bluuebunny/crossref_metadata_2025 huggingface dataset:
Induction of hepatic glycogenesis in the fetal rat
Authors: Gruppuso P. A. , Brautigan D. L.
Published: December 2017

We have performed an in vivo study to test the hypothesis that induction of fetal hepatic glycogenesis is stimulated by insulin and involves activation of protein phosphatase type-1. Control animals and the following two experimental groups were studied: maternal fasting for 48 h prior to term and chronic maternal hyperinsulinemia for 5 days prior to term. Maternal fasting led to decreased fetal hepatic glycogen content and fetal growth retardation. In contrast, no decrease in fetal hepatic glycogen content or fetal weight occurred with maternal hyperinsulinemia despite fetal hypoglycemia and fetal hypoinsulinemia. In neither model were fetal hepatic synthase phosphatase or phosphorylase phosphatase activities affected. In control fetuses, the appearance of hepatic glycogen from days 17 to 21 of gestation correlated with induction of glycogen synthase. Phosphorylase phosphatase and synthase phosphatase activities already were present on day 17 of gestation and changed little through term. However, phosphatase catalytic protein reactive with anti-phosphatase type-1 antibodies did increase approximately fivefold from day 18 to 21. In adult animals fasted for 48 h, 50% of hepatic glycogen synthase phosphatase activity was lost, whereas phosphorylase phosphatase activity was stimulated fourfold. The apparent size of protein phosphatase type-1 catalytic subunit as detected by Western immunoblotting was altered by fasting in the adult but not by substrate restriction (maternal fasting) in the fetus.(ABSTRACT TRUNCATED AT 250 WORDS)
Developmental changes in adrenergic regulation of fetal arginine vasopressin secretion
Authors: Ervin M. G. , Padbury J. F. , Ross M. G. , Leake R. D. , Fisher D. A.
Published: December 2017

Fetal adaptation to the extrauterine environment is associated with profound alterations in pulmonary, renal, and cardiovascular functions. Coincident with these changes are a variety of endocrine responses including concomitant increases in plasma catecholamine and arginine vasopressin (AVP) levels. In view of the demonstrated interaction between the sympathoadrenal system and the neurohypophysis in adult mammals, we questioned whether increases in plasma catecholamine levels in the fetus affect fetal plasma AVP levels and whether catecholamine-AVP interactions change developmentally. Chronically catheterized fetal lambs at either 131 +/- 1 (preterm) or 142 +/- 1 days (term) received graded infusions of either epinephrine (E) or norepinephrine (NE) at rates of 0.04, 0.2, 0.75, 1.5, and 3.0 micrograms.min-1.kg-1 during successive 40-min infusion periods. Plasma AVP concentrations in term animals significantly increased (1.4 +/- 0.1 to 5.1 +/- 1.6 pg AVP/ml) in response to E infusion of 0.75 microgram.min-1.kg-1 or greater. The log-linear dose response curves for each animal were used to determine the minimum plasma E concentration required to stimulate AVP secretion or "threshold." The mean plasma E threshold for AVP secretion was significantly lower in term animals (1.4 +/- 0.4 ng/ml) than in preterm animals (6.6 +/- 0.9 ng/ml). Plasma E levels were positively correlated with plasma AVP levels (r = 0.90) above the threshold value in both groups. Changes in plasma AVP levels were observed in preterm or term animals in response to NE only at the highest infusion rate studied.(ABSTRACT TRUNCATED AT 250 WORDS)
Transport of glutamine across blood-facing membranes of perfused rat jejunum
Authors: Taylor P. M. , Egan C. J. , Rennie M. J.
Published: December 2017

Transport of glutamine and other neutral amino acids across the blood-facing membranes of isolated, dually perfused rat jejunum was measured using a paired-tracer isotope-dilution technique. Glutamine, asparagine, histidine, alanine, and leucine showed mutual inhibition of transport. The major component of physiological glutamine transport was saturable (Km = 0.88 +/- 0.15 mM, Vmax = 454 +/- 49 nmol.g-1.min-1; mean +/- SE), stereospecific and Na-independent and appeared to exhibit symmetry of glutamine transport; it most resembled system L. The minor Na-dependent component of glutamine transport resembled system A, i.e., it transported N-methylaminoisobutyric acid (Km approximately equal to 10 microM, Vmax approximately equal to 1.2 nmol.g-1.min-1). At 0.5 mM glutamine transport was insensitive to insulin and glucagon and was unaffected by perfusate pH (7.0-7.8). Glutamine extracted by the jejunum is rapidly utilized; at physiological blood glutamine concentrations the basolateral glutamine-transporter flux may thus not only restrict intestinal glutamine catabolism but also the consequent release of glutamine-derived ammonia (a substrate and stimulant of ureogenesis) into the portal circulation.
Medium-chain fatty acids increase glucose production in normal and low birth weight newborns
Authors: Bougneres P. F. , Castano L. , Rocchiccioli F. , Gia H. P. , Leluyer B. , Ferre P.
Published: December 2017

To study the pathogenesis of hypoglycemia in low birth weight infants, glucose production was measured in five hypotrophic and four premature newborns with glycemia of 45 +/- 6 and 59 +/- 10 mg/dl, respectively. Hepatic glucose output averaged 5.7 +/- 0.4 and 5.3 +/- 0.5 mg.kg-1.min-1 in these neonates vs. 8.2 +/- 0.5 mg.kg-1.min-1 in five normal at term newborns and was correlated with glycemia (P less than 0.02). Despite normal plasma free fatty acids, the low birth weight infants had low ketone levels of 163 +/- 72 and 126 +/- 65 vs. 263 +/- 60 microM in normals. Oral administration of medium-chain triglycerides to the neonates increased their circulating ketones by two- to threefold and restored near-normal glycemia (51 +/- 9 and 76 +/- 8 mg/dl) and production of glucose (6.7 +/- 0.7 and 6.6 +/- 0.8 mg.kg-1.min-1) in the hypotrophic and premature vs. normals (8.7 +/- 0.7 mg.kg-1.min-1). Individual rates of glucose production correlated with ketone concentrations (P less than 0.02). We conclude that the hypoglycemia characterizing low birth weight neonates is primarily due to impaired glucose production. That exogenous lipids were able to increase glucose production indicates that fatty acid oxidation plays an important glucoregulatory role in the human newborn.
Mobilization of glucoregulatory hormones and glucose by hypothalamic locomotor centers
Authors: Vissing J. , Iwamoto G. A. , Rybicki K. J. , Galbo H. , Mitchell J. H.
Published: December 2017

