Hypocholesterolemic effect of anhydrous milk fat ghee is mediated by increasing the secretion of biliary lipids

The anhydrous milk fat ghee is one of the important sources of fat in the Indian diet. Our earlier studies showed that rats fed diets containing greater than 2.5 wt% of ghee had lower levels of serum cholesterol compared with rats fed diets containing groundnut oil. To evaluate the mechanism of the hypocholesterolemic effect of ghee, male Wistar rats were fed a diet containing 2.5 or 5.0 wt% ghee for a period of 8 weeks. The diets were made isocaloric with groundnut oil. Both native and ghee heated at 120 degrees C containing oxidized lipids were included in the diet. The ghee in the diet did not affect the 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase activity in the liver microsomes, but it significantly increased biliary excretion of cholesterol, bile acids, uronic acid, and phospholipids. The rats fed ghee had lower levels of cholesterol esters in the serum as well as in the intestinal mucosa. Both native and oxidized ghee influenced cholesterol metabolism. These results indicate that supplementation of diets with ghee lipids would increase the excretion of bile constituents and lower serum cholesterol levels.     

Differential incorporation of dietary conjugated linolenic and linoleic acids into milk lipids and liver phospholipids in lactating and suckling rats

Interest in health benefits of conjugated fatty acids is growing. The present study compared the incorporation pattern of dietary conjugated linolenic acids (CLnA) into milk with that of conjugated linoleic acids (CLA). Lactating Sprague-Dawley rats (Day 1) were divided into five groups fed the control diet (n=4) or one of four experimental diets supplemented with 1–2% CLA or CLnA mixture (n=8 each). Supplementation of 1% and 2% CLA led to enrichment of 4.17% and 8.57% CLA, respectively, while supplementation of 1% and 2% CLnA resulted in enrichment of only 0.98% and 1.71% CLnA in the milk lipids, demonstrating the transfer of CLnA from maternal diet to milk was discriminated. When the lactating rats were given a diet containing a CLnA mixture of 9t,11t,13t-, 9c,11t,13t- and 9c,11t,13c-CLnA isomers, two CLA isomers, namely, 9t,11t (0.59–0.90%) and 9c,11t (1.21–1.96%), were found in the milk, suggesting that three CLnA isomers were Δ-13 saturated. Dietary CLnA at 1–2% had no effect on liver phospholipid (PL) fatty acid composition of both maternal and suckling rats, whereas dietary CLA increased docosahexaenoic acid (4c,7c,10c,13c,16c,19c-22:6) and palmitic acid (16:0) proportionally in the PL of maternal rats, but it suppressed 16:0 in the PL of suckling rats. It is concluded that maternal rats incorporate CLnA isomers into milk differently from that of CLA isomers. Most interesting is that maternal rats can metabolically convert CLnA to CLA.     

Effect of the ingestion of thermically treated fat on blood lipids and blood lipoproteins in the rat

The effect on rats fed on a diet with 15% solid frying fat (diet B) is compared to the effect of a diet with 15% of the same fat but in the raw state (diet A). After 10 weeks being fed on these diets serum triglycerides, phospholipids, total cholesterol, free cholesterol, esterified cholesterol, high density lipoprotein-cholesterol and free fatty acid levels were checked. Percentage of very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins as well as the composition of these lipoproteins was determined in parallel. Rats fed on diet B showed a significant increase in phospholipids and a significant decrease in VLDL when compared to those fed on diet A. Phospholipids on LDL decreased significantly in diet B fed rats. The data obtained seem to indicate that the hypercholesterolemic tendency induced by frying fat is neutralized by a decrease in VLDL levels.     

