Metabolism of chylomicron arachidonic and linoleic acid in the rat

Chyle and chylomicrons, obtained after feeding thoracic duct cannulated rats [3H]arachidonic (20:4) and [14C]linoleic acid (18:2) in cream, were injected i.v. into recipient animals. 7.5-15 min after injection, the 14C/3H ratio of the triacylglycerols remaining in plasma was about half of that in the injected chylomicrons, indicating that the chylomicron remnants formed retained relatively more [3H]20:4 than [14C]18:2. The 14C/3H ratio of plasma diacylglycerols was about 6-fold lower than that of plasma free fatty acids. The proportion of [3H]20:4 found in plasma cholesteryl esters was several-fold higher than that of [14C]18:2. Inhibition of hepatic lipase by a specific antiserum did not significantly influence the clearance of triacylglycerols, but increased the amount of 3H in plasma diacylglycerols. It also prevented the rapid clearance of phosphatidylethanolamine from plasma. The liver uptake of [3H]20:4 exceeded that of [14C]18:2. Antiserum against hepatic lipase diminished the difference. In contrast, the 14C/3H ratio of adipose tissue was higher than that of the injected chyle lipoproteins.     

Time-course of utilization of [stearic or lignoceric acid]sphingomyelin from high-density lipoprotein by rat tissues

Utilization of stearic and lignoceric acids supplied by high-density lipoprotein (HDL) sphingomyelin to different tissues was followed for 24 h after rats were injected with HDL containing [[1-14C]stearic (18:0) or [1-14C]lignoceric (24:0) acid [Me-3H]choline]sphingomyelin. Both isotopes reached a maximum in tissue lipids 3-12 h after injection and were recovered mainly in the liver (30%) and small intestine (3%), whereas the other tissues contained approx. 1% or less of the injected dose. All the tissues were able to take up some intact sphingomyelin from HDL and hydrolyze it. In the lung and erythrocytes, the 3H:14C ratio of sphingomyelin remained unchanged throughout the studied period, while an increase in the isotopic ratio was observed in the kidney due to the 3H choline moiety re-used for synthesis of new sphingomyelin. Conversely, the isotopic ratio of sphingomyelin decreased in the liver, indicating a saving of the 14C-labelled fatty acids, especially 24:0. Furthermore, [24:0]ceramide in the liver remained at a high level (6% of the injected dose), whereas [18:0]ceramide decreased to 1%. When the tissues were examined 24 h after injection, the proportion of the 14C linked to sphingomyelin in the total 14C was always higher for both kinds of sphingomyelin than the molar proportion of sphingomyelin in the whole of lipid classes. However, in the majority of the extra-hepatic tissues, more [14C]18:0 than [14C]24:0 was recovered in sphingomyelin, and more 14C radioactivity from 18:0 than from 24:0 was redistributed in the other lipids. The choline moiety from both kinds of sphingomyelin was re-used to synthesize phosphatidylcholine, especially in the liver (up to 20% of the injected dose). All these results show that utilization of sphingomyelin from HDL by tissues normally occurs in vivo and that this phenomenon should be taken into account in the study of the phospholipid turnover of cell membranes. They also show that metabolism of sphingomyelin from HDL in the liver and other tissues is dependent on the sphingomyelin acyl moiety.     

Metabolism of vitamin D. A new cholecalciferol metabolite, involving loss of hydrogen at C-1, in chick intestinal nuclei

