Production of VLDL and vitellogenin(s) in oestrogen-challenged hypothyroid chickens

Compared with normal control birds of the same breed, obese strain (OS) White Leghorn chickens, exhibiting classical symptoms of hypothyroidism, were generally half as responsive to an oestrogen challenge in terms of synthesis of VLDL and vitellogenins, despite having livers which were, on the average, twice as large. Even the few OS birds which were laying eggs and therefore enjoying a degree of thyroid function, failed to exhibit normal responses to hyperdynamic doses of oestrogens. However, simultaneous injections of triiodothyronine (T3), in the physiological range, and hyperdynamic doses of oestrogenic substances (Ayerst Co., mainly oestrone) into OS chickens resulted in serum levels of VLDL and vitellogenins which were more than double those achieved without thyroid hormone treatment. Untreated OS birds were found typically to exhibit a unique hyperlipaemia (i.e. increased synthesis of serum triglyceride and phospholipid without corresponding increases in synthesis of apoprotein B (normally associated with VLDL and LDL) or apoprotein A-1 (normally associated with HDL). This type of hyperlipaemia resulted in formation of large lipid micelles which imparted turbidity to the serum. Injection of oestrogenic substances into two OS chickens especially hyperlipaemic in this unique fashion resulted in rapid liver production of apoprotein B. By 2 days post injection the levels of apoprotein B in the sera were increased fifteen times over original levels. The initially turbid sera were completely cleared by 36 h post oestrogen treatment. Since the VLDL present during the first 2 days floated at faster rates than those present at 6 days following injection of oestrogen, it appears that newly synthesized apoprotein B (very likely as lipoprotein B) can combine with existing lipid micelles in the plasma, thus ultimately dispersing the larger lipid micelles into lipoproteins of a size consistent with the loss of turbidity.     

The influence of three days or three weeks of force feeding on the transport of plasma lipids in young female chickens (Gallus gallus L.).

1. Ten-week old broiler females were force-fed (FF) for 3 days or 3 weeks. 2. Control livers were lighter in weight and contained less total lipid, neutral lipid and phospholipid than either FF group, which did not differ. 3. Radioactivity incorporated into liver neutral lipid fractions from 1-[14C]acetate injection was greater in birds FF 3 weeks than controls. Those FF 3 days were intermediate. In all groups, the triglyceride fraction contained 90-94% of isolated radioactivity, the cholesterol fraction 4-8% and the cholesterol ester fraction 1-2%. 4. Plasma lipids were elevated in the birds FF for 3 weeks, but not in those FF 3 days. After injection of 1-[14C]acetate, plasma lipid specific radioactivities were not different between the 3 groups at 20 and 60 min post injection, but were greater in the controls at 120 min.     

Feeding the nitric oxide synthase inhibitor L-N(omega)nitroarginine elevates serum very low density lipoprotein and hepatic triglyceride synthesis in rats

This study was conducted to study the influence of dietary L-N(omega)nitroarginine (L-NNA), a nitric oxide (NO) synthase inhibitor, on serum lipids and lipoproteins and on the activities of enzymes related to lipid metabolism in rats. Feeding rats a diet containing 0.2 g/kg L-NNA for 5 weeks elevated serum concentrations of triglyceride, cholesterol, phospholipid, and free fatty acid and reduced serum nitrate (an oxidation product of NO). The elevation in serum triglyceride was mainly due to the elevation in very low density lipoprotein (VLDL) triglyceride. Contents of cholesterol and phospholipid in the VLDL fraction also were elevated by L-NNA. L-NNA treatment caused significantly higher activity of hepatic microsomal phosphatidate phosphohydrolase (the rate-limiting enzyme in triglyceride synthesis) and lower activity of hepatic carnitine palmitoyltransferase (the rate-limiting enzyme in fatty acid oxidation). Activities of hepatic enzymes responsible for fatty acid synthesis such as glucose-6-phosphate dehydrogenase, malic enzyme, and fatty acid synthase were unaffected by L-NNA. The activity of hepatic microsomal phosphocholine cytidyltransferase (the rate-limiting enzyme in phosphatidylcholine synthesis) was reduced significantly by L-NNA. Our results suggest that lower NO production caused the elevations in hepatic triglyceride synthesis by higher esterification of fatty acid and lower fatty acid oxidation, leading to an enrichment of VLDL triglyceride.     

