Toxic effects of warfarin in rats fed different diets

Toxic doses of warfarin were administered (0.8 mg/kg, po) daily for 5 days to one group of rats (250–300 g) fed oat groats and to another fed Purina laboratory chow. Five rats from each dietary group were sacrificed at 5, 29, 53, 77 and 101 hr after the initial dose. The plasma warfarin concentration increased more rapidly in the oat-fed rats than in those fed chow; however, the liver warfarin: plasma warfarin ratio following the first dose of warfarin indicated that the chow-fed rats were removing the warfarin from the plasma more rapidly. Presumably, the rate of metabolism of warfarin was more rapid in the chow-fed than in the oat-fed rats because the prothrombin times in the former increased at a slower rate. Apparently, less liver damage occurred in the chow-fed rats because they had lower plasma fibrinogen concentrations than those fed oats. There was a 50% decline in the hematocrit values in both groups. The linear decline in the total plasma protein in each group was a function of linear declines in plasma albumin and α-globulin. In both groups, the β- and γ-globulins remained stable until 101 hr, at which time they increased. It was concluded that the response of rats to repeated toxic oral doses of warfarin was influenced by protein in the diet; rats fed higher protein diets were more tolerant to warfarin.     

Liver and plasma levels of descarboxyprothrombin (PIVKA II) in vitamin K deficiency in rats

Descarboxyprothrombin (PIVKA II) is a precursor of prothrombin without biological activity, and it increases with vitamin K deficiency. We studied the time course changes in liver and plasma levels of PIVKA II during the progress of vitamin K deficiency in rats. Good correlation was observed between liver PIVKA II and plasma PIVKA II and between liver or plasma PIVKA II and plasma prothrombin in experiments in which rats were fed a vitamin K-deficient diet. Feeding of a vitamin K-deficient diet or fasting caused marked increases in liver and plasma PIVKA II in male rats and a weaker response in female rats. Warfarin, a vitamin K antagonist, caused an abrupt increase in liver PIVKA II, but the increase in plasma PIVKA II was delayed about 3 hr. Plasma prothrombin decreased from about 30 min later. Factor VII decreased similarly to prothrombin, and changes in the prothrombin time and activated partial thromboplastin time were slower than the changes in these substances. Sex differences were not seen in these warfarin actions. These observations indicate that liver and plasma PIVKA II are sensitive markers of vitamin K deficiency in rats, and assay of PIVKA II can be useful for analyzing the action mechanism of drugs which influence blood coagulation.     

Effects of DI-(2-ethylhexyl) phthalate on the content and composition of hepatic mitochondrial and microsomal phospholipids in the rat

Feeding a 20% casein diet containing di-(2-ethylhexyl) phthalate (DEHP) at a 0.5% level to young male rats for 7 days resulted in a significant increase in hepatic phospholipids (PL), based either on per unit weight of the liver or on protein. Although the concentration of PL increased in both the mitochondrial and the microsomal fractions, the magnitude of the increase was much more marked in the former. The increase of PL in hepatic microsomal and mitochondrial fractions was attributed to increases in phosphatidylethanolamine (PE) and phosphatidylcholine (PC). In terms of percentage composition, PE increased significantly, whereas PC remained unchanged, leading to an elevation in the PE/PC ratio in both fractions. A similar response was observed in rats fed 0.1 to 0.5% DEHP for 30 days. Although hepatic PL accumulation was observed in rats fed a diet containing different dietary levels of casein and corn oil, the extent of the increase was much greater on a low protein diet. DEHP caused a decrease in the concentration of hepatic triglycerides (TG), and the magnitude of the reduction appeared to be greater in rats fed diets containing zero or low levels of essential fatty acids. The fatty acid profiles of PE and PC were modified differently by DEHP. Of interest was a significant increase in arachidonic acid in PE and a decrease in PC in two subcellular fractions examined. The rate of swelling of isolated mitochondria from the livers of rats fed DEHP was markedly slower than that of the controls. Some structural changes were also observed by electron microscopy.     

