scholarly journals Monosaccharide transport in the mammary gland of the intact lactating rat

1984 ◽  
Vol 218 (1) ◽  
pp. 213-219 ◽  
Author(s):  
L C Threadgold ◽  
N J Kuhn
Keyword(s):  
Mammary Gland ◽  
Glucose Transport ◽  
Intracellular Water ◽  
Limiting Factor ◽  
Transport Capacity ◽  
Tissue Water ◽  
Monosaccharide Transport ◽  
Rate Limiting ◽  
Total Tissue

The Michaelis-Menten equation for the utilization of competing substrates was applied to the uptake of 2-deoxy[3H]glucose into the mammary gland of anaesthetized lactating rats. Intracellular water was calculated from total tissue water and sucrose space. Fed rats had a mean transport capacity of 2.2 mumol/min per g of tissue, giving an actual glucose transport in vivo of 1.1 mumol/min per g. Transport decreased by 90% on overnight starvation and returned to normal by 2 h of re-feeding. Similar changes were observed in the 1 min or 5 min transport of circulating 3-O-methylglucose. Transport of 3-O-methylglucose in starved rats was restored towards normal by insulin. In fed rats it increased between parturition and day 12 of lactation. The findings support the proposal that transport is a rate-limiting factor in the mammary utilization of carbohydrate.

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.

Espace extracellulaire, perméabilité à l'inuline et accumulation de L-alanine dans l'intestin isolé de Grenouille

1973 ◽  
Vol 51 (1) ◽  
pp. 22-28
Author(s):  
Joël de la Noüe ◽  
André Gagnon
Keyword(s):  
Extracellular Space ◽  
Muscle Layer ◽  
Solute Concentration ◽  
Tissue Water ◽  
Intracellular Amino Acid ◽  
Inulin Space ◽  
Total Tissue ◽  
Frog Intestine

In order to calculate the intracellular concentration of accumulated L-alanine, the extracellular space (inulin-14C) of frog intestine was measured. To check the validity of the technique, frog liver and gastrocnemius were used too. By scraping proximal portions of intestine, the inulin space was found to be similar (around 20% of total tissue water) in both the muscle layer and the mucosa. The mucosal epithelium is an imperfect barrier to inulin while the serosa is very permeable. These results suggest that the interstitial solute concentration is best approximated by equating it to that of the serosal solution. The in vitro inulin space, compared to the in vivo one, increases with time, as does the cellular hydration. The data obtained from measurements of extracellular space and from L-alanine uptake show that the intracellular amino acid is in a free state.

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.

Hemorrhagic shock impairs myocardial cell volume regulation and membrane integrity in dogs

1987 ◽  
Vol 252 (6) ◽  
pp. H1203-H1210
Author(s):  
J. W. Horton
Keyword(s):  
Hemorrhagic Shock ◽  
Cell Volume ◽  
Volume Regulation ◽  
Membrane Integrity ◽  
Cell Volume Regulation ◽  
Calcium Entry ◽  
Tissue Water ◽  
Total Tissue

An in vitro myocardial slice technique was used to quantitate alterations in cell volume regulation and membrane integrity after 2 h of hemorrhagic shock. After in vitro incubation in Krebs-Ringer-phosphate medium containing trace [14C]inulin, values (ml H2O/g dry wt) for control nonshocked myocardial slices were 4.03 +/- 0.11 (SE) for total water, 2.16 +/- 0.07 for inulin impermeable space, and 1.76 +/- 0.15 for inulin diffusible space. Shocked myocardial slices showed impaired response to cold incubation (0 degrees C, 60 min). After 2 h of in vivo shock, total tissue water, inulin diffusible space, and inulin impermeable space increased significantly (+19.2 +/- 2.4, +8.1 +/- 1.9, +34.4 +/- 6.1%, respectively) for subendocardium, whereas changes in subepicardium parameters were minimal. Shock-induced cellular swelling was accompanied by an increased total tissue sodium, but no change in tissue potassium. Calcium entry blockade in vivo (lidoflazine, 20 micrograms X kg-1 X min-1 during the last 60 min of shock) significantly reduced subendocardial total tissue water as compared with shock-untreated dogs. In addition, calcium entry blockade reduced shock-induced increases in inulin impermeable space and inulin diffusible space. In vitro myocardial slice studies confirm alterations in subendocardial membrane integrity after 2 h of in vivo hemorrhagic shock. Shock-induced abnormalities in myocardial cell volume regulation are reduced by calcium entry blockade in vivo.