Amiodarone-induced changes in lipid metabolism

Hypothyroidism is a major cause of secondary hypercholesterolemia. Amiodarone treatment alters both the levels of serum lipids and thyroid hormones. We investigated whether the amiodarone-induced changes in lipid metabolism are related to the changes in thyroid hormone levels. Eighteen patients received amiodarone (31 +/- 3 g cumulative dose) for six weeks. Serum triglyceride, total-cholesterol, high density lipoprotein-cholesterol and its subfractions, apolipoproteins B and AI, and plasma post-heparin lipoprotein lipase and hepatic triglyceride lipase activities were determined. Amiodarone treatment caused significant increases in serum total-cholesterol (baseline 4.4 +/- 0.21 (SE), 6 weeks 5.12 +/- 0.26 mmol/l, P less than 0.01), in low density lipoprotein cholesterol (baseline 2.61 +/- 0.26, 6 weeks 3.36 +/- 0.21 mmol/l, P less than 0.05) and in apolipoprotein B (baseline 1.95 +/- 0.15, 6 weeks 2.26 +/- 0.13 mmol/l, P less than 0.01) concentrations. Serum high density lipoprotein and its subfractions, or apolipoprotein AI levels did not change. Plasma post-heparin lipoprotein lipase activity increased (baseline 137 +/- 21, 6 weeks 168 +/- 21 U/ml, P less than 0.01) while hepatic triglyceride lipase did not change. Amiodarone also caused an increase in serum thyroxine (baseline 110 +/- 8, 6 weeks 136 +/- 6 mmol/l, P less than 0.05), although values remained in euthyroid range. In summary, amiodarone therapy increased the concentrations of atherogenic lipoproteins in the serum similar to that seen in hypothyroidism. On the other hand the effect of amiodarone on lipoprotein lipase was opposite to that seen in hypothyroidism. Therefore, amiodarone-induced changes in lipid metabolism cannot be explained solely on the basis of the changes in circulating thyroid hormone levels.     

Fluidity characteristics of bovine thyroid plasma membranes

Highly purified plasma membranes of bovine thyroid were obtained by differential pelleting followed by discontinuous gradient centrifugation in a swing-out rotor. Subfractions of plasma membranes were prepared by affinity chromatography on Con A-Sepharose. The final membrane fractions were enriched 25-30-fold over homogenate in 5'-nucleotidase and alkaline phosphatase and displayed a protein to phospholipid ratio of 1.67 and a cholesterol to phospholipid molar ratio of 0.55. The phospholipid composition did not deviate appreciably from that of whole tissue except for the higher sphingomyelin level (22.5 vs. 14.0%). The predominant fatty acids were palmitic (16:0), oleic (18:1), stearic (18:0) and linoleic (18:2) acid. The physical state of the membrane was studied by (i) calculation of the lipid structural order parameter SDPH from steady-state fluorescence anisotropy determinations of the hydrophobic probe 1,6-diphenyl-1,3,5-hexatriene (DPH); (ii) estimation of the lateral diffusion coefficient of pyrene following excimer formation. These parameters were determined in native thyroid plasma membranes and in reconstituted vesicles, obtained by detergent dialysis from octylglucoside solubilized membrane components. The presence of membrane protein or neutral lipids induced more restraint on the movements of the fluorophores. The lipid order parameter, SDPH was mainly determined by the neutral lipids. Subfractions of plasma membrane enriched in luminal membranes have a slightly lower fluidity (higher SDPH and lower Ddiff values) than subfractions enriched in basolateral membranes. This difference appears to be due to both differences in lipid as well as protein composition. Under physiological conditions, no significant alterations in probe dynamics could be observed upon addition of thyrotropin or cholera toxin, even at micromolar concentrations.     

