Changes of Islet Size and Islet Size Distribution Resulting from Protein-Malnutrition in Lean (Fa/Fa) and Obese (fa/fa) Zucker Rats

TSE, ELIZABETH O, FRANCINE M GREGOIRE, BRIGITTE REUSENS, CLAUDE REMACLE, JOSEPH J HOET, PATRICIA R JOHNSON, JUDITH S STERN. Changes of islet size and islet size distribution resulting from protein malnutrition in lean (Fa/Fa) and obese (fa/fa) Zucker rats. Potential alterations in islet size and islet size distribution resulting from protein malnutrition were studied in lean (Fa/Fa) and obese (fa/fa) Zucker rats. The purpose was to investigate whether the distribution of enlarged islets in obese rats was altered by low-protein feeding. Four-week-old, male, lean and obese Zucker rats were fed either a diet containing 20% (w/w) protein (control diet) or a diet containing 5% (w/w) protein (low-protein diet) for 3 weeks. Pancreata were dissected at autopsy and immunostained for insulin. Islet size and distribution were determined by morphometric analysis. Body-weight gain, food intake, and serum insulin and glucose were also measured. After 3 weeks on the diets, serum insulin was significantly lower in both lean (-75%) and obese (-54%) rats fed low protein compared with that in controls. However, obese rats were still hyperinsulinemic compared with lean rats. Protein malnutrition resulted in a shift in distribution of islets to smaller size both in lean and in obese rats, with an increase in the population of small islets (100 μm²) and a decrease in the population of large islets (>20,000 μ;m²). In lean and obese rats fed low protein, β-cell weight was significantly lower, B cell volume fraction tended to decrease, and islet number per section area was significantly elevated when compared with controls. Taken together, these results show that protein deficiency alters the endocrine pancreas in both lean and obese Zucker rats. Although the decrease in islet size and the shift in distribution to smaller islets most likely contribute to the decrease in serum insulin concentration, these changes appear insufficient to normalize hyperinsulinemia in the obese Zucker rat.     

Management of dietary essential metals (iron,copper, zinc,chromium and manganese) by Wistar and Zucker obese rats fed a self-selected high-energy diet

The balances and content of essential elements (iron, copper, zinc, chromium and manganese) in the body of Wistar, Zucker lean and Zucker obese rats fed a reference or cafeteria diet from day 30 to 60 after birth have been studied. Intestinal iron absorption compensated for low iron content of the cafeteria diet and the extra needs of growth and fat deposition. It can be assumed that the altered energy regulation processes that afflict the genetically obese rat are not directly related to altered iron metabolism. Obese Zucker rats had lower copper tissue concentrations than lean rats, but when fed a cafeteria diet the differences between Zucker rats strains disappear. This cannot be traced to large differences in diet copper concentration. A low diet availability of zinc—such as that of cafeteria-fed fa/fa rats—is easily compensated for by increasing absorption. So, as a consequence, we can conclude that genetic obesity did not impair zinc absorption. There was no deficit of zinc in any of the groups studied; the rats have enough capacity to extract zinc within a wide range of dietary concentrations. The absorption of dietary chromium was inversely proportional to its concentration. The ability to extract chromium from the diet and the very low urinary losses are a consequence of its scarcity in most dietary items. Despite wide variations in the manganese of the diets, the absorption rates were practically unchanged except for obese rats fed the cafeteria diet. It seems that this low absorptive capacity is enough to supply the rat with the manganese it needs, since a sizeable—but subjected to 8-fold-span variations-proportion is lost in the urine. This alone points towards a considerable excess of manganese in both diets studied. Obesity does not have a significant effect on the abilities to absorb and retain minerals, since these processes were more related to dietary availability. Management of essential metals by obese rats depends whether this condition is genetic or induced by diet. Most of the differences observed can be related to differences in diet concentration, to the excess fat content or different metabolic attitude to use substrates of obese animals. The data presented show that the cafeteria diet used adequately serves the mineral needs of the rat, since the rat adapts its absorbing and retaining strategies to match the dietary availability of these minerals.     

