��:�����:�: ���f;��'::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: THE PIG AS MODEL . Maternal and Fetal Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Infant Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbohydrate and Lipid Metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Amino Acid Metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vitamin and Mineral Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The pig as a model for human nutrition

Taurine in the central nervous system and the mammalian actions of taurine

Met metabolism occurs primarily by activation of Met to AdoMet and further metabolism of AdoMet by either the transmethylation-transsulfuration pathway or the polyamine biosynthetic pathway. The catabolism of the methyl group and sulfur atom of Met ultimately appears to be dependent upon the transmethylation-transsulfuration pathway because the MTA formed as the co-product of polyamine synthesis is efficiently recycled to Met. On the other hand, the fate of the four-carbon chain of Met appears to depend upon the initial fate of the Met molecule. During transsulfuration, the carbon chain is released as alpha-ketobutyrate, which is further metabolized to CO2. In the polyamine pathway, the carboxyl carbon of Met is lost in the formation of dAdoMet, whereas the other three carbons are ultimately excreted as polyamine derivatives and degradation products. The role of the transamination pathway of Met metabolism is not firmly established. Cys (which may be formed from the sulfur of Met and the carbons of serine via the transsulfuration pathway) appears to be converted to taurine and CO2 primarily by the cysteinesulfinate pathway, and to sulfate and pyruvate primarily by desulfuration pathways in which a reduced form of sulfur with a relatively long biological half-life appears to be an intermediate. With the exception of the nitrogen of Met that is incorporated into polyamines, the nitrogen of Met or Cys is incorporated into urea after it is released as ammonium [in the reactions catalyzed by cystathionase with either cystathionine (from Met) or cystine (from Cys) as substrate] or it is transferred to a keto acid (in Cys or Met transamination). Many areas of sulfur-containing amino acid metabolism need further study. The magnitude of AdoMet flux through the polyamine pathway in the intact animal as well as details about the reactions involved in this pathway remain to be determined. Both the pathways and the possible physiological role of alternate (AdoMet-independent) Met metabolism, including the transamination pathway, must be elucidated. Despite the growing interest in taurine, investigation of Cys metabolism has been a relatively inactive area during the past two decades. Apparent discrepancies in the reported data on Cys metabolism need to be resolved. Future work should consider the role of extrahepatic tissues in amino acid metabolism as well as species differences in the relative roles of various pathways in the metabolism of Met and Cys.

Metabolism of Sulfur-Containing Amino Acids

Absorption of Cholesterol Mechanisms of cholesterol absorption. The second source of cholesterol entering the miscible pools is dietary or exogenous cholesterol. The essential features of the proce...

Regulation of Cholesterol Metabolism

Regulation of cholesterol metabolism. I.

Turnover of taurine in rat tissues.

SummaryNine-week-old swine were fed the bile acid sequestrant, cholestyramine, at 2% and 4% of the diet for successive 4-week periods. Cholestyramine increased bile acid excretion about 10-fold, but the rate of liver biosynthesis of cholesterol was 19 times higher in the cholestyramine fed pigs than in the control pigs. This marked increase in cholesterol synthesis was apparently sufficient to prevent a decrease in plasma cholesterol levels. Feeding 4% cholestyramine (approximately 70 g/day) had no effect on growth, food efficiency, organ weights, plasma lipids and aorta cholesterol. Liver cholesterol levels were decreased slightly, liver vitamin A stores were decreased about one-third, and excretion of fecal fat and cholesterol-like (Lieberman-Burchard reactive) materials were increased in the cholestyramine fed pigs.

Donald L. Schneider

Papers

Turnover of taurine in rat tissues.

Effect of cholestyramine on cholesterol metabolism in young adult swine.

Growth of baby pigs fed infant soybean formulas.

Delay of sexual maturity in chickens by Sterculia foetida oil.

Comparison of fructose and glucose in the diet of alloxan-diabetic rats.