1. A comparison was made of the nature and intestinal intracellular distribution of the metabolites formed in vitamin D-deficient chicks from [4-(14)C]cholecalciferol and [1-(3)H]cholecalciferol. 2. The simultaneous administration of the two radioactive substances showed the presence in blood, liver, intestine, kidney and bone of cholecalciferol, its ester, 25-hydroxycholecalciferol and a further metabolite of cholecalciferol more polar than 25-hydroxycholecalciferol. The (3)H/(14)C ratios in these four radioactive components were the same as that of the dosed material (4.7:1) with the exception of the most polar material. The (3)H/(14)C ratio was lower in the fourth, most polar, metabolite (0.4:1-1.8:1) in all tissues examined, with the exception of blood. 3. In the chick intestine the polar metabolite accounted for almost 70% of the radioactivity in this tissue after a dose of 0.5mug. of [4-(14)C,1-(3)H]cholecalciferol. This polar metabolite from the intestine also had the lowest (3)H/(14)C ratio of all the tissues. It appears that in the chick intestine the polar metabolite reaches a maximum concentration of 1ng./g. of tissue, above which it cannot be increased irrespective of the dose of the vitamin. 4. The intestinal intracellular organelle with the highest concentration of (14)C radioactivity is the nucleus, and this radioactivity is almost entirely due to the polar metabolite with the lowered (3)H/(14)C ratio, in this case <0.2:1. It appears to be further localized in the chromatin of the nuclei. However, about half of the polar metabolite in the intestine is extranuclear. 5. Double-labelled 25-hydroxycholecalciferol was prepared and after its administration to vitamin D-deficient chicks the polar metabolite with the lowered (3)H/(14)C ratio was detected in liver, kidney, intestine, bone, muscle and heart. 6. None of the polar metabolite with the lowered (3)H/(14)C ratio was detected 16hr. after dosing with either the double-labelled vitamin or the double-labelled 25-hydroxycholecalciferol in blood and adipose tissue of vitamin D-deficient chicks, nor in the intestine, liver and kidney of supplemented birds. 7. The reasons for this loss of (3)H relative to (14)C are discussed in relation to possible chemical structures of this new polar metabolite.     

Comparative utilization in vivo of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose and [1-C14] palmitate in the rat

Female rats were injected i.v. with comparable trace amounts of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose, or [1-14C] palmitate, and killed 30 min afterwards. The radioactivity remaining in plasma at that time was maximal in animals receiving [U-14C] glucose while the appearance of radioactive lipids was higher in the [U-14C] glycerol animals than in other groups receiving hydrosoluble substrates. The carcass, more than the liver, was the tissue where the greatest proportion of radioactivity was recovered, while the greatest percentage of radioactivity appeared in the liver in the form of lipids. The values of total radioactivity found in different tissues were very similar when using either labelled glucose or glycerol but the amount recovered as lipids was much greater in the latter. The maximal proportion of radioactive lipids appeared in the fatty-acid form in the liver, carcass, and lumbar fat pads when using [U-14C] glycerol as a hydrosoluble substrate, and the highest lipidic fraction appeared in adipose tissue as labelled, esterified fatty acids. In the spleen, heart, and kidney, most of the lipidic radioactivity from any of the hydrosoluble substrates appeared as glyceride glycerol. The highest proportion of radioactivity from [1-14C] palmitate appeared in the esterified fatty acid in adipose tissue, being followed in decreasing proportion by the heart, carcass, liver, kidney, and spleen. Thus at least in part, both labelled glucose and glycerol are used throughout different routes for their conversion in vivo to lipids. A certain proportion of glycerol is directly utilized by adipose tissue. The fatty acids esterification ability differs among the tissues and does not correspond directly with the reported activities of glycerokinase, suggesting that the alpha-glycerophosphate for esterification comes mainly from glucose and not from glycerol.     

Evaluation of radiation dose resulting from the ingestion of [3H]- and [14C]thymidine in the rat

Average doses to rat tissues from the ingestion of 2-[14C]thymidine were compared with those from methyl-[3H]thymidine or 6-[3H]thymidine. Among the three precursors, [14C]thymidine gave the highest dose to spleen and small intestine. The doses to other tissues from [14C]thymidine were almost the same or lower as compared with those from [3H]thymidine, irrespective of the 9 times higher beta-ray energy of 14C than that of 3H. In the case of [14C]thymidine, most of the dose was given by radioactivity incorporated into the organic tissue constituents (non-volatile radioactivity). In the case of [3H]thymidine, however, the dose contributions by non-volatile radioactivity were very small and the major contributions were rather from volatile radioactivity (3HHO), formed by degradation of [3H]thymidine. No significant difference in their total doses was found between the two [3H]precursors, but the dose from non-volatile radioactivity alone was 2-3 times higher with methyl-[3H]thymidine than with 6-[3H]thymidine. Estimates of the dose to cell nuclei in various tissues after the ingestion of [3H]thymidine were also made in order to predict more precisely possible radiation hazards.     