Recent studies suggest that, in addition to classical humoral metabolic feedback mechanisms, the mobilization of glucoregulatory hormones and glucose in exercise may be regulated by motor centers in the brain. We, therefore, studied the effect of electrically stimulating the posterior hypothalamic locomotor region (PHLR) for 10 min in decorticated (n = 6) and alpha-chloralose-anesthetized (n = 8) cats. Blood pressure and heart rate were measured, and blood samples were drawn for analysis of hormones and metabolites before, during, and after 10 min of PHLR stimulation. Feedback from contracting muscles was prevented by neuromuscular blockade in decorticated cats and by the anesthesia in anesthetized cats. In decorticated cats, PHLR stimulation elicited increases (2 P less than 0.05) in glucose production (delta 54 +/- 16 mumol.min-1.kg-1), plasma glucose (delta 2.2 +/- 0.7 mmol/l), epinephrine (delta 4.9 +/- 1.8 pmol/l), norepinephrine (delta 2.2 +/- 0.9 pmol/l), glucagon (delta 16 +/- 5 pmol/l), decreases (2 P less than 0.05) in plasma insulin (delta 27 +/- 7 pmol/l), and increases (2 P less than 0.05) in blood pressure (delta 48 +/- 9 mmHg) and heart rate (delta 26 +/- 7 beats/min). In anesthetized cats, PHLR stimulation elicited increases (2 P less than 0.05) in glucose production (delta 12 +/- 4 mumol.min-1.kg-1), plasma glucose (delta 0.4 +/- 0.1 mmol/l), blood pressure (delta 39 +/- 7 mmHg), and heart rate (delta 28 +/- 7 beats/min), whereas changes in catecholamine and insulin concentrations did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)
Stimulation of plasma inactive renin by dexamethasone in the cat
Authors: Glorioso N. , Troffa C. , Tonolo G. , Melis M. G. , Manunta P. , Soro A. , Madeddu P. , Pazzola A. , Pala F.
Published: December 2017

An inactive form of renin in human plasma is the biosynthetic precursor, prorenin. The cat is a good animal model for studies of inactive renin. The gene for human renin contains sequences homologous to the glucocorticoid consensus sequence. The response of cat plasma (active and inactive renin) and of angiotensinogen to administration of dexamethasone (0.5 mg/kg im, daily) was studied in ketamine-sedated cats (20 mg/kg im). Inactive renin increased by twofold after 7 days of dexamethasone (P less than 0.01). After a 7-day recovery period, it returned to base line. Active renin did not change. Angiotensinogen fell by 35% (P less than 0.01). The time course of the selective increase of plasma inactive renin showed that inactive renin began to rise after 2 days, peaking after 5 days. Ketamine alone induced inactive renin to rise slightly but significantly (P less than 0.05), although the magnitude of the increment was much less than that observed in ketamine-sedated cats receiving dexamethasone (P less than 0.01). Active renin did not change, whereas angiotensinogen was reduced by 25% (P less than 0.01). Our findings support the hypothesis that glucocorticoids might have a selective role in the synthesis and/or secretion of the precursor of renin, at least in the cat.
Effects of age and level of physical activity on plasma norepinephrine kinetics
Authors: Poehlman E. T. , McAuliffe T. , Danforth E.
Published: December 2017

We examined the effects of age and physical activity on plasma norepinephrine (NE) kinetics in active and inactive older and younger men. NE kinetics were estimated by calculation of the rates of NE appearance and clearance during infusion of tritiated norepinephrine [( 3H]-NE). Older active men had the highest level of plasma NE (pg/ml) and NE appearance (microgram.min-1.FFW-1, where FFW is fat-free weight) relative to younger men and inactive older men. NE clearance (l.min-1.FFW-1) was not influenced by age or physical activity. No significant associations were noted between percent body fat, supine blood pressure with resting levels of NE, NE appearance, and NE clearance. We concluded that 1) chronic participation in physical activity by older men, but not younger men, is associated with higher resting levels of plasma NE and NE appearance and 2) the degree of adiposity does not influence plasma NE kinetics in healthy younger and older men. The level of physical activity is an influencing factor on plasma NE and NE appearance into circulation in healthy older men.
Sensitivity to Cd2+ but resistance to Ni2+ of Ca2+ inflow into rat pancreatic islets
Authors: Plasman P. O. , Hermann M. , Herchuelz A. , Lebrun P.
Published: December 2017

The presence of different types [long lasting (L) and transient (T)] of active voltage-operated Ca2+ channels in islet cells was investigated by comparing the effects of Cd2+, Ni2+, and 1,4-dihydropyridines on 45Ca uptake, 45Ca efflux, and insulin release in intact rat pancreatic islets. In several other excitable cells the L-channel has been shown to be modulated by 1,4-dihydropyridines and Cd2+, whereas the T-channel was reported to be sensitive to Ni2+. Nifedipine and Cd2+ inhibited whereas BAY K 8644 enhanced the glucose (11.1, 22.2 mM)-stimulated short-term 45Ca uptake, 45Ca efflux, and insulin release. In contrast, the stimulatory effects of glucose (11.1, 22.2 mM) on 45Ca uptake, 45Ca efflux, and insulin release were unaffected by Ni2+. These findings confirm that glucose provokes Ca2+ entry mainly by activating voltage-sensitive Ca2+ channels of the L-type and suggest that the B-cell plasma membrane is not equipped with active T-type Ca2+ channels.
Effects of antimineralocorticoid RU 26752 on steroid-induced hypertension in rats
Authors: Kalimi M. , Opoku J. , Agarwal M. , Corley K.
Published: December 2017

