Weanling Rats Research Articles

In vitro biosynthesis of prostaglandin E2 by kidney medulla of essential fatty acid deficient rats

Weanling rats were fed either a semisynthetic diet with no fat, with 28% by wt partially hydrogenated fish oil, or with 28% by wt arachis oil(control diet) for 6 or 7 1/2 months. The in vitro conversion of arachidonic acid to prostaglandin E2 by homogenates of the rat kidney medulla was measured by gaschromatography with electron capture detection. The kidney medulla of essential fatty acid deficient animals showed increased activity for the in vitro conversion of exogenous arachidonic acid to prostaglandin E2 when compared to the controls. The change of the enzymatic activity in the essential fatty acid deficient animals was reversible, as shown by refeeding. Inhibition of the prostaglandin synthetase was found at exogenous substrate concentrations higher than 50-100 muM.

Utilization of L-Methionine Sulfoxide, L-Methionine Sulfone and Cysteic Acid by the Weanling Rat

Three experiments were conducted to test the ability of weanling rats to utilize the oxidized forms of the sulfur amino acids methionine and cysteine for growth. In the first two experiments, diets were fed which contained graded levels of methionine, methionine sulfoxide and methionine sulfone. The third experiment included a comparison of two dietary levels of cysteine and cysteic acid. The 2 week weight gain and food consumption data indicated that methionine sulfoxide was utilized for growth with only 60% of the efficiency of that achieved by rats fed methionine. Methionine sulfone was not utilized for growth. Analysis of plasma sulfur amino acids showed that the rat has a limited capacity to utilize methionine sulfoxide by effecting its reduction to methionine. Cysteic acid did not support weight gain. This amino acid appeared to be rapidly catabolized to taurine. It was concluded that methionine sulfone and cysteic acid cannot be utilized by the weanling rat. Methionine sulfoxide cannot fully meet the dietary requirement of the rat methionine because of its limited capacity to reduce this amino acid.

The effect of reinstatement stimulus conditions on the maintenance of long-term memory.

Weanling rats trained on an appetitive SDSdelta discrimination were subsequently exposed to different components of the training stimulus for 15 min each week for 10 successive weeks. On the week following the final stimulus exposure retention was measured by a 2-hr relearning test. Those subjects exposed to all acquisition cues (SDSdelta with reinforcement), as well as those exposed to Sdelta conditions alone, demonstrated enhanced retention relative to a control group receiving no reinstatement experience. All other exposure conditions including presentation of SD with reinforecement were either ineffective or impaired retention.

Dietary linoleic acid and lipogenesis in rat adipose tissue.

Weanling rats were fed diets in which linoleic content varied from 0.4 to 11%. The changes of epididymal adipose tissue lipogenesis from glucose do not depend upon the linoleic content of the diets.

The influence of stimulus pairing and of the shuttle-shock contingency in the performance of shuttle responses to a buzzer by weanling rats

Weanling (20-day old) and adult Wistar rats were submitted to four different training procedures in a shuttle-box. Each of the training procedures involved 50 5-sec buzzers and a variable number of 1.5 mA footshocks. Performances of shuttle responses to the buzzer was similar in both age groups both in a “no pairing-no contingency” situation (shocks at random intervals from buzzers irrespective of the performance of shuttle responses or not), and in a classical conditioning situation (shocks paired to buzzers on every trial, also irrespective of whether or not there was shuttling to the buzzer). However, the incidence of shuttle responses to the buzzer was much lower in the weanling group in two other tests in which there was a contingency of shocks upon shuttle responses: one in which the buzzer-shock interval was randomly variable (i.e., no “pairing”), and another one in which the two stimuli were paired (a typical two-way avoidance paradigm). It is concluded that 20-day old rats are unable to cope with a shuttle-shock instrumental contingency, while being as able as adult rats to develop shuttle responses through a drive process or through a “pairing” (classical) process.

Transport of retinol from the blood to the retina: an autoradiographic study of the pigment epithelial cell surface receptor for plasma retinol-binding protein

Weanling rats were injected with 125I-labeled retinol binding protein and their ocular tissues were examined by light and electron microscope autoradiography at 10 min and 1 hr after injection. Combined with earlier work on isolated cells, the results show that receptors for retinol binding protein are present on the basal and lateral plasma membrane of retinal pigment epithelial cells. The pigment epithelium of the pars plana and ciliary body also contain plasma membrane receptors for retinol binding protein. In appears as though the entire plasma membrane of the ciliary pigment epithelium contains receptors for the binding protein.