Effect of alcohol on the metabolic conversion of 14C erucic acid in the liver of rats receiving rapeseed or peanut oil]

The effects of addition of ethanol to diets containing rapeseed or ground nut oil on the metabolic conversions of 14 14C erucic and 9-10 3H oleic acid were studied in the rat liver. 1. Whatever the diet more 14C than 3H radioactivity was recovered in liver lipids 2 and 19 hours after injection of labelled fatty acids. Ethanol has little effect on this incorporation. 2. Only small amounts of 3H oleic acid were converted. 3. In all cases, the metabolic conversion of erucic acid was identical: the main part of 14C was not recovered as erucic acid but was present in other monounsaturated fatty acids n-9: oleic acid (18 : 1), which was the most labelled acid, 16 : 1, 20 : 1 and nervonic acid (24 : 1). 4. The amount of erucic acid converted to shorter chain fatty acids was unchanged by addition of ethanol but the alcohol increased the proportion of 14C radioactivity recovered as nervonic acid. This latter effect was opposite to the effect of rapeseed oil diet, which consisted in a decrease in the conversion of erucic to nervonic acid. 5. A high amount of 14C radioactivity was recovered in the F.F.A. fraction of the liver as an unknown compound (13 and 80% of 14C radioactivity respectively after 2 and 19 h.) Its identification is presently under investigation.     

Synthesis of [1,2-3H2]cholecalciferol and metabolism of [4-14C,1,2-3H2]- and [4-14C,1-3H]-cholecalciferol in rachitic rats and chicks

[1,2-(3)H(2)]Cholecalciferol has been synthesized with a specific radioactivity of 508mCi/mmol by using tristriphenylphosphinerhodium chloride, the homogeneous hydrogen catalyst. With doses of 125ng (5i.u.) of [4-(14)C,1-(3)H(2)]cholecalciferol the tissue distribution in rachitic rats of cholecalciferol and its metabolites (25-hydroxycholecalciferol and peak P material) was similar to that found in chicken with 500ng doses of the double-labelled vitamin. The only exceptions were rat kidney, with a very high concentration of vitamin D, and rat blood, with a higher proportion of peak P material, containing a substance formed from vitamin D with the loss of hydrogen from C-1. Substance P formed from [4-(14)C,1,2-(3)H(2)]cholecalciferol retained 36% of (3)H, the amount expected from its distribution between C-1 and C-2, the (3)H at C-1 being lost. 25-Hydroxycholecalciferol does not seem to have any specific intracellular localization within the intestine of rachitic chicks. The (3)H-deficient substance P was present in the intestine and bone 1h after a dose of vitamin D and 30min after 25-hydroxycholecalciferol. There was very little 25-hydroxycholecalciferol in intestine at any time-interval, but bone and blood continued to take it up over the 8h experimental period. It is suggested that the intestinal (3)H-deficient substance P originates from outside this tissue. The polar metabolite found in blood and which has retained its (3)H at C-1 is not a precursor of the intestinal (3)H-deficient substance P.     

Effects of human pancreatic lipase-colipase and carboxyl ester lipase on eicosapentaenoic and arachidonic acid ester bonds of triacylglycerols rich in fish oil fatty acids

Fish oil chylomicrons, obtained from mesenteric duct chyle of rats fed [3H]20:5 and [14C]20:4 or [3H]20:5 and [14C]18:2 in a fish oil emulsion, were incubated with human pancreatic lipase-colipase, human carboxyl ester lipase (CEL) and human duodenal contents. With duodenal contents, the triacylglycerols labelled with [3H]20:5 and [14C]20:4 were rapidly converted to free fatty acids (FFA) and monoacylglycerols. Also during incubation with lipase-colipase the [3H]- and [14C]triacylglycerols disappeared completely and at equal rates, but in this case much [3H]20:5 and [14C]20:4 accumulated in diacylglycerols. When CEL was also added, the rate of disappearance of [3H]- and [14C]triacylglycerols increased and the radioactivity of diacylglycerols decreased markedly. During incubation of chylomicrons labelled with [3H]20:5 and [14C]18:2 with lipase-colipase, the rates of hydrolysis of [3H]- and [14C]triacylglycerols were similar, but more [3H]20:5 than [14C]18:2 accumulated in diacylglycerols. The accumulation of [3H]diacylglycerol was reduced by adding CEL. Also when fatty acids were analyzed by gas chromatography, 20:5 was enriched in remaining triacylglycerol and in diacylglycerol after incubation with lipase-colipase alone. The data thus indicate that both lipase-colipase and CEL participate in the hydrolysis of 20:5 and 20:4 ester bonds of dietary triacylglycerol.     

