Effect of castration and anatomical site on the plasma membrane structure and the activities of adenylate cyclase and 5'-nucleotidase in pig adipocytes.

The effects of castration on fat cell plasma membrane structure and enzyme activities (adenylate cyclase and 5'-nucleotidase) were studied in pig adipose tissues in two fat deposits (subcutaneous and perirenal). Castration induced a fat cell enlargement in both tissues. Membrane cholesterol content was reduced and fluidity was increased in perirenal fat from castrated animals. Castration had no effect on 5'-nucleotidase activity which was higher in subcutaneous than in perirenal in both kinds of animals. Adenylate cyclase activity was studied in the presence of different effectors: isoproterenol-stimulations of the enzyme were not affected by castration but were site-specific. GppNHp-stimulated activities were increased in subcutaneous fat from castrated animals. Castration had no influence on forskolin stimulations. The magnitude of GppNHp- and forskolin-stimulated activities were found to be tissue-dependent. Membrane results are discussed in relation with castration-induced fat cell enlargement.

Dietary (n-6) polyunsaturated fatty acids affect beta-adrenergic receptor binding and adenylate cyclase activity in pig adipocyte plasma membrane.

The effect of dietary (n-6) polyunsaturated fatty acids (sunflower oil) on pig adipocyte beta-adrenoreceptor and adenylate cyclase activity was examined. Two adipose sites (subcutaneous and perirenal) were compared. The existence of two affinity classes for beta-adrenoreceptors was evidenced. Adenylate cyclase stimulation by isoproterenol was higher in the perirenal fat than in the subcutaneous fat, in parallel to a higher beta-adrenoreceptor density. When sunflower oil was included in the diet, the adenylate cyclase response to beta-agonists was greater, particularly in perirenal fat, as was the affinity of the adrenoreceptors in their high affinity state. However, the number of beta-adrenoreceptors was lower, suggesting that these are spare receptors. Adenylate cyclase stimulation by 5'-guanylylimidophosphate also revealed site- and diet-specific variations indicating alterations at the Gs-protein level. The adenylate cyclase catalytic activity (reflected by the forskolin-stimulated response) in the control group was higher in the subcutaneous fat than in the perirenal fat. In the sunflower oil-fed pigs, the catalytic activity was greater in the perirenal fat relative to controls, leading to similar values in both adipose tissues of sunflower oil-fed pigs. This indicates that the cyclase catalytic subunit activity also depends on the anatomical site of the fat deposit and is influenced by the diet as well. Correlation between these changes in the adenylate cyclase system are discussed in relationship with alterations in the plasma membrane structure.

Effects of dietary fat and adipose tissue location on insulin action in young boar adipocytes.

1. Regulation of lipogenesis and lipolysis by insulin was studied on adipocytes isolated from 100 kg Large white male pigs. Two adipose tissues were studied: subcutaneous and perirenal. Animals were fed either a control low fat diet or a diet containing 14.7% sunflower seed oil. 2. The cell diameter was higher in the group fed the sunflower diet. 3. De novo lipogenesis was decreased for each adipose tissue in the group fed the sunflower diet. The perirenal site had a higher lipogenic activity than subcutaneous site whatever the diet. 4. Insulin did not significantly stimulate lipogenesis but had an important antilipolytic effect on stimulated lipolysis by isoproterenol. 5. The antilipolytic action of insulin was higher in perirenal adipocytes with the control diet. With the sunflower diet, the decrease was about 54.4% for subcutaneous adipocytes, whereas the inhibition was decreased in perirenal adipocytes. Addition of theophylline reversed the antilipolytic action of insulin. 6. Insulin binding was not affected neither by the dietary fat nor by the adipose tissue location. 7. Absence of de novo lipogenesis stimulation by insulin was not due to an impairment in insulin binding. 8. The different effects of dietary fat and adipose tissue location on the antilipolytic action of insulin could not be explained by a modification of insulin binding but rather by a latter event, probably at a post-insulin binding stage.

Effects of castration, dietary fat and adipose tissue sites on adipocyte plasma-membranes cyclic AMP phosphodiesterase activity in the pig.

1. cAMP Phosphodiesterase activity and kinetic parameters (Km and Vmax) were measured in subcutaneous and perirenal adipocyte plasma membranes from Large White male and castrated pigs. The animals were fed a control low fat diet or a sunflower diet enriched with linoleic acid (C18:2 n-6). 2. Phosphodiesterase activity, low Km and Vmax were lowered by castration. 3. In animals fed the sunflower diet, phosphodiesterase activity decreased without affecting either Km or Vmax. 4. Phosphodiesterase activity was higher in perirenal sites than in subcutaneous ones, particularly in male pigs. This may be explained by a lower Km or a higher cAMP phosphodiesterase affinity to cAMP in perirenal sites. 5. Theophylline was a potent inhibitor of phosphodiesterase activity principally in perirenal sites. 6. The intermediate role of cAMP phosphodiesterase in adenylate cyclase activity and lipolytic processes is discussed.

