Repleted Rats Research Articles

Omega-3 fatty acid deficiency increases stearoyl-CoA desaturase expression and activity indices in rat liver: Positive association with non-fasting plasma triglyceride levels

Although omega-3 ( n−3) fatty acids negatively regulate triglyceride biosynthesis, the mechanisms mediating this effect are poorly understood, and emerging evidence suggests that stearoyl-CoA desaturase (Scd1) is required for de novo triglyceride biosynthesis. To investigate this mechanism, we determined the effects of perinatal n−3 deficiency and postnatal repletion on rat liver Scd1 mRNA expression and activity indices (liver 16:1/16:0 and 18:1/18:0 ratios), and determined relationships with postprandial (non-fasting) plasma triglyceride levels. Rats were fed conventional diets with or without the n−3 fatty acid precursor α-linolenic acid (ALA, 18:3 n−3) during perinatal development (E0-P100), and a subset of rats fed the ALA− diet were switched to the ALA+ diet post-weaning (P21-P100, repletion). Compared with controls, rats fed the ALA− diet exhibited significantly lower liver long-chain n−3 fatty acid compositions and elevations in monounsaturated fatty acid composition, both of which were normalized in repleted rats. Liver Scd1 mRNA expression and activity indices (16:1/16:0 and 18:1/18:0 ratios) were significantly greater in n−3 deficient rats compared with controls and repleted rats. Among all rats, liver Scd1 mRNA expression was positively correlated with liver 18:1/18:0 and 16:1/16:0 ratios. Plasma triglyceride levels, but not glucose or insulin levels, were significantly greater in n−3 deficient rats compared with controls and repleted rats. Liver Scd1 mRNA expression and activity indices were positively correlated with plasma triglyceride levels. These preclinical findings demonstrate that n−3 fatty acid status is an important determinant of liver Scd1 mRNA expression and activity, and suggest that down-regulation of Scd1 is a mechanism by which n−3 fatty acids repress constitutive triglyceride biosynthesis.

Omega-3 fatty acid deficiency selectively up-regulates delta6-desaturase expression and activity indices in rat liver: prevention by normalization of omega-3 fatty acid status

This study investigated the effects of perinatal dietary omega-3 (n-3) fatty acid depletion and subsequent repletion on the expression of genes that regulate long-chain (LC) polyunsaturated fatty acid biosynthesis in rat liver and brain. It was hypothesized that chronic n-3 fatty acid deficiency would increase liver Fads1 and Fads2 messenger RNA (mRNA) expression/activity and that n-3 fatty acid repletion would normalize this response. Adult rats fed the n-3-free diet during perinatal development exhibited significantly lower erythrocyte, liver, and frontal cortex LCn-3 fatty acid composition and reciprocal elevations in LC omega-6 (n-6) fatty acid composition compared with controls (CONs) and repleted rats. Liver Fads2, but not Fads1, Elovl2, or Elovl5, mRNA expression was significantly greater in n-3-deficient (DEF) rats compared with CONs and was partially normalized in repleted rats. The liver 18:3n-6/18:2n-6 ratio, an index of delta6-desturase activity, was significantly greater in DEF rats compared with CON and repleted rats and was positively correlated with Fads2 mRNA expression among all rats. The liver 18:3n-6/18:2n-6 ratio, but not Fads2 mRNA expression, was also positively correlated with erythrocyte and frontal cortex LCn-6 fatty acid compositions. Neither Fads1 or Fads2 mRNA expression was altered in brain cortex of DEF rats. These results confirm previous findings that liver, but not brain, delta6-desaturase expression and activity indices are negatively regulated by dietary n-3 fatty acids.

