scholarly journals Lactogenesis in the rat. Metabolism of uridine diphosphate galactose by mammary gland

1968 ◽  
Vol 106 (3) ◽  
pp. 743-748 ◽  
Author(s):  
N. J. Kuhn
Keyword(s):  
Mammary Gland ◽  
Synthetase Activity ◽  
Uridine Diphosphate ◽  
Parallel Increase ◽  
Hydrolytic Activities ◽  
Before And After ◽  
Rat Mammary Gland ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Rate Limiting

1. Lactose synthetase activity in the rat mammary gland increases during the last day of pregnancy from an essentially zero value. There is a parallel increase of tissue lactose and of glucose 6-phosphate dehydrogenase activity. 2. Mammary-gland homogenates prepared both before and after parturition hydrolyse the lactose precursors glucose 6-phosphate, glucose 1-phosphate, UDP-glucose, UDP-galactose and also maltose, but not lactose. 3. A role of lactose synthetase as the rate-limiting enzyme for lactose biosynthesis and the possible significance of the hydrolytic activities are discussed with respect to lactogenesis.

scholarly journals Phosphoribosyl pyrophosphate and phosphoribosyl pyrophosphate synthetase in rat mammary gland. Changes in the lactation cycle and effects of diabetes, insulin and phenazine methosulphate

1986 ◽  
Vol 238 (2) ◽  
pp. 553-559 ◽  
Author(s):  
S Kunjara ◽  
M Sochor ◽  
N Salih ◽  
P McLean ◽  
A L Greenbaum
Keyword(s):  
Mammary Gland ◽  
Fold Increase ◽  
Pentose Phosphate ◽  
Diabetic Rat ◽  
Synthetase Activity ◽  
Phosphoribosyl Pyrophosphate ◽  
Rat Mammary Gland ◽  
Lactation Cycle ◽  
Phenazine Methosulphate

Changes in the tissue content of phosphoribosyl pyrophosphate (PPRibP), glucose 6-phosphate, ribose 5-phosphate (Rib5P), RNA and DNA, of the activity of PPRibP synthetase (EC 2.7.6.1) and the conversion of [1-14C]- and [6-14C]-glucose into 14CO2 were measured at mid-lactation in the normal and diabetic rat and in pregnancy, lactation and mammary involution in the normal rat. The PPRibP, glucose 6-phosphate and Rib5P contents increase during pregnancy and early lactation to reach a plateau value at mid-lactation, before falling sharply during weaning. The PPRibP content, PPRibP synthetase activity and flux of glucose through the oxidative pentose phosphate pathway (PPP) all change in parallel during the lactation cycle. Similarly, after 3 and 5 days duration of streptozotocin-induced diabetes, ending on day 10 of lactation, there were parallel declines in PPRibP content, PPRibP synthetase and PPP activity. The effect of streptozotocin was prevented by pretreatment with nicotinamide and partially reversed by insulin administration. Addition of insulin to lactating rat mammary-gland slices incubated in vitro significantly raised the PPRibP content (+47%) and the activity of the PPP (+40%); phenazine methosulphate, which gives a 2-fold increase in PPP activity, raised the PPRibP content of lactating mammary gland slices by approx. 3-fold. It is concluded that Rib5P, generated in the oxidative segment of the PPP, is an important determinant of PPRibP synthesis in the lactating rat mammary gland and that insulin plays a central role in the regulation of the bioavailability of this precursor of nucleotide and nucleic acid synthesis.

scholarly journals Regulation of acetyl-CoA carboxylase in rat mammary gland. Effects of starvation and of insulin and prolactin deficiency on the fraction of the enzyme in the active form in vivo

1982 ◽  
Vol 204 (1) ◽  
pp. 273-280 ◽  
Author(s):  
Elizabeth M. McNeillie ◽  
Victor A. Zammit
Keyword(s):  
Mammary Gland ◽  
Enzyme Activities ◽  
Enzyme Concentration ◽  
Acetyl Coa Carboxylase ◽  
Initial Activity ◽  
Acetyl Coa ◽  
Activity Ratios ◽  
Rat Mammary Gland ◽  
Rate Limiting

