bluuebunny/crossref_metadata_2025 huggingface dataset:
Gluconeogenesis from labeled carbon: estimating isotope dilution
Authors: Kelleher J. K.
Published: December 2017

To estimate the rate of gluconeogenesis from steady-state incorporation of labeled 3-carbon precursors into glucose, isotope dilution must be considered so that the rate of labeling of glucose can be quantitatively converted to the rate of gluconeogenesis. An expression for the value of this isotope dilution can be derived using mathematical techniques and a model of the tricarboxylic acid (TCA) cycle. The present investigation employs a more complex model than that used in previous studies. This model includes the following pathways that may affect the correction for isotope dilution: 1) flux of 3-carbon precursor to the oxaloacetate pool via acetyl-CoA and the TCA cycle; 2) flux of 4- or 5-carbon compounds into the TCA cycle; 3) reversible flux between oxaloacetate (OAA) and pyruvate and between OAA and fumarate; 4) incomplete equilibrium between OAA pools; and 5) isotope dilution of 3-carbon tracers between the experimentally measured pool and the precursor for the TCA-cycle OAA pool. Experimental tests are outlined which investigators can use to determine whether these pathways are significant in a specific steady-state system. The study indicated that flux through these five pathways can significantly affect the correction for isotope dilution. To correct for the effects of these pathways an alternative method for calculating isotope dilution is proposed using citrate to relate the specific activities of acetyl-CoA and OAA.
Effects of local administration of GH and IGF-1 on longitudinal bone growth in rats
Authors: Isgaard J. , Nilsson A. , Lindahl A. , Jansson J. O. , Isaksson O. G.
Published: December 2017

The effect of local administration of growth hormone (GH) and insulinlike growth factor 1 (IGF-1) on longitudinal bone growth was studied in the proximal tibia of hypophysectomized rats, by using the tetracycline method. Human GH (hGH) stimulated local bone growth when administered into the epiphysial growth plate, into the epiphysis through an implanted cannula, or into the knee joint intraarticularly. In contrast, hGH administration into the metaphysis did not cause such a stimulation. The effect of hGH was dose dependent, and the lowest daily dose of hGH that caused a stimulation was 50 ng. hGH produced by cloned bacteria was as effective as pituitary-derived hGH, excluding the possibility of a pituitary growth factor being the active compound. GH from other mammalian species (rat GH, ovine GH, and bacterially produced bovine GH) also stimulated local bone growth. Ovine prolactin (oPRL) stimulated local bone growth but the threshold dose of oPRL was approximately 100 times higher than that of hGH, suggesting that contamination of this preparation by GH may account for the stimulation. Reduced carboxymethylated human GH, that has a greatly reduced anabolic activity, did not stimulate local bone growth. Local administration of 5 micrograms of bacterially produced human IGF-1 per day produced a small but significant effect on unilateral bone growth. Simultaneous administration of hGH had no additive effect with, nor did it potentiate, the stimulatory effect of IGF-1. The present study confirms and extends earlier investigations, showing that local injection of GH at the site of the epiphysial growth plate stimulates unilateral bone growth. The study also shows that local administration of IGF-1 stimulates longitudinal bone growth.
Refined carbohydrate increases blood pressure and catecholamine excretion in SHR and WKY
Authors: Fournier R. D. , Chiueh C. C. , Kopin I. J. , Knapka J. J. , DiPette D. , Preuss H. G.
Published: December 2017

In spontaneously hypertensive (SHR) and normotensive (WKY) rats fed different diets, blood pressure (BP) increased significantly in both strains when the carbohydrate (CHO) source was from refined rather than from natural ingredients. This BP increase was observed whether sucrose, glucose, or starch was the principal CHO. Urinary excretion of norepinephrine, dopamine, and, to some extent, epinephrine also increased, while myocardial concentrations were unaffected. Despite a comparable elevation of catecholamine excretion in both SHR and WKY rats fed high amounts of refined CHO, the BP increases were greater in the former. The strain differences were explained by the known dissimilar response of their blood vessels to catecholamines. The results suggest that BP elevation after high CHO ingestion is mediated via increased catecholamine production and/or release, thus implying a neurogenic mechanism.
Insulin binding and glucose transport activity in cardiomyocytes of a diabetic rat
Authors: Almira E. C. , Garcia A. R. , Boshell B. R.
Published: December 2017

We studied insulin binding and glucose transport in isolated adult cardiomyocytes from rats with 2-wk streptozotocin-induced diabetes. At 37 degrees C, cells from diabetic rats bound less 125I-insulin and exhibited lower rates of 3-O-methylglucose transport than cells from control rats. In contrast, the amount of 125I-insulin bound to myocytes at 4 degrees C was the same in both groups. Preincubation of cells from both groups with 10-10,000 ng/ml insulin significantly increased their basal rates of glucose transport by approximately 40%. However, the augmented rates in diabetics were still approximately 36% lower than the corresponding insulin-stimulated rates in the controls. When the glucose transport data were expressed as percent maximal insulin effect and plotted as a function of the amount of insulin bound, the curves obtained from both diabetic and nondiabetic controls were superimposable. These data demonstrate that 1) heart cells from diabetic rats bind less insulin than from control rats under conditions in which they exhibit impaired glucose transport rates, 2) there is no apparent difference in total receptor number between the two groups, but internalization of intact insulin appears to be diminished in diabetes, 3) coupling exists between insulin binding and glucose transport in both groups, and 4) these impaired processes are completely reversed by insulin treatment in vivo but not in vitro.
Effect of training on insulin binding to rat skeletal muscle sarcolemmal vesicles
Authors: Grimditch G. K. , Barnard R. J. , Kaplan S. A. , Sternlicht E.
Published: December 2017

