published_or_final_version / Pharmacology and Pharmacy / Master / Master of Philosophy

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Plasma total, low density lipoprotein (LDL) and high density lipoprotein (HDL) cholesterol concentrations increase immediately following birth. Interestingly, this increase is greater in breast-fed infants than in infants fed formula. The reason(s) why there are differences in plasma cholesterol concentrations between breast-fed and formula-fed infants is not known. However, this difference may be a consequence of the variations in lipid composition between milk and infant formula. Little is known regarding the specific effects of the lipid component(s) of infant diets on the expression of genes involved in hepatic lipid metabolism. The studies presented in this thesis determined whether the addition of cholesterol, arachidonic acid [20:4(n-6)] and docosahexaenoic acid [22:6(n-3)] to formula, and the positional distribution of fatty acids in formula triglycerides increases plasma cholesterol in formula-fed piglets to levels observed in milk-fed piglets. In study #1, piglets were fed from birth to 18 days of age with either a conventional infant formula (conventional formula) or a formula with synthesized triglycerides (TG) (synthesized TG formula). The conventional infant formula had 70% of the total 16:0, representing 23% of total fatty acids, esterified at the sn-1 and 3 positions of the formula triglyceride. The synthesized TG formula contained a similar percentage of 16:0, representing 23% of total fatty acids, but had 47% of the total 16:0 esterified at the centre (sn-2) position of the formula triglyceride. Each of the conventional and synthesized TG formulae were provided either without (<0.10 mM) or with 0.65mM cholesterol added to formula, 0.52mmol/L as unesterified cholesterol and 0.13 mmol/L as cholesterol oleate. A reference group of piglets was also fed sow milk. In study #1, the levels of hepatic HMG-CoA reductase mRNA, 7-a-hydroxylase (C7H) mRNA, and acetyl CoA carboxylase (ACC) mRNA were higher in the formula-fed than milk-fed piglets, irrespective of the formula cholesterol content or the positional distribution of fatty acids in the formula triglyceride. This was accompanied by lower plasma total and HDL cholesterol concentrations, lower hepatic triglyceride concentrations and lower concentrations of bile acids, cholesterol and phospholipid in bile of the formula-fed than milk-fed piglets. Adding cholesterol to the formula increased hepatic cholesterol concentrations and decreased hepatic levels of fatty acid synthase (FAS) mRNA, but had no effect on the plasma cholesterol concentrations of the formula-fed piglets. Directing 16:0 to the sn-2 position of the formula triglyceride led to lower plasma total cholesterol and triglyceride concentrations, lower concentrations of bile acids in bile, lower hepatic levels of FAS mRNA and activity, and higher hepatic levels of ACC mRNA than in piglets fed the conventional formula. In study #2, piglets were fed the conventional formula either without or with egg phospholipid (9.5g/L) to provide 0.8% 20:4(n-6) and 0.3% 22:6(n-3) of total fatty acids, or sow milk from birth to 15 days of age. Supplementing the conventional formula with egg phospholipid resulted in higher levels of 20:4(n-6) and 22:6(n-3) in liver and bile phospholipid, higher plasma HDL concentrations, higher bile acid and phospholipid concentrations in bile and lower hepatic ACC mRNA levels in the formula-fed piglets. The levels of 20:4(n-6) and 22:6(n-4) in liver and bile phospholipid were also higher in the piglets fed the supplemented formula than in the piglets fed milk. A significant inverse relation was found between the levels of hepatic ACC mRNA and the percentage of 20:4(n-6) in liver triglyceride and the percentage of 22:6(n-3) in liver phospholipid. Egg phospholipid supplementation of formula had no effect on hepatic LDL receptor mRNA or hepatic FAS activity and mRNA in the formula-fed piglets. The piglets fed either the supplemented or the conventional formula had lower levels of plasma cholesterol and higher levels of hepatic HMG-CoA reductase activity and mRNA and C7H mRNA than piglets fed milk. These studies show that early diet, that is, milk compared to formula feeding, results in lower levels of hepatic HMG-CoA reductase activity and mRNA and C7H mRNA accompanied by higher plasma cholesterol concentrations in piglets. Supplementing formula with cholesterol or the preferential esterification of 16:0 at the sn-2 position of the formula triglyceride did not raise plasma cholesterol concentrations and had no effect on hepatic HMG-CoA reductase activity and mRNA or C7H mRNA in formula-fed piglets. Supplementing formula with egg phospholipid, increased bile and liver phospholipid 20:4(n-6) and 22:6(n-3), decreased the levels of hepatic ACC mRNA and increased the concentrations of bile acids and phospholipid in bile. These findings suggest that milk-fed piglets have lower rates of hepatic cholesterol synthesis, lower rates of conversion of cholesterol to bile acids and the lipid present in sow milk and formula may be metabolized differently. These findings are significant in that they raise the question as to whether or not this effect of early diet will continue through to adulthood and influence metabolic response to diet fat.