Vitamin K reversible hypoprothrombinemia in rats. II. Efficacy of vitamin K on latamoxef-induced coagulopathy in rats

Feeding of a vitamin K-deficient diet caused the development of hypoprothrombinemic changes in rats such as prolongation of prothrombin time (PT) and activated partial thromboplastin time (APTT), decreases in plasma prothrombin and clotting factor VII levels, and an increase in the descarboxyprothrombin (PIVKA) level in both plasma and liver. Successive administrations of latamoxef (LMOX) to the vitamin K-deficient rats resulted in the further enhancement of these changes. After the development of hypoprothrombinemia with LMOX, a single subcutaneous injection of vitamin K1 normalized most of these abnormalities in blood coagulation parameters within 6 hr. When vitamin K was given at 200 micrograms/kg, PT, APTT and the plasma PIVKA level showed normal values for at least 8 days even when the animals were fed a vitamin K-deficient diet and treated with LMOX during the recovery period. The amount of vitamin K required to maintain most of the blood coagulation parameters in the normal range was about 3 micrograms/kg/day. The plasma level of vitamin K was higher than 0.3-0.5 ng/ml when the blood coagulation parameters were maintained in the normal range.     

Pharmacokinetics and pharmacodynamics of warfarin at steady state.

1 The relationship between warfarin dose, total and free plasma warfarin concentration, and anticoagulant effect was examined at several steady-state levels in fifteen patients during withdrawal of warfarin therapy. 2 Total plasma clearance was significantly correlated with the free fraction in plasma (r=0.955). 3 There was an age related decline in the dose of warfarin, and in the total and free plasma warfarin concentrations required to produce the same anticoagulant effect. However, neither total nor free plasma warfarin clearances varied with age. 4 Individual patients' log concentration-effect relationships were linear above a prothrombin ratio of 1.2 and there was a significant correlation (r=-0.586) between the slope and the free fraction of warfarin in plasma. It is suggested that plasma protein binding may reflect the interaction between warfarin and its effector site in the hepatocyte.     

Influence of dietary pectin on intestinal microfloral metabolism and toxicity of nitrobenzene

Intestinal microfloral metabolism of nitrobenzene is essential for the production of methemoglobin. Since dietary pectin alters intestinal microflora, these studies were designed to examine the effects of dietary pectin on nitrobenzene-induced methemoglobinemia. Male Fischer-344 rats were fed either AIN-76A (purified diet containing 5% cellulose), AIN-76A with 5% pectin replacing the cellulose, or NIH-07 (cereal-based diet containing 8.4% pectin) for 28 days. Following this period, nitrobenzene (200 mg/kg) was administered by gastric intubation, and methemoglobin concentrations were determined after 1, 2, 4, 8, and 24 hr. Nitrobenzene-induced methemoglobinemia was evident as early as 1 hr, peaked at 4 hr, and diminished thereafter in rats fed NIH-07 diet. In contrast, nitrobenzene-induced methemoglobinemia was not detectable in rats fed AIN-76A; however, inclusion of 5% pectin in this diet resulted in methemoglobinemia comparable to that of NIH-07-fed animals at 4, 8, and 24 hr. Administration of 400 or 600 mg/kg nitrobenzene resulted in significant diet-related differences in methemoglobinemia. Administration of 600 mg/kg nitrobenzene to animals fed NIH-07 resulted in the highest methemoglobin concentrations (64 ± 1%); those fed AIN-76A had the lowest (20 ± 5%), and those fed AIN-76A containing pectin had intermediate methemoglobin concentrations (44 ± 6%). No diet-related differences in the microbial population of the stomach or small intestine were observed. However, the number of anaerobes present in the ceca of rats fed AIN-76A containing pectin was 2 to 2.5 times greater than that of rats fed AIN-76A. In vitro reductive metabolism of [¹⁴C]nitrobenzene was significantly greater in the cecal contents of rats fed NIH-07 than that in the cecal contents of either of the groups fed the AIN-76A-based diets. These studies indicate that intestinal microfloral metabolism and red blood cell toxicity of nitrobenzene is markedly different in animals fed cereal-based versus purified diets. Furthermore, since inclusion of pectin into the purified diet diminishes the magnitude of these effects, differences in dietary composition of fermentable carbohydrates in cereal-based and purified diets may mediate differences in metabolism and toxicity of nitrobenzene.     