Evidence for different isotopic enrichments of acetyl-CoA used for cholesterol synthesis in the liver and intestine: a study in the rat by mass fragmentography after intravenous infusion of [13C]acetate

Wistar rats were killed 4 h after an intravenous infusion of [1,2-13C]- and [1-14C]acetic acid sodium salt (39 mg, 12.5 microCi/ml, constant rate: 1.2 ml/h). At this time, labeled free cholesterol movements between the organs are still weak and cholesterol labeling in each tissue mainly originates from the in situ incorporation of the exogenous substrate. In male rats, the specific radioactivity of free cholesterol was found to be higher in the intestine (mucosa and wall) than in the liver and plasma. In female and in cholestyramine-fed male rats, cholesterol 14C labeling was close to that of male rats in the intestine, and was markedly higher in the liver. The same variations of 13C excess, calculated by mass fragmentography, indicated that there was no isotopic effect between 13C and 14C precursors. The advantage of this method consisted in obtaining the proportions of labeled molecules according to their molecular weight (M + 1-M + 11) for each sample. Then the distribution of 13C atoms in newly synthesized cholesterol was assessed in each sterogenesis site. In the intestine, about 3/4 of the 13C atoms were found in molecules of weight of at least M + 4 (after incorporation of at least two labeled acetate units). This proportion was only 1/3 in hepatic and plasma free cholesterol. These distinct 13C-labeling patterns clearly indicate that local variations occurred in the isotopic enrichment of acetyl-CoA used for cholesterol formation. Whatever the experimental conditions of this study, cholesterol was synthesized from an acetyl-CoA more 13C enriched in the intestine than in the liver. Such variations probably result from the different dilutions of exogenous acetyl-CoA by the endogenous pool in the liver and intestine. Consequently, the 14C or 13C incorporations measured in the liver and intestinal sterols do not account for absolute rates of cholesterol production by these organs. This study also indicated that after a few hours of infusion, free cholesterol labeling in the plasma originated mainly from cholesterol newly formed in the liver, even when acetate incorporation into cholesterol was higher in the intestine than in the liver.     

Tissue distribution, elimination, and metabolism of [3H]leukotriene C4 by the conscious marine toad, Bufo marinus.

Tissue distribution, elimination, and metabolism of 3H-labelled leukotriene (LT) C4 were studied in ureter-catheterized conscious marine toads, Bufo marinus. Six and 24 h after injection, organs containing the highest percent of injected radioactivity were small intestine, liver, and kidney. Radioactivity declined in these organs at 24 h by approximately threefold. Peak elimination time for radioactivity in the urine was between 2 and 4 h after the injection. During the 24-h collection period, 55.2 +/- 0.2% of the injected radioactivity was eliminated in the urine. Polar metabolites represented 40.3 +/- 1.1, 57.3 +/- 5.6, and 62.8 +/- 1.6% of the radioactivity at 2, 4, and 6 h, respectively. The primary urinary polar metabolite was 20-carboxy-LTE4, with 18-carboxydinor-LTE4 and 20-hydroxy-LTE4 also present. [3H]LTE4 decreased from 37.2 +/- 1.8% at 2 h to 15.8 +/- 3.3 and 15.0 +/- 2.1% of the radioactivity at 4 and 6 h, respectively. Bile radioactivity was low. N-Acetyl-LTE4 was not detected in urine or bile samples. Radioactivity in the pan water was 14.3 +/- 2.4 and 15.8 +/- 2.5% of the injected radioactivity, at 6 and 24 h, respectively, suggesting that the skin was a route for excretion of leukotrienes. The marine toad is an interesting model demonstrating both similarities and differences from mammals in distribution, elimination, and metabolism of peptide leukotrienes.     

High-energy diets produce different effects on fatty acid synthesis in brown adipose tissue, white adipose tissue and liver in the rat

The influence of feeding rats a high-energy diet for 7 days on fatty acid synthesis in brown adipose tissue, white adipose tissue and liver of the rat was investigated. The incorporation of 3H2O and [U-14C]glucose into fatty acid was measured in vivo. The rats fed the high-energy diets had higher rates of fatty acid synthesis in white adipose tissue than the controls fed on chow, while fatty acid synthesis in brown adipose tissue and liver was either decreased or unchanged relative to that of controls fed on chow. After an oral load of [U-14C]glucose the incorporation of radioactivity into tissue fatty acid was several-fold higher in brown adipose tissue than in white adipose tissue in rats fed on chow. In rats fed the high-energy diets, incorporation of radioactivity into fatty acid in brown adipose tissue was decreased while that into white adipose tissue was either increased (Wistar rats) or unchanged (Lister rats).     

