Studies on the origin of milk fat. A further study of bovine serum lipoproteins and an estimation of their contribution to milk fat

1. Tritium-labelled palmitic acid combined in olive-oil triglycerides was introduced into the rumen of a lactating cow and the specific radioactivity of the lipids of milk and of the lipoproteins of both jugular and mammary venous serum was measured. 2. As previously found in a similar experiment with [(3)H]stearic acid, the specific radioactivity of the triglyceride fraction of the dextran sulphate-precipitable lipoproteins reached a maximum earlier and greater than that of the milk fat. 3. This fraction was the only lipid separated that had a significant arteriovenous difference in concentration, and is therefore identified as the main circulating lipid precursor of milk fat. 4. Although the non-esterified fatty acids showed no arteriovenous difference in concentration, they showed a negative difference in specific radioactivity that could have occurred only at the expense of the triglycerides of the precipitable lipoproteins. 5. The mean specific radioactivity of the triglycerides immediately after removal from the blood is calculated and shown to be very close in value to that of the corresponding fraction in mammary venous serum. 6. By comparison of the mean specific radioactivities of milk fat and of this precursor, its contribution is calculated as 36%. 7. This value is discussed with reference to the concentration of C(16) and C(18) fatty acids in milk fat and it is concluded that substantial amounts of these acids must have been derived from a source other than preformed circulating lipids.     

Incorporation of palmitic acid-1-14C into lipids of pharate adult tissues of Bombyx mori

Incorporation of palmitic acid-1-¹⁴C into pharate adult tissues and their lipid components of Bombyx mori was investigated. Rapid incorporation of radioactivity took place predominantly in fat body and haemolymph lipids, and partially in ovarian lipids immediately after the injection at the middle stage of pharate adult development. The major parts of the radioactivities in fat body, haemolymph and ovary were distributed in triglycerides and phospholipids, diglycerides, and triglycerides, respectively. The patterns of time course of incorporation of radioactivity into lipid components of pharate adult tissues suggest that the major form of lipid released from fat body may be diglycerides and the diglycerides in haemolymph are probably the main source of ovarian triglycerides.     

Lipid metabolism in the testis of the ram

1. Analysis of rams testes revealed that phosphatidylcholine was the major phospholipid and accounted for about 40% of the total. Only small amounts of choline plasmalogen were present. 2. The ratio of phosphatidylcholine to choline plasmalogen in the testis was very different from that occurring in the spermatozoa. This result was in contrast with those for rat testis and rat spermatozoa (obtained from the head of the epididymis), where the ratio of the two lipids was very similar. 3. Infusions of [(32)P]orthophosphate into the testicular artery of rams resulted in incorporation of radioactivity into most phospholipids; phosphatidylinositol labelling accounted for 68% and 39% of the radioactivity after infusions lasting 3hr. and 5hr. respectively. 4. With the exception of phosphatidic acid the specific radioactivity of phosphatidylinositol was higher than that of any other lipid. 5. After the infusion of [U-(14)C]glucose, triglycerides accounted for about 60% of the radioactivity in testicular neutral lipids, whereas diglycerides had only about 15% of the radioactivity. 6. Palmitic acid (16:0) was the major component both in neutral lipids and phospholipids of ram testes. 7. The effects of gonadotrophic hormones (luteinizing hormone and follicle-stimulating hormone) on the incorporation of [(32)P]orthophosphate into total testicular phospholipids in vivo were also examined.     

Lipid composition of the fat body and haemolymph and its relation to lipid release in Oncopeltus fasciatus

Lipid composition of the fat body and haemolymph of male milkweed bug, Oncopeltus fasciatus, was determined. Triglycerides were the predominant lipids of the fat body while diglycerides accounted for the major lipid in the haemolymph. Sterols, sterol esters, and non-esterified fatty acids were present in both fat body and haemolymph besides triglycerides and diglycerides. Only traces of monoglycerides were detected.Gas chromatographic analysis of the fatty acids revealed a difference in the fatty acid composition between fat body and haemolymph glycerides and sterol esters. Oleate and linoleate were the predominant unsaturated fatty acids in both fat body and haemolymph lipids and in the milkweed seeds as well.When fat body was labelled in vivo and in vitro with ¹⁴C-palmitate, the fatty acid was incorporated largely into the triglycerides. When the prelabelled fat body was incubated with a medium containing haemolymph the fat body released lipids mainly as diglycerides. Some radioactivity was observed in the triglycerides and non-esterified fatty acids also.Electrophoretic analysis of the incubation medium containing the haemolymph revealed that the released lipids were bound to three haemolymph lipoprotein bands. Lipid mobilization, release, and transport in Oncopeltus are discussed in relation to studies on other insects.     