The effect of mineralocorticoid antagonist RU 26752 on the development and maintenance of hypertension produced by long-term administration of mineralocorticoid agonist aldosterone has been investigated. Uninephrectomized, saline-drinking male Sprague-Dawley rats were subcutaneously implanted with either placebo (control) pellets or pellets containing 100 micrograms aldosterone, 50 mg RU 26752, or 100 micrograms aldosterone plus 50 mg RU 26752. Aldosterone treatment resulted in an increase in blood pressure to 165 +/- 5 mmHg over the control value of 105 +/- 2 mmHg within 3 wk of experimental period. RU 26752 given alone had no observable hypertensinogenic effect. However, RU 26752 administered with aldosterone significantly prevented the hypertension produced by aldosterone alone. RU 26752 when given with aldosterone was able to prevent the aldosterone-induced increase in saline consumption, increase urine output, and reduce urinary Na+ excretion. The results presented suggest that long-term administration of antimineralocorticoid RU 26752 in vivo to Sprague-Dawley rats prevents the aldosterone-induced hypertension.
Constant specific activity input allows reconstruction of endogenous glucose concentration in non-steady state
Authors: Cobelli C. , Toffolo G.
Published: December 2017

In vivo studies on the glucose system often require its perturbation by an exogenous input of glucose, whereas glucose turnover is assessed by infusing a glucose tracer. The constant infusion represents the usual format of tracer administration, but it has no clear advantage other than simplicity. Here we propose a different tracer infusion format. It consists of infusing the tracer in parallel with unlabeled glucose so as to maintain a constant specific activity in the infusate. This protocol does not increase experimental complexity and provides new information on the glucose system in non-steady state by allowing reconstruction of the endogenous component of glucose concentration. This reconstruction only requires very general assumptions, such as tracer-tracee indistinguishability and mass conservation; in particular it is independent of the glucose model structure, i.e., number of compartments and their interconnections. A proof of the result is given for a general nonlinear model of the glucose system. The constant specific activity input is also advantageous for non-steady-state calculations, because it reduces the variation in the measured plasma glucose specific activity. The glucose system has served as the prototype, but the protocol is applicable to other blood-borne substances. The radioactive tracer case has been considered, but the same results apply to stable isotope tracers as well; in this case they also become relevant in a somewhat different context, i.e., kinetic studies in steady state.
Endurance training increases metabolic rate and norepinephrine appearance rate in older individuals
Authors: Poehlman E. T. , Danforth E.
Published: December 2017

We examined the effects of an 8-wk endurance training program (cycling exercise) on resting metabolic rate (RMR) and norepinephrine (NE) kinetics in 19 older persons (64 +/- 1.6 yr). Before and after training, RMR, NE kinetics, maximal O2 consumption (VO2max), body composition, supine blood pressure, estimated energy intake, and fasting levels of glucose, insulin, and thyroid hormones were measured. RMR increased 10% after training. Resting concentrations of NE increased 24% after training due to a 21% increase in NE appearance rate and no change in NE clearance. Training increased VO2max (14%; P less than 0.01) and energy intake (12%; P less than 0.01), whereas no change was noted in body composition. Supine blood pressure and plasma glucose were lower after training, whereas no change was noted in fasting levels of plasma insulin. The increase in RMR was associated with a higher rate of NE appearance (r = 0.57; P = 0.05) and with increase in energy intake (r = 0.56; P = 0.05). Together these two factors accounted for 49% (r2) of the variation of the change in RMR. Changes in blood pressure were not associated with changes in NE kinetics. We conclude that endurance training increases total energy expenditure in older individuals by the direct energy cost of physical activity and by elevating RMR. This increase is partially mediated by an increased NE appearance rate and increased food intake in healthy older individuals.
Ventromedial hypothalamic stimulation enhances peripheral glucose uptake in anesthetized rats
Authors: Sudo M. , Minokoshi Y. , Shimazu T.
Published: December 2017

Effects of electrical and chemical stimulation of the ventromedial (VMH) and lateral hypothalamic (LH) nuclei on glucose uptake in peripheral tissues were studied by the 2-deoxy-D-[3H]glucose (2-[3H]DG) method in anesthetized rats. Electrical stimulation of the VMH increased the rate constant of glucose uptake in brown adipose tissue (BAT; 8 times), heart (3 times), and skeletal muscles (1.5 times) but not in white adipose tissue, diaphragm, and brain, without detectable changes in plasma insulin levels. Chemical stimulation of the VMH by microinjection of L-glutamate also enhanced the rate constant of glucose uptake in BAT, heart, and skeletal muscles preferentially, which indicates that the enhancement of glucose uptake in these tissues is derived from activation of VMH neurons. The increased rate of glucose uptake in BAT in response to VMH stimulation was effectively suppressed by surgical sympathetic denervation, suggesting a mediation of the sympathetic nerve in this effect. On the other hand, electrical stimulation of the LH had no appreciable effect on 2-[3H]DG uptake in any tissues. It is concluded that glucose uptake in certain peripheral tissues is accelerated selectively by activation of VMH neurons, the action of which is independent of plasma insulin but which is probably via the sympathetic nervous system.
In vivo location of the rate-limiting step of hexose uptake in muscle and brain tissue of rats
Authors: Furler S. M. , Jenkins A. B. , Storlien L. H. , Kraegen E. W.
Published: December 2017