Differences in Bone Turnover and Skeletal Response to Thyroid Hormone Treatment Between Estrogen-Depleted and Repleted Rats

This study was undertaken to compare the effect of supraphysiological doses of thyroxine (T4) on bone metabolism in SHAM and OVX young adult rats. Female Sprague Dawley rats (220 +/- 2 g, approx. 5 months of age) were divided into four groups of eight animals each. The animals were intraperitoneally injected 6 days per week with vehicle (Vh): 0.001 N NaOH/0.9% NaCl (SHAM+Vh and OVX+Vh) or 250 microg of thyroxine/kg/day (SHAM+T4 and OVX+T4) during a 5-week period. Serum T4 and osteocalcin (BGP), urinary pyridinolines (Pyr), and creatinine (creat) were determined. At the beginning and at end of the experiment, skeletal bone mineral content (BMC), bone mineral density (BMD), and area (A) of the total skeleton, femur, spine, and whole tibia, as well as proximal, middle, and distal areas of the tibia were assessed by dual X-ray absorptiometry (DXA) in an ultra-high-resolution mode. T4 treatment of the SHAM rats did not induce significant changes in BGP level or Pyr/creat excretion compared with the SHAM+Vh control group. However, these two biochemical bone markers significantly increased due to T4 treatment in OVX rats compared with both OVX+Vh and SHAM+T4 groups (P < 0.05 and P < 0.001, respectively). The OVX+T4 group had a significantly lower DeltaBMD than SHAM+T4 rats in all studied regions (P < 0.05) except for the middle tibia region. OVX+T4 groups presented a significantly lower DeltaBMC and DeltaA compared with SHAM+T4 animals (P < 0.001). OVX+T4 rats significantly impaired the DeltaBMD in the femur (P < 0.01), spine (P < 0.05), whole (P < 0.05) and middle (P < 0.05) tibia whereas T4 treatment of SHAM rats only affected, significantly, the whole (P < 0.05) and the proximal tibia region (P < 0.01). T4 treatment affects bone growth in young adult rats. The effect is significantly greater in the estrogen-depleted than in the estrogen-repleted state. The bone site most adversely affected by T4 treatment depends on the estrogen status. The proximal tibia (principally trabecular bone) was the most affected area in estrogen-repleted rats. Conversely, in OVX rats, the middle tibia (principally cortical bone) presented the greatest decrease in bone density.

Effect of high dietary zinc on plasma ceruloplasmin and erythrocyte superoxide dismutase activities in copper-depleted and repleted rats.

The effect of moderately high dietary zinc (Zn) on the activities of plasma (PL) ceruloplasmin (CP), and PL and erythrocyte (RBC) copper (Cu), Zn superoxide dismutase (SOD) was determined in weanling rats fed Cu-deficient (DEF; < 1 mg Cu/kg), marginal (MAR; 2 mg Cu/kg), or control (CON; 5 mg Cu/kg) copper diets containing normal or high Zn (HZn; 60 mg/kg) for 4 wk and supplemented with oral Cu (CuS; 5 mg/L) in drinking water for 0, 1, 3, or 7 d. PL Cu decreased (67% compared to CON; p < or = 0.05) in the DEF and increased to control level after 3 d of CuS; increased in the MAR group after 1 d of CuS. HZn reduced overall PL Cu by 27% in all groups, but did not alter the linear increase in PL Cu between 0 and 3 d of Cu S. PL CP activity altered concomitantly with PL Cu levels: The time course of increase in CP activity after 0-3 d of CuS was not influenced by HZn in the diet and CP declined in the DEF group by 92%. There was no correlation between dietary Cu level and PL CP. PL SOD activity decreased by 46% (p < or = .05) in the DEF group, increased to control activity after 1 d of CuS and declined slightly after 7 d; MAR diet did not alter PL SOD. HZn diet increased PL SOD activity in all groups by 150%, reduced activity in the DEF and MAR groups by 65 and 37% and delayed the recovery of PL SOD after CuS. RBC SOD declined in the DEF and MAR groups by 56 and 33% (p < or = 0.05) and did not respond to CuS; HZn diet did not influence RBC SOD activity. These data indicate that moderately high Zn in the diet reduces PL Cu, but not PL CP activity or the recovery of PL Cu or CP activity after oral CuS of Cu-deficient rats, modifies the response of PL SOD to dietary Cu, but does not influence RBC SOD activity.

