Time course of changes in plasma glucose and insulin concentrations and mammary-gland lipogenesis during re-feeding of starved conscious lactating rats.
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ABSTRACT:
SUBMITTER: Mercer SW
PROVIDER: S-EPMC1147308 | biostudies-other | 1986 Oct
REPOSITORIES: biostudies-other
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Project description:Arteriovenous glucose difference across the mammary gland of the lactating rat was used as an 'instantaneous' monitor of mammary glucose uptake. Plasma [glucose] and arteriovenous glucose difference varied according to whether Halothane, diethyl ether or sodium pentobarbitone anaesthesia was used. In pentobarbitone-treated rats a 60% glucose extraction in the fed state decreased to 5% after 18 h starvation, and recovered to 40% and 59% after 15 min and 60 min re-feeding respectively. The increase and decrease in plasma [fatty acids] and the depletion and restoration of hepatic glycogen mostly followed similar time courses. Re-feeding was accompanied by a brief surge of plasma [insulin]. Starved lactating rats showed a markedly greater capacity than age-matched virgin rats in the oral and intraperitoneal glucose tolerance tests. Mammary glucose uptake in the starved rat was significantly restored by oral or intraperitoneal glucose or by insulin, but not by acetoacetate or by heparin-induced elevation of plasma [fatty acids]. The role of insulin and of possible changes in mammary sensitivity to insulin in the return of mammary glucose uptake on re-feeding is discussed.
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Project description:1. Oral administration of triacylglycerol (triolein) to starved/chow-refed lactating rats suppressed the lipogenic switch-on in the mammary gland in vivo. 2. A time-course study revealed that triolein, administered at 30 min after the onset of refeeding, had no influence on lipogenic rate in the mammary gland between 30 and 60 min, but markedly decreased it between 60 and 90 min. Glucose uptake by the mammary gland (arteriovenous difference) increased by 30 min of refeeding, as did lactate production. Between 30 and 90 min glucose uptake remained high in the control animals, but glucose uptake and net C3-unit uptake were decreased in the triolein-loaded animals by 90 min. 3. Triolein increased [glucose 6-phosphate] in the gland and simultaneously decreased [fructose 1,6-bisphosphate], indicative of a decrease in phosphofructokinase activity. This cross-over occurred at 60 min, i.e. immediately before the inhibition of lipogenesis, and by 90 min had reached 'starved' values. 4. Triolein had no effect on plasma [insulin] nor on whole-blood [glucose], [lactate] or [3-hydroxybutyrate]; a small increase in [acetoacetate] was observed. 5. Infusion of the lipoprotein lipase inhibitor, Triton WR1339, abolished the suppression of mammary-gland lipogenesis by triolein and the increase in the [glucose 6-phosphate]/[fructose 1,6-bisphosphate] ratio, suggesting a direct influence of dietary lipid on mammary-gland glucose utilization and phosphofructokinase activity.
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Project description:Administration of insulin with glucose to starved lactating rats, which activates pyruvate dehydrogenase [M. A. Baxter & H. G. Coore (1978) Biochiem. J. 174, 553-561], restored lipogenesis in mammary gland in vivo to 50% of the value observed in refed (2.5 h) rats. The correlations between pyruvate dehydrogenase activity and the rate of lipogenesis persisted in isolated acini. Activation of pyruvate dehydrogenase in vitro with dichloroacetate increased lipogenesis from [6-14C]glucose in acini from starved and refed rats by 250% and 100% respectively. However, in the presence of dichloroacetate, only 70% of the increased flux through pyruvate dehydrogenase was converted into lipid in acini from starved rats, whereas all of the increase could be accounted for as lipid in acini from refed rats. Addition of insulin plus dichloroacetate was required to obtain maximal rates of lipogenesis in acini from starved rats. Similarly, insulin increased the incorporation of [1-14C]acetate into lipid only in acini from starved rats. Although the activity of pyruvate dehydrogenase plays an important role in the control of mammary-gland lipogenesis, the evidence presented suggests a second regulatory site which is insulin-sensitive and is located after the generation of cytosolic acetyl-CoA.
