Estimation of the pentose cycle in the perfused cow's udder

Wood, Harland G.; Peeters, G; Verbeke, R; Lauryssens, M.; Jacobson, Bertil

doi:10.1042/bj0960607

Cited by 42 publications

(31 citation statements)

References 22 publications

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“…The calculated percentage of metabolism of glucose 6-phosphate pool to galactose moiety of lactose during early lactation was about 92% in 87.5%HF cattle and 80% in 50%HF cattle (Chaiyabutr et al 2000c). The percentages of these values were consistent with the results reported in normally fed goats and bos Taurus cows (Wood et al, 1965;Linzell, 1968). During lactation advance to late lactation, the percentages of these values decreased markedly in 87.5%HF cattle.…”

Section: Recycling = (T3-t14)×100/t3supporting

confidence: 81%

Control of Mammary Function During Lactation in Crossbred Dairy Cattle in the Tropics

Chaiyabutr¹

2012

Milk Production - Advanced Genetic Traits, Cellular Mechanism, Animal Management and Health

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Section: Recycling = (T3-t14)×100/t3supporting

confidence: 81%

Control of Mammary Function During Lactation in Crossbred Dairy Cattle in the Tropics

Chaiyabutr¹

2012

Milk Production - Advanced Genetic Traits, Cellular Mechanism, Animal Management and Health

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“…These results agree with prolonged treatment of rbST in crossbred HF cows, which percentage of glucose 6-phosphate metabolized via the pentose phosphate pathway were variable in different stages of lactation (Chaiyabutr et al, 2008b). However, these findings differed to those studies in the isolated perfused udder of cow by Wood et al (1965), in which about 23-30% of the glucose was metabolized via the pentose phosphate pathway. It is probable that no consideration of the recycling of glucose 6-phosphate metabolized via the pentose cycle in the udder with the consequent loss of 3 H from glucose 6-phosphate (Davis and Bauman, 1974).…”

Section: Discussionsupporting

confidence: 56%

“…The concentration of milk lactose was determined by spectrophotometry (Teles et al, 1978). Lactose radioactivity was determined after isolation by the hydrolysis method (Wood et al, 1965). Milk fatty acids was extracted from 1 ml of an aliquot thawed milk in 2 mL of Dole's solution (Dole, 1956), (iso-propanol 40: n-heptane 10: 1N H 2 SO 4 1, v/v) shaking in water bath for 30 min.…”

Section: Chemical Methods: Radiochemicals For [U-mentioning

confidence: 99%

Effects of Cooling and Supplemental Bovine Somatotropin on Milk Production relating to Body Glucose Metabolism and Utilization of Glucose by the Mammary Gland in Crossbred Holstein Cattle

Sitprija¹

2010

American Journal of Biochemistry and Biotechnology

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Problem statement:The low milk yield and shorter persistency of lactation of dairy cattle is the major problem for the dairy practices in the tropics. High environmental temperatures and rapid decline of plasma growth hormone level can influence milk production. Regulation of the milk yield of animals is mainly based on the mechanisms governing the quantity of glucose extracted by the mammary gland for lactose biosynthetic pathways. The mechanism(s) underlying the effects of cooling and supplemental bovine somatotropin on milk production relating to body glucose metabolism and intracellular metabolism of glucose in the mammary gland of crossbred Holstein cattle in the tropics have not been investigated to date. Approach: Ten crossbred 87.5% Holstein cows were divided into two groups of five animals each. Animals were housed in Normal Shade barn (NS) as non-cooled cows and cows in the second group were housed in barn which was equipped with a two Misty-Fan cooling system (MF) as cooled cows. Supplementation of recombinant bovine Somatotropin (rbST) (POSILAC, 500 mg per cow) were performed in both groups to study body glucose metabolism and the utilization of glucose in the mammary gland using a continuous infusion of [3-3 H] glucose and [U-14 C] glucose as markers in early, mid and late stages of lactation. Results: Milk yield significantly increased in both groups during supplemental rbST with a high level of mammary blood flow. Body glucose turnover rates were not significant different between cooled and non-cooled cows whether supplemental rbST or not. The glucose taken up by the mammary gland of both non-cooled and cooled cows increased flux through the lactose synthesis and the pentose cycle pathway with significant increases in NADPH formation for fatty acid synthesis during rbST supplementation. The utilization of glucose carbon incorporation into milk appeared to increase in milk lactose and milk triacylglycerol but not for milk citrate during supplemental rbST in both non-cooled and cooled cows in early and mid lactation. Conclusion: The present study demonstrated that local changes for biosynthetic capacity within the mammary gland would be a factor in identification of the utilization of substrates in the rate of decline in milk yield. The proportion of glucose was metabolized less for lactose synthesis, but metabolized more via the Embden-Meyerhof pathway and the tricarboxylic acid cycle as lactation advanced to late lactation in both cooled and non-cooled cows whether supplemental rbST or not.