Effect of dietary fat on whole body fatty acid synthesis in weanling rats

The effect of dietary fat on body composition, whole body lipogenesis, and enzyme activity was measured in rats over the first 16 weeks post-weaning. Rats were fed either a low fat (5% w/w fat) or high fat (20% w/w fat) diet for the first 4 weeks. After this time all rats were fed the low fat diet. The results showed no significant effect of diet on the rate of fat synthesis over the first 8 weeks of the experiment. However, the activities of the enzymes of fatty acid synthesis [glucose 6-phosphate dehydrogenase, malic enzyme, adenosine triphosphate-citrate lyase, acetyl-coenzyme A carboxylase (ACCX), fatty acid synthetase] were dependent on the age and dietary status of the animals. The exact pattern depended on the specific enzyme and the tissue source. No significant differences in pyruvate dehydrogenase (PDH) activity were observed. Mathematical analysis of the enzyme activities suggested that ACCX and PDH were the most likely sites of fat synthesis regulation. In addition, an examination of body composition and overall weight retention showed that the "weight increasing" effect of a high fat diet could be completely reversed by subsequent feeding of a low fat diet. However, the reversal required an additional 12 weeks. Interestingly, at this time the rats switched from a high fat to a low fat diet had a lower body weight and lower body fat content than rats fed a low fat diet throughout the course of the experiment.     

Diurnal variations of plasma lipoproteins and liver lipids in rats fed starch sucrose or fat

The incidence of the dietary source of energy on lipid transport and accumulation was investigated over a full nycthemeral cycle in adapted rats fed ad libitum. Starch, sucrose and lard were compared. Lipoprotein composition of the plasma, liver and plasma lipids and insulinemia were analyzed every 3 hours over 24 hours. The pattern of VLDL concentration was dependent on the nature of the energetic substrate. Feeding starch resulted in a remarkable stability of lipoproteins, liver and plasma lipids, despite clearcut diurnal variations in plasma non esterified fatty acids, insulinemia and liver glycogen. In sucrose-fed rats VLDL rose to a sharp maximum in the post prandial period (9-12:00) and were totally cleared by 18:00. In fat-fed rats, HDL were elevated during the night, suggesting a possible stimulation of their synthesis by dietary fat in the intestine. LDL were constantly elevated with peak values at 21:00 while VLDL were very low, even at night, despite elevated levels of non-esterified fatty acids. It is concluded that, in animals adapted to a high fat-diet, a high level of circulating non esterified fatty acids is not sufficient to promote the synthesis of VLDL. The main regulating factor appears to be the intensity of hepatic lipogenesis which is stimulated by sucrose and inhibited by lard. No correlation was found between variations in plasma VLDL and insulinemia.     

Effect of dietary cardiac glycosides on blood pressure regulation in rats

To investigate the possible physiological significance of dietary cardiac glycosides in blood pressure regulation, the blood pressure of normal Sprague Dawley rats raised on a regular diet, which naturally contains large amounts of Na+-pump inhibitors, was compared with that of rats on a purified synthetic diet, which contains no Na+-pump specific inhibitors, and with that of rats on a synthetic diet supplemented with 10 microg x mL(-1) ouabain or 10 microg x mL- convallatoxin in the drinking water. After 6 weeks on the synthetic diet, the systolic blood pressure in the synthetic diet group was significantly elevated (145 +/- 5 vs. 128 +/- 4 mmHg, P < 0.05). At 10 weeks it reached a plateau (154 +/- 3 vs. 122 +/- 3 mmHg, P < 0.05). Plasma renin activity and Na+ level were significantly higher in animals fed synthetic diets than in the regular diet group (P < 0.01). Administration of either losartan or lisinopril or a switch to a low salt synthetic diet (0.03% sodium) normalized the synthetic diet-induced high blood pressure. Supplementation of the synthetic diet with the cardiac glycosides delayed the onset of the increase in blood pressure for 4 weeks. Plasma aldosterone levels were approximately doubled in the cardiac glycoside-treated groups. Higher plasma Na+ levels and hematocrit values present in the synthetic diet group were normalized by the glycoside supplements. These results suggest that supplemental dietary cardiac glycosides exert bidirectional effects on blood pressure regulation through actions that modulate extracellular fluid and electrolyte balance.     

Dietary effects of bitter gourd oil on blood and liver lipids of rats.

