Need for dietary control by caloric restriction in rodent toxicology and carcinogenicity studies

The conditions under which laboratory animals are maintained can powerfully influence the results of toxicological studies utilized for risk assessment. Nutrition is of importance in toxicological bioassays and research, because diet composition and the conditions under which it is fed can affect the metabolism and activity of xenobiotic test substances and alter the results and reproducibility of long‐term studies. It is known that ad libitum (AL) overfed sedentary laboratory rodents suffer from an early onset of degenerative disease and diet‐related tumors that lead to poor survival in chronic bioassays. AL‐fed animals are not well‐controlled subjects for any experimental studies. Examination of study‐to‐study variability in food consumption, body weight, and survival in carcinogenicity studies for the same strain or stock of rodents shows tremendous laboratory‐to‐laboratory variability. However, a significant correlation between average food (calorie) consumption, adult body weight, and survival has been clearly established. The use of moderate dietary restriction (DR) results in a better controlled rodent model with a lower incidence or delayed onset of spontaneous diseases and tumors. Operationally simple, moderate DR significantly improves survival, controls adult body weight and obesity, reduces age‐related renal, endocrine, and cardiac diseases, increases exposure time, and increases the statistical sensitivity of these expensive, chronic bioassays to detect a true treatment effect. A moderate DR regimen of 70‐75% of the maximum unrestricted AL food intake is recommended as a nutritionally intelligent, well‐established method in conducting well‐controlled toxicology and carcinogenicity studies.     

Diet, caloric restriction, and the rodent bioassay

The diet can significantly alter the results of toxicity and carcinogenicity studies. Ad libitum (AL) overfeeding of excessive calories to sedentary adult rodents is one of the most poorly controlled variables affecting the current rodent bioassay. AL-overfed rodents develop an early onset of adverse metabolic events, endocrine- disruptive degenerative diseases, and tumors that result in early morbidity and mortality. AL food consumption is extremely variable, but has a strong correlation with adult body weight, obesity, and survival. AL feeding of diets with modified protein, fiber, and energy content are not as effective as simple, moderate dietary (caloric) restriction (DR) in controlling these study variables. Moderate DR (70-75% of adult AL) is operationally simple and controls adult body weights, prevents obesity, and improves health and survival by reducing or delaying diet- related endocrine, renal, and cardiac diseases. Moderate DR provides a uniform rodent model, increases treatment exposure time, and increases the statistical sensitivity of these chronic bioassays to detect true treatment effects. Feeding a balanced diet by a moderate DR regimen of 70-75% of the maximum, unrestricted adult AL food intake is recommended for conducting well-controlled toxicity and carcinogenicity studies.      

The association of serum leptin with the reduction of food intake and body weight during electroacupuncture in rats

Previous studies indicate that acupuncture or electroacupuncture (EA) treatment reduces body weight and food intake in rats by increasing the level of anoretic peptides and decreasing that of orexigenic peptides in the hypothalamus. Considering a well-established role of leptin as a major regulator for feeding behavior in the hypothalamus, we hypothesized that EA might exert its effect via increasing serum leptin levels. In this study, we tested our hypothesis by evaluating the effects of EA on food intake and body weight, as well as on serum leptin levels in rats. Rats were randomly divided into 3 groups: AL (fed ad libitum with no treatments), Holder (fed ad libitum with daily holder restraint) and EA (fed ad libitum with daily holder restraint and 100 Hz EA stimulation) groups. During the four-week experimental period, daily food intake and body weight were measured. At the end of the experiment, levels of serum leptin and corticosterone, and plasma epinephrine (Epi) and norepinephrine (NE) were determined. Here we demonstrate that EA treatment indeed led to reduction of food intake and body weight, and to an increase of serum leptin levels. The level of Epi, NE, and corticosterone increased in the Holder group, but such increase in the level of aforementioned stress hormones was not observed in the EA group. Overall, our results suggest that EA treatment reduces food intake and body weight in rats possibly through increasing leptin levels, and that this effect of EA is not due to the stress caused by the daily holder restraint.     

