bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of physical training on insulin release and glucose utilization by islet cells and liver glucokinase activity in the rat
Authors: Zawalich W. , Maturo S. , Felig P.
Published: December 2017

The effect of physical training on insulin release and glucose utilization by perifused islets and on liver glucokinase activity was examined in rats that exercised spontaneously by running (in wheel cage) up to 4-6 mi/day for 36 +/- 4 days and in sedentary controls kept in standard cages. Perifusion of islets with 4 mM glucose resulted in comparable rates of insulin release from islets obtained from trained and sedentary control rats. In contrast, when the perifusion glucose concentration was raised to 10 mM, the biphasic increase in insulin release was 40-50% lower in the trained rats as compared with untrained rats. This decrease in glucose-stimulated insulin release occurred in the face of comparable rates of glucose utilization by islets from control and trained rats. Glucose phosphorylation by liver homogenates from trained rats was reduced at all concentrations of glucose examined (0.5-100 mM). The calculated glucokinase activity was diminished by 40%, whereas hexokinase activity was decreased by 15% in the livers from trained rats. We conclude that 1) hypoinsulinemia induced by exercise training is due to decreased sensitivity of the beta-cell to the stimulant action of glucose independent of changes in islet cell utilization of glucose, and 2) exercise training results in a diminution of liver glucokinase activity that may be a consequence of the hypoinsulinemia.
Rat calcium-binding proteins: distribution, development, and vitamin D dependence
Authors: Thomasset M. , Parkes C. O. , Cuisinier-Gleizes P.
Published: December 2017

The tissue distribution, developmental changes, and the vitamin D dependence in the rat of two calcium-binding proteins [CaBPs, 28,000 and 10,000 Mr (28 and 10 K)] were examined. The radioimmunoassays used employed specific antibodies to either the human cerebellar CaBP (28 K protein) or to the smaller rat intestinal CaBP (10 K protein). The assay for the 28 K CaBP may be used to detect this protein in a number of mammalian species and tissues, whereas the 10 K CaBP assay appears to be specific only for the rat intestinal CaBP. This report demonstrates that the tissue distribution of the two CaBPs is different in the rat. High levels of the 28 H protein were found in the cerebellum and kidney, whereas the smaller CaBP was concentrated in the duodenum, jejunum, and cecum. Many other organs and tissues contained small quantities of both CaBPs. Developmental studies indicated some variability in the concentration of the CaBPs. Duodenum, kidney, and cerebellum all contained small amounts of one of the CaBPs prior to birth. Adult levels in all three tissues were already reached at 30 postpartum days. Levels of both CaBPs began to decline in rats older than 2 mo. The vitamin D dependence appeared to reflect cell turnover in that the duodenal and kidney CaBPs showed a vitamin D dependence not observed for the cerebellar protein.
Inhibition by insulin of cellular autophagy in proximal tubular cells of rat kidney
Authors: Pfeifer U. , Warmuth-Metz M.
Published: December 2017

Adult male Sprague-Dawley rats were injected intraperitoneally with 5 U insulin/kg body wt (45 animals). As determined by quantitative electron microscopy, the volume fraction and the numerical density of autophagic vacuoles (AV) in proximal tubular cells decreased within 10 min by 46 and 26%, respectively. A partial recovery of the AV volume fraction was observed 20 and 30 min after the injection contrary to our previous findings with liver (J. Cell Biol. 78: 152-167, 1978). In an additional experiment (12 animals) it was shown that an insulin dose of 0.5 U but not of 0.05 U/kg body wt reduced the AV volume fraction to an extent similar to that of 5 U. To eliminate possible secondary effects, Ringer solution containing 0.8 microM insulin was dropped intravitally for 15 min to one pole of the decapsulated kidney and Ringer solution without additions to the other pole (8 animals). After intravital fixation, the AV volume fraction and numerical density in proximal tubular cells was found to be reduced under the influence of insulin by 22 and 36%, respectively. This data shows that insulin inhibits the process of cellular autophagy in proximal tubular cells of the kidney.
Interorgan metabolism of amino acids in streptozotocin-diabetic ketoacidotic rat
Authors: Brosnan J. T. , Man K. C. , Hall D. E. , Colbourne S. A. , Brosnan M. E.
Published: December 2017

Amino acid concentrations in whole blood, liver, kidney, skeletal muscle, and brain were measured and arteriovenous differences calculated for head, hindlimb, kidney, gut, and liver in control and streptozotocin-diabetic rats. In the control rats, glutamine was released by muscle and utilized by intestine, intestine released citrulline and alanine, liver removed alanine, and the kidneys removed glycine and produced serine. In diabetic rats, the major changes from the pattern of fluxes seen in the normal rat were the release of many amino acids from muscle, with glutamine and alanine predominating, and the uptake of these amino acids by the liver. Glutamine removal by the intestine was suppressed in diabetes, but a large renal uptake of glutamine was evident. Branched-chain amino acids were removed by the diabetic brain, and consequently, brain levels of a number of large neutral amino acids were decreased in diabetes.
Apparent [3H]1,25-dihydroxyvitamin D3 uptake by canine and rodent brain
Authors: Gascon-Barre M. , Huet P. M.
Published: December 2017

