bluuebunny/crossref_metadata_2025 huggingface dataset:
Altered partition of threonine metabolism in pigs by protein-free feeding or starvation
Authors: Ballevre O. , Houlier M. L. , Prugnaud J. , Bayle G. , Bercovici D. , Seve B. , Arnal M.
Published: December 2017

Kinetic aspects of threonine (Thr) metabolism were examined in growing pigs fed a well-balanced diet (C), an isocaloric protein-free diet (PF), or starved (S) for 48 h. With the use of continuous simultaneous infusion of L-[1-13C]Thr, [1-14C]sarcosine, and 2-[1-14C]ketobutyrate (KB) for 10 h, estimates were made of rates of Thr incorporated into protein (S), released from body proteins (B), and oxidized through the catabolic pathways of L-Thr 3-dehydrogenase (TDG) and threonine dehydratase (TDH). In the C group S was 185, B was 138, Thr disposal to glycine (DRThr-Gly) was 47, and Thr disposal to KB (DRThr-KB) was 7 mumol.h-1.kg-1. Consequently, Thr balance was +48 mumol.h-1.kg-1. In the PF-fed pigs, S, B, DRThr-Gly, and DRThr-KB were significantly reduced by 38, 15, 74, and 75%, respectively. In the S group, S, B, and DRThr-Gly were significantly reduced by 47, 17, and 55%, respectively, but DRThr-KB was similar to the C group. DRThr-Gly in all groups was highly correlated with TDG enzyme activity measured in liver homogenates. By contrast with in vivo results, TDH enzyme activity was increased by 88% (P less than 0.05) in the S group and decreased by 27% (not significant) in the PF group compared with the C group. The TDH pathway accounted for 13, 12, and 27% of total Thr oxidation in the C, PF, and S groups, respectively. These results suggest that Thr conservation in protein-depleted states (PF and S groups) occurred mainly by a decrease of Thr oxidation and that the partition through these pathways was only altered when energy was completely withdrawn.
Attenuated responses of muscle protein synthesis to fasting and insulin in adult female rats
Authors: Baillie A. G. , Garlick P. J.
Published: December 2017

One-year-old adult female rats were fasted for 12 or 36 h followed by a 30-min infusion of insulin. The responses of the fractional rate of protein synthesis (Ks) in the individual muscles (measured in vivo) to fasting were small and mostly nonsignificant. After 12 h of fasting, only the epitrochlearis muscle (ET) showed a significant decrease in Ks, and, even after 36 h of fasting, a significant decrease in Ks was seen in only ET, extensor digitorum longus, and tensor fasciae latae (TFL). After the 36-h fast, infusion of insulin restored the fed Ks in all muscles except TFL. The fiber-type composition of the individual muscles appeared to influence the muscles' responsiveness to the fasting, since the highly glycolytic TFL was the most sensitive (particularly after 36 h of fasting), whereas the highly oxidative adductor longus and soleus muscles were unaffected by either fasting or insulin. In a second experiment, refeeding of fasted adult rats also had little effect on Ks, consistent with the low sensitivity to fasting shown by the first experiment. The parallel results in the two experiments confirmed that the low responsiveness to fasting and insulin infusion in these adult rats was not a result of failure to absorb in “fed” animals or insufficient levels of insulin during insulin infusions. In contrast, a third experiment showed that muscle protein synthesis in the gastrocnemius muscle from young adult (5-mo-old) female rats was significantly reduced after only 12 h of fasting.
Diverse effects of insulin-like growth factor I on glucose, lipid, and amino acid metabolism
Authors: Boulware S. D. , Tamborlane W. V. , Matthews L. S. , Sherwin R. S.
Published: December 2017

The metabolic effects of recombinant human insulin-like growth factor I (rhIGF-I) on glucose, amino acid, and free fatty acid (FFA) metabolism were examined in nine healthy nonobese subjects. Each received a 3-h primed continuous infusion of rhIGF-I (20 micrograms/kg bolus, 0.4 microgram.kg-1.min-1) while maintaining euglycemia using an exogenous glucose infusion. Total IGF-I levels increased from 125 +/- 11 to 444 +/- 22 ng/ml, and free IGF-I levels rose from undetectable to 73 +/- 5 ng/ml. Insulin levels fell from 95 +/- 9 to 64 +/- 8 pM, and C-peptide fell from 453 +/- 48 to 206 +/- 29 pM; circulating glucagon levels also declined from 72 +/- 9 to 42 +/- 4 pg/ml, rhIGF-I produced a two- to threefold increase in glucose uptake as measured by [3H] glucose (from 10.3 +/- 0.6 to 27.4 +/- 3 mumol.kg-1.m-1), and, despite the fall in insulin secretion, there was a marked 60-70% inhibition of hepatic glucose production. Furthermore, FFA and branched-chain amino acids declined by 40-60% (411 +/- 58 to 165 +/- 36 and 406 +/- 23 to 219 +/- 14 microM, respectively). Our data demonstrate that rhIGF-I has potent effects on glucose (hepatic and peripheral), lipid, and amino acid metabolism in normal humans. The scope of the actions of rhIGF-I closely resemble those of insulin, despite a concomitant inhibitory effect on insulin secretion.
Effects of amiloride analogues on AVP binding and activation of V1-receptor-expressing cells
Authors: Thibonnier M. , Bayer A. L. , Simonson M. S. , Douglas J. G.
Published: December 2017

