Age-related changes in biological parameters in Zucker rats

High dose astaxanthin lowers blood pressure and increases insulin sensitivity in rats: are these effects interdependent?

The present investigation in Sprague-Dawley rats (SD) was designed to examine effects of astaxanthin (Asta) at different doses on elevated blood pressure (BP) and glucose-insulin perturbations produced by heavy sucrose ingestion. We also examined effects of Asta on BP during restraint stress. SD were divided into six groups each containing eight rats. All SD ate a basic diet of ground regular rat chow with sucrose added at 30% w/w. The Control group received only the basic diet containing added sucrose, while the other five groups each received the same diet with added test material: captopril, (30 mg/Kg), pioglitazone (15.0 mg/Kg), low Asta (25 mg/Kg), medium Asta (50 mg/kg) or high Asta (100 mg/Kg). Many tests were carried out to examine the mechanisms behind the effects of Asta on BP (serum ACE activity, losartan challenge, and LNAME challenge) and the glucose-insulin system (glucose tolerance, HOMA measurement, and insulin challenge). In SD, a relatively low dose of Asta decreased SBP, but produced no major changes in the glucose-insulin system simulating results from a previous study using Zucker Fatty Rats. Increasing the dose of Asta resulted in both a lowering of elevated systolic BP and enhanced insulin sensitivity determined by many different estimations. BP lowering was consistent with changes in the renin-angiotensin (RAS) and nitric oxide (NO) systems. At the examined doses of each, captopril lowered BP in SD without influencing glucose-insulin metabolism, whereas pioglitazone favorably affected glucose-insulin metabolism while showing essentially no effects on BP. Accordingly, Asta beneficially affects both sucrose-induced elevations of BP and insulin resistance at relatively high doses in SD. Also, Asta at higher doses lessens restraint stress, whereas, captopril and pioglitazone did not at the doses examined, even though they influenced the BP and glucose-insulin systems respectively.

Effects of simmondsin on food intake, growth, and metabolic variables in lean (+/?) and obese (fa/fa) Zucker rats

Incorporation of 2·5 g/kg of the anorexigen, simmondsin, in the diet resulted in food intake reduction in both lean and obese Zucker rats; however, the obese rats were much more sensitive to the food intake-reducing activity of simmondsin. In both obese and lean simmondsin-treated Zucker rats, growth was slower than in control rats, but was the same as that in pair-fed animals. The 24 h heat production pattern showed a smaller diurnal variation and a lower mean in obese rats than in lean rats. Food intake reduction, as a result of either simmondsin treatment or pair feeding, caused a decrease in mean heat production. Simmondsin treatment, but not pair feeding, caused a decrease in the diurnal variation of heat production. Plasma total cholesterol levels were increased in both simmondsin-treated and pair-fed obese and lean Zucker rats compared with control animals; this increase was mainly due to an increase in HDL-cholesterol levels. Blood leptin levels in both obese and lean rats decreased with decreased food intake and decreased fat deposition, but in obese rats, simmondsin treatment resulted in an additional decrease in leptin levels. It is concluded that the food intake-reducing effect of simmondsin is more pronounced in obese Zucker rats than in their lean littermates, and except for the simmondsin-specific effects on leptin and total cholesterol values in obese littermates, the effects of simmondsin are related to food intake restriction in obese and lean Zucker rats.

Insulin receptor exon 11+/− is expressed in Zucker (fa/fa) rats, and chlorogenic acid modifies their plasma insulin and liver protein and DNA