We examined the hypothesis that the exercise training-induced increase in skeletal muscle insulin sensitivity is mediated by adaptations in insulin binding to sarcolemmal (SL) insulin receptors. Insulin binding studies were performed on rat skeletal muscle SL isolated from control and trained rats. No significant differences were noted between groups in body weight or fat. An intravenous glucose tolerance test showed an increase in whole-body insulin sensitivity with training, and specific D-glucose transport studies on isolated SL vesicles indicated that this was due in part to adaptations in skeletal muscle. Enzyme marker analyses revealed no differences in yield, purity, or contamination of SL membranes between the two groups. Scatchard analyses indicated no significant differences in the number of insulin binding sites per milligram SL protein on the high-affinity (15.0 +/- 4.1 vs. 18.1 +/- 6.4 X 10(9)) or on the low-affinity portions (925 +/- 80 vs. 884 +/- 106 X 10(9)) of the curves. The association constants of the high-affinity (0.764 +/- 0.154 vs. 0.685 +/- 0.264 X 10(9) M-1) and of the low affinity sites (0.0096 +/- 0.0012 vs. 0.0102 +/- 0.0012 X 10(9) M-1) also were similar. These results do not support the hypothesis that the increased sensitivity to insulin after exercise training is due to changes in SL insulin receptor binding.
Dopamine inhibits maitotoxin-stimulated pituitary 45Ca2+ efflux and prolactin release
Authors: Login I. S. , Judd A. M. , MacLeod R. M.
Published: December 2017

We examined the hypothesis that dopaminergic inhibition of prolactin release is coupled to modulation of cellular calcium flux. Dispersed female rat pituitary cells were prelabeled in 45Ca2+ and perifused to determine simultaneously fractional calcium efflux and prolactin release, as stimulated by maitotoxin, a calcium channel activator. The integrated response of each parameter to 5 ng/ml maitotoxin was obtained in individual perifusion columns in the absence or presence of various concentrations of dopamine. Maitotoxin-stimulated calcium efflux was suppressed by dopamine concentrations of 0.01 microM and greater (P less than 0.01) and achieved a maximal effect at approximately 0.1 microM, at which calcium efflux was reduced by 50%. Maitotoxin-stimulated prolactin release was inhibited by 0.03 microM dopamine and greater concentrations (P less than 0.01), and at a concentration of approximately 10.0 microM dopamine the effect became maximal at approximately 85% suppression. Haloperidol (0.1 microM) blocked the effects of 0.1 microM dopamine on both parameters. Simultaneous suppression of maitotoxin-stimulated calcium efflux and prolactin release by concentrations of dopamine within the nanomolar range suggests that dopamine receptor activation is negatively coupled to modulation of calcium flux in the physiological regulation of prolactin secretion.
CBG does not restrict blood-brain barrier corticosterone transport in rabbits
Authors: Pardridge W. M. , Eisenberg J. , Fierer G. , Kuhn R. W.
Published: December 2017

The metabolic clearance rate of corticosterone in rabbits is unrelated to the physiological concentration of corticosteroid binding globulin (CBG) in rabbit plasma. This suggests that corticosterone is available for transport into peripheral tissues in rabbits from the circulating CBG-bound pool, similar to what is known to occur in rat liver. This hypothesis was tested in the present studies, which investigate the transport of corticosterone into rabbit brain from the circulating rabbit or human CBG-bound pool. Corticosterone was readily exchangeable in brain capillaries in vivo from the circulating albumin-bound and rabbit or human CBG-bound pools. The involvement of specific CBG receptors on brain capillary endothelia in this process was investigated with [3H]-labeled human CBG prepared by reductive methylation. The transport of [3H]CBG across rabbit brain capillaries in vivo was immeasurably low, and no specific binding of this radiolabeled plasma protein to isolated brain capillaries in vitro was observed at 37 degrees C during incubations up to 120 min. These studies indicate that the rabbit is a novel system for assessing the role of CBG in delivering corticosterone to peripheral tissues in vivo and that specific endothelial CBG receptors may not participate in the transport process.
Mechanism of increased hepatic concentration of carnitine by clofibrate
Authors: Paul H. S. , Gleditsch C. E. , Adibi S. A.
Published: December 2017

Our previous studies have shown that treatment of rats with clofibrate, a hypolipidemic drug, greatly increases the total concentration of carnitine in the liver (H. S. Paul and S. A. Adibi, J. Clin. Invest. 64: 405-412, 1979). In the present experiment we have investigated some possible mechanisms to account for this increase. Clofibrate treatment (30 mg/100 g rat/day for 2 wk) increased significantly the concentration (nmol/g, mean +/- SE, 6 rats) of both free (289 +/- 21 vs. 1,747 +/- 131) and acylcarnitine (87 +/- 11 vs. 412 +/- 42). These increases were not the result of redistribution of carnitine among tissues or due to a decrease in urinary excretion. In view of previous observations that thyroid hormones increase the hepatic concentrations of carnitine, and clofibrate treatment causes a hyperthyroid state in the liver, we investigated the effect of clofibrate in thyroidectomized rats. Clofibrate treatment of thyroidectomized rats also increased the concentration of free (423 +/- 25 vs. 1,460 +/- 123) and acylcarnitine (35 +/- 6 vs. 305 +/- 31) in the liver. Finally, clofibrate treatment significantly increased the urinary excretion of trimethyllysine, a precursor of carnitine (31 +/- 3 vs. 47 +/- 4 nmol/mg creatinine, mean +/- SE, 5 rats). Our data suggest that clofibrate treatment stimulates hepatic synthesis of carnitine by increasing the availability of its precursor, trimethyllysine. This effect of clofibrate is independent of thyroid hormone.
Beta-adrenergic agonists increase amplitude of LH release in orchidectomized rats
Authors: Petrovic S. L. , Bedran De Castro J. C. , McCann S. M.
Published: December 2017

