bluuebunny/crossref_metadata_2025 huggingface dataset:
Angiotensin II causes sustained elevations in cytosolic calcium in glomerulosa cells
Authors: Kramer R. E.
Published: December 2017

Studies were conducted to examine the effects of angiotensin II on cytosolic free calcium concentration in bovine adrenal glomerulosa cells maintained in primary culture. The calcium indicator, fura-2, and discontinuous dual-wavelength fluorescence spectroscopy were used to measure cytosolic free calcium in superfused adherent cell monolayers. Basal cytosolic free calcium concentration was 63.7 +/- 3.3 nM. The threshold concentration for angiotensin II-stimulated increases in cytosolic calcium was 10(-14)-10(-13) M, and maximal elevation of cytosolic calcium was produced by 10(-9) M angiotensin II. Angiotensin II (10(-13) M) produced a gradual increase in cytosolic calcium concentration that plateaued after 3-5 min of superfusion at a level approximately 1.2 times that of control cells. The calcium signal invoked by a maximal concentration (10(-9) M) of angiotensin II, in contrast, was characterized by an immediate, intense (approximately 8-fold) increase in cytosolic calcium concentration that decayed within 5 min to a lower, but sustained, level 2.5-3 times that of control cells. The calcium signals invoked by intermediate concentrations (10(-12)-10(-10) M) of angiotensin II exhibited dose-dependent increases in magnitude and a gradual transition in nature between those invoked by threshold and maximal concentrations of the peptide. The effect of angiotensin II to increase cytosolic calcium concentration was accompanied by an increase in aldosterone output. The increase in steroidogenesis was most closely correlated with the magnitude of the initial calcium signal. At high concentrations (10(-10) and 10(-9) M) of angiotensin II, there was a clear dissociation between aldosterone output and the magnitude of the sustained calcium signal.(ABSTRACT TRUNCATED AT 250 WORDS)
Perinatal expression of the atrial natriuretic factor gene in rat cardiac tissue
Authors: Wu J. P. , Deschepper C. F. , Gardner D. G.
Published: December 2017

The expression of the atrial natriuretic factor (ANF) gene was examined in the perinatal rat ventricle. The late fetal ventricle (day -3 relative to parturition) demonstrated a modest level of ANF gene expression. This expression increased at the time of birth and peaked on day +1 after birth. Atrial ANF immunoreactivity (irANF) increased gradually during the postpartum period (day +1 to 2-3 wk of age), while ventricular irANF as well as ventricular ANF mRNA levels fell over the same interval. This decrease in ANF gene expression resulted from a decrease in activity of the same major transcription start site employed in the adult atria and ventricle. Plasma irANF levels were very high in the neonatal period and decreased over the ensuing 2-3 wk, a profile similar to that seen for ventricular ANF gene expression. In situ hybridization histochemistry revealed that, while adult rat ventricular ANF mRNA was predominantly confined to the subendocardial layer, neonatal ventricles expressed the ANF gene throughout approximately 50% of the inner wall thickness. These findings suggest that the ANF gene is responding to regulatory stimuli that appear at or near the time of parturition and dissipate in the early neonatal period.
Alterations of the hypothalamic GnRH interpulse interval sequence over the normal menstrual cycle
Authors: Santoro N. , Butler J. P. , Filicori M. , Crowley W. F.
Published: December 2017

Luteinizing hormone (LH) is released in a pulsatile fashion from the anterior pituitary in response to hypothalamic gonadotropin-releasing hormone (GnRH) secretion. Previous autocorrelation analysis of the sequence of interpulse intervals of LH secretion in normal men has supported the hypothesis that the underlying hypothalamic mechanism of GnRH secretion governing episodic LH release is a renewal process, indicating that hypothalamic "memory," if present, does not extend back further in time than the preceding secretory pulse. A similar analysis of pulsatile LH secretion was undertaken in 45 studies of normal women, obtained throughout the menstrual cycle. Analysis of these studies revealed a process consistent with renewal throughout the follicular and early luteal phases. However, this relationship appears to break down in the mid-to-late luteal phase, indicating that alternative feedback pathways provide an overriding influence on the underlying renewal process of hypothalamic GnRH secretion. Pulsatile progesterone secretion by the corpus luteum, which first emerges at this stage of the menstrual cycle, may be the agent responsible for this feedback.
Thermogenesis after lateral hypothalamic lesions: contributions of brown adipose tissue
Authors: Corbett S. W. , Kaufman L. N. , Keesey R. E.
Published: December 2017

The role of brown adipose tissue in the thermogenic response to lateral hypothalamic (LH) lesions was investigated. Interscapular brown adipose tissue (IBAT) temperatures were measured during the hours following bilateral electrolytic LH lesions in male rats sedated with pentobarbital sodium. Local temperature changes were also recorded from skin and colonic sites. Consistent with the view that brown adipose tissue plays a primary role in the hyperthermia produced by LH lesions, IBAT depot temperature rose before, at a faster rate, and to a higher level than the other sites. In two subsequent experiments, oxygen consumption, activity, and core temperature were monitored in freely moving male rats with LH lesions, both in warm (25 degrees C) and cold (5 degrees C) environments. The results of these experiments provide some support for the view that LH lesions produce an increase in the regulated level of body temperature. This hyperthermic and hypermetabolic state seems to be mediated, in part, by brown fat thermogenesis and may represent a general increase in sympathetic nervous activity induced by the lesion.
Precursors to glycogen in ovine fetuses
Authors: Levitsky L. L. , Paton J. B. , Fisher D. E.
Published: December 2017