The uptake of glucose proceeds via facilitated transport from the plasma followed by phosphorylation of intracellular glucose. We have quantified the relative contribution of transport and phosphorylation to the overall rate of hexose utilization into the quadriceps muscle (red and white) and cerebellum of rats anesthetized with pentobarbital sodium. The method employed simultaneous infusions of radiolabeled 3-O-methyl-D-glucose and 2-deoxy-D-glucose. Results were expressed in terms of a parameter ft*, which has theoretical limits of 0 and 1 corresponding to phosphorylation and transport limitation, respectively. In cerebellum, basal rates of transport and phosphorylation were comparable (ft* = 0.32 +/- 0.02). Under conditions of hyperglycemia plus maximum insulin stimulation, phosphorylation limited glucose utilization to a greater extent (ft* = 0.12 +/- 0.02). No effect of hyperinsulinemia alone was observed. In red muscle, transport determined overall glucose utilization in the basal (ft* = 0.96 +/- 0.05) and euglycemic insulin-stimulated states (ft* = 0.90 +/- 0.02). A shift of the rate-limiting step from transport toward phosphorylation was observed in insulin-stimulated red muscle when blood glucose (ft* = 0.64 +/- 0.05) or epinephrine levels (ft* = 0.66 +/- 0.07) were elevated. Neither effect was seen in white muscle. We conclude that the transport step dominates but is not the only determinant of muscle hexose utilization under all conditions.
Cephalic phase insulin release in normal weight males: verification and reliability
Authors: Teff K. L. , Mattes R. D. , Engelman K.
Published: December 2017

The existence and reliability of cephalic phase insulin release (CPIR) were tested in 20 normal weight males. Each subject was challenged three times with the same food stimulus over a 5-day period. Four baseline blood samples were taken at 5-min intervals before food ingestion and then every 2 min for 16 min postingestion. Significant increases in plasma insulin were found at 4 min postingestion on each trial day. CPIR was found to be highly reproducible between trials (r = 0.83; P less than 0.001). Fifty percent of the subjects exhibited a significant increase of plasma insulin above their own baseline mean on the first trial, whereas 75 and 72% exhibited increases on trials 2 and 3, respectively. Only two subjects (10%) did not demonstrate a response on any trial. A significant decline in plasma glucose was observed at 4 min postingestion on trials 2 and 3. No significant changes in plasma glucagon were found during any trial day. This study confirms a reliable CPIR in normal weight males.
Regulation of lipolysis and ketogenesis by norepinephrine in conscious dogs
Authors: Connolly C. C. , Steiner K. E. , Stevenson R. W. , Neal D. W. , Williams P. E. , Alberti K. G. , Cherrington A. D.
Published: December 2017

The lipolytic and ketogenic effects of norepinephrine (NE) at levels present in the circulation or the synaptic cleft during stress were examined in the overnight-fasted conscious dog. Insulin and glucagon were maintained at basal levels while NE, at a rate of either 0.04 (n = 6) or 0.32 micrograms.kg-1.min-1 (n = 5), or saline (n = 6) was infused for 3 h. NE rose from 129 +/- 17 to 442 +/- 85 pg/ml (P less than 0.05) and 100 +/- 24 to 3,244 +/- 807 pg/ml (P less than 0.05) with the low and high infusion rates, respectively (unchanged with saline infusion). There were no significant changes in lipolysis or ketogenesis with saline infusion. Both low and high NE infusion produced sustained increases in glycerol (from 72 +/- 20 to 119 +/- 24 microM and 59 +/- 19 to 248 +/- 32 microM, respectively, both P less than 0.05), while nonesterified fatty acids (NEFA) rose from 609 +/- 85 to 952 +/- 100 and 767 +/- 140 to 2,054 +/- 199 microM (both P less than 0.05). Ketone levels and net hepatic production rose significantly only with the high NE infusion (from 88 +/- 10 to 266 +/- 46 microM and 1.30 +/- 0.26 to 7.62 +/- 1.48 mumol.kg-1.min-1, respectively, both P less than 0.05). The ratio of net hepatic ketone production to NEFA uptake rose 54% with high NE infusion. In conclusion, at circulating levels seen during stress, NE stimulates lipolysis but does not directly influence ketogenesis. At circulating levels projected to exist in the synaptic cleft during stress, NE has a potent lipolytic effect and stimulates ketogenesis.
Neuronal uptake, metabolism, and release of tritium-labeled norepinephrine during assessment of its plasma kinetics
Authors: Eisenhofer G. , Esler M. D. , Goldstein D. S. , Kopin I. J.
Published: December 2017

The extent to which intravenously infused [3H]norepinephrine ([3H]NE) is stored within and released by sympathetic nerves (tracer recycling) was examined by assessment of its plasma concentrations and by those of its intraneuronal metabolite dihydroxyphenylglycol (DHPG). Tracer recycling, as assessed by perturbations to steady-state plasma [3H]NE, was not apparent in humans during sympathetic activation by orthostasis or exercise. During intense electrical stimulation of cardiac sympathetic nerves after an [3H]NE infusion in dogs, plasma [3H]NE was higher in coronary sinus than arterial plasma, consistent with tracer recycling by cardiac sympathetic nerves. The specific activity of released [3H]NE was similar to that of [3H]NE and [3H]DHPG in cardiac tissue, indicating that both released [3H]NE and [3H]DHPG were derived from the same pool of neuronally stored [3H]NE. During intravenous infusion of [3H]NE in humans, plasma [3H]NE reached a steady state within 12 min and remained constant, whereas plasma [3H]DHPG increased progressively, reflecting metabolism of an increasing amount of [3H]NE leaking from sympathetic vesicles. Plasma concentrations of [3H]DHPG approached or exceeded those of [3H]NE after the end of radiotracer infusions and in the venous drainage of the heart and liver. Thus, to avoid error during assessment of plasma [3H]NE kinetics, an analytical step should be employed to separate plasma [3H]DHPG from [3H]NE. Because [3H]DHPG is derived from [3H]NE within the neuron, the specific activity of neuronally stored [3H]NE could be assumed to be no higher than the specific activity of plasma [3H]DHPG. This provided a means to estimate the maximum extent of tracer recycling, thereby indicating that, during intravenous infusion of [3H]NE, tracer recycling contributed negligibly (less than 5%) to steady-state plasma [3H]NE at normal levels of sympathetic activity.
Big ANF: large-molecular-weight ANF in rabbit plasma. II. Acid dissociation and HPLC of dissociated irANF
Authors: Wilson N. , Yakoleff V. , Claybaugh J. R.
Published: December 2017