Yolk lipids and their fatty acids in the wild and captive ostrich (Struthio camelus)

A comparative study has been made of the major lipid fractions and their fatty acid compositions in the yolk of eggs from ostriches under wild and farmed conditions. There were no differences in the lipid contents and proportions of the lipid fractions between the two groups of yolks. In both groups of yolks triacylglycerol and phospholipid were the major fractions. In the eggs from the wild ostriches, all the lipid fractions displayed substantial concentrations of C18 polyunsaturated fatty acids, triacylglycerol being particularly rich in linolenic acid and phospholipid rich in linoleic acid; phospholipid displayed substantial concentrations also of C20 and C22 polyunsaturates. There were considerable differences in the fatty acid compositions between the yolks. Those from the farmed birds displayed lower proportions of C18 polyunsaturates, particularly linolenic acid, throughout the lipid fractions. Compensatory increases were displayed most obviously in the concentrations of oleic acid and palmitoleic acid as well as other acids. The distinctive and extensive changes in fatty acid composition, particularly relating to the polyunsaturates, are discussed with respect to overall dietary requirements and specificities for embryo metabolism and possible effects on reproductive performance.     

Captivity diets alter egg yolk lipids of a bird of prey (the American kestrel) and of a galliforme (the red-legged partridge)

The salient feature of the fatty acid profile of kestrel eggs collected in the wild was the very high proportion of arachidonic acid (15.2%+/-0.7% of fatty acid mass, n=5) in the phospholipid fraction of the yolk. Kestrels in captivity fed on day-old chickens produced eggs that differed from those of the wild birds in a number of compositional features: the proportion of linoleic acid was increased in all the lipid fractions; the proportion of arachidonic acid was increased in yolk phospholipid and cholesteryl ester; the proportion of alpha-linolenic acid was decreased in all lipid classes, and that of docosahexaenoic acid was decreased in phospholipid and cholesteryl ester. Partridge eggs from the wild contained linoleic acid as the main polyunsaturate of all the yolk lipid fractions. Captive partridges maintained on a formulated diet very rich in linoleic acid produced eggs with increased levels of linoleic, arachidonic, and n-6 docosapentaenoic acids in the phospholipid fraction; reduced proportions of alpha-linolenic acid were observed in all lipid classes, and the proportion of docosahexaenoic acid was markedly reduced in the phospholipid fraction. Thus, captive breeding of both the kestrel and the partridge increases the n-6/n-3 polyunsaturate ratio of the yolk lipids.     

A role for IL-15 in driving the onset of spontaneous autoimmune thyroiditis?

The obese strain (OS) of chickens, which suffers from spontaneous autoimmune thyroiditis, is an excellent animal model for Hashimoto's thyroiditis and provides a unique opportunity to investigate the mechanisms underlying and driving the onset of the disease. Following recent advances in cloning chicken cytokines, we can now begin to investigate the role of cytokines in driving the lymphoid infiltration of the thyroid seen in these birds from day 7 posthatch. Using real-time quantitative RT-PCR, we characterized the expression of IFN-gamma, IL-1beta, IL-2, IL-6, IL-8, IL-15, and IL-18 in thyroids from OS birds and control CB line birds, both in the embryo just before hatch (embryonic day 20) and at 3 and 5 days posthatch. All of these cytokines were up-regulated compared with levels in thyroids from CB birds, at least at some time points, with some evidence for coordination of regulation, e.g., for the proinflammatory cytokines IL-1beta and IL-8. Only IL-15 was up-regulated at all time points. IL-15 was also shown to be up-regulated in spleens of OS birds at embryonic day 20 and 5 days posthatch, suggesting that IL-15 is constitutively up-regulated in this line of birds. This could explain the general immune system hyperreactivity exhibited by OS chickens and may be a factor driving the lymphoid infiltration of the thyroid.     