The brain uptake of [3H]1,25-dihydroxyvitamin D3 ([3H]1,25(OH)2D3) was studied during steady-state conditions using the multiple-indicator dilution technique in dogs. The fractional [3H]1,25(OH)2D3 uptake was evaluated at 0.8 +/- 0.15% during a single passage through the dog brain. Evaluation of the [3H]1,25(OH)2D3 uptake by the vitamin D-replete and vitamin D-depleted rat brain indicated that 30 min after its injection, the fractional uptake was not influenced by the vitamin D status of the animals or by the amount of [3H]-1,25(OH)2D3 injected. In the rodent the fractional [3H]-1,25(OH)2D3 brain accumulation was between 0.16 and 0.20%, whereas the brain-to-serum ratio varied between 5 and 6%. Protein-binding studies of serum [3H]1,25(OH)2D3 indicated that, at 37 degrees C, 94.8 +/- 0.4% of the hormone was protein bound 30 min after its intravenous injection. These observations suggest that 1,25(OH)2D3 is able to cross the blood-brain barrier. However, its limited brain uptake in relation to its serum concentration suggests that the hormone does not penetrate freely into the central nervous system and that its brain uptake may be related to the free circulating 1,25(OH)2D3 concentration perfusing the blood-brain barrier.
Lipogenesis in the sand rat (Psammomys obesus)
Authors: Kalderon B. , Adler J. H. , Levy E. , Gutman A.
Published: December 2017

Synthesis of fatty acids was measured in the liver and in epididymal adipose tissue of sand rats and albino rats. In chow-fed sand rats the rate of hepatic lipogenesis, as measured by the incorporation of 3H2O into fatty acids, was four- to sevenfold higher than in albino rats and in sand rats on a low-calorie saltbush diet. The contribution of [14C]glucose to lipogenesis in sand rat liver was lower than in albino rats. In fed sand rats lipogenesis incorporating 3H2O was stimulated by casein but not by glucose. In adipose tissue, lipogenesis measured 1 h after administration of 3H2O was much lower in sand rats than in albino rats. In vitro incorporation of [14C]glucose or acetate into adipose tissue fatty acids was negligible. In adipose tissue, uptake of very-low-density lipoproteins (VLDL) and lipoprotein lipase activity were sevenfold higher than in albino rats. Activities of NADP-malate dehydrogenase, acetyl CoA carboxylase, and fatty acid synthetase were considerably higher in the liver of chow-fed sand rats than in albino rats. It was concluded that obesity in sand rats originates from hepatic lipogenesis without a significant contribution of local fatty acid synthesis in adipose tissue.
Incorporation of radioactive phospholipid into subclasses of high-density lipoproteins
Authors: Tall A. R. , Blum C. B. , Grundy S. M.
Published: December 2017

The incorporation of orally administered phospholipid into plasma high-density lipoproteins (HDL) was studied in three subjects. Plasma was analyzed by equilibrium density gradient ultracentrifugation, 5, 6, and 8 h after ingestion of 1.1 g [3H-choline, 14C-dilinoleoyl]phosphatidylcholine. At all time points in all subjects, there was a peak of phosphatidylcholine specific activity in fractions of density approximately 1.10-1.13 g/ml, corresponding to the subclass previously designated HDL2a. There was also a more variable, smaller peak of specific activity of phospholipids in HDL2b (1.063-1.100 g/ml) and in fractions of density approximately 1.19 g/ml. In the 1.10-1.13 fraction, 97 and 71%, respectively, of the 3H and 14C radioactivity were in phospholipids. The 3H/14C ratio was similar in phospholipids of HDL subfractions, the d less than 1.07 fraction, and in the administered phospholipid. The results show preferential transfer or exchange or absorbed phosphatidylcholine into specific subclasses of HDL.
Splanchnic and renal metabolism of insulin in human subjects: a dose-response study
Authors: Ferrannini E. , Wahren J. , Faber O. K. , Felig P. , Binder C. , DeFronzo R. A.
Published: December 2017

Kinetic analyses of insulin metabolism were performed in 32 healthy subjects with hepatic-venous or renal-venous catheters, in whom steady-state conditions of hyperinsulinemia or hyperglycemia were achieved with the use of the glucose-insulin clamp technique. In the basal state, the splanchnic bed removed 42 +/- 2% of the insulin influx. After graded insulin infusions with maintenance of euglycemia, stable arterial insulin levels of 35-1,430 microU/ml were attained. Splanchnic insulin extraction was constant (approximately 60%) at physiological insulin levels but fell (to 29 +/- 1%, P less than 0.02) at supraphysiological (greater than 500 microU/ml) concentrations. The metabolic clearance rate of infused insulin was essentially constant within the physiological concentration range. Hyperglycemia (+125 mg/100 ml) did not alter splanchnic insulin extraction. Basally, the kidneys extracted 0.04 +/- 0.01 mU X min-1 X kg-1 or 25 +/- 5% of arterial insulin. Renal insulin clearance (3.9 +/- 0.4 ml X min-1 X kg-1) represented over 80% of the extrasplanchnic insulin clearance. Hyperglycemia (+125 mg/100 ml) had no effect on renal insulin extraction. In conclusion, a) both splanchnic and renal insulin removal are independent of glycemia and increase in proportion to plasma insulin concentration within the physiological range; b) splanchnic uptake is the dominant mechanism of removal of insulin from the circulation whether the route of delivery is portal or peripheral; and c) the kidneys account for the greater part of extrasplanchnic insulin metabolism.
Interactions between magnesium and calcium in beta-cell-rich pancreatic islets
Authors: Berggren P. O. , Bergsten P. , Gylfe E. , Larsson R. , Hellman B.
Published: December 2017