Tissue spaces in rat heart, liver, and skeletal muscle in vivo

1998 ◽  
Vol 275 (5) ◽  
pp. R1530-R1536 ◽  
Author(s):  
Julie Cieslar ◽  
Ming-Ta Huang ◽  
Geoffrey P. Dobson
Keyword(s):  
Skeletal Muscle ◽  
Rat Heart ◽  
Gastrocnemius Muscle ◽  
Interstitial Space ◽  
Glyceric Acid ◽  
Sprague Dawley ◽  
Tissue Water ◽  
Intracellular Space ◽  
Total Tissue

Tissue spaces were determined in rat heart, liver, and skeletal muscle in vivo using isotopically labeled [14C]inulin. Tracer was injected into the jugular vein of pentobarbital-anesthetized male Sprague-Dawley rats. After a 30-min equilibration period, a blood sample was taken, and heart, liver, and gastrocnemius muscle were excised and immediately freeze clamped at liquid nitrogen temperatures. The extracellular inulin space was 0.209 ± 0.006 ( n = 13), 0.203 ± 0.080 ( n = 7), and 0.124 ± 0.006 (SE) ml/g wet wt tissue ( n = 8) for heart, liver, and skeletal muscle, respectively. Total tissue water was 0.791 ± 0.005 ( n = 9), 0.732 ± 0.002 ( n = 9), and 0.755 ± 0.005 ml/g wet wt tissue ( n = 10) for heart, liver, and skeletal muscle, respectively. Expressed as a percentage of total tissue water, the intracellular space was 73.6, 72.2, and 83.7% for heart, liver, and skeletal muscle, respectively. With use of 2,3-diphospho-d-glyceric acid as a vascular marker, the interstitial space was calculated by subtracting the counts in tissue due to whole blood from total tissue counts and dividing by plasma counts. The interstitial space was 18.8, 22.4, and 14.5% of total tissue water, with accompanying plasma spaces of 7.7, 5.3, and 1.8% for heart, liver, and gastrocnemius muscle, respectively. The tracer method used in this study provides a quantitative assessment of water distribution in tissues of nonnephrectomized rats that has applications for calculation of tissue ion and metabolite concentrations, gradients, and fluxes under normal and pathophysiological conditions.

Muscle glucose transport: interactions of in vitro contractions, insulin, and exercise

1988 ◽  
Vol 64 (6) ◽  
pp. 2329-2332 ◽  
Author(s):  
S. H. Constable ◽  
R. J. Favier ◽  
G. D. Cartee ◽  
D. A. Young ◽  
J. O. Holloszy
Keyword(s):  
Glucose Transport ◽  
Prolonged Exposure ◽  
Contractile Activity ◽  
Intracellular Water ◽  
Control Value ◽  
High Insulin ◽  
Muscle Glucose Transport ◽  
High Insulin Concentration

Exercise increases permeability of muscle to glucose. Normally, the effects of exercise and a maximal insulin stimulus on glucose transport are additive. However, the combined effect on rat epitrochlearis muscle permeability to 3-O-methylglucose (3-MG) of a maximal insulin stimulus followed by in vitro contractile activity of 1.24 +/- 0.06 mumol.10 min-1.ml intracellular water-1 was no greater than that of either stimulus alone. We found that this absence of an additive effect was caused by prolonged exposure to an unphysiologically high insulin concentration (20,000 microU/ml for 60 min), which, in addition to stimulating glucose transport, appears to prevent further increases in permeability to glucose. When the treatments were reversed and muscles were first stimulated to contract and then incubated with 20,000 microU/ml insulin, 3-MG uptake (mumol.10 min-1.ml intracellular water-1) increased from a control value of 0.26 +/- 0.03 to 1.80 +/- 0.15, compared with 1.04 +/- 0.06 for contractile activity alone, 1.21 +/- 0.08 for insulin, and 1.88 +/- 0.11 for exercise (swimming) plus insulin. Swimming plus in vitro contractile activity did not have a greater effect than contractile activity alone. Our results provide evidence that 1) the effect of exercise on muscle permeability to glucose is mediated solely by a process associated with contractile activity, and 2) it is advisable to avoid the use of unphysiologically high insulin concentrations in studies designed to elucidate in vivo actions of insulin.

scholarly journals Water Compartmentalization and Spread of Ischemic Injury in Thick-Slice Ischemia Model

2002 ◽  
Vol 22 (1) ◽  
pp. 80-88 ◽  
Author(s):  
Sabina Hrabětová ◽  
Kevin C. Chen ◽  
Daniel Masri ◽  
Charles Nicholson
Keyword(s):  
Water Content ◽  
Extracellular Space ◽  
Cell Swelling ◽  
Extracellular Potassium ◽  
Tissue Water ◽  
Diffusion Analysis ◽  
Artificial Cerebrospinal Fluid ◽  
Water Redistribution ◽  
Total Tissue