Tissue distribution of retinol and its metabolites after administration of double-labelled retinol.

The tissue concentrations and distribution of radioactivity present in retinol and its metabolites were investigated in vitamin A-deficient rats 24h after injection of physiological doses (10mug) of [6, 7-14C2, 11,12-3H2] retinol. The highest concentration of radioactivity was observed in the adrenals, followed by kidney, spleen, liver, intestine and blood. The total radioactivity was greatest in urine, followed in descending order by liver, kidney, blood and intestine. The 14C/3H ratios of crude light-petroleum extracts in the liver, intestines, lungs, heart and faeces were similar to the ratio of the injected retinol dispersion. However, the 14C/3H ratios in the adrenals, kidney, spleen, blood, brain and urine were quite different from that of injected retinol. Alumina chromatography of the kidney and intestinal extracts demonstrated that retinol and retinyl palmitate are the principal forms of vitamin A present. However, alumina chromatography of the liver extract did not reveal the presence of retinol but yielded a major compound with a low 14C/3H ratio. That this compound was not retinol was shown by its inability to react with ethanolic HC1 to yield anhydroretinol. The distribution of radioactivity in ether-soluble, acidic and water-soluble fractions of urine indicated that most of the radioactivity was present in the acidic and water-soluble fractions. The 14C/3H ratios in ether-soluble and acidic fractions were higher than that of injected retinol, whereas in the water-soluble fraction the ratio was similar to the injected material.     

Fatty acid synthesis in liver and adipose tissue of normal and genetically obese (ob/ob) mice during the 24-hour cycle.

1. The synthesis of long-chain fatty acids de novo was measured in the liver and in regions of adipose tissue in intact normal and genetically obses mice throughout the daily 24h cycle. 2. The total rate of synthesis, as measured by the rate of incorporation of 3H from 3H2O into fatty acid, was highest during the dark period, in liver and adipose tissue of lean or obese mice. 3. The rate of incorporation of 14C from [U-14C]glucose into fatty acid was also followed (in the same mice). The 14C/3H ratios were higher by a factor of 5-20 in parametrial and scapular fat than that in liver. This difference was less marked during the dark period (of maximum fatty acid synthesis). 4. In normal mice, the total rate of fatty acid synthesis in the liver was about twofold greater than that in all adipose tissue regions combined. 5. In obese mice, the rate of fatty acid synthesis was more rapid than in lean mice, in both liver and adipose tissue. Most of the extra lipogenesis occurred in adipose tissue. The extra hepatic fatty acids synthesized in obese mice were located in triglyceride rather than phospholipid. 6. In adipose tissue of normal mice, the rate of fatty acid synthesis was most rapid in the intra-abdominal areas and in brown fat. In obese mice, all regions exhibited rapid rates of fatty acid synthesis. 7. These results shed light on the relative significance of liver and adipose tissue (i.e. the adipose 'organ') in fatty acid synthesis in mice, on the mino importance of glucose in hepatic lipogenesis, and on the alterations in the rate of fatty acid synthesis in genetically obese mice.     

The pattern of fatty acid synthesis in lactating rabbit mammary gland studied in vivo

The biosynthesis of fatty acids has been studied in lactating rabbits at 6h after intravenous injection of sodium [1-(14)C]acetate. The specific radioactivities of the individual fatty acids (C(6:0) to C(14:0)) and the proportions of these fatty acids synthesized were similar in mammary tissue and milk. Hexanoic acid had the highest specific radioactivity, and the C(8:0)-C(14:0) fatty acids had similar specific radioactivities, which were about five times those of C(16) and C(18) acids. No radioactivity was detected in fatty acids of chain length C(14) in these tissues were similar to those of the long-chain fatty acids in the milk and mammary gland. The results show that the C(4:0)-C(14:0) fatty acids are synthesized within the mammary gland rather than by fatty acid uptake from circulating blood or by oxidation of long-chain fatty acids within the gland. We conclude that de novo synthesis of esterified fatty acids in vivo by this tissue has a high degree of chain-length specificity.     

