Effect of type of protein on food intake of rats fed high protein diets

The effects of type of protein on intake of a high protein diet after adapting rats to a low protein diet were examined in rats trained to eat a 5.2% (N X 6.25) protein diet containing a mixture of casein, lactalbumin, egg white and soy protein, in a single 3-hour period per day. Food intake was measured from 0-15, 15-30, 30-90, and 90-180 minutes. After a 2-week adjustment period, rats were presented with a 40% (N X 6.25) protein purified diet containing only one of the 4 proteins mentioned above or a mixture of these 4 proteins. During the first 15-minute interval, rats eating diets containing protein mixture, lactalbumin, egg white or soy protein depressed their intake significantly compared with the average intake of the 3-day pre-test period, whereas rats eating casein diet increased their intake. During the last 90-minute interval of the first day, all rats depressed their intake, those rats eating casein the least and those rats eating egg white the most. On the second day, rats offered lactalbumin depressed their intake 52.5% for the 3-hour period and rats offered casein depressed their intake 34.3%. Rats eating soy protein, egg white and protein mixture increased their intake from day 1 to day 2. These experiments show that type of protein affects rats' initial intake when they are offered a high protein diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Subcutaneous glycerol injection fails to reduce food intake in rats fed a high protein diet

To test whether glycerol utilization might contribute to glycerol-induced hypophagia, cumulative food intake was measured following subcutaneous glycerol injection in rats fed a high carbohydrate (HC), a high fat (HF) or a high protein (HP) diet, because food composition is known to influence the activity of several glycerol metabolizing enzymes. In additional experiments, the effect of glycerol injection on plasma glycerol, blood glucose, and liver glycogen levels was also investigated in HC-, HF-, and HP-rats. Subcutaneous glycerol injection (6.3 mmoles/kg b.w.) significantly reduced food intake in HC- and HF-rats, but failed to decrease feeding in HP-rats. Five hours after glycerol injection, plasma glycerol levels were significantly elevated in HP-rats, but did not differ from the glycerol levels of controls in HC- and HF-rats. Subcutaneous glycerol injection did not affect blood glucose concentration or liver glycogen content 5 hours after injection in any feeding group. The results suggest that oxidation of the injected glycerol might contribute to the glycerol-induced hypophagia in HC- and in HF-rats.     

Metabolism of L-cysteine in rats fed low and high protein diets

L-Cysteine (5.0 mmol per kg of body weight) was intraperitoneally injected into rats fed a 25% casein or 5% casein diet. Concentrations of acidic and neutral amino acids in various tissues were determined 2 h later. In the rats fed the 25% casein diet there was a tendency for tissue amino acid and glutathione levels to be slightly lower than controls. In the 5% casein diet group, however, concentrations of tissue amino acids and glutathione generally increased after L-cysteine administration. S-(2-Hydroxy-2-carboxyethylthio)cysteine (HCETC,3-mercaptolactate-cysteine disulfide), though in trace amounts, was detected in kidney and blood plasma in the 5% casein diet group. Increases in cysteine-glutathione disulfide in liver, kidney and erythrocytes in the 5% casein diet group were considerable. These results indicate that L-cysteine was rapidly metabolized in the 25% casein diet group through the oxidative pathway, while in the 5% casein diet group, in which liver cysteine dioxygenase activity is supposed to be quite low, the oxidative metabolism of L-cysteine decreased and part of the L-cysteine was metabolized through the transaminative pathway. Administration of 15.0 mmol L-cysteine per kg of body weight to rats fed the 25% casein diet resulted in an increase in cysteine-glutathione disulfide in liver, kidney and erythrocytes, and the appearance of HCETC in blood plasma.(ABSTRACT TRUNCATED AT 250 WORDS)     

Megestrol acetate increases short-term food intake in zinc-deficient rats

Rats offered a zinc-deficient (-Zn) diet voluntarily reduce their food intake within 3-4 days. Megestrol acetate (MA) is an appetite-stimulating drug used to treat cachexia of chronic diseases. In previous work, we found MA administration to male rats increased consumption of a -Zn diet. This approach would provide a useful tool for nutritional studies in which nutrient intake, except for zinc, would be maintained. The present study further examined the use of MA to increase consumption of a -Zn diet over a longer time period in both male and female rats. Rats were fed either a -Zn or a zinc-adequate (+Zn) diet. In Experiment 1, rats were treated orally with 0, 20, 50 or 100 mg MA/kg BW in corn oil for 21 days. MA stimulated intake of the -Zn diet in a linear manner. In Experiments 2 and 3, male and female rats, respectively, were fed the -Zn or +Zn diets and treated with 100 mg MA/kg BW for 21 days. In both experiments, MA administration increased intake of the -Zn diet to levels similar to the +Zn diet through Day 14. MA increased the hypothalamic neuropeptide Y (NPY) concentration in male rats, but did not affect serum IGF-I. MA administration improved growth of female but not male rats fed the -Zn diet. In females, serum IGF-I was not lower in zinc-deficient rats, which may have allowed the improved growth response with MA. Hence, MA administration may be a useful tool to increase consumption of a -Zn diet in short-term studies.     