Calcium-magnesium interactions, total amounts of intracellular magnesium, and insulin release were studied in beta-cell-rich pancreatic islets from ob/ob mice. Mg2+ inhibited the uptake of intracellular 45Ca and insulin release induced by glucose or high concentrations of potassium. Omission of Mg2+ from a Ca2+-deficient medium resulted in an increased efflux of 45Ca, whereas the characteristic glucose inhibition of the efflux was diminished. After addition of Mg2+ to a Mg2+-depleted medium, the glucose-stimulated 45Ca efflux was markedly reduced. Mg2+ inhibited the basal efflux of 45Ca, and this effect was preceded by a transient stimulation. Ca2+ but not Mg2+ stimulated 45Ca efflux in a medium depleted of Ca2+, Mg2+, and Na+. The data indicate that Mg2+ interferes with Ca2+ entry through voltage-dependent Ca2+ channels. Mg2+ may also inhibit the outward transport of Ca2+ from the cells at a site different from the Na+-Ca2+ countertransport mechanism. The total amount of intracellular magnesium remained unaffected by glucose and was not changed unless the ionic composition of the mediums were changed grossly. Under physiological conditions it is therefore unlikely that fluctuations in the intracellular Mg2+ concentration are part of the mechanism by which the functionally important Ca2+ is regulated.
Protein and amino acid metabolism in posterior hemicorpus of acutely uremic rats
Authors: Flugel-Link R. M. , Salusky I. B. , Jones M. R. , Kopple J. D.
Published: December 2017

Protein synthesis and degradation and net uptake and release of amino acids and minerals were examined in the perfused hemicorpus of bilaterally nephrectomized and sham-operated control rats. Animals were studied 30 h after surgery. In comparison with controls, uremic rats had greater urea N appearance (net urea generation) and lower plasma and muscle concentrations of most amino acids. Muscle protein synthesis was not altered, but protein degradation was greater in uremic versus sham rats. There was greater net release of phenylalanine, tyrosine, alanine, total nonessential amino acids, total amino acids, potassium, and phosphorus from the perfused hemicorpus of uremic rats and greater release of citrulline from sham rats. ATP, creatine phosphate, cAMP, and activities of cathepsin B1, cathepsin D, and alkaline protease were not different in muscles of the uremic versus sham rats. Thus, in acutely uremic rats there is increased protein wasting in the hemicorpus due to enhanced protein degradation. The enhanced protein degradation does not appear to be due to increased muscle cathepsin B1, cathepsin D, or alkaline protease activities.
Retention of calcium in intestinal wall of the rabbit by treatment with a glucocorticoid
Authors: Eiler H. , Lyke W. A.
Published: December 2017

In this work, consideration was given to the possibility that increased retention of Ca in the intestinal wall may have resulted in the glucocorticoid-treated animal. Rabbits were treated with pharmacological doses of either dexamethasone, estrogen, or progesterone during 1 wk. Two milliliters of solution containing Ca (plus Mg, K, and Na) were infused into a double-ligated (4 cm apart) gut loop (jejunum). In addition, an adjacent loop was double ligated but received no infusion. Uterine horns were treated in the same way as the gut and were used as controls to test for organ specificity. After the organs were infused with the calcium solution, they were returned into the abdominal cavity for a 4-h period. Dexamethasone treatment was given to a different group of rabbits in which neither surgery was performed nor mineral solution was infused into the lumen of the intestine; in this experiment calcium concentrations were measured in the mucosa, submucosa, and serosa layer obtained from the duodenum, midjejunum, and distal jejunum. In rabbits subjected to surgery, the concentration of Ca in the whole wall of the intestine of the dexamethasone-treated rabbits (45.4 +/- 2.6 mM/kg dry tissue) was twice as large as in controls (22.6 +/- 3.2 mM/kg dry tissue) (P less than 0.05). Mg concentrations were moderately (17%) increased (P less than 0.05). In the group of rabbits receiving dexamethasone but not subjected to surgery, the concentration of Ca in the duodenum (mucosa, submucosa, and whole wall), midjejunum (whole wall), and distal jejunum (submucosa) was significantly (P less than 0.05) elevated as compared with controls. In these rabbits, the duodenum was the most affected segment of the intestine. The effect of dexamethasone was both organ and steroid specific but not mineral specific. This result suggests that one of the effects of the glucocorticoid (dexamethasone) treatment on the intestinal wall was to increase the retention of Ca.
Metabolic responses to intraduodenal glucose loading in insulin-infused diabetic dogs
Authors: Stevenson R. W. , Orskov H. , Parsons J. A. , Alberti K. G.
Published: December 2017

The hormonal and metabolic responses to an intraduodenal glucose load (0.5 g/kg) were first determined in eight normal dogs before diabetes (alloxan/streptozotocin) was induced and then comparison made of the responses to the glucose load when normal plasma glucose profiles were recreated by preprogrammed infusion of insulin via the portal or peripheral circulations. Basal intraportal and peripheral insulin infusions at 0.021 +/- 0.001 and 0.022 +/- 0.000 U . kg-1 . h-1, respectively, for 16 h to fasting diabetic dogs normalized peripheral plasma levels of glucose (5.5 +/- 0.3 and 5.6 +/- 0.6 mmol/liter, respectively), immunoreactive insulin (IRI) (11.5 +/- 1.2 and 16.4 +/- 1.6 microU/ml), glucagon (65 +/- 7 and 62 +/- 5 pg/ml), lactate (0.63 +/- 0.04 and 0.54 +/- 0.03 mmol/liter), and alanine (0.236 +/- 0.037 and 0.191 +/- 0.008 mmol/liter). However, peripheral but not intraportal infusion of insulin depressed levels of glycerol, nonesterified fatty acids (NEFA), and 3-hydroxybutyrate (0.074 +/- 0.006 vs. 0.109 +/- 0.013, P less than 0.01; 0.67 +/- 0.04 vs. 0.84 +/- 0.09, P less than 0.05; and 0.018 +/- 0.004 vs. 0.059 +/- 0.015 mmol/liter, P less than 0.01, respectively). With the preprogrammed insulin infusions used to normalize plasma glucose profiles to the intraduodenal glucose load, all hormonal and metabolic responses were normalized during intraportal infusion (IRI, 72.5 +/- 4.2 microU/ml; glucagon, 66 +/- 10 pg/ml; lactate, 1.06 +/- 0.10 mmol/liter; alanine, 0.251 +/- 0.042 mmol/liter; glycerol, 0.043 +/- 0.013 mmol/liter; NEFA, 0.24 +/- 0.03 mmol/liter; and 3-hydroxybutyrate, 0.012 +/- 0.007 mmol/liter) but marked hyperinsulinemia (103.2 +/- 6.1 microU/ml) and depressed glycerol, NEFA, and 3-hydroxybutyrate responses at 2 h (0.056 +/- 0.005, 0.52 +/- 0.10, and 0.019 +/- 0.010 mmol/liter, respectively) resulted during peripheral infusion. Therefore, only the portal route of insulin infusion achieved complete metabolic normalization during glucose loading in diabetic dogs.
Role of gluconeogenesis in epinephrine-stimulated hepatic glucose production in humans
Authors: Sacca L. , Vigorito C. , Cicala M. , Corso G. , Sherwin R. S.
Published: December 2017

