Total Liver Vitamin Research Articles

The Effect of Dietary Fatty Acid Composition on Liver Retinyl Ester (Vitamin A Ester) Composition in the Rat

The dependence of liver retinyl ester (vitamin A ester) composition on dietary fatty acid composition was studied in rats. Weanling male Sprague-Dawley rats were fed purified test diets containing 8% of one of 10 test triglycerides (either tributyrin, tricaproin, tricaprylin, tricaprin, trilaurin, trimyristin, tripalmitin, tristearin, triolein, trilinolein) or corn oil (a mixed triglyceride) for 23 d after an initial 1-wk stabilization period. Essential fatty acids were provided by safflower oil (8 g/kg diet). Total liver fatty acid composition showed the expected responses to dietary fatty acid intake; short-chain and medium-chain fatty acids were readily elongated to palmitate and stearate, and palmitate and stearate were readily desaturated. Consumption of oleate or linoleate (as their triglycerides) markedly enriched their concentrations in liver lipids. The proportions of palmitate were generally greater in liver retinyl esters than in total liver fatty acids, and the proportions of oleate were less. However, retinyl ester composition was significantly affected by dietary triglyceride, particularly by diets providing long-chain fatty acids. Total liver vitamin A levels were depressed in the group fed trilinolein.

Influence of dietary vitamin E on the intermembrane transfer of alpha-tocopherol as mediated by an alpha-tocopherol binding protein.

The effect of dietary vitamin E on the intermembrane transfer of (3R)-alpha-tocopherol, a spontaneous process accelerated in the presence of an alpha-tocopherol binding protein (alpha TBP), was examined. The transfer activity of this cytosolic liver protein was assayed via in vitro transfer of (3R)-alpha-[3H]tocopherol (alpha[3H]T) from egg lecithin liposomes to human erythrocyte ghosts (EG). Male Fisher 344 rats (1 and 20 months old) were fed diets containing 0, 30, and 500 mg/kg vitamin E (dl-alpha-tocopheryl acetate) for 15 weeks. Liver cytosol fractions were assayed for alpha[3H]T transfer activity (alpha TTA). Among young rats, those fed vitamin E-deficient diets had the highest alpha TTA, 5.02 +/- 3.10 pmole alpha[3H]T/min (mean +/- SD), which was different (P less than 0.05) from the spontaneous transfer rate of 2.10 pmole/min. Neither young rats fed 30 and 500 mg/kg vitamin E diets nor any of the aged rats showed alpha TTA which differed significantly from the spontaneous transfer rate. To examine the relationship between hepatic alpha-tocopherol levels and alpha TTA, alpha-tocopherol concentration per gram of wet liver was assayed by HPLC. A steep positive slope (6.39 +/- 1.46 pmole min-1 nmole g-1) and strong correlation (r = 0.873) between hepatic alpha-tocopherol and alpha TTA were observed (P less than 0.005) among young vitamin E-deficient rats. The data indicates that alpha TTA varies directly with hepatic alpha-tocopherol concentration when total liver vitamin E stores are very low. Thus, alpha TBP-mediated transfer of alpha-tocopherol may be manifest only when vitamin E status is compromised.

A Marginal Vitamin A Status Alters the Distribution of Vitamin A among Parenchymal and Stellate Cells in Rat Liver

The aim of this study was to determine whether the distribution of vitamin A between parenchymal and stellate cells in rats with low vitamin A liver reserves is different from that observed in rats with adequate reserves. Retinol and retinyl esters were quantitated in parenchymal and stellate cells of the livers of three groups (n=3) of adult Sprague-Dawley rats with mean total liver vitamin A reserves of 1.2, 14.5 and 28.9 µg retinol/g fresh liver for groups 1, 2 and 3, respectively. The amount of vitamin A per 106 cells was similar in parenchymal and stellate cells of group 1, whereas in groups 2 and 3, a much higher amount was found in stellate cells (11-fold and 27-fold higher, respectively). In group 1, 83% of the liver vitamin A was present in parenchymal cells. As liver stores rose, however, a progressively greater amount was stored in stellate cells. In group 3, 82% of the liver vitamin A was found in stellate cells. In groups 2 and 3, 87–91% of the vitamin A was found as retinyl ester, whereas in group 1, 52% was found as retinol. The retinyl ester composition was similar in parenchymal and stellate cells, major esters being palmitate (84%) and stearate (10%), with smaller amounts of oleate (2.5%) and other esters. Thus, in rats with low liver vitamin A reserves, most of the liver vitamin A is found in parenchymal cells.