The ‘initial’ (I), endogenous phosphatase-activated (A) and citrate-activated (C) activities of acetyl-CoA carboxylase were measured in mammary-gland extracts of pregnant and lactating rats. There was a 10-fold increase in the A and C enzyme activities in the transition from early to peak lactation [cf. data of Mackall & Lane (1977) Biochem. J.162, 635–642], but there was no significant increase in the ratio of the initial activity to the A and C activities of the enzyme. Starvation (24h) or short-term (3h) streptozotocin-induced diabetes both resulted in a 40% decrease in I/A and I/C activity ratios. In starvation this was accompanied by a decrease in the absolute values of the A and C activities such that the initial activity in mammary glands of starved animals was 45% that in glands from fed animals. Insulin treatment of starved or diabetic animals 60min before killing increased the I activity without affecting the A or C enzyme activities. Removal of the pups for 24h from animals in peak lactation (weaning) resulted in a marked but similar decrease in all three activities such that, although the initial activity was only 10% of that in suckled animals, the I/A and I/C activity ratios remained high and unaltered. Inhibition of prolactin secretion by injection of 2-bromo-α-ergocryptine gave qualitatively similar results to those during weaning. Simultaneous administration of ovine prolactin completely prevented the effects of bromoergocryptine. It is suggested that the initial activity of acetyl-CoA carboxylase in rat mammary gland is regulated by at least two parallel mechanisms: (i) an acute regulation of the proportion of the enzyme in the active state and (ii) a longer-term modulation of enzyme concentration in the gland. Insulin appeared to mediate its acute effects through mechanism (i), whereas prolactin had longer-term effects on enzyme concentration in the gland. A comparison of initial enzyme activities (I) obtained in the present study with rates of lipogenesis measured in vivo [Agius & Williamson (1980) Biochem. J.192, 361–364; Munday & Williamson (1981) Biochem. J.196, 831–837] gave good agreement between the two sets of data for all conditions studied except for 24h-starved and streptozotocin-diabetic animals. It is suggested that acetyl-CoA carboxylase activity is rate-limiting for lipogenesis in the mammary gland in normal, fed, suckled or weaned animals but that in starved and short-term diabetic animals changes in the activity of the enzyme by covalent modification alone may not be sufficient to maintain the enzyme in its rate-limiting role.

Abstract 261: Robust Cardioprotection Afforded by a Previously Unrecognized Link between the Unfolded Protein Response and the Hexosamine Biosynthetic Pathway

2014 ◽  
Vol 115 (suppl_1) ◽  
Author(s):  
Zhao V Wang ◽  
Yingfeng Deng ◽  
Ningguo Gao ◽  
Zully Pedrozo ◽  
Dan Li ◽  
...  
Keyword(s):  
Unfolded Protein Response ◽  
Biosynthetic Pathway ◽  
Ischemia Reperfusion ◽  
Uridine Diphosphate ◽  
Hexosamine Biosynthetic Pathway ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response ◽  
Rate Limiting

Background: The hexosamine biosynthetic pathway (HBP) generates UDP-GlcNAc (uridine diphosphate N-acetylglucosamine) for glycan synthesis and O-linked GlcNAc (O-GlcNAc) protein modifications. Despite the established role of the HBP in glucose metabolism and multiple diseases, regulation of the HBP remains largely undefined. Methods & Results: Here, we show that spliced Xbp1 (Xbp1s), the most conserved signal transducer of the unfolded protein response (UPR), is a direct transcriptional activator of the HBP. We demonstrate that the UPR triggers activation of the HBP by means of Xbp1s-dependent transcription of genes coding for key, rate-limiting enzymes. We establish that this previously unrecognized UPR-HBP axis is triggered in a variety of stress conditions known to promote O-GlcNAc modification. We go on to demonstrate that Xbp1s, acutely stimulated by ischemia/reperfusion (I/R) in heart, confers robust cardioprotection against I/R injury. We also show that HBP induction is required for this cardioprotective response. Mechanistically, HBP may mediate the adaptive branch of the UPR by activating autophagy and ER-associated degradation. Conclusion: These studies reveal that Xbp1s couples the UPR to the HBP, promoting robust cardioprotection during I/R.