To evaluate the contribution of gluconeogenesis to epinephrine-stimulated glucose production, we infused epinephrine (0.06 micrograms X kg-1 X min-1) for 90 min into normal humans during combined hepatic vein catheterization and [U-14C]alanine infusion. Epinephrine infusion produced a rise in blood glucose (50-60%) and plasma insulin (30-40%), whereas glucagon levels increased only at 30 min (19%, P less than 0.05). Net splanchnic glucose output transiently increased by 150% and then returned to base line by 60 min. In contrast, the conversion of labeled alanine and lactate into glucose increased fourfold and remained elevated throughout the epinephrine infusion. Similarly, epinephrine produced a sustained increase in the net splanchnic uptake of cold lactate (four- to fivefold) and alanine (50-80%) although the fractional extraction of both substrates by splanchnic tissues was unchanged. We conclude that a) epinephrine is a potent stimulator of gluconeogenesis in humans, and b) this effect is primarily mediated by mobilization of lactate and alanine from extrasplanchnic tissues. Our data suggest that the initial epinephrine-induced rise in glucose production is largely due to activation of glycogenolysis. Thereafter, the effect of epinephrine on glycogenolysis (but not gluconeogenesis) wanes, and epinephrine-stimulated gluconeogenesis becomes the major factor maintaining hepatic glucose production.
Cerebral glucose metabolism during 30 minutes of moderate hypoxia and reoxygenation
Authors: Kintner D. , Fitzpatrick J. H. , Louie J. A. , Gilboe D. D.
Published: December 2017

In 50 separate experiments, isolated canine brain preparations were subjected to 15 or 30 min of either PaO2 30 mmHg or PaO2 40 mmHg perfusion followed by up to 60 min of reoxygenation at a normal PaO2. The cerebral metabolic rate for glucose (CMRGlu) increased 70-80% after 2 min of hypoxia but then returned to nearly the normal rate by the end of the 30-min period of hypoxia. Glycolytic flux appeared to be facilitated in both groups initially but was inhibited as the hypoxic period continued. This slowing of glycolysis after 15 or 30 min of hypoxia appears to be modulated by the regulatory enzyme phosphofructokinase. Glucose equivalents metabolized, based on CMRGlu plus brain glucose and glycogen disappearance, far exceed the glucose equivalents that can be accounted for on the basis of oxygen utilization and brain lactate formation. Thus, during hypoxia, some of the glucose equivalents must be utilized for synthesis of other metabolites. The glycolytic intermediates returned to normal after reoxygenation in the PaO2 40 mmHg preparations, but the PaO2 30 mmHg preparations continued to show evidence of decreased glycolysis and a lingering lactacidosis. Although posthypoxic oxygen uptake was sufficient to oxidize all glucose entering the brain, there was no significant release of accumulated lactate into the blood. Thus, the decrease in brain tissue lactate must have been the result of lactate oxidation. A significant amount of the glucose entering the brain during the posthypoxic period appears to be used for metabolite synthesis rather than energy production.
Effect of blood pH and ischemia on kinetic constants for cerebral glucose transport
Authors: Yanushka J. M. , Costello D. J. , Gilboe D. D.
Published: December 2017

In 117 experiments, the isolated canine brain was subjected either to 4-min pulses with blood ranging from pH 6.8 to 7.8, 30 min of hypoxia (PaO2 30 mmHg or 40 mmHg), or 30 min of complete ischemia followed by 60 min of perfusion with normal oxygenated blood. Unidirectional and net glucose fluxes were measured under all experimental conditions, and kinetic constants were calculated for unidirectional transport at each pH and after ischemia. In brains perfused with blood having a PaO2 of 30 or 40 mmHg, we observed a 58 and a 55% increase, respectively, in the net flux; however, there was no significant change in the unidirectional flux either during hypoxia or during the recovery period. Exposure of the brains to blood with a pH of 6.8, 7.0, and 7.2 had no effect on the unidirectional flux; however, as pH was raised above 7.4 both the Km and Vmax increased, reaching a maximum of 12.06 +/- 2.34 mM and 2.38 +/- 0.28 mumol X g-1 X min-1, respectively, at pH 7.8. The V/K ratio was unchanged. After 30 min of ischemia, there was a significant change (P less than 0.05) in the Km of the unidirectional glucose transport process from a control value of 5.84 +/- 1.75 mM to 17.40 +/- 5.50. These studies suggest that unidirectional flux is impaired after ischemia due to a decrease in the carrier's affinity for glucose; however, the observed changes are apparently unrelated to a fall in tissue pH. A similar mechanism is believed to be responsible for the decrease in unidirectional glucose flux after hypoxia.
Cytotoxic effects of alloxan treatment in vitro on monolayer cultures of neonatal rat pancreas
Authors: Gorray K. C. , Baskin D. G. , Fujimoto W. Y.
Published: December 2017