Bitter gourd is widely used as an edible plant in Asia. In this study, we evaluated the effects of bitter gourd oil (BGO) on the blood and liver lipids of rats. Three groups of rats were given a basal diet (AIN-93G) containing 7% fat by weight. The dietary fat consisted of soybean oil (control), soybean oil + BGO (6.5:0.5, w/w; 0.5% BGO), or soybean oil + BGO (5:2, w/w; 2.0% BGO). This fat treatment gave 3.4 and 15.4% of cis(c)9,trans(t)11,t13-18:3 in the dietary fat of 0.5 and 2.0% BGO, respectively. Fatty acid analysis showed the occurrence of c9,t11-18:2 in the liver of rats fed BGO diets, whereas this conjugated linoleic acid (CLA) isomer was not detected in the liver of rats fed the control diet. Furthermore, dietary BGO decreased the concentration of 18:2n-6 and increased the concentration of 22:6n-3. The formation of the CLA isomer in the liver lipids of rats fed BGO diets could be explained by either of the following two metabolic pathways, namely, enzymatic biohydrogenation of c9,t11,t13-18:3 or enzymatic isomerization of c9,c12-18:2. The BGO diets had significantly reduced free cholesterol levels with a trend toward an increase in HDL cholesterol, but there was no significant change in the total cholesterol. The dietary BGO also affected the level of plasma hydroperoxides. A slight but significant increase in hydroperoxides was found in the rats fed 2.0% BGO. This may be attributed to the lower oxidative stability of c9,t11,t13-18:3 in BGO.     

The anhydrous milk fat, ghee, lowers serum prostaglandins and secretion of leukotrienes by rat peritoneal macrophages

Ghee, the anhydrous milk fat, is one of the most important sources of dietary fat in India. Male Wistar rats were fed diets containing 2.5, 5.0 and 10 wt% ghee for a period of 8 weeks. The diets were made isocaloric with groundnut oil. The results showed that serum thromboxane levels decreased by 27-35%, and 6-keto-prostaglandin F1alpha by 23-37% when ghee was incorporated at level of 10% in the diet. Prostaglandin E2 levels in serum and secretion of leukotrienes B4, C4 and D4 by peritoneal macrophages activated with calcium ionophore decreased when increased amounts of ghee from 2.5 to 10% were included in the diet. Arachidonic acid levels in macrophage phospholipids decreased when incremental amounts of ghee were fed to rats. These studies indicate that ghee in the diet not only lowers the prostaglandin levels in serum but also decreases the secretion of leukotrienes by macrophages.     

Gastric lipolysis of milk lipids in suckling rats

Fatty acid composition of the major lipid classes in stomach contents of suckling rats at 1, 5, 10, 17 and 20 days of lactation was compared to that of milk lipids. In milk, 98% of fatty acids were in triacylglycerols at all lactation times. Medium-chain fatty acid concentrations increased from 8% in colostrum to 26% at day 5. Fatty acid composition of stomach acylglycerols at all lactation times was different from that of milk triacylglycerols, containing less medium-chain fatty acids, 8:0 and 10:0. This preferential hydrolysis was also shown by higher concentrations of medium-chain fatty acids in the free fatty acid fraction. The lipolysis of medium-chain fatty acids from triacylglycerols resulted in the appearance of di- and monoacylglycerols with 50-100% higher amounts of 14:0 and 16:0. The similar fatty acid composition of products suggests that considerable lipolysis occurred in stomachs of suckling rats even at 1 day of age. Although there was a 10-fold increase in milk consumption, the extent of lipolysis was similar throughout the suckling period because of a parallel rise in lingual lipase levels.     

Effect of dietary fat on biliary lipids composition of gallbladder bile in miniature swine (Sus scrofa).

1. Weaning animals (34 days old) were fed for 6 months with four diets that differed only in the quantity and quality of fat sources (control group 3.2% (w/w), lard-fed group 7.6% (w/w), olive-oil-fed group 10.4% (w/w), and sunflower-oil-fed group 10.5% (w/w). Samples were collected and assessed after animals were killed at 6 months of age. 2. Our results show that the quality of fat did not alter biliary lipids composition of the gallbladder bile composition in miniature swine after 6 months adaptation to the diet, except for a significant increase of the phospholipid concentration in the lard-fed group with regard to the control group. 3. The highest and lowest bile cholesterol saturation indices were observed in sunflower and lard-fed groups, respectively showing in all cases saturation indices far from the saturation point.