Utilization of endogenous lipid by the isolated perfused rat heart

1. The lipids of the rat heart have been studied with regard to amount, classes present and fatty acid composition of free fatty acids, triglycerides and phospholipids. Myocardial lipid contained 300μmoles of total fatty acid/g. dry wt. of which only 2–4μmoles were free; the remainder was esterified, chiefly as phospholipid. Neutral esters, of which triglyceride was the principal form, made up 15% of the total fatty acids. 2. When normal hearts were perfused with a nutrient-free medium until exhaustion, the triglyceride concentration declined from 43 to 13μmoles/g. dry wt. The content of phospholipids, partial glycerides and cholesteryl esters did not change. When the lipids of the rat heart were labelled with [1-¹⁴C]palmitate before perfusion with non-nutrient medium, radioactivity disappeared from the triglyceride, diglyceride and free fatty acid fractions, but not from the phospholipid or other ester classes. 3. These experiments support the view that only a small fraction of the total cardiac lipid, principally triglycerides and to a smaller extent diglycerides, is available as a source of fuel in the absence of exogenous substrate.     

Transport of lipids in insects

Many insect species are almost completely dependent on lipids for their metabolic needs, although this is usually a function of developmental stage. The primary storage organ is the fat body, which can constitute 50% of the fresh weight of the insect and also acts as the major metabolic center (analogous to the vertebrate adipose tissue and liver). Bathing the fat body (and all other tissues and organs) is the hemolymph, the main functions of which are to transport nutrient substrates to utilization sites and to deliver metabolic wastes to the excretory system. Although neutral lipids are stored as triglycerides, in times of need they appear to be endergonically released into the hemolymph as diglycerides in the majority of insects thus far studied (particularly silkmoths and locusts). Indeed, diglycerides constitute the largest neutral lipid fraction in the hemolymph of silkmoths, locusts, cockroaches, bugs, etc. In the hemolymph the diglyceride is found as a constituent of specific lipoproteins, and one specific lipoprotein class (lipoprotein I; high density lipoprotein) appears to be necessary for the transport of diglyceride from the fat body cell into the hemolymph. This particular lipoprotein is also involved in the transport of cholesterol from the gut into the hemolymph. Thus, lipoprotein I appears to be the major neutral lipid and sterol transport agent in the insects studied and, in addition, plays a regulatory role in the release of both diglycerides and sterols. Hemolymph lipoprotein II (very high density lipoprotein) may be important in providing protein and lipid to the insect ovary during oogenesis. Ecdysone, the polyhydroxy steroidal insect molting hormone, is probably carried "free" in the hemolymph, although reports exist of specific hemolymph-binding proteins in some species. The other major insect growth hormone, juvenile hormone, is transported by hemolymph lipoproteins in silkmoths and locusts and by a lower molecular weight hemolymph protein in the tobacco hornworm.     

Interaction of plasma apolipoproteins with lipid monolayers.