Monolayer cultures of neonatal rat pancreas were exposed briefly (5 min) to alloxan and were then maintained for several days (up to 14 days) to examine the long-term effects of alloxan exposure on B cells. Alloxan (0-10 mM) caused a dose-dependent reduction in rates of insulin release during the first 24 h after treatment. This reduction persisted throughout the period of observation. Rates of glucagon release were unaltered by all concentrations of alloxan tested. Spontaneously decomposed alloxan had little or no effect on rates of insulin release. The simultaneous presence of high concentrations of glucose during exposure of cells to alloxan exerted a rapid protective effect against alloxan toxicity that was both glucose and alloxan dose dependent. Alloxan treatment of pancreatic monolayer cultures may allow for a comparison of those actions of alloxan that are directly on and specific for islet B cells. Furthermore, alloxan-treated cultures may represent a unique in vitro system for studying the physiology and biochemistry of other islet cell types in cultures in which B cells and insulin are reduced, as well as for studying glucose interactions with the B cell.
Absorption, distribution, and transport of vitamin D3 and 25-hydroxyvitamin D3 in the rat
Authors: Dueland S. , Pedersen J. I. , Helgerud P. , Drevon C. A.
Published: December 2017

The absorption of [14C]vitamin D3 and 25-[3H]hydroxyvitamin D3 into the mesenteric lymph and portal vein after simultaneous instillation in rat duodenum has been studied. The appearance of both isotopes in the mesenteric lymph and portal vein during the first 2 h was negligible. After 2-4 h the isotopes appeared both in the lymph and portal vein. The appearance of 25-[3H]hydroxyvitamin D3 in the mesenteric lymph was faster than that of [14C]vitamin D3. Total recovery in the lymph during 24 h for [14C]vitamin D3 and 25-[3H]hydroxyvitamin D3 was 15.2 and 14.3%, respectively. While 80% of vitamin D3 in mesenteric lymph was recovered in the chylomicrons (d less than 1.006 g/ml), 94% of 25-hydroxyvitamin D3 was recovered in the protein fraction with d greater than 1.21 g/ml. Seventy-one percent of 25-hydroxyvitamin D3 in the protein fraction was associated with the alpha-globulins. Both vitamin D3 and 25-hydroxyvitamin D3 that were recovered in the chylomicrons (d less than 1.006 g/ml) were transferred in vitro to the lymph fraction with d greater than 1.006 g/ml. Less than 12% of 25-hydroxyvitamin D3 was recovered in the liver after intravenous injection of mesenteric lymph labeled with 25-[3H]hydroxyvitamin D3. Previously, under similar conditions 40% of administered vitamin D3 was recovered in the liver.
In vitro regulation of human monocyte insulin receptors by insulin and 1-methyl-3-isobutylxanthine
Authors: Whitson R. H. , Kaplan S. A.
Published: December 2017

Monocytes separated from human blood by Ficoll-Hypaque and adherence to polystyrene flasks were maintained successfully in culture for 7 days. The cultured cells showed normal morphology and good viability. The insulin binding properties of the cultured monocytes were also identical to those of fresh monocytes. In vitro pretreatment of the monocytes with insulin decreased both the number and affinity of insulin receptors, resulting in a 72% reduction in the binding of tracer quantities of 125I-insulin. Insulin-induced receptor down regulation was dose-dependent and specific to the insulin receptor. Monocytes pretreated with insulin in the presence of the cyclic nucleotide phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine (MIX) lost significantly fewer insulin receptors than monocytes treated with insulin alone. Tracer binding to these cells was 62% of control levels. MIX had no effect on basal insulin binding. The cAMP analogues N6,O2'-dibutyryl cAMP and 8-bromo-cAMP did not counteract insulin-induced receptor downregulation by themselves and did not significantly enhance the effects of MIX. These results indicate that MIX may counteract insulin receptor downregulation by a cAMP-independent process.
Cyclic AMP changes in guinea pig mammary gland and milk
Authors: Loizzi R. F.
Published: December 2017

Cyclic AMP was measured in guinea pig mammary gland biopsies from midpregnancy through lactation and in daily milk samples throughout lactation. The results indicate that mammary gland cAMP levels rise sharply in late pregnancy to a prepartum peak and then drop abruptly at partus. This is similar to the pattern observed by others in rat and mouse although the guinea pig does not undergo a prepartum progesterone withdrawal. In animals with a 3-wk lactation period, milk cAMP concentration decreases approximately 40% between days 10 and 20, whereas the mammary gland level increases 22% per unit wet tissue weight. Although milk concentrations of lactose and cAMP are weakly correlated, a strong correlation exists between the total collected daily outputs of these two substances. The results suggest that, as lactation proceeds, mammary gland cAMP levels gradually increase, whereas milk cAMP levels decrease. Concurrently, lactose output decreases as lactation proceeds. These observations are consistent with first, a milk secretory route for regulating mammary gland cAMP levels (in addition to synthesis and hydrolysis), and second, an inhibitory action of cAMP on lactose synthesis.
Hyperosmolarity and cardiac function in chronic diabetic rat heart
Authors: Bielefeld D. R. , Pace C. S. , Boshell B. R.
Published: December 2017