Serum and thyroid tissue lipids in patients with thyroid tumors in euthyroidism

Plasma lipids of 24 euthyroid subjects with thyroid adenoma and non-toxic primary differentiated thyroid carcinoma (papillary and follicular types) were assessed and compared with a similar investigation conducted on 20 normal subjects. A parallel study with thyroid tumor tissues examined the lipid changes which occurred in the same group of patients. These were compared with the picture seen in 5 normal thyroids. The investigations examined the changes in total lipids; total, free and esterified cholesterol; total phospholipids; lecithin; cephalin and sphingomyelin; triglycerides and free fatty acids in both serum and thyroid tissue. Compared with normal subjects, the serum lipids were almost identical except for the concentration of free fatty acids which showed significantly lower values in the group with neoplastic changes. Tissue analysis of the cancerous thyroid however revealed a marked rise in virtually all lipid fractions but the cholesterol seemed to dominate the picture. The differential studies of total phospholipids for thyroid tissue membrane lipids further revealed a significant increase in the lecithin and sphingomyelin components of total phospholipids as well as the esterified cholesterol fraction in thyroid carcinoma. The changes in thyrophospholipids were more marked in females normal thyroids than males. An attempt has been made through evaluation of the results derived from differential lipid studies to elucidate the role of some of the various fractions determined and the possible effect of the changes described on thyroid hormone metabolism.     

Changes in fatty acid composition of rat liver and serum induced by distal small bowel resection

The serum lipid composition and the fatty-acid profiles of the major lipid fraction (triglycerides, esterified cholesterol, and phospholipid) of liver and serum were examined 6 weeks after both 50% and 75% distal small bowel resection (DSBR). Total serum lipid content did not modify after DSBR. Esterified cholesterol and phospholipid levels of the serum did not significantly change after the operation. However, a significant increase in both free cholesterol and triglyceride levels was observed after DSBR. Different fatty acid changes in the liver and serum lipid fractions were found after DSBR, with the greatest differences in the hepatic esterified cholesterol fraction. These results suggest that DSBR affects both the lipid composition and the fatty acid composition of major lipid fraction of liver and serum.     

Effects of Dietary Polychlorinated Biphenyls and Protein Level on Liver and Serum Lipid Metabolism of Rats

The effects of polychlorinated biphenyls (PCB) and dietary protein level on the liver and serum lipid metabolism of rats were studied. Rats were fed an experimental diet containing 7 or 30% casein with or without 0.1 % PCB for 24 days. Dietary PCB increased the level of triglyceride, phospholipid and cholesterol in the liver. The accumulation of triglyceride and cholesterol in liver was markedly increased with a low protein diet. The incorporation of injected ³H₂O into liver cholesterol was increased by PCB, but not affected by the dietary level of protein. The incorporation of the tracer into liver fatty acids was not increased by PCB intake. Dietary PCB also raised serum cholesterol and phospholipid, while PCB decreased triglyceride level, especially in rats on low protein diet. In addition, PCB intake clearly raised serum high density lipoprotein and diminished very low density lipoprotein. In the low protein group, PCB markedly repressed the incorporation of ³H₂O into serum lipids. The results suggest that the hepatic lipids accumulation by the addition of 0.1 % PCB to a low protein diet might be mainly ascribed to a repression in the transport of triglyceride from liver to blood. KEY WORDS: PCB, dietary protein, liver lipids, serum lipoprotein.     

Biochemical reactivity of aortic connective tissue in chickens treated with cholesterol diet in combination with a nonspecific immunization or with epinephrine and thyroxine

Our previous work showed that only changes in aortic lipids and no change in connective tissue components occurred in hatched chickens, fed for four months a cholesterol atherogenic diet. The aim of this study was to test if combination of atherogenic stimuli will activate the connective tissue of aorta.Newly hatched chickens were fed a diet containing 2% cholesterol and in addition immunized with bovine serum albumen. Another group was administered epinephrine and thyroxine in excessive doses. The treatment lasted 6 to 7 weeks. In isolated aortas the amount and rate of synthesis of collagen, activity of prolyl hydroxylase and collagenase and the amount of total cholesterol were measured. With the exception of significantly increased lipid content, neither parameter reflecting the connective tissue and collagen metabolism was affected by the various atherogenic stimuli. It is concluded that in young chickens the changes in cholesterol content in aortic tissue preceded eventual activation of connective tissue components.     