A large-molecular-weight form of atrial natriuretic factor (ANF) was found in rabbit plasma. When extraction of plasma utilizing octadecylsilane cartridges is employed, this big ANF is not retained by the cartridge. When this material is dissociated with acid, immunoreactive ANF (irANF) is released. Of the acids tested, formic and acetic acid (0.05 M) were indicated as the most effective in causing the dissociation. High-performance liquid chromatography analysis of dissociated ANF, confirmed by coelution with synthetic peptides, disclosed the presence of ANF-(99-126) and ANF-(103-126) in a ratio of approximately 2:1. Atriopeptin I was detected in most of the samples analyzed, but atriopeptin II was only detected in one analysis. Despite the wide spectrum of the antiserum used for detection of irANF in the eluent fractions, only immunoreactive peaks coeluting with the four standards were detected. We therefore conclude that big ANF is a bound form of atrial peptides found in normal circulation.
How valid are isotopic measurements of fatty acid oxidation?
Authors: Heiling V. J. , Miles J. M. , Jensen M. D.
Published: December 2017

These studies were performed 1) to compare two isotopic methods (3H2O and 14CO2 production) of measuring free fatty acid (FFA) oxidation; 2) to determine whether isotopic estimates of fatty acid oxidation during hypoinsulinemia are plausible when compared with those obtained using indirect calorimetry; and 3) to examine whether the delay between the exit of [14C]FFA from plasma and the appearance of 14CO2 in breath is accounted for solely by bicarbonate kinetics. Studies in 11 healthy volunteers revealed that [14C]- and [3H]FFA tracers provide similar estimates of FFA turnover and oxidation. Isotopic estimates of fatty acid oxidation were less than those of indirect calorimetry under basal conditions but equaled or exceeded indirect calorimetry estimates after 3 h of acute hypoinsulinemia (somatostatin induced). After stopping tracer infusions, the half-life of plasma [14C]FFA was 3.7 +/- 0.1 min. The half-life of 14CO2 decay from [14C]bicarbonate was 37 +/- 1 min, and the half-life of 14CO2 decay after discontinuation of [14C]FFA infusion was 141 +/- 10 min. Intracellular preoxidative fatty acid pools (possibly triglycerides) most probably account for the marked delay between the exit of FFA tracers from plasma and the appearance of isotopic markers of oxidation in measurable spaces. This delay can result in erroneous estimates of “FFA oxidation.” We conclude that tracer measurements of FFA oxidation are invalid under most circumstances.
Effects of recombinant IGF-I on protein and glucose metabolism in rTNF-infused lambs
Authors: Douglas R. G. , Gluckman P. D. , Breier B. H. , McCall J. L. , Parry B. , Shaw J. H.
Published: December 2017

Achieving nitrogen accretion in patients with critical surgical illness or cancer cachexia is often not possible by the simple provision of calories and nitrogen. Cachexia may result from the metabolic derangements caused by release of inflammatory mediators such as tumor necrosis factor (TNF). We wished to determine whether recombinant human insulin-like growth factor I (rhIGF-I) preserves its protein-sparing effects in the face of high plasma TNF concentrations. Primed constant infusions of [15N]urea and [6-3H]glucose tracers were used to measure protein and glucose kinetics in fasted lambs. The lambs were divided into four groups: two groups received normal saline infusions of 480 min, and two groups received recombinant TNF (rTNF) infusions of 1 microgram.kg-1.h-1. During the last 300 min, one of the normal saline and one of the rTNF-infused groups were infused with rhIGF-I at a dose of 50 micrograms.kg-1.h-1. rTNF infusion resulted in the lambs becoming febrile and significantly increased plasma cortisol, glucagon, and insulin levels. rhIGF-I infusion in the control animals reduced the rate of loss of protein by 15% (P less than 0.01) and increased the rate of peripheral glucose clearance by 55% (P less than 0.01). rhIGF-I infusion in the rTNF-treated animals reduced the rate of net protein loss by 15% (P less than 0.01) and caused similar changes in glucose kinetics, as were observed in the control animals. We conclude that as rhIGF-I preserves its protein anabolic action in the face of high rTNF levels, further investigation into a possible clinical role for rhIGF-I in severe surgical illness is warranted.
Mechanisms of increased lipoprotein lipase in fat cells of obese Zucker rats
Authors: Fried S. K. , Turkenkopf I. J. , Goldberg I. J. , Doolittle M. H. , Kirchgessner T. G. , Schotz M. C. , Johnson P. R. , Greenwood M. R.
Published: December 2017

The mechanisms underlying the increased activity of lipoprotein lipase (LPL) in adipocytes of genetically obese Zucker rats was studied. Relative rates of LPL synthesis (percent of total protein synthesis) determined by biosynthetic labeling and specific immunoprecipitation were similar in isolated fat cells from lean and obese rats, in the absence or presence of insulin. Insulin stimulated LPL synthesis as a result of a general increase in protein synthesis, and this effect was more marked in the obese fat cells. Levels of LPL mRNA, as a percent of total RNA, were also similar in fat cells from lean and obese rats. In contrast, when the data are calculated on a per fat cell basis, rates of LPL synthesis per fat cell are ninefold higher in obese compared with lean cells, accounting for the increase in LPL activity per fat cell. Fat cells from lean and obese rats showed similar rates of binding and degradation of purified bovine milk 125I-labeled LPL per unit fat cell surface area. Thus, on a per cell basis, rates of LPL turnover are increased in enlarged Zucker rat adipocytes, but there is no specific abnormality in the cellular regulation of LPL. Increases in LPL activity in obese rat adipocytes are related to an overall hyperresponsiveness to insulin effects on protein synthesis.
Interaction of ANP with endothelin on cardiovascular, renal, and endocrine function
Authors: Ota K. , Kimura T. , Shoji M. , Inoue M. , Sato K. , Ohta M. , Yamamoto T. , Tsunoda K. , Abe K. , Yoshinaga K.
Published: December 2017