Relative Amount and Ester Composition of Vitamin A in Rat Hepatocytes as a Function of the Method of Cell Preparation and of Total Liver Stores

The aim of this study was to determine the cellular distribution of vitamin A in the liver of adult, well-nourished Sprague-Dawley rats with different stores of this vitamin. Three groups of three rats each were fed AIN-76 diet. Each group received an oral supplement of either 0, 2, or 12 mg of retinol. Retinol and retinyl esters were measured in the whole liver, in hepatocytes isolated either by gravity sedimentation or by centrifugal elutriation, and in the supematant solution recovered after hepatocyte sedimentation. Dietary supplementation with vitamin A increased the liver stores from 138 to 390 μg/g. A mean of 5% of the liver vitamin A was found in hepatocytes isolated by centrifugal elutriation. This percentage tended to decrease as liver vitamin A increased. In contrast, a mean of 38% of total liver vitamin A was found in hepatocytes isolated by gravity sedimentation over a threefold range of liver reserves. Whereas the retinol concentration in hepatocytes remained constant, the percentage of total vitamin A as retinyl esters, which accounted for more than 96% of the total vitamin A, increased as liver stores increased. The retinyl ester composition was similar in all three groups, major esters being palmitate (76–82%), stearate (9–12%), oleate (5–7%), and linoleate (3–4%). Over a threefold range of liver vitamin A concentrations in well-nourished rats, therefore, we estimate that only 10–20% of the total vitamin A in liver is present in the parenchymal cells.

Relation of the relative dose response to liver concentrations of vitamin A in generally well-nourished surgical patients

In 12 adult, generally well-nourished, surgical patients, liver vitamin A concentrations obtained by the analysis of liver biopsies were compared with the relative dose response (RDR). RDR is defined as the percentage increase in plasma retinol level relative to the plasma retinol level 5 h after the oral administration of a standard oral dose (450 µg) of retinyl acetate. Liver vitamin A values, expressed as retinol, and corresponding RDR values were 14 µg/g (28%), 30 µg/g (15%), and 58 to 434 µg/g (0 to 12%). Other indicators of vitamin A nutriture, which did not correlate with liver vitamin A concentrations in this group, were serum retinol level, serum retinol-binding protein concentration, and the percentage saturation of serum retinol-binding protein. The relative distribution of fatty acyl esters in liver retinyl ester did not change with total liver reserves. The relative percentage of retinol to total liver vitamin A, however, was higher (>5%) when reserves were ≤30 µg/g. Although the RDR cutoff point of >14% suggested earlier by others is in reasonable accord with our results, a somewhat higher RDR cutoff value (possibly 20%) may agree better with the suggested criterion of a liver vitamin A concentration of 20 µg/g, expressed as retinol, as a minimally adequate reserve.

The Storage Form of Vitamin A in Rat Liver Cells

After collagenase treatment of perfused rat liver, isolated washed hepatocytes (parenchymal cells) and washed nonparenchymal cells contained 13–53% and 5–9%, respectively, of the total vitamin A in rat liver. After Pronase E and DNase digestion of liver, nonparenchymal cells contained 1–6% of the total liver vitamin A content. By density-gradient centrifugation, hepatocytes were divided into six fractions, which contained fewer lipid globules per cell and less vitamin A per cell as the cell density increased. In our procedures, lipocytes could not be isolated after either collagenase or pronase E and DNase digestion of liver. Of the total liver vitamin A, 40–80% was found in very low density, vitamin A-containing globules, which have a median diameter of 1.7 µm (range 0.4–4.6 µm), show intense yellow-green fluorescence under UV illumination and contain >95% of their vitamin A in ester form. The distribution of vitamin A among cells and vitamin A globules in rats dosed with vitamin A was the same as in undosed rats. The possible interaction of lipocytes and different classes of hepatocytes in the storage and mobilization of vitamin A is discussed.

The effects of salicylate on enzymes of vitamin K metabolism.

