The metabolism of glutamine in resting and concanavalin-A-stimulated lymphocytes was investigated. In incubated lymphocytes isolated from rat mesenteric lymph nodes, the rates of oxygen and glutamine utilization and that of aspartate production were approximately linear with respect to time for 60 min, and the concentrations of adenine nucleotides plus the ATP/ADP or ATP/AMP concentration ratios remained approximately constant for 90 min. The major end products of glutamine metabolism were glutamate, aspartate and ammonia: the carbon from glutamine may contribute about 30% to respiration. When both glucose and glutamine were presented to the cells, the rates of utilization of both substances increased. Evidence was obtained that the stimulation of glycolysis by glutamine could be due, in part, to an activation of 6-phosphofructokinase. Starvation of the donor animal increased the rate of glutamine utilization. The phosphoenolpyruvate carboxykinase inhibitor mercaptopicolinate decreased the rate of glutamine utilization by 28%; the rates of accumulation of glutamate and ammonia were decreased, whereas those of lactate, aspartate and malate were increased. The mitogen concanavalin A increased the rate of glutamine utilization (by about 51%). The rate of [3H]thymidine incorporation into DNA caused by concanavalin A in cultured lymphocytes was very low in the absence of glutamine; it was increased about 4-fold at 1 microM-glutamine and was maximal at 0.3 mM-glutamine; neither other amino acids nor ammonia could replace glutamine.

Glutamine is utilized at a high rate (fourfold higher than that of glucose) by isolated incubated lymphocytes and produces glutamate, aspartate, lactate and ammonia. The pathway for glutamine metabolism includes the reactions catalysed by glutaminase, aspartate aminotransferase, oxoglutarate dehydrogenase, succinate dehydrogenase, fumarase, malate dehydrogenase and phosphoenolpyruvate carboxykinase. In fact little if any of the carbon of the glutamine that is used is converted to acetyl‐CoA for complete oxidation. For this reason, the oxidation of glutamine is only partial and, in an analogous manner to the terminology used to describe the partial oxidation of glucose to lactate as glycolysis, the term glutaminolysis is used to describe the process of partial glutamine oxidation. The role of glutaminolysis in lymphocytes and perhaps other rapidly dividing cells is to provide both nitrogen and carbon for precursors for synthesis of macromolecules (e.g. purines and pyrimidines for DNA and RNA) and also energy. However, the rate of glutamine utilization by lymphocytes is markedly in excess of the precursor requirements (which are at most 4%) and if glutamine was vitally important in energy production it would be expected that more would be converted to acetyl‐CoA for complete oxidation via the Krebs cycle. Indeed most of the energy for lymphocytes may be obtained by the complete oxidation of fatty acids and ketone bodies. Consequently the role of the high rate of glutaminolysis in lymphocytes and other rapidly dividing cells may be identical to that of glycolysis: the high rates provide ideal conditions for the precise and sensitive control of the rate of use of the intermediates of these pathways for biosynthesis when required. High rates of glycolysis and glutaminolysis can be seen as part of a mechanism of control to permit synthesis of macromolecules when required without any need for extracellular signals to make more glucose or glutamine available for these cells. In order to maintain a high rate of glutaminolysis despite fluctuation in the plasma level of glutamine, the flux through the glutaminolytic pathway can be controlled and the key processes in the lymphocyte that may play a role in this process include glutamine transport across the cell and mitochondrial membranes, glutaminase and oxoglutarate dehydrogenase. Changes in the intracellular concentration of Ca2+ may play a role in control of one or more of these reactions. The glutamine that is normally made available from protein digestion in the lumen of the intestine is probably completely utilized by cells of the small intestine so that the glutamine which is essential for lymphocytes and other rapidly dividing cells is made available via amino acid metabolism in muscle. This may be one reason for increased rates of muscle protein degradation during injury, infection, burns and surgery, when the activity of both the immune system and cellular repair processes are increased. Whether limitations in muscle metabolism and glutamine production could ever ...

Functionally significant vitamin D deficiency affects BMD and bone turnover markers among Saudi Arabian men and is largely attributed to older age, obesity, sedentary lifestyle, no education, poor exposure to sunlight, smoking, and poor dietary vitamin D supplementation. The data suggest that an increase in PTH cannot be used as a marker for vitamin D deficiency.

