Carbohydrate and Lipid Metabolism

Beubler and Badhri (1990) used the PGE2-induced net fluid secretion in the jejunum and colon in the rat to evaluate the antisecretory effects of antidiarrhoeal drugs. Polyethylene catheters were placed into the jejunum and colon and Tyrode solution was instilled into the loops. Net fluid transfer rates were determined gravimetrically 30 min after instillation of Tyrode solution. 

Beubler E, Badhri P (1990) Comparison of the antisecretory effects of loperamide and loperamide oxide in the jejunum and the colon of rats in vivo. J Pharm Pharmacol 42 689-692 

Pillai NR (1992) Anti-diarrhoeal activity of Punica granatum in experimental animals. Int J Pharmacognosy 30 201-204 Robert A, Nezamis JE, Lancaster C et al. (1976) Enteropool-ing assay a test for diarrhea produced by prostaglandins. Prostaglandins 11 809-828 

Shook JE, Burks TF, Wasley JWF, Norman JA (1989) Novel calmodulin antagonist CGS 9343B inhibits secretory diarrhea. J Pharmacol Exp Ther 251 247-252 

Such anaerobic metabolism can sustain life in animal cells only for short periods. However, if there is free access of oxygen, pyruvic acid passes from the above Meyerhof sequence to the tricarboxylic acid cycle (see Section 4.5), where it is completely oxidized to carbon dioxide and water. Alternative pathways exists for degrading glucose, through pentose phosphate in vertebrates, the choice of reactions varying with different tissues (see under bacteria below). All of the cell s ribose, so important in the synthesis of nucleic acids, comes from the pentose type of glycolysis. 

The following paragraphs summarize variations of glycolysis in invertebrates. 

of antimonial (m) Antimony potassium tartrate (4.58) Stibophen (4.57) 

Another example of deviant biochemistry in protozoa is the utilization, by Entamoeba histolytica, of pyrophosphate in place of the usual ATP, as a coenzyme for phosphofructokinase (Beeves, Serrano and South, 1976). The major path of glucose utilization in this parasite is formation of pyruvate from phospho-gluconate and from 2-keto-3-deoxy-6-phosphogluconate (Florkin and Mason, 1960). 

When nutrients are present in excess, many bacteria accumulate special energy reserves such as glycogen or j8-hydroxybutyric acid (Wilkinson, 1966). Yeasts, and some bacteria, convert pyruvic acid to ethanol (instead of lactic acid), an idiosyncrasy which Man has carefully exploited. 

Several instances are known where enzymes performing similar functions in two species are chemically distinct. Examples of such analogous enzymes are mentioned below under helminths , and several more will be found in Section 4.6. The following paragraphs summarize variations of glycolysis in invertebrates. 

Insect muscle utilizes the Meyerhof sequence only as far as pyruvate, and the NADH produced during triosephosphate oxidation seems to be reoxidized by the reduction of dihydroxyacetone phosphate to glycerophosphate (Chance and Sacktor, 1958). The major sugar in the plasma is a,a-trehalose, a disaccharide of glucose, and it plays a major part in the glucose transport system of insects (Wyatt and Kalf, 1957). For a review of insect biochemistry, see Goodwin (1965). 

Helminths are characterized by a high rate of carbohydrate metabolism associated with incomplete substrate oxidation. This is the case whether they live anaerobically (as intestinal worms do) or aerobically (like schistosomes). The Meyerhof sequence is the major metabolic pathway in worms for the utilization of carbohydrate. Trehalose (see above) plays an important part in helminth carbohydrate metabolism. For a review of helminth biochemistry, see von Brand (1974). 

The schizont stage of the malarial parasite utilizes the Mayerhof sequence efficiently to convert glucose to lactic acid. In Entamoeba histolytica the major pathway of glucose utilization is the formation of pyruvate from 

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Madin, K.A.C. Crowe, J.H. (1975). Anhydrobiosis in nematodes carbohydrate and lipid metabolism during dehydration. Journal of Experimental Zoology, 193, 335-41. 

Saz, H.J. and Lescure, O.L. (1966) Interrelationships between the carbohydrate and lipid metabolism of Ascaris lumbricoides egg and adult stages. Comparative Biochemistry and Physiology 18, 845-857. 

Physioiogicai There is an extensive literature that deals with the effects ginseng on CNS function, but effects are also seen in neuroendocrine function, carbohydrate and lipid metabolism, the immune system, and cardiovascular function (Gillis 1997). Ginsenosides induce a decrease in heart rate and have biphasic effects on blood pressure, with decreases preceded by a slight increase (Kaku et al. 1975). Ginsenoside Rgl had the most potent effects on blood pressure. Little or no effect is observed on respiration. 