Behavioral effects of dietary cholesterol in rats tested in experimental models of mild stress and cognition tasks

Abnormalities in serum cholesterol levels of patients with mood disorders have been identified in epidemiological studies. However, evidence for an influence of dietary cholesterol on behavioral models is poor. Here, we investigated the behavioral changes of Wistar male rats fed a 2% cholesterol-enriched diet for 2 months in experimental models of depression and anxiety, such as the forced swim test (FST) paradigm and the novelty-induced grooming sampling test (NGT). The correlation between behavioral depression and impaired cognitive capacity was also examined testing rats in the Morris water maze (MWM) task one day after the FST. Different groups of rats fed various dietary regimens, were subjected to acute or repeated treatment (14 days) with clomipramine hydrochloride (50 or 25 mg/kg), diazepam (1 mg/kg) or with the peripheral benzodiazepine receptors (PBRs) antagonist, isoquinoline PK11195 (1 mg/kg) injected intraperitoneally (i.p.). Rats fed the cholesterol-enriched diet showed a significant decrease of grooming score in the NGT and of immobility time in the FST in comparison to animals fed a standard diet. Furthermore, the anxiolytic and antidepressant effects of diazepam and clomipramine were not affected by the different diets. Only after repeated treatment, PK11195 impaired the performance of animals fed a standard diet in the FST, and exhibited an anxiolytic-like profile in animals fed either the cholesterol-enriched or the standard diet. The improved performance in the FST was followed by a better learning performance in the acquisition phase of the MWM. These results suggest that effects of cholesterol-enriched diet on the behavioral reaction of rats in experimental models of mild stress may involve PBRs. They deserve attention in order to clarify the clinical correlation between plasma cholesterol levels and mood disorders in humans.     

Effects of cysteine on the pharmacokinetics of intravenous chlorzoxazone in rats with protein-calorie malnutrition

The effects of cysteine on the pharmacokinetics of chlorzoxazone (CZX) and one of its metabolites, 6-hydroxychlorzoxazone (OH-CZX), were investigated after intravenous administration of CZX, 25 mg/kg, to control rats (4-week fed on 23% casein diet) and rats with PCM (4-week fed on 5% casein diet) and PCMC (PCM with oral cysteine supplementation, 250 mg/kg, twice daily during the fourth week). In rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity (AUC) of OH-CZX (436 compared with 972 microgmin/ml) and the percentages of intravenous dose of CZX excreted in 8-h urine as OH-CZX (20.2 compared with 38.5%) were significantly smaller than those in control rats. The above data indicated that the formation of OH-CZX from CZX decreased significantly in rats with PCM due to a significant decrease in chlorzoxazone-6-hydroxylase activity (328 compared with 895 pmol/min/mg protein) in the rats. The results were expected since in rats with PCM, hepatic CYP2E1 expression and its mRNA levels decreased significantly as compared to control, and CZX was metabolized to OH-CZX primarily by CYP2E1 in rats. By cysteine supplementation (rats with PCMC), some pharmacokinetic parameters restored fully (hepatic microsomal chlorzoxazone 6-hydroxylation activity based on both mg protein and nmol CYP450) or partially (total body clearance and apparent volume of distribution at steady state of CZX, and AUC, terminal half-life and 8-h urinary excretion of OH-CZX) to control levels.     

Comparative pharmacokinetics of coumarin anticoagulants. XIV: relationship between protein binding, distribution, and elimination kinetics of warfarin in rats.

The relationships between the protein binding, distribution in the body, and kinetics of elimination of warfarin were studied. Individual rats eliminated warfarin by apparent first-order kinetics, with a biological half-life of 5.9-41 hr and a total plasma clearance of 2.4-22 ml kg(-1) hr(-1). There is a strong positive correlation between the apparent volume of distribution (Vd) and the elimination rate constant (kel). There was no apparent concentration dependance of warfarin binding to serum proteins over a wide concentration range, but there were pronounced intersubject variations in protein binding, with the free fraction of drug (f) in serum ranging from 0.172 x 10(-2) to 1.53 x 10(-2). There are strong positive correlations between f and kel, f and Vd, and f and the kidney-serum concentration ratio of warfarin. Consistent with theory, there is an excellent positive linear correlation between f and total plasma clearance of the drug. The intersubject variation in f is not related to variations in serum albumin or total protein concentration. There is a strong correlation between values of f for serum and liver homogenate in individual animals, consistent with the lack of correlation between f in serum and the liver-serum concentration ratio of warfarin. These results show that the pronounced intersubject variation in the elimination of warfarin observed in this investigation was related to interindividual differences in plasma protein binding of the drug. The differences in protein binding cannot be ascribed to differences in plasma protein concentrations and may reflect configurational differences of proteins or the presence of an endogenous displacing agent at different concentrations.     