The role of intravenously (iv) injected adrenergic agonists in the pulsatile secretion of luteinizing hormone (LH) was examined in unanesthesized, freely behaving, castrated male rats. The alpha 2-adrenergic receptor agonist, clonidine (25 micrograms/kg), and the alpha 1-adrenergic agonist, (-)-phenylephrine (12.5 micrograms/kg), did not significantly alter pulsatile release of LH. The physiological beta 2-adrenergic receptor agonist, (-)-epinephrine (2.5 micrograms/kg), significantly increased the mean plasma concentrations of plasma LH and the amplitude of the LH pulses over a period of 70 min. The specific beta 2-receptor agonist, salmefamol, significantly increased the mean plasma concentrations of LH and especially the average amplitude of LH pulses over 70-80 min in a dose-related fashion following the injection of doses from 25 to 125 micrograms/kg. The frequency of LH pulses was not significantly increased by either agonist at any of the doses employed. Salmefamol-induced increases in plasma LH could be prevented by the beta-adrenergic blocker, bornaprolol (FM-24), in a dose-related manner. When injected together with synthetic LH-releasing hormone (400 ng/kg), salmefamol (125 micrograms/kg) significantly increased the mean plasma concentrations of LH over 70 min compared with values in controls receiving LH-releasing hormone only. The data support the concept that beta-agonists act on their receptors in the pituitary to facilitate LH-releasing hormone-induced discharge of LH.
Calcium pump activity of sarcoplasmic reticulum in diabetic rat skeletal muscle
Authors: Ganguly P. K. , Mathur S. , Gupta M. P. , Beamish R. E. , Dhalla N. S.
Published: December 2017

Ca2+ pump activity of skeletal muscle microsomes containing fragments of sarcoplasmic reticulum was examined in rats 8 wk after the induction of chronic diabetes by an intravenous injection of streptozotocin (65 mg/kg). In comparison with the control values, both ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase activities were increased in the microsomal fraction from diabetic rats. These changes were seen as early as 7 days after streptozotocin injection and were apparent at various times of incubation (1-10 min) as well as at different concentrations of free Ca2+ (10(-7)-5 X 10(-5) M Ca2+). Insulin administration to diabetic animals for 2 wk reversed Ca2+ uptake and ATPase activities to control levels. The increase in microsomal ATPase activity of the diabetic preparation due to cAMP-dependent protein kinase or calmodulin was greater than in the control microsomes and the depression by a specific inhibitor of protein kinase, but not of calmodulin, was greater in diabetic muscle. The enhanced Ca2+ pump activity was associated with altered phospholipid composition and protein profile of the diabetic preparations. The rate of Ca2+ release from microsomal vesicles was unaffected by the diabetic condition. Isometric contractile force development as well as positive dF/dt and negative dF/dt of the skeletal muscle from diabetic animals were higher at different pulse strengths (0.5-100 V) and at different Ca2+ concentrations (0.25-2.5 mM). These results suggest that diabetes is associated with enhanced sarcoplasmic reticular Ca2+ pump activity, and this may account for the hyperfunction of skeletal muscle in this disease.
Effect of plasma concentrations of ovarian steroids on their passage into uterine lumen in rabbits
Authors: Eiler H.
Published: December 2017

Significant increment of blood-borne ovarian steroids are found in the uterine lumen 1 h after mating. Is the transfer of ovarian steroids into the uterus determined by the peripheral blood concentrations of the ovarian steroids? To answer this question, rabbits, ovariectomized 24 h earlier, were infused over a 1-h period with either estradiol (E2; 0.7 and 7.0 micrograms/h), progesterone (P4; 74 and 740 micrograms/h), or testosterone (T; 0.45 and 4.5 micrograms/h). E2, P4, and T were determined in the tissue and flushings of the uterus and tissue and flushings of the esophagus and plasma. A different group of rabbits was infused with E2 (0.7 micrograms), P4 (74 micrograms), and T (0.45 microgram/h) combined. The increase in plasma steroid concentration after infusion of either E2, P4, or T was reflected in an elevation of these steroids in the uterine lumen, albeit not in the same ratios as found in plasma. The simultaneous infusion of E2, P4, and T blocked completely the passage of T and decreased (P less than 0.05) the passage of E2 into the lumen of the uterus. Treatments did not affect the steroid concentration in the wall of the uterus. It was concluded that the content of E2, P4, or T in the uterine flushing increased when E2, P4, or T was infused individually. However, when these steroids were infused together, there was selective inhibition of the transfer process.
Glycogen depletion and increased insulin sensitivity and responsiveness in muscle after exercise
Authors: Zorzano A. , Balon T. W. , Goodman M. N. , Ruderman N. B.
Published: December 2017