Beneficial effect of moderate food restriction in toxicity studies in rats

Moderate food restriction (FR) has been established as a nutritionally appropriate and well-controlled method with long-term beneficial effects in conducting toxicity and carcinogenicity studies in rodents. This study describes the early effects of moderate FR on toxicity study parameters in rats and on the variability of these parameters. Physical signs, body weight, food and water consumption, and clinical pathology parameters were examined in a 4-week study in which rats were moderately food-restricted or fed ad libitum (AL). There were no diet-related differences in physical signs, hematology or urinalysis. FR-related changes were observed in body weight and serum biochemistry; however, most of the changes involved anti-aging alterations and/or physiological adjustment to FR. Moderate FR resulted in low variability and good reproducibility in body weight. The present results indicate that moderate FR does not impair study parameters and increases statistical sensitivity. Therefore, a moderate FR feeding regimen is beneficial not only for long-term but also for short-term toxicity studies in rats.     

Testicular effects of cyclohexylamine hydrochloride in the rat

Testicular effects of cyclohexylamine hydrochloride (CHA) were investigated in Wistar and Sprague-Dawley rats. Groups of 25 rats were fed diets containing 6000, 2000 and 600 ppm CHA for 90 days and in addition ad lib., pair-fed and paired-weight control groups were used to assess the role of reduced food intake in the development of testicular lesions.Rats fed diets containing 6000 and 2000 ppm CHA showed significant decreases in food consumption, body weight and body weight gain. However, significant increases in the incidence of testicular lesions were found only in those animals fed 6000 ppm CHA. Absence of a similar incidence of lesions in either the paired-weight of pair-fed control groups indicated that inanition was not primarily responsible for the development of the lesions. The toxicological significance of these findings is discussed.     

Normal catch-up growth in rats severely food-restricted prior to lesions of the dorsomedial hypothalamic nucleus: the first 48 hours

Following a brief period of ad lib (AL) feeding, 45-day-old male Sprague-Dawley rats were either fed AL or food-restricted (REST) for 21 days to 50% of the intake of the AL rats. At this time, some AL and some REST rats received electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL), whereas other AL and REST rats were sham-operated (CON). Following this, all rats were refed (REF) AL and killed two days later. At this time, DMNL-REST + REF and DMNL-AL weighed as much as CON-REST + REF and CON-AL, whereas the body weight of the DMNL-AL group began to separate from the CON-AL group; carcass lipid and protein were normal among the groups. DMNL-AL laid down more % lipid and % protein/g food eaten than CON-AL; this was not the case in the REST + REF groups. DMNL-AL were hypophagic vs. CON-AL, but DMNL-REST + REF ate as much as CON-REST + REF. Compared to DMNL-AL, DMNL-REST + REF increased their food intake more than four-fold and also utilized food energy more efficiently than DMNL-AL rats. Epididymal fat pads and kidneys were smaller in REST + REF vs. AL groups, irrespective of brain manipulation. Plasma glucose and growth hormone were normal among the groups, but plasma insulin concentrations were higher in REST + REF DMNL and CON groups vs. DMNL-AL and CON-AL, respectively. Glucose incorporation into epididymal fat pad lipid and CO2 and liver lipid was elevated in REST-REF groups vs. respective AL groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of food restriction on hepatotoxicity of carbon tetrachloride in rats

Five-week-old Sprague-Dawley rats of both sexes were assigned to two types of feeding condition. One was fed ad libitum (AL) on commercial chow and another was fed a restricted amount of the chow (FR), approximately 75% of that fed in the AL condition. In each feeding condition, animals were orally administered carbon tetrachloride (CCl4) at levels of 0 (control), 0.1 or 0.2 ml/kg 6 days a week for 8 weeks. Lesions of the liver (hepatic cellular degeneration and fibrosis) and of the kidney (proximal tubular vacuolation and glomerular sclerosis) induced by CCl4 were aggravated in the FR group. The FR-control showed a higher metabolic activity of aniline in the liver than the AL-control group. Plasma lipid-peroxide (LPO) level was higher in the AL-control group than in the FR-control group. With CCl4 0.2 ml/kg treatment, however, the plasma LPO level was reversed between the AL and the FR groups. Taking together these somewhat unexpected results, it was concluded that (1) 25% food restriction increases toxicity of repeatedly administered CCl4 in rats, and (2) aggravation of CCl4 toxicity may be partly due to enhanced metabolic activation of CCl4 resulting from food restriction.     