To assess the interaction of endothelin (ET) with atrial natriuretic peptide (ANP) on cardiovascular and renal function, arginine vasopressin (AVP) release, and the renin-angiotensin-aldosterone system, either a low or high dose of ET (4 or 12 pmol.kg-1.min-1) was administered with ANP (26 pmol.kg-1.min-1) for 45 min after the initial infusion of ANP alone in anesthetized dogs. In the other groups, either ANP or saline alone was administered for 90 min. ANP alone decreased blood pressure (BP), cardiac output (CO), plasma aldosterone, and plasma renin activity (PRA), increased urinary Na and K excretion (UNaV and UKV, respectively) and urine flow (UF), but did not affect plasma AVP. The low dose of ET had no effect on these ANP-induced changes. However, the high dose of ET curtailed the responses to ANP, increased BP and PRA, and decreased UNaV, UKV, and UF associated with decreased renal plasma flow and glomerular filtration rate. High ET also further potentiated the decrease in CO and the increase in total peripheral resistance induced by ANP and increased plasma AVP. These results indicate that a dose of ET one-half that of ANP (on the molar ratio) may have completely counteracted vascular, hormonal, and renal responses to ANP.
Role of cAMP in mediating effects of fasting on dephosphorylation of insulin receptor
Authors: Begum N. , Graham A. L. , Sussman K. E. , Draznin B.
Published: December 2017

We studied the effect of fasting on phosphotyrosine phosphatase (PTPase) activities in particulate (PF) and cytosolic (CF) fractions of rat adipocytes and liver. PTPase activity was assessed using [32P]tyrosine insulin receptor (IR). In adipocytes, 48 h fasting significantly inhibited PTPase activity. Dephosphorylation of IR by PF and CF PTPases was reduced by 80 and 65%, respectively. Similar reductions of lesser magnitude were observed in fasted rat livers. The effect of fasting was completely reversed by either refeeding or by incubating "fasted" adipocytes for 2 h in tissue culture medium containing 5 mM glucose. Neither 20 mM glucose nor the presence of insulin influenced phosphatase activity. Because fasting is accompanied by elevated protein kinase C (PKC) and adenosine 3',5'-cyclic monophosphate (cAMP) levels, we examined their influence on adipocyte PTPases. Neither activation (1 microM 12-O-tetradecanoylphorbol-13-acetate) nor inhibition (20 microM sphingosine) of PKC affected PTPase activity. In contrast, cAMP (2 mM) significantly inhibited PTPase activity (80% inhibition at 2 h), and its effect was prevented by a cAMP antagonist RpcAMP. Fasting- and cAMP-induced inhibition of PTPase activity was restored by incubating PF with trypsin (4 micrograms/ml for 5 min), which separated the putative inhibitors from the phosphatases. We conclude that fasting-induced inhibition of PTPases is mediated by elevated cAMP levels, most likely by activating phosphatase inhibitors.
Uncomplicated surgery, but not general anesthesia, decreases muscle protein synthesis
Authors: Essen P. , McNurlan M. A. , Wernerman J. , Vinnars E. , Garlick P. J.
Published: December 2017

The impact of anesthesia and surgery on protein metabolism is not well characterized. The single effect of general anesthesia and the combined effects of surgery and general anesthesia on protein synthesis in skeletal muscle were studied in metabolically healthy patients (n = 14) undergoing elective abdominal surgery. The rate of muscle protein synthesis was calculated from the increase in enrichment of [1-13C]leucine in protein during 90 min after an intravenous infusion of [1-13C]leucine (0.05 g/kg, 20 atom percent excess). The 1-13C enrichments of plasma leucine and plasma alpha-ketoisocaproate were used to indicate the enrichment of muscle free leucine. The protein synthesis rate was unaffected by general anesthesia; however, at the end of surgery, a 31.5% decline was seen from 2.19(2.13,2.33)%/24 h before anesthesia to 1.50(1.21,1.77)%/24 h (P less than 0.05) immediately after cholecystectomy while the patients were still under general anesthesia.
Vasopressin regulates human sleep by reducing rapid-eye-movement sleep
Authors: Born J. , Kellner C. , Uthgenannt D. , Kern W. , Fehm H. L.
Published: December 2017

In two double-blind experiments, effects of intravenous infusion of arginine vasopressin (AVP) on sleep were evaluated in 2 groups of 10 men (20-35 yr). In experiment I, subjects were tested on two occasions, during which they received either placebo or 0.33 IU/h AVP. In experiment II, on three different occasions, subjects received either placebo or 0.66 or 0.99 IU/h AVP. Infusions were administered between 2200 and 0700 h. Nocturnal plasma AVP concentrations were close to the upper limit of the normal physiological range during 0.66 IU/h AVP (16.6 +/- 2.2 pg/ml) but markedly exceeded this range during 0.99 IU/h AVP (25.0 +/- 1.6 pg/ml). Results indicate primary effects of AVP on rapid-eye-movement (REM) sleep, with moderate reductions in REM sleep during 0.33 IU/h AVP (averaging -10.5%) and with substantial reductions in REM sleep (-24.0%) during 0.66 IU/h AVP. During 0.99 IU/h AVP the effect did not further increase (-24.4%). Less consistent effects of AVP were an increase in stage 2 sleep and in time awake. Effects of AVP were not mediated by changes in cortisol or blood pressure. Results suggest AVP to participate in REM sleep regulation under normal physiological conditions.
Role of brain kallikrein-kinin system in regulation of adrenocorticotropin release
Authors: Madeddu P. , Anania V. , Alagna S. , Troffa C. , Parpaglia P. P. , Tonolo G. , Demontis M. P. , Varoni M. V. , Fattaccio C. , Glorioso N.
Published: December 2017