Differences in fatty acid distributions in adipose tissue and fatty acid synthetase levels in the liver were determined in Strain A/ST mice of different ages and diets. Since fatty acids have been found to be influential in many disease processes such as heart disease and cancer, which become more prevalent with increasing age, it is important to understand the processes of fat metabolism and changes that occur during the life-stage of senescence. Fatty acid distributions were determined by gas liquid chromatography and fatty acid synthetase (FAS) activities by spectrophotometry.The data from FAS analyses indicated that the mice fed the highfat palmitic acid and low-fat corn oil diets were similar to previous research. The mice fed the stearic acid diets had FAS activity that was affected in a very different manner than other high-fat diets.The results of this study also indicated that aging does not significantly effect the distribution of fatty acids in the adipose tissue of experimental mice. Weight gain in the middle age mice appears to be the result of an increase in all types of fatty acids and not just increased storage of one or a few types. / Department of Biology

A doença arterial coronária (DAC) tem sido a maior causa de morte por doenças nos paises ocidentais. Existem vários fatores responsáveis pela iniciação e progressão desta doença - fatores ambiental ou genético. Muitos fatores de risco para a DAC estão relacionados a alterações do metabolismo lipídico, como acúmulo de lipoproteína de baixa densidade (LDL) no plasma seguida da deposição da lipoproteína na parede arterial. Recentemente, foi demonstrado que uma emulsão rica em colesterol que se assemelha a composição lipídica da LDL liga-se aos receptores que captam a lipopoteína da circulação e internalizam-na no citoplasma. A emulsão, denominada LDE, é feita sem proteína mas quando injetada na circulação sangüínea adquire várias apolipoproteínas (apo) como apo E que pode ser reconhecida pelo receptor de LDL. A apo E tem mais afinidade pelo receptor do que a apo B, a apo que liga a LDL nativa ao receptor. No presente estudo, para esclarecer o processo metabólico que a LDL enfrenta no plasma e o processo de captação da lipoproteína pelos vasos, a LDE marcada com colesterol livre-3H (CL) e oleato de colesterol-14C (CE) foi injetada em 10 pacientes portadores de DAC (57 ± 2,2 anos) submetidos à cirurgia de revascularização miocárdica. Amostras de sangue foram coletadas em intervalos de tempo pré-determinados. A radioatividade presente nas alíquotas de plasma foi determinada por cintilação líquida e a taxa fracionai de remoção (TFR) calculada por análise compartimental. Os fragmentos dos enxertos de aorta, artérias radial e torácica interna, veia safena e pericárdio removidos durante o procedimento cirúrgico foram coletados para extração lipídica, separação por cromatografia de camada delgada e quantificação radioativa. A remoção plasmática do CE da LDE foi similar a do CL da LDE (0,0617 ± 0,0087 vs 0,0528 ± 0,0123, p = 0,5635, respectivamente). A captação do CL da LDE foi maior do que a do CE da LDE na aorta (21% vs 3,1%, p = 0,0049), artéria torácica interna (10,3% vs 2%, p = 0,0007) e veia safena (8% vs 2%, p = 0,0326). Nos