Glucose metabolism, intracellular

Fig. 7.16. Ketoconazole had no effect on human effective in vivo permeability (Pefr) of R/S-verapamil, antipyrine, and D-glucose. The data suggest that extensive intracellular metabolism (in the enterocyte mediated by CYP 3A4) of substrates such as R/S-verapamil...

Hemolytic anemia results from decreased RBC survival time due to destruction in the spleen or circulation. The most common etiologies are RBC membrane defects (e.g., hereditary spherocytosis), altered Hb solubility or stability (e.g., sickle cell anemia [see Chap. 34] and thalassemias), and changes in intracellular metabolism (e.g., glucose-6-phosphate dehydrogenase deficiency). Some drugs cause direct oxidative damage to RBCs (see Appendix 3). 

A paper published six decades ago was the first to draw attention to the possibility that a change in the rate of transport of a molecule across the plasma membrane conld play a role in regulation of both intra- and extracellnlar metabolism that is, the regulation of the blood glncose level and the intracellular metabolism of glucose. The paper was entitlied A hypothesis of insulin action is proposed which attributes to insulin the role of facilitating the rate of transport of some hexoses into the cell as opposed to a direct effect on intracellular metabolism (Levine et al. 1950). 

Hormones regulate intracellular metabolic processes. Insulin intensifies transfer (transport) of the glucose in the cell and decreases its level in the circulating blood. Glucagon increases the sugar level in the blood. The two hormones are synthesized by the pancreas. Antibodies discern foreign bodies in an organism. 

Intracellular metabolism of amino acids requires their transport across the cell membrane. Transport of L-amino acids occurs against a concentration gradient and is an active process usually coupled to Na -dependent carrier systems as for transport of glucose across the intestinal mucosa (Chapter 12). At least five transport systems for amino acids (with overlapping specificities) have been identified in kidney and intestine. They transport neutral amino acids, acidic amino acids, basic amino acids, ornithine and cystine, and glycine and proline, respectively. Within a given carrier system, amino acids may compete for transport (e.g., phenylalanine with tryptophan). Na+-independent transport carriers for neutral and lipophilic amino acids have also been described, d-Amino acids are transported by simple diffusion favored by a concentration gradient. 

A major effect of insulin is on the adipose tissue, both in regard to glucose uptake and intracellular metabolic effects. The major metabolic conversion in response to insulin is a dephosphorylation of hormonesensitive lipase to convert this enzyme into the inactive form. A second important metabolic aspect is an increase in synthesis and secretion to the blood-vessel surface of lipoprotein lipase. This enzyme is responsible for breaking down circulating triacylglycerols, particularly from VLDL as well as from chylomicrons, into fatty acids and glycerol. 

Rice bran is the richest natural source of B-complex vitamins. Considerable amounts of thiamin (Bl), riboflavin (B2), niacin (B3), pantothenic acid (B5) and pyridoxin (B6) are available in rice bran (Table 17.1). Thiamin (Bl) is central to carbohydrate metabolism and kreb s cycle function. Niacin (B3) also plays a key role in carbohydrate metabolism for the synthesis of GTF (Glucose Tolerance Factor). As a pre-cursor to NAD (nicotinamide adenine dinucleotide-oxidized form), it is an important metabolite concerned with intracellular energy production. It prevents the depletion of NAD in the pancreatic beta cells. It also promotes healthy cholesterol levels not only by decreasing LDL-C but also by improving HDL-C. It is the safest nutritional approach to normalizing cholesterol levels. Pyridoxine (B6) helps to regulate blood glucose levels, prevents peripheral neuropathy in diabetics and improves the immune function. 

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