As judged by its ability to stimulate glucose uptake and alpha-aminoisobutyric acid (AIB) transport, the sensitivity and the responsiveness of perfused rat muscle to insulin are enhanced after moderately intense treadmill exercise. In fed rats, these enhanced effects of insulin are predominantly restricted to muscles that performed work as evidenced by glycogen depletion. The present study was designed to examine the relationship between glycogen depletion per se and the postexercise changes in insulin action. Toward this end, fed and 48-h starved rats were run on a treadmill for 45 min at moderate intensity, and glucose and AIB uptake were then assessed using the isolated perfused hindquarter preparation. Glycogen is depleted in red muscles such as the soleus and red fibers of the gastrocnemius in fed rats immediately after such exercise, whereas, in starved rats, muscle glycogen is unchanged. As previously shown, the stimulation by insulin of glucose utilization by the hindquarter and AIB transport into red muscles was substantially increased in fed rats after the treadmill run. This was due to increases in both insulin sensitivity and responsiveness. In starved rats, the treadmill run also enhanced the ability of insulin to stimulate these processes; however, this was solely due to an increase in insulin sensitivity. No change in insulin responsiveness was observed. The results indicate that the enhanced sensitivity of muscle to insulin after exercise is not dependent on glycogen depletion, whereas increased insulin responsiveness does not occur in its absence. They also suggest that the mechanisms by which prior exercise acts to increase insulin sensitivity and responsiveness are different.
Influence of serum Ca concentration on circulating molecular forms of PTH in three species
Authors: D'Amour P. , Labelle F. , Lecavalier L. , Plourde V. , Harvey D.
Published: December 2017

The influence of serum calcium concentration on total circulating parathyroid hormone (PTH) and on the relative amount of intact PTH-(1-84) and large carboxyterminal fragments was studied in the canine and bovine species and in man. Serum calcium was modified through infusions of CaCl2 or EDTA and samples obtained in time for the measurement of serum calcium and PTH concentrations. Pools of serum, corresponding to specific serum calcium concentrations, were analyzed by gel chromatography in all species. PTH was measured with a carboxyterminal radioimmunoassay. In basal conditions, total serum PTH was composed mostly of large carboxyterminal fragments, intact PTH-(1-84) representing less than 25% of the hormone in any species. With hypercalcemia, (greater than or equal to 2.0 mg/dl), total serum PTH decreased only to 40% of the original value measured in all species, despite serum calcium concentrations of over 13 mg/dl. The relative amount of intact PTH-(1-84) remained unchanged in the bovine and canine species and slightly decreased in man. Hypocalcemia (less than or equal to 2.0 mg/dl) induced a 300-450% increase in the basal PTH value measured. The relative amount of intact PTH-(1-84) became as or more important than carboxyterminal fragments in the canine species and in man, respectively, and remained slightly less in the bovine species. Despite small quantitative variations between species, these results indicate that changes in serum calcium concentration induced acute modification in PTH secretion or PTH peripheral metabolism, altering the ratio of intact hormone to carboxyterminal fragments in circulation.
Elevation of plasma renin activity by alpha-adrenoceptor agonists in conscious dogs
Authors: Blair M. L. , Chen Y. H. , Hisa H.
Published: December 2017

Experiments were performed in conscious trained dogs to determine whether renal alpha-adrenergic receptors mediate stimulation or inhibition of renin release. All dogs were uninephrectomized and surgically prepared with chronically indwelling catheters in the aorta, vena cava, and remaining renal artery at least 8 days before experiment. Direct renal artery (ia) infusion of the alpha-adrenoceptor agonist phenylephrine, 0.25 or 0.50 microgram X kg-1 X min-1 for 30 min, increased plasma renin activity (PRA) to 145 +/- 13 and 212 +/- 28% of control, respectively, within 5 min of drug infusion (P less than 0.01) in conscious sodium-replete dogs. In contrast, intravenous phenylephrine infusion decreased PRA by 50% (P less than 0.001). The increase in PRA observed during ia phenylephrine infusion was prevented by renal alpha-adrenoceptor blockade with phenoxybenzamine but not by beta-adrenoceptor blockade with propranolol. Methoxamine, another alpha-adrenoceptor agonist, also increased PRA when infused ia in both sodium-replete dogs and in dogs maintained on a low-sodium diet. In dogs with renal arterial electromagnetic flowprobes, ia phenylephrine infusion increased PRA without decreasing total renal blood flow. In summary, stimulation of renal alpha-adrenoceptors increases PRA in conscious dogs. This stimulation can occur in the absence of significant changes in total renal blood flow.
Neurotensin releases norepinephrine differentially from perfused hypothalamus of sated and fasted rat
Authors: Lee T. F. , Rezvani A. H. , Hepler J. R. , Myers R. D.
Published: December 2017

The central injection of neurotensin (NT) has been reported to attenuate the intake of food in the fasted animal. To determine whether endogenous norepinephrine (NE) is involved in the satiating effect of NT, the in vivo activity of NE in circumscribed sites in the hypothalamus of the unanesthetized rat was examined. Bilateral guide tubes for push-pull perfusion were implanted stereotaxically to rest permanently above one of several intended sites of perfusion, which included the paraventricular nucleus (PVN), ventromedial nucleus (VMN), and the lateral hypothalamic (LH) area. After endogenous stores of NE at a specific hypothalamic locus were radiolabeled by microinjection of 0.02–0.5 mu Ci of [3H]NE, an artificial cerebrospinal fluid was perfused at the site at a rate of 20 microliter/min over successive intervals of 5.0 min. When 0.05 or 0.1 micrograms/microliter NT (0.03–0.6 mM) was added to the perfusate, the peptide served either to enhance or reduce the local release of NE at 50% of the sites of perfusion. In these experiments, the circumscribed effect of NT on the characteristics of catecholamine efflux depended entirely on the state of hunger or satiety of the rat. That is, when NT was perfused in the fully satiated rat, NE release was augmented within the PVN or VMN; conversely, NE release was inhibited in the LH. In the animal fasted for 18–22 h, NT exerted an opposite effect on the activity of NE within the same anatomical loci in that the efflux of NE was enhanced in the LH but attenuated or unaffected in the PVN or VMN.(ABSTRACT TRUNCATED AT 250 WORDS)
Fate of circulating renin in conscious rats
Authors: Kim S. , Iwao H. , Nakamura N. , Ikemoto F. , Yamamoto K.
Published: December 2017

