Regulation of pathways of glucose metabolism in kidney. The effect of experimental diabetes on the activity of the pentose phosphate pathway and the glucuronate-xylulose pathway.

Measurements have been made of the activities of enzymes of the pentose phosphate pathway, the glucuronate-xylulose pathway, hexokinase and phosphofructokinase in kidney of diabetic and normal rats. The activities of these enzymes keep pace with kidney growth, remaining constant per gram tissue but showing a marked increase on the basis of total activity per 100 g body wt. The formation of ¹⁴CO₂ from [1-¹⁴C]glucose and [6-¹⁴C]glucose by kidney slices from diabetic rats was decreased to approximately half the control value; evidence was obtained for an equivalent dilution of the glucose 6-phosphate pool. Correction of the ¹⁴CO₂ yields for the change in specific activity of glucose 6-phosphate yielded values consistent with the enzyme profile. Calculations from specific yields of ¹⁴CO₂ provided evidence for an increased flux of glucose via the pentose phosphate pathway in the kidney in diabetes. The results are discussed in relation to kidney hypertrophy in diabetes and the requirement for ribose 5-phosphate and NADPH for biosynthetic reactions and in relation to the thickening of the basement membrane in diabetes. These results are in accord with the concept of glucose overutilization by non-insulin-requiring tissues.     

Effect of experimental diabetes on the activity of hexokinase isoenzymes in tissues of the rat

The effect of experimental diabetes on the activity of hexokinase isoenzymes was studied in a wide range of tissues of the rat. In the tissues known to require insulin for glucose phosphorylation, the activity of hexokinase was markedly decreased; the fall being mainly in the Type IV (Glucokinase) in liver and Type II in other tissues, these tissues also exhibit glucose underutilization in diabetes. In the tissues which are commonly known not to require insulin, the activity of Type I hexokinase was significantly increased, these tissues exhibit aspects of glucose overutilization in diabetes in particular kidney and lens. These changes are discussed in relation to Spiro's hypothesis of glucose under and overutilization in tissues in diabetes.     

Changes in the levels of catecholamines, hexokinase and glucose 6-phosphate dehydrogenase in red cell aging

The activity of the enzymes hexokinase and glucose 6-phosphate dehydrogenase and the level of catecholamines were measured in isolated rat Red Blood Cells (RBC) during cellular aging. The results clearly showed a linear decline in the two enzyme profiles with corresponding increase in age of RBC. A decrease of 75-85% in the activities were found in the oldest cell fractions as compared to the youngest. The levels of glycosylated haemoglobin and catecholamines were found to increase with aging. A correlation can probably be established between the enzyme activities, the levels of glycosylated haemoglobulin and catecholamines during aging.     

Changes in erythrocyte glutathione peroxidase and glutathione reductase in alloxan diabetes

Glutathione peroxidase and glutathione reductase activities were measured in erythrocytes from control, diabetic and insulin-treated diabetic rats. A significant decrease in the activity of glutathione peroxidase and an increase in the glutathione reductase activity were found with increase in the time of diabetes which may result in the alteration in the activity of the pentose phosphate pathway by the modulation of the levels of NADPH. Insulin administration reverses the change in the activity of glutathione peroxidase but does not reverse the glutathione reductase activity during diabetes. The overall changes may be due to changes in the levels of insulin, triiodothyronine and thyroxine.     

Hexokinase isoenzymes in diabetes

Hexokinase is present in the tissues in four isoenzymic forms. Cerebral tissue contains predominantly Type I hexokinase which is believed to be insulin-insensitive. In cerebral tissue about 60 to 70% of the hexokinase is bound to the particulate fraction. The changes in the distribution of hexokinase Type I and Type II together with the bound and free hexokinase have been studied in control, diabetic and diabetic animals treated with insulin. The results indicate that the presence of insulin is essential for the normal binding of the hexokinase to the particulate fraction. In heart tissue, Type II hexokinase bound to the pellet shows a significant decrease in diabetes, which is reversed on insulin administration.     