Growth, liver lipid and blood amino acids in rats fed ethanol with an adequate diet

The weight, histology and RNA, DNA, protein and lipid content of the liver and arterial and portal plasma amino acid concentrations were determined in male Sprague-Dawley rats fed a liquid diet which met AIN-76A standards with 36% of the calories supplied by ethanol. The dietary components of the dry mixture in percentages by weight included 20% casein, 22% sucrose, 43% dextrin, 5% corn oil, vitamins, minerals and other dietary factors. For feeding these were suspended in distilled water containing 2.5% xanthan gum with or without ethanol to supply 1 kcal/ml. The feeding method employed perforated neoprene discs floated on top of the suspended diet to control evaporative losses. Animals were pair fed or ad libitum fed for 8-10 weeks. Gain/feed ratios were virtually identical for ethanol-fed rats and their pair-fed controls. Ethanol intake of ad libitum fed rats averaged 14.8, 10.3 and 7.4 g/kg BW/day after 1, 5 and 10 weeks, respectively. No chemical or histological evidence of liver fat accumulation or significant differences in arterial or portal amino acid concentrations were detected in animals fed ethanol. The lack of apparent ethanol toxicity is discussed in relation to the results of others and to our earlier report of increased orotic acid excretion by ethanol-fed rats.     

Noninvolvement of hypertriglyceridemia and hyperleptinemia in blood pressure increases induced by dietary lard in rats

We investigated whether hypertriglyceridemia and hyperleptinemia are involved in the development of increases in blood pressure induced by dietary lard. Rats received either chow alone or chow in which 50% of the energy content was from substituted lard. Each group was divided into two groups according to whether the diet included bezafibrate or not. In another series of experiments, rats were fed either chow alone or chow in which 50% of the energy content was from substituted lard, safflower oil, or sucrose. Systolic blood pressure (SBP) was measured every week during each 7-week feeding period. A steady-state plasma glucose method was used to determine insulin sensitivity after lard substitution with or without bezafibrate. After the 7-week feeding period, the plasma levels of glucose, immunoreactive insulin, triglyceride and leptin were measured. In rats fed with a high lard diet, SBP, plasma levels of immunoreactive insulin, triglyceride, leptin and steady-state plasma glucose concentrations significantly increased, compared with levels of these substances in controls. Bezafibrate treatment completely reversed these effects. In rats fed with a high safflower oil or a high sucrose diet, no significant change was seen in SBP and plasma immunoreactive insulin levels. However, the plasma triglyceride levels were increased by dietary lard or sucrose. Moreover, the plasma leptin level was also increased by dietary lard and safflower oil. Neither dietary hypertriglyceridemia nor hyperleptinemia were involved in the development of increases in blood pressure induced by dietary lard.     

The effects of age and dietary protein restriction on the pharmacokinetics of theophylline in the rat

The influence of dietary protein levels on theophylline kinetics was examined in male Fischer 344 virgin rats of 2, 14 and 20 months of age fed for four weeks on a 23% (control) or 5% (low) protein diet ad libitum. Protein deficiency led to a significant decrease in body weight gain for the 2 month old rats (10.9% versus 26.5%). In addition, decreases in total body weight of 7.5% and 15.3% were seen for the 14 and 20 month old rats, respectively, on a low protein diet. Total proteins and albumin levels in plasma were not significantly affected by age or dietary protein levels. After intravenous administration of 10 mg/kg aminophylline, the average mean residence time (MRT) was significantly longer in 20 month old rats as compared to the younger rats, while 14 month old rats had a greater elimination rate constant than the 2 and 20 month old rats. There were significant reductions in the mean steady-state apparent volume of distribution (Vss) in the 2 and 14 month old rats on a low protein diet of 31% and 18%, respectively, while there was no difference between the diets in 20 month old rats. In addition, the Vss decreased from 0.71 L/kg to 0.57 L/kg in the 2 and 20 month old rats, respectively, on a normal protein diet. Dietary protein deficiency led to a significant reduction of total body clearance from approximately 73 to 45 ml/hr/kg in the 2 and 14 month old rats.2+p     

Effects of dietary fats and proteins on rat testicular steroidogenic enzymes and serum testosterone levels.