Availability of Selenium in Dough and Biscuit in Comparison to Wheat Meal

We studied the availability of selenium in processed foods and whole wheat diets for restoring the Se content and glutathione peroxidase (GSHPx) activity in the blood and liver of selenium-depleted rats. The Se content in the rat diets ranged from 225 to 342 micrograms Se/kg diet. Different selenium sources and different Se amounts had little influence on the Se levels in the blood and liver of repleted rats. Se from processed foods did not completely restore the GSHPx activity in whole blood and liver as happened with Se coming from wheat. These results indicate that it is the milling processes of the flour production, and not the cooking, which decrease the availability of Se for GSHPx synthesis in rats.

Repletion of Folate-Depleted Rats with an Amino Acid—Based Diet Supplemented with Folic Acid

Folate depletion and repletion protocols are not well standardized. Weanling rats were moderately depleted of folate in 28 d with a folate-free purified diet based on 17% amino acids as the nitrogen source. They were then folate repleted for 23 d with the amino acid diet supplemented with either 125, 250, 500, 1000 or 2000 micrograms folic acid/kg. Hematology, growth and tissue folate levels were measured in subsets of the rats when they were 24 (baseline), 52 (depleted) and 75 d old (repleted). The same measurements were made in control rats that had been fed 2 mg folic acid/kg of the amino acid diet for the same period of time. Our findings show that with repletion, growth of previously depleted rats is in direct proportion with the level of supplementation up to 1000 micrograms folic acid/kg diet. Serum folate levels of repleted rats also increased in proportion to supplementation between 500 to 2000 micrograms/kg diet, and liver folate levels increased proportionally with the level of supplement within the range of 125 to 2000 micrograms/kg diet. The 2000 micrograms/kg supplement was sufficient to restore liver folate levels equivalent to that of controls, but body weight and serum folate levels failed to catch up with that of controls in the 23-d repletion period. There was a nonlinear relationship between serum and liver folate levels: serum folate remained constant at about 6 micrograms/l as liver folate increased to about 7 micrograms/g, then serum folate diverged by increasing to 120 micrograms/l with only minor increases in liver folate.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of 1 alpha, 25-dihydroxycholecalciferol on iron metabolism.

Chronic administration of hypercalcemic doses of 1 alpha, 25-dihydroxycholecalciferol to intact, vitamin-D repleted rats for 4 weeks, enhanced net intestinal absorption of iron and liver iron stores. Daily net iron and calcium absorptions were found to be significantly correlated in both control and treated rats. In duodenal loop experiments, pretreatment with 1 alpha, 25-dihydroxycholecalciferol reversed the adverse effect of high Ca/Fe ratio on iron absorption. The increased intestinal absorption of iron did not result in a change of serum iron levels nor of total iron binding capacity due to the enhanced incorporation of absorbed iron into liver ferritin. The curve of uptake of 59Fe into circulating red cells of treated rats suggested retarded release of the isotope from stores. The hypothesis is advanced that the systemic metabolic defect (tissue hypoxia, raised erythropoietin levels) produced by 1 alpha, 25-dihydroxycholecalciferol is responsible for the disruption of the physiological coordination between iron stores and intestinal absorption.

Decreased antibody formation in iron-deficient rat pups—effect of iron repletion

Rats were fat diets containing 6, 12, or 250 ppm iron throughout gestation and lactation. On day 17, pups immunized with sRBC were used to determine antibody synthesis by the Jerne plaque assay. In both iron-deficient groups, antibody formation was decreased by at least 50% compared to controls. For 3 weeks beginning on day 21, iron-deficient pups were fed either a control diet (35 ppm iron) or the same iron-deficient diet as fed to the dam. IgG and IgM formation was only slightly improved in repleted rats and remained significantly below that of rats fed the control diet throughout the experiment. In contrast, 250 ppm iron pups fed an iron-deficient diet postweaning had significantly decreased IgG and IgM production compared to littermates fed a control diet postweaning. Maternal iron deficiency during the critical pre- and postnatal growth periods may result in long-term impairment of humoral immunity that is not corrected by dietary iron repletion after weaning.