Postprandial hepatic glycogenesis in the adult animal is now felt to proceed largely through gluconeogenic pathways rather than directly from glucose. The ovine fetus, like the mature sheep, lacks specific hepatic glucokinase. Therefore, we examined the role of lactate as a fetal glycogenic precursor in seven chronically catheterized 125-day sheep fetuses. Fetuses were infused with L-[U-14C]lactate and D-[3-3H]glucose (50 microCi load, 50 microCi/h for 5 h), while maternal glucose was maintained at 50 mg/dl. Mean fetal hepatic glycogen specific activity (microCi/mg x 10(3] was 0.82 +/- 0.08 for 14C and 2.6 +/- 0.4 for 3H, whereas fetal renal glycogen specific activity was 0.46 +/- 0.22 for 14C and 0.78 +/- 0.16 for 3H. In contrast, [14C]glucose specific activity was undetectable in blood (limit of detectability 1 microCi/mg x 10(3] and mean [3H]glucose specific activity was 8.9 +/- 1.3 microCi/mg x 10(3]. The least detectable specific activity of [14C]glucose did not differ significantly from the [14C]glycogen enrichment in liver, whereas [3H]glucose specific activity was significantly (P less than 0.02) greater than [3H]glycogen enrichment. We conclude that glycogenesis from glucose is partly through the indirect gluconeogenic route and that lactate may be a glycogenic precursor in the ovine fetus.
Rates and tissue sites of non-insulin- and insulin-mediated glucose uptake in humans
Authors: Baron A. D. , Brechtel G. , Wallace P. , Edelman S. V.
Published: December 2017

In vivo glucose uptake can occur via two mechanisms, namely, insulin-mediated glucose uptake (IMGU) and non-insulin-mediated glucose uptake (NIMGU). Although the principal tissue sites for IMGU are skeletal muscle, the tissue sites for NIMGU at a given serum glucose concentration are not known. To examine this issue, rates of whole body glucose uptake (Rd) were measured at basal and during glucose clamp studies performed at euglycemia (approximately 90 mg/dl) and hyperglycemia (approximately 220 mg/dl) in six lean healthy men. Studies were performed during hyperinsulinemia (approximately 70 microU/ml) and during somatostatin-induced insulinopenia to measure IMGU and NIMGU, respectively. During each study, leg glucose balance (arteriovenous catheter technique) was also measured. With this approach, rates of whole body skeletal muscle IMGU and NIMGU can be estimated, and the difference between overall Rd and skeletal muscle glucose uptake represents non-skeletal muscle Rd. The results indicate that approximately 20% of basal Rd is into skeletal muscle. During insulinopenia approximately 86% of body NIMGU occurs in non-skeletal muscle tissues at euglycemia. When hyperglycemia was created, whole body NIMGU increased from 128 +/- 6 to 213 +/- 18 mg/min (P less than 0.01); NIMGU into non-skeletal muscle tissues was 134 +/- 11 and 111 +/- 6 mg/min at hyperglycemia and euglycemia, respectively, P = NS. Therefore, virtually all the hyperglycemia induced increment in NIMGU occurred in skeletal muscle. During hyperinsulinemia, IMGU in skeletal muscle represented 75 and 95% of body Rd, at euglycemia and hyperglycemia, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Alpha-adrenergic modulation of glutathione metabolism in isolated rat hepatocytes
Authors: Estrela J. M. , Gil F. , Vila J. M. , Vina J.
Published: December 2017

Glutathione metabolism was studied in isolated hepatocytes from 48-h starved rats. Phenylephrine (10 microM, final concentration) was incubated in the presence of a mixture of L-glutamine, glycine, L-serine, and L-methionine (at 10 times their normal plasma concentration). Alpha-adrenergic stimulation provoked a decrease in glutathione (GSH) synthesis. This effect was accompanied by an enhanced efflux of glutathione from the cells. Phenylephrine stimulated the rate of glutathione disulfide (GSSG) formation; however, this effect was clearly insufficient to explain the disappearance of GSH. Our results suggest that the decrease in cellular GSH levels observed under conditions of shock, stress, or peripheral inflammation can be explained by a dual effect, i.e., an increase in glutathione efflux and an inhibition of its synthesis.
Effect of insulin on [3H]deoxy-D-glucose pharmacokinetics in the rat
Authors: Furler S. M. , Jenkins A. B. , Kraegen E. W.
Published: December 2017

Despite its increasing use in physiological animal investigations, there has been no systematic study of the whole body kinetics of 2-deoxy-D-glucose (2DG) or its modification by insulin. A previously proposed model that included processes representing transport across cell walls and intracellular phosphorylation of 2DG was investigated. The model predictions were compared with the plasma disappearance of 2DG observed in the rat following intravenous bolus injection. Experiments were performed during euglycemia at varying levels of hyperinsulinemia. The model was adequate to describe empirically the experimental data after a correction was made for urine loss. However, the variation in model parameters with plasma insulin concentration was not consistent with the expected action of insulin on cellular efflux. A possible explanation could be a shift in the rate-limiting step from glucose transport to another prephosphorylation process under conditions of high tissue uptake. This suggests that either intracellular or extracellular diffusion may constitute a significant barrier to 2DG (and glucose) uptake under some conditions.
GHRF causes biphasic stimulation of SRIF secretion from rat hypothalamic cells
Authors: Richardson S. , Twente S. , Audhya T.
Published: December 2017