It is known that certain dietary fats can modulate rat testosterone metabolism. In the current study we have investigated testicular steroidogenic enzyme activities and serum testosterone levels in rats fed diets containing either different protein sources (casein, fishmeal, whey) or different lipid sources (soybean oil, docosahexaenoic acid (DHA), seal oil, fish oil, lard). The diets examined reflect different marine oils and proteins which are significant components of Northern Canadian diets. Male rats (42-45 days old, 6 per group), were assigned to specific diets for 42 days. On the 43rd day of the study, rats were sacrificed and blood plasma and testes frozen (-80 degrees C) until analysis. Microsomal steroidogenic enzyme activities (3beta-HSD, 17-OHase, C-17,20-lyase, 17beta-HSD) were measured radiometrically. There were no differences in enzyme activities between the three dietary protein sources. In contrast, compared with the standard casein diet, all lipid sources caused reductions in C-17,20-lyase activity (>50%); seal oil and fish oil reduced 17-OHase activity (approximately 30%) and soybean oil, DHA fish oil and lard reduced 17beta-HSD activity (approximately 30%). No effect on 3beta-HSD activity was evident. Serum testosterone levels were determined using ELISA kits and were not affected by any diet with the exception of the soybean oil diet which was significantly elevated compared with the casein protein diet. Body and testis weights were not affected by diet. In conclusion, these data demonstrate that some dietary lipid sources caused reductions in testicular 17-OHase and C-17,20-lyase activities but not to the extent that serum T levels were affected, while soybean oil caused elevated serum testosterone in the absence of elevated steroidogenic enzyme activities.     

Vitamin K-reversible hypoprothrombinemia in rats: comparison of hypoprothrombinemic changes in various strains of rats caused by vitamin K deficiency and antibiotic treatment

Hypoprothrombinemic changes were compared in rats fed various vitamin K-deficient diets. Changes such as prolongation of prothrombin time and activated partial thromboplastin time, decrease in plasma levels of prothrombin and clotting factor VII, and increase in plasma descarboxyprothrombin, appeared in rats maintained on vitamin K-deficient diet, but in rats on ordinary diet (vitamin K-sufficient diet). As the development of hypoprothrombinemia was not significantly different among animals fed various vitamin K-deficient diets, the blood coagulation parameters were concluded to be regulated only by the vitamin K level. Following the development of hypoprothrombinemia, hemorrhaging in various organs was detected in vitamin K-deficient rats, with strain differences in the severity of hemorrhage; Fischer and Wistar strains were more sensitive than the Sprague Dawley strain. Administration of a beta-lactam antibiotic, latamoxef (LMOX), to vitamin K-deficient rats led to enhancement of the hypoprothrombinemic conditions, but LMOX-associated changes in plasma enzyme levels were not detected.     

Warfarin and metabolism of vitamin K1

To further examine the hypothesis that warfarin inhibits prothrombin synthesis by interfering with the cyclic interconversion of vitamin K₁ and phylloquinone epoxide, the metabolism of tracer doses of labeled vitamin K₁ was studied in anticoagulant-treated rats. A tracer dose of [³H]K₁ initially turned over with a half-life of 2.2 hr in the liver, but after 5 hr the degradation rate decreased considerably. Warfarin caused hepatic [³H]K₁ levels to drop to 50 per cent of controls 5 min after administration of the vitamin, and over 10 hr the concentration of [³H]K₁ was 26–36 per cent of control levels. This decrease in vitamin K₁ was not large enough to account for the inhibition of prothrombin synthesis by warfarin. Thirty-five min after warfarin administration, there was more [³H]phylloquinone epoxide in the liver than labeled vitamin and over 10 hr the [³H]epoxide: [³H]K₁ ratio varied from 1.6 to 3.0. In addition to increasing the relative amount of [³H]epoxide, warfarin and phenylindanedione also increased hepatic metabolites more polar than vitamin K₁ or epoxide. However, warfarin did not increase plasma or urinary radioactivity. The urine was the principal excretory route for metabolites of vitamin K₁. 2-Diethylaminoethyl-2,2, diphenylvalerate hydrochloride (SKF 525-A) inhibited the turnover of [³H]K₁ but did not decrease the [³H]polar metabolites in the liver in control or warfarin-treated rats. The drug also did not inhibit the epoxidation of the vitamin to phylloquinone epoxide. The metabolism of vitamin K₁ was not altered by vitamin K deficiency or chronic administration of the vitamin. After a small dose of warfarin (35 μg/100 g body wt), plasma prothrombin decreased for 14 hr and then slowly rose but did not reach 90 per cent of normal until 3 days after administration of anticoagulant. The epoxide: K₁ ratio in the liver, measured by injecting a tracer dose of [³H]K₁, was 0.90 at 6 hr when prothrombin synthesis was completely blocked. The ratio dropped to 0.52 just before prothrombin started to rise at 14 hr and remained around 0.5 during the slow climb of plasma prothrombin toward the normal level. These low ratios were unexpected in animals in which prothrombin synthesis was partially or completely blocked. Hepatic epoxide: K₁ ratios of 11.4 and 1.3 were observed in warfarin-treated rats in which prothrombin synthesis was stimulated by injections of 0.1 mg [³H]K₁ plus 0.4 mg [³H]epoxide and 0.1 mg [³H]K₁ respectively. Therefore, there appears to be a lack of correlation of epoxide: K₁ ratios and prothrombin synthesis.     

