Status In Streptozotocin-induced Diabetic Rats Research Articles

Beneficial role of ferulic acid supplementation on lipid profile status in streptozotocin-induced diabetic rats

Background: Diabetes is a chronic metabolic disorder marked by persistent elevated blood sugar concentrations and disturbances in the metabolism of carbohydrates, lipids, and proteins. Several functional foods and naturally occurring compounds derived from plants have therapeutic potential for managing diabetes and its associated metabolic abnormalities of lipids. Ferulic acid is a bioactive compound present in numerous functional foods. It provides an extensive array of health advantages, encompassing a diverse spectrum of benefits.Objective:The objective of this study was to assess the effect of 50 mg/kg body weight of Ferulic acid (FA50) on the lipid profile status in diabetic rats induced with Streptozotocin (STZ).Materials and methods: Experimental diabetes was created on male albino Sprague Dawley rats. The rats were categorized into five distinct groups- Normal (Group 1), Normal+ FA50 (Group 2), Diabetic control (Group 3), Diabetic + FA50 (Group 4), and Diabetic + Glibenclamide (Group 5). Diabetes was induced in Group 3, 4, and 5 by administering an I.P (intraperitoneal) injection of STZ (40 mg/kg body weight). Rats of groups 2 and 4 were orally administered with 50 mg of FA per rat’s body weight in Kg. Group 5 was treated with Glibenclamide (5 mg/ Kg body weight) daily for two months. On the 60th day, rats from all groups were euthanized, and blood samples were gathered for the purpose of conducting biochemical assessments.Results: The injection of STZ resulted in a significant increase in blood glucose, HbA1c, and lipid profile markers in the experimental rats. Oral administration of Ferulic acid and Glibenclamide drug to diabetic rats significantly (P ≤ 0.05) lowered hyperglycemia, triglycerides, and total cholesterol compared to the diabetic control group. Moreover, the administration of Ferulic acid significantly increased the levels of HDL-cholesterol and regulated the Apo lipoprotein A1- Apo lipoprotein B levels.Conclusion: The current research demonstrates the advantageous impact of Ferulic acid in improving lipid-related metabolic complications associated with diabetes.Keywords: Nutraceuticals, Ferulic acid, Streptozotocin, Diabetes, Lipid profile

The therapeutic potential of “Crataegus azarolus” on zinc, lipid profile, and antioxidant status in streptozotocin-induced diabetic rats with zinc-deficient diet

The therapeutic potential of “Crataegus azarolus” on zinc, lipid profile, and antioxidant status in streptozotocin-induced diabetic rats with zinc-deficient diet

Testicular oxidative stress and apoptosis status in streptozotocin-induced diabetic rats after treatment with rooibos (Aspalathus linearis), honeybush (Cyclopia intermedia), and sutherlandia (Lessertia frutescens) infusions

Objective: To investigate the testicular oxidative stress and apoptosis status, as well as the sperm functional parameters in streptozotocin (STZ) induced diabetic rats following treatment with rooibos (Aspalathus linearis), honeybush (Cyclopia intermedia) and sutherlandia (Lessertia frutescens) infusions. Methods: Diabetes was induced by injecting fourteen-week-old adult male Wistar rats (250-300 g) with a single intraperitoneal injection of STZ (45 mg/kg body weight). Fifty rats were randomly divided into five groups: the vehicle group received 0.1 M citrate buffer, the diabetic control group received 45 mg/kg STZ, the diabetic+rooibos group received 45 mg/kg STZ + 2.0% rooibos, the diabetic+honeybush group received 45 mg/kg STZ + 4.0% honeybush, and the diabetic+sutherlandia group received 45 mg/kg STZ + 0.2% sutherlandia. Rats were sacrificed 7 weeks after induction of diabetes mellitus. The testes and epididymides were harvested and weighed after induction. Spermatozoa were retrieved from the cauda epididymis for motility, concentration, and morphology analysis, and the testis was used for all biochemical assays. Oxidative stress was determined by measuring malondialdehyde levels, catalase, and superoxide dismutase activities, while apoptotic biomarkers were evaluated by Western blotting assays. Results: After induction of diabetes, rats in the diabetic control group, diabetic+rooibos group, diabetic+honeybush group, and diabetic+sutherlandia group presented with significantly elevated blood glucose levels as compared with the vehicle group (P Conclusions: Rooibos, honeybush and sutherlandia infusions may partly alleviate diabetes-induced sperm function impairment by reducing oxidative stress.

