M.T.Ravi Subbiah

Nature of fecal sterols and intestinal bacterial flora

Sterol excretion in the spontaneously atherosclerosis-susceptible White Carneau (WC) pigeon, the Silver King (SK) pigeon and the Show Racer (SR) pigeon was studied by thin layer chromatography (TLC), argentation TLC and gas liquid chromatography. Unlike man and the chicken, these pigeons excreted no coprostanol or coprostanone derivatives of sterols. Moreover incubation of14C-labeled cholesterol with pigeon feces indicated that, also unlike man and the chicken, these pigeons are unable to convert it to coprostanol. Bacteriologic examination revealed the absence of gram-negative anaerobic flora and of members of the genusBifidobacterium in both the WC and SR pigeons. On the other hand, one of the two SK pigeons examined showed evidence of the presence of bothBacteroids fragilis andB. bifidum in the upper intestinal tract. Although no qualitative experiments were performed, no unusual characteristics of the aerobic flora were noted in these pigeons. In addition, analysis of human stool specimens indicated a “normal” bowel flora. The flora of the intestinal tract of the chicken is similar to that of the human. Because of this similarity, it appears that differences in environment (living conditions, diets) between the human and the chicken are of little consequence. The results obtained in this study suggest the possibility that the anaerobic gram-negative flora and sponsible, at least in part, for the chemical conversion of cholesterol to coprostanol.

Effect of enhancement of cholesterol degradation during neonatal life of guinea pig on its subsequent response to dietary cholesterol

The effect of feeding cholestyramine to neonatal guinea pigs on their subsequent plasma cholesterol levels and response to dietary cholesterol were studied. Male neonatal guinea pigs were suckled for 6 days. One group was maintained on a 1.1% cholestyramine diet for 6 weeks and the control group weaned normally. Both groups of guinea pigs were then fed a standard diet of Guinea Pig Chow for 6 weeks. During the standard diet period bile acid and neutral sterol excretion rates were significantly higher in the group previously treated with cholestyramine than the control group despite the similarity in plasma cholesterol levels. When both groups of guinea pigs were subjected to a 0.5% cholesterol diet for 4 weeks, plasma cholesterol levels were significantly lower in the group previously treated with cholestyramine than the control group. The plasma cholesterol levels continued to be significantly lower in the group previously treated with cholestyramine after an additional four weeks on standard diet. These results suggest that stimulation of cholesterol catabolism in the neonatal period can influence the subsequent response to dietary cholesterol.

Effect of estrogens on the activities of cholesteryl ester synthetase and cholesteryl ester hydrolases in pigeon aorta

This study is the first to report the effect of conjugated equine estrogens on the acitivity of cholesteryl ester synthetase and cholesteryl ester hydrolases in the aorta. In spontaneously atherosclerosis-susceptible White Carneau pigeons, estrogens significantly decreased (P less 0.01) the activity of cholesteryl ester synthetase and increased (P less than 0.01) the cholesteryl ester hydrolase activity in the microsomal fraction of the aorta. There was no effect on the cholesteryl ester hydrolase activity in the supernatant fraction. The inhibition of cholesteryl ester synthesis and the stimulation of cholesteryl ester hydrolase might be responsible for the decreased content of cholesteryl esters noted in pigeon aorta after estrogen treatment.

Prostaglandin E2 biosynthesis and effect in pigeon aorta possible role in atherogenesis

This study for the first time examines the biosynthesis and effect of prostaglandin E2 (PGE2) in aorta during genetic atherosclerosis. Biosynthesis of PGE2 from [1-14C]arachidonic acid was investigated in the aorta of spontaneously atherosclerosis-susceptible White Carneau pigeons and was compared with that of the atherosclerosis-resistant Show Racer breed. Most of the PGE2 synthetase activity was located in the microsomes. The synthesis was linear up to an hour and was optimal at pH 7.4. The formation of PGE2 in the aorta in the White Carneau pigeons was significantly higher (P less than 0.01) than that in age-matched Show Racer pigeons. In vitro PGE2 strongly inhibited the cholesteryl ester hydrolase activity (51.6% inhibition at 4 X 10(-7) M concentration) in the supernatant fraction of the aorta. On the basis of (1) the increased formation of PGE2 in the aorta of atherosclerosis-susceptible pigeons and (2) its effect on specific enzymes that control cholesteryl ester concentration in aorta, it is hypothesized that PGE2 synthesized at a higher rate in damaged aorta has a significant role in cholesteryl ester accumulation during atherogenesis.