不同质量蛋白质对肾损害大鼠钙平衡的影响

目的：研究大豆蛋白对肾损害大鼠钙平衡的影响。方法：选择3月龄健康雄性SD大鼠40只，按体质量从小到大排序采用完全随机化原则分为4组，每组10只。标准饲料对照组：喂食含有14％酪蛋白饲料；大豆蛋白饲料组：喂食含有14％大豆分离蛋白饲料；混合饲料Ⅰ组：喂食含有7％酪蛋白加7％大豆分离蛋白饲料；混合饲料Ⅱ组：喂食含有7％酪蛋白加14％大豆分离蛋白饲料。实验期用腺嘌呤灌胃共21天建立肾损害大鼠模型，各组大鼠喂养相应饲料6周。测量指标：钙摄入量、尿钙、粪钙、血肌酐、尿素、白蛋白、钙、磷，骨钙。结果：大豆蛋白饲料组和混合饲料I组实验检测项目无明显统计学差异，与另外两组相比，血肌酐、尿素、磷低，血钙、钙表观吸收率、钙储留量和骨钙高，差异有统计学意义（P〈0．05）。结论：蛋白质含量水平在14％条件下，含大豆蛋白的饲料更有助于促进钙平衡。‘     

Influence of indometacin farnesil on blood coagulation. Comparison with indomethacin in normal rats and warfarin induced hypoprothrombinemic rats

The influence of indometacin farnesil (IMF), a prodrug of indomethacin, on blood coagulation was compared with indomethacin (Ind) in normal rats and warfarin treated rats. In normal rats, 30 mg/kg of Ind very markedly shortened the extrinsic coagulation time and decreased the hematocrit, GOT, GPT and ALP in plasma at 24 hr after administration, but 3 mg/kg of Ind and both 10 and 100 mg/kg of IMF did not influence any parameter. In warfarin treated rats, 2.5 mg/kg of Ind decreased the normal prothrombin level at 48 hr, and 10 mg/kg of Ind prolonged the blood coagulation time, decreased the normal prothrombin level and hematocrit, and increased the PIVKA-II level. Moreover, at 48 hr, 3 of 6 rats in the 10 mg/kg Ind-administered group died due to intestinal bleeding. IMF at all dosages examined did not affect any of the above parameters.     

Effects of Ginkgo biloba extract on the pharmacokinetics and pharmacodynamics of tolbutamide in protein-restricted rats

Objectives Effects of repeated administration of Ginkgo biloba extract on pharmacokinetics and pharmacodynamics of tolbutamide were examined in rats fed a low‐protein diet. Methods Rats were given a low (7% casein) or control (20% casein) protein diet for 21 days and administered Ginkgo biloba extract (100 mg/kg per day) for the last 5 days. Tolbutamide was co‐administered on the last day. Blood glucose and plasma tolbutamide concentrations were determined over the subsequent 12 h and the activity of hepatic cytochrome P450s were determined at 12 h after dosing. Key findings There were significant decreases in body weight, the ratio of liver to body weight, and plasma albumin concentrations in rats on the low‐protein diet compared with controls. The hypoglycaemic effect of tolbutamide was significantly greater and the concentration of the drug in plasma was higher in the former group. The repeated administration of Ginkgo biloba extract had little influence on the hypoglycaemic effect of tolbutamide, but tended to decrease the drug concentration in plasma of control rats, while it reduced significantly the hypoglycaemic action and plasma concentration of tolbutamide in the protein‐restricted rats. Conclusions The effects of Ginkgo biloba extract on the pharmacokinetics and pharmacodynamics of tolbutamide were significantly enhanced in rats on the low‐protein diet.     