In vivo studies confirmed that chlorogenic acid (CGA) improved glucose tolerance and mineral pool distribution in obese Zucker (fa/fa) rats. We found a significant decrease (P<.05) in postprandial blood glucose concentrations, which may have been due to an improved sensitivity to insulin. Impaired glucose tolerance and insulin resistance have been associated with differences in the hepatic mRNA expression of the spliced variants of the insulin receptor at exon 11. Spliced variants of the insulin receptor have not been studied in obese Zucker (fa/fa) rats, and no information exists about the effects of CGA in vivo as a possible insulin sensitizer. Thus, we studied the in vivo effect of CGA on plasma insulin concentrations during a glucose tolerance test, liver protein and DNA concentrations, the hepatic activity of glucose-6-phosphatase (G-6-PASE) and the mRNA expression of the two variants of the insulin receptor at exon 11. Zucker (fa/fa) rats were implanted with jugular vein catheters. Chlorogenic acid was administered (5 mg/kg body weight per day) for 3 weeks via intravenous infusion. In the CGA-treated group, areas under the curve (AUC) for blood glucose and plasma insulin improved (P<.005), and the protein and DNA concentrations in the liver increased (P<.05). No significant differences (P>.05) were found between groups for the hepatic G-6-PASE activity. The insulin receptor exon 11(+) and the exon 11(-) variants were expressed in the liver of Zucker (fa/fa) rats without significant changes (P>.05). Chlorogenic acid improved some cellular mechanisms that are stimulated by insulin.

Increased susceptibility of fat-laden Zucker-rat hepatocytes to bile acid-induced oncotic necrosis: an in vitro model of steatocholestasis

Metabolic liver disorders cause chronic liver disease and liver failure in childhood. Many of these disorders share the histologic features of steatosis and cholestasis, or steatocholestasis. In this study we sought to (1) develop an in vitro model of steatocholestasis, (2) determine the mechanisms of cell death in this model, and (3) determine the role of mitochondrial disturbances in this model.

METHODS

Hepatocytes were isolated from 8-week-old obese (fa/fa) and lean Zucker rats. Cell suspensions were treated with glycochenodeoxycholic acid (GCDC), after which reactive oxygen species (ROS) generation, oncotic necrosis, apoptosis, and ATP content were assessed. Isolated liver mitochondria were exposed to GCDC and analyzed for ROS generation, mitochondrial membrane-permeability transition (MPT), and cytochrome c release. Oncotic necrosis was significantly increased and apoptosis reduced in fa/fa hepatocytes exposed to GCDC compared with that in lean hepatocytes. Necrosis occurred by way of an ROS- and MPT-dependent pathway. Basal and dynamic ATP content did not differ between fa/fa and lean hepatocytes. GCDC stimulated ROS generation, MPT, and cytochrome c release to a similar extent in purified mitochondria from both fa/fa and lean rats. These findings suggest that fat-laden hepatocytes favor a necrotic rather than an apoptotic cell death when exposed to low concentrations of bile acids. The protective effects of antioxidants and MPT blockers suggest novel therapeutic strategies for the treatment of steatocholestatic metabolic liver diseases.

Effects of niacin-bound chromium, Maitake mushroom fraction SX and (-)-hydroxycitric acid on the metabolic syndrome in aged diabetic Zucker fatty rats