Effects of hypo- and hyper-thyroidism on in vivo lipogenesis in fed and fasted rats

Thyroidectomized rats (T) daily injected with either 0, 0.1, 1.8 or 25 microgram of L-thyroxine/100 g body wt. were compared with intact controls (C). The appearance of radioactivity in fatty acids 30 min after the i.p. injection of (3-14C)pyruvate was reduced in adipose tissue and enhanced in liver of T+25, being no differences between the other groups and C. (14C)-Fatty acids are reduced with 3 h of fasting only in the adipose tissue of T+1.8 and C, while 24 h produces a reduction in liver in the T+1.8, T+25 and C, and in adipose tissue in the T+1.8 and C animals. The highest percentage of radioactivity was observed in the liver glyceride glycerol fraction, being greater in T+25 than in the other groups. Fasting produces an increment in the (14C)-glyceride glycerol fraction. Being significant only in thehypothyroid animals in both liver and adipose tissue. The most sensitive parameter to fasting was the formation of (14C)-non-saponifiable lipid in both the C and T+1.8 animals, while it does not change in T+0 or T+0.1, but is enhanced within 24 h in the adipose tissue of T+25. It is proposed that most of the observed changes are due to the other endocrine disfunction s which appear in hypo- and hyperthyroidism, as the in vivo results do not comply with in vitro effects of thyroxine onlipogenesis of others.     

Evidence of accumulation of ceramides containing [14C] nervonic acid in the rat lung following injection of [14C] erucic acid

A mixture of albumin-bound [¹⁴C]erucate and [³H]oleate was injected into rats fed a stock pellet diet containing 4% by weight of lipid. Chylomicrons containing the same labelled fatty acids were also injected into rats fed diets containing 15% by weight of rapeseed oil (48% of erucic acid), canbra oil (< 5% of erucic acid) or ground nut oil (no erucic acid). Lung lipids were analyzed at various times after injection.In all cases, except in the rapeseed oil diet group, ¹⁴C radioactivity of lung ‘monoacylglycerol’ was ten times higher than ³H radioactivity. More than 85% of this ¹⁴C radioactivity was found in nervonic acid (24:1). It was shown by TLC and GLC analysis that 85–90% of the ¹⁴C radioactivity of this fraction was in ceramides (N-acyl-4-sphingenine).Ceramides containing [¹⁴C] nervonic acid disappeared from the lung with time and their incorporation with time into sphingomyelin was also observed. The absence of accumulation of ³H and ¹⁴C (18:1) in ceramides showed that oleic acid was not incorporated into sphingomyelin in the same way as nervonic acid.In the rapeseed oil diet group, there was no accumulation of ¹⁴C radioactivity in ceramides and conversion of erucic acid into nervonic acid was less, and into oleic acid more, than in other diet groups indicating a possible enzyme adaptation.     

Serum half-life, distribution, hepatic uptake and biliary excretion of alpha-tocopherol in rats

The serum clearance of alpha-[3H]tocopherol has been studied after intravenous injection of intestinal lymph labeled in vivo with radioactive alpha-tocopherol. The half-life of the injected alpha-[3H]tocopherol was approx. 12 min. Fractionation of plasma by ultracentrifugation 10 min after injection of lymph showed that 91% of the radioactive alpha-tocopherol remaining in plasma was located in chylomicrons (d less than 1.006 g/ml) and 7.8% in high-density lipoproteins (HDL, 1.05 less than d less than 1.21 g/ml). 2 h after administration of alpha-tocopherol, about 35% of the radioactivity recovered in plasma was associated with chylomicrons and approx. 51% with HDLs. alpha-[3H]Tocopherol was initially taken up by the liver, which contained more than 50% of the injected radioactivity after 45-60 min. Separation of parenchymal and nonparenchymal cells demonstrated a preferential uptake of alpha-[3H]tocopherol by the parenchymal liver cells. After 24 h about 11% of the injected dose was recovered in the liver. Considering whole organs the liver, adipose tissue and skeletal muscle had the highest content of radioactivity after 24 h. Furthermore, about 14% of the administered dose was recovered in bile during 24 h draining.     