Effects of pre-feeding on food-approach latency and food consumption speed in food deprived rats

Deprived rats were trained to receive a major portion of their daily food ration in meal segments of five 45 mg food pellets, presented for 36 sec each at 72 sec intervals. Latency to make oral contact with first pellets did not change over 18 meal segments, while the time to complete the eating of meal segments increased progressively. Pre-feeding with 45 or 90 pellets had little effect on latencies except in the last few trials in the 90-pellet condition. Pre-feeding had a marked effect on time to complete segments, increasing it in proportion to the number of pellets consumed. Thus satiation caused a progressive change in speed of eating, while it caused an all-or-none change in initiation of eating. That is, animals responded to new food pellets with normal latency up to the point when they stopped responding completely. With repeated testing the effects of prefeeding on both speed and latency measures was reduced; the animals ate more steadily, and came to eat every pellet, as familiarity with the situation increased.     

Effect of exercise on Hepatic cholesterof of rats fed diets high in saturated or unsaturated fats

Summary Rats have been fed diets containing 24.2% coconut or corn oil or an equal mixture of each for 14–18 weeks. Half of the animals in each dietary group were exercised by running in motor-driven work wheels throughout the entire experimental period. During the final 10–14 weeks, these exercised animals ran continuously for 60 min at 1.0 mph or faster each day. Comparisons between sedentary groups revealed that hepatic cholesterol and excretion of digitonin precipitated sterols in the feces increased (P < 0.01) as the per cent of unsaturated fat (corn oil) in the ingested food increased. In contrast, total liver lipid decreased (P < 0.01) as the consumption of corn oil increased. No change in plasma cholesterol occurred in the sedentary rats in response to the three diets. Hepatic cholesterol of the exercised groups was significantly less (P < 0.05–P < 0.01) than that of their respective control groups (same diet). However, the group fed the corn oil diet had a significantly higher (P < 0.01) liver cholesterol after exercise than did the exercised group fed the coconut oil diet. Liver lipid was reduced (P < 0.01) by exercise in the corn oil and mixed corn-coconut oil fed groups. Plasma cholesterol and sterol excretion were unchanged by the exercise program.This investigation supported by Research Grant HE 08262 from the National Heart Institute, National Institutes of Health, U.S. Public Health Service.     

Effect of intravenous nutrient infusions on food intake in rats

To assess the effect of gut signals on food intake two types of nutrients were infused intravenously for 17.5 hours in 17 hour fed rats. In the first experiment a solution of 25% d-glucose and 4.25% amino acids (Travasol) was infused at levels of 26 and 52 kcal/day for two consecutive four-day periods. During infusion periods, food intake was reduced from saline baseline levels by 18.9 +/- 1.7 and 34.8 +/- 1.8 kcal/day, respectively. This represents an oral intake reduction of approximately 70% of the infused calories. In contrast, food intake was reduced 17.4 +/- 1.7 kcal/day below saline baseline levels when 40 kcal of Nutralipid were infused. The reduction in food intake was only 43% of the lipid calories infused. These results indicate that infusions of glucose and amino acids are more effective than infusion of fats in inhibiting daily food intake, that gut signals associated with absorption of fat provide important satiety signals and that removal of fat from the bloodstream has relatively little effect on daily food intake.     

Dietary preference behavior in rats fed bitter tasting quinine and sucrose octa acetate adulterated diets

Rats were fed a bitter and presumably toxic quinine adulterated diet and a more bitter, but non-toxic sucrose octa acetate (SOA) adulterated diet. In two-diet preference tests the animals initially preferred the quinine diet over the SOA diet. After being fed only the SOA diet for four days the rats switched their preference to this diet during a subsequent two-diet preference test. In 10 day single diet tests the rats ate significantly more of the SOA diet than of the quinine diet. The results are consistent with the hypothesis that the toxic effects of quinine result in the formation of a conditioned taste aversion to the diet, and indicate that rats can distinguish between two bitter diets and develop a preference for the more bitter, but non-toxic one.     

Sexual dimorphism in the regulation of caloric intake and body weight of rats fed different diets

Female, androgenized female (AF), and male rats were given access to 1 of 3 diets—chow (C), high-dextrose (D-chow:dextrose, 2:1), and high-fat (F-chow:Crisco, 2:1) for 2 months. Caloric intake (CI), water intake, and body weights were monitored daily. Responses to gonadectomy and a single injection of estradiol benzoate (EB) were also studied. For females, F- and C-fed rats had comparable CI's, whereas D-fed rats chronically ate much less. For males, F-fed rats overate, whereas C- and D-fed rats had comparable CI's. The pattern of CI of AF rats fed the 3 diets was intermediate between that of males and females. Male rats were less responsive to the anorexic effects of EB than were the other two groups, and the F-diet potentiated the anorexic effects of EB in all three groups. Results are discussed in terms of a sex difference in the hypothalamic regulation of feeding behavior which is modulated by gonadal hormones.     