Highly purified 125I-labeled rat renal renin (125I-renin) was given intravenously to conscious rats to study the fate of circulating renin. Specific antirat renin antiserum was used to identify the labeled renin molecules. In sham-operated rats, the disappearance of 125I-renin from the plasma showed two exponential components with a half-life of 6.7 +/- 0.4 min for the rapid component and 65.1 +/- 5.7 min for the slow component. The metabolic clearance rate was 11.4 +/- 1.0 ml X min-1 X kg-1. In bilaterally nephrectomized rats, the metabolic clearance rate of 125I-renin was reduced by 55%, but the half-life of the slow component remained unchanged. Seventy percent hepatectomy caused a 54% decrement in the metabolic clearance and prolonged the half-life of the slow component. Five minutes after injection of 125I-renin, approximately 59 and 11% of the administered 125I-renin had accumulated in the liver and the kidneys, respectively, and at later time points the 125I-renin was highly concentrated in these organs. High-performance liquid chromatographic analysis of the liver and kidney extracts demonstrated that 125I-renin was catabolized by these organs. Biliary excretion of 125I-renin was negligible. Urinary excretion of 125I-renin up to 120 min was approximately 2% of the injected dose. We conclude that both the liver and the kidney are responsible for the clearance of circulating renin, with participation of the liver being predominant.
Regulation of 25-hydroxyvitamin D3 metabolism in chick embryo
Authors: Turner R. T. , Graves J. S. , Bell N. H.
Published: December 2017

We investigated the time course of the development of renal 25-hydroxyvitamin D-1-hydroxylase and 25-hydroxyvitamin D-24-hydroxylase in chick embryos grown in the presence and absence of the eggshell. In embryos with the eggshell, the specific activity (SA) of 25-hydroxyvitamin D-1-hydroxylase in kidney homogenates increased from 0.68 fmol X min-1 X mg protein-1 at 12 days of gestation to a peak of 2.55 +/- 0.50 fmol X min-1 X mg-1 protein-1 at 17 days. In contrast, the SA of 25-hydroxyvitamin D-24-hydroxylase decreased from 2.5 fmol X min-1 X mg protein-1 to 0.90 +/- 0.25 fmol X min-1 X mg protein-1 during the interval. The total plasma calcium was significantly reduced in embryos without shells at 14 to 15 days of gestation (1.1 +/- 0.1 mM, mean +/- SE) compared with normal embryos of the same gestation (2.3 +/- 0.3 mM, P less than 0.002). In embryos without the eggshell, renal 25-hydroxyvitamin D-1-hydroxylase increased from 6.0 to 8.2 +/- 0.6 fmol X min-1 X mg protein-1 at 17 days of gestation and was from four- to sixfold higher than corresponding enzymatic activities for intact embryos. The increased enzyme activity resulting from loss of the eggshell was due to an increase in Vmax. The findings indicate that renal 25-hydroxyvitamin D-1-hydroxylase and 25-hydroxyvitamin D-24-hydroxylase in the chick embryo exhibit activity and show a large capacity for regulation in response to changes in calcium metabolism.
Effect of insulin on in vivo glucose utilization in individual tissues of anesthetized lactating rats
Authors: Burnol A. F. , Ferre P. , Leturque A. , Girard J.
Published: December 2017

Glucose utilization rate has been measured in skeletal muscles, white adipose tissue, and mammary gland of anesthetized nonlactating and lactating rats. During lactation, basal glucose utilization is decreased by 40% in periovarian white adipose tissue and by 65% in epitrochlearis and extensor digitorum longus but not in soleus muscle. This may be related to the lower blood glucose and plasma insulin concentrations observed during lactation. Basal glucose utilization rate in the mammary gland was, respectively, 18 +/- 2 and 350 +/- 50 micrograms/min in nonlactating and lactating rats. During the euglycemic hyperinsulinemic clamp, a physiological increment in plasma insulin concentration (231 +/- 18 in lactating vs. 306 +/- 24 microU/ml in nonlactating rats) induces a similar increase in glucose utilization rate in skeletal muscles (except soleus) and white adipose tissue in the two groups of rats. Furthermore this low increase in plasma insulin concentration does not alter mammary glucose utilization rate in nonlactating rats but induces the same increase (sevenfold over basal) as a maximal insulin concentration in lactating rats. These data show that the active mammary gland is the most insulin-sensitive tissue of the lactating rat that has been tested. The overall increase in insulin sensitivity and responsiveness that has been described in lactating rats can then mainly be attributed to the presence of the active mammary gland.
Role of acidosis in regulating hepatic nitrogen metabolism during fasting in conscious dog
Authors: Cersosimo E. , Williams P. E. , O'Donovan D. , Lacy D. B. , Abumrad N. N.
Published: December 2017