Long-term distribution and metabolism of [1-14C]dolichol injected intravenously into rats

We have previously shown that [1-14C]dolichol mixed in vitro with rat serum and injected intravenously is rapidly cleared from the circulation and appears primarily in the liver. One day after injection the liver accounted for 80% of the isotope in whole animals, whereas after 130 days it represented only 50%. During the 130 days the specific radioactivity (dpm/g liver) decreased by more than 20-fold. In contrast, the spleen retained at 130 days 85% of the radioactivity initially present and its specific radioactivity decreased by only a factor of two. At this time small amounts of isotope were also found in carcass (internal organs removed), gastrointestinal tract and contents, and lungs. Trace amounts of radioactivity were extractable from testes and kidneys, while the heart and brain were essentially free of radioactivity. At all times after injection nearly all the radioactivity present in all tissues was still associated with dolichol. Only trace amounts of [1-14C]dolichyl fatty acyl ester and no [1-14C]phosphorylated derivatives of dolichol were present in the liver and spleen removed 156 days postinjection. Fractionation of liver between 1h and 93 days after injection suggested that [1-14C]dolichol becomes associated primarily with a lysosome-enriched fraction. The accumulation of [1-14C]dolichol in this and other subcellular compartments involved both an inward and outward flow of radioactivity, suggesting that deposition of dolichol in lysosomes is not a one-way terminal process.     

Dynamic appearance of [4-14C] dehydroepiandrosterone and [7 alpha-3H] dehydroepiandrosterone sulphate metabolites in urine of normal and obese female subjects.

[4-14C]-Dehydroepiandrosterone and [7 alpha-3H]-Dehydroepiandrosterone sulphate were injected simultaneously to normal and obese female subjects. The percentage recovery of 14C and 3H radioactivies in dehydroepiandrosterone sulphate, androsterone sulphate, etiocholanolone sulphate, androsterone glucuronoside and etiocholanolone glucuronoside was determined in the day-to-day urine collections for 72 hr. Results showed a normal total 3H recovery and a poor 14C recovery in urinary conjugates of obese patients. The rate of appearance of 3H activity was not identical in the individual metabolites of normal subjects, and it was not normal in obesity. Overweight subjects exhibited an acceleration in [7 alpha-3H]-Dehydroepiandrosterone sulphate metabolism to androsterone glucuronoside. The observation regarding the rate of appearance of urinary conjugates bearing 14C isotope correlate with our previous finding in which a glandular overproduction of free dehydroepiandrosterone was found and an uptake of this steroid by the adipose tissue was suggested. Our results showed that the poor recovery of 14C radioactivity in urine of obese female subjects was not an aspecific consequence of illness.     

Alterations in Oral [1-14C] 18:1n-9 Distribution in Lean Wild-Type and Genetically Obese (ob/ob) Mice

Obesity may result from altered fatty acid (FA) disposal. Altered FA distribution in obese individuals is poorly understood. Lean wild-type C57BL/6J and obese C57BL/6J^ob/ob mice received an oral dose of [1-¹⁴C]18:1n-9 (oleic acid), and the radioactivity in tissues was evaluated at various time points. The ¹⁴C concentration decreased rapidly in gastrointestinal tract but gradually increased and peaked at 96 h in adipose tissue, muscle and skin in lean mice. The ¹⁴C concentration was constant in adipose tissue and muscle of obese mice from 4h to 168h. ¹⁴C-label content in adipose tissue was significantly affected by genotype, whereas muscle ¹⁴C-label content was affected by genotype, time and the interaction between genotype and time. There was higher total ¹⁴C retention (47.7%) in obese mice than in lean mice (9.0%) at 168 h (P<0.05). The ¹⁴C concentrations in the soleus and gastrocnemius muscle were higher in obese mice than in lean mice (P<0.05). Perirenal adipose tissue contained the highest ¹⁴C content in lean mice, whereas subcutaneous adipose tissue (SAT) had the highest ¹⁴C content and accounted for the largest proportion of total radioactivity among fat depots in obese mice. More lipid radioactivity was recovered as TAG in SAT from obese mice than from lean mice (P<0.05). Gene expression suggested acyl CoA binding protein and fatty acid binding protein are important for FA distribution in adipose tissue and muscle. The FA distribution in major tissues was altered in ob/ob mice, perhaps contributing to obesity. Understanding the disparity in FA disposal between lean and obese mice may reveal novel targets for the treatment and prevention of obesity.