Effect of Coenzyme Q10 Supplementation on Liver Total Oxidant/Antioxidant Status in Streptozotocin-induced Diabetic Rats

Effect of Coenzyme Q10 Supplementation on Liver Total Oxidant/Antioxidant Status in Streptozotocin-induced Diabetic Rats

Beneficial effects of Stevioside on AGEs, blood glucose, lipid profile and renal status in streptozotocin-induced diabetic rats.

The advanced glycated end products (AGEs) are formed in the diabetic patients; it is a major cause of macrovascular and microvascular complications in diabetes. Clinically there is no treatment available for the AGEs. Stveoside (Stv), a sweetener has potent anti-diabetic and anti-oxidant activity. Hence, we investigated its use in prevention of AGEs formation using in vitro and in vivo models. Diabetes was induced by streptozotocin (STZ). These rats were kept without treatment till blood HbA1c was markedly increased. They were then divided into 5 groups and treated orally with vehicle or Metformin (MET) or Stv respectively for 28 days. Every 7th day, animals were tested for body weight and blood glucose (BG). On the last day of treatment, all the groups were evaluated for physiological and biochemical parameters, histopathology and AGEs; N-carboxymethyl-lysine (CML) estimation. Stv showed inhibition of AGEs in in vitro as well as in in vivo respectively. Positive effects were seen on the BG, lipid profile and urine parameters as well it showed reduced formation of CML. It also showed antihyperglycaemic, antihyperlipedemic and nephroprotective activities. The present study provides scientific rationale for the use of Stv as a sweetener with additional benefits in diabetes.

Propolis improves pregnancy outcomes and placental oxidative stress status in streptozotocin-induced diabetic rats

BackgroundThis study assessed the effects of propolis alone or combined with insulin on maternal status, pregnancy outcomes and placental oxidative stress in streptozotocin-induced diabetic rats.MethodsForty female rats were randomly assigned into five groups (n = 8/group) i.e. non-DM (non-diabetes), DM (diabetes), DM + Propolis (diabetes on propolis orally); DM + Insulin (diabetes on insulin subcutaneously) and DM + Combined (diabetes on propolis and insulin) groups. Propolis and insulin were given at 300 mg/kg/day orally and 5.0 IU/kg/day subcutaneously, respectively, for 4 weeks.ResultsFasting blood glucose, conception period, implantation losses, foetal blood glucose and placental oxidative stress markers such as malonaldehyde and protein carbonyl were significantly higher while maternal weight gain, foetal body weight and total antioxidant capacity were significantly lower in DM group compared with non-DM group. These changes were significantly improved in rats treated with propolis or insulin alone with greater significant effects in rats treated with both propolis and insulin.ConclusionThis study may suggest the protective effects of propolis against DM-induced impaired pregnancy outcomes and placental oxidative stress with greater effects when combined with insulin.

Ameliorative Effects of Aloe Vera Gel Extract on Circulatory and Tissue Lipid Profile Status in Streptozotocin-Induced Diabetic Rats

Diabetes is characterized by hyperglycaemia with alterations of lipid parameters. The effects of Aloe vera (A.V) gel extract on lipid profiles of streptozotocin-induced diabetic rats were investigated. Seventy-two male albino rats were randomly divided into six groups of 12 rats each; control, diabetic control, 4 ml/kg and 8 ml/kg body weight (b.w.) A.V, 10 mg/kg b.w. glibenclimide and non-diabetic 8 ml/kg b.w. A.V groups. They were treated for 14 and 28 days. The plasma and HDL lipid profiles (triacylglycerols, cholesterol and phospholipids) of the diabetic rats were significantly (p<0.05) increased, while those of the VLDL+LDL, RBC, RBC membrane and organs were observed to be significantly (p<0.05) reduced, when compared to the control after 14 and 28 days of treatment. A.V gel extract significantly (p<0.05) ameliorated the disruptions observed in the lipid profiles of the diabetic and thus provide a scientific rationale for the use of Aloe vera as a therapeutic agent.Bangladesh J Med Biochem 2016; 9(1): 11-26