The mechanism of salicylate-induced hypoprothrombinaemia has been investigated in the rat. Salicylate administration produced an increase in the percentage of the total liver vitamin that was present as vitamin K 2,3-epoxide, but the addition of salicylate did not influence vitamin K epoxide reductase activity in-vitro. Neither did it influence vitamin K-dependent carboxylase or vitamin K epoxidase activity. Both cytosolic and microsomal DT-diaphorase activities were, however, inhibited about 50% by 75 microM sodium salicylate. Salicylate inhibition was also observed when vitamin K quinone and NADH or dithiothreitol were used to support carboxylation. To achieve 50% inhibition required 0.5 mM salicylate with NADH as a reductant and 4 mM salicylate when dithiothreitol was the reductant. These results suggest that the main effect of salicylate on vitamin K metabolism is to inhibit quinone reductases and may be useful in explaining the inhibition of the biosynthesis of vitamin K-dependent clotting factors that occurs in salicylate-induced hypothrombinaemia. These data also demonstrate that the percentage of total liver vitamin present as vitamin K epoxide can be increased by agents that do not have a direct effect on the vitamin K epoxide reductase in-vitro.

Association of cellular retinol-binding protein and several lipid hydrolase activities with a vitamin A-containing high-molecular-weight lipid-protein aggregate from rat liver cytosol

A fluorescent, high-molecular-weight, lipid-protein aggregate was partially isolated from the cytosol fraction of rat liver by gel filtration on columns of Sepharose 4B or 6B. This aggregate was composed of approximately equal parts of protein and of lipid (mainly triglycerides), and was found to contain approximately 19% of the total liver vitamin A (predominantly as retinyl esters). Most of the liver cellular retinol-binding protein (CRBP) was found associated with the fluorescent, lipid-protein aggregate, along with much of the retinyl palmitate hydrolase activity present in the liver cytosol. The lipid-protein aggregate, and its several vitamin A-related components, all displayed an apparent hydrated density between 1.052 and 1.090 in the ultracentrifuge. CRBP in association with the lipid-protein aggregate was not immunoreactive in the CRBP radioimmunoassay. CRBP was, however, released from this aggregate and rendered immunoreactive by addition of detergents (e.g., Triton X-100). Three other lipid hydrolytic activities were also found in association with the lipid-protein aggregate, namely, triolein, cholesteryl oleate, and dipalmitoyl phosphatidylcholine hydrolase activities. These several hydrolytic activities were all found to be stimulated optimally by the addition of either sodium cholate or bovine serum albumin. With the information available, it is not clear whether this lipid-protein aggregate is formed in vitro, during liver homogenization, or whether it represents a specific lipoprotein with a significant functional role that exists in vivo in the liver cell.

Hepatic vitamin A status of rats during feeding of the hepatocarcinogen 2-aminoanthraquinone

Dietary administration of the dyestuff intermediate 2-aminoanthraquinone (AAQ) at a 2% level for periods of 2, 4, 8 or 12 weeks decreased the total liver vitamin A significantly ( P < 0.001) at all time periods in both male and female rats, compared to controls and pair-fed controls, respectively. A decrease in the body weights of AAQ-fed rats was much more pronounced in the females than male rats.

Association Between Plasma and Liver Vitamin A Levels in the Calf; Weanling Pig, Rabbit and Rat; and Adult Goat Fed Fixed Intakes of Vitamin A

To reexamine the relationship between plasma and liver vitamin A levels, data from various species of animals fed fixed intakes of vitamin A ester (expressed as retinol equivalents/kg liver weight/day) were vitamin A ester (expressed as retinol equivalents/kg live weight/day) were studied. The intakes ranging from deficient to toxic were for 48 calves, 4 to 17,600 micrograms; 39 pigs, 17.6 to 19,842 micrograms; 86 rabbits, 4.5 to 287 micrograms; 138 rats, 4 to 16,384 micrograms; and 40 goats, 1 to 17,640 micrograms. Following the feeding of these intakes for periods of between 5 and 133 weeks, blood and liver samples were taken for vitamin A determinations. Plasma vitamin A concentrations reached minimum values at low liver vitamin A levels whereas liver vitamin A levels reached maximum values at high plasma vitamin A concentrations. Upon elimination of data pairs at the extremes, linear regressions of log10 (total liver vitamin A) on plasma vitamin A concentrations and of plasma vitamin A concentrations on log10 (total liver vitamin A) were statistically significant. Therefore it was possible to estimate within limits the log10 (total liver vitamin A) from plasma vitamin A. Applicable limits were for the calf 8 to 46 micrograms/100 ml of plasma, for the pig 14 to 32, for the rabbit 14 to 74, for the rat 5 to 51 and for the goat 22 to 55. Simple correlation coefficients were 0.92, 0.60, 0.93, 0.92 and 0.75.

