Gilbert A. Leveille

Lipid biosynthesis and transport in the domestic chick (Gallus domesticus)

Abstract 1. 1. Lipogenesis in the domestic chick ( Gallus domesticus ) was studied by administering acetate-1- 14 C and glucose-U- 14 C and isolating the 14 C-labeled lipids from body tissues. 2. 2. Between 90 and 95 per cent of de novo fatty acid synthesis in the chick appears to take place in the liver. 3. 3. The primary function of chick adipose tissue appears to be one of lipid storage rather than lipid synthesis. 4. 4. Triglyceride occurring in the plasma as β- or low-density lipoprotein is the main transport form of lipid from liver to adipose tissue. 5. 5. The possible sources of labeled free fatty acids appearing in the plasma shortly after isotope administration are discussed.

Lipogenesis in isolated adipose tissue of the domestic chick (Gallus domesticus)

Abstract 1. 1. Isolated adipose tissue of the domestic chick (Gallus domesticus) has a low lipogenic capacity. 2. 2. This tissue utilizes more acetate and pyruvate than glucose for fatty acid synthesis. 3. 3. In the presence of unlabelled glucose, insulin did not stimulate the incorporation of acetate-1-C14 or pyruvate-2-C14 into fatty acids, but stimulated the incorporation of glucose-U-C14 into glyceride-glycerol. 4. 4. The activity of the pentose cycle dehydrogenase enzymes is low in both chick liver and adipose tissue homogenates. 5. 5. Malic enzyme activity is high in chick liver homogenates and may be a primary source of reducing equivalents for lipid synthesis in this organ.

In Vivo Lipogenesis in the Domestic Chicken

Summary The ability of chicks to utilize glucose-U-14C and acetate-1-14C as substrates for lipid synthesis has been studied. Chicks readily incorporated glucose and acetate carbon into fatty acids and nonsaponifiable lipids of liver and adipose tissue. Glucose-U-14C was also utilized for glyceride-glycerol formation. The relative importance of adipose tissue and liver as sites of fatty acid synthesis was estimated. Chick adipose tissue was found to be of minor importance as compared to liver, accounting for no more than 30% of total fatty acid synthesis.

Acetyl CoA Carboxylase and Fatty Acid Synthetase Activities in Liver and Adipose Tissue of Meal-fed Rats

Summary The activities of acetyl CoA carboxylase and fatty acid synthetase in liver and adipose tissue of meal-eating (limited to a single, daily, 2-hr meal) and nibbling (adlibitum-fed) rats were determined. The activities of both enzymes were significantly higher in adipose tissue but not liver of meal-eating as compared to nibbling animals. This observation is in accord with the concept that adipose tissue is the primary site of fatty acid biosynthesis and the major site of the lipogenic adaptive changes induced by meal-feeding.

In vivo fatty acid synthesis in adipose tissue and liver of meal-fed rats.

Summary The results of these studies show that lipogenesis is enhanced in liver and adipose tissue of intact rats as a consequence of meal-feeding. Fatty acid synthesis was approximately 200-fold higher in adipose tissue and 9-fold higher in liver of meal-fed as compared to nibbling rats. Increases in fatty acid radioactivity in adipose tissue, liver and serum were observed between 6 and 9 hours after the initiation of the meal. A possible explanation for these changes is proposed. Serum glucose and serum liver total lipid and cholesterol levels were also determined and no significant alterations due to meal-feeding were noted. From the observed rates of glucose-U-14C incorporation into liver and adipose tissue fatty acids an estimate was made of the relative importance of these tissues as sites of fatty acid synthesis. These calculations suggest that in the nibbling rat 50-90% of the fatty acids are synthesized in adipose tissue whereas when fatty acid synthesis is stimulated by meal-feeding, adipose tissue apparently accounts for about 95% of the total fatty acids synthesized.

In vitro hepatic lipogenesis in the hen and chick

Abstract 1. 1. An incubation system containing 10 mM acetate and 5 mM glucose produced a maximal rate of fatty acid synthesis. Using this system it was shown that chick liver slices synthesized fatty acids in a linear fashion over a 3-hr incubation period. 2. 2. The ability of liver slices from chicks and hens to utilize acetate-1- 14 C for lipid synthesis and oxidation to CO 2 was found to be similar.