The complex interactions of the hypothalamic releasing peptides somatostatin (SRIF) and growth hormone (GH)-releasing hormone (GHRF), which regulate GH secretion, are still incompletely understood. To further scrutinize these interactions, we have studied the effects of GHRF on SRIF secretion from dispersed adult rat hypothalamic cells. Rat GHRF caused calcium- and dose-dependent stimulation of SRIF release in static 1-h incubations. SRIF release was stimulated by GHRF in a concentration range of 1-100 nM. However, the extended dose-response curve was biphasic in nature, with a significantly lower SRIF response in the presence of 1 microM GHRF vs. 100 nM GHRF. SRIF release, stimulated by another secretagogue (10 microM veratridine), was not affected by the presence or absence of 1 microM GHRF, suggesting the lack of toxic impairment of hypothalamic cell function by GHRF at this concentration. In conclusion, a biphasic stimulatory pattern of SRIF secretion in response to GHRF was observed in experiments employing dispersed rat hypothalamic cells. The biphasic SRIF response pattern to GHRF may be relevant in the physiological regulation of GH secretion.
Glucose intolerance in thyrotoxic rats: role of insulin, glucagon, and epinephrine
Authors: Ikeda T. , Mokuda O. , Tominaga M. , Mashiba H.
Published: December 2017

To elucidate the possible role of insulin, glucagon, and epinephrine on glucose intolerance in thyrotoxicosis, the secretion of insulin and glucagon in vivo (glucose, arginine, and epinephrine infusion tests) and in perfused pancreas and the hepatic action of insulin, glucagon, and epinephrine in perfused liver were investigated in experimental thyrotoxic rats (induced by thyroxine injection, 20 micrograms/kg sc, for 7 days). In thyrotoxic rats, fasting blood glucose (87 +/- 5 mg/dl, mean +/- SD) and plasma insulin (16 +/- 3 microU/ml) were significantly (P less than 0.001) higher than those in controls (74 +/- 5 mg/dl and 8 +/- 1 microU/ml), respectively. In glucose infusion test (0.5 g/kg iv), blood glucose, plasma insulin, and glucagon responses in thyrotoxic rats were not significantly different from those in controls. In arginine infusion test (5 mg/min for 20 min iv), the increments in blood glucose and plasma insulin after arginine in thyrotoxic rats were not significantly different from those in controls. Plasma glucagon response was almost the same in both groups. In epinephrine infusion test (100 micrograms/kg iv), the increments in blood glucose and plasma insulin in thyrotoxic rats were significantly greater than those in controls. In perfused pancreas, insulin and glucagon secretions in response to 16.7 mM glucose or 6.4 mM arginine in the presence of 5.5 mM glucose in thyrotoxic rats were not different from those in controls.(ABSTRACT TRUNCATED AT 250 WORDS)
Neuropeptide Y mobilizes Ca2+ and inhibits adenylate cyclase in human erythroleukemia cells
Authors: Motulsky H. J. , Michel M. C.
Published: December 2017

Neuropeptide Y (NPY), a peptide often coreleased with catecholamines, appears to be an important component of the sympathetic nervous system, but little is known about the molecular basis of its action. We introduce here human erythroleukemia (HEL) cells as a new model system for studies of NPY action. NPY inhibited adenosine 3,5'-cyclic monophosphate (cAMP) accumulation in HEL cells with a 50% effective concentration (EC50) of 3 nM. Additionally NPY increased intracellular Ca2+, as assessed by fura-2 fluorescence, with a similar EC50. Pretreatment with pertussis toxin blocked both responses, suggesting the involvement of one or more G proteins. Chelating extracellular Ca2+ with EGTA did not reduce the Ca2+ signal, demonstrating mobilization from intracellular stores rather than influx. Experiments with various agents demonstrated that the Ca2+ mobilization was not secondary to lowering of cAMP levels, formation of arachidonic acid products, or Na+-H+ exchange. Ca2+ mobilization also did not appear to be associated with inositol phosphate generation. In conclusion, we demonstrate for the first time that NPY, in addition to inhibiting adenylate cyclase, also can elevate intracellular Ca2+. HEL cells should prove useful in further studies of the molecular basis of NPY action.
Effect of physical activity on calcium and phosphorus metabolism in the rat
Authors: Yeh J. K. , Aloia J. F. , Yasumura S.
Published: December 2017

Changes in skeletal mass, nutritional calcium and phosphorus balance, and intestinal calcium absorption were studied in four groups of rats: control, exercise allowing free access to food, exercise with pair-feeding to control levels, and immobilization. The exercise regimen consisted of treadmill running 25 m/min, 60 min/day, 5 days/wk for 13 wk; rats were immobilized by bilateral sciatic denervation. The total body Ca (TBCa) was measured by neutron activation analysis as an index of skeletal mass. Standard metabolic balance techniques were used to determine calcium and phosphorus balance, and an in situ duodenal loop ligation preparation was used to study the active and passive intestinal Ca transport processes. Exercise promoted a positive Ca and P balance and increased the skeletal mass, largely as a result of an increase in 1,25-dihydroxyvitamin D and an enhancement of the intestinal Ca absorption efficiency. Urinary excretion of Ca and P did not differ from control levels and food intake was not a factor because pair-fed rats responded to exercise almost identically to those fed ad libitum. Conversely, immobilization caused a decrease in TBCa and a lower Ca and P balance. These effects are the result of an increased urinary mineral excretion, greater endogenous fecal excretion, and decreased mineral absorption efficiency in the intestine.
Isolated pituitary cells: glucocorticoids do not rapidly suppress ACTH secretion in response to CRF
Authors: Familari M. , Funder J. W.
Published: December 2017