Vitamin A Deficiency and the Metabolism of Glycosaminoglycans and Ascorbic Acid in the Rat

Weanling rats were fed diets with and without the addition of retinyl palmitate at 6,500 units/kg. The supplemented groups were fed either ad libitum or food was restricted daily to that amount consumed by the group of rats receiving the unsupplemented diet. After a 10 week experimental period, signs of vitamin A deficiency were observed (growth plateau, xerophthalmia) and liver values as retinol were only 1% of control values. Relative to the two control groups, vitamin A deficiency resulted in approximately 30% lower liver, 50% lower blood and 40% lower urinary ascorbic acid. Vitamin A deficiency did not appear to result in significant and direct impairment of GAG sulfate metabolism. Although the total amount of GAG in rat skin was increased, the composition of GAG fractions did not appear to be altered by vitamin A deficiency. Studies regarding the incorporation and disappearance of 35S-sulfate in vivo into GAG fractions obtained from skin indicated no serious impairment in GAG turnover with vitamin A deficiency. Twenty-four hour urine samples were also collected for estimation of 35SO4 excreted in GAG and non-GAG fractions. Likewise, little change was observed with respect to radioactivity associated with sulfate fractions excreted in urine. Although many previous studies have directly linked vitamin A with sulfation of GAG, the results reported here suggest that if there is an alteration in GAG sulfate metabolism, it is probably an indirect consequence of vitamin A status.

Rat testicular lipids and dietary isomeric fatty acids in essential fatty acid deficiency.

Weanling rats were fed essential fatty acid-deficient diets, either completely fat-free, or with partially hydrogenated fish oil (PHFO, 28 wt %), or with fractions derived from PHFO containing primarily positional isomers of trans-eicosenoate (20:1, 3 wt %) or trans-docosenoate (22:1, 3 wt %). Control animals were fed a peanut oil-containing diet (28 wt %). After 5 or 15 weeks on the diet, the content of neutral and phosphorus-containing lipids in the testes was determined. The fatty acid distribution in major lipid classes was analyzed for animals fed the diets for 15 weeks. The testicular stage of maturation or degeneration was assessed by histology. The group fed PHFO exhibited signs of complete testicular degeneration, or lack of maturation, already after 5 weeks, whereas the animals on the diets with the very long chain monoenoic acids suffered severe degenerations only after 15 weeks. In the PHFO-fed rats, a sharp decline in the concentration of testicular triacylglycerols was observed. In all of the essential fatty acid-deficient groups, an increase in testicular sphingomyelin was observed. Cholesterol levels were fairly similar among all dietary groups. The total testicular fatty acids of the PHFO-fed animals contained somewhat more eicosadienoic acid than found in the other groups, and somewhat less (n-9)-acids. In all EFA-deficient groups, (n-6)-acids were lowered, in particular in triacylglycerols and phosphatidyl cholines. The PHFO group did not show a lower (n-6)-concentration than the other deficient groups, in spite of the more severe symptoms of deficiency. There was no evidence of a major accumulation of long chain isomeric fatty acids in the degenerated testes of the PHFO-, 20:1-, and 22:1-fed groups.

Transit Time Changes with Age in the Gastrointestinal Tract of the Rat

Using 85Sr-labelled microspheres as nonabsorbable markers, the effect of age on gastrointestinal propulsion motility was determined in conscious rats. There was no significant correlation between the gastric emptying rate or the propulsion motility of the small intestine and the age of the rats. However, the transit time of the intestinal content in the caecum in adult (17- to 20-month-old) rats was about fivefold the value found in weanling (19-day-old) rats. Also the transit time of the large intestine was found to be prolonged by about 70% during the life span investigated.