Previous studies in our laboratories have demonstrated that niacin-bound chromium (NBC), Maitake mushroom and (-)-hydroxycitric acid (HCA-SX) can ameliorate hypertension, dyslipidemias and diabetes mellitus, and therefore may be useful in weight management. In the present study, we used aged, diabetic Zucker fatty rats (ZFR) (70-75 weeks) in order to determine whether NBC, fraction SX of Maitake mushroom (MSX) and 60% (-)-hydroxycitric acid (HCA-SX) from Garcinia cambogia, alone or in combination, can affect certain aspects of the metabolic syndrome. Syndrome X or metabolic syndrome has been described as a concurrence of disturbed glucose and insulin metabolism, overweight and abdominal fat distribution, mild dyslipidemia, and hypertension, which are associated with subsequent development of type 2 diabetes mellitus and cardiovascular disease. Four groups of eight ZFR were gavaged daily with different supplements. For the initial three weeks, the control group of ZFR received only water, the second group received NBC 40 mcg elemental chromium/day, the third group received MSX 100 mg/day and the last group received HCA-SX 200 mg/day. During weeks 4-6, the doses of each treatment were doubled. The control animals lost approximately 50 g body weight (BW) per rat over 6 weeks of treatment, which is characteristic of these animals in declining health. In contrast, eight ZFR receiving NBC lost approximately 9 g BW per rat, while rats consuming MSX lost 16 g BW per rat. However, ZFR receiving HCA-SX simulated the pattern in the control group because these animals lost approximately 46 g BW per rat. The wide individual variations resulted in a lack of statistical significance among groups. Nevertheless, 75% of the ZFR in the control group lost more than 50 g BW over the 6 weeks duration, whereas none of the ZFR receiving NBC, 25% of the ZFR receiving MSX and 57% of the ZFR receiving HCA-SX lost over 50 g BW over the 6 weeks of the study. ZFR in all 3 treatment groups showed significantly lower blood pressures as compared to control, which seemed to be dose related. The general trend was for renal and liver blood parameters, hepatic and renal lipid peroxidation and DNA fragmentation to improve due to the supplementation of these natural products. Treatment of animals with a combination of these three novel supplements resulted in a lower SBP and maintenance of BW compared to control animals. These results demonstrate that elderly diabetics and even aging individuals might benefit from a similar regimen.

Hypoglycemic agent YM440 suppresses hepatic glucose output via gluconeogenesis by reducing glucose-6-phosphatase activity in obese Zucker rats

Using a glucose clamp, we had shown that YM440, (Z)-1,4-bis[4-[(3,5-dioxo-1,2,4-oxadiazolidin-2-yl)methyl]phenoxy]but-2-ene, reduced the increased hepatic glucose output in obese Zucker rats. We further examined effects of YM440 on 14C-incorporation from [14C]bicarbonate into blood glucose via gluconeogenesis, and on gluconeogenic enzymatic activities. Fed obese Zucker rats showed a 4-fold increase of 14C-incorporation into blood glucose compared to that in lean rats. Glucose-6-phosphatase and fructose-1,6-bisphosphatase activities in obese rats were increased 1.4-fold and 1.6-fold compared with lean rats. YM440 (300 mg/kg for 2 weeks) decreased 14C-incorporation into blood glucose by 29% in obese rats. Glucose-6-phosphatase but not fructose-1,6-bisphosphatase activity was reduced by YM440 and closely correlated with 14C-incorporation into blood glucose, indicating a key role for glucose-6-phosphatase in hepatic glucose output. These results suggest that the increased gluconeogenesis in obese rats is mainly due to the increased activities of glucose-6-phosphatase and fructose-1,6-bisphosphatase and that YM440 suppresses hepatic glucose output by reducing glucose-6-phosphatase activity.

Effects of dual angiotensin-converting enzyme and neutral endopeptidase 24-11 chronic inhibition by mixanpril on insulin sensitivity in lean and obese Zucker rats

The aim of this study was to examine the effects of chronic (8-day) oral treatment with the dual angiotensin-converting enzyme (ACE) and neutral endopeptidase 24-11 (NEP) inhibitor mixanpril (25 mg/kg twice a day), compared with the ACE inhibitor captopril (25 mg/kg twice a day), on whole body insulin-mediated glucose disposal in young (10-week) and old (19-week) obese Zucker rats (ZOs). Moreover, the effects of chronic mixanpril administration on femoral blood flow at rest and during an insulin infusion were assessed. In the young ZOs, mixanpril decreased the glucose response during an IV glucose tolerance test more effectively than did captopril (-49 and -30%, respectively, p < 0.05). Incremental glucose area under the curve in mixanpril-treated ZOs was then no longer different from that observed in vehicle-treated lean rats (1,592 +/- 175 and 1, 470 +/- 104 mg/dl x min, respectively). The beneficial effects resulting from mixanpril or captopril administration were observed in ZOs but not in lean littermates. In the old ZOs, mixanpril induced higher glucose infusion rates to maintain euglycemia than did captopril during a hyperinsulinemic euglycemic clamp test (+92 and +35%, respectively, p < 0.001). However, the glucose infusion rates in mixanpril-treated ZOs remained much lower than that observed in vehicle-treated lean rats (9.4 +/- 0.7 mg/kg/min vs 28.6 +/- 1.0 mg/kg/min, p < 0.001). Mixanpril did not affect resting femoral vascular bed hemodynamics but restored the femoral blood flow response to insulin infusion. In conclusion, in ZOs, chronic dual ACE/NEP inhibition improves whole body insulin-mediated glucose disposal more effectively than does ACE inhibition alone. This beneficial effect seems to be restricted to conditions of insulin resistance and not directly linked to the improvement in the femoral blood flow response to insulin.