fragmentos de artéria radial (14,4% vs 4,3%) e de pericardio (2,2% vs 0,3%), a captação do CL tendeu ser maior do que a captação do CE, porém não foi estatisticamente confirmado. A taxa de esterificação foi maior nos fragmentos de aorta, de toráxica interna e de pericárdio do que nos fragmentos de veia safena (p < 0,001). Concluindo, a LDE foi captada pelos vasos e pericardio em quantidades concideráveis e a captação do CL pelos tecidos foi maior do que a do CE. Ainda, a taxa de esterificação do colesterol livre foi mais intensa nos fragmentos de aorta e torácica interna do que nos fragments de veia safena. / Coronary artery disease (CAD) is the main mortality cause in western countries. There are many factors responsible for the onset and progression of the disease - either environmental or genetic. Many risk factors in CAD are related with disorders of lipid metabolism, such as accumulation of low-density lipoprotein (LDL) in the plasma with deposition of the lipoprotein in the arterial wall. Recently, it was shown that a cholesterol-rich emulsion that mimics the lipid composition of LDL binds to the receptors that take-up the lipoprotein from the circulation and internalizes it into the cytoplasm. The emulsion, denominated LDE, is made without protein but when injected into the bloodstream it picks-up several apolipoproteins (apo) such as apo E that can be recognized by the LDL receptor. Apo E has even more affinity for the receptor than apo B, the apo that binds native LDL to the receptors. In the current study, aiming to clarity the metabolic processes that LDL undergoes in the plasma and the process of lipoprotein uptake by the vessels, LDE labeled with 3H- Cholesterol (CL) and 14C-Cholesteryl Oleate (CE) was injected into 10 CAD patients (57 ± 2,2 yr.) scheduled to be submitted to myocardial revascularization surgery. Blood samples were collected over 24 hour at pre-established intervals. Radioactivity present in plasma aliquots was determined in a scintillation solution and the fractional clearance rate (FCR) was calculated by compartimental analysis. The gratt\'s fragments of aortic, radial, internal thoracic arteries, safenous vein and pericardium discarded during the surgical procedure were collected for lipid extraction, separation by thin layer chromatography and radioactive counting. The removal from plasma of the LDE CE was similar to that of the LDE CL (0,0617 ± 0,0087 vs 0,0528 ± 0,0123, p = 0,5635, respectively). The uptake of LDE CL was greater than that of LDE CE in aorta (21% vs 3,1%, p = 0,0049), internal toracic artery (10,3% vs 2%, p = 0,0007) and safenous vein (8% vs 2%, p = 0,0326). In the radial artery (14,4% vs 4,3%) and pericardium (2,2% vs 0,3%) fragments, the CL uptake also tended to be greater than that of CE, but this was not statistically confirmed. The esterification rate was greater in the aorta, internal thoracic artery and pericardium fragments than in safenous vein fragments (p < 0,001). In conclusion, LDE was taken-up by vessels and pericardium at considerable amounts and LDE CL uptake by those tissues was greater than that of CE. In addition, the cholesterol esterification rate was more intense in the aorta and internal thoracic artery than in venous fragments.