Na+,K+-ATPase and Mg2+-ATPase Activities in Different Regions of Rat Brain During Alloxan Diabetes

The effect of alloxan diabetes on the activities of Na+,K+-ATPase and Mg2+-ATPase was studied in three regions of rat brain at various time intervals after the onset of diabetes. It was observed that Na+,K+-ATPase activity increased at early time intervals after diabetes, followed by a recovery to near control levels in all three regions of the brain. There was an overall increase in Mg2+-ATPase activity in all the regions. A reversal of the effect was observed with insulin administration to the diabetic rats.     

Effect of imipramine hydrochloride on the activity of gamma-aminobutyric acid transaminase in regions of the rat brain

The effect of intraperitoneal injection of imipramine hydrochloride on the activity of gamma-aminobutyric acid transaminase was determined in three regions of the rat brain.The cerebral hemispheres did not show a significant change in the activity of gamma-aminobutyric acid transaminase. Cerebellum and brain stem, both, however, showed a very significant decrease in the activity of the enzyme at 15 and 30 minutes after drug administration. At 90 minutes after drug administration, the activity of gamma-aminobutyric acid transaminase had returned to nearly control values.     

The modifying effect of manganese on the enzymic profiles and pathways of carbohydrate metabolism in rat liver and adipose tissue during development

The effect of Mn²⁺ on the pattern of emergence of enzymes in rat liver and adipose tissue was studied in weaned rats given a milk diet (high fat) or sucrose-casein diet (high carbohydrate) for three weeks. Addition of Mn²⁺ to the high fat diet was associated with induction of key glycolytic, lipogenic and pentose pathway enzymes in both liver and adipose tissue; parallel increases were found in the incorporation of [1-¹⁴C] glucose into lipid and CO₂. Mn²⁺ induced a change in the profile of enzyme activity similar in pattern to that found in rats given a high sucrose diet or that produced by insulin treatment. Mn²⁺ appears partially to overcome the regulatory feed-back mechanisms of the high fat diet and to provide a signal for the coordinated increase of glucose catabolic and lipogenic processes.     

Three Dimensional Structure of Mammalian Tachykinin Peptide Neurokinin B Bound to Lipid Micelles

Abstract

Neurokinin B (NKB), a decapeptide of mammalian origin exhibits a variety of biological activities such as regulatory functions in reproduction, pre-eclampsia and neuroprotection in Alzheimer's disease. In order to gain insight into structure-function relationship, three- dimensional structure of NKB has been investigated using CD spectropolarimetry and two-dimensional proton nuclear magnetic resonance (2D ¹H-NMR) spectroscopy in aqueous and membrane mimetic solvents. Unambiguous NMR assignments of resonances have been made with the aid of correlation spectroscopy (DQF-COSY and TOCSY) experiments and Nuclear Overhauser Effect Spectroscopy (NOESY) experiments. Distance constraints obtained from the NMR data have been used to generate a family of structures, which have been refined using restrained energy minimization and dynamics. Our data show that a helical structure is induced in NKB, in presence of perdeuterated dodecyl phosphocholine (DPC) micelles, a membrane model system. Further, the conformation adopted by NKB in presence of DPC micelles represents a structural motif typical of neurokinin-3 selective agonists.     

Trigonella foenum graecum seed powder protects against histopathological abnormalities in tissues of diabetic rats

Premature visual impairment due to lens opacification is a debilitating characteristic of untreated diabetes. Lens opacification is primarily due to the insolubilization of crystallins, proteins essential for lens optical properties, and recent studies have suggested that a major cause of this insolubilization may be the unregulated proteolysis of crystallins by calpains. These are intracellular cysteine proteases whose activation requires the presence of calcium (Ca2+) and elevated levels of lens Ca2+ is a condition associated with both diabetic cataractogenesis and other forms of the disorder. A number of calpains have been identified in the lens, including calpain 2, calpain 10 and two isozymes of calpain 3: Lp82 and Lp85. The use of animal hereditary cataract models have suggested that calpain 2 and/or Lp82 may be the major calpains involved in murine cataractogenesis with contributions from calpain 10 and Lp85. However, calpain 2 appears to be the major calpain involved in murine diabetic cataractogenesis and the strongest candidate of the calpains for a role in human types of cataractogenesis. Here, we present an overview of recent evidence on which these observations are based with an emphasis on the ability of calpains to proteolyse lens crystallins and calpain structural features, which appear to be involved in the Ca2+-mediated activation of these enzymes.