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Project description:Depression of carbohydrate digestion by oral administration of acarbose, a glucosidase inhibitor, led to a 75% inhibition of the re-activation of lipogenesis in vivo in the mammary gland of 18 h-starved lactating rats refed with 5 g of chow diet. Rates of [1-14C]glucose incorporation in vitro into lipid and CO2 in mammary-gland acini isolated from refed animals were elevated compared with acini from starved rats, but acarbose treatment completely prevented this stimulation. Gastric intubation of glucose led to a large stimulation of lipogenesis in the mammary gland of starved lactating rats, similar to that induced by refeeding with chow diet; this was dependent on the amount of glucose given and the time elapsed between glucose administration and injection of 3H2O for the measurement of lipogenesis. The switch-on of lipogenesis in the mammary gland of starved lactating rats, by refeeding or by intubation of glucose, was associated with a decrease in the ratio of [glucose 6-phosphate]/[fructose 1,6-bisphosphate] in the gland, indicative of an increase in phosphofructokinase activity. A time-course study revealed that the ratio decreased rapidly over the first 30 min of chow refeeding, after which a large surge in lipogenesis was seen. Acarbose, given 25 min after the onset of refeeding, led to a stepwise increase in the ratio, in parallel with the observed decrease in lipogenic activity. It is concluded that the control of lipogenesis in the mammary gland is closely linked to the availability of dietary carbohydrate. An important site of regulation of lipogenesis in the gland appears to be at the level of phosphofructokinase. A possible role of insulin in the regulation of phosphofructokinase activity, and the acute modulation of insulin-sensitivity in the gland during the starved-refed transition, are discussed.
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Project description:BACKGROUND:Nutrition affects milk composition thus influencing its nutritional properties. Nutrition also modifies the expression of mammary genes, whose regulation is not fully understood. MicroRNAs (miRNA) are small non coding RNA which are important post-transcriptional regulators of gene expression by targeting messenger RNAs. Our goal was to characterize miRNA whose expression is regulated by nutrition in the lactating goat mammary gland, which may provide clues to deciphering regulations of the biosynthesis and secretion of milk components. METHODOLOGY/PRINCIPAL FINDINGS:Using high-throughput sequencing technology, miRNomes of the lactating mammary gland were established from lactating goats fed ad libitum or deprived of food for 48 h affecting milk production and composition. High throughput miRNA sequencing revealed 30 miRNA with an expression potentially modulated by food deprivation; 16 were down-regulated and 14 were up-regulated. Diana-microT predictive tools suggested a potential role for several nutriregulated miRNA in lipid metabolism. Among the putative targets, 19 were previously identified as differently expressed genes (DEG). The functions of these 19 DEG revealed, notably, their involvement in tissue remodelling. CONCLUSION/SIGNIFICANCE:In conclusion, this study offers the first evidence of nutriregulated miRNA in the ruminant mammary gland. Characterization of these 30 miRNA could contribute to a clearer understanding of gene regulation in the mammary gland in response to nutrition.
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Project description:BackgroundThe mammary gland is a dynamic organ that undergoes important physiological changes during reproductive cycles. Until now, data regarding the characterisation of miRNA in the mammary gland have been scarce and mainly focused on their abnormal expression in breast cancer. Our goal was to characterise the microRNA (miRNA) involved in mechanisms regulating the mammary function, with particular focus on the lactation stage.Methodology/principal findingsUsing high-throughput sequencing technology, the exhaustive repertoires of miRNA expressed (miRNome) in mouse and bovine mammary glands during established lactation were identified, characterized and compared. Furthermore, in order to obtain more information on miRNA loading in the RNA-induced silencing complex (RISC), the miRNome was compared with that obtained from RNA associated with the AGO2 protein (AGO2-miRNome) in mouse lactating mammary gland. This study enabled the identification of 164 and 167 miRNA in mouse and bovine, respectively. Among the 30 miRNA most highly expressed in each species, 24 were common to both species and six of them were preferentially highly expressed in lactating than non-lactating mammary gland. The potential functional roles of these 24 miRNA were deduced using DIANA-miRPath software, based on miRNA/mRNA interactions. Moreover, seven putative novel miRNA were identified. Using DAVID analysis, it was concluded that the predicted targets of two of these putative novel miRNA are involved in mammary gland morphogenesis.Conclusion/significanceOur study provides an overview of the characteristics of lactating mouse and bovine mammary gland miRNA expression profiles. Moreover, species-conserved miRNA involved in this fundamental biological function were identified. These miRNomes will now be used as references for further studies during which the impact of animal breeding on the miRNA expression will be analysed.
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Project description:RNA-Seq enables the generation of extensive transcriptome information providing the capability to characterize transcripts (including alternative isoforms and polymorphism), to quantify expression and to identify differential regulation in a single experiment. Our aim in this study was to take advantage of using RNA-Seq high-throughput technology to provide a comprehensive transcriptome profiling of the sheep lactating mammary gland. Eight ewes of two dairy sheep breeds with differences in milk production traits were used in this experiment (four Churra and four Assaf ewes). Milk samples from these animals were collected on days 10, 50, 120 and 150 after lambing to cover the various physiological stages of the mammary gland across the complete lactation. RNA samples were extracted from milk somatic cells. The RNA-Seq dataset was generated using an Illumina HiSeq 2000 sequencer. The information reported here will be useful to understand the biology of lactation in sheep, providing also an opportunity to characterize their different patterns on milk production aptitude.
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