Aloe vera gel improves behavioral deficits and oxidative status in streptozotocin-induced diabetic rats

Oxidative stress has a major role in progression of diabetes-related behavioral deficits. It has been suggested that Aloe vera has anti-diabetic, antioxidative, and neuroprotective effects. The present study was designed to determine the effects of Aloe vera gel on behavioral functions, oxidative status, and neuronal viability in the hippocampus of streptozotocin (STZ)-induced diabetic rats. Fifty five adult male Wistar rats were randomly divided into five groups, including: control (normal saline 8ml/kg/day; P.O.), diabetic (normal saline 8ml/kg/day; P.O.), Aloe vera gel (100mg/kg/day; P.O.), diabetic+Aloe vera gel (100mg/kg/day; P.O.) and diabetic+NPH insulin (10 IU/kg/day; S.C.). All treatments were started immediately following confirmation of diabetes in diabetic groups and were continued for eight weeks. Behavioral functions were evaluated by employing standard behavioral paradigms. Additionally, oxidative status and neuronal viability were assessed in the hippocampus. The results of behavioral tests showed that diabetes enhanced anxiety/depression-like behaviors, reduced exploratory and locomotor activities, decreased memory performance, and increased stress related behaviors. These changes in diabetic rats were accompanied by increasing oxidative stress and neuronal loss in the hippocampus. Interestingly, eight weeks of treatment with Aloe vera gel not only alleviated all the mentioned deficits related to diabetes, but in some aspects, it was even more effective than insulin. In conclusion, the results suggest that both interrelated hypoglycemic and antioxidative properties of Aloe vera gel are possible mechanisms that improve behavioral deficits and protect hippocampal neurons in diabetic animals.

An evaluation of aversive memory and hippocampal oxidative status in streptozotocin-induced diabetic rats treated with resveratrol

The present study evaluated the effects of streptozotocin (STZ)-induced diabetes on aversive memory, free radical content and enzymatic antioxidant activity in the hippocampus of adult Wistar rats submitted to oral treatment with resveratrol. Animals were divided into eight groups: non-diabetic rats treated with saline (ND SAL), non-diabetic rats treated with resveratrol at a dose 5mg/kg (ND RSV 5), non-diabetic rats treated with resveratrol at a dose 10mg/kg (ND RSV 10), non-diabetic rats treated with resveratrol at a dose 20mg/kg (ND RSV 20), diabetic rats treated with saline (D SAL), diabetic rats treated with resveratrol at a dose 5mg/kg (D RSV 5), diabetic rats treated with resveratrol at a dose 10mg/kg (D RSV 10) and diabetic rats treated with resveratrol at a dose 20mg/kg (D RSV 20). The animals received oral gavage for 35days. The contextual fear conditioning task was performed to evaluate aversive-based learning and memory. The oxidative status was evaluated in the hippocampus, by measuring the free radical content – using a 2′,7′-dichlorofluorescein diacetate probe – and enzymatic antioxidant activities, such as superoxide dismutase and glutathione peroxidase. Our main behavioral results demonstrated that rats from the D RSV 10 and D RSV 20 groups showed an increase in freezing behavior when compared, respectively, to the ND RSV 10 (p<0.01) and ND RSV 20 (p<0.05). Oxidative stress parameters remained unchanged in the hippocampus of all the experimental groups. In contrast to previous experimental findings, our study was unable to detect either cognitive impairments or oxidative stress in the hippocampus of the diabetic rats. We suggest additional long-term investigations be conducted into the temporal pattern of STZ-induced diabetic disruption in memory and hippocampal oxidative status, as well as the effects of resveratrol on these parameters, in a time and dose-dependent manner.

Avocado Oil Improves Mitochondrial Function and Decreases Oxidative Stress in Brain of Diabetic Rats.

Diabetic encephalopathy is a diabetic complication related to the metabolic alterations featuring diabetes. Diabetes is characterized by increased lipid peroxidation, altered glutathione redox status, exacerbated levels of ROS, and mitochondrial dysfunction. Although the pathophysiology of diabetic encephalopathy remains to be clarified, oxidative stress and mitochondrial dysfunction play a crucial role in the pathogenesis of chronic diabetic complications. Taking this into consideration, the aim of this work was to evaluate the effects of 90-day avocado oil intake in brain mitochondrial function and oxidative status in streptozotocin-induced diabetic rats (STZ rats). Avocado oil improves brain mitochondrial function in diabetic rats preventing impairment of mitochondrial respiration and mitochondrial membrane potential (ΔΨm), besides increasing complex III activity. Avocado oil also decreased ROS levels and lipid peroxidation and improved the GSH/GSSG ratio as well. These results demonstrate that avocado oil supplementation prevents brain mitochondrial dysfunction induced by diabetes in association with decreased oxidative stress.