Effect of Ventromedial and Dorsomedial Hypothalamic Lesions on Circadian Corticosterone Rhythms

Weanling rats received bilateral electrolytic lesions in the dorsomedial (DMH) or ventromedial (VMH) hypothalamic areas destroying primarily the dorsomedial (DMN) or ventromedial (VMN) hypothalamic nuclei. Sham-operated rats served as controls. Lesions in the VMN and DMN, both of which have previously been shown to disrupt normal diurnal feeding rhythms, were also observed to disrupt normal plasma corticosterone rhythms in the present study. The a.m. values of plasma corticosterone in the DMN-lesioned rats were higher than the sham-operated controls. In the p.m., the values of both VMN- and DMN-lesioned rats were lower than those of the controls but unchanged in comparison to their own a.m. concentrations. This disruption of the normal diurnal plasma corticosterone rhythm persisted for at least 9 post-operative weeks.

Food Intake Regulation in the Weanling Rat: Effects of the Most Limiting Essential Amino Acids of Gluten, Casein, and Zein on the Self-selection of Protein and Energy

The effects of altering the quality of the dietary protein source on the self-selection of protein and energy by the weanling rat simultaneously offered a choice of two diets differing only in protein concentration were tested. The protein-energy selected was measured when the first limiting amino acid lysine was added to gluten; when lysine, methionine, or the first four limiting amino acids were added to gluten or to casein; or when the nutritional quality of zein was altered by manipulation of the content of tryptophan, lysine, or the four most limiting amino acids. The additions of lysine to gluten caused a decrease in the protein-energy selected and an increase in growth rate of the weanling rat. However, improving the amino acid balance of casein or zein did not have this effect. It was concluded that the selection of protein and energy by weanling rats is not related to the nutritional quality of the protein fed.

Correlation between the Plasma Tryptophan to Neutral Amino Acid Ratio and Protein Intake in the Self-selecting Weanling Rat

The relationship between changes in blood plasma amino acids and the quantity of protein and energy self-selected by the weanling rat, simultaneously offered two diets varying only in protein concentration, was examined. The changes in the quantity of protein and energy consumed by the rats, which were brought about by the addition of the essential limiting amino acids and groups of essential amino acids to gluten, casein, and zein, were not linearly related to alterations in the total plasma amino acid concentrations or to the accumulation of the added amino acids in the blood plasma. However a consistent relationship between food intake and plasma acids was identified when the plasma tryptophan to neutral amino acid ratio was correlated with the protein intake selected. It is postulated that the ratio of tryptophan to neutral amino acids in the plasma is involved in, or reflects, a mechanism regulating protein intake.

Effect of polychlorinated biphenyls and thiamin deficiency on liver metabolism in growing rats.

Weanling rats were fed a thiamln‐deficlent diet containing 0, 10, or 500 ppm Aroclor 1254 (AR) ad libitum for 28 days. Control animals without and with AR at both levels received an oral thiamin supplement. Fasting blood glucose levels were determined at weekly intervals. The effects of AR, thiamin deficiency, and their interaction on liver cytosol and mitochondrial redox states and on cytoplasmic phosphorylation state as calculated from metabolite concentrations in freeze‐clamped livers were determined. Liver lipid and various parameters of lipid synthesis, transport, and storage were also studied. A R treatment and thiamin deficiency resulted in enlarged livers, increased liver lipid, increased lipid synthesis, decreased plasma free fatty acids, and decreased carcass lipids. AR treatment and thiamin deficiency increased the oxidized state of the mitrochondrial NAD∗/NADH couples and similarly Increased the cytoplasmic NADP∗/ NADPH couple associated with isocitrate dehydrogenase activity. These effects we...

Feeding studies in weanling rats with dorsomedial hypothalamic lesions: Maintenance of competence to compensate for additional calories

Weanling rats received bilateral electrolytic lesions in the dorsomedial hypothalamus primarily destroying the dorsomedial hypothalamic nuclei (DMN). Sham-operated rats served as controls. After a 14 day postoperative period during which food intake (lab chow) and body weight were recorded, each of the above groups were subdivided into 2 groups. One DMN group and one sham-operated control group were continued on lab chow alone throughout the remainder of the study. The other DMN group and the second control group were given additional calories in the form of a liquid diet by stomach tube during 2 separate periods of 10 and 14 days, respectively, to increase their caloric intake beyond that taken in spontaneously. Both tube-fed groups reduced their ad lib caloric intake from chow considerably and to the same extent. Body weight gains were similar in tube-fed versus non-tube-fed rats, whether with or without DMN lesions. After the second, 14-day-long tube feeding period, however, DMN rats regulated their body weight somewhat less precisely than the controls. This may be related to their reduced food intake during that time period. The data indicate that weanling rats with DMN lesions, despite their basic hypophagia, do not show a deficit in caloric metering and gross body weight regulation.