The effects of reduced dietary intake upon the body and organ weights, and some clinical chemistry and haematological variates of the young Wistar rat

Two groups, one of each sex, of 5-week-old Wistar rats were fed ab lib for 5 weeks with a commercial diet (LAD 2). Four other groups of each sex, were given the same diet daily; each male received 21, 19, 17 or 15 g and each female 17, 16, 15 or 13 g. In a second experiment, in addition to the groups fed ad lib, each day for 5 weeks males were given 30 ('daily ad lib' group), 23, 22 or 21 g and females 25 ('daily ad lib' group), 19, 18 or 17 g. Rats, particularly males, fed ad lib showed differences, e.g. in body weight, with rats fed 'daily ad lib' even though food consumption was similar. Rats fed reduced amounts of diet had smaller livers, increased haemoglobin concentration, erythrocyte count, haematocrit, and plasma chloride. These rats excreted an increased volume of more alkaline urine of lower specific gravity with more precipitated triple phosphate than rats fed ad lib. In the comparisons of the modestly reduced food intake groups with the ad lib groups the significant decreases found in plasma protein, urea and alkaline phosphatase activity probably arose mainly from differences in post-prandial intervals. In groups where the reduction in food intake was greater, the decreases observed were not wholly dependent upon the post-prandial interval.     

Mechanisms of increased liver tissue repair and survival in diet-restricted rats treated with equitoxic doses of thioacetamide.

Moderate dietary or caloric restriction (DR) modulates animal physiology in a beneficial fashion. Previously, we have reported an equitoxic dose experiment where liver injury in DR male Sprague-Dawley rats exposed to a low dose of thioacetamide (TA, 50 mg/kg) was similar to that observed in ad libitum fed (AL) rats exposed to a 12-fold higher dose (600 mg/kg). Paradoxically, the AL rats experienced 90% mortality while all of the DR rats, with the same amount of initial bioactivation-mediated liver injury, survived. The protection observed in the DR rats was due to efficient compensatory liver tissue repair, which was delayed and attenuated in the AL rats, leading to progression of liver injury. The objective of the present study was to investigate the molecular mechanisms of the enhanced tissue repair in the DR rats upon equitoxic challenge with TA. Promitogenic mechanisms and mediators such as proinflammatory cytokines (TNF-alpha and IL-6), growth factors (TGF-alpha and HGF), and inducible nitric oxide synthase (iNOS) were estimated over a time course after equitoxic challenge (50 mg/kg to DR vs. 600 mg/kg to AL rats). Except for TNF-alpha, all other molecules were expressed earlier and in greater amount in the DR rats. IL-6 was 10-fold greater and peaked 12 h earlier; HGF also peaked 12 h sooner in the DR rats, when it was 2.5-fold greater than the value in the AL rats. TGF-alpha expression in livers of DR rats increased after TA administration and peaked at 24 h. In the AL rats, it was lower and peaked at 36 h. Diet restriction alone induced iNOS 2-fold in the DR rats and remained elevated until 12 h after TA administration, then declined thereafter. The lower iNOS activity in the AL rats further decreased after TA injection. DR rats exhibited higher apoptosis after thioacetamide administration, which further increased the efficiency of tissue repair. Taken together, these data indicate that even though the liver injury is near equal in AL and DR rats, sluggish signal transduction leads to delayed liver regeneration, progression of liver injury, and death in the AL rats. The equitoxic dose experiment indicates that stimulation of tissue repair is independent of the extent of initial liver injury and is governed by physiology of diet restriction. DR stimulates promitogenic signaling leading to a quick and timely response upon liver injury, arrest of progressive injury on one hand, and recovery from injury on the other, paving the way for survival of the DR rats.     