The monolayer technique has been used to study the interaction of lipids with plasma apolipoproteins. Apolipoprotein C-II and C-III from human very low density lipoproteins, apolipoprotein A-I from human high density lipoproteins and arginine-rich protein from swine very low density lipoproteins were studied. The injection of each apoprotein underneath a monolayer of egg phosphatidy[14C]choline at 20 mN/m caused an increase in surface pressure to approximately 30 mN/m. With apolipoprotein C-II and apolipoprotein C-III there was a decrease in surface radioactivity indicating that the apoproteins were removing phospholipid from the interface; the removal of phospholipid was specific for apolipoprotein C-II and apolipoprotein C-III. Although there was a removal of phospholipid from the monolayer, the surface pressure remained constant and was due to the accumulation of apoprotein at the interface. The rate of surface radioactivity decrease was a function of protein concentration, required lipid in a fluid state and, of the lipids tested, was specific for phosphatidylcholine. Cholesterol and phosphatidylinositol were not removed from the interface. The addition of 33 mol% cholesterol to the phosphatidylcholine monolayer did not affect the removal of phospholipids by apolipoprotein C-III. The addition of phospholipid liposomes to the subphase greatly facilitated the apolipoprotein C-II-mediated removal of phospholipid from the interface. Although apolipoprotein A-I and arginine-rich protein gave surface pressure increases, phospholipid was only slightly removed fromthe interface by the addition of liposomes. Based on these findings, we conclude that the apolipoproteins C interact specifically with phosphatidylcholine at the interface. This interaction is important as it relates to the transfer of the apolipoproteins C and phospholipids from very low density lipoproteins to other plasma lipoproteins. The addition of human plasma high density lipoproteins or very low density lipoproteins to the subphase increased the apolipoprotein C-mediated removal of phosphatidyl[14C]choline from the interface 3--4 fold. Low density lipoproteins did not affect the rate of decrease. During lipolysis of very low density lipoproteins to the subphase increased the apolipoprotein C-mediated removal of with the lipid monolayer. Lipolysis experiments were performed in a monolayer trough containing a surface film of egg phosphatidyl[14C]choline and a subphase of very low density lipoproteins and bovine serum albumin. Lipolysis was initiated by the addition of purified milk lipoprotein lipase to the subphase. As a result of lipolysis, there was a decrease in surface radioactivity of phosphatidylcholine. The pre-addition of high density lipoproteins decreased the rate of decrease in surface radioactivity...     

Effect of carbon tetrachloride administration on the synthesis of triglycerides and phospholipids in rat liver

In vivo incorporation of choline-methyl-(14)C into liver lecithin and its biosynthetic precursors was studied in CCl(4)-treated rats. Radioactivity in cytidine diphosphoryl (CDP-)choline and lecithin was reduced to one-third of control levels, whereas that of phosphorylcholine was increased to 4.7 times control levels. Incorporation of phosphorylcholine-(32)P into lecithin by homogenates prepared from livers of CCl(4)-treated animals was reduced, but conversion of CDP-choline-(32)P to lecithin by the isolated microsomal fraction did not show any significant depression. A block in the synthesis of CDP-choline is indicated. The in vivo utilization of methionine for lecithin synthesis was not affected. After intravenous injection of palmitic acid-1-(14)C, radioactivity of triglycerides from microsomal and mitochondrial fractions was markedly lower than the controls, whereas radioactivity of triglycerides in the soluble fraction was greatly increased. Radioactivity of diglycerides changed from 0.5% of total lipids in the control to 10% of total lipids in CCl(4)-treated animals. Incorporation of palmitic acid into phospholipids was also suppressed. The results demonstrate that synthesis of both phospholipids and triglycerides is inhibited in rats 4-5 hr after CCl(4) administration.     

Metabolism of (1-14C)-palmitic acid in the cat's brain]

Following injection into the cerebral ventricles of conscious cats, (1-14C) palmitic acid was rapidly taken up and incorporated into a variety of brain lipids. The peak of uptake of (1-14C) palmitic acid, about 50% of injected radioactive material, into the brain tissue was obtained within the first 24 h following its administration. Thereafter, the radioactivity slowly decreased reaching the least value by the end of the second week. The most heavily labelled lipids were the phospholipids, while the free fatty acids were appreciably labelled. Small percentage of the radioactive material was found in monoglycerides, diglycerides and triglycerides. The least incorporation was into cholesterol esters.     

Exogenous lipid transport by the haemolymph lipoproteins in Periplanet a americana

To investigate the transport of exogenous lipids by the haemolymph lipoproteins, two kinds of experiments were carried out: in some experiments the insects were given a test-meal of double labelled tripalmitin (U³H glycerol, 1-¹⁴C palmitic acid) and were killed either 2 hr or 6 days later. In other experiments each insect received 2 identical test-meals: (9–10³H palmitic acid) tripalmitin and 6 days later (1-¹⁴C palmitic acid) tripalmitin. The insects were killed 2 hr after the ingestion of the second test meal. The lipids bound to the lipoproteins from the different fractions separated by electrophoresis of the haemolymph were analysed.The amount of labelled lipids transported by the haemolymph was much higher at 2 hr than at 6 days. The ingested triglycerides were absorbed unchanged or resynthetized from the products of their hydrolysis. The lipids released from the midgut into the haemolymph were found to be associated to lipoproteins carrying high amounts of triglycerides and exhibiting little or no electrophoretic mobility; the lipids released from the fat body into the haemolymph were mostly diglycerides; the glycerol released from the hydrolysis of exogenous triglycerides was not used in resynthesis of glycerides.     