Shuttle behavior in weanling and in adult rats

Weanling rats (20–21 days old) and adult rats (55–70 days old) were submitted to conditioning and to pseudoconditioning tests in a shuttle-box. The young animals made less conditioned avoidance responses than the adults in an acquisition session and in addition they showed no retention of these responses. Performance of pseudoconditioned shuttling was similar in both groups. The younger rats made more intertrial crossings in both tests and more orienting responses to the buzzer during pseudoconditioning than the adults. Since in 20- to 21-day-old rats the hippocampal system is not fully mature, the present data agree with existing hypotheses which attribute to this structure a role both in inhibition and in learning and memory consolidation. It is possible, however, that behavioral differences between weanling and adult rats may be due to biochemical or physiological differences in other regions of the brain.

Effect of selected dietary additives on the incidence of dental caries in the rat.

Weanling rats fed a cariogenic diet supplemented with carbamyl phosphate, in combination with egg shell meal and trace elements, showed a striking reduction in the incidence of caries. The cariostatic efficacy of carbamyl phosphate is significant because it stimulates fluid movement within odontoblasts via the hypothalamic-parotid gland endocrine axis.

Effect of a low protein diet and isoenergetic amounts of a high protein diet in the weanling rat on the free amino acids of the brain.

Giving weanling rats a low protein diet for 56 days retarded the growth of the brain, whereas giving isoenergic amounts of a high protein diet did not. The low protein diet resulted in higher concentrations of aspartic acid, glycine, alanine and histidine in the plasma and of glycine and histidine in the brain. The concentration of methionine was unchanged in the plasma, but raised in the brain. Isoenergetic amounts of the high protein diet did not change the concentration of plasma amino acids, but resulted in some changes in brain amino acids. On rehabilitation the plasma and brain amino acids of the low protein animals returned to normal.

The effect of an acute light cycle change on adrenal rhythmicity in prepubertal rats.

24 and 28 day old rats, raised in a 14 h light: 10 h dark (14:10) cycle, showed a clear serum corticosterone (B) peak at the beginning of the dark period (18.00 h) with an amplitude of 25-30 mug%. Other B values during the 24 h period were lower (9-12 mug%). Rats raised in a 8.5:15.5 cycle had a B peak (after onset of the dark period, at 22.00 h). Rats raised in constant light (LL) showed no variation in B throughout the 24 h. Weanling rats raised in a 8.5:15.5 cycle appeared to synchronize more rapidly to a 14:10 cycle than did rats raised in LL. When placed in LL at weaning, rats raised either in 14:10 or 8.5:15.5 had lost their periodicity by day 24. When rats raised in 8.5:15.5 were shifted to LL or 14:10 after weaning age (day 24), the pattern of response was different. One day after the shift, rats placed in a 14:10 cycle displayed a pattern of B synchronized to the normal 14:10 pattern for rats born and raised in that light cycle. This synchrony persisted for at least 3 days. Rats placed in 14:10 at 21 days of age did not show a fully synchronized pattern until day 28. It can be concluded that weanling rats exposed to a light-dark cycle adapt quickly to a new light cycle and that older prepubertal rats shift even more quickly.

An investigation in rats, into the metabolic consequences of early ingestion of dietary carbohydrates.

Weanling rats were given diets containing a high proportion of either glucose, sucrose or fructose until they reached 200 g weight, when they were either transferred to a control (chow) diet for 4 weeks or killed. The results were compared with rats receiving a control diet throughout. The triglyceride (TG) and cholesterol levels in liver and in serum had returned to values similar to the control animals 4 weeks after being given the control diet. The fatty acid profile of liver TG and adipose lipid tended to take longer to return to normal.

Effect of Nitrogen Restriction on the Utilization of α-Ketoisovalerate for Growth in the Weanling Rat

Effect of Nitrogen Restriction on the Utilization of α-Ketoisovalerate for Growth in the Weanling Rat