Effects of dietary protein on food and water intake in spontaneously hypertensive rats

We have been studying the development of hypertension in spontaneously hypertensive rats (SHR) fed a low protein diet. The effects of a low protein diet upon food and water intake were examined. Body weight gain, food and water intake were measured in three to twenty-three week-old SHR and Wistar Kyoto rats (WKY) fed diets containing 8%, 15% or 25% casein. Body weights of SHR and WKY fed an 8% casein diet were significantly lower at 23 weeks than rats on the higher protein diets, although both groups on the 8% diet consumed more food and water per g of body weight. In addition, SHR fed an 8% casein diet drank less water per gram of food than WKY or SHR fed 15% and 25% casein diets. These results indicate that changes in food and water intake, as a consequence of low protein diets, should be an additional consideration when examining the effects of dietary protein on the development of hypertension.     

Arctium lappa ameliorates endothelial dysfunction in rats fed with high fat/cholesterol diets

ABSTRACT: BACKGROUND: Arctium lappa L. (Asteraceae), burdock, is a medicinal plant that is popularly used for treating hypertension, gout, hepatitis, and other inflammatory disorders. This study was performed to test the effect of ethanol extract of Arctium lappa L. (EAL) seeds on vascular reactivity and inflammatory factors in rats fed a high fat/cholesterol diet (HFCD). METHOD: EAL-I (100 mg * kg1/day), EAL-II (200 mg * kg1/day), and fluvastatin (3 mg * kg1/day) groups initially received HFCD alone for 8 weeks, with EAL supplementation provided during the final 6 weeks. RESULTS: Treatment with low or high doses of EAL markedly attenuated plasma levels of triglycerides and augmented plasma levels of high-density lipoprotein (HDL) in HFCD-fed rats. Chronic treatment with EAL markedly reduced impairments of acetylcholine (ACh)-induced relaxation of aortic rings. Furthermore, chronic treatment with EAL significantly lowered systolic blood pressure (SBP) and maintained smooth and flexible intimal endothelial layers in HFCD-fed rats. Chronic treatment with EAL suppressed upregulation of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and E-selectin in the aorta. Chronic treatment with EAL also suppressed increases in matrix metalloproteinase (MMP)-2 expression. These results suggested that EAL can inhibit HFCD-induced vascular inflammation in the rat model. CONCLUSION: The present study provides evidence that EAL ameliorates HFCD-induced vascular dysfunction through protection of vascular relaxation and suppression of vascular inflammation.     

Effect of melatonin on total food intake and macronutrient choice in rats

Melatonin, a hormone secreted in a rhythmic manner over 24 h mainly by the pineal gland, is used to alleviate the symptoms of jetlag and treat sleeping problems. The objective of the present study was to examine the effects of a 7-h phase-shift from the natural peak of melatonin secretion on total food intake and macronutrient selection. Forty-eight adult Wistar rats of both sexes were divided in three dietary groups, each group offered a simultaneous and different choice of a carbohydrate- and a protein-rich diet. Macronutrient intakes following intraperitoneal administration of four doses of melatonin (3000, 6000, 10 000 and 15 000 pg/ml blood) at dark onset were examined. Melatonin increased short- (4 h postinjection) and long-term (12 h postinjection) nocturnal total food intake in both male and female rats, mainly with the two highest doses. This effect of melatonin was mainly due to a short-term increase of intake across all carbohydrate-rich diet preparations (dextrin/cornstarch, cornstarch, and sucrose/cornstarch) and across genders. This consistent effect of melatonin on the intake of carbohydrate-rich diets with contrasting sensory attributes rules out the possibility that melatonin acts on sensorymotor pathways, thus suggesting that melatonin's effect on food intake is controlled by the carbohydrate content of the diet. In contrast, melatonin could be affecting some sensory or motor processes peculiar to the ingestion of protein since it increased protein-rich diet intake inconsistently across the various preparations (casein, soy isolate, and egg protein) as well as genders. This evidence supports the view that melatonin acts as a time indicator, reinforcing the animals with a “night cue”, and favors predominant carbohydrate intake normally occurring at the beginning of the activity period.     

Phosphate and the development of nephrocalcinosis in rats fed diets containing alpha protein.

It has been suggested that nephrocalcinosis in rats fed diets containing alkali-treated soy protein may be due to a high availability of phosphate in the diet. In the present study, the development of nephrocalcinosis in rats fed a diet containing 20% alpha protein (an alkali-treated soy protein) was compared with that in rats fed the same diet supplemented with additional phosphate. Phosphate supplementation of the alpha protein diet produced a form of nephrocalcinosis that was morphologically different, at both the light- and electronmicroscopic level, from that obtained with the unsupplemented diet but was quite similar to that obtained with a phosphate-supplemented standard commercial laboratory diet. Levels of serum and urinary calcium and phosphorus and urinary cyclic AMP suggested that a phosphate-induced secondary hyperparathyroidism was present in the rats fed either of the phosphate-supplemented diets, but not in the rats fed the unsupplemented alpha protein diet. The results of this study suggest that nephrocalcinosis in rats fed a diet containing 20% alpha protein, without additional phosphate, is not typically phosphate-induced.