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“…They further compared the distributions of 14 C in the glucose and galactose moieties of milk lactose from cows' udders perfused with blood containing [1-14 C]-, [2-14 C]-, and [6-14 C]glucose. On the basis of these data, they concluded that the glucose moiety primarily arose from free glucose but that the galactose came, in part, from hexose phosphate intermediates as a result of the pentose phosphate pathway activity (33). They estimated the proportional glucose utilization in the mammary gland: 1) 20 -30% via the pentose cycle, 2) ϳ10% by the Embden-Meyerhof pathway, and 3) 60 -70% converted into lactose (33).…”

Section: Low-carbohydrate/high-fat Dietmentioning

confidence: 99%

Precursors of hexoneogenesis within the human mammary gland

Mohammad

Maningat

Sunehag

et al. 2015

American Journal of Physiology-Endocrinology and Metabolism

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The human mammary gland is capable of de novo synthesis of glucose and galactose (hexoneogenesis); however, the carbon source is incompletely understood. In this study, we investigated the role of acetate, glutamine, lactate and glycerol as potential carbon sources for hexoneogenesis. Healthy breastfeeding women were studied following a 24-h fast on two occasions separated by 1-3 wk. Five women were infused with [U-13 C]lactate or [1,2-13 C2]glutamine and five women with [U-13 C]glycerol or [1,2-13 C2]acetate. Enrichments of 13 C in plasma and milk substrates were analyzed using GC-MS. Infusion of labeled lactate, glycerol, glutamine, and acetate resulted in plasma glucose being 22.0 Ϯ 3.7, 11.2 Ϯ 1.0, 2.5 Ϯ 0.5, and 1.3 Ϯ 0.2% labeled, respectively. Lactate, glutamine, or acetate did not contribute to milk glucose or galactose (0 -2%). In milk, 13 C-free glycerol enrichment was one-fourth that in plasma but free glycerol concentration in milk was fourfold higher than in plasma. Using [U-13 C]glycerol and by accounting for tracer dilution, glycerol alone contributed to 10 Ϯ 2 and 69 Ϯ 11% of the hexoneogenesis of milk glucose and galactose, respectively. During [U-13 C]glycerol infusion, the ratio of M3 enrichment on 4 -6 carbons/M3 on 1-3 carbons of galactose was higher (P Ͻ 0.05, 1.22 Ϯ 0.05) than those of glucose in plasma (1.05 Ϯ 0.03) and milk (1.07 Ϯ 0.02). Reanalysis of samples from a previous study involving [U-13 C]glucose infusion alone suggested labeling a portion of galactose consistent with pentose phosphate pathway (PPP) activity. We conclude that, although lactate contributed significantly to gluconeogenesis, glycerol alone provides the vast majority of substrate for hexoneogenesis. The relative contribution of the PPP vs. the reversal Embden-Meyerhof pathway to hexoneogenesis within the human mammary gland remains to be determined. galactose; lactose synthesis; gluconeogenesis; pentose phosphate pathway; stable isotopes GC-MS WE PREVIOUSLY DEMONSTRATED (26) that plasma glucose is the predominant but not the exclusive carbon source of milk lactose (80% during the fed state and 60% following 24 h of fasting). Thus, the mammary gland is capable of de novo synthesis of glucose and galactose, a process we termed hexoneogenesis. During feeding, hexoneogenesis contributes 20% of the carbon in lactose (10 and 30% of glucose and galactose, respectively) (20,26,27). Over a 14-to 42-h fast, hexoneogenesis increases to account for ϳ40% of lactose production (ϳ30% of glucose and ϳ50% of galactose) (18,20,21,26,27). However, the precursor carbon source for hexoneogenesis remains largely unknown.We hypothesize that those traditional gluconeogenic substrates for hepatic glucose production will also serve as precursors for hexoneogenesis. Lactate, a predominant gluconeogenic precursor in humans, accounts for 50 -70% of the total gluconeogenic flux in normal humans (3,12). Another significant precursor of glucose synthesis (particularly in the kidney) is glutamine, which together with glutamic acid are the most ab...

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Estimation of the pentose cycle in the perfused cow's udder

Cited by 42 publications

References 22 publications

Control of Mammary Function During Lactation in Crossbred Dairy Cattle in the Tropics

Control of Mammary Function During Lactation in Crossbred Dairy Cattle in the Tropics

Effects of Cooling and Supplemental Bovine Somatotropin on Milk Production relating to Body Glucose Metabolism and Utilization of Glucose by the Mammary Gland in Crossbred Holstein Cattle

Precursors of hexoneogenesis within the human mammary gland

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