Effect of chronic ethanol ingestion on the metabolism of copper, iron, manganese, selenium, and zinc in an animal model of alcoholic cardiomyopathy

Alcoholic cardiomyopathy (AC) is one of the diseases caused by alcohol abuse, and there has been considerable debate about the possibility that nutritional factors may be important in the etiology of AC. In addition, there is evidence that ethanol may affect the metabolism of trace elements. The purpose of this investigation was to determine if chronic ethanol administration produces changes in the metabolism of the essential metals copper, iron, manganese, zinc, and selenium using an animal model of AC. Eighteen male Sprague-Dawley rats were divided into three groups: an ad libitum control group (AL), a pair-fed control group (PF), and an ethanol-dosed group (ETOH). The latter group received gradually increasing concentrations (5-25%) of ethanol in the drinking water for 15 wk. Food intake was monitored and urine and feces collected for a 4-d period during the study to determine ethanol effects on trace-element balance. Growth of both the PF and ETOH animals was inhibited. Ethanol produced substantial increases in liver manganese and decreases in liver copper and zinc. Metal concentrations in heart and concentrations in other tissues studied (spleen, testes, brain, bone, kidney, and muscle) did not differ significantly among the groups, except for testes selenium and kidney zinc. Reduced food intake and ethanol ingestion were associated with a reduced percentage of ingested selenium excreted in the urine. Deficiencies of copper, iron, manganese, selenium, and zinc in myocardial tissue are not likely to be involved in the pathogenesis of AC in the rat.     

Temporal Changes in Tissue Repair Permit Survival of Diet-Restricted Rats from an Acute Lethal Dose of Thioacetamide

Although, diet restriction (DR) has been shown to substantiallyincrease longevity while reducing or delaying the onset of agerelateddiseases, little is known about the mechanisms underlying thebeneficial effects of DR on acute toxic outcomes. An earlierstudy (S. K. Ramaiah et al., 1998, Toxicol. Appl. Pharmacol.150, 12–21) revealed that a 35% DR compared to ad libitum(AL) feeding leads to a substantial increase in liver injuryof thioacetamide (TA) at a low dose (50 mg/kg, ip). Higher liverinjury was accompanied by enhanced survival. A prompt and enhancedtissue repair response in DR rats at the low dose (sixfold higherliver injury) occurred, whereas at equitoxic doses (50 mg/kgin DR and 600 mg/kg in AL rats) tissue repair in AL rats wassubstantially diminished and delayed. The extent of liver injurydid not appear to be closely related to the extent of stimulatedtissue repair response. The purpose of the present study wasto investigate the time course (0–120 h) of liver injuryand liver tissue repair at the high dose (600 mg TA/kg, ip,lethal in AL rats) in AL and DR rats. Male Sprague-Dawley rats(225–275 g) were 35% diet restricted compared to theirAL cohorts for 21 days and on day 22 they received a singledose of TA (600 mg/kg, ip). Liver injury was assessed by plasmaALT and by histopathological examination of liver sections.Tissue repair was assessed by [³H]thymidine incorporation intohepatonuclear DNA and proliferating cell nuclear antigen (PCNA)immunohistochemistry during 0–120 h after TA injection.In AL-fed rats hepatic necrosis was evident at 12 h, peakedat 60 h, and persisted thereafter until mortality (3 to 6 days).Peak liver injury was approximately twofold higher in DR ratscompared to that seen in AL rats. Hepatic necrosis was evidentat 36 h, peaked at 48 h, persisted until 96 h, and returnedto normal by 120 h. Light microscopy of liver sections revealedprogression of hepatic injury in AL rats whereas injury regressedcompletely leading to recovery of DR rats by 120 h. Progressionof injury led to 90% mortality in AL rats vs 30% mortality inDR group. In the surviving AL rats, S-phase DNA synthesis wasevident at 60 h, peaked at 72 h, and declined to base levelby 120 h, whereas in DR rats S-phase DNA synthesis was evidentat 36 h and was consistently higher until 96 h reaching controllevels by 120 h. PCNA studies showed a corresponding increasein cells in S and M phase in the AL and DR groups. DR resultedin abolition of the delay in tissue repair associated with thelethal dose of TA in ad libitum rats. Temporal changes and highertissue repair response in DR rats (earlier and prolonged) arethe conduits that allow a significant number of diet restrictedrats to escape lethal consequence.     