Influence of Excess Vitamin E on Vitamin A Toxicity in Rats

Male Holtzman rats (78 g) were fed semipurified 16% protein diets for 8 weeks using a food grade soy protein concentrate as the protein source. The basal diet (A) contained added DL-methionine (0.26%) and adequate amounts of vitamins A (14,535 IU/kg as retinyl acetate) and E (60 IU/kg as DL-alpha-tocopheryl acetate) and all other required nutrients. Experimental diets included: (B) basal plus 600 IU of vitamin E/kg; (C) basal plus 6,000 IU of vitamin E/kg; (D) basal plus 2.9 X 10(6) IU of vitamin A/kg; (E) basal plus 2.9 X 10(6) IU of vitamin A plus 600 IU of vitamin E/kg; and (F) basal plus 2.9 X 10(6) IU of vitamin A plus 6,000 IU of vitamin E/kg. Both vitamin A and vitamin E had a significant (P less than 0.05) effect on growth. There was an increase in growth with vitamin E intake and a decrease in growth with vitamin A intake. The net result of these two effects was that the groups fed both vitamins tended to be quite close in mean values to the group fed only the basal diet. Vitamin A significantly (P less than 0.05) increased relative weights of spleen and testes; vitamin E reduced that effect. Vitamin E also significantly (P less than 0.05) reduced relative adrenal weight whereas vitamin A significantly increased it. The two effects tend to cancel each other in the sense that the group fed both vitamins had an average relative adrenal weight quite close to that of the group fed only the basal diet. However, vitamin A still had an effect even when 6,000 IU of vitamin E was fed. The interaction effect of the two vitamins was significant (P less than 0.05) for plasma total protein and liver vitamin A. There was an increase in liver vitamin A with increasing levels of vitamin E in the diet. Blood urea nitrogen and plasma cholesterol were unchanged. A significant interaction of vitamins A and E was found to effect plasma total protein, liver vitamin A, and relative weight of spleen and testes.

Distribution and biochemical effects of DDT, DDD and DDE in penned double-crested cormorants

Concentrations, distribution and chronic effects of DDT, DDD and DDE were determined in penned cormorants ( Phalacrocorax a. auritus) treated with 2, 5 and 10 mg of a combination of these compounds daily in their diet. Birds stressed by a one-half decrease in food after the cessation of 9 weeks of treatment and birds that died of DDT toxicity showed a marked increase in brain and liver residues and a decrease in carcass residues. Higher brain residue levels were significantly correlated with decreased body weight ( p < 0.01) and carcass lipid content ( p < 0.05). DDD concentrations in the brain were found to be the best indicator of DDT toxicity. Brain concentrations ranged from 24 to 85 ppm in birds that died of toxic effects and from 0.4 to 29 ppm in survivors, indicating that 30 ppm was diagnostic of toxicity. Brain concentrations of DDT and metabolites in wild cormorants indicated no immediate danger of toxicity. Average residue levels in the carcass of wild adult cormorants was 1.00 ppm for DDD and 10.6 ppm for the total of DDT, DDD and DDE. This represents a total body burden of 2.2 mg of DDD and 23.3 mg of the DDT complex as adult cormorants averaged 2200 g in body weight. Analysis of total liver vitamin A indicated a significant decrease of vitamin A due to treatment. An analysis of variance showed a significant decrease in liver ( p < 0.05) and heart weights ( p < 0.05) due to treatment but not brain or spleen weights when analyzed as percentage of body weight. A significant negative correlation was found between liver weight and brain concentrations of DDE + DDD + DDT ( p < 0.05). No significant effects due to treatment were found on blood chemistry values.

Quantitative aspects of the urinary and fecal excretion of radioactive metabolites of vitamin A in the rat.

Urinary and fecal excretion of radioactive metabolites has been followed for 8 days (12 days in one group) in groups of rats having different initial body stores of vitamin A and given a single oral dose of 11,12-3H-retinyl acetate in oil. During the collections animals were fed a vitamin A deficient diet except for one group which was given laboratory chow throughout. At the end of the collection period animals were killed for determination of liver, kidney, and plasma vitamin A and radioactivity. Specific activities were similar in the three tissues; total liver vitamin A contents ranged from undetectable to 7700 μg. Excretion of fecal and urinary radioactivity was high initially but fell to apparently stable levels by day 8. When the combined urinary and fecal excretion was expressed in terms of the liver vitamin A equivalent (ELV), there was a gradual increase in excretion rate with the logarithm of liver vitamin A up to 150–300 μg/g liver; thereafter the rate of excretion increased more rapidly with liver stores to the highest level studied, 500–550 μg/g. In the initial phase the ELV values were 4–10 μg/day, rising to 22–24 μg/day in the second phase. These studies suggest that (a) a portion of newly absorbed vitamin A is metabolized before mixing with general body pools and probably without greatly altering the metabolism of endogenous vitamin A, (b) after equilibration of body pools, urinary excretion of radioactivity should be a useful index in experimental studies of factors affecting vitamin A metabolism, and (c) chemical determination of urinary metabolites of vitamin A is a potential index of vitamin A nutritional status.