Immunogenetic and ontogenetic studies of chickens with selective IgA deficiency and autoimmune thyroiditis

In addition to spontaneous hypothyroidism and autoimmune thyroiditis, chickens of the obese strain (OS) have a high incidence of selective IgA deficiency. Elevated levels of serum IgM also occur in many OS chickens. The IgA deficiency begins by 2 weeks, the age when hypothyroidism is developing. Like thyroiditis, a greater incidence of IgA deficiency was noted in OS birds homozygous for the B¹ allele than for the B⁴ allele of the major histocompatibility locus. Although IgA deficiency occurs in both sexes, it is found in a higher frequency in females than males (2:1). An abnormal ontogenesis of immunological competence may influence both traits.     

Serum lipoproteins in the spiny lobster, Panulirus interruptus.

1. Most of the lipids in the hemolymph of the spiny lobster, Panulirus interruptus, were associated with a high density lipoprotein (HDL3). The lipid of this lipoprotein was composed of phospholipid (88%), sterol (4%) and triglyceride (3%). 2. In animals fed 14C-labeled triglyceride radioactivity was not seen in the serum until 12 hr after feeding. Most of this serum radioactivity was associated with phosphatidyl choline. 3. Electron micrographs showed that negatively stained high density lipoproteins of the lobster had a polymorphic appearance.     

Effects of cortisol on lipid and lipoprotein synthesis in rat hepatocytes]

Under in vivo conditions cortisol induces moderate hyperlipidemia followed by an increase in the phospholipid and triglyceride concentrations in the blood and a decrease of cholesterol; similar changes were observed in the liver. At all time intervals studied cortisol inhibits the phospholipid and cholesterol syntheses and decreases the specific radioactivities of the lipids in the mitochondrial fraction. The hormone has an inhibiting effect on the fatty acid synthesis at early postinjection stages. The phospholipid synthesis is increased after adrenalectomy and is then inhibited after injection of the hormone. A single injection of ACTH or cortisol causes suppression of phospholipid and cholesterol syntheses and a decrease in their specific radioactivities in the mitochondria. A similar effect is observed under stress conditions. In addition, the hormone inhibits the synthesis of lipoprotein apoproteins of very low and high densities. After 5 hours following the hormone injection the lipoprotein apoprotein synthesis in the liver is activated; the activation of apoprotein synthesis is also observed after adrenalectomy. However, the injection of the hormone to adrenalectomized rats decreases the apoprotein synthesis. It was shown that in blood serum cortisol affects the conversions of very low density lipoproteins into low density lipoproteins, thus providing for hyperlipidemia.     

Physicochemical properties of lipids: new strategies to manage fatty acid bioavailability.

Fatty acid bioavailability can be managed through the physicochemical properties of lipid such as lipid-droplet size, lipid-droplet ultrastructure (lipids organization between core and surface), structure of triglycerides and of phospholipids. The lipid-droplet size exhibits a major effect on lipase activity during lipid digestion. The lipid-droplet ultrastructure is a dynamic factor controling lipase interaction at the lipid interface via the surface phospholipid layer, and also lipase activity via the proportion of triglyceride molecules able to locate at the surface. Triglyceride structure affects in a strong manner digestion, absorption and fatty acid metabolism. Finally, optimal fatty acid transport to specific tissues is dependent on the vehicle molecule (triglyceride or ethyl ester or phospholipid). All these aspects provide convincing support for the possibility of using biotechnologically remodeled lipids with specific physicochemical properties for health benefits.     