The possibility of a direct rapid suppressive effect of glucocorticoids on stimulated adrenocorticotropic hormone (ACTH) release was investigated in perifused normal pituitary cells attached to microcarriers. Forty-eight hours after attachment to Cytodex beads, cells were transferred to two columns (one experimental, one control), perifused at a rate of 300-350 microliters/min, and equilibrated for 3 h. Either rat or ovine corticotropin-releasing factor (CRF; 2 nM) were used to stimulate ACTH release, and fractions collected every 5 min were assayed for immunoreactive ACTH. Concomitant treatment with CRF and glucocorticoids (dexamethasone 100 nM or corticosterone 1 microM), or glucocorticoid pretreatment for up to 2 h, did not affect the release of ACTH occasioned by repetitive 5-min exposures to CRF at 30-min intervals. In addition, when ovine CRF was given as two 30-min infusions 1 h apart, neither concomitant steroid administration nor steroid pretreatment for 90 min affected the release of ACTH compared with controls. The lack of rapid steroid inhibition was not an artifact of enzymatic dispersion or microcarrier attachment, since no rapid inhibitory response was seen with acutely perifused rat anterior pituitary quarters. We thus conclude that in vitro rapid inhibitory effects of glucocorticoids on ACTH release do not occur at the level of the pituitary. Accordingly such action in vivo presumably reflects acute steroid-induced effects on the hypothalamus or higher centers.
Regulation of Na-dependent Pi transport by parathyroid hormone in osteoblast-like cells
Authors: Selz T. , Caverzasio J. , Bonjour J. P.
Published: December 2017

In the present work we investigated the influence of parathyroid hormone (PTH) on the transport of inorganic phosphate (Pi) in the osteoblast-like cell line UMR-106. Pi was transferred from the extra- to the intracellular compartment by means of a Na-dependent transport system with an apparent binding affinity for both Pi and Na similar to that recently observed in the osteoblast-like cell line ROS 17/2.8 (Calcif. Tissue Int. 43: 83-87, 1988). Exposure of confluent UMR-106 cells to PTH (10(-9)-10(-7) M) induced a concentration-related stimulation of the Na-dependent Pi transport (NaPiT). An increase in NaPiT was observed after a 1-h exposure to 10(-7) M PTH, with the maximal response occurring at 4-6 h. (PTH, 35.6 +/- 0.3; vehicle, 27.4 +/- 0.2 pmol.microgram DNA-1.4 min-1, P less than 0.001). The stimulatory effect of PTH on NaPiT was not associated with a change in the Na-dependent alanine transport. A positive correlation was observed between the increase of NaPiT and that of cAMP in response to various concentrations of PTH. Stimulation of cAMP by forskolin (10(-4) M) mimicked the effect of PTH on NaPiT. Kinetic analysis of the PTH-induced stimulation of NaPiT indicated an increase in Vmax (PTH, 226.9 +/- 6.9; vehicle, 182.9 +/- 1.9 pmol Pi/microgram DNA, P less than 0.001), with no change in Km. The increase in NaPiT by either PTH or forskolin was followed by a transient inhibition from 6 to 24 h that was associated with a decrease in the Na-dependent alanine transport.(ABSTRACT TRUNCATED AT 250 WORDS)
Chronic exercise compensates for insulin resistance induced by a high-fat diet in rats
Authors: Kraegen E. W. , Storlien L. H. , Jenkins A. B. , James D. E.
Published: December 2017

We examined whether chronic exercise prevents insulin resistance developing in the high-fat-fed (HFF) rat, a model that otherwise develops profound peripheral insulin resistance. Insulin action (euglycemic clamp plus 2-[3H]deoxy-D-glucose-[14C]glucose tracer technique) was examined after 3 wk in sedentary control and sedentary or wheel cage exercise-trained HFF rats. At the whole body level, a reduction in peripheral insulin potency in HFF rats was prevented by concomitant chronic exercise; the 30-40% reduction in insulin-stimulated whole body net glucose utilization in sedentary HFF rats was abolished. Responses in individual muscles, however, suggested that the chronic exercise effect may be a compensation for, rather than a correction of insulin resistance induced by a high-fat diet; in six of eight muscles examined it produced an upward additive shift rather than a left shift in insulin dose response. Chronic exercise increased both muscle glycolytic flux and glycogen storage rates in the HFF rats, suggesting that glucose transport may be involved. We conclude that increased physical activity is beneficial in counteracting high-fat diet-induced insulin resistance. Different processes appear to be involved in the development of diet-induced insulin resistance in muscle and its amelioration by regular exercise.
Evidence for functional thromboxane A2-prostaglandin H2 receptors in human placenta
Authors: Hedberg A. , Mento P. F. , Liu E. C. , Hollander A. M. , Wilkes B. M.
Published: December 2017

The aim of this investigation was to study the role of thromboxane (TX) A2 in the modulation of human fetoplacental vascular resistance. By use of the isolated perfused fetoplacental cotyledon, TX generation (measured by direct radioimmunoassay of TXB2) was demonstrated on the fetal side of the placental circulation. The stable TX mimetic U-46619 caused a dose-dependent increase in perfusion pressure that was inhibited by the TX receptor antagonist SQ 29548. To further characterize the putative TXA2-prostaglandin H2 receptors, binding studies were performed in placental membranes using [3H]SQ 29548. Kinetic analysis revealed rapid and reversible specific binding of [3H]SQ 29548. Saturation binding and Scatchard analysis indicated radioligand binding to a single class of receptors (dissociation constant, 9.11 +/- 0.60 nM; receptor density, 103 +/- 8 fmol/mg protein, n = 4). Prostaglandins D2, E1, E2, F2a, and I2 did not inhibit the specific binding of [3H]SQ 29548 at concentrations less than or equal to 10 microM. This study demonstrates that the human placenta produces and releases TXA2, which can act locally via specific receptor sites to constrict the fetoplacental vasculature.
Attenuation of the osmotic release of vasopressin by enkephalins in dogs
Authors: Matsui K. , Kimura T. , Ota K. , Shoji M. , Inoue M. , Iitake K. , Yoshinaga K.
Published: December 2017