Ascorbic acid supplementation and copper status in rats

The effect of a high concentration (1%, w/w) of ascorbic acid in a Cu-adequate (150 μmol/kg) purified diet was studied in rats. After 6 wk, ascorbic acid had significantly reduced Cu concentrations in muscle and bone. The estimated whole body content of Cu in rats fed ascorbic acid was reduced by 20%. Within 1 d after oral administration of⁶⁴Cu, the recovery of the dose in feces was increased in rats fed ascorbic acid, suggesting that the vitamin depresses intestinal absorption of Cu. After intraperitoneal (ip) administration of⁶⁴Cu, the rate of loss of the dose from the body was decreased in rats fed ascorbic acid. This study suggests that the ascorbic acid induces a decreased efficiency of intestinal Cu absorption, which in turn triggers mechanisms to preserve Cu in the body stores. This is supported by the observation that the feeding of a Cu-deficient diet (5 μmol/kg) had similar effects, although more pronounced.     

Uptake of radiolabeled copper from portal blood containing fructose or glucose

The present investigation was designed to study the uptake of⁶⁷Cu when administered directly, into the portal vein, along with either functose or glucose, by the liver and extrahepatic tissues. Following weaning, male Sprague-Dawley rats were fed for 3 wk either commercial laboratory ration (chow) or semipurified diets deficient in Cu (0.6 ppm) or supplemented with Cu (6.0 ppm) and containing 62% carbohydrate as either fructuse or cornstarch. After an overnight fast, a single dose of rat plasma (0.1 mL) containing fructose or glucose extrinsically labeled with⁶⁷Cu was injected directly into their portal vein. Although not always statistically significant, rats fed chow retained more radioactivity in the liver and several extrahepatic tissues when⁶⁷Cu was administered with fructose than with glucose. Regardless of Cu status, rats fed diets containing fructose retained more radioactivity in extrahepatic tissues than rats fed starch. There was an increased uptake of⁶⁷Cu by the liver, blood, muscle, and fat pad when fructose as compared to glucose was injected in combination with the isotope. These data strongly suggest that Cu requirements or utilization are greater when fructose is the main dietary carbohydrate. The results may also in part explain the reason for the increased severity of Cu deficiency in rats fed fructose.     

Change in apparent and true absorption and retention of dietary zinc with age in rats

Two groups of 16 rats each were fed the same diet with 12.9 ppm Zn. Nine days after each animal was injected with⁶⁵Zn for assessing fecal zinc of endogenous origin, zinc intake and excretion were determined for a six-day period at the age of about five (group I) and nine (II) weeks. At mean growth rates of 5.1 and 5.2 g/day, food consumption per gram of gain was 2.01 g in group I vs 2.86 g in II. Overall, zinc retention amounted to 21 vs 25 μg Zn/g of gain. Apparent absorption averaged 92 vs 74% of Zn intake (132 vs 189 μg/day), while true absorption averaged 98 vs 92%. It was concluded that endogenous fecal zinc excretion was limited to the indispensable loss (F _em) in group I (7 μg/day), while it exceeded this minimum loss in group II (33 μg/day). True retention, which reflected total zinc utilization (true absorption times metabolic efficiency), was derived from apparent absorption plusF _em (11 μg/day for group II according to the greater metabolic body size of the rats). It averaged 98% of Zn intake in group I vs 80% in group II. The mean metabolic efficiency was 100% vs 87%. The conclusion was that these marked differences between age groups in utilizing the dietary zinc reflected the efficient homeostatic adjustments in absorption and endogenous excretion of zinc to the respective zinc supply status.     

Differential Responsiveness of Obese (fa/fa) and Lean (Fa/Fa) Zucker Rats to Cytokine-Induced Anorexia