Mechanisms of the different effect of sucrose on the quantity of lipids in the blood and liver of experimental animals]

Experiments on rats showed that inclusion of sucrose into the composition of diets with increased or normal carbohydrate content accelerated the synthesis in the liver of apoproteins of pre-beta-lipoproteins and their loading with endogenously formed lipids, promoted a more intensive secretion of lipoproteins of very low density into the blood and an increase in it of the triglyceride level. However, the rate of the lipid compensation with the protein of pre-beta-lipoproteins in the liver depends also on the qualitative ratio of the carbohydrate and fat components in the diet. In using the diet with sucrose with the physiological ratio of carbohydrates and fats (2:1) there was noted a lower load of apoproteins of pre-beta-lipoproteins with lipids, this leading to an increase of the latter in the liver.     

Elevation of corticosteroid-binding globulin in obese strain (OS) chickens: possible implications for the disturbed immunoregulation and the development of spontaneous autoimmune thyroiditis

Basal plasma levels of corticosterone and corticosteroid-binding globulin (CBG) have been investigated in Obese strain (OS) chickens afflicted with spontaneous autoimmune thyroiditis (SAT). Corticosterone was determined radioimmunologically, and CBG by using a highly sensitive radioligand saturation assay. OS chickens displayed total corticosterone levels not different from healthy normal White Leghorn (NWL) chickens. CBG, however, was found to be twice as high in OS chickens as compared with their healthy counterparts, irrespective of sex or age. This quantitative difference in the CBG level is not compensated for by either altered affinity or specificity of the molecule. Furthermore, no differences were found in the response of OS and NWL lymphocytes to the suppressive effect of glucocorticoids in vitro. We therefore assume that OS animals are deficient in free, hormonally active corticosterone. An additional indication for such a diminished glucocorticoid tonus was that in vivo treatment of OS chickens with glucocorticoid hormones, thus increasing the free and active hormone fraction, normalizes the T cell hyperreactivity and significantly reduces thyroid infiltration. Possible pathophysiological implications of a diminished glucocorticoid tonus for spontaneous autoimmunity, as well as possible explanations for the beneficial effects of glucocorticoid treatment on the development of SAT, are discussed.     

Metabolism of endogenous sterol ester by the superovulated rat ovary in vitro

Sterol, glyceride and phospholipid were found to account for more than 90% (w/w) of the lipid extracted from whole superovulated rat ovaries. These lipids, together with non-esterified fatty acids, were assayed in slices of the tissue after incubation for various times. Whereas the concentrations of triglyceride, diglyceride and phospholipid did not change significantly during incubation, that of sterol ester markedly decreased and those of free sterol, monoglyceride and non-esterified fatty acid increased. Evidence is presented that in this tissue (in contrast with other mammalian tissues) the main endogenous substrate for respiration is fatty acid derived from sterol ester.     

Changes in cellular composition during magnesium deficiency.

1. Concentrations and compositions of liver, serum and milk lipids of cows were measured during 6 days' starvation and serum lipids during 60 days' re-feeding. 2. The concentration of free fatty acid in serum increased fivefold during starvation. 3. The content of total lipid in liver (g/100g of liver dry matter) doubled owing to a 20-fold increase in triglyceride, an eightfold increase in cholesterol ester, a three fold increase in free fatty acid and a 20% increase in cholesterol. There were no changes in the content or composition of liver phospholipids. 4. Starvation lowered the concentrations of total lipid, phospholipid and cholesterol ester of dextran sulphate-precipitable serum lipoproteins. Total lipid and cholesterol ester concentrations in lipoproteins of d greater than 1.055 and in lipoproteins not precipitable by dextran sulphate decreased from day 4 of the starvation period and during the first 20 days' re-feeding. 5. During starvation there were decreases in percentages of stearic acid and increases in oleic acid in serum free fatty acids and triglycerides and in liver neutral lipid. 6. Throughout starvation total milk lipid yield decreased, yields and percentages of C4-14 fatty acids decreased and percentages of C18 fatty acids increased. 7. It is suggested that accumulation of triglyceride in liver may be caused by increased uptake of plasma free fatty acids without corresponding increase in lipoprotein secretion.