Introdução: Os efeitos do treinamento físico sobre o metabolismo de lípides têm sido bastante estudados, mas a situação diametralmente oposta, qual seja, a de pacientes acamados sob cuidados prolongados, tem sido pouco investigada. A avaliação de possíveis impactos derivados da imobilização é importante, pois o período de restrição ao leito pode gerar fatores de risco aterogênicos. Outro ponto relevante é a concentração e o aspecto funcional da HDL, que é fator de proteção anti-aterogênico e estudos têm mostrado a concentração diminuída em indivíduos sedentários. Objetivo: Investigar os efeitos da imobilização prolongada sobre o perfil de lípides, apolipoproteínas e a transferência de lípides para a HDL em pacientes acamados. Métodos: Foram estudados 23 pacientes acamados por um período maior que 90 dias de internação no Hospital Auxiliar de Suzano do Hospital das Clínicas da Faculdade de Medicina da USP. Foram avaliados o perfil lipídico, a concentração das apolipoproteínas, CETP, LCAT e LDL oxidada. No ensaio de transferência de lípides, as amostras de plasma foram incubadas com a nanopartícula artificial marcada com 3H-éster de colesterol, 14C-fosfolípides, 3H-triglicérides e 14C-colesterol livre. A quantificação da transferência de lípides da nanopartícula foi feita após a precipitação da fração não HDL. Os dados dos pacientes acamados foram comparados com os obtidos de 26 voluntários sedentários saudáveis, pareados por idade e sexo. Resultados: A média de internação dos acamados foi de 817 dias. As concentrações de colesterol não-HDL (148 ± 36 vs 125±40 mg/dL, p<0,05), LDL-C (124±31 vs 96±36 mg/dL, p<0,01), HDL-C (45±10 vs 36±13 mg/dL, p<0,01) foram menores no grupo acamado, enquanto que os triglicérides foram iguais entre os grupos. A apo A-I (134±20 vs 111±24 mg/dL) foi menor nos acamados (p<0,01), e a apo B não apresentou diferença entre os grupos. A LDL oxidada (53±13 vs 43±12 mg/dL) foi menor no grupo acamado (p<0,05), enquanto que a CETP e LCAT não diferiu entre os grupos. As transferências para HDL de éster de colesterol (6,24±1,1% vs 4,80±1,2%), colesterol livre (4,04±1,1% vs 3,05±1,1%), fosfolípides (19,06±1,3% vs 17,32±2,0%) e triglicérides (3,65±0,7% vs 3,06±0,6%) estavam diminuídas nos acamados comparado ao grupo sedentário (p<0,01). Conclusões: O sedentarismo extremo dos pacientes acamados afetou a concentração do HDL-C, apo A-I e as transferências lipídicas da nanopartícula para HDL. Mesmo a menor atividade física exercida no dia-a-dia dos sedentários pode ser determinante na concentração e no metabolismo da HDL. Apesar da menor concentração do LDL-C e os triglicérides não serem diferentes dos sedentários, o status de HDL mostrou-se alterado nos acamados. Devido à importante função anti-aterogênica da HDL, essas alterações metabólicas devem ser um motivo de atenção adicional na assistência a esses pacientes para a prevenção de eventos cardiovasculares. / Introduction: The effects of physical training on lipid metabolism have been deeply studied, but the diametrically opposite situation such as the long-term care bedridden patients, has been little investigated. The evaluation of immobilization impacts is important, because the bedridden period may take to atherogenic risk factors. Another relevant point is the concentration and functional aspects of HDL, that is an anti-atherogenic protection factor and studies have shown lower concentration in sedentary subjects. Objective: To investigate the effects of long-term immobilization on lipid profile, apolipoproteins and lipid transfer to HDL in bedridden patients. Methods: Twenty-tree bedridden patients under a period over than 90 days from the Auxiliary Hospital of the University of São Paulo Medical School in the city of Suzano, state of São Paulo were selected for the study. The lipid profile, apolipoproteins, CETP, LCAT and oxidized LDL concentration were evaluated. In the lipid transfer assay, the plasma samples were incubated with an artificial nanoparticle labeled with 3H-cholesteryl-esters, 14C-phospholipids, 3H-triglycerides and 14C-unesterified cholesterol. The lipids transferred from nanoparticle to HDL were quantified in the supernatant after chemical precipitation of non-HDL fractions. Data from bedridden patients were compared with those obtained from 26 healthy sedentary volunteers, paired for age and sex. Results: The average of hospitalization period of the bedridden was 817 days. The concentration of non-HDL cholesterol (148±36 vs 125±40 mg/dL, p<0.05), LDL-C (124±31 vs 96±36 mg/dL, p<0.01), HDL-C (45±10 vs 36±13 mg/dL, p<0.01), were lower in bedridden group, whereas the triglycerides were equal between the groups. The apo A-I (134±20 vs 111±24 mg/dL) was lower in bedridden (p<0.01), and the apo B was not different between the groups. The oxidized LDL (53±13 vs 43±12 mg/dL) was lower in bedridden group (p<0.05), whereas the CETP and LCAT was not different between the groups. The lipid transfer to HDL of cholesteryl-esters (6.24±1.1% vs 4.80±1.2%), unesterified cholesterol (4.04±1.1% vs 3.05±1.1%), phospholipids (19.06±1.3% vs 17.32±2.0%) and triglycerides (3.65±0.7% vs 3.06±0.6%) were decreased in bedridden patients compared to sedentary group (p<0.01). Conclusions: The extreme sedentary of bedridden patients affected the HDL-C and apo A-I concentration and the lipid transfer from nanoparticle to HDL. Even the low levels of physical activity exerted in the day-to-day life of sedentary subjects can be determinants of HDL concentration and metabolism. Despite their lower LDL-C and the triglycerides not different from sedentary subjects, the HDL status was clearly further altered in the bedridden. Due to the important anti-atherogenic functions of HDL, those metabolic alterations should be an additional matter of concern in the management of those patients to prevent cardiovascular events.