Serum hyperosmolarity is commonly associated with the poorly controlled diabetic state. The current investigation revealed that increased perfusate osmolarity using either glucose or mannitol caused a gradual decline in the aortic output of hearts from both normal and diabetic rats. However, aortic output decreased less rapidly in hearts from diabetic rats. Decreasing the extracellular calcium concentration to a level resulting in one-third of the maximal aortic output elicited a greater and more prolonged increase in aortic output from the diabetic compared with the normal heart when perfusate osmolarity was progressively increased. The coronary conductance of diabetic rat hearts improved when hyperosmolar solutions of either mannitol or glucose were utilized, irrespective of the external calcium ion concentration. In normal hearts, the coronary conductance tended to decline at higher perfusate osmolarities. The increased coronary conductance may play a role in the enhanced performance of diabetic hearts at higher levels of osmolarity. Hyperosmolar solutions influence the performance of hearts from chronic diabetic rats in a positive inotropic manner at low extracellular calcium concentrations (1 mM). These lower calcium levels are close to the normal physiological range of the freely ionized serum calcium. This effect is greater in hearts from diabetic animals than from normal animals and is similar to that obtained when perfusate calcium is increased. The results suggest that hyperosmolar solutions enhance calcium availability in the hearts of diabetic animals.
Direct alpha-adrenergic stimulation of hepatic glucose production in human subjects
Authors: Rosen S. G. , Clutter W. E. , Shah S. D. , Miller J. P. , Bier D. M. , Cryer P. E.
Published: December 2017

Six normal humans each underwent infusions of 1) saline; 2) propranolol; 3) somatostatin; 4) somatostatin with propranolol; and 5) somatostatin with propranolol plus phentolamine on separate occasions. Propranolol alone had no effect on glucose production or plasma glucose. Somatostatin alone produced the expected initial decrease followed by an increase in both hepatic glucose production and plasma glucose. beta-Adrenergic blockade with propranolol displaced the glucose production (MANOVA, P = 0.0220) and plasma glucose (MANOVA, P = 0.0057) somatostatin response curves to higher levels, whereas alpha-adrenergic blockade with phentolamine combined with beta-adrenergic blockade displaced the glucose production (MANOVA, P = 0.0281) and plasma glucose (MANOVA, P = 0.0134) somatostatin response curves to lower levels. Because plasma insulin, C-peptide, and glucagon were suppressed comparably under all three conditions and plasma glucose concentrations were comparable initially, this represents direct alpha-adrenergic stimulation of hepatic glucose production in postabsorptive humans demonstrable when the primary glucoregulatory hormones are withdrawn and beta-adrenergic mechanisms are blocked. It is best attributed to sympathetic neural norepinephrine release.
Rapid changes in hepatic glucose output after a pulse of growth hormone in dogs
Authors: Vaitkus P. , Sirek A. , Norwich K. H. , Sirek O. V. , Unger R. H. , Harris V.
Published: December 2017

In response to a single intravenous injection of bovine growth hormone (GH, 100 micrograms/kg) the non-steady-state turnover of glucose, as well as portal levels of insulin (IRI), glucagon (IRG), somatostatin (SRIF), and glucose were determined in normal conscious dogs. Using the two-compartment model validated to calculate rapid turnover changes and tracer infusion methods, the rate of hepatic output of glucose [Ra(t)] was found to be increased, reaching a maximum of 224 mg/min, 7.4 times the basal rate, 4 min after injection of GH. Ra(t) returned to its basal level 35 min later in a damped oscillatory manner. Hormone determinations were carried out in portal venous blood drawn every 2 min for 2 h from an indwelling catheter. IRG peaked 2 min after GH injection and levels of IRI, SRIF, and glucose peaked between 4 and 8 min. Hormone concentrations returned to normal, i.e., were oscillating around base-line levels, about 30 min after GH. These experiments demonstrate for the first time in vivo that a pulse of GH causes transient changes of glucose turnover and measurable alterations of the hormonal homeostasis in the splanchnic area.
Nutritional influences on lipogenesis and thermogenesis after a carbohydrate meal
Authors: Acheson K. J. , Schutz Y. , Bessard T. , Ravussin E. , Jequier E. , Flatt J. P.
Published: December 2017

In vivo lipogenesis and thermogenesis were studied for 24 h after ingestion of 500 g of carbohydrate (CHO) in subjects who had consumed either a high-fat, a mixed, or a high-CHO diet during the 3-6 days preceding the test. CHO oxidation and conversion to fat was significantly less in the high-fat diet group (222 +/- 5 g) than in the mixed (300 +/- 13 g) or high-CHO diet (331 +/- 7 g) groups, resulting in a greater glycogen storage in the high-fat (278 +/- 6 g) than in the other two groups (197 +/- 11 and 170 +/- 2 g). Net lipogenesis occurred sooner and lasted longer in the high-CHO group, amounting to 0.8 +/- 0.5, 3.4 +/- 0.6, and 9 +/- 1 g of lipid synthesized in the high-fat, mixed, and high-CHO groups, respectively. The thermic effect of the CHO load was 5.2 +/- 0.5% on the high-fat, 6.5 +/- 0.4% on the mixed diet, and 8.6 +/- 0.4% on the high-CHO diet. Significant relationships were demonstrated between the postabsorptive nonprotein respiratory quotient and net lipogenesis after the CHO load (r = 0.82) and between net lipogenesis and the increase in energy expenditure (r = 0.71). It is concluded that the antecedent diet influences the amount of net lipogenesis and the magnitude of thermogenesis after a large CHO test meal. However, lipogenesis remains too limited even after such large CHO intakes to cause an increase in the body's fat content.
Reduced postprandial heat production with gavage as compared with meal feeding in human subjects
Authors: LeBlanc J. , Cabanac M. , Samson P.
Published: December 2017