Developmental immunotoxicity of lead in the rat: influence of maternal diet

The effect of maternal dietary protein intake on lead-induced developmental immunotoxicity was studied in female Fischer 344 rats receiving lead acetate (250 ppm) or sodium acetate (control) in the drinking water during breeding and pregnancy until parturition. Dams were fed isocaloric diets (either 20% casein or 10% casein) from 2 wk prior to mating until the end of lactation. After weaning, dams and female offspring were given the 20% casein diet and regular water. Immune function was assessed in dams at 8 wk postpartum and in offspring at 13 wk of age. Dams showed no marked difference in any of the immune endpoints examined, regardless of diet or lead treatment. In contrast, lead exposure during early development produced a subsequent significant reduction of both the delayed-type hypersensitivity response and interferon gamma production in adult offspring independent of maternal diet. Lead-exposed offspring from the high-dietary-protein group had significantly elevated production of both interleukin-4 and tumor necrosis factor alpha(TNF-alpha) with increased relative spleen weight and a decreased body weight compared to offspring in the lead control group. In contrast, lead-exposed offspring from dams receiving the low-protein diet had no marked change in TNF-alpha levels, relative spleen weight, or body weight, while interleukin-4 levels were significantly reduced compared with the lead control group. In conclusion, maternal dietary protein intake can modulate the immunotoxic effects of lead exposure during early development. This occurred at levels of protein intake and doses of lead exposure that produced no detectable effect on the maternal immune system.     

Retinoid-induced hemorrhaging and bone toxicity in rats fed diets deficient in vitamin K

The recent increase in the clinical use of synthetic vitamin A compounds has led to concern of possible side effects. Some of these effects are known to be influenced by dietary levels of vitamin K. We therefore compared the toxic effects of 13-cis-retinoic acid (13cisRA), retinyl acetate (ROAc), and N-(4-hydroxyphenyl)retinamide (4HPR) in male Sprague-Dawley rats maintained on diets containing different levels of vitamin K. Animals were fed either an NIH-07 diet supplemented with menadione (3.1 ppm vitamin K3), an NIH-07 diet not supplemented with menadione, or an AIN-076 purified diet devoid of vitamin K. The retinoids had no effect on prothrombin times of animals fed the supplemented diet. When menadione was omitted from the diet, however, 4HPR-dosed animals had elevated prothrombin times. This effect was observed as early as Day 7 and was accompanied by one confirmed hemorrhagic death. 13cisRA-dosed animals showed no change in prothrombin times. In the high-dose ROAc group, there was a twofold increase in prothrombin times but only after prolonged dosing. In animals fed the NIH-07 diets, 13cisRA and ROAc induced multiple bone fractures at all dose levels. In contrast, 4HPR administered at the highest dose induced only one fracture in one animal. Animals fed the purified diet lost weight faster and diet sooner than those maintained on the other diets. Bone fractures were not observed in these animals because of early deaths resulting from hemorrhaging. For all retinoid-dosed groups maintained on the purified diet, changes in prothrombin times occured as early as 1 week. The order of effect was 4HPR greater than ROAc greater than 13cisRA, with increases in prothrombin times correlating with increases in hemorrhagic deaths. Hence, the degree of retinoid-induced hemorrhage, but not the incidence of bone fractures, was inversely related to vitamin K levels in the diet. 13cisRA and ROAc, but not 4HPR, caused a dose-dependent reduction in plasma osteocalcin, an effect that correlated with retinoid-induced bone effects. In contrast, serum alkaline phosphatase was elevated in animals dosed with 13cisRA or 4HPR but not in those dose with ROAc. For this enzyme, the electrophoretic pattern on agarose gel showed a decrease, compared to controls, in the major isozyme in serum of ROAc-dosed animals. Hence, plasma osteocalcin is a better predictor of retinoid-induced bone effects than serum alkaline phosphatase.