Water compartmentalization was studied in a thick-slice (1000 μm) model of ischemia by combining water-content measurements with extracellular diffusion analysis. Thick slices bathed in artificial cerebrospinal fluid continually gained water. Total tissue water content was increased by 67% after 6 hours of the incubation. Diffusion measurements using the tetramethylammonium method showed that the extracellular space, typically occupying 20% of brain tissue in vivo, was decreased to 10% at 30 minutes and 15% at 6 hours in both deep and superficial layers of thick slices. Quantification of water compartmentalization revealed that water moved initially from the extracellular space into the cells. Later, however, both compartments gained water. The initial cell swelling was accompanied by dramatic shifts in potassium. An initial rise of extracellular potassium to about 50 mmol/L was measured with a potassium-selective microelectrode positioned in the center of the thick slice; the concentration decreased slowly afterwards. Potassium content analysis revealed a 63% loss of tissue potassium within two hours of the incubation. In thick slices, ionic shifts, water redistribution, and a loss of synaptic transmission occur in both deep and superficial layers, indicating the spread of ischemic conditions even to areas with an unrestricted supply of nutrients.

In vivo Nitrate Reductase Activity in Leaves of Pearl Millet, Pennisetum americanum (L.) Leeke

1987 ◽  
Vol 14 (2) ◽  
pp. 125 ◽  
Author(s):  
SV Chanda ◽  
AK Joshi ◽  
PN Krishnan ◽  
YD Singh
Keyword(s):  
Nitrate Reductase ◽  
Reductase Activity ◽  
Potassium Phosphate ◽  
Limiting Factor ◽  
Growth Stages ◽  
In Vivo Assay ◽  
Rate Limiting ◽  
Nr Activity

In the in vivo assay of nitrate reductase (NR) in P. americanum leaves, addition of 1% (v/v) Triton X-100, potassium phosphate buffer (80 mM, pH 7.4) and 1.13 mM NADH to the assay medium resulted in maximum activity. With increasing concentration of NADH, saturation-type kinetics were observed. Based on this data metabolic pool concentration for NADH and apparent Km for nitrate reductase were determined. In field studies with cultivars BJ-104, J-104 and 5141-A of P. americanum, the relative limitation of NO3-, NADH and nitrate reductase in NO3- assimilation was determined. NR activity was measured by four modifications of the in vivo assay technique (with NO3-, with NADH, without NO3- and NADH and with both NO3- and NADH additions to the reaction mixture) and with one in vitro technique. For all the cultivars, NADH was the major rate-limiting factor for in vivo assay during early growth stages, while at later stages, NO3- was limiting. At no stage was NR rate-limiting. It is concluded that NR activity alone may not serve as biochemical marker for improved efficiency of utilisation of nitrogen in P. americanum.

scholarly journals Small Intestinal Glucose Transport

1967 ◽  
Vol 50 (5) ◽  
pp. 1173-1182 ◽  
Author(s):  
Alan K. Rider ◽  
Harold P. Schedl ◽  
George Nokes ◽  
Streeter Shining
Keyword(s):  
Glucose Transport ◽  
Absorption Rate ◽  
Distal Segment ◽  
Glucose Absorption ◽  
In Vivo Studies ◽  
Intestinal Segments ◽  
Small Intestinal ◽  
Rate Limiting

Proximal and distal small intestinal segments of the rat were perfused in situ at two different rates with isotonic solutions containing glucose in concentrations ranging from 25 to 600 mg/100 ml. Absorption was measured as glucose disappearance rate from the lumen. Glucose absorption had not previously been studied at intraluminal concentrations above and below blood glucose. Absorption was more rapid from the proximal segment. In both segments absorption was independent of perfusion rate and of whether glucose was analyzed by counting 14C or by the Somogyi method. The latter finding suggests that of the unidirectional fluxes, flux out of the bowel is much greater than flux into the bowel. In contrast to the findings in previous studies neither segment showed rate-limiting kinetics, and the Michaelis-Menten analysis was not applicable. The form of the curve depicting absorption rate in relation to concentration differed between the two segments. At the higher concentrations absorption rate continued to increase much more rapidly in the proximal than in the distal segment. The observations could not be explained by known mechanisms of glucose transport and illustrate the difficulties of achieving biochemically and physiologically meaningful in vivo studies of intestinal absorption.

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