To assess the possible role of circulating enkephalins in the osmotic release of vasopressin, Met5 (M-Enk)- or Leu5-enkephalin (L-Enk) dissolved in 0.9 or 10% NaCl was infused to either anesthetized or conscious dogs at a dose of 3.5 nM.kg-1.min-1 for 15 min. Intravenous infusion of M-Enk or L-Enk produced 150- to 200-fold increases in their plasma levels, and the elevated levels were maintained during the infusion. Although blood pressure (BP) in anesthetized dogs decreased significantly during L-Enk infusion, BP in conscious dogs was unaffected by both enkephalins. Neither M-Enk nor L-Enk infusion affected plasma vasopressin concentration (PAVP) in these anesthetized and conscious dogs that were not osmotically stimulated. PAVP in conscious time control dogs increased significantly after start of 10% NaCl infusion in spite of an increase in BP. M-Enk or L-Enk significantly blunted the increase in PAVP induced by 10% NaCl infusion. This attenuation was not accompanied by any significant changes in plasma sodium concentration and BP compared with those of time control dogs. Thus increase in plasma enkephalins attenuates the osmotic release of vasopressin.
Proinsulin mRNA levels in fasting and fed ADX rats: evidence for an indirect effect of glucocorticoids
Authors: Fiedorek F. T. , Permutt M. A.
Published: December 2017

To determine whether glucocorticoids are required to maintain pancreatic proinsulin mRNA levels during dietary manipulation, rats were adrenalectomized (ADX) or sham operated (SO) and subsequently fasted or pair fed for 2 days. Proinsulin mRNA concentrations were 54 +/- 8% lower (P less than 0.05) in fed ADX rats and 47 +/- 10% lower (P less than 0.01) in fasted ADX rats relative to values in fed and fasted SO rats, respectively. When ADX rats were fasted for 24 h and either refed 20% sucrose for 30 h or injected with dexamethasone (DEX) 0.125 mg/kg ip every 12 h for three doses, circulating plasma glucose levels were restored and pancreatic proinsulin mRNA concentrations rose 3.3 and 2.7-fold, respectively (each P less than 0.05). Plasma glucose and proinsulin mRNA levels (n = 40) were correlated (r = 0.58, P less than 0.0001). We conclude that the regulation of proinsulin mRNA concentration does not absolutely require endogenous glucocorticoids, since either adequate sucrose intake in ADX rats or physiological glucocorticoid responses in fasted rats suffice to restore pancreatic mRNA concentrations. It appears that glucocorticoid stimulation of pancreatic proinsulin mRNA levels is mediated indirectly through its regulation of glucose metabolism.
Effect of hypercalcemia-producing tumor on 1,25(OH)2D3 biosynthesis in athymic mice
Authors: Kukreja S. C. , York P. A. , Nalbantian-Brandt C. , Shevrin D. H. , Favus M. J.
Published: December 2017

Serum 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels are low in patients with malignancy-associated hypercalcemia (MAH), whereas murine models of MAH have high circulating 1,25(OH)2D3. To determine the effects of a hypercalcemia-producing tumor on circulating 1,25(OH)2D3, in vitro 25-hydroxyvitamin D1-hydroxylase (1OHase) activity was measured in kidneys from BALB/c athymic mice implanted with a hypercalcemia-producing human lung tumor. Twelve days of low-phosphorus diet (LPD) in control animals lowered serum phosphorus to levels found in tumor-bearing mice fed normal phosphorus diet (NPD; 4.1 +/- 0.3 vs. 4.4 +/- 0.7 mg/dl, P = NS) and increased 1OHase activity (1.6 +/- 0.2 vs. 3.9 +/- 0.7 pmol.mg protein-1.5 min-1, NPD vs. LPD, P less than 0.05). 1OHase activity was greater in tumor-bearing animals fed NPD compared with control animals fed LPD (8.4 +/- 0.6 vs. 3.9 +/- 0.7 pmol.mg protein-1.5 min-1, P less than 0.01). High-phosphorus intake suppressed 1OHase activity in both control and tumor-bearing animals. Seven days of parathyroid hormone infusion in control animals fed NPD raised serum calcium (9.4 +/- 0.2 vs. 13.3 +/- 1.6 mg/dl, P less than 0.05) and suppressed 1OHase activity (0.25 +/- 0.02 vs. 0.02 +/- 0.002 pmol.mg protein-1.5 min-1, P less than 0.001). The inverse relationship of serum phosphorus and 1OHase activity was much steeper in the tumor-bearing animals, with greater enzyme activity at comparable levels of serum phosphorus. The present study indicates that 1) factors produced by the tumor stimulate 1OHase activity, and 2) hypophosphatemia is required for expression of enhanced enzyme activity.
Oxidative fuel metabolism during mild hypoglycemia: critical role of free fatty acids
Authors: Caprio S. , Gelfand R. A. , Tamborlane W. V. , Sherwin R. S.
Published: December 2017

We examined oxidative fuel metabolism (indirect calorimetry) during mild insulin-induced hypoglycemia in normal subjects. Four groups of studies (4 h each) were performed: 1) insulin alone (0.3 mU.kg-1.min-1, 2) insulin plus heparin, 3) insulin plus propranolol, and 4) insulin plus propranolol plus heparin (starting at 75 min). In all groups, insulin rose threefold (approximately 20 microU/ml), whereas glucose concentrations fell by approximately 20 mg/dl (to 65-70 mg/dl) due to a transient decrease in glucose production; glucose uptake did not change. During insulin alone, carbohydrate oxidation rose markedly during the 1st 60-90 min (by 85%, P less than 0.05) as circulating free fatty acids (FFA) and fat oxidation declined. Subsequently, FFA rose and carbohydrate oxidation declined toward base line. The latter changes were completely abolished by propranolol and restored when propranolol-induced suppression of FFA was overcome by addition of heparin. Heparin, by preventing the insulin-induced fall in FFA, also blocked the early rise in carbohydrate oxidation. We conclude that small increments in insulin markedly stimulate carbohydrate oxidation without increasing glucose uptake. This effect is due to the exquisite sensitivity of lipolysis to insulin and is overcome by catecholamine release during hypoglycemia. Mild hyperinsulinemia promotes glucose metabolism primarily through indirect effects on FFA.
Alternative method for minimal model analysis of intravenous glucose tolerance data
Authors: Weber K. M. , Martin I. K. , Best J. D. , Alford F. P. , Boston R. C.
Published: December 2017