Pathophysiological and pharmacological concentrations of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in the cerebrospinal fluid (CSF) induce anorexia in normal rats. Obesity in humans and rodents is associated with increased TNF-α messenger RNA and protein levels in various cell types. This suggests that obese individuals may have differential regulation of cytokine production and dissimilar responsiveness to cytokines. In the present study, we investigated the effects of the intracerebroventricular (ICV) microinfusion of TNF-α (50, 100, and 500 ng/rat), IL-1β (1.0, 4.0, and 8.0 ng), and TNF-α (100 ng) plus IL-1β (1.0 ng) on obese (fa/fa) and lean (Fa/Fa) Zucker rats. The results show that: TNF-α and IL-1β, and the concomitant administration of TNF-a and IL-ip decreased the short-term (4 hours), nighttime (12 hours), and total daily food intakes in obese and lean rats; IL-1β was more potent relative to TNF-α; obese rats showed greater responsiveness to IL-1β: 8.0 ng IL-1β, for example, decreased the 12-hour food intake by 52% in obese and 22% in lean rats. On the other hand, obese and lean rats did not exhibit a significantly different responsiveness to the anorexia induced by 50,100, or 500 ng TNF-α at the 4-hour period; and the concomitant ICV administration of TNF-α and IL-1β induced anorexia with additive (4-hour period) or synergistic (12-hour and 24-hour periods) effects in obese rats. The effect of TNF-α plus IL-1β in lean rats was greater than additive for the 12-hour and 24-hour periods. The difference in suppression of total daily food intake by TNF-α plus IL-1β in obese (-43%) versus lean (-23%) rats was significantly different (p<0.01). The results show that obese (fa/fa) and lean (Fa/Fa) Zucker rats have differential responsiveness to the ICV microinfusion of two different classes of cytokines.     

Changes in UCP expression in tissues of Zucker rats fed diets with different protein content

The effect of dietary protein content on the uncoupling proteins (UCP) 1, 2 and 3 expression in a number of tissues of Zucker lean and obese rats was studied. Thirty-day-old male Zucker lean (Fa/?) and obese (fa/fa) rats were fed on hyperproteic (HP, 30% protein), standard (RD, 17% protein) or hypoproteic (LP, 9% protein) diets ad libitum for 30 days. Although dietary protein intake affected the weights of individual muscles in lean and obese animals, these weights were similar. In contrast, huge differences were observed in brown adipose tissue (BAT) and liver weights. Lean rats fed on the LP diet generally increased UCP expression, whereas the HP group had lower values. Obese animals, HP and LP groups showed higher UCP expression in muscles, with slight differences in BAT and lower values for UCP3 in subcutaneous adipose tissue. The mean values of UCP expression in BAT of obese rats were lower than in their lean counterpart, whereas the expression in skeletal muscle was increased. Thus, expression of UCPs can be modified by dietary protein content, in lean and obese rats. A possible thermogenic function of UCP3 in muscle and WAT in obese rats must be taken into account.     

Effects of low copper and high zinc intakes and related changes in Cu,Zn-superoxide dismutase activity on DMBA-induced mammary tumorigenesis

The effect of low copper and high zinc intakes on Cu,Zn-superoxide dismutase (Cu,Zn-SOD) activity and mammary tumorigenesis induced by 9,10-dimethyl-1,2-benzanthracene (DMBA) was investigated. Groups of 40 weanling female Sprague-Dawley rats were fed a modified AIN-76 diet containing the following (/kg diet): 1 mg Cu (0.016 mmol) and 30 mg Zn (0.459 mmol); 6 mg Cu (0.094 mmol) and 30 mg Zn (0.459 mmol) (control); or 6 mg Cu (0.094 mmol) and 150 mg Zn (2.295 mmol) for 21 wk. At 5 wk, 30 rats/group were given 4 mg (15.6 mumol) DMBA in corn oil intragastrically, and controls (10/group) received corn oil alone. Erythrocyte Cu,Zn-SOD activity was measured at 3, 5 (just before DMBA), 9, 13, 17, and 21 wk. The group fed the high-Zn diet had a slightly lower weight gain and food consumption. DMBA treatment had no effect on these parameters. Plasma and liver Cu concentration decreased in the low-Cu group. Femur zinc was significantly elevated in the high-Zn group. Erythrocyte Cu,Zn-SOD activity was decreased in the low-Cu group from 3 to 21 wk and was significantly elevated in the high-Zn group at 3 and 5 wk. In the low-Cu group, there were 5 nonmalignant adenomas and 3 malignant adenocarcinomas; in the control group, there were 4 adenomas and 3 adenocarcinomas; in the high-Zn group, there were 5 adenomas and 3 adenocarcinomas. No relationship between Cu,Zn-SOD activity and the presence of tumors could be found.     