Lipid metabolism in Trypanosoma brucei, the causative agent of African sleeping sickness, differs from its human host, allowing a plethora of novel drug targets to be discovered and validated. Cytidine diphosphate diacylglycerol (CDP-DAG) is a central lipid intermediate produced by the enzyme CDP-DAG synthase (CDS), but nothing was known about CDS in T. brucei. Only one gene encodes CDS in Trypanosoma brucei (Tb927.7.220) and this was shown to encode a functional CDS by overexpression in E. coli and complementation of a yeast CDS null, which was created during this study. Expression and activity of TbCDS was confirmed in T. brucei, and was shown to be essential in both life cycle stages. Disruption of TbCDS altered the lipid profile of T. brucei, confirming a central role for CDP-DAG in phospholipid synthesis. Biochemical and morphological characterisation of mutants in TbCDS expression elucidated at least two separately localised and regulated pools of CDP-DAG and phosphatidylinositol in T. brucei. In bloodstream form these pools are localised to the Golgi and the ER, however in procyclics it is possible that both of these pools are localised to the Golgi, since no phosphatidylinositol synthase protein was detected in the ER of procyclics. Reduction in TbCDS was shown to affect cell cycle regulation and Golgi segregation possibly due to a depletion of phosphorylated phosphatidylinositols (PIPs). These studies also indicate that phosphatidylglycerol may be synthesised by the phosphatidylglycerol-phosphate synthase which may be capable of using phosphatidylserine as a substrate in a headgroup swapping reaction. TbCDS has now been genetically validated as a drug target, and has highlighted novel aspects of lipid biosynthesis in T. brucei. Collectively, these findings highlight the central role played by TbCDS and the new knowledge gained here may lead to the discovery and validation of other novel drug targets against African sleeping sickness.