Effect of prostaglandins E1 and F1α on the activities of cholesteryl ester synthetase and cholesteryl ester hydrolases of pigeon aorta in vitro

The in vitro effects of prostaglandins E1 and F1alpha on the activity of cholesteryl ester synthetase and cholesteryl ester hydrolase activities of the pigeon aorta were examined. It was found that prostaglandin E1 markedly inhibited the cholesteryl ester hydrolase activity in the supernatant fraction and slightly inhibited the cholesteryl ester synthetase activity. Prostaglandin F1alpha, however, modestly stimulated the cholesteryl ester hydrolase activity both in the microsomal and in the supernatant fraction of the aorta. These observations strongly warrant further studies on the role of prostaglandins in atherogenesis.

Uptake of campesterol in pigeon intestine.

Abstract Campesterol was the major plant sterol found in the gastrointestinal tract, liver, and plasma of pigeons fed diets containing large amounts of β-sitosterol and small amounts of campesterol. On feeding plant sterol mixtures, it was found that campesterol was taken up preferentially by the pigeon intestine.

Sterol and bile acid metabolism during development. 3. Occurrence of neonatal hypercholesterolemia in guinea pig and its possible relation to bile acid pool

The relationship of the changes in plasma cholesterol to bile acid pool was studied in the newborn guinea pig. Plasma cholesterol reached the maximum on the fifth day and gradually declined to adult levels. The cholesterol concentration in the high density lipoproteins (HDL) was higher in the newborn guinea pig than in the adult. Plasma triglycerides peaked on the third day and decreased markedly. The bile acid pool increased progressively after birth with a 13-fold increase at 5 days of age. While the hepatic triglycerides decreased sharply in the newborn guinea pig, hepatic cholesterol increased in the first 5 days and then decreased to adult levels. This study has described the occurrence of neonatal hypercholesterolemia in the guinea pig and its possible relationship to the low level of bile acid synthesis.

Sterol and bile acid metabolism during development. 1. Studies on the gallbladder and intestinal bile acids of newborn and fetal rabbit

Bile acid composition and content in the intestine and gallbladder of newborn and fetal rabbits were investigated. Unlike the circumstances in adult rabbits, the bile acids were conjugated with both taurine and glycine. The major bile acids of the fetus and newborn rabbit were cholic acid, chenodeoxycholic acid, and deoxycholic acid. This is different from the known bile acid composition of adult rabbits, in which deoxycholic acid is the major bile acid (greater than 80%). The proportion of chenodeoxycholic acid was higher in the fetal than in the newborn tissues. The total bile acid pool in the newborn was higher than in the fetus. In the fetus, large proportions of bile acids (60.9%) were associated with the gallbladder fraction, whereas in the newborn the bulk of the bile acids were found with the intestinal fraction (64.4%).

Presence of cholesterol ester synthetase activity in guinea pig gallbladder epithelium

Abstract This study is the first to demonstrate the presence of cholesteryl ester synthetase activity in the gallbladder epithelium. Using epithelium of the guinea pig gallbladder, the study demonstrated that the enzyme was localized mainly in the particulate fraction. The enzyme required CoA and ATP for activity and displayed a pH optimum of 7.0. The uptake of biliary cholesterol by gallbladder (shown by other investigators) and the presence of cholesteryl ester synthetase activity (demonstrated in this study) suggest that the gallbladder epithelium has an active role which might be important in conditions of cholesterol supersaturation in bile.

Studies in spontaneously atherosclerosis-susceptible and resistant pigeons: Nature of plasma and aortic sterols, steryl esters, and free fatty acids☆☆☆

Abstract 1. 1. Comparison of atherosclerosis-susceptible White Carneau pigeons with atherosclerosis-resistant Show Racers showed increased aortic sterol content, sterol esterification, and oleic acid of steryl esters. 2. 2. Unlike plasma, the oleic/linoleic acid ratio in aortic steryl ester fatty acids between the two breeds differed. 3. 3. Plasma and aortic free fatty acids from both breeds are similar. 4. 4. The lower aorta of White Carneau pigeons showed a higher sterol content, sterol esterification, and oleic acid concentrations than that of Show Racers. 5. 5. Cholestanol has been identified in the aorta of both breeds, with high concentrations in the distal aorta of White Carneau pigeons.