Effects of food deprivation and high fat diet on immunoreactive dynorphin A(1–8) levels in brain regions of Zucker rats

The levels of immunoreactive dynorphin A(1–8) (ir-DYN8) were measured in discrete brain regions of lean Zucker rats subjected to food deprivation for 72 hr and to a high fat diet, and in fatty Zucker rats after food deprivation for 72 hr. Fatty rats showed higher concentrations of ir-DYN8 in the cortex and midbrain, when compared to lean rats fed a stock diet ad lib. Food deprivation increased ir-DYN8 levels in the cortex of lean rats and fatty rats and in the hippocampus of fatty rats, but decreased its content in the striatum of lean rats and in the midbrain of fatty rats. The high fat diet increased ir-DYN8 levels in the cortex and midbrain of lean rats. These results suggest that ir-DYN8 levels in extrahypothalamic structures of Zucker rats could be differentially modified under conditions of hereditary obesity and dietary manipulations.     

Effect of coix on plasma, liver, and fecal lipid components in the rat fed on lard- or soybean oil-cholesterol diet

To determine the influence of dietary coix on lipid metabolism, the effect of coix on plasma, liver, and fecal lipid components was studied using Sprague-Dawley male rats. All rats were divided into four groups, and the rats of each group were fed the coix-lard diet, coix-soybean oil diet, or the respective control diets (containing 1% cholesterol each) for 27 days. Plasma and liver cholesterol levels in the coix-lard diet group significantly decreased as compared with those in the control group, whereas there was no effect on the fecal excretion of cholesterol. The decreases in the concentrated liver triglyceride and the increases in the fecal excretion of triglyceride were found in coix-soybean oil diet group. Moreover, liver and fecal phospholipid levels in both coix diet groups significantly increased. But there were no significant changes in plasma and fecal bile acids in either coix diet group. These results suggest the possibilities that coix may have an inhibitory action on cholesterol synthesis in liver, a facilitating effect on biliary excretion of triglyceride, and an acceleratory action on phospholipid synthesis in liver.     

Anemia associated with changes in iron and iron-59 utilization in copper deficient rats fed high levels of dietary ascorbic acid and iron

The influence of dietary copper, iron, and ascorbic acid on iron utilization was examined in a 2×2×2 factorial experiment. Male Sprague-Dawley weanling rats were fed copper-deficient (Cu-, 0.42 μg Cu/g) or copper-adequate (Cu+, 5.74 μg Cu/g) diets that contained one of two levels of iron (38 or 191μg Fe/g) and ascorbic acid (0 or 1% of the diet). These eight diets were fed for 20 d, and rats received an oral dose of 4 μCi iron-59 on d 15. Compared to Cu+ rats, the Cu− rats had 27% lower hemoglobin levels with 45, 59, and 65% lower cytochrome c oxidase (CCO) activities in the liver, heart, and bone marrow, respectively (p<0.0001). High dietary iron or ascorbic acid did not alter hemoglobin in Cu+ rats. However, hemoglobin was 23% lower in Cu− rats fed the highest, rather than the lowest levels of iron and ascorbic acid. Liver CCO was decreased (p<0.02) in Cu− rats fed high iron. Among Cu− rats, ascorbic acid did not influence CCO but decreased hemoglobin by 17% (p<0.001), reduced the percentage of absorbed iron-59 in the erythrocytes by 91% (p<0.05) and depressed the percentage apparent absorption of iron (p<0.05). These results suggest that the effects of elevated dietary iron and ascorbic acid on iron utilization are influenced by copper status.     

Increased excretion of bile acids by genetically hyperlipoproteinemic Zucker rat

Fecal excretion of neutral sterols and bile acids was measured in age-matched hyperlipoproteinemic Zucker obese rats and their lean litter mates. The bile acid excretion (mg/day ± SEM) in Zucker rats was significantly higher (p<0.01) when compared to lean controls (Zucker obese rats 41.68 ± 2.86; lean controls 29.85 ± 1.50). Neutral sterol excretion in both the groups of rats was similar. Total fecal steroid excretion (mg/day ± SEM) in Zucker rats was significantly higher (p<0.01) than in lean controls (Zucker obese rats 52.33 ± 3.50; lean controls 39.23 ± 2.16. The Zucker rat thus mimics the increased bile acid excretion noted previously in human Type IV hyperlipoproteinemia and could serve as an ideal animal model for studying the interrelationship between bile acid excretion and very low density lipoprotein metabolism.     