A role for linoleic acid in erythrocytes infected with Plasmodium berghei

Unesterified fatty acids were measured in mouse erythrocytes infected either with chloroquine-susceptible (CS) or with chloroquine-resistant (CR) lines of Plasmodium berghei. This work was undertaken to identify candidates for the lipid involved in ferriprotoporphyrin IX (FP) polymerization. Linoleic, oleic, palmitic, and stearic acids were quantified by gas chromatography/mass spectrometry. In total, they increased 4-fold with CS infections and 6-fold with CR infections. Treating infected mice with chloroquine did not affect the amounts of unesterified fatty acids in erythrocytes. Of the four fatty acids, only linoleic acid increased disproportionately to the total. It increased 16-fold for the CS line and 35-fold for the CR line. The method could detect monoglycerides but they were below the limit of detection. It could not detect diglycerides, triglycerides or phospholipids. Triglycerides and phospholipids have been tested previously, however, and found to be ineffective at promoting FP polymerization. Therefore, other than linoleic acid, the lipids most likely to be involved in FP polymerization are diglycerides. We tested dilinoleolyglycerol in the present work and found it to be an effective promoter of FP polymerization. These results suggest that linoleic acid or a diglyceride containing it has the critical role of promoting FP polymerization in malaria parasites.     

Hormonal influence on uterine lipids.

The effects of oestrogen (OE), progesterone (P) and oestrogen plus progesterone (OEPP) on uterine lipids of adult ovariectomized rats were studied. Administration of gonodal hormones brought about considerable alterations in total lipids, mainly due to an increase in phospholipids and glycerides in the case of OE and P groups. Even though the total cholesterol remained unaltered, a marked alteration in its fractions was evident in all the groups. Oestrogen seems to decrease all the glyceride classes while progesterone induces accumulation ot triglycerides with concomitant decrease in mono- and diglycerides. Individual classes of phospholipids show marked alterations in their distribution in all the groups studied.     

In vivo incorporation of l-[14C]serine into phospholipids and proteins of the subcellular fractions of developing rat brain

A study was conducted on the in vivo incorporation of l -[¹⁴C]-serine into the lipids and proteins of the various subcellular fractions of the developing rat brain before and during the stage of active myelination. The total radioactivity in the various fractions at 12 days of age was higher than that at 3 days, while the radioactive specific activity was reversed. The specific activities of the proteins and lipids were higher at 3 days of age with the exception of the subcellular fraction containing myelin. At both ages the lipids of the various cellular fractions had similar specific activities, a finding that suggests a common source for lipid biosynthesis. Incorporation of radioactivity into the various phospholipids was in the following order: phosphatidyl serine > phosphatidyl ethanolamine > phosphatidal serine > sphingomyelin and phosphatidyl choline. Of all the phospholipids, the plasmalogens increased most in total radioactivity during the period when meylination was most active. Serine-containing phospholipids appear to be most tightly bound to proteins. The brain mitochrondrial fraction contained most of the phosphatidyl serine decarboxylase activity with some activity in the nuclei. Biosynthesis of phosphatdyil ethanolamine through decarboxylation of phosphatidyl serine could take place in rat brain. Four unidentified radioactive metabolites were found in the acid-soluble fraction in addition to l -[¹⁴C]serine.     

Zinc deficiency and the activities of lipoprotein lipase in plasma and tissues of rats force-fed diets with coconut oil or fish oil

The present study was performed to investigate the effect of zinc deficiency on the activities of lipoprotein lipase in postheparin serum and tissues of rats fed diets containing either coconut oil or fish oil as dietary fat, using a bifactorial experimental design. To ensure an adequate food intake, all the rats were force-fed by gastric tube. Experimental diets contained either 0.8 mg zinc/kg (zinc-deficient diets) or 40 mg zinc/kg (zinc-adequate diets). The effects of zinc deficiency on the activities of lipoprotein lipase in postheparin serum and postprandial triglyceride concentrations and distribution of apolipoproteins in serum lipoproteins depended on the type of dietary fat. Zinc-deficient rats fed the coconut oil diet exhibited a reduced activity of lipoprotein lipase in postheparin serum and adipose tissue, markedly increased concentrations of triglycerides in serum, and a markedly reduced content of apolipoprotein C in triglyceride-rich lipoproteins and high density lipoproteins compared with zinc-adequate rats fed coconut oil. By contrast, zinc-deficient rats fed the fish oil diet did not exhibit reduced activities of lipoprotein lipase in postheparin serum and adipose tissue and increased concentrations of serum lipids compared with zinc-adequate rats fed the fish oil diet. This study suggests that a reduced activity of lipoprotein lipase might contribute to increased postprandial concentrations of serum triglycerides observed in zinc-deficient animals. However, it also demonstrates that the effects of zinc deficiency on lipoprotein metabolism are influenced by dietary fatty acids.     