We evaluated whether the brain kallikrein-kinin system plays a role in the regulation of adrenocorticotropin (ACTH) release in rats. Intracerebroventricular (icv) injection of bradykinin (0.24 nmol) increased plasma immunoreactive ACTH (irACTH) levels (from 93 +/- 4 to 200 +/- 12 pg/ml, P less than 0.01). This effect was prevented by icv kinin antagonist at 15.4 nmol/h (from 98 +/- 5 to 108 +/- 6 pg/ml; not significant). The antagonist did not alter the increase in plasma irACTH levels induced by icv corticotropin-releasing factor (CRF), arginine vasopressin, or prostaglandin E2. Melittin (7 nmol/h icv) increased plasma irACTH from 95 +/- 4 to 268 +/- 7 pg/ml (P less than 0.01). This effect was prevented by icv kinin antagonist (15.4 nmol/h), kallikrein antibodies (13 pmol/h), or indomethacin (0.28 mmol/h). ACTH response to melittin was not altered by antagonists of CRF or vasopressin. Intra-arterial injection of insulin (0.3 IU/kg body wt) reduced plasma glucose levels to a similar extent in rats given icv kinin antagonist or vehicle; the ACTH response to insulin-induced hypoglycemia was slightly less in rats given kinin antagonist than in those given vehicle (55 +/- 5 vs. 86 +/- 4 pg/ml, P less than 0.05). The brain kallikrein-kinin system may play a role in the regulation of ACTH secretion in stimulated conditions.
Increased serum clearance and degradation of 125I-labeled IGF-I in protein-restricted rats
Authors: Thissen J. P. , Davenport M. L. , Pucilowska J. B. , Miles M. V. , Underwood L. E.
Published: December 2017

Dietary protein restriction in young rats stunts growth and decreases serum insulin-like growth factor I (IGF-I) concentrations. To investigate the possibility of a diet-induced accelerated clearance of IGF-I, the clearance of 125I-labeled IGF-I was determined by measuring the radioactivity in serum obtained at different intervals after bolus injection in 5-wk-old rats that had received either a normal 15% protein diet (P15; n = 6) or a 5% protein isocaloric diet (P5; n = 7) for 1 wk. The clearance and volume of distribution of 125I-IGF-I were increased in P5 rats by 58 and 75%, respectively, whereas the terminal elimination half-life was not changed. The calculated IGF-I production rate was decreased by 40% in P5 rats. The intermediate distribution phase (alpha) was twofold faster in P5 than in P15 animals, and 125I-IGF-I was preferentially bound to IGF binding proteins in the 40-kDa complex in P5 rats. These observations might explain the increased clearance and degradation of IGF-I in the P5 rats. Dietary protein restriction appears to lower serum IGF-I concentrations by both decreasing its production rate and increasing its clearance.
Effect of hypercorticism on regulation of skeletal muscle glycogen metabolism by insulin
Authors: Coderre L. , Srivastava A. K. , Chiasson J. L.
Published: December 2017

The effects of hypercorticism on the regulation of glycogen metabolism by insulin in skeletal muscles was examined by using the hindlimb perfusion technique. Rats were injected daily with either saline or dexamethasone (0.4 mg.kg-1.day-1) for 14 days and were studied in the fed or fasted (24 h) state under saline or insulin (1 mU/ml) treatment. In fed controls, insulin resulted in glycogen synthase activation and in enhanced glycogen synthesis. In dexamethasone-treated animals, basal muscle glycogen concentration remained normal, but glycogen synthase activity ratio was decreased in white and red gastrocnemius and plantaris muscles. Furthermore, insulin failed to activate glycogen synthase and glycogen synthesis. In the controls, fasting was associated with decreased glycogen concentrations and with increased glycogen synthase activity ratio in all four groups of muscles (P less than 0.01). Dexamethasone treatment, however, completely abolished the decrease in muscle glycogen content as well as the augmented glycogen synthase activity ratio associated with fasting. Insulin infusion stimulated glycogen synthesis in fasted controls but not in dexamethasone-treated rats. These data therefore indicate that dexamethasone treatment inhibits the stimulatory effect of insulin on glycogen synthase activity and on glycogen synthesis. Furthermore, hypercorticism suppresses the decrease in muscle glycogen content associated with fasting.
Gonadotropin and cAMP modulation of IGE binding protein production in ovarian granulosa cells
Authors: Grimes R. W. , Samaras S. E. , Barber J. A. , Shimasaki S. , Ling N. , Hammond J. M.
Published: December 2017

Porcine granulosa cells (GC) produce insulin-like growth factor (IGF) binding protein (BP)-3 and IGFBP-2 in culture. A gonadotropin, follicle-stimulating hormone (FSH), dramatically inhibited GC production of these IGFBPs in control cultures and in cultures stimulated by insulin plus epidermal growth factor (EGF) or IGF-I plus EGF. Stimulators of adenylate cyclase (forskolin, cholera toxin) and a derivative of adenosine 3',5'-cyclic monophosphate (cAMP), 8-bromoadenosine 3',5'-cyclic monophosphate, inhibited IGFBP synthesis in a manner similar to FSH. In contrast, the antagonist of cAMP action, (R)-p-adenosine 3',5'-cyclic phosphorothioate [(R)-p-cAMPS], significantly stimulated production of IGFBP-3 and IGFBP-2 compared with controls. This stimulatory effect of (R)-p-cAMPS was counteracted by cotreatment with FSH in a dose-dependent manner. Finally, treatment of GC cultures with FSH plus 3-isobutyl-1-methylxanthine resulted in a significant reduction in cellular content of mRNA coding for IGFBP-3 with no change in IGFBP-2 mRNA. In summary, agents that elevate intracellular cAMP were found to mimic the effects of FSH on IGFBP production.
Effects of insulin and dexamethasone on lipoprotein lipase in human adipose tissue
Authors: Appel B. , Fried S. K.
Published: December 2017