Regional difference of ROS generation, lipid peroxidaton, and antioxidant enzyme activity in rat brain and their dietary modulation

One of the potential causes of age-related neuronal damage can be reactive oxygen species (ROS), as the brain is particularly sensitive to oxidative damage. In the present study, we investigated the effects of aging and dietary restriction (DR) on ROS generation, lipid peroxidation, and antioxidant enzymes in cerebrum, hippocampus, and cerebellum of 6-, 12-, 18-, and 24-month-old rats. ROS generation significantly increased with age in cerebrum of ad libitum (AL) rats. However, no significant age-difference was observed in hippocampus and cerebellum. DR significantly decreased ROS generation in cerebrum and cerebellum at 24-months. On the other hand, the increased lipid peroxidation of AL rats during aging was significantly reduced by DR in all regions. Our results further showed that catalase activity decreased with age in cerebellum of AL rats, which was reversed by DR, although SOD activity had little change by aging and DR in all regions. In a similar way, glutathione (GSH) peroxidase activity increased with age in cerebrum of AL rats, while DR suppressed it at 24-months. These data further support the evidence that the vulnerability to oxidative stress in the brain is region-specific.     

Upregulated promitogenic signaling via cytokines and growth factors: potential mechanism of robust liver tissue repair in calorie-restricted rats upon toxic challenge.

Previously we reported that moderate calorie restriction or diet restriction (DR, calories reduced by 35% for 21 days) in male Sprague-Dawley rats protects from a lethal dose of thioacetamide (TA). DR rats had 70% survival compared with 10% in rats fed ad libitum (AL) because of timely and adequate compensatory liver cell division and tissue repair in the DR rats. Further investigation of the mechanisms indicate that enhanced promitogenic signaling plays a critical role in this stimulated tissue repair. Expression of stimulators of promitogenic signaling interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS), hepatocyte growth factor (HGF), transforming growth factor-alpha (TGF-alpha), and epidermal growth factor receptor (EGFR) were studied during liver tissue repair after TA-induced liver injury. Plasma IL-6 was significantly higher in the DR rats, with 6-fold higher expression at 48 h after TA administration. Immunohistochemical localization revealed significantly higher expression of IL-6 in the hepatic sinusoidal endothelium of DR rats. Expression of TGF-alpha and HGF was consistently higher in the livers of DR rats from 36 to 72 h. EGFR, which serves as a receptor for TGF-alpha, was higher in DR rats before TA administration and remained higher till 48 h after TA intoxication. DR-induced 2-fold increase in hepatic iNOS activity is consistent with early cell division in DR rats after TA challenge. These data suggest that the reason behind the higher liver tissue repair after TA-induced hepatotoxicity in DR rats is timely and higher expression of the growth stimulatory cytokines and growth factors. It appears that the physiological effects of DR make the liver cells vigilant and prime the liver tissue promptly for liver regeneration through promitogenic signaling upon toxic challenge.     

The effects of chronic nicotine on meal patterns, food intake, metabolism and body weight of male rats

It is unclear what contribution food intake and metabolism have in causing weight loss after administering a dose of nicotine equivalent to smoking one to three packs of cigarettes per day because previous studies have been of a very short duration. To address this question, male Sprague Dawley rats were housed in computerized food intake modules and fed 45 mg pellets: Group 1 [nicotine injected with 1.4 mg/kg/day (free base), fed ad libitum]; and Group 2 [saline injected and pair-fed by computer with Group 2]; and Group 3 [saline injected (i.p.), fed ad libitum]. The rats received 4 equally spaced injections over the dark phase. Treatment consisted of: Phase 1 (nicotine or saline for 14 days), Phase 2 (all rats saline for 8 days and Phase 3 (pair-fed group “unyoked” for 6 days)). Nicotine inhibited food intake over the first 6 days. On termination of nicotine, there was no compensatory hyperphagia in either Groups 1 or 2; and their body weight was reduced starting on day 5 until day 28. In another study, rats were housed in an indirect calorimetry system. Saline or nicotine was injected for 14 days, as noted above; then all rats were injected with saline for 4 days and then no injections for 10 days to follow changes in body weight. Energy expenditure (Kcal/Kg^0.75) was measured for 18 days. Nicotine significantly reduced food intake on 7 of 14 days of nicotine injections. The body weight of the nicotine injected rats was significantly reduced starting on day 3 until day 25. There were no differences in energy expenditures of the groups, which suggested that a decrease in food intake and not an increase in metabolism was the reason the rats lost weight after administering nicotine.     