Vitamin B6 supplementation improves oxidative stress and enhances serum paraoxonase/arylesterase activities in streptozotocin-induced diabetic rats.

The purpose of this study was to investigate the effects of vitamin B6 (Vit B6) on oxidant and antioxidant status in streptozotocin-induced diabetic rats. Thirty-two Wistar rats were divided into four groups: control (C), control + Vit B6 group (C + Vit B6), diabetes (D), and diabetes + Vit B6 group (D + Vit B6). Vit B6 (4 mg/kg body weight) was administered in drinking water for 4 weeks after the induction of diabetes. Vitamin B6 reduced serum total cholesterol level in the C + Vit B6 (P < 0.01) and D + Vit B6 (P < 0.05) groups. Plasma and tissue malondialdehyde levels were reduced in the C + Vit B6 and D + Vit B6 groups. Whole blood glutathione peroxidase (GSH-Px) and erythrocyte superoxide dismutase (SOD) activities were higher in the D group (P < 0.05). GSH-Px and SOD activities were increased in C + Vit B6 group while these parameters decreased in the D + Vit B6 group. Paraoxonase and arylesterase activities were decreased in the D group while they were increased in C + Vit B6 and D + Vit B6 groups. The results of present study suggest that vitamin B6 supplementation might be a promising adjunctive agent for improving oxidative stress and metabolic disturbances and for preventing diabetic complications including atherogenesis.

Protective effect of esculetin on hyperglycemia-mediated oxidative damage in the hepatic and renal tissues of experimental diabetic rats

Diabetes mellitus is the most common serious metabolic disorder and it is considered to be one of the five leading causes of death in the world. Hyperglycemia-mediated oxidative stress plays a crucial role in diabetic complications. Hence, this study was undertaken to evaluate the protective effect of esculetin on the plasma glucose, insulin levels, tissue antioxidant defense system and lipid peroxidative status in streptozotocin-induced diabetic rats. Diabetic rats exhibited increased blood glucose with significant decrease in plasma insulin levels. Extent of oxidative stress was assessed by the elevation in the levels of lipid peroxidation markers such as thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides (HP) and conjugated dienes (CD); reduction in the enzymic antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST); nonenzymic antioxidants Vitamin C, E and reduced glutathione (GSH) were observed in the liver and kidney tissues of diabetic control rats as compared to control rats. Oral supplementation of esculetin to diabetic rats for 45 days significantly brought back lipid peroxidation markers, enzymic and nonenzymic antioxidants to near normalcy. Moreover, the histological observations evidenced that esculetin effectively rescues the hepatocytes and kidney from hyperglycemia mediated oxidative damage without affecting its cellular function and structural integrity. These findings suggest that esculetin (40 mg/kg BW) treatment exerts a protective effect in diabetes by attenuating hyperglycemia-mediated oxidative stress and antioxidant competence in hepatic and renal tissues. Further, detailed studies are in progress to elucidate the molecular mechanism by which esculetin elicits its modulatory effects in insulin signaling pathway.

Effect of 2-hydroxy-4-methoxy benzoic acid isolated from Hemidesmus indicus on erythrocyte membrane bound enzymes and antioxidant status in streptozotocin-induced diabetic rats