Influence of age on in vitro lipid biosynthesis and enzymatic activity in pig adipose tissue.

Summary Lipogenesis, as measured by the incorporation of glucose-U-14C into fatty acids by adipose tissue slices was determined periodically in 8 pigs from the age of 35 days (9.0 kg) to 180 days (90.0 kg). In the suckling pig, the capacity for fatty acid synthesis was very low, presumably due to the high-fat content of sow milk. Upon ingestion of the high-carbohydrate diet, fatty acid synthesis increased rapidly and reached a peak at 67 days of age. From 67 days of age there was a gradual decrease in the capacity for fatty acid synthesis with advancing age. Changes in the activities of citrate-cleavage enzyme and malic enzyme occurred in parallel with the changes in fatty acid synthesis, supporting the participation of these enzymes in lipogenesis in pig adipose tissue.

Lipid metabolism in isolated adipose tissue of the domestic pig (Sus domesticus).

Abstract 1. 1. The lipogenic capacity of adipose tissue of the domestic pig ( Sus domesticus ) was studied in vitro using tissue slices and free adipose tissue cells. With both systems pig adipose tissue demonstrated a high lipogenic capacity. 2. 2. Both glucose and acetate were readily utilized by pig adipose tissue for fatty acid synthesis, but glucose was the chief precursor of glyceride-glycerol. 3. 3. Subcutaneous adipose tissue appears to have a superior lipogenic capacity to that obtained from within the abdomen (mesenteric fat). 4. 4. Lipogenesis from glucose in adipose tissue taken from mature pigs (6 months old) does not appear to be dependent upon the presence of added insulin. 5. 5. The activity of the pentose cycle dehydrogenase enzymes and malic enzyme is high in abdominal and subcutaneous adipose tissue of the pig.

Metabolic consequences of dietary medium-chain triglycerides in the pig

Summary Lipid metabolism was studied in pigs fed diets containing corn oil, lard, tallow, coconut oil, or medium-chain triglyceride (MCT). The ingestion of diets containing tallow, lard, corn oil, or coconut oil resulted in approximately a 50% depression in the capacity for fatty acid synthesis in adipose tissue as measured by the incorporation of glucose-U-14C into fatty acids. The ingestion of MCT resulted in a significantly lower rate of fatty acid synthesis than observed in adipose tissue from the pigs fed the control diet, but MCT was less inhibitory than the other sources of fat. The activities of malic enzyme and citrate cleavage enzyme were significantly reduced by all fat sources except MCT. Plasma cholesterol levels were increased by feeding 10% dietary corn oil, tallow, lard, or coconut oil as compared with the pigs fed low-fat control diets. Pigs ingesting MCT-supplemented diets had plasma cholesterol levels similar to those of pigs consuming the low-fat diet. The ingestion of 10% MCT resulted in a 5-fold increase in plasma ketone levels. A hypothesis is discussed to explain the metabolic consequences of MCT ingestion in the pig.

Metabolic Adaptation Induced by Meal-eating in the Pig

The effect of periodicity of eating on adipose tissue lipogenesis and enzymatic activity was investigated in pigs subjected to the following eating schedules. One group was fed ad libitum (nibbler) from a self-feeder; another group was allowed access to food daily from 8 AM to 10 AM only (meal-fed 2 hr/24) and the third group was allowed access to food from SAM to 10 AM every other day (meal-fed 2 hr/48). In addition the influence of periodicity of eating on weight gain, efficiency of food utilization, and on carcass character istics was determined. There was no significant difference in daily gain between the nibblers and those fed a 2-hour meal daily. However, both the nibbling pigs and those fed a 2-hour meal daily gained faster than pigs fed a single 2-hour meal every other day. Pigs fed a single daily meal (2 hr/24) were more efficient in food utilization than the nibbling animals. Seven hours after meal ingestion the incorporation of glucose-U-HC into fatty acids was significantly greater in adipose tissue slices from meal-fed pigs than from the pigs fed ad libitum. Adi pose tissue slices from pigs fed every other day (2 hr/48) had a higher rate of lipogenesis than did adipose tissue slices from pigs fed a single daily meal (2 hr/ 24). The results obtained from biopsy samples taken at three different times support the concept that a hyperlipogenic state can be produced in the pig by restricting the time in which the animal had access to food. J. Nutr. 102: 1115-1122, 1972.