Specific alterations in different adipose tissues of pig adipocyte plasma membrane structure by dietary lipids.

The effect of dietary n-6 polyunsaturated fatty acid content on pig adipocyte plasma membrane was studied with two types of adipose tissues: subcutaneous backfat layer and perirenal fat. When pigs were fed a diet containing 15 percent sunflower oil, the n-6 polyunsaturated fatty acid content in the membranes increased in both tissues parallel to a decrease in the n-9 monounsaturated fatty acid content. An increase in membrane fluidity measured by fluorescence polarization was observed particularly in subcutaneous tissue, in spite of a higher level of some membrane rigid components: the sphingomyelin/phosphatidylcholine ratio was increased in the subcutaneous tissue, whereas the cholesterol/phospholipid ratio was increased in the perirenal one. The latter results gave evidence for a depot-dependent modification in the membrane structure by dietary lipids.

Dependence between 5'-nucleotidase activity and phosphatidylcholine content in pig adipocyte plasma membrane. Absence of relationship with membrane physical state.

1. 5'-Nucleotidase activity has been examined in pig adipocyte plasma membrane, in two different adipose sites. 2. Membrane fluidity has been investigated using 1,6-diphenylhexatriene (DPH). 3. In this work, evidence was found for a tissue specificity of 5'-nucleotidase (E.C. 3.1.3.5) activity. 4. The enzyme activity was highly correlated to the membrane phosphatidylcholine content. 5. The latter parameters remained unmodified when large alterations in membrane composition and physical state were produced by means of the dietary n-6 PUFA content manipulations.

Influence of different dietary fats on the incorporation of exogenous fatty acids into rat adipose glycerides.

Male Wistar rats were fed for 6 wk either a control low fat diet (1.5% sunflower seed oil) or a diet containing 10% fat: either saturated (coconut oil, cocoa butter) or unsaturated (olive oil, sunflower seed oil). In each dietary condition, in vitro incorporation of exogenously added fatty acids (ranging from capric to oleic acid) was studied in epididymal adipose glycerides. Analysis of variance of data revealed that there was a significant effect of the diet x substrate interaction. When results were expressed per cell lipid weight medium-chain fatty acids (capric and lauric) were esterified to a lesser extent than long-chain fatty acids regardless of the nature of dietary fat (saturated vs. unsaturated). The nature of dietary fat was found to have no effect on the incorporation of medium-chain fatty acids. Feeding saturated fats resulted in an increase of incorporation of long-chain fatty acids into adipose glycerides whereas feeding unsaturated fats did not modify fatty acid incorporation. Modifications of mean fat cell size by dietary fat could not account for all the observed variations.

Food intake in captive leverets before weaning and the composition of the milk of the brown doe-hare (Lepus europaeus).

Daily milk and solid food intakes were studied in leverets before weaning and during 52 lactations in captive doe-hares. Changes in milk composition were studied in parallel during 11 other lactations. With the mode of feeding used (one nursing per 24 hr), milk and solid food intakes were recorded for the first 30 neonatal days. The profile of milk intake had three phases: it showed an increase between D0 and D12, a plateau between D12 and D22, and a decrease between D22 and D30. Solid food intake began at D7 and increased significantly from D14. The mean levels of dry matter, fat and protein in doe hare's milk were similar to those in rabbit's milk The amino acid composition of total protein resembled that of rabbit's milk. There were fewer medium-chain fatty acids (8:0-14:0) in here's milk than in rabbit's milk and the levels of some major minerals (Ca, P, K) were also different. The levels of protein and medium-chain fatty acids (except 14:0) increased significantly with time. On the other hand, the levels of long-chain fatty acids (except 18:0 and 18:3, N = 3) decreased significantly. There was no significant change in the other factors studied.

Comparative study of endogenous fecal fatty acids in germ-free and conventional rats.

The effects of gastrointestinal flora on the quantitative and qualitative aspects of "endogenous" fecal fatty acid excretion were studied in the rat using germ-free (GF) and conventional (CVL) animals, lipid-free diet and open-tubular gas-liquid chromatography. Gastrointestinal flora slightly increased endogenous excretion of fatty acids. Analysis of fatty acids from different fecal lipid fractions showed that the presence of a microflora in the gastrointestinal tract extensively modified the qualitative aspects of endogenous fecal fatty acid spectra. In total endogenous fecal lipids, concentrations of mono and polyunsaturated fatty acids (from C16 to C22) were 3.5 times higher in GF rats, while concentrations of even-numbered and saturated fatty acids were 1.5 times higher in CVL rats. Odd-numbered fatty acids (from C11:10 to C2:0) represented 6.5% of total endogenous fecal fatty acids in CVL rats vensus 1.5% in GF rats. Branched-chain fatty acid (even-and-odd-numbered, iso and anteiso) concentrations were 12.9% in CVL rats versus 2.0% in GF rats. Results clearly showed that the gastrointestinal flora was the main source of odd-numbered fatty acids and branched-chain fatty acids in endogenous fecal lipids. However, a secondary source may also exist since these fatty acids represented 3.5% of the total endogenous fatty acids in GF rats.