This study was designed to investigate the role that acidosis plays in the metabolic responses to fasting. Eighteen conscious dogs with surgically implanted catheters in the femoral artery and in the hepatic, portal, and renal veins were studied. Six were fasted for 24 h and 12 were fasted for 4 days (96 h). On the day of the study, six 4-day fasted dogs were infused intravenously with NaHCO3 (10 mumol X kg-1 X min-1) for 3 h, while the rest received saline and acted as controls. Splanchnic balances of glutamine, alanine, blood urea nitrogen, ammonia, lactate, beta-hydroxybutyrate, and acetoacetate were estimated using the Fick principle. Blood flow to the splanchnic and renal beds were estimated using indocyanine green and p-aminohippurate extraction methods, respectively. The infusion of NaHCO3 nearly abolished the base deficit associated with fasting and normalized arterial bicarbonate levels but did not alter blood pH. It suppressed but did not abolish hepatic glutamine output by 60%. This was associated with a shift in cytoplasmic and mitochondrial redox potentials of the hepatocyte as evident by a decrease in hepatic production of beta-hydroxybutyrate and an increase in hepatic production of acetoacetate and a decrease in hepatic lactate utilization. Concomitantly, renal glutamine uptake decreased. Glutamine release of skeletal muscle was unchanged. The data suggest that hepatic glutamine synthesis and release seen with 4-day fasting has two components: a bicarbonate-dependent component that is influenced by the redox potential of the hepatocyte and a bicarbonate-independent component, the nature of which is not yet clear.(ABSTRACT TRUNCATED AT 250 WORDS)
Thermic effect of food: possible implication of parasympathetic nervous system
Authors: Nacht C. A. , Christin L. , Temler E. , Chiolero R. , Jequier E. , Acheson K. J.
Published: December 2017

To investigate the effect of the autonomic nervous system on the thermic response to food ingestion, respiratory exchange measurements were performed on seven healthy young men for 1 h and 45 min before and 6 h after ingestion of a mixed meal, approximately 560 kcal, 53% carbohydrate, 30% fat, and 17% protein (control) and under the same conditions during infusion of either propranolol (80 micrograms/kg bolus and 1 microgram.kg-1.min-1), atropine (10 micrograms/kg and 10 micrograms.kg-1.min-1), or atropine plus propranolol. The postabsorptive resting metabolic rates were the same on each occasion and were slightly altered by drug treatment. The thermic responses to the meal were the same with the control and propranolol tests (9.3 +/- 0.9 and 9.2 +/- 0.5%, respectively) and were greater (P less than 0.001) than with atropine 3.6 +/- 0.6% and atropine plus propranolol 3.3 +/- 0.8%. Blockade of the sympathetic nervous system does not decrease the thermic response to food taken orally, whereas muscarinic receptor blockade does. Although some confounding effects of atropine might explain some of this decrease, our results suggest that the parasympathetic nervous system is involved in the thermic effect of food.
Hepatic extraction of somatostatin in conscious dogs
Authors: Chap Z. , Ishida T. , Jones R. H. , Pena J. R. , Vinik A. , Field J. B.
Published: December 2017

Fractional hepatic extraction of endogenous somatostatin immunoreactivity was examined in conscious dogs with Doppler flow probes on the portal vein and hepatic artery and catheters in the portal and hepatic veins and carotid artery before and after induction of hypoglycemia by infusion of insulin. Insulin infusion (1 and 2 mU.kg-1.min-1) decreased arterial plasma glucose from 76 +/- 4 mg/dl to a nadir of 41 +/- 2 mg/dl. Basal portal vein somatostatin was 117 +/- 11 pg/ml, which was significantly greater than the 97 +/- 12 pg/ml in the hepatic vein (P less than 0.05) and 79 +/- 8 pg/ml in the carotid artery (P less than 0.05). Hypoglycemia significantly augmented portal vein somatostatin to 206 +/- 32 pg/ml with parallel increases in the hepatic vein and carotid artery. The mean basal fractional hepatic extraction of total somatostatin immunoreactivity was 9 +/- 6% and was unchanged during hypoglycemia (14 +/- 4%). Column chromatography of the portal vein somatostatin immunoreactivity in the basal period yielded three peaks with most of the material eluting with somatostatin-14 and the void volume. Very little somatostatin-28 was detected. There was very little hepatic extraction of the void volume material while approximately 50% of somatostatin-14 was removed by that organ. After insulin-induced hypoglycemia, there was the greatest percent increase in somatostatin-28 and a doubling of somatostatin-14 and the void volume material. Most of the somatostatins-14 and -28 were removed by the liver, while extraction of the void volume material was negligible.(ABSTRACT TRUNCATED AT 250 WORDS)
ANF and exocrine pancreas: ultrastructural autoradiographic localization in acinar cells
Authors: Chabot J. G. , Morel G. , Belles-Isles M. , Jeandel L. , Heisler S.
Published: December 2017

Atrial natriuretic factor (ANF) binding sites have been recently demonstrated to be present in exocrine pancreas by an in vitro autoradiographic approach. An autoradiographic study was carried out to identify the exocrine cells containing ANF binding sites and to monitor the fate of 125I-labeled ANF in acinar cells after removal of pancreas at specific time intervals (1-30 min) after intravenous administration. At the light microscopic level, silver grains were found over acinar and centroacinar cells. Concomitant injection of an excess of unlabeled ANF inhibited the binding of labeled peptide by approximately 60%. At the electron microscopic level, the time-course study in acinar cells has revealed that of the cell compartments examined, plasma membrane, Golgi apparatus, mitochondria, and zymogen granules, the nucleus had distinct labeling patterns. Plasma membrane was maximally labeled 1 and 2 min after injection with 125I-ANF. Golgi apparatus was significantly labeled from 2 to 30 min after injection, mitochondria from 1 to 30 min after injection, zymogen granules at 1 and 15 min, and the nucleus only at 30 min. The lysosomal compartment was not labeled during the 30-min observation period. These results suggest that after binding to the plasma membrane, ANF is rapidly internalized and distributed to the intracellular organelles as a function of time. Labeling of the zymogen granules suggests that they may bind ANF and that the atrial peptide may be secreted by acinar cells. The significance of association of radioactivity with mitochondria and nuclei remains to be elucidated but may represent intracellular sites of action of ANF complementary to those on plasma membranes.
Renin substrate release in response to perturbations of renin-angiotensin system
Authors: Eggena P. , Barrett J. D.
Published: December 2017