Plasma total, low density lipoprotein (LDL) and high density lipoprotein (HDL) cholesterol concentrations increase immediately following birth. Interestingly, this increase is greater in breast-fed infants than in infants fed formula. The reason(s) why there are differences in plasma cholesterol concentrations between breast-fed and formula-fed infants is not known. However, this difference may be a consequence of the variations in lipid composition between milk and infant formula. Little is known regarding the specific effects of the lipid component(s) of infant diets on the expression of genes involved in hepatic lipid metabolism. The studies presented in this thesis determined whether the addition of cholesterol, arachidonic acid [20:4(n-6)] and docosahexaenoic acid [22:6(n-3)] to formula, and the positional distribution of fatty acids in formula triglycerides increases plasma cholesterol in formula-fed piglets to levels observed in milk-fed piglets. In study #1, piglets were fed from birth to 18 days of age with either a conventional infant formula (conventional formula) or a formula with synthesized triglycerides (TG) (synthesized TG formula). The conventional infant formula had 70% of the total 16:0, representing 23% of total fatty acids, esterified at the sn-1 and 3 positions of the formula triglyceride. The synthesized TG formula contained a similar percentage of 16:0, representing 23% of total fatty acids, but had 47% of the total 16:0 esterified at the centre (sn-2) position of the formula triglyceride. Each of the conventional and synthesized TG formulae were provided either without (<0.10 mM) or with 0.65mM cholesterol added to formula, 0.52mmol/L as unesterified cholesterol and 0.13 mmol/L as cholesterol oleate. A reference group of piglets was also fed sow milk. In study #1, the levels of hepatic HMG-CoA reductase mRNA, 7-a-hydroxylase (C7H) mRNA, and acetyl CoA carboxylase (ACC) mRNA were higher in the formula-fed than milk-fed piglets, irrespective of the formula cholesterol content or the positional distribution of fatty acids in the formula triglyceride. This was accompanied by lower plasma total and HDL cholesterol concentrations, lower hepatic triglyceride concentrations and lower concentrations of bile acids, cholesterol and phospholipid in bile of the formula-fed than milk-fed piglets. Adding cholesterol to the formula increased hepatic cholesterol concentrations and decreased hepatic levels of fatty acid synthase (FAS) mRNA, but had no effect on the plasma cholesterol concentrations of the formula-fed piglets. Directing 16:0 to the sn-2 position of the formula triglyceride led to lower plasma total cholesterol and triglyceride concentrations, lower concentrations of bile acids in bile, lower hepatic levels of FAS mRNA and activity, and higher hepatic levels of ACC mRNA than in piglets fed the conventional formula. In study #2, piglets were fed the conventional formula either without or with egg phospholipid (9.5g/L) to provide 0.8% 20:4(n-6) and 0.3% 22:6(n-3) of total fatty acids, or sow milk from birth to 15 days of age. Supplementing the conventional formula with egg phospholipid resulted in higher levels of 20:4(n-6) and 22:6(n-3) in liver and bile phospholipid, higher plasma HDL concentrations, higher bile acid and phospholipid concentrations in bile and lower hepatic ACC mRNA levels in the formula-fed piglets. The levels of 20:4(n-6) and 22:6(n-4) in liver and bile phospholipid were also higher in the piglets fed the supplemented formula than in the piglets fed milk. A significant inverse relation was found between the levels of hepatic ACC mRNA and the percentage of 20:4(n-6) in liver triglyceride and the percentage of 22:6(n-3) in liver phospholipid. Egg phospholipid supplementation of formula had no effect on hepatic LDL receptor mRNA or hepatic FAS activity and mRNA in the formula-fed piglets. The piglets fed either the supplemented or the conventional formula had lower levels of plasma cholesterol and higher levels of hepatic HMG-CoA reductase activity and mRNA and C7H mRNA than piglets fed milk. These studies show that early diet, that is, milk compared to formula feeding, results in lower levels of hepatic HMG-CoA reductase activity and mRNA and C7H mRNA accompanied by higher plasma cholesterol concentrations in piglets. Supplementing formula with cholesterol or the preferential esterification of 16:0 at the sn-2 position of the formula triglyceride did not raise plasma cholesterol concentrations and had no effect on hepatic HMG-CoA reductase activity and mRNA or C7H mRNA in formula-fed piglets. Supplementing formula with egg phospholipid, increased bile and liver phospholipid 20:4(n-6) and 22:6(n-3), decreased the levels of hepatic ACC mRNA and increased the concentrations of bile acids and phospholipid in bile. These findings suggest that milk-fed piglets have lower rates of hepatic cholesterol synthesis, lower rates of conversion of cholesterol to bile acids and the lipid present in sow milk and formula may be metabolized differently. These findings are significant in that they raise the question as to whether or not this effect of early diet will continue through to adulthood and influence metabolic response to diet fat. / Graduate and Postdoctoral Studies / Graduate