Fatty Acid Incorporation in Normal and Degenerating Rat Sciatic Nerve In Vivo

Abstract: Labeled palmitic acid ([16-¹⁴C]palmitate) (0).5 μCi) was injected into rat sciatic nerves in vivo to characterize thc incorporation of this fatty acid into complex peripheral nerve lipids after time lapses of 1 min to 2 weeks. For the first 30 min after intraneural injection, the label was concentrated in nerve diglycerides. Thereafter, the relative diglyccride label declined rapidly, and phospholipid radioactivity rose steadily. After 120 min, phospholipids contained over 70% of the total lipid radioactivity. Among the phospholipids, phosphatidylcholine had the largest percentage of total phospholipid label, and acylation of lysophosphatidylcholine accounted for approximately 75% of this label. With time, there was conversion of [16-¹⁴C]palmitate to other long-chain fatty acids by elongation and desaturation. Phosphatidic acid was labeled also, suggesting the operation of the de novo biosynthetic mechanism. However, the specific radioactivity of 1,2-diacylglycerol was much higher than that of phosphatidic acid, suggesting phosphorylation of diglycerides by diglyceride kinase. After nerve section and survival of 2 h to 50 days, the injection of [16-¹⁴C]palmitate into the degenerating distal segment revealed an overall decline of phospholipid labeling and a commensurate increase of triglyceride radioactivity. Phosphatidylcholine in degenerating nerve contained a larger percentage of the fatty acid label than that in normal nerve. Almost all of the labeling was due to acylation of lysophosphatidylcholine, implying a much smaller contribution of the de novo pathway. Phosphatidylethanolamine and phosphatidylserine showed a relative loss of radioactivity. The changes were apparent at 1 day, but not at 2 h, suggesting loss of homeostatic control, presumably by interruption of axonal flow. An incidental observation was the stimulation of phosphatidylcholine biosynthesis by acylation of lysophosphatidylcholine in the contralateral unoperated sciatic nerve.     

Activation of lipoprotein lipase by lipoprotein fractions of human serum

Triglycerides in fat emulsions are hydrolyzed by lipoprotein lipase only when they are "activated" by serum lipoproteins. The contribution of different lipoprotein fractions to hydrolysis of triglycerides in soybean oil emulsion was assessed by determining the quantity of lipoprotein fraction required to give half-maximal hydrolysis. Most of the activator property of whole serum from normolipidemic, postabsorptive subjects was in high density lipoproteins. Low density lipoproteins and serum from which all lipoprotein classes were removed had little or no activity. Also, little activator was present in guinea pig serum or in very low density poor serum from an individual with lecithin:cholesterol acyltransferase deficiency, both of which are deficient in high density lipoproteins. Human very low density lipoproteins are potent activators and are much more active than predicted from their content of high density lipoprotein-protein. Per unit weight of protein, very low density lipoproteins had 13 times the activity of high density lipoproteins. These observations suggest that one or more of the major apoproteins of very low density lipoproteins, present as a minor constituent of high density lipoproteins, may be required for the activation process.     

Structure of egg yolk very low density lipoprotein. Polydispersity of the very low density lipoprotein and the role of lipovitellenin in the structure

Egg yolk very low density lipoprotein contained on the average 75% of lipid which could be extracted by ether and 25% of a residual lipoprotein, the classical lipovitellenin. The ether-extracted lipid was composed of 75% triglycerides, 7% sterols, 2% mono- and diglycerides, and 16% phospholipids. Lipovitellenin contained 48% lipid composed of 87% phospholipids, 11% triglycerides, and 2% sterols. The protein vitellenin was composed for the most part of units of 74,000 and 270,000 daltons molecular weight.Egg yolk very low density lipoprotein is polydisperse. Preparative ultracentrifugation separated it into six fractions of different average molecular size, and gel chromatography separated it into five. The fractions of larger molecular size contained more lipid and triglyceride than did the fractions of smaller molecular size. The proteins of the fractions appeared to be similar.Egg yolk very low density lipoproteins appear to be a series of molecules composed of cores of lipid of varying sizes with each core surrounded by a layer of lipovitellenin, which is composed principally of glycoprotein and phospholipid.     