Chlorogenic acid modifies plasma and liver concentrations of: cholesterol, triacylglycerol, and minerals in (fa/fa) Zucker rats

Chlorogenic acid, a phenolic compound found ubiquitously in plants, is an in vitro antioxidant and metal chelator. Some derivatives of chlorogenic acid are hypoglycemic agents and may affect lipid metabolism. Concentrations of cholesterol and triacylglycerols are of interest due to their association with diseases such as non-insulin-dependent-diabetes- mellitus and obese insulin resistance. As little is known about the effects of chlorogenic acid in vivo, studies using obese, hyperlipidemic, and insulin resistant (fa/fa) Zucker rats were conducted to test the effect of chlorogenic acid on fasting plasma glucose, plasma and liver triacylglycerols and cholesterol concentrations. Aditionally, the effects of chlorogenic acid on selected mineral concentrations in plasma, spleen, and liver were determined. Rats were implanted with jugular vein catheters. Chlorogenic acid was infused (5 mg/Kg body weight/day) for 3 weeks via intravenous infusion. Chlorogenic acid did not promote sustained hypoglycemia and significantly lowered the postprandial peak response to a glucose challenge when compared to the same group of rats before Chlorogenic acid treatment. In Chlorogenic acid-treated rats, fasting plasma cholesterol and triacylglycerols concentrations significantly decreased by 44% and 58% respectively, as did in liver triacylglycerols concentrations (24%). We did not find differences (p > 0.05) in adipose triacylglycerols concentration. Significant differences (p < 0.05) in the plasma, liver, and spleen concentration of selected minerals were found in chlorogenic acid-treated rats. In vivo, chlorogenic acid was found to improve glucose tolerance, decreased some plasma and liver lipids, and improve mineral pool distribution under the conditions of this study.

Cardiovascular complications of non-insulin-dependent diabetes: the JCR:LA-cp rat

Diabetes is a serious medical and financial burden on western societies. It is the seventh leading cause of death in the United States and Canada. The disease is due to a primary defect in glucose tolerance and carbohydrate metabolism resulting from either a deficiency of insulin (Insulin-dependent (type I) diabetes mellitus - IDDM) or a state of insulin resistance (Non-insulin-dependent (type II) diabetes mellitus - NIDDM). NIDDM comprises greater than 80% of total diabetic cases. Associated with the primary metabolic defects are equally deleterious secondary complications affecting the renal, ocular, nervous and cardiovascular systems. The cardiovascular complications account for a major proportion of diabetic mortality. As such, it is of paramount importance to develop or find an animal model expressing complications homologous to the human condition. Many models of NIDDM are available to the diabetic researcher but choosing an accurate one can be difficult. The following compares the advantages and limitations of one such model, the JCR:LA-cp rat to other NIDDM models commonly used today.