The mechanisms by which insulin and glucocorticoids modulate lipoprotein lipase (LPL) synthesis and degradation were examined in human adipose tissue fragments maintained in organ culture. Tissue fragments were cultured for 7 days in serum-free medium supplemented with or without insulin (7 nM) and with or without dexamethasone (30 nM), a synthetic glucocorticoid. Responses of LPL activity to both insulin and dexamethasone were obtained at doses within the physiological range. At a maximal dose, insulin increased heparin-releasable and total LPL activity (approximately 7-fold) by specifically increasing the rate of LPL synthesis (approximately 5-fold) determined by pulse labeling with [35S]methionine and [35S]cysteine and immunoprecipitation. Dexamethasone added in the presence of insulin increased heparin-releasable and total LPL activity approximately 8-fold but did not alter rates of LPL synthesis compared with insulin alone. Pulse-chase studies showed that the rate of LPL degradation was markedly slowed in the presence of dexamethasone plus insulin compared with insulin alone. These data suggest that, in human adipose tissue, insulin is essential for maintaining rates of LPL synthesis and that cortisol may play a key role in regulating human adipose tissue LPL at the posttranslational level by inhibiting the degradation of newly synthesized LPL.
Increased plasma FFA uptake and oxidation during prolonged exercise in trained vs. untrained humans
Authors: Turcotte L. P. , Richter E. A. , Kiens B.
Published: December 2017

We studied the effect of local muscle adaptations on free fatty acid (FFA) metabolism during prolonged exercise in trained and untrained subjects. Six trained (T) and six untrained (UT) young human males exercised for 3 h at 60% of their individual maximal dynamic knee extension capacity. The contribution of blood and plasma metabolites as well as intramuscular substrates to oxidative metabolism in the thigh was calculated from arteriovenous differences and femoral-venous blood flow as well as from muscle biopsies in subjects that were continuously infused with [1-14C]palmitate. Arterial plasma FFA concentration increased over time in both T and UT. Fractional uptake of FFA across the thigh remained unchanged over time in T (15%) but decreased in UT (from 15 to 7%), especially during the last hour of exercise. Thus FFA uptake increased linearly over time in T (96 +/- 20 to 213 +/- 20 mumol.min-1.kg-1), whereas it leveled off after 2 h in UT (74 +/- 16 to 133 +/- 46) even though FFA delivery increased similarly in T and UT. Percentage oxidation was similar in T and UT; thus total FFA oxidation was higher in T. Glucose uptake increased in both groups over time and was significantly higher in UT during the last hour of exercise. In conclusion, during prolonged knee extension exercise, FFA uptake increases linearly with FFA delivery in the trained thigh, whereas in the untrained thigh uptake becomes saturated with time. This difference partly explains the increased lipid oxidation in T vs. UT and suggests, furthermore, that local muscle adaptations to training are important for the utilization of FFA during prolonged exercise.
Epinephrine augments cortisol secretion from isolated perfused adrenal glands of guinea pigs
Authors: Mokuda O. , Sakamoto Y. , Kawagoe R. , Ubukata E. , Shimizu N.
Published: December 2017

To determine direct effects of epinephrine on adrenal cortisol secretion, bilateral adrenal glands were isolated from guinea pigs, together with bilateral kidneys, aorta, and inferior caval vein for influent and effluent routes. The preparation was perfused with oxygenated Krebs-Ringer bicarbonate solution (pH 7.4) containing 10 mM glucose, 0.2% bovine serum albumin, and 4.6% dextran. The perfusate cortisol level was elevated by the addition of epinephrine in a dose-dependent manner at concentrations greater than 100 pg/ml and increased eightfold as high as the basal level at 1 micrograms/ml epinephrine. The stimulatory effect of epinephrine on cortisol secretion was completely abolished by phentolamine, an alpha-adrenergic antagonist but was not affected by propranolol, a beta-adrenergic antagonist. These results demonstrate that epinephrine has a direct stimulatory effect on adrenal cortisol secretion via an alpha-adrenergic mechanism and also suggest that not only adrenocorticotropin but also epinephrine is a most important factor for the regulation of cortisol secretion.
Na+-H+ antiport and monensin effects on cytosolic pH and iodide transport in FRTL-5 rat thyroid cells
Authors: Smallridge R. C. , Gist I. D. , Kiang J. G.
Published: December 2017

Na+-H+ exchange may proceed via an endogenous antiporter or by exposure to the Na+ ionophore monensin. We investigated the characteristics of Na+-H+ exchange induced by antiporter stimulation and by monensin in FRTL-5 rat thyroid cells. We also examined the effects of intracellular pH (pHi) changes on iodide uptake and efflux. pHi was determined using 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. The resting pHi was 7.33 +/- 0.02 units; this level correlated directly with extracellular pH. In acid-loaded cells, Km for external Na+ activation of the antiporter was 7.1 mM and maximum velocity was 0.3801 delta pH units/min. Dimethylamiloride was 42 times more potent than amiloride in inhibiting sodium-dependent recovery in acidified cells. Metabolic inhibition reduced the initial alkalinization rate. Monensin increased pHi, and this response was dependent on extracellular Na+ and HCO3- but not on antiporter function. Low-dose monensin (1 microM) and 1 mM NH4Cl enhanced 125I uptake. High-dose monensin (100 microM), but not NH4Cl, reduced iodide uptake. Neither NH4Cl nor monensin altered 125I efflux. Thus FRTL-5 cells possess an amiloride-sensitive Na+-H+ exchanger, which is not essential for maintaining basal pHi but is affected by ATP depletion. Monensin also alkalinizes these cells but independently of the antiporter. Iodide uptake, but not efflux, is affected by changes in intracellular Na+ and H+ levels.