Serum lipids in normal and abnormal subjects; observations on controlled experiments

The relationship of diet to serum lipids and to atherosclerosis is a controversial subject. The data presented indicate that diets containing very large amounts of vegetable fat are consistently associated with a sharp fall in serum cholesterol and phospholipid, whereas administration of equal amounts of fat of animal origin is associated with a rise of the serum lipids to levels noted on an average mixed diet. In critical evaluation of elderly hospitalized diabetic patients with advanced atherosclerosis it was observed that there was close mathematical correlation between serum content of cholesterol, "lipoproteins," and phospholipids. There was no obvious correlation between the degree or kind of atherosclerosis and any one of the lipid entities followed. Coronary occlusion occurred in a patient with one of the lowest levels of cholesterol and of lipoprotein.     

Biochemistry of radioiodinated free fatty acids

Summary Radioiodinated free fatty acids have been developed to study myocardial metabolism non-invasively in man. In the present study the distribution of radiolabeled lipids in the myocardium and in arterial and coronary sinus blood was evaluated following injection of three commonly used iodinated fatty acids in fasted (n = 5) and lactate loaded (n = 3) dogs. Five minutes after simultaneous i.v. injection of radioiodinated 17-I-heptadecanoic acid (IHDA),15-(p-I-phenyl) pentadecanoic acid (IPPA) and 15-(p-I-phenyl)-3,3-dimethylpentadecanoic acid (DMIPPA) a biopsy specimen and samples of arterial and coronary sinus blood were taken. After extraction and TLC the relative distribution of radioactivity in the aqueous phase (containing the oxidation products), pellet and organic phase was calculated. The organic phase was further divided into phospholipids, diglycerides, free fatty acids, triglycerides and cholesterolesters. Seventy two percent of IHDA was oxidized, 36% of IPPA and 7% of DMIPPA. The organic phase consisted primarily of triglycerides and phospholipids. The ratios of triglycerides to phospholipids were about the same for IHDA, IPPA and DMIPPA (0.58, 0.65 and 0.50, respectively). Free IHDA in tissue samples was low (4%) and elevated for IPPA and DMIPPA, (17% and 37%). During lactate loading triglycerides were higher for all three fatty acids. For IHDA and IPPA this increase was paralleled by a decrease in the aqueous phase, in case of DMIPPA the aqueous phase remained the same. Five minutes after injection most of the organic phase of both arterial and coronary sinus blood consisted of the injected fatty acids, the aqueous phase contained oxidation products. There were only minor differences during lactate loading. During the evaluation of scintigraphic patterns of the radioiodinated fatty acids under normal conditions (eg at rest) and during elevated lactate levels (eg during exercise) the differences in distribution must therefore be considered.     

Effect of dietary ghee--the anhydrous milk fat, on blood and liver lipids in rats

Dairy products are important sources of dietary fat in India. Anhydrous milk fat, viz., ghee, is consumed as such in the diet and also is used for frying the dishes. Ghee contains high levels of saturated fatty acids and cholesterol, which are considered risk factors for cardiovascular diseases. In the present study, ghee, at levels ranging from 0.25 to 10%, was included in a nutritionally balanced AIN-76 diet fed to Wistar rats for a period of 8 weeks. The serum lipid profiles of these animals showed a dose dependent decrease in total cholesterol, low density lipoproteins and very low density lipoproteins cholesterol, and triglyceride levels when ghee was present at levels greater than 2.5% in the diet. Liver cholesterol and triglycerides also were decreased in these animals. When ghee was included as a sole source of fat at a 10% level, polyunsaturated fatty acids in the serum and liver lipids were reduced significantly. Similar results were observed when ghee was subjected to a higher temperature (120 degrees C) to generate cholesterol oxidation products and fed to the animals. Although cholesterol oxidation products were not accumulated in serum, significant amounts were accumulated in liver only when ghee was fed as a sole source of fat at a 10% level. This study revealed that the consumption of ghee up to a 10% level in the diet altered blood lipid profiles in such a manner as not to elevate the risk factors for cardiovascular diseases.