The rates of utilization of both glucose and glutamine are high in rapidly dividing cells such as enterocytes, lymphocytes, thymocytes, tumour cells; the oxidation of both glucose and glutamine is only partial, glucose to lactate and glutamine to glutamate, alanine or aspartate; and these partial processes are termed glycolysis and glutaminolysis respectively. Both processes generate energy and also provide precursors for important biosynthetic processes in such cells. However, the rates of utilization of precursors for macromolecular biosynthesis are very low in comparison to the rates of partial oxidation, and energy generation per se may not be the correct explanation for high rates of glycolysis and glutaminolysis in these cells since oxidation is only partial and other fuels can be used to generate energy. Both the high fluxes and the metabolic characteristics of these two processes can be explained by application of quantitative principles of control as applied to branched metabolic pathways (Crabtree & Newsholme, 1985). If the flux through one branch is greatly in excess of the other, then the sensitivity of the flux of the low-flux pathway to regulators is very high. Hence, it is suggested that, in rapidly dividing cells, high rates of glycolysis and glutaminolysis are required not for energy or precursor provision per se but for high sensitivity of the pathways involved in the use of precursors for macromolecular synthesis to specific regulators to permit high rates of proliferation when required - for example, in lymphocytes in response to a massive infection.

Sclerostin is a secreted Wnt antagonist produced almost exclusively by osteocytes that regulates bone mass. However, there is currently limited information on the determinants of sclerostin in a large population-based study. The main objectives of the present study were to: (1) establish reference normative interval values for serum sclerostin in randomly selected healthy premenopausal women; (2) study the changes in serum sclerostin in relation to age in premenopausal and postmenopausal women and the factors that may influence bone turnover; and (3) determine the effect of menopausal status on serum sclerostin. A total of 1803 women were studied (including [n ¼ 1235] premenopausal, and [n ¼ 568] postmenopausal women, respectively, aged 20 to 79 years). A total of 443 healthy premenopausal women (aged 35 to 45 years) were used to establish reference normative intervals for serum sclerostin. All women studied were medically examined and had their bone mineral density values obtained for the lumbar spine (L 1 -L 4 ) and femoral neck according to a detailed inclusion criteria. In all women, values of serum sclerostin increased with increasing age up to the age of 45 years, and remained increased in postmenopausal women. Significant increases were evident in serum sclerostin in postmenopausal women with increasing years since menopause. Using stepwise multiple linear regression analysis, several variables were identified as determinants of serum sclerostin, including age, parathyroid hormone, estradiol (E 2 ), and follicle-stimulating hormone (FSH) for premenopausal women; age, FSH, and E 2 for postmenopausal women; and age, serum osteocalcin, FSH, and E 2 in the entire sample studied. Further studies are needed to establish the potential role of this increase in mediating the known age-related impairment in bone formation. ß

Vitamin D deficiency is highly prevalent among healthy Saudi pre-and postmenopausal women and largely attributed to obesity, poor exposure to sunlight, poor dietary vitamin D supplementation, and age.

