phosphatase treatment. Compared to lean controls, insulin-stimulated glucose transport was depressed by 61% (p < 0.05) in obese Zucker rats. The insulin receptor and insulin receptor substrate-1 contents were decreased by 14% (p < 0.05) and 16% (p < 0.05), respectively, in skeletal muscle of obese Zucker rats. In vivo insulin-induced tyrosine phosphorylation of insulin receptor and insulin receptor substrate-1 was depressed by 82% (p < 0.05) and 86% (p < 0.05), respectively. In the meantime, in vitro insulin-stimulated receptor tyrosine kinase activity in obese rats was decreased by 39% (p < 0.05). Dephosphorylation of the insulin receptor by prior alkaline phosphatase treatment increased insulin-stimulated receptor tyrosine kinase activity in both lean and obese Zucker rats, but the increase was three times greater in obese Zucker rats (p < 0.05). These findings suggest that excessive serine/threonine phosphorylation of the insulin receptor in obese Zucker rats may be a cause for insulin resistance in skeletal muscle.     

ACE inhibition lowers angiotensin II-induced chemokine expression by reduction of NF-kappaB activity and AT1 receptor expression

OBJECTIVE: Angiotensin converting enzyme (ACE) inhibitors significantly improve survival in patients with atherosclerosis. Although ACE inhibitors reduce local angiotensin II (AngII) formation, serine proteases form AngII to an enormous amount independently from ACE. Therefore, our study concentrates on the effect of the ACE-inhibitor ramiprilat on chemokine release, AngII receptor (ATR) expression, and NF-kappaB activity in monocytes stimulated with AngII. METHODS AND RESULTS: AngII-induced upregulation of IL-8 and MCP-1 protein and RNA in monocytes was inhibited by the AT1R-blocker losartan, but not by the AT2R-blocker PD 123.319. Ramiprilat dose-dependently suppressed AngII-induced upregulation of IL-8 and MCP-1. The suppressive effect of ramiprilat on AngII-induced chemokine production and release was in part caused by downregulation of NF-kappaB, but more by a selective and highly significant reduced expression of AT1 receptors as shown in monocytes and endothelial cells. CONCLUSION: In our study we demonstrated for the first time that ramiprilat reduced expression of AT1R in monocytes and endothelial cells. In addition, ramiprilat downregulated NF-kappaB activity and thereby reduced the AngII-induced release of IL-8 and MCP-1 in monocytes. This antiinflammatory effect, at least in part, may contribute to the clinical benefit of the ACE inhibitor in the treatment of coronary artery disease.     

Age-related decrease in sensitivity to glucagon and dibutyryl cyclic AMP inhibition of fatty acid synthesis in hepatocytes isolated from obese female Zucker rats

Hepatocytes were isolated from 3 and 5 month old female genetically obese Zucker rats and their lean littermate controls. An age-dependent loss in sensitivity of fatty acid synthesis to inhibition by both glucagon and dibutyryl cyclic AMP was observed with hepatocytes from the obese rats. Hepatocytes from lean animals were much more sensitive to these agents, regardless of age. Low concentrations of glucagon and dibutyryl cyclic AMP actually produced some stimulation of fatty acid synthesis with hepatocytes prepared from the older obese rats. 5-Tetradecyloxy-2-furoic acid, a compound which inhibits fatty acid synthesis, was a very effective inhibitor of fatty acid synthesis by hepatocytes isolated from all rats used in the study. An inhibition of lactate plus pyruvate accumulation and a strong stimulation of glycogenolysis occurred in response to both glucagon and dibutyryl cyclic AMP with hepatocytes from both age groups of lean and obese rats. The results suggest that with aging of the obese female Zucker rat some step of hepatic fatty acid synthesis becomes progressively less sensitive to inhibition by glucagon and dibutyryl cyclic AMP. This may play an important role in maintenance of obesity in these animals.