Testicular Damage Associated with Zinc Deficiency in Pre- and Postpubertal Rats: Response to Zinc Repletion

These studies concern histological changes in the testes of pre- and postpubertal zinc-deficient and repleted rats. Three experiments in volved a total of 69 rats. In experiment 1, 12 weanling rats were fed a zinc-deficient (0.5 ppm) diet, ad libitum; 11 were fed a zinc-sufficient (100 ppm) diet and pair-fed to the zinc-deficient group; and 10 were fed the zinc-sufficient diet, ad libitum. After 26 days of being fed the different diets, one testis with the epididymis was surgically removed (hemicastrated) from each animal for histological examination. The rats fed the zinc-deficient diet were then fed the zinc-sufficient diet, ad libitum, for 30 or 41 days. Pair-feeding between the zinc-sufficient group and the zinc-deficient-repleted group was continued. The results indicated that 26 days of zinc depletion caused general immaturity of the testis and varied degrees of degeneration of the germinal epithelium compared to controls. After the zinc repletion period of 30 or 41 days, the remaining testis, epididymis, and sperm count were normal in all previously deficient animals. In experiment 2, 10 weanling rats were fed a marginally zinc-deficient diet (4 ppm) for 90 days and after hemicastration showed degenerative changes in the testes. All animals were then fed a zinc-sufficient (100 ppm) diet, with two animals killed every 15 days during a period of 75 additional days. The degenerative changes were not completely reversed during the 75-day repletion period, and only 4 out of 10 testes showed definite improvement. In experiment 3, 26 weanling rats were fed a zinc-adequate diet (15 ppm) for 42 days at which time 3 were killed to assure adequacy of the diet for maintenance of the testes and to confirm sexual maturity. When 12 of these postpubertal animals were fed the deficient diet for up to 68 days, a wide range of testicular damage occurred. Forty-two days of zinc repletion of the remaining 11 postpubertal rats, did not reverse the damage. In toto, the experiments suggest that a prepubertal short-term zinc deficiency resulted in degenerative changes that were repaired by repletion. In contrast, the degenerative changes of the testes of postpubertal zinc-deficient rats were not reversible to any significant extent.pre-pubertal zinc deficiency post-pubertal zinc deficiency testicular damage and repair

A specific dietary zinc requirement for the growth of Walker 256/M1 tumor in the rat

To determine the specific effect of zinc status on the growth of Walker 256/M1 carcinosarcomas young male rats were pair-fed either a control or zinc-deficient diet for 14 days, were implanted with tumors and killed 7 days later. Half of the deficient rats were repleted with zinc for the 7 days after tumor implantation. In deficient rats, tumor weights were decreased 70% (p less than 0.005), tumor necrosis was 3-fold greater (p less than 0.05) and tumor zinc concentrations were decreased 23 to 37% (p less than 0.005). A specific zinc effect was observed by a 2-fold increase in tumor weights in repleted rats (p less than 0.05) with marked decreases in tumor necrosis (p less than 0.05) and 29 to 84% increases in tumor zinc concentrations (p less than 0.005). Since there were no decreases in organ weights of zinc-deficient animals and no correlation between final tumor weights and postimplant changes in carcass weights, the results indicate a specific inhibitory effect of zinc deficiency independent of a nonspecific malnutrition.

Angiotensin-sodium interaction in blood pressure maintenance of renal hypertensive and normotensive rats.

A specific inhibitor of angiotensin II was used in rats to investigate whether angiotensin is involved in the maintenance of blood pressure in one-kidney Goldblatt hypertension, in which plasma renin levels are not usually increased. The inhibitor produced marked falls in blood pressure, often down to normal levels in the hypertensive animals only when they were depleted in sodium and not after sodium repletion. Much lesser but still significant falls in blood pressure were also produced in normotensive sodium-depleted rats but not in repleted rats. We conclude that the importance of angiotensin for maintaining blood pressure is largely determined by its relation to available sodium or fluid volume, since the renin component in maintenance of either the hypertensive or the normotensive state could be exposed only by sodium deprivation. Therefore, volume expansion per se or other pressor factors may be involved in maintaining blood pressure of these sodium-replete normotensive or hypertensive animals.

Vitamin D deficiency and neutral amino acid absorption in the rat intestine.

SummaryIntestinal neutral amino acid absorption was studied in vitamin D-depleted and repleted rats using α-aminoisobutyric acid. Vitamin D had no effect on absorption or concentration of α-aminois...