The minimal models of glucose-insulin kinetics were used to analyze sets of data obtained from human subjects and dogs during frequently sampled intravenous glucose tolerance tests (FSIGTs). Analysis of some data sets from both species resulted in poor identification of parameters. To improve the parameter resolution, the information base on which the parameters are estimated was enlarged. This was accomplished by incorporating into the analysis 1) glucose data obtained between 0 and 8 min of the FSIGT and some of the insulin data obtained prior to the insulin peak and 2) a second set of FSIGT data for each individual obtained during a physiological perturbation. As a result, data analysis was considerably enhanced, with parameter fractional standard deviation being routinely reduced to less than 0.5. Analysis of stimulated data with noise levels for glucose and insulin set between 0.05 and 0.15 confirmed the improvement in parameter estimates. This modified approach to analysis of FSIGTs therefore consistently leads to well-defined kinetic descriptions of experimental data in various situations and supports the usefulness of the minimal model in examining the complex interplay between the parameters that influence overall glucose tolerance.
Impaired very low-density lipoprotein-triglyceride catabolism in acute and chronic fructose-fed rats
Authors: Hirano T. , Mamo J. C. , Poapst M. E. , Kuksis A. , Steiner G.
Published: December 2017

Very low-density lipoprotein (VLDL)-triglyceride (TG) catabolism was compared in rats given chow and either a 10% fructose (F) or 10% glucose (G) drinking solution for both acute (A) (16 h) and chronic (C) (14 days) periods. VLDL-TG were labeled in F and G donor rats using different isotopic forms of glycerol. A mixture of the VLDLs was injected into F and G recipients and the decline in plasma TG radioactivities used as a measure of clearance. VLDL-TG from F donors was cleared more slowly than VLDL-TG from G donors. In F recipients, the half-life of VLDL-TG from either F or G donors was longer than that in G fed recipients. VLDL from the AF group, had a lower apoprotein E-to-C apoprotein ratio (E/C) than VLDL from the AG group. VLDL from both F groups had a lower E/C than did that from control rats. The E/C negatively correlated with plasma VLDL-TG. CF and CG VLDL had elevated CIII0 and lower CIII3 levels compared with their respective A groups and controls. The ratio of VLDL apoprotein B100, B95, and B48 did not differ between treatments. AF and AG VLDL were larger and enriched in TG compared with control or the CF and CG groups. The saturated fatty acid-to-unsaturated fatty acid ratio in VLDL-TG was higher in the G groups and AF group compared with controls. The present study suggests that the E/C may be lowered as a result of F consumption, thereby contributing to the impairment in VLDL-TG removal.
Structure-kinetic relationships of choriogonadotropin and related molecules
Authors: Liu L. , Southers J. L. , Cassels J. W. , Banks S. M. , Wehmann R. E. , Blithe D. L. , Chen H. C. , Nisula B. C.
Published: December 2017

To assess how profound differences in carbohydrate and/or polypeptide structures affect parameters of plasma disappearance of glycoprotein hormones, we calculated and compared the initial volume of distribution, rate constants, and metabolic clearance rates of several highly purified human choriogonadotropin (hCG) analogues in monkeys. hCG, deglycosylated hCG, desialylated hCG, or core fragment of hCG-beta purified from pregnancy urine (beta-core) was administered as a rapid intravenous injection to adult male cynomolgus monkeys (n = 3/group). The metabolic clearance rates of deglycosylated hCG, beta-core fragment, and desialylated hCG were increased 15-, 47-, and 152-fold, respectively, over that of hCG. Their corresponding initial volumes of distribution, however, remained essentially unchanged compared with that of hCG and approximated the estimated plasma volume. In contrast, the fast and slow rate constants of plasma disappearance of the hCG analogues were increased as much as 18- and 23-fold, respectively, relative to those of hCG. These studies of structure-kinetic relationships in primates show that major carbohydrate and polypeptide modifications of a glycoprotein hormone cause profound changes in the rate constants of the disappearance curves without changes in the initial volume of distribution.
HDL subfractions and adipose tissue metabolism in the reduced-obese state
Authors: Eckel R. H. , Yost T. J.
Published: December 2017

The effect of weight reduction on fasting serum lipids and lipoproteins and adipose tissue lipoprotein lipase responsiveness to insulin was assessed immediately after and 3 mo subsequent to a mean 11.7% weight reduction in 14 women. Whereas reduction in fasting serum triglycerides persisted after 3 mo, reductions in serum cholesterol, low-density lipoprotein cholesterol and high-density lipoprotein (HDL) cholesterol were not found at 3 mo. In fact, at 3 mo, levels of HDL cholesterol were higher than before weight reduction. Maintenance of the reduced-obese state also increased the HDL2-to-HDL3 cholesterol ratio (P less than 0.01), an effect strongly associated with the change in the responsiveness of adipose tissue lipoprotein lipase to insulin (r = 0.821, P less than 0.001). Moreover, after maintenance of the reduced-obese state, the HDL2-to-HDL3 cholesterol ratio also increased after the ingestion of corn oil and a 6-h insulin-glucose infusion, a response not present before weight reduction. Thus the effect of weight reduction on serum lipids and lipoproteins was not only time dependent, but for HDL, was strongly associated with changes in adipose tissue metabolism.
Impairment of glucose disposal by infusion of triglycerides in humans: role of glycemia
Authors: Felley C. P. , Felley E. M. , van Melle G. D. , Frascarolo P. , Jequier E. , Felber J. P.
Published: December 2017