In the present study, the effect of 2-hydroxy-4-methoxy benzoic acid isolated from roots of Hemisdesmus indicus on the erythrocyte membrane bound enzymes and antioxidant status in streptozotocin-induced diabetic rats was investigated. The streptozotocin-induced diabetic rats were treated with 2-hydroxy-4-methoxy benzoic acid (500 μg/kg/day) for 7 weeks by oral intubation and compared with glibenclamide, a standard hypoglycemic agent (100 mg/kg). The erythrocyte membrane was isolated and the activity of Na+/K+-dependent ATPases, Ca2+-ATPases, Mg2+-ATPases were determined. Superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase, vitamins C, vitamin E, plasma reduced glutathione and erythrocyte glutathione, reduced glutathione content in the tissues was also assayed. Administration of 2-hydroxy-4-methoxy benzoic acid to diabetic rats significantly (F>0.05 and P<0.001) elevated the activity of total ATPases, Na+/k+ ATPase, Mg2+ ATPase and Ca2+ ATPase to near normal level. The activities of catalase, superoxide dismutase and glutathione peroxidase and glutathione-S-transferase in erythrocytes were decreased significantly (F>0.05; P<0.001) in diabetic rats. Diabetic rats treated with 2-hydroxy-4-methoxy benzoic acid showed a significant (F>0.05; <0.001) increase in the enzymic antioxidants in erythrocytes. The elevated levels of vitamin E and low level of vitamin C and glutathione level in plasma and erythrocytes were observed in diabetic rats when compared to control rats and were restored significantly (F>0.05; P<0.001) after the administration of 2-hydroxy-4-methoxy benzoic acid. This study concludes administration of 2-hydroxy-4-methoxy benzoic acid supports the restoration of antioxidant defence, reduces the free radial production, lipid peroxidation and the glycosylation of haemoglobin in diabetic rats.

Protective effect of dietary ginger on antioxidant enzymes and oxidative damage in experimental diabetic rat tissues

The role of oxidative stress has been reported in various diabetic complications. This study was undertaken to evaluate the protective effect of ginger, a medicinal plant, on the tissue antioxidant defence system and lipid peroxidative status in streptozotocin-induced diabetic rats. An increased reactive oxygen species and insufficient antioxidant activity are associated with diabetes mellitus, which is mainly responsible for diabetic pathogenesis. The role of ginger as antioxidant markers of liver and kidney were investigated. The antioxidant effect of the ginger was compared with glibenclamide, a well-known hypoglycaemic drug. The diabetic rats exhibited lower activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GP x), and glutathione reductase (GR) and reduced glutathione (GSH) content and higher level of malondialdehyde (MDA) in hepatic and renal tissues as compared with normal rats. The activities of all parameters were found to be increased, except MDA in ginger-treated diabetic rats, in hepatic and renal tissues. Ginger supplementation, for 30 days to diabetic rats, resulted in significant dose-dependent hypoglycaemic and antioxidant activities. These findings suggest that ginger treatment exerts a therapeutic protective effect in diabetes by decreasing oxidative stress, and hepatic and renal damage.

Biochemical evaluation of the protective effect of Aegle marmelos (L.), Corr. leaf extract on tissue antioxidant defense system and histological changes of pancreatic β-cells in streptozotocin-induced diabetic rats

Oxidative stress is produced under diabetic conditions and is likely involved in the progression of pancreatic damage found in diabetes. This study was undertaken to evaluate the protective effect of Aegle marmelos leaf extract, a medicinal plant, on the tissue antioxidant defense system and lipid peroxidative status in streptozotocin-induced diabetic rats. Ethanol extract of A. marmelos was administered orally for 30 days (150 mg/kg body weight/day) to diabetic rats. Activity of the three primary scavenger enzymes (superoxide dismutase, catalase, and glutathione peroxidase), levels of glutathione, and lipid peroxidation were estimated in plasma and pancreas of diabetic rats and compared to the reference drug, glibenclamide (600 µg/kg body weight/day). A significant increase in the levels of plasma glucose, vitamin E, ceruloplasmin, lipid peroxides, and a concomitant decrease in the levels of vitamin C and reduced glutathione were observed in diabetic rats. The activities of antioxidant enzymes were altered in diabetic rats. These alterations were reverted back to near normal levels after treatment with A. marmelos and glibenclamide. Histopathological studies also revealed the protective effect of A. marmelos on pancreatic β-cells. The present study indicates that extract of A. marmelos modulates the activity of enzymic and nonenzymic antioxidants and enhances the defense against reactive oxygen species–generated damage in diabetic rats.