Endogenous excretion and true absorption of cobalt as affected by the oral supply of cobalt

At the end of a 49-d experiment with 32 growing male rats, a period of 8 d was used to determine endogenous excretion and true absorption as well as apparent absorption and retention of cobalt with the aid of the isotope dilution technique. For this purpose, a single im dose of⁵⁸Co was applied at d 35 of the experiment. After that, urine and feces were collected separately from d 8 to 15 after injection of the isotope. The specific cobalt activity of the liver was used as an endogenous reference source. The basal diet provided 5.9 ppb cobalt, the different treatment groups were obtained by supplementing the diet with 0, 10, 50, 250, or 1250 ppb cobalt. The different diets were offered from the beginning of the experiment. In the balance period, apparent and true absorption as well as fecal excretion behaved similar to cobalt intake, whereas urinary excretion increased more rapidly with increasing cobalt supply. Endogenous fecal excretion accounted for 3.5 ng Co/d in the groups fed the diets without and with 10 ppb cobalt. An increase was not observed until supplementing the diet with 50 ppb cobalt. This increase between 250 and 1250 ppb cobalt was higher than the corresponding increase in the dietary cobalt supply. This indicates that endogenous fecal excretion might be more important for homeostatic regulation at a higher dietary cobalt concentration. Endogenous renal excretion as calculated from the results of the isotope dilution technique showed a similar kind of response to increasing cobalt supply as endogenous fecal loss. Nevertheless, the elimination of excessive cobalt mainly took place by adjusting urinary excretion, whereas the variations in true absorption and endogenous fecal excretion had no quantitative importance. Apparent and true absorption were on average 28.0 and 29.8%, respectively, of the cobalt intake. In the case of retention, a marked decline was observed from 19% in the depletion group to 3% with 1250 ppb cobalt, again demonstrating the importance of urinary excretion for controlling the cobalt content of the organism.     

Effect of dietary protein, alfalfa, and zeolite on excretory patterns of 5',5',7',7'-[3H]zearalenone in rats

A series of experiments was conducted to determine how dietary protein, alfalfa, or zeolite influence the excretory patterns of zearalenone (Z), a uterotropic mycotoxin synthesized by Fusarium fungi. Rats were fed diets containing 16.3% casein, 40% casein, 11.2% casein + 25% alfalfa, or 25% casein + 25% alfalfa. Also fed were diets containing 0, 1, 2, or 5% anion exchange zeolite. Tracer doses of [3H]Z were administered either as a constituent of the diet or as a topical application on the skin at the base of the skull. When Z was administered orally, no differences were seen in the fraction of the dose excreted in urine or feces as a result of varying dietary levels of alfalfa and protein. Topical doses resulted in rats fed 25% casein + 25% alfalfa or 40% casein excreting more Z in urine than those fed 25% alfalfa or 16.3% casein. Fecal excretion of Z was greatest for rats fed 25% casein + 25% alfalfa whereas rats fed 40% casein excreted more fecal Z than those fed 16.3% casein. Feeding Z to rats receiving dietary zeolite resulted in a positive correlation between dietary zeolite and fecal excretion of Z but a negative correlation with urinary excretion of Z. Topical administration of Z produced a positive correlation between dietary zeolite and fecal Z excretion but no effect on urinary excretion. It may be concluded that protein and alfalfa treatments alleviate Z toxicosis through increased metabolism whereas zeolite binds Z in the digestive tract to prevent absorption.     

Effects of fatty (fa) allele and high-fat diet on adipose tissue leptin and lipid metabolism.