Vitamin A Activity of Corn Carotenes for Swine

Three trials, using 204 weanling pigs, were conducted to estimate the vitamin A potency of corn carotenes for the pig. The pigs were depleted of their vitamin A stores by feeding a wheat- or milo-based diet until serum vitamin A levels approached or fell below 10 μg/100 ml. After depletion the pigs were assigned at random to one of the following seven repletion diets: 1) basal diet; 2) basal diet supplemented with 3 levels of carotene from corn or corn gluten meal, or both, with carotene concentrations from 1.04 to 10.3 mg/kg of diet; 3) basal diet supplemented with 3 levels of all-trans-retinyl palmitate, with retinyl palmitate concentrations from 73 to 654 μg/kg diet. Repletion diets were fed until the pigs reached market weight. Serum vitamin A determinations were made initially and periodically throughout the trials. Liver vitamin A stores were monitored by collecting livers from three or four pigs from each of the three trials at the start and end of depletion, and from all pigs at the end of repletion. The carotenes in corn and corn gluten meal were separated by column chromatography, identified as to structural and stereoisomeric form, and quantitated spectrophotometrically. Estimates of vitamin A potency were based on total liver vitamin A stores which the carotenes supported during repletion. Estimating equations were calculated by regressing the logarithm of total vitamin stores in milligrams/liver on total milligrams of carotene or retinyl palmitate consumed during repletion. Conversion efficiencies were calculated by dividing the regression coefficients for carotene by the regression coefficients for retinyl palmitate. At higher levels of carotene intake, when corn gluten meal was included in the repletion diets, 1 mg of carotene had a vitamin A potency of 123 to 174 IU. When corn was the only source of carotenes and the concentration was more typical of corn-soy swine diets, 1 mg of carotene had a vitamin A potency of 261 IU. It would appear that the NRC relationship, between 1 mg of dietary carotene and 500 IU of vitamin A activity, exaggerates the usefulness of corn carotenes for swine when liver vitamin A storage is used as the criterion.

Vitamin a Activity of Carotenes in Corn Silage Fed to Lambs

This study was conducted to compare the biopotency of the carotenes in corn silage with all-trans-retinyl palmitate for purposes of supporting liver vitamin A storage when fed to sheep. Fifty-six Western lambs with an average initial weight of 22.6 kg were fed a pelleted vitamin A depletion diet ad libitum for 110 days. Initial serum vitamin A levels of 28.3 μg/100 ml dropped to 20.0 μg/100 ml at the end of depletion. The lambs were allotted at random to 1 of 4 repletion diets. Lot 1 received corn silage ad libitum plus 0.16 kg/lamb/day of a protein-mineral-vitamin supplement. The total carotene content of the corn silage was 8.1 mg/kg (fresh basis, 28% dry matter). Lots 2, 3 and 4 received the modified depletion diet (90% dry matter) supplemented with 0.52, 1.55 and 4.65 mg of all-trans-retinyl palmitate/kg, respectively. After 70 days of repletion, serum vitamin values were 41.6, 20.4, 40.2 and 48.3 μg/100 ml for lots 1 through 4, respectively. Final liver vitamin A values (milligrams per liver), in the same order, were 12.29, 1.92, 8.35 and 15.36. The linear regression of total liver vitamin A stored with daily dietary intake of retinyl palmitate was calculated to be Ŷ = 1.6038 + 1.4516X, where Ŷ = mg vitamin A/liver and X = mg of all-trans-retinyl palmitate ingested/lamb/day. Using this regression and interpolating from liver vitamin A storage when corn silage was consumed, it was established that 1 mg of corn silage carotenes was equivalent to 0.24 mg (436 IU) of all-trans-retinyl palmitate.

Effect of chlorophenoxyisobutyrate on rat liver non-saponifiables.