Objectives: To evaluate calcium-regulating hormones and parathyroid hormone-related peptide (PTHrP) in normal human pregnancy and postpartum in women not deficient in vitamin D. Design: A prospective longitudinal study was conducted in pregnant Saudi women during the course of pregnancy (n ¼ 40), at term and 6 weeks postpartum (n ¼ 18). Maternal concentrations of serum calcidiol and calcitriol were determined, together with those of serum intact-parathyroid hormone (PTH), PTHrP, calcitonin, osteocalcin, human placental lactogen (hPL), prolactin, vitamin D binding protein, alkaline phosphatase, calcium, phosphate and magnesium. A group of non-pregnant women (n ¼ 280) were included for comparative purposes. Results: The calcidiol concentrations decreased (meanϮS.D.) significantly from 54Ϯ10 nmol/l in the first trimester to 33Ϯ8 nmol/l in the third trimester (P < 0:001) and remained decreased at term and postpartum (both P < 0:001). The calcitriol concentration increased through pregnancy, from 69Ϯ17 pmol/l in the first trimester to 333Ϯ83 pmol/l at term (P < 0:001). Intact-PTH concentrations increased from 1.31Ϯ0.25 pmol/l in the first trimester to 2.26Ϯ0.39 pmol/l in the second trimester, but then declined to values of the first trimester and increased significantly postpartum (4.02Ϯ0.36 pmol/l) (P < 0:001). PTHrP concentration increased through pregnancy from 0.81Ϯ0.12 pmol/l in the first trimester to 2.01Ϯ0.22 pmol/l at term and continued its increase postpartum (2.63Ϯ0.15 pmol/l) (P < 0:001). Significant positive correlations were evident between PTHrP and alkaline phosphatase up to term (r ¼ 0:051, P < 0:001) and between PTHrP and calcitriol (r ¼ 0:46, P < 0:001), osteocalcin (r ¼ 0:23, P < 0:05) and prolactin (r ¼ 0:41, P < 0:05) during pregnancy. Osteocalcin started to increase from 0.13Ϯ0.01 nmol/l in the second trimester, through pregnancy and postpartum (P < 0:001). Calcitonin was increased more than twofold by the second trimester compared with the first trimester (P < 0:001) and subsequently decreased (P < 0:001). Prolactin concentrations were significantly greater in the second (6724Ϯ1459 pmol/l) and third (8394Ϯ2086 pmol/l) trimesters compared with values before pregnancy (P < 0:001). hPL increased throughout the course of pregnancy, reaching a maximum at term (7.61Ϯ2.57 mIU/ml). There was no direct correlation between serum calcitriol concentrations during pregnancy and serum prolactin (r ¼ ¹0:12, P < 0:19) or serum hPL (r ¼ 0:17, P < 0:21). Significant changes were observed in the serum concentrations of calcium and phosphate, but not in that of magnesium, during the course of pregnancy; calcium concentrations showed a maximal decrease at term. Conclusions: Changes in serum PTHrP during the course of pregnancy, at term and postpartum have been demonstrated, suggesting that the placenta (during pregnancy) and mammary glands (postpartum) are the main sources of PTHrP. No support for the concept of 'physiological hyperparathyroidism' of pregnancy could be demonstrated in the present work. The ...

1. The maximum activity of hexokinase in lymphocytes is similar to that of 6-phosphofructokinase, but considerably greater than that of phosphorylase, suggesting that glucose rather than glycogen is the major carbohydrate fuel for these cells. Starvation increased slightly the activities of some of the glycolytic enzymes. A local immunological challenge in vivo (a graft-versus-host reaction) increased the activities of hexokinase, 6-phosphofructokinase, pyruvate kinase and lactate dehydrogenase, confirming the importance of the glycolytic pathway in cell division. 2. The activities of the ketone-body-utilizing enzymes were lower than those of hexokinase or 6-phosphofructokinase, unlike in muscle and brain, and were not affected by starvation. It is suggested that the ketone bodies will not provide a quantitatively important alternative fuel to glucose in lymphocytes. 3. Of the enzymes of the tricarboxylic acid cycle whose activities were measured, that of oxoglutarate dehydrogenase was the lowest, yet its activity (about 4.0mumol/min per g dry wt. at 37 degrees C) was considerably greater than the flux through the cycle (0.5mumol/min per g calculated from oxygen consumption by incubated lymphocytes). The activity was decreased by starvation, but that of citrate synthase was increased by the local immunological challenge in vivo. It is suggested that the rate of the cycle would increase towards the capacity indicated by oxoglutarate dehydrogenase in proliferating lymphocytes. 4. Enzymes possibly involved in the pathway of glutamine oxidation were measured in lymphocytes, which suggests that an aminotransferase reaction(s) (probably aspartate aminotransferase) is important in the conversion of glutamate into oxoglutarate rather than glutamate dehydrogenase, and that the maximum activity of glutaminase is markedly in excess of the rate of glutamine utilization by incubated lymphocytes. The activity of glutaminase is increased by both starvation and the local immunological challenge in vivo. This last finding suggests that metabolism of glutamine via glutaminase is important in proliferating lymphocytes.