The present study was designed to assess the role of hyperglycemia (150 mg/dl) vs. euglycemia (90 mg/dl) on glucose metabolism in vivo during the infusion of a triglyceride emulsion (Intralipid). Seven young healthy volunteers were studied on four occasions using the hyperinsulinemic clamp technique, twice during euglycemia and twice during hyperglycemia, without or with Intralipid. Glucose oxidation (O) was calculated from continuous respiratory exchange measurements, and glucose storage (S) was obtained as the difference between total glucose disposal (M) and O. Two-way analysis of variance with interaction term demonstrated 1) a significant increase for M with hyperglycemia and a decrease with Intralipid; no interaction, and 2) in euglycemia, O/M and S/M occurred in one-to-one ratios; on the other hand, during 150-mg/dl hyperglycemia, the ratio dropped roughly to 1:2. Intralipid had no effect on the ratio, and no interaction could be observed. These results suggest the existence of physiological regulatory mechanisms by which 1) the rise in plasma free fatty acid inhibits both oxidative and nonoxidative glucose disposal, and 2) the rise in glycemia stimulates predominantly nonoxidative glucose disposal.
Glucose uptake and flux through phosphofructokinase in wounded rat skeletal muscle
Authors: Forster J. , Morris A. S. , Shearer J. D. , Mastrofrancesco B. , Inman K. C. , Lawler R. G. , Bowen W. , Caldwell M. D.
Published: December 2017

Skeletal muscle injured with lambda-carrageenan has increased aerobic glycolysis. To assess the regulation of this process, the tissue concentrations of glycolytic intermediates, the flux through phosphofructokinase (PFK), and the intracellular concentrations of PFK effectors were examined in wounded rat skeletal muscle and in macrophages, the predominant inflammatory cell in the early stages of this wound model. Autoradiography demonstrated increased 2-deoxy-D-glucose uptake in wounded tissue compared with nonwounded muscle. 2-Deoxy-D-glucose was localized to the cellular infiltrate. The glycolytic intermediate concentrations demonstrated a facilitation of PFK in macrophages and wounded tissue as compared with nonwounded muscle. Wounded tissue had twice the flux through PFK compared with nonwounded muscle (10.0 +/- 0.6 wounded vs. 4.9 +/- 0.4 mumol.h-1.g-1 nonwounded). Macrophages had the highest flux through PFK (63.7 +/- 5.7 mumol.h-1.g-1) and when coincubated with muscle, the combined flux through PFK was equal to that of wounded muscle. The increase in glycolysis associated with wounded tissue may be explained by increased glucose uptake and increased flux through PFK by the inflammatory cells present in wounded tissue.
Generalized decrease in brain glucose metabolism during fasting in humans studied by PET
Authors: Redies C. , Hoffer L. J. , Beil C. , Marliss E. B. , Evans A. C. , Lariviere F. , Marrett S. , Meyer E. , Diksic M. , Gjedde A. , et al.
Published: December 2017

In prolonged fasting, the brain derives a large portion of its oxidative energy from the ketone bodies, beta-hydroxybutyrate and acetoacetate, thereby reducing whole body glucose consumption. Energy substrate utilization differs regionally in the brain of fasting rat, but comparable information has hitherto been unavailable in humans. We used positron emission tomography (PET) to study regional brain glucose and oxygen metabolism, blood flow, and blood volume in four obese subjects before and after a 3-wk total fast. Whole brain glucose utilization fell to 54% of control (postabsorptive) values (P less than 0.002). The whole brain rate constant for glucose tracer phosphorylation fell to 51% of control values (P less than 0.002). Both parameters decreased uniformly throughout the brain. The 2-fluoro-2-deoxy-D-glucose lumped constant decreased from a control value of 0.57 to 0.43 (P less than 0.01). Regional blood-brain barrier transfer coefficients for glucose tracer, regional oxygen utilization, blood flow, and blood volume were unchanged.
Body fat from body density: underwater weighing vs. dual-photon absorptiometry
Authors: Wang J. , Heymsfield S. B. , Aulet M. , Thornton J. C. , Pierson R. N.
Published: December 2017

We measured fat in 286 healthy volunteers by underwater weighing (FUWW) and dual-photon absorptiometry (FDPA) to develop a translation table for the differing results from these entirely different techniques and to study the sources of these differences. In 99 males and 187 females aged 19-94 yr, fatness was 7-47%. Prediction equations are presented for FUWW-FDPA (delta F), density of lean body mass (DLBM), and FDPA. FUWW and FDPA were significantly different from each other (P less than 0.01). Calculated DLBM is less than the assumed constant of 1.10 (P less than 0.01), ranging widely from 1.05 to 1.13 and being highly correlated with the ratio of total body bone mineral to lean body mass (TBBM/LBM). delta F, the differences between FUWW and FDPA measurements in individual subjects, varied widely (-7 to +11% in males and -18 to +13% in females). The difference was positively correlated with the DLBM. FUWW was no better than anthropometrics in equations for predicting FDPA. The FDPA predicted from anthropometrics showed smaller standard errors than when FUWW was used. Neither anthropometrics nor FUWW equations are clearly superior to those previously available.
Hepatic glycogen in humans. I. Direct formation after oral and intravenous glucose or after a 24-h fast
Authors: Radziuk J.
Published: December 2017