The postprandial changes in resting metabolic rate (RMR) were measured in eight subjects after the ingestion of 735 kcal taken in the form of a meal or fed by stomach tube. A much larger increase in RMR was found with meal feeding (MF) as compared with tube feeding (TF). Measurements of respiratory quotient (RQ) indicated that the increase in RMR with MF is related to increased glucose oxidation, whereas with TF it is possibly explained primarily by the cost of energy storing. Determination of plasma norepinephrine (NE) indicated that the sympathetic nervous system is activated by MF but not by TF. Similarly, plasma glucose and insulin determinations have shown that the secretion of insulin is increased during food ingestion but only with the MF situation. Thus in the 30 min after the beginning of the meal, an increased glucose oxidation was observed that is possibly related to an enhanced NE and insulin secretion; such effects were nonexistent in the TF situation. These results would not substantiate the notion of the specific dynamic action of food and would indicate that independent of the composition of the ingested nutrients, the postprandial increase in RMR is also influenced by sensory and cognitive stimulations.
Metabolic responses to tyramine and cold in young male Sprague-Dawley and Fischer 344 rats
Authors: Kiang-Ulrich M. , Horvath S. M.
Published: December 2017

Significant differences in responses to intraperitoneally injected tyramine or cold exposure (-10 degrees C) were observed in young (3-4 mo) male Sprague-Dawley (S-D) and Fischer 344 (F344) rats cold-acclimated (CA) or non-cold-acclimated (non-CA). Non-CA S-D and F344 rats respond to tyramine by increased O2 uptake and elevation of colonic temperature, but, as we had reported previously, the optimal doses of tyramine required was significantly different for these two strains, i.e., 2 mg/kg for F344 vs. 20 mg/kg for S-D. The response to tyramine was significantly potentiated by cold acclimation in both strains of rats. Despite the different dosages of tyramine given to the animals, similar increases in O2 uptakes and colonic temperatures were observed. Differences between these two strains were also evident in their responses to a cold challenge (3 h, -10 degrees C). The ranking for cold tolerance (-10 degrees C) was as follows: CA F344 greater than non-CA F344 greater than CA S-D greater than non-CA S-D. These differences between the two strains suggest that interpretations regarding the response of rats to stressful conditions must be made with caution and appreciation of strain differences.
Insulin-mediated potassium uptake is normal in uremic and healthy subjects
Authors: Alvestrand A. , Wahren J. , Smith D. , DeFronzo R. A.
Published: December 2017

We examined the ability of physiological hyperinsulinemia to enhance potassium and glucose uptake by splanchnic and peripheral tissues in 12 chronically uremic subjects by using the euglycemic insulin clamp technique in combination with hepatic and femoral venous catheterization. In control subjects, the decline in plasma potassium concentration averaged 0.95 +/- 0.05 meq/liter. Splanchnic (67 +/- 10.3 mu eq/min) and leg (22.2 +/- 1.4 mu eq/min) potassium uptake accounted for 43 and 59%, respectively, of the total amount of potassium that was translocated from the extracellular to intracellular fluid compartment. In uremic individuals, the decline in plasma potassium concentration (0.98 +/- 0.10) was similar to controls. Likewise, the mean splanchnic (66.6 +/- 6.1 mu eq/min) and leg (22.4 +/- 1.6 mu eq/min) potassium uptakes were similar to controls. These results indicate that insulin-mediated potassium uptake is not altered by uremia. In contrast, insulin-mediated glucose uptake is markedly impaired. These observations suggest that the various actions of insulin can be differentially impaired by uremia and that steps distal to the insulin receptor must be responsible for the insulin resistance.
Adrenalectomy reverses insulin resistance in muscle from obese (ob/ob) mice
Authors: Ohshima K. , Shargill N. S. , Chan T. M. , Bray G. A.
Published: December 2017

Glucose transport and insulin resistance in the skeletal muscle of the genetically obese (ob/ob) mouse has been studied in animals at 6-7 wk of age using an in situ perfused hindquarter preparation. Rates of glucose uptake and the uptake of radioactively labeled 2-deoxy-D-glucose were lower in muscles from intact ob/ob mice than in those from their lean littermates. Following adrenalectomy the basal rate of glucose or 2-deoxy-D-glucose uptake in the ob/ob mice was restored to normal. The uptake of 2-deoxyglucose was tested at two insulin concentrations. In lean mice, adrenalectomy had no effect on 2-deoxyglucose uptake. Adrenalectomy, however, restored the responsiveness to insulin in the ob/ob mouse to normal. The activity ratio of muscle glycogen synthase was elevated by insulin but the effect was greater in the lean animals with or without adrenal glands than in the obese mouse. Adrenalectomy in the obese mouse did not correct this defect.
Changes in cytosolic ionized calcium induced by activators of secretion in GH3 cells
Authors: Snowdowne K. W. , Borle A. B.
Published: December 2017

Cytosolic ionized calcium (Cai) was measured in GH3 cells with aequorin incorporated by hypoosmotic shock treatment. Cai rose from 0.4 to 1.3 microM after the administration of 10(-7) M thyrotropin-releasing hormone (TRH) and from 0.3 to 1.1 microM after depolarization caused by high-K concentration (60 mM). Repeated TRH stimulations decreased the magnitude of the Cai response. This magnitude was directly related to the interval between stimuli. Incubations in low-calcium media (0.13 mM Ca) for 0.5 h did not alter the Cai response to TRH, but incubations in Ca-free media reduced the response. These results suggest that TRH mobilized calcium from an endogenous pool of Ca that can be depleted and replenished. The rise in Cai induced by K depolarization was slower than that evoked by TRH (time constant, t = 9 s for TRH and t = 111 s for K depolarization). Even when Cai was elevated by K depolarization, it could still be further increased by TRH, suggesting that these two stimuli mobilize calcium from two different pools and by different mechanisms.
1,25-Dihydroxyvitamin D3 normalizes maternal food consumption and pup growth in rats
Authors: Brommage R. , Jarnagin K. , DeLuca H. F.
Published: December 2017