N-Acylethanolamines (NAEs) are endogenous plant lipids hydrolyzed by fatty acid amide hydrolase (FAAH). When wildtype Arabidopsis thaliana seeds were germinated and grown in exogenous NAE 12:0 (35 µM and above), growth was severely reduced in a concentration dependent manner. Wildtype A. thaliana seeds sown on exogenous abscisic acid (ABA) exhibited similar growth reduction to that seen with NAE treatment. AtFAAH knockouts grew and developed similarly to WT, but AtFAAH overexpressor lines show markedly enhanced sensitivity to ABA. When low levels of NAE and ABA, which have very little effect on growth alone, were combined, there was a dramatic reduction in seedling growth in all three genotypes, indicating a synergistic interaction between ABA and NAE. Notably, this synergistic arrest of seedling growth was partially reversed in the ABA insensitive (abi) mutant abi3-1, indicating that a functional ABA signaling pathway is required for the full synergistic effect. This synergistic growth arrest results in an increased accumulation of NAEs, but no concomitant increase in ABA levels. The combined NAE and ABA treatment induced a dose-dependent increase in ABI3 transcript levels, which was inversely related to growth. The ABA responsive genes AtHVA22B and RD29B also had increased expression in both NAE and ABA treatment. The abi3-1 mutant showed no expression of ABI3 and AtHVA22B, but RD29B expression remained similar to wildtype seedlings, suggesting an alternate mechanism for NAE and ABA interaction. Taken together, these data suggest that NAE metabolism acts through ABI3-dependent and independent pathways in the negative regulation of seedling development.

Three experiments were conducted to determine the relationship of milk fat secretion to concentration and ratio of rumen fermentation products, blood metabolic parameters, ration characteristics, and certain enzymic activity involved in fatty acid synthesis. In Experiment I, 21 cows in mid-lactation were randomized according to milk production to (1) roughage ration (~22% CF) restricted to NRC; (2) concentrate ration (~12% CF) ad libitum; or (3) concentrate ration (~12% CF) restricted to NRC and fed for 30 days. Ad libitum concentrate showed higher dry matter intake (DMI), body weight (BW), milk production than restricted concentrate. The opposite was true for fat test. Concentrate rations (ad libitum and restricted) when compared to roughage showed higher values for DMI, BW, milk production, serum glucose, molar proportion propionate and valerate and lower values for fat test and molar proportion acetate. In Experiment II, 24 cows 180 d. post parturition, were assigned to four rations based on anticipated parturition. Rations were: (1) roughage ad libitum (~20% CF); (2) concentrate ad libitum (~10% CF); (3) concentrate restricted (~10% CF) to NRC; and (4) normal ration (~14% CF) ad libitum. Cows on ad libitum and restricted concentrate consumed less dry matter, acid detergent fiber, neutral detergent fiber and crude protein than control cows (roughage and normal). Cows fed control rations gained more weight than concentrate fed cows. No difference was found for milk production. Milk protein was higher for control cows. Concentrate cows had lower fat test than control cows. Cows on all rations decreased fat test up to week three or four but by week eight or nine, concentrate fed cows had decreased to their lowest fat test. Energy restriction improved milk fat secretion compared to ad libitum intake after the eighth week. Molar proportion VFA favored propionate for concentrate cows and was similar for restricted and ad libitum concentrate. Total ruminal VFA concentration was higher for ad libitum concentrate cows and those cows showed slightly higher glucose and smaller blood acetate compared to control. Twelve cows in mid-lactation were fed the rations of Experiment II to determine the effect of available energy intake on activity of key enzymes of fatty acid synthesis. Activity of 6-phosphogluconate dehydrogenase was not different among rations. Mammary tissue showed from five to six times higher activity than adipose tissue. Fat tissue activity tended to be higher for concentrate rations compared to roughage. No differences among rations were found for glucose 6-phosphate dehydrogenase nor isocitrate dehydrogenase. Mammary tissue was 21 to 28 times more active than adipose tissue for latter enzyme. Fatty acid synthetase showed no difference in activity due to rations, but mammary tissue was seven to ten times more active than adipose tissue. / Ph. D.