The role of the kidney in the regulation of plasma renin substrate and the release of this protein from rat liver slices were investigated. Physiological and pharmacological maneuvers were performed to perturb the renin-angiotensin system, including 24-h bilateral nephrectomy and furosemide administration to change renin and adrenalectomy and administration of dexamethasone to alter renin substrate. In the normal physiological range of plasma renin activity (PRA), no statistically significant linear relationship was evident between PRA and either plasma renin substrate or renin substrate released from liver slices. Stimulation of renin substrate by nephrectomy and dexamethasone administration were additive. Nephrectomy was also shown not to induce the release of a renin substrate-stimulating factor.
Uptake of thyroxine by the perfused rat liver: implications for the free hormone hypothesis
Authors: Mendel C. M. , Cavalieri R. R. , Weisiger R. A.
Published: December 2017

To investigate the mechanism by which thyroxine (T4) in plasma enters hepatic cells, we measured the rate constants for uptake of free T4 by the perfused rat liver and for dissociation of T4 from its plasma binding proteins. Quantitative autoradiography of liver lobules after perfusion with [125I]T4 indicated an apparent rat constant for removal of free T4 from the sinusoids of at least 1.1 +/- 0.2 s-1. Single-pass extraction of T4 from human serum was 10.6 +/- 1.7% at physiological flow rates (1 ml.min-1.g liver-1). Rate constants for dissociation of T4 from plasma binding proteins at 37 degrees C (determined by rapid filtration) were 0.017 +/- 0.002 s-1 for human thyroid hormone-binding globulin, 0.080 +/- 0.015 s-1 for human thyroid hormone-binding prealbumin, and greater than 0.5 s-1 for human albumin. To investigate the factors that determine the concentration of T4 within hepatic cells, we analyzed the above data together with data reported in the literature on the equilibrium-binding constants and the rate constant for cellular metabolism of T4. Analysis of all of these data using a previously published mathematical model leads to the following conclusions for the physiological state: 1) metabolism, not uptake, is rate limiting to removal of T4 from plasma by the liver; 2) binding equilibrium is present in the intrahepatic plasma; 3) intracellular T4 is in equilibrium with the free T4 pool in plasma (and maintenance of this equilibrium may be an important function of plasma thyroid hormone-binding proteins); and 4) the concentration of T4 within the liver is proportional to the concentration of free T4 in the plasma. Our data do not allow us to determine definitively whether hepatic uptake of T4 occurs only from the free T4 pool in plasma or also from the protein-bound pool by interaction of one or more of the binding proteins with the liver cell. However, mathematical analysis indicates that this distinction is irrelevant to steady-state intracellular hormone concentrations when equilibrium exists between the plasma and cytosolic pools of hormone.
Measurement of forearm oxygen consumption: role of heating the contralateral hand
Authors: Astrup A. , Simonsen L. , Bulow J. , Christensen N. J.
Published: December 2017

The classical forearm technique widely used for studies of skeletal muscle metabolism requires arterial cannulation. To avoid arterial puncture it is becoming more common to arterialize blood from a contralateral hand vein by local heating. This modification and the classical method have produced contradictory results regarding the contribution of skeletal muscle to glucose-induced thermogenesis. The effect on forearm circulation and the metabolism of heating the contralateral hand was examined before and after an oral glucose load. The results suggest that contralateral heating increases subcutaneous blood flow and decreases skeletal muscle blood flow. This facilitates mixing of superficial blood with deep venous blood. Contralateral heating increased deep venous oxygen saturation and abolished the pronounced glucose-induced increase in oxygen consumption observed in the control experiments after glucose. Heating increased rectal temperature by 0.6 degrees C, and plasma norepinephrine levels were increased compared with the control experiments. The present study explains the conflicting reports on glucose-induced thermogenesis in skeletal muscle and warns against heating the contralateral hand when using the forearm technique.
Evaluation of pulse-detection algorithms by computer simulation of hormone secretion
Authors: Guardabasso V. , De Nicolao G. , Rocchetti M. , Rodbard D.
Published: December 2017

A versatile method is presented for generating synthetic hormonal time series, containing peaks at known locations, to be used to objectively evaluate both the false-negative (F-) and false-positive (F+) statistical error rates of computerized pulse-detection algorithms. Synthetic data are generated by assuming hormone secretion to occur as a succession of instantaneous release pulses, distributed as Poisson events, separated by quiescent intervals. The pulses are convolved to simulate cumulation of consecutive events and clearance of the hormone. Randomly generated errors, corresponding in magnitude to typical experimental measurement error, are then added to the convolved series. The choice of different values for simulation parameters (e.g., frequency and amplitude of pulses) allows one to emulate some typical physiological patterns of hormone secretion for luteinizing hormone, growth hormone, and thyrotropin or other hormones. Various subsets can be extracted from a simulated time series to study the effect of sampling frequency on the detection of pulses. We show that in sampled series the "observable frequency" of pulses is less than the true nominal frequency. Methods for evaluating pulse-detection algorithms and expressing the results are presented. Simulations of LH secretion were analyzed with the program DETECT. We show that minimizing F+ error rates only might lead to excessively high F- rates. A proper choice of sampling frequency and program probability levels can be made to provide acceptable F+ and F- error rates for various patterns of hormone secretion.
Phlorizin-induced normoglycemia partially restores glucoregulation in diabetic dogs
Authors: Hetenyi G. , Gauthier C. , Byers M. , Vranic M.
Published: December 2017