Maternal food consumption, maternal body weight loss, and pup growth were studied in the following six groups of rats: vitamin D-deficient, vitamin D3-replete, vitamin D3-replete but pair-fed with the vitamin D-deficient rats and rats given either 50, 150, or 450 pmol/day of 1,25-dihydroxyvitamin D3 as their sole source of vitamin D by continuous infusion from an Alzet osmotic minipump. As expected, vitamin D-deficient rats were hypocalcemic and lost body weight, and their pups stopped growing at 1 wk of age. Food consumption by the vitamin D-deficient rats was one-third that of the vitamin D3-replete rats. Although normalization of plasma calcium levels was not perfect, 1,25-dihydroxyvitamin D3 treatment led to normal maternal food consumption, prevented maternal body weight loss, and promoted normal pup growth. Pups from the vitamin D3-replete rats pair-fed with the vitamin D-deficient rats did not grow properly and their dams lost body weight. These data indicate that 1,25-dihydroxyvitamin D3 is fully capable of replacing vitamin D3 in promoting maternal food consumption in lactating rats and that maintaining adequate food consumption is a major factor in the stimulatory effect of vitamin D3 on pup growth and hence milk production. The anorexia and reduced milk production of vitamin D-deficient lactating rats did not result from changes in plasma glucose or triglyceride levels.
Effect of age and dietary calcium on renal 25(OH)D metabolism, serum 1,25(OH)2D, and PTH
Authors: Armbrecht H. J. , Forte L. R. , Halloran B. P.
Published: December 2017

The purpose of this study was to determine how serum 1,25(OH)2D, renal production of [3H]1,25(OH)2D and [3H]24,25(OH)2D from [3H]25(OH)D, and serum IPTH change with age and dietary Ca restriction. Male Fischer 344 rats aged 3, 13, and 25 mo were placed on either a high-Ca (1.2%) or low-Ca (0.02%) vitamin D-replete diet. After 4 wk, serum was collected, and renal conversion of [3H]25(OH)D3 to [3H]1,25(OH)2D3 and [3H]24,25(OH)2D3 was measured in vitro using isolated renal cortical slices. Serum 1,25(OH)2D and renal [3H]1,25(OH)2D3 production were markedly reduced in 13- and 25-mo-old rats compared with 3-mo-old rats fed the low-Ca diet. In 3-mo-old rats, feeding the low-Ca diet increased serum 1,25(OH)2D by 18-fold and renal [3H]1,25(OH)2D3 production by threefold compared with feeding the high-Ca diet. In 25-mo-old rats, dietary Ca had no effect on these parameters. Renal [3H]24,25(OH)2D3 production was increased in the 13- and 25-mo-old rats compared with the 3-mo-old rats. Serum IPTH increased with age regardless of diet and was significantly increased by the low-Ca diet in 3-mo but not in 13- or 25-mo-old rats. The changes in serum 1,25(OH)2D and renal [3H]1,25(OH)2D3 production observed in this study may account for the previously observed age-related decline in intestinal Ca absorption in this animal model.
Bone histomorphometry in vitamin D-deficient rats infused with calcium and phosphorus
Authors: Weinstein R. S. , Underwood J. L. , Hutson M. S. , DeLuca H. F.
Published: December 2017

Defective mineralization of bone and cartilage is the classical histological finding in vitamin D deficiency. Whether this represents a direct effect on mineral deposition or is a consequence of the decreased calcium and phosphorus levels that result from impaired intestinal absorption is not clear. A method has been developed in which vitamin D-deficient rats have plasma calcium and phosphorus levels maintained in the normal range by continuous infusion. Histomorphometric analysis of undecalcified tibiae from these animals was compared with that of rats given vitamin D. Epiphyseal growth plate thickness, trabecular osteoid volume, and mean osteoid seam width were not increased. Moreover, the administration of two time-spaced courses of tetracycline revealed that the mineralization rate and the time interval between apposition and subsequent mineralization of osteoid (mineralization lag time) were identical to those in rats treated with vitamin D. Trabecular bone volume was increased (osteosclerosis) in the vitamin D-deficient rats. In vitamin D-deficient controls without infusions, the osteosclerosis was mostly osteoid, whereas the excess bone was well mineralized in the vitamin D-deficient rats infused with calcium and phosphorus. Osteosclerosis in vitamin D-deficient animals may result from both decreased bone resorption and increased osteoid apposition. This study provides firm evidence that vitamin D is not essential for mineralization in young growing rats. Decreased availability of calcium and phosphorus thus may be the sole basis of the mineralization defect seen in vitamin D deficiency.
Measurement of total and organ-specific norepinephrine kinetics in humans
Authors: Esler M. , Jennings G. , Korner P. , Blombery P. , Sacharias N. , Leonard P.
Published: December 2017

A variety of biochemical tests, most notably measurement of the plasma concentration of norepinephrine, have been used to quantify overall sympathetic nervous system activity in humans. Plasma norepinephrine values provide a fallible index of sympathetic activity in that they are dependent in part on the rate of removal of norepinephrine from plasma. Measurement of the rate of release of norepinephrine to plasma is a better guide to overall sympathetic nervous tone because it avoids this confounding influence of norepinephrine plasma clearance. The overall norepinephrine spillover measurement, however, suffers from one major limitation: the sources of the released norepinephrine are not identified. Recently developed radiotracer techniques allow the estimation of regional sympathetic nervous activity from measurements of the organ-specific norepinephrine spillover rate. We find that the lungs are the main source of norepinephrine release to plasma, with mean pulmonary norepinephrine spillover of 159 ng/min constituting 40% of total norepinephrine release. Pulmonary norepinephrine release exceeded the combined norepinephrine spillover from the heart (3%), kidneys (17%), and hepatomesenteric circulation (8%).