Diabetes mellitus is a very common metabolic disease that is caused by absolute or relative insulin deficiency. The lack of this peptide hormone (see p. 76) mainly affects carbohydrate and lipid metabolism. Diabetes mellitus occurs in two forms. In type 1 diabetes (insulin-dependent diabetes mellitus, IDDM), the insulin-forming cells are destroyed in young individuals by an autoimmune reaction. The less severe type 2 diabetes (non-insulin-dependent diabetes mellitus, NIDDM) usually has its first onset in elderly individuals. The causes have not yet been explained in detail in this type. 

Glucagon, a peptide of 29 amino acids, is a product of the A cells of the pancreas. It is the antagonist of insulin and, like insulin, mainly influences carbohydrate and lipid metabolism. Its effects are each opposite to those of insulin. Glucagon mainly acts via the second messenger cAMP (see p. 384). 

Contain details of metabolic pathways that are only shown in outline in the main text for reasons of space. This applies in particular to the synthesis and degradation of the amino acids and nucleotides, and for some aspects of carbohydrate and lipid metabolism. 

Carbohydrate and lipid metabolism Effects of implants on carbohydrate metabolism appear to be minimal. Carefully observe diabetic and prediabetic patients. 

CN190 Zulet, M. A., A. Barber, H. Garcin, P. Higueret, and ]. A. Martinez. Alterations in carbohydrate and lipid metabolism induced by a diet rich in coconut oil and cholesterol in a rat model. J Am Coll Nutr 1999 18(1) 36-42. 

LT045 Reed, M.J., K. Meszaros, L. J. Entes, et al. Effect of masoprocol on carbohydrate and lipid metabolism in a rat model of type II diabetes. Diabetologia 1999 42(1) 102-106. 

PO027 Hopewell, R., R. Yeater, and I. Ullrich. Soluble fiber Effect on carbohydrate and lipid metabolism. Progress Food Nutr Scil993 17(2) 159-182. 

SOOl 7 Hikino, H., M. Takahashi, C. Konno, A. Ishimori, T. Kawamura, and T. Namiki. Effect of glycans of Sacchmum officinarum on carbohydrate and lipid metabolism of rats. J Ethnopharmacol 1985 14(2-3) 261-268. 

These hormones also have profound effects on the function of the liver. Some of these effects are deleterious and will be considered below in the section on adverse effects. The effects on serum proteins result from the effects of the estrogens on the synthesis of the various 2 globulins and fibrinogen. Serum haptoglobins produced in the liver are depressed rather than increased by estrogen. Some of the effects on carbohydrate and lipid metabolism are probably influenced by changes in liver metabolism (see below). 

Carbohydrate and Lipid Metabolism Are Integrated by Hormonal and Allosteric Mechanisms... 

VITAMIN B (Pyridoxine). Infrequently called adermine or pyridoxol, this vitamin participates in protein, carbohydrate, and lipid metabolism. The metabolically active form of B6 is pyridoxal phosphate, the structures of which are ... 

The 1990 report of the International Consensus Development Meeting stated the following regarding the effects of oral contraceptives on carbohydrate and lipid metabolism (19) All currently used oral contraceptives... 

Lee GA, Rao MN, Granfeld C. The effects of HIV protease inhibitors on carbohydrate and lipid metabolism. Curr Infect Dis Rep. 2004 6 471H-82. 

Some of the effects on carbohydrate and lipid metabolism are probably influenced by changes in liver metabolism (see below). 

Boden, G., X. Chen, J. Ruiz, G.D.V. van Rossum, and S. Turco. 1996. Effects of vanadyl sulfate on carbohydrate and lipid metabolism in patients with non-insulin-dependent diabetes mellitus. Metabol. 45 1130-1135. 

Goodridge, A.G. (1987). Dietary regulation of gene expression enzymes involved in carbohydrate and lipid metabolism. Ann. Rev. Nutr. 1 157— 185. 

In addition to being incorporated into tissue proteins, amino acids, after losing their nitrogen atoms by deamination and/or transamination, may be catabolized to yield energy or to form glucose. Conversely, the nonessential amino acids may be synthesized from carbohydrate metabolism intermediates and ammonia or from essential amino acids. This section is devoted to the mechanisms of such metabolic processes and their interrelationships with carbohydrate and lipid metabolic pathways. 

Actions of growth hormone on carbohydrate and lipid metabolism... 

GH clearly has effects on carbohydrate and lipid metabolism, the protein-synthetic machinery, expression of specific proteins, and cell differentiation and proliferation. For a hormone concerned with the overall control of somatic growth such a wide spread of activities is potentially physiologically meaningful. It is at least possible that GH mediates these various actions via several different intracellular mechanisms and that it will not be possible to identify any one action as of key importance. 

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