The plasma concentration of glucagon (IRG), catecholamines, and hepatic glucose production (Ra) were followed in insulin-induced hypoglycemia in dogs before (normal) and at 14-21 and again at 89-119 days after the injection of alloxan (diabetic). Some diabetic dogs were also tested when euglycemia was restored by phlorizin. In the normal state plasma IRG and epinephrine were raised by a factor of 3 and 15, respectively. Ra increased in two phases, an early peak (350% basal) was followed by a plataeu at about twice basal. In diabetes, irrespective of its duration, plasma IRG was decreased in hypoglycemia, and the rise in plasma epinephrine was significantly reduced. Ra remained unchanged. In phlorizin-treated euglycemic diabetic dogs plasma IRG fell, and the response in plasma epinephrine remained blunted. There was no early rise in Ra, but the same elevated plateau was reached at the same time as in normal animals. In conclusion, the following is observed in diabetic dogs. 1) The sensitivity of alpha-cells to insulin is maintained, but that to hypoglycemia is lost. The concentration of plasma catecholamines is raised less than in normals. With no increase in plasma glucagon this rise is not sufficient to increase Ra. 2) Restoration of euglycemia with phlorizin does not restore normal IRG and epinephrine responses to hypoglycemia but restores the delayed increase of Ra. Thus the restoration of euglycemia in severely diabetic dogs partially restores the responses of the liver, but not of the alpha-cell or sympathetic discharge, to hypoglycemia.
Atrial natriuretic peptide suppresses osmostimulated vasopressin release in young and elderly humans
Authors: Clark B. A. , Elahi D. , Fish L. , McAloon-Dyke M. , Davis K. , Minaker K. L. , Epstein F. H.
Published: December 2017

Atrial natriuretic peptide (ANP) may suppress vasopressin release, but the dynamics of this interaction as well as the influence of age have not been defined. We studied six or seven young (19-40 yr old) and seven elderly volunteers (65-83 yr old) under two circumstances: 1) after infusion of 5% saline (0.04 ml.kg-1.min-1) for 2 h and 2) after the same infusion given with simultaneous synthetic human ANP (0.05 micrograms.kg-1.min-1). Hypertonic saline alone produced a progressive rise in plasma vasopressin with increasing serum sodium. During hypertonic saline alone, vasopressin levels began to rise at an increment in serum sodium of 1.67 +/- 0.35 mM in the young and 1.43 +/- 0.32 mM in the elderly and rose linearly with increasing serum sodium. When ANP was infused with hypertonic saline (with peak ANP levels of approximately 1,000 pM), vasopressin levels began to rise at an increment in serum sodium of 4.43 +/- 0.67 mM in the young and 4.57 +/- 0.43 mM in the elderly (P less than 0.01 vs. saline alone). Furthermore, the vasopressin response for any given serum sodium was significantly reduced in both young and elderly subjects, resulting in a rightward displacement of the curve relating vasopressin response to sodium concentration (P less than 0.001). In conclusion, ANP not only suppresses vasopressin but raises the threshold for release of vasopressin in response to osmotic stimulation in both young and elderly individuals. High circulating ANP levels may be responsible in part for the suppression of vasopressin levels and water diuresis seen during states of volume expansion.
Big ANF: large-molecular-weight ANF in plasma. I. Gel filtration and affinity chromatography studies
Authors: Wilson N. , Yakoleff V. , Keeler R.
Published: December 2017

A large molecular form of immunoreactive atrial natriuretic factor (irANF) was demonstrated in plasma of rabbit and rat on the basis of gel filtration experiments. This big ANF was not retained by octadecylsilane cartridges and cross-reacted with four anti-ANF antisera of different specificities. Gel filtration in acid, but not in 8 M urea, resulted in material with elution characteristics of irANF. Affinity chromatography and gel electrophoresis of big ANF suggested that the material was similar to albumin. However, high concentrations of big ANF were found in analbuminemic rats, with characteristics similar to those seen in rabbit and normal rats (affinity and gel chromatography and gel electrophoresis). We thus conclude that big ANF represents a bound form of ANF in circulation and that the carrier is similar to but not identical with albumin.
Biogenesis of dicarboxylic acids in rat liver homogenate studied by 13C labeling
Authors: Jin S. J. , Tserng K. Y.
Published: December 2017

The aim of this investigation is to assess whether long-chain fatty acids can be a substrate for omega-oxidation and the subsequent beta-oxidation to produce medium-chain dicarboxylic acids normally found in urine. Isolated rat liver 10,000 g supernatant and pellet fractions were used as the source of enzymes. The metabolism of palmitate was studied using [1,2,3,4-13C4]hexadecanoic acid as tracer. Selected ion monitoring mass spectrometry was utilized for the determination of isotope enrichments in precursor and products. Palmitate was found to be a good substrate for omega-oxidation; the rate was only slightly slower than decanoate. The beta-oxidation of [1,2,3,4-13C4]hexadecanedioic acid yielded labeled adipic, suberic, and sebacic acids. Isotope distribution in these dicarboxylic acids consisted mostly of unlabeled molecules (M + 0) and molecules labeled with four 13C (M + 4), in agreement with a beta-oxidation initiated equally from both carboxyl ends of the precursor. Significant enrichments (1-8%) with only two 13C labels (M + 2) indicate a partial bidirectional beta-oxidation. The direct metabolic conversion of hexadecanedioate to succinate was documented by the significant enrichment (1.40-1.90%) in M + 4 of succinate. These data indicate that long-chain fatty acids can be a substrate for the production of medium-chain dicarboxylates and the eventual direct conversion to succinate.