Evaluation of teratogenic potential of sodium sulfite in rats

The teratogenicity of sodium sulfite was examined in Wistar rats. The pregnant rats were fed diets containing 5, 2.5, 1.25, 0.63 or 0.32% of sodium sulfite heptahydrate(Na2SO3.7H2O) ad libitum from day 8 to 20 of pregnancy. Maternal toxicity, as evidenced by decreased body weight gain and decreased food consumption was observed at the 5% group, but no clinical signs of toxicity were observed. A significant reduction in the fetal body weight of both sexes was observed in all dose groups except 2.5% group. No significant differences in the numbers of live fetuses and intrauterine death (dead fetuses and resorptions) or sex ratios of fetuses were found between the sodium sulfite-treated and control groups. Fetal external, skeletal and internal malformations were not observed at any dose level. However, several types of skeletal and internal variations as well as delayed ossifications were observed in some groups treated with sodium sulfite, but the incidences were not significantly different from controls. Also, some fetuses with dilatation of the renal pelvis and the lateral ventricle were found in all groups except 1.25% group, but there was no dose-response. The live birth index and survival rate of offspring within 4 weeks and their body weight gain at 3 weeks after birth were not affected by sodium sulfite-treatment. In conclusion, sodium sulfite (0, 0.32, 0.63, 1.25, 2.5 or 5.0% as Na2SO3.7H2O) administered in the diet to Wistar rats during days 8-20 of pregnancy produced related signs of fetal toxicity but no evidence of teratogenicity.     

A 13-week sub-chronic dietary toxicity study of a cruciferin-rich canola protein isolate in rats

The objective was to evaluate the safety of a cruciferin-rich canola protein isolate (Puratein^®) when fed as a protein source at various dietary levels to rats for 13-weeks. The study included four groups (20 animals/sex/group) of young Sprague Dawley rats. They were fed ad libitum with an AIN-93 G based protein-free diet added respectively with 5%, 10% and 20% (w/w) Puratein^® (test article) or 20% (w/w) vitamin-free casein (control article). Protein levels were adjusted in all groups at 18% using vitamin-free casein. Body weights, food consumption, locomotor activity and behavioral and clinical pathology parameters were recorded at various points of the study, followed by macroscopic examination, determination of organ weights and microscopic tissue examination. There were no test article-related effects on body weight, food consumption, clinical observations, functional observational battery, motor activity, clinical pathology, or ophthalmic examinations. A slightly higher thyroid/parathyroid weight (g/100 g BW) noted in the 20% Puratein^® group was not correlated with histopathological changes. The no-observed-effect-level (NOEL) was 10%, whereas the no-observed-adverse-effect-level (NOAEL) was the highest fed level of 20%, equivalent to 11.24 g/kg BW/day for males and 14.11 g/kg BW/day for females. The cruciferin-rich canola protein isolate (Puratein^®) was considered safe under the conditions tested.     

Effects of undernutrition on transit time and body weight of rats.

Rats given 50% and 25% of their ad lib food intake were taken as undernourished, while those on ad lib intake served as controls. Water was given ad lib for all rats. Body weight of all rats was measured daily. It showed decrease in undernourished groups but not to the extent expected from calorie intake. Fifty tiny (1-2 mm) orange coloured plastic markers mixed with food were given to all rats, at 11.00 p.m., and were collected from faeces at regular intervals of 1 h each till 80% of markers were obtained. Period (hrs) for collection of 80% markers was taken as total transit time. It showed increase with increased undernutrition (ad lib 38.9 +/- 2.1 hrs, 50% cal 68.2 +/- 5.3 hrs, 25% cal 105.00 +/- 3.3 hrs). Delayed transit time in the undernourished by prolonging contact period between food and absorptive surface of intestine probably caused increase in absorption of nutrients and thus counteracted against the loss in body weight of underfed rats.     