Effect of selenium and vitamin E supplementation on lipid abnormalities in plasma, aorta, and adipose tissue of Zucker rats

Twenty-nine obese female Zucker rats (fa/fa) were fed with a laboratory chow supplemented or not with a selenium-rich yeast (Selenion), or Selenion + vitamin E, or vitamin E alone. Twelve lean female Zucker rats (Fa/Fa) of the same littermates fed with the same diet were used as control. After 32 wk of diet, obesity induced a large increase in plasma insulin and lipid levels. A significant decrease in the plasma vitamin E/triglycerides ratio (p<0.005) and an increase in plasma thiobarbituric reactive substances (TBARS) (p<0.005) were also observed. Plasma selenium and vitamin E increased in all supplemented rats. The plasma insulin level was decreased by selenion supplementation and the vitamin E/triglycerides ratio was completely corrected by double supplementation with Selenion + vitamin E. TBARS were also efficiently decreased in two obese groups receiving vitamin E. In plasma, adipose tissue and aorta, obesity induced an increase in palmitic acid (C16:0), a very large increase in monounsaturated fatty acids (palmitoleic acid C16:1, stearic acid C18:1) associated with a decrease in polyunsaturated n-6 fatty acids (linoleic acid C18:2 n-6, arachidonic C20:4 n-6). These alterations in fatty acid distribution were only partly modulated by Se and vitamin E supplements. However, in the aorta, antioxidant treatment in obese rats significantly reduced the increase in C16:0 and C16:1 (p<0.05 and p<0.01, respectively) and the decrease in arachidonic acid (p<0.05). These changes could be beneficial in the reduction of insulin resistance and help to protect the vascular endothelium.

Long-term and rapid regulation of ob mRNA levels in adipose tissue from normal (Sprague Dawley rats) and obese (db/db mice, fa/fa rats) rodents

Increased levels of mRNA transcribed from the ob gene in adipose tissue of obese/hyperinsulinaemic Zucker (fa/fa) rats were detectable as early as 3 weeks after birth and continued to rise there after in parallel with body weight and serum insulin. mRNA levels of two other fat-specific genes (ARL4, FST44) were unaltered. In C57BL/KsJ db/db mice, ob mRNA levels also increased in parallel with body weight and serum insulin, and remained elevated in older animals when insulin levels decreased. In heterozygous control animals (db/+; fa/Fa), mRNA levels were comparable with those in the homozygous controls. In normal Sprague Dawley rats, the ob mRNA increased continuously, but more slowly than in Zucker rats, in parallel with body weight and insulin levels, and reached 15 times higher levels in the heaviest rats (400 g) studied. In Sprague Dawley rats made diabetic by an injection of streptozotocin, ob mRNA levels were reduced by approximately 50% after 24 h. A 24-h fasting period reduced the ob mRNA by 50% in lean Sprague Dawley and Fa/Fa, but not in obese Zucker fa/fa rats, although insulin levels were reduced in both groups. These data indicate that ob mRNA levels increase in both normal and obese rodents in parallel with age, body weight and serum insulin, reflecting an early (Zucker rats, db-mice) or slowly developing (Sprague Dawley rats) resistance to leptin and insulin. This increase does not appear to be mediated by the recently described rapid regulation of ob mRNA by insulin, but seems to be due to a different, long-term control mechanism which signals the size of the fat depots.

Incorporation of delta 6- and delta 5-desaturation fatty acids in liver microsomal lipid classes of obese Zucker rats fed n - 6 or n - 3 fatty acids

The aim of this work was to study the effect of dietary n - 6 (as borage oil) and of n - 3 (as fish oil) fatty acids on the incorporation--in liver microsomal lipid classes--of fatty acids involved in delta 6- and delta 5-desaturations in obese Zucker rats compared with their lean littermates and with Wistar control rats. We observed that body and liver weights were decreased when obese Zucker rats were fed the fish oil diet. The major part of the radioactivity was recovered, in the obese Zucker rats, into the neutral lipids and especially into the triacylglycerols, while it was recovered into the phospholipid classes, especially into phosphatidylcholine, in the two other strains. Results show, in all phenotypes, an increased alpha-linolenic acid delta 6-desaturation in PL classes when the rats were fed the fish oil diet. However, a decreased linoleic acid delta 6- and delta 5-desaturation was observed in obese Zucker rats fed the fish oil diet. The fish oil diet favours the n - 3 fatty acid biosynthesis and incorporation into liver microsomal lipid classes to the prejudice of the n - 6 fatty acid series. The fatty acid incorporation is simultaneously regulated by the genetical phenotype and dietary fatty acids.