Leptin is an adipocyte-secreted hormone that binds hypothalamic receptors and potently decreases food intake. Leptin receptor defects in homozygous mutant Zucker fatty ( fa/fa) rats lead to massive obesity, hyperphagia, decreased energy expenditure, and insulin resistance, while the phenotype of heterozygous ( Fa/fa) lean rats lies between lean ( Fa/Fa) and obese ( fa/fa) rats. Whether heterezygotes exhibit specific changes in lipid metabolism in a diet-responsive manner is not clear. Thus, the specific aim of this study was to test whether the presence of one fa allele modulates lipid metabolism and leptin, and whether these effects are exacerbated by high-fat diet. We demonstrate that the presence of one fa allele significantly increases lipogenesis in adipose tissue assessed by glycerol-3-phosphate dehydrogenase (GPDH) and fatty acid synthase (FAS) activities. FAS is more responsive to high-fat diets than GPDH in Fa/fa rats. Adipose tissue leptin levels are significantly higher in fat pads of Fa/fa compared to Fa/Fa rats. Moreover, Fa/fa rats fed high-fat diet show an additional two-fold increase in leptin levels compared to wild type rats on the same diet. Collectively, these results indicate that the presence of one fa allele increase adipocyte lipogenic enzyme activities, which results in hyperleptinemia concurrent with increased adiposity.     

Hypothalamic Monoaminergic Activity in 11-Week-Old Cold-Exposed Female Lean (Fa/Fa) and Obese (fa/fa) Zucker Rats

We previously reported that serotonergic activity was reduced in the ventromedial hypothalamic nucleus (VMN) of obese vs. lean male Zucker rats. To verify that this reduction was associated with genotype rather than gender, we measured monoamines and their major metabolites in hypothalamic nuclei of ll-week-old female lean (Fa/Fb) and obese (fa/fb) Zucker rats. In addition, since the thermic response to cold is reported to differ between lean and obese rats, some rats were also exposed to 9° or 22° C for 2h to determine if cold exposure altered hypothalamic monoaminergic activity. As in males, levels of 5-hydroxyindoleacetic acid [5-HIAA; major metabolite of serotonin (5-HT)] and the ratio of 5-HIANS-HT were lower in the VMN of obese vs. lean females (P = 0.008, 0.001, respectively). S-HIANS-HT was also reduced in the paraventricular (PVN) and suprachiasmatic nuclei (SCN) of the obese compared to the lean females. Cold exposure significantly stimulated brown fat mitochondria1 GDP binding in lean but not obese rats. Similarly, levels of norepinephrine, dopamine (DA), 5-HIAA, and 5-HT in the PVN, and 5-HIAA in the SCN increased in cold-exposed lean but not obese rats. In contrast, VMN and preoptic 3,4-dihydroxyphenylacetic acid (DOPAC; major metabolite of DA) increased in the cold-exposed obese but not lean animals. We conclude that: (1) the blunted peripheral response to cold in obese vs. lean Zucker rats is accompanied by altered hypothalamic monoaminergic activity, the physiological role of which needs further evaluation; and 2) depressed VMN serotonergic activity is associated with the obese genotype (fa/fa) rather than gender and as such may contribute to the reduced sympathetic and enhanced parasympathetic outflow from the VMN .     

Effect of dietary Platycodon grandiflorum on the improvement of insulin resistance in obese Zucker rats

The effect of dietary Platycodon grandiflorum on the improvement of insulin resistance and lipid profile was investigated in lean (Fa/-) and obese (fa/fa) Zucker rats, a model for noninsulin dependent diabetes mellitus. Dietary Platycodon grandiflorum feeding for 4 weeks resulted in a significant decrease in the concentration of plasma triglyceride in both lean and obese Zucker rats. Furthermore, dietary Platycodon grandiflorum markedly decreased both plasma cholesterol and fasting plasma insulin levels, and significantly decreased the postprandial glucose level at 30 min during oral glucose tolerance test in obese Zucker rats. Although there was no statistical significance, the crude glucose transporter 4 protein level of obese rats fed Platycodon grandiflorum tended to increase when compared with that of obese control rats. Therefore, the present results suggested that dietary Platycodon grandiflorum may be useful in prevention and improvement of metabolic disorders characterized by hyperinsulinemia states such as noninsulin dependent diabetes mellitus, syndrome X, and coronary artery disease.     