Effects of methylphenidate on food and water consumption at different body weights.

The effects of intraperitoneally administered methylphenidate at 0, 1.5, 3.0, 6.0, and 12.0 mg/kg were studied in two experiments. Experiment 1 determined the effects of methylphenidate on 0.5, 1.0, 2.0, and 24 hr post injection food and water consumption in rats at ad lib feeding body weights. Experiment 2 determined the post injection effects of methylphenidate on 0.5, 1.0 and 2.0 hr food and water and 24 hr water consumption in rats maintained at 80% ad lib feeding body weight due to partial food deprivation. The results of Experiment 1 indicate that when animals are feeding ad lib at normal body weight food and water consumption is decreased for 2 hr following the administration of the lowest 1.5 mg/kg dose of methylphenidate. Methylphenidate in doses as high as 12.0 mg/kg has no effect on 24 hr food and water consumption under these conditions. The results of Experiment 2 indicate that when animals are maintained at reduced body weight due to partial food deprivation, food consumption for 2 hr is significantly decreased by the highest, 12.0 mg/kg, dose of methylphenidate. These effects are observed within the first 30 min post injection when methylphenidate decreases food consumption in a dose dependent manner. Methylphenidate has no effect on water consumption under these conditions. The effects of methylphenidate on ingestive behavior are discussed in terms of previous experiments and the possible differential effects on motor activity at different body weights under different stimulus conditions.     

Ethanol administration in the drinking fluid to pregnant rats as a model for the fetal alcohol syndrome

Addition of ethanol (ET) to the drinking fluid of pregnant rats has been questioned as an experimental model for the fetal alcohol syndrome (FAS). This model, however, closely simulates human alcohol intake, and in this study we used a modified version of previous protocols to overcome their major defects. A group of female rats was given 10% ET in drinking fluid for one week, 15% for the second week, 20% for the third, and 25% for the fourth, at the end of which they were mated with non-treated males and given 25% ET throughout gestation. Three groups of non-ET treated sex and age-matched rats were studied in parallel: (1) normal controls receiving solid diet ad lib, (2) paired fed rats, and (3) rats fed ad lib the solid diet mixed with 50% fiber. In the ET group, food intake decreased as ET consumption augmented, the ET calories comprising over 30% of the total energy intake during pregnancy. Total energy intake was similar for ET group and normal controls, and was higher than in paired fed animals or those on 50% fiber diet. Body weight gain in ET rats was similar to those on 50% fiber diet, lower than in normal controls and higher than in paired fed animals. At the 21st day of gestation, rats on ET had plasma ethanol levels of 147 +/- 18 mg/dl and higher plasma osmolality than in the other groups studied. In ET rats, fetal body weight was lower than in either normal controls or rats on 50% fiber diet, and fetal body length was shorter than in any other group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of ethanol on pregnant rats and their offspring

Pregnant rats were intubated with either 1.0 or 2.0 g/kg of ethanol daily throughout gestation. Pair-fed vehicle-treated, and nontreated rats fed ad libitum, served as control groups for ethanol-treated animals. Ethanol treatment reduced food and water consumption and attenuated the gain in body weight of pregnant animals relative to nontreated animals fed ad libitum. Litter size, litter weight, and the mean weight per pup were reduced in both the ethanol-treated and pair-fed control groups. There was no evidence of gross malformations in any of the offspring. Since the reduction in litter size and litter weights did not differ significantly between ethanol-treated and pair-fed controls, the effects of treatment with ethanol appeared to be related to a reduction in maternal intake of calories rather than to the direct effect of ethanol on the developing fetus.There were no significant differences between any of the groups of offspring on one-way shock avoidance learning, water maze escape learning, spontaneous alternation, or brightness discrimination learning in tests beginning at 75 days of age. Thus, at the doses of alcohol used in this study, there was no evidence of behavioral teratogenesis comparable to that reported for higher doses in animals or in man characterized by the fetal alcohol syndrome.