Decreased activity of (Ca2+ + Mg2+)-adenosine triphosphatase (ATPase) and a hormone-specific defect in insulin regulation of ATPase in kidney basolateral membranes from obese fa/fa rats

The plasma membrane enzyme (Ca2+ + Mg2+)-adenosine triphosphatase (ATPase) is hormonally regulated and may participate in Ca2+ signaling by removing excess Ca2+ from the cell. Therefore, observations of a hormone-specific loss of insulin stimulation of ATPase in kidney membranes from non-insulin-dependent diabetic (NIDDM) rats may reflect their insulin-resistant state. Consequently, to evaluate whether additional insulin-resistant conditions are associated with impaired function of ATPase and with loss of regulation of the enzyme by insulin, studies were extended to investigate (Ca2+ + Mg2+)-ATPase activities and hormonal regulation of the enzyme in kidney basolateral membranes from obese and lean Zucker rats. (Ca2+ + Mg2+)-ATPase activity was lower in membranes from obese rats compared with lean rats. Maximal velocity (Vmax) of the enzyme activity was 29.2 +/- 2.6 nmol Pi/mg/min in obese rats versus 57.2 +/- 6.5 in lean rats (P < .05). However, the affinity of the enzyme for Ca2+ was similar in obese and lean rats (Km Ca2+, 0.23 +/- 0.025 v 0.23 +/- 0.032 mumol/L Ca2+). Also, the Km for ATP of the enzyme was similar in membranes from obese and lean rats. Insulin, parathyroid hormone (PTH), and cyclic adenosine monophosphate (cAMP) stimulated the ATPase activity in membranes from lean rats in a dose-dependent manner (15% to 28%). Also, the protein kinase C (PKC) stimulator 12-O-tetradecanoyl phorbol-13-acetate (TPA) increased the ATPase activity in membranes from lean rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Fiber type composition and enzyme activities of muscles in two models of obese rats

1. In oxidative (soleus) and glycolytic (extensor digitorum longus) muscles of obese Zucker rats, a significant decrease in the percentage of relative area occupied by glycolytic fibers was observed. 2. The activity of citrate synthase and beta-hydroxy-acyl-CoA-dehydrogenase was significantly higher in muscles of obese than of lean Zucker rats. 3. In rats, 6 weeks after lesion of the ventromedial hypothalamus, no changes were observed. 4. This indicates that neither the proportion of oxidative fibers, nor the oxidative capacities are decreased in skeletal muscles of obese rats suggesting that insulin resistance cannot be ascribed to a higher glycolytic-oxidative fiber ratio.

Cardiovascular abnormalities associated with human and rodent obesity

Obesity is a major risk factor for cardiovascular disease. However, a direct link between these two states is difficult to establish, since obesity frequently occurs with other disease states such as diabetes, hypertension and atherosclerosis. Clinical studies have clearly shown that uncorrected obesity is associated with cardiac hypertrophy and compromised ventricular function. A number of rodent models of obesity have been studied in terms of cardiovascular adaptations. Cardiac function of the obese Zucker rat appears to be normal at a younger age. Only after several months is depression in cardiac function discernable. These animals are mildly hypertensive, but do not exhibit the characteristic increase in cardiac output associated with human obesity. A unique characteristic of JCR:LA-cp rat is that they develop atherosclerotic and myocardial lesions. Hearts from these animals will maintain normal function when perfused with physiological levels of calcium. At higher calcium concentrations, however, mechanical function becomes impaired. Dietary-induced obese rats exhibit many of the hemodynamic alterations associated with human obesity, but there is no evidence to-date that these animals will develop severe cardiac depression. Short-term weight reduction apparently has beneficial cardiovascular effects, but weight cycling may be harmful. Given the widespread occurrence of obesity, further studies are warranted to characterize the cardiac manifestations of this condition.