Chlorophenoxyisobutyrate (CPIB) when fed in the diet at 0.2% for periods of from 3 to 25 days increased liver weight by 28% and increased total liver ubiquinones by 75%. This increase did not change succinate-neotetrazolium reductase activity. Although serum cholesterol levels were significantly reduced, no changes were observed in total liver cholesterol or vitamin A. The data suggest that this hypocholesterolemic agent, although it increases ubiquinone, does not adversely affect the above enzyme activity nor does it modify vitamin A utilization as determined from liver stores.

β-Carotene vs. Retinyl Acetate for the Baby Pig and the Effect upon Ergocalciferol Requirement

Twenty-four pigs were used in a study to compare the utilization of dietary fermentation β-carotene with retinyl acetate by the baby pig and to determine whether β-carotene has a rachitogenic effect which may increase the vitamin D requirement. Purified isolated-soy diets containing 2.5, 6.25 or 12.5 μg of ergocalciferol/kg and containing either 8 mg/kg of fermentation β-carotene or 688 μg/kg of retinyl acetate were used in a 5-week feeding period. Total liver vitamin A storage of pigs receiving preformed vitamin A was about twice that of pigs receiving β-carotene (2.4 mg vs. 1.2 mg). Neither bone composition nor strength were greatly affected by source of vitamin A activity. In this experiment β-carotene did not increase the need for ergocalciferol above that normally required by baby pigs fed a soy protein diet containing retinyl acetate.

Effect of Low Environmental Temperature on the Metabolism of Vitamin A (Retinol) in the Rat

The effects of low environmental temperature on liver vitamin A utilization of rats were examined after two, four and six weeks of exposure at 5°. Total liver vitamin A levels were unchanged. The weight gain of animals at 5° was always less than the weight gain at 25°. An increased utilization of vitamin A was indicated if the utilization of the vitamin was expressed as a ratio of the amount of vitamin A removed from the liver to the weight gain of the animal. The increase in the vitamin A depletion ratio observed in the 4-week cold-exposed rats was abolished by administration of thiouracil at a level of 0.1% in the diet. An increased requirement for vitamin A in the cold was indicated by the reduced survival time of vitamin A-deficient rats exposed to cold. In addition, at least 20 times more retinoic acid was necessary to maintain growth and survival in the cold than at 25°.

The effect of dietary folate deficiency on the synthesis of methylcobalamin in the chick.

The ratio of liver methylcobalamin to total liver vitamin B12 was estimated in a group of one‐week‐old chicks fed a folate‐free diet, and a group of three‐week‐old chicks fed a diet of insufficient folate content to allow normal growth but sufficient to delay mortality. The ratio in these groups was compared with those in control chicks fed a diet of adequate folate content.The ratio of liver methylcobalamin/total liver B12 was significantly lower in the one‐week‐old chicks fed a folate‐free diet, than in their controls, but the ratios in the three‐week‐old chicks fed a diet of limited folate content and their controls were similar.The significance of these findings is assessed and possible explanations for the inconsistency between the findings in the two folate deficient groups are discussed.

Vitamin A Activity of Fermentation β-Carotene for Swine

Two experiments were conducted with 171 weanling pigs to provide an estimate of the biopotency of fermentation carotenoids produced by Blakeslea trispora, and to estimate the vitamin A and β-carotene requirement of the depleted 50-kg pig. Vitamin A depletion for 7 weeks lowered serum vitamin A concentration from 23 to 4 µg/100 ml, and lowered liver vitamin A concentration from 35 to 2 µg/g of dry tissue. Repletion levels of fermentation β-carotene ranged from 0.5 to 3.5 mg/kg of diet and of all-trans vitamin A1 palmitate from 250 to 2000 IU/kg of diet. Using total liver vitamin A after 9 weeks of repletion as the criterion, one mole of fermentation β-carotene had 11.5% of the biopotency of one mole of all-trans vitamin A1 palmitate. The minimal requirements for gains from 50 to 100 kg body weight did not exceed 0.5 mg of fermentation β-carotene or 250 IU of vitamin A palmitate/kg of diet. However, 3.5 mg of fermentation β-carotene or 1000 IU of vitamin A palmitate/kg diet were required to restore serum vitamin A concentration to predepletion levels. Liver vitamin A concentration or total liver vitamin A increased linearly with increasing dietary increments of either fermentation β-carotene or vitamin A palmitate. This relationship was represented by the equation Y = -0.636 + 0.002 X for fermentation β-carotene and by Y = -4.87 + 0.0174 X for all-trans vitamin A1 palmitate, where Y = milligrams of total liver vitamin A after 9 weeks repletion and X = international units of fermentation β-carotene or of vitamin A palmitate per kilogram of diet.