Comparison of Tissue Metal Concentrations in Zucker Lean, Zucker Obese, and Zucker Diabetic Fatty Rats and the Effects of Chromium Supplementation on Tissue Metal Concentrations

Diabetes results in several metabolic changes, including alterations in the transport, distribution, excretion, and accumulation of metals. While changes have been examined in several rat models of insulin resistance and diabetes, the metal ion concentrations in the tissues of Zucker lean, Zucker obese (an insulin resistance and early stage diabetes model), and Zucker diabetic fatty (ZDF, a type 2 diabetes model) have not previously been examined in detail. The concentration of Cu, Zn, Fe, Mg, and Ca were examined in the liver, kidney, heart and spleen, and Cr concentration in the liver and kidney of these rats were examined. Zucker obese rats have a reduction in the concentration of Cu, Zn, Fe, Mg in the liver compared to ZDF and/or lean Zucker rats, presumably as a result of the increased fat content of the liver of the obese rats. ZDF rats have increased concentrations of kidney Cu compared to the lean rats, while kidney Ca concentrations are increased in the Zucker obese rats. Spleen Fe concentrations are decreased in Zucker obese rats compared to the lean rats. No effects on metal concentrations in the heart were observed between the lean, obese, and ZDF rats, and no effects on Cr concentrations were identified. Cr(III) complexes have previously been shown to have beneficial effects on the signs of insulin resistance in Zucker obese and ZDF rats. The effects of daily gavage administration of chromium picolinate ([Cr(pic)₃]) (1 mg?Cr/kg body mass), CrCl₃ (1 mg?Cr/kg body mass), and Cr3 ([Cr₃O(propionate)₆(H₂O)₃]⁺) (33 μg and 1 mg?Cr/kg body mass) on metal concentrations in these tissues were examined. Treatment with CrCl₃ and Cr3, but not [Cr(pic)₃], at 1 mg?Cr/kg resulted in a statistically significant accumulation of Cr in the kidney of lean and obese but not ZDF rats but resulted in lowering the elevated levels of kidney Cu in ZDF rats, suggesting a beneficial effect on this symptom of type 2 diabetes.     

Copper metabolism in analbuminaemic rats fed a high-copper diet

Copper metabolism in male Nagase analbuminaemic (NA) rats was compared with that in male Sprague Dawley (SD) rats fed purified diets containing either 5 or 100 mg Cu/kg diet. Dietary copper loading increased hepatic and kidney copper concentrations in both strains to the same extent, but baseline values were higher in the NA rats. There was no strain difference in true and apparent copper absorption nor in faecal endogenous and urinary copper excretion. NA rats had higher levels of radioactivity in kidneys at 2 hr after intraperitoneal administration of ⁶⁴Cu. As based on the distribution of added ⁶⁴Cu, about 70% of plasma copper appeared to be in the non-protein compartment in the NA rats, whereas in SD rats, it was only about 1%. It is concluded that the NA rats are able to maintain a relatively normal metabolism of copper, even after dietary copper challenge. In the NA rats, zinc concentrations in kidneys, liver and urinary zinc excretion were elevated when compared with SD rats. The high-copper diet did not affect tissue zinc concentrations and apparent zinc absorption in both strains of rats.     

True absorption and endogenous fecal excretion of manganese in relation to its dietary supply in growing rats

A conventional balance study with 48 male weanling rats was conducted to determine true absorption and endogenous fecal excretion of manganese (Mn) in relation to dietary Mn supply, following the procedures of a previously adapted isotope dilution technique. After 10 d on a diet with 1.5 ppm Mn, eight animals each were assigned to diets containing 1.5, 4.5, 11.2, 35, 65, or 100 ppm Mn on a dry-matter basis. Three days later, each rat was given an intramuscular⁵⁴Mn injection and kept on treatment for a balance period of 16 d. Apparent Mn absorption assessed for the final 8 d, averaged 8.6 μg/d without significant treatment effects, although Mn intake ranged from 18.6 to 1200 μg/d, in direct relation to dietary Mn concentrations. Mean fecal excretion of endogenous Mn for the six treatments was 0.9, 2.7, 7.4, 11.0, 16.3, and 17.7 μg/d, respectively. These values delineate the rates to which true absorption exceeded apparent rates. True absorption, as percent of Mn intake, averaged 28.7, 15.9, 11.7, 6.1, 3.4, and 2.0, respectively, as compared with mean values of 23.9, 10.9, 6.2, 3.4, 1.2, and 0.5 for percent apparent absorption. It was concluded that both true absorption and endogenous fecal excretion markedly responded to Mn nutrition and that the reduction in the efficiency of true absorption was quantitatively the most significant homeostatic response for maintaining stable Mn concentrations in body tissues.