The formation of hepatic glycogen by the direct pathway is assessed in humans 1) after a 12-h fast and oral loading (100 g) or 2) intravenous infusion (90 g) and 3) after a 24-h fast and the same oral glucose load. The methodology used is based on the double tracer method. [3–3H]glucose is infused at a constant rate for the determination of the metabolic clearance of glucose. [1–14C]glucose is administered with the glucose load. One hour after absorption or the intravenous glucose infusion is terminated, a glucagon infusion is initiated to mobilize the glycogen labeled with [1-14C]glucose and formed during the absorptive period. At this time a third tracer, [6-3H]glucose, is administered to measure glucose clearance. It was found that after the 12-h fast and oral glucose loading 7.2 +/- 1.1 g of hepatic glycogen appears to be formed directly from glucose compared with 8.4 +/- 1.0 g after the same load and a 24-h fast and 8.5 +/- 0.4 g after a 12-h fast and an equivalent intravenous glucose infusion. When the amount of label ([14C]glucose) mobilized that was not corrected for metabolic recycling was calculated, the data suggested that the amount of glycogen formed by gluconeogenic pathways was probably at least equal to that formed by direct uptake. It was also approximately 60% greater after a 24-h fast. It can be concluded that the amount of hepatic glycogen formed directly from glucose during glucose loading is not significantly altered by the route of entry or the extension of the fasting period to 24 h. The data suggest, however, that gluconeogenetic formation of glycogen increases with fasting.
Alterations of glucose transporter systems in insulin-resistant uremic rats
Authors: Jacobs D. B. , Hayes G. R. , Truglia J. A. , Lockwood D. H.
Published: December 2017

To further define the cellular alteration(s) involved in the impaired glucose transport associated with chronic uremia, we examined the concentration and translocation of glucose transport systems in adipocytes isolated from partially nephrectomized uremic rats. Uremic animals, compared with matched controls, had increased blood urea nitrogen and serum insulin, whereas serum glucose was unchanged. In agreement with previous work, 125I-insulin binding to its receptor was unaltered and transport of 2-deoxy-D-glucose was decreased in both the absence (basal) and presence of a maximal (7 nM) insulin concentration by 44 and 35%, respectively. To assess the movement and concentration of glucose transport systems in various membrane fractions prepared from basal and insulin-treated (20 nM) uremic fat cells, the technique of D-glucose-inhibitable cytochalasin B binding was utilized. In plasma membranes isolated from these cells the concentration of glucose transporters was decreased by 16 (P less than 0.01) and 30% (P less than 0.005) in basal and insulin-treated cells, respectively. Concomitantly, microsomal membranes prepared from uremic cells treated in the absence and presence of insulin had a 28 (P less than 0.01) and 15% (P less than 0.05) decrease in concentration of glucose transport systems, respectively. Additionally, glucose transporter concentration was significantly decreased by 17% (P less than 0.025) in total membranes prepared from uremic cells. Thus, impairment of glucose transport in uremic fat cells can be attributed to a postbinding defect that, at least in part, results from a decrease in the total concentration of glucose transporters.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of insulin and glucose oxidation in mediating the protein catabolism of burns and sepsis
Authors: Jahoor F. , Shangraw R. E. , Miyoshi H. , Wallfish H. , Herndon D. N. , Wolfe R. R.
Published: December 2017

We have investigated the responsiveness of protein kinetics to insulin and the role of glucose oxidation rate as a mediator of the protein catabolic response to burn injury and sepsis by assessing the response of leucine and urea kinetics to a 5-h hyperinsulinemic euglycemic clamp with and without the simultaneous administration of dichloroacetate (DCA) (to further increase glucose oxidation via stimulation of pyruvate dehydrogenase activity) in eight severely burned and eight septic patients. Leucine and urea kinetics were measured by the primed-constant infusions of [1(-13)C]leucine and [15N2]urea. Compared with controls, basal leucine kinetics (flux and oxidation) were significantly elevated (P less than 0.01) in both groups of patients. Hyperinsulinemia elicited significant (P less than 0.05) decreases in leucine kinetics in both groups of patients. Consistent with this observation, hyperinsulinemia caused urea production to decrease significantly (P less than 0.05) in both patient groups. The administration of DCA to patients during hyperinsulinemia elicited a significant increase in glucose oxidation rate compared with the clamp rate (P less than 0.05), and the percent of glucose uptake oxidized increased from 45.5 +/- 5.5 to 53.5 +/- 4.8%; yet the response of leucine and urea kinetics to the clamp plus DCA was not different from the response to the clamp alone. These results suggest that the maximal effectiveness of insulin to suppress protein breakdown is not impaired and that a deficit in glucose oxidation or energy supply is probably not playing a major role in mediating the protein catabolic response to severe burn injury and sepsis.
Optimal design of sampling schedules for studying glucose kinetics with tracers
Authors: Cobelli C. , Ruggeri A.
Published: December 2017

Minimum size sampling schedules for estimating glucose kinetic parameters from an impulsive (bolus) tracer injection in normal humans and rats are presented. Glucose kinetics are described by a two-compartment linear model, and reference values of the parameters are estimated from a data base with many samples. The optimal sampling schedule (OSS) is determined in each individual by using a D-optimal criterion and consists of four samples. A population optimal sampling schedule (POSS) applicable to all the individuals of a given population is then determined, and its reliability and efficiency in recovering kinetic parameters (e.g., rate constants, plasma clearance rate, and mean residence time) is assessed. The influence of model and measurement error on OSS is discussed. Moreover, the adoption of an enhanced POSS (EPOSS, 8 samples) is shown to improve accuracy and precision of parameter estimates in a predictable manner. Finally some suggestions are given for obtaining more information from turnover studies using a constant infusion of tracer, with or without a priming pulse of tracer.