Bile flow, biliary lipids and bile acid pool have been studied in growing pigs adapted to a semipurified diet of 2, 10 or 20% lard. After a 5-day period of apparent digestibility measurement, bile secretion was studied in previously fistulated pigs. The apparent digestibility of lard was maintained at a very high level, whatever quantity of lard was ingested. Daily bile acid output was 49% higher with the 10% lard diet than with the 2% lard diet, whereas no further increase was observed with the 20% lard diet. There was a direct relationship between bile acid output and pool size. Biliary phospholipid output increased by 29.0% between 2 and 10% dietary lard and by 69.5% between 10 and 20% lard. The corresponding rise in biliary cholesterol output was +33% between 2 and 10 or 10 and 20% lard in the diet. A study of biliary kinetics showed that this adaptation of biliary lipid to dietary fat was observed whatever time of the light/dark cycle was considered. These results, together with a recent demonstration of the implication of endogenous phospholipids in fat digestion, suggested that, in the course of biliary lipid adaptation to dietary fat content, biliary phospholipid could act in synergy with bile salt, resulting in the maintenance of excellent dietary fat digestion.

This study was conducted to examine the effect of insulin on lipid metabolism of adipocytes during pregnancy and lactation in ewes. During the first 3 mo of pregnancy, metabolism of adipocytes from omental adipose tissue was characterized by a high rate of de novo lipogenesis (90 to 125 nmol of acetate incorporated into lipids.2 h-1.10(6) cells-1) and a 38% reduction in response to beta-lipolytic stimulus (isoproterenol 10(-6) M). Simultaneously, there was a rise in the number of high-affinity insulin receptors (Kd = .2 nM), and insulin binding characteristics showed a decrease in the negative cooperativity phenomenon. Moreover, lipogenesis stimulated by insulin (1 mU/ml) increased in comparison with observations in nonpregnant ewes. The last third of pregnancy and early lactation were characterized by a marked fall in lipogenesis and a simultaneous increase in isoproterenol-stimulated lipolysis. During lactation, the number of total insulin receptors was decreased by 62% and insulin stimulation of lipogenesis became inefficient. Results suggest that insulin plays a direct role in adipose tissue metabolism during pregnancy.

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.

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.

The effect of dietary fats on phospholipid class distribution and fatty acid composition was studied in rat fat cell plasma membrane. Three groups of male Wistar weanling rats were fed for 8 wk three diets differing in the amount and nature of the fats: 1.5% sunflower oil (low fat control; LFC), 10% sunflower oil (high fat, unsaturated; HFU), 1.5% sunflower oil + 8.5% cocoa butter (high fat, saturated; HFS). Plasma membranes were prepared from epididymal adipocytes. The amount and type of dietary fat significantly altered membrane phospholipid distribution. Phospholipid content was lowered with HFU as compared to LFC or HFS diets, but no changes were observed for cholesterol. Phosphatidylinositol (PI) and phosphatidylserine (PS) were less affected by dietary changes than were other phospholipid classes. Major changes were detected for phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin (SM) contents. No large changes in PC and PE fatty acid compositions were observed between the LFC and HFS groups, but the HFU diet induced several changes. Correlations with plasma membrane 5'-nucleotidase activities are discussed.