Combined Treatment of Rutin and Vitamin C Improves the Antioxidant Status in Streptozotocin-Induced Diabetic Rats

Combined Treatment of Rutin and Vitamin C Improves the Antioxidant Status in Streptozotocin-Induced Diabetic Rats

Bacopa monnieri modulates antioxidant responses in brain and kidney of diabetic rats

Role of oxidative stress has been reported in various diabetic complications including neuropathy, nephropathy and cardiopathy. This study was undertaken to evaluate the protective effect of Bacopa monnieri, a medicinal plant, on tissue antioxidant defense system and lipid peroxidative status in streptozotocin-induced diabetic rats. Extract of B. monnieri was administered orally, once a day for 15 days (at doses 50, 125 and 250 mg/(kg bw)) to diabetic rats. Activity of antioxidant enzymes (SOD, Catalase, and GPx), levels of GSH and lipid peroxidation were estimated in kidney, cerebrum, cerebellum and midbrain of diabetic rats and compared to reference drug, Glibenclamide. Administration of plant extract to diabetic rats showed significant reversal of disturbed antioxidant status and peroxidative damage. Significant increase in SOD, CAT, GPx activity and levels of GSH was observed in extract treated diabetic rats. The present study indicates that extract of B. monnieri modulates antioxidant activity, and enhances the defense against ROS generated damage in diabetic rats.

Indian herbs result in hypoglycemic responses in streptozotocin-induced diabetic rats

Abstract The main aim of this study was to evaluate the protective effect of selected Indian herbal hypoglycemic agents on oxidative stress and antioxidant status in streptozotocin-induced diabetic rats. Oral administration of aqueous extracts of Momordica charantia , Allium sativum , Azadirachta indica , and Ocimum sanctum led to marked lowering of blood sugar level in diabetic rats. Free radical–induced lipid peroxidation is associated with numerous disease processes, including diabetes mellitus. Our results revealed an increased level of plasma lipid peroxide associated with diminution of the corresponding antioxidant enzymes in red blood cells, namely, catalase, glutathione reductase, glutathione peroxidase, and superoxide dismutase after marked depletion of glutathione in diabetic rats. Treatment with herbal hypoglycemic agents, that is, M charantia , A sativum , A indica , and O sanctum , not only inhibited the process of lipid peroxidation but also significantly reactivated the antioxidant enzymes and restored glutathione levels in the rat model. We conclude that the herbal plants tested possess both antidiabetic and antioxidative activities and that their proper use in diet may help decrease the oxidative load in diabetes mellitus. Furthermore, these herbs might help in minimizing diabetic-related complications such as diabetic retinopathy, neuropathy, and nephropathy.

Effect of Coccinia indica leaves on antioxidant status in streptozotocin-induced diabetic rats

The antioxidant effect of an ethanolic extract of Coccinia indica leaves, an indigenous plant used in Ayurvedic medicine in India, was studied in Streptozotocin-diabetic rats. Oral administration of Coccinia indica leaf extract (CLEt) (200 mg/kg body weight) for 45 days resulted in a significant reduction in thiobarbituric acid reactive substances and hydroperoxides. The extract also causes a significant increase in reduced glutathione, superoxide dismutase, catalase, glutathione peroxidase and glutathione-S-transferase in liver and kidney of streptozotocin diabetic rats, which clearly shows the antioxidant property of CLEt. The effect of CLEt at 200 mg/kg body weight was more effective than glibenclamide

Effect of Insulin Treatment or Zinc Supplementation on Vitamin A Status in Streptozotocin-Induced Diabetic Rats.

A Using streptozotocin-induced diabetic rats, we examined the effects of zinc supplementation and insulin treatment on the metabolic availability of vitamin A. All diabetic animals exhibited an elevated plasma glucose (>18 mmol/liter) level within 48 h of intravenous streptozotocin injection. The untreated diabetic rats exhibited a reduction in body weight gain, with a 50% increase in daily food intake. In diabetic animals treated with insulin for 4 weeks, the plasma glucose, body weight gain, and daily food intake were comparable to those of the non-diabetic controls. The plasma concentration of vitamin A was significantly reduced in the diabetic animals, whereas the hepatic content of vitamin A in them was significantly elevated. Treatment with implantable insulin resulted in both plasma and liver concentrations of vitamin A returning to the control non-diabetic levels. Dietary zinc supplementation (120 µg/g diet for 4 weeks) failed to improve the plasma concentration of vitamin A. These results suggest that the impaired metabolic availability of vitamin A in the presence of diabetes is caused by insulin deficiency.