Effects of two different medium-chain triglycerides (tri C8:O and tri C12:O) on liver lipids in the growing rat.

Results presented in this study emphasize the long-term effects of dietary fatty acid chain length on some biochemical parameters of the liver in the growing rat. High levels of medium-chain fatty acids feeding (C8:O and C12:O) from 40 to 340 g of body weight induced liver growth and lipid contents intermediary between values recorded with a lipid-free diet and with a diet containing long-chain fatty acids. No steatosis was recorded but neutral lipid contents appeared to be correlated with the dietary fatty acid chain length while phospholipid contents remained much more stable. In the four tested nutritional conditions, only dodecanoïc or lauric acid (C12:O) feeding induced important alterations in the fatty acid pattern of liver neutral lipids. Medium-chain fatty acids, and even lauric acid which was intensely esterified in adipose tissue triglycerides, did not appreciably modify the fatty acid composition of liver phospholipids and were not esterified in it.

Comparison of long term lipogenic effects of two different medium-chain triglycerides (tri C8: O and tri C12 : O) in the growing rat.

During the growth (35 g-340 g), and as compared to results obtained with a lipid-free diet or a diet containing long-chain fatty acids, high levels of Tri C8 : O or Tri C12 : O did not change the quantitative aspects of proteinogenesis and lipogenesis balances. The incorporation of Tri C8 : O into the diet did not change the fatty acid composition of body lipid stores while the incorporation of Tri C12 : O induced a lipogenesis characterized by the disappearance of about 50% of the n-9 and n-7 unsaturated fatty acids, the emergence of an equivalent amount of saturated fatty acids in C12 and C14, and the decrease of hexadecanoic or palmitic acid concentration. Titers of saturated fatty acids with a melting point higher than 40 degrees C increased from 34% to 64%. Results suggested an efficient inhibition of fatty acid biosynthesis de novo by C12 : O, associated with an impossibility for microsomal enzymes to assume the elongation of a sufficient amount of C12 : O to maintain C16 : O concentration and to furnish an important amount of substrate (C18 : O) to delta-9-stearoyl coenzyme A desaturase for oleic acid synthesis. Introducing dodecanoic acid into the diet of growing animals appears to be the most efficient method for increasing the degree of saturation of body lipids without changing the concentrations of long-chain saturated fatty acids.

[Effects of prolonged ingestion of dodecanoic or lauric acid on the secretion of fatty acids in the rat mammary gland]. / Effets de l'ingestion prolongée d'acide dodécanoïque ou laurique sur la secrétion d'acides gras par la mamelle chez la Ratte.

Dodecanoic or lauric acid (C 12 : 0) ingestion before and during lactation causes profound changes in the fatty-acid secretion by Rat mammary gland. Lauric acid concentration in milk lipids may reach 35% of total fatty-acids; saturated fatty-acids represent 80% of total secreted fatty-acids. When exogenous lauric acid supply is given, mammary tissue does not efficiently regulate the qualitative aspects of fatty-acid secretion.

Effects of maternal dodecanoic or lauric acid (C12:0) feeding on milk fatty acid secretion and lipogenesis in the suckling rat.

Lauric acid feeding induced large alterations in mammary gland fatty acid secretion. It was highly incorported in milk triglycerides, suggesting that mammary gland was not able to efficiently regulate the qualitative aspects of medium-chain fatty acid secretion. These modifications in milk fatty acid secretion did not alter pup growth, lipogenesis balance or the classic parameters of the pup liver during the suckling period. Nevertheless, maternal lauric acid feeding induced important alterations in the qualitative aspects of pup lipogenesis before weaning.

[Effect of unsaturated dietary fats on growth and lipogenesis in rats]. / Influence du degré d'insaturation des lipides alimentaires sur la croissance et la lipogénèse chez le rat

In the growing rats weighting between 70 and 300 g, when 20% of the total daily energy intake consists either of 'lard (with 36% oleic acid) or sunflowerseed oil (with 61% linoleic acid)', lipogenesis, proteinogenesis, feed efficiency ratio and body compositions are identical. With the nutritional conditions used during these experiments, the occurrence of a high level of polyunsaturated fatty acids level in the diet cannot be considered as an exogenous factor able to modify the parameters studied.