Short term natriuretic responses in the conscious Zucker obese rat

Renal clearance studies were conducted in conscious, chronically catheterized obese and lean Zucker rats to investigate the natriuretic responses to i) acute IV infusion of isotonic NaCl = 5% of total body weight and ii) IV infusion of alpha rat atrial natriuretic peptide (ANP) in a dose of 300 ng/kg/min. In the baseline state, arterial blood pressure (BP) was significantly higher in obese vs lean rats. Absolute values of GFR and sodium excretion were similar but lower in obese vs lean rats when factored for body weight. In the 2 h period during and after NaCl infusion, obese rats showed a greater natriuresis vs lean while BP rose significantly and similarly. ANP infusion was natriuretic in obese rats but had no effect on lean rats. ANP lowered BP in both groups but BP remained higher in obese vs lean rats at all times. These studies show that in the chronic, unstressed preparation the 6-8 month old, female Zucker obese rat has a higher BP vs the 6-8 month old lean Zucker. The short term natriuretic response to either a NaCl load or ANP infusion is greater in obese vs lean Zuckers and the depressor response to ANP is intact in obese Zuckers. Thus the higher BP in this model of obesity is unlikely to be due to either a defective response to ANP or to a defect in the renal response to acute sodium challenge.

Delta 6 and delta 5 desaturase activities in liver from obese Zucker rats at different ages

delta 6 Desaturation of linoleic acid (18:2 n-6) and delta 5 desaturation of dihomo-gamma-linolenic acid (20:3 n-6) were measured in liver microsomes from genetically obese Zucker rats (fa/fa) and from their lean littermates (Fa/--). Both groups were fed a balanced commercial diet. The rats were 6, 9 and 12 weeks old, which corresponded to stages in their active growth period. The content of total fatty acids and n-6 polyunsaturated fatty acids in whole liver and liver microsomes was also determined in order to ascertain how the desaturase activities measured in vitro reflected regulation of essential fatty acid metabolism in vivo. Contrary to values obtained for delta 6 desaturation, delta 5 desaturation at nonsaturating substrate levels were lower in obese rats than in lean controls. In contrast, at saturating substrate level, the maximal delta 5 desaturase activities were the same in both phenotypes and they increased with age. Study of delta 5 desaturation kinetics (1/V vs 1/S) showed that Vm did not differ between 12-week-old obese and lean rats, whereas KM in obese rats was much lower than in controls, expressing the very low affinity of the enzyme for the substrate in obese animals. The fatty acid composition of liver lipids reflected the results of desaturase activities in vitro. In particular, the ratios 20:4 n-6/20:3 n-6 were lower in obese rats than in lean rats, which can be explained by the lower conversion of 20:3 n-6 into 20:4 n-6 by delta 5 desaturation.(ABSTRACT TRUNCATED AT 250 WORDS)

[Fatty acid composition of platelet phospholipids and plasma lipids in obese Zucker rats]

The purpose of this work was to see whether hyperlipaemia observed in genetically obese Zucker rats (fa/fa) was associated with differences in fatty-acid composition of plasma triacylglycerols, plasma phospholipids and of platelet phospholipids, in comparison with the control lean rats (Fa/-). Results showed that plasma triacylglycerols and phospholipids were increased in obese rats. In triacylglycerols, the amount of saturated and monounsaturated fatty acids was highly increased whereas the amount of the n-6 and n-3 polyunsaturated fatty acids was little modified. In plasma phospholipids, saturated and monounsaturated fatty acids were also increased, as were the n-3 fatty acids (except C 18:3 n-3); the n-6 fatty acids were little increased except C 20:3 n-6 which was markedly increased. These results concerning the amounts of fatty acids have their counterpart in their relative proportions of fatty acids. Data thus obtained suggest that conversion of linoleic acid (C 18:2 n-6) into arachidonic acid (C 20:4 n-6) was decreased in obese rats, particularly the delta 5 desaturation step. On the contrary, conversion of linolenic acid (C 18:3 n-3) into higher polyenes seemed increased. Thrombocytosis was not modified in the obese rat, but the volume of the platelets was increased. Platelet phospholipids exhibited the same modifications as plasma phospholipids but with different magnitude. Saturated and monounsaturated fatty acids were little augmented, n-3 fatty acids were more augmented (except C 18:3 n-3 acid which was unchanged); n-6 fatty acids were not modified except C 20:3 n-6 acid which was highly increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered drug-serum protein binding in the genetically obese Zucker rat