The role of insulin in the regulation of AMP-activated protein kinase in lactating rat mammary gland

1992 ◽  
Vol 20 (3) ◽  
pp. 306S-306S ◽  
Author(s):  
MIHAJLO R. MILIC ◽  
KAREN A. OTTEY ◽  
SARVJINDER TAKHAR ◽  
MICHAEL R. MUNDAY
Keyword(s):  
Mammary Gland ◽  
Protein Kinase ◽  
Rat Mammary Gland ◽  
Amp Activated Protein Kinase

scholarly journals Control of glucose metabolism in isolated acini of the lactating mamary gland of the rat. Effects of oleate on glucose utilization and lipogenesis

1978 ◽  
Vol 170 (3) ◽  
pp. 609-613 ◽  
Author(s):  
A M Robinson ◽  
D H Williamson
Keyword(s):  
Mammary Gland ◽  
Glucose Metabolism ◽  
Glucose Utilization ◽  
Substrate Utilization ◽  
Inhibitory Effects ◽  
Rat Mammary Gland

Oleate (1mM) had only small inhibitory effects on glucose utilization and lipogenesis in acini isolated from rat mammary gland. Esterification of [1-14C]oleate was unaffected by insulin but were decreased by 60% by acetoacetate (2mM). Glycerol (1mM), but not insulin, relieved this inhibition. These experiments provide further support for the role of acetoacetate in regulating substrate utilization by the gland.

scholarly journals The role of nucleoside diphosphatase in a uridine nucleotide cycle associated with lactose synthesis in rat mammary-gland Golgi apparatus

1977 ◽  
Vol 168 (3) ◽  
pp. 423-433 ◽  
Author(s):  
N J Kuhn ◽  
A White
Keyword(s):  
Mammary Gland ◽  
Uridine Nucleotide ◽  
Lactose Synthase ◽  
Bivalent Metal Ions ◽  
Ump Kinase ◽  
Rat Mammary Gland ◽  
Lactose Synthesis ◽  
Galactose Utilization ◽  
Nucleoside Diphosphatase

1. UDP-galactose utilization by isolated Golgi vesicles or rat mammary gland synthesizing lactose causes accumulation of UMP but not UDP, although UDP is the immediate product of lactose synthase (EC 2.4.1.22). 2. This can be ascribed to a nucleoside diphosphatase (EC 3.6.1.6), specific for UDP, GDP and IDP, activated by bivalent metal ions and apparently located on the luminal face of the Golgi membrane. 3. The uridine diphosphatase activity exceeds the total galactosyltransferase activity 5-fold, and is estimated to maintain UDP at about 14 micrometer within the Golgi lumen. 4. Evidence is given that UMP, but not UDP, penetrates the membrane and that UMP is rephosphorylated to UDP by a UMP kinase located in the cytosol. 5. Golgi-cytosol relationships with respect to lactose synthesis are formulated in terms of a uridine nucleotide cycle which throws new light on the energy cost and possible regulation of lactose synthesis.

scholarly journals Role of fructose 2,6-bisphosphate in mammary gland of fed, starved and re-fed lactating rats

1985 ◽  
Vol 232 (3) ◽  
pp. 931-934 ◽  
Author(s):  
S Ward ◽  
N J Kuhn
Keyword(s):  
Mammary Gland ◽  
Intracellular Concentration ◽  
Limiting Factor ◽  
Maximal Rate ◽  
Physiological Conditions ◽  
Highly Sensitive ◽  
Lactating Mammary Gland ◽  
Rate Limiting

The fructose 2,6-bisphosphate (Fru-2,6-P2) content and intracellular concentration of lactating mammary gland was measured in fed, starved and re-fed rats. There was little or no change on starvation, and about 1.5-fold rise on re-feeding, contrasting with estimated glycolytic changes of about 10-fold. The 6-phosphofructokinase (PFK-1) activity of mammary extracts was highly sensitive to added Fru-2,6-P2 under all conditions examined, and appeared to approach saturation at physiological concentrations of this effector. The activity of mammary PFK-1 measured under optimal and ‘physiological’ conditions suggested that this enzyme operates in vivo at about 24% of maximal rate, and is likely to be an important rate-limiting factor in mammary glycolysis.

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