Drug-serum protein binding was evaluated in genetically obese Zucker rats, their lean littermates, and lean Sprague-Dawley rats. The free fraction (fp) of phenytoin was significantly higher in the obese rat (fp = 0.177) compared to its lean littermate (fp = 0.136), apparently due to displacement by free fatty acids. Conversely, diazepam and propranolol fp values were decreased in the obese Zucker rat (fp = 0.107 and fp = 0.122, respectively) compared to the lean Zucker rat (fp = 0.140 and fp = 0.174, respectively). Evidence strongly suggests that the increased binding of propranolol was not due to elevations in the serum concentrations of alpha1-acid glycoprotein (as is the case in the human obese population). Rather, the decreased fp for both diazepam and propranolol was a result of increased lipoprotein partitioning. Strain differences between the lean Zucker rat and lean Sprague-Dawley rat were also evident, with serum binding of the Sprague-Dawley rat more closely resembling the obese Zucker rat.

Comparison of glycogen stores in 3- and 7-month-old lean and obese Zucker rats under fed and fasted conditions

Glycogen content (mg/g) and stores (mg) were determined in 3- and 7-month-old obese and lean Zucker rats, under fed and fasted (48 hr) conditions. Hepatic content was higher in fed obese than in lean rats (3 months: 90 vs 70; 7 months: 107 vs 74); it was exhausted after fasting in lean but decreased by 56% in obese rats. Muscle content in fed obese and lean animals did not differ; it decreased comparably after fasting. Myocardial content was higher in fed obese than lean rats (3 months: 7.2 vs 3.6; 7 months: 7.5 vs 6.3); it was enhanced with fasting (10.0 vs 7.5). Total glycogen stores were higher in obese than in lean animals (3 months: 2500 vs 1400; 7 months: 4000 vs 2000) because of the hepatic store. The discussion includes a comparison with available data, taking into account methodological aspects, lipid stores and the FFA/carbohydrate interrelationship.

Effects of thyroid hormones on adipose tissue development in Sherman and Zucker rats

It has been reported that mild hyperthyroidism in the young Sherman rat induces adipose tissue hyperplasia, concomitant with cell size reduction, and that hypothyroidism induces opposite effects. The present experiments were designed to study the evolution of cellularity in retroperitoneal and epididymal adipose tissue during a long term thyroxine (T4) treatment or in T4-treated rats, after the treatment had been stopped. In both cases, hyperplasia was transient with the observation that the adipocyte number observed in 3-mo-old control rats was reached earlier in T4-treated rats. In hypothyroid rats, hypoplasia was also transient, because once the treatment was stopped, the cell number overtook that of controls. Zucker rats were also treated with T4, because hypoplasia has been observed in young obese (fa/fa) rats and these rats are reported to be hypothyroid. T4 treatment increased their adipocyte number up to the level of nonobese (Fa/fa) untreated rats, while hypertrophy, although reduced, was persistent. In Sherman and Zucker rats, adipose tissue lipoprotein lipase activity was decreased by T4 treatment in parallel with and perhaps because of adipocyte size reduction. We suggest that hyperplasia induced by thyroid hormones results from a precocious differentiation of preadipocytes and does not necessarily imply an increased preadipocytes multiplication.