We tested the interactions between amiloride analogues and V1 vascular arginine vasopressin (AVP) receptors of human platelets, rat glomerular mesangial cells, and A7r5 smooth muscle cells by using radioligand binding techniques, intracellular calcium monitoring, platelet aggregation, and cell contraction techniques. Amiloride analogues were competitive inhibitors of both the agonist [3H]AVP and the tritiated V1 antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-O-methyl)tyrosine]AVP ([3H]d(CH2)5Tyr(Me)AVP) binding to V1 AVP receptors in the three different cell types used. The order of potency was ethylisopropyl amiloride (EIPA) greater than Benzamil greater than amiloride. AVP mobilization of intracellular calcium was blocked by the V1 antagonist d(CH2)5Tyr(Me)AVP and was reduced by EIPA in a dose-dependent manner. Moreover, EIPA also inhibited prostaglandin F2 alpha mobilization of intracellular calcium. Alkalinization of the intracellular pH with ammonium chloride reversed the inhibitory effect of EIPA but not that of the V1 antagonist on AVP-induced calcium mobilization. Both amiloride and EIPA blocked AVP-induced aggregation of human platelets and contraction of mesangial cells and glomeruli preparations independently of receptor site antagonism. In conclusion, amiloride analogues interfere with activation of V1 vascular receptors by AVP at different levels including binding to the receptor site, mobilization of intracellular calcium, cell contraction or aggregation, and presumably alteration of intracellular ion transports.
Relationship between ammonia, heart rate, and exertion in McArdle's disease
Authors: Coakley J. H. , Wagenmakers A. J. , Edwards R. H.
Published: December 2017

We studied plasma ammonia and exercise tolerance in six patients with McArdle's disease (myophosphorylase deficiency, type V glycogenosis) during incremental cycle ergometry. Tests were performed either in the postabsorptive state or after supplementation with branched-chain amino and 2-oxoacids and glucose. Glucose and branched-chain 2-oxoacid combined increased total work performed from control 49 +/- 22 to 80 +/- 36 kJ (P less than 0.05). Glucose alone also improved total work performed from 49 +/- 22 to 64 +/- 33 kJ (P less than 0.05). Branched-chain 2-oxoacids alone had a variable effect, and branched-chain amino acids were of no benefit. Correlations between plasma ammonia and heart rate for individual patients were r = 0.99, P less than 0.01; r = 0.95, P less than 0.01; r = 0.84, P less than 0.01; r = 0.76, P less than 0.01; r = 0.73, P less than 0.01; and r = 0.63, P less than 0.05 and between ammonia and perceived exertion for all patients combined was r = 0.70, P less than 0.0001. In two patients, correlation of ammonia with heart rate at a power output of 60 W was r = 0.91, P less than 0.001 and at 40 W was r = 0.77, P less than 0.001. We conclude that ammonia is either a mediator or a marker of the metabolic events leading to fatigue.
Systemic and regional acetate kinetics in dogs
Authors: Bleiberg B. , Beers T. R. , Persson M. , Miles J. M.
Published: December 2017

Little is known about the sites of production and uptake of acetate in nonruminants. We placed blood sampling catheters in the femoral artery and in the femoral, portal, hepatic, and renal veins of mongrel dogs (n = 11). The animals were studied in the conscious state 2 wk later during a primed continuous infusion of [1-14C]acetate. Systemic acetate turnover, oxidation, and clearance were determined, as well as regional uptake and release, by measuring 14CO2 excretion as well as plasma concentration and specific activity at the five sampling sites. Results showed systemic acetate turnover was 8.8 +/- 1.9 mumol.kg-1.min-1, approximating 5% of energy expenditure in dogs. Simultaneous uptake and release of acetate was demonstrated in intestine, liver, kidney, and hindlimb. The intestine was the greatest contributor to acetate production, whereas the liver was the most important site of uptake. Plasma acetate oxidation was 77 +/- 4% of turnover. Both systemic clearance (129 +/- 22 ml.kg-1.min-1) and tissue fractional extraction (68-85%) were many times greater than values reported for glucose, free fatty acids, lactate, or amino acids. In conclusion, most tissues simultaneously take up and release acetate in dogs. This may represent a mechanism for interorgan transport of energy, especially under conditions of caloric deprivation.
Effects of prorenin on blood pressure and plasma renin concentrations in stroke-prone spontaneously hypertensive rats
Authors: Hosoi M. , Kim S. , Takada T. , Suzuki F. , Murakami K. , Yamamoto K.
Published: December 2017

To examine the possible activation of prorenin in the circulation, recombinant rat prorenin was intravenously given to pentobarbital-anesthetized rats. Bolus injection of prorenin at the dose of 100 micrograms angiotensin I (ANG I).h-1.kg-1 into Wistar rats, leading to a 15-fold increase in plasma prorenin concentrations (from 27 +/- 6 to 393 +/- 75 ng ANG I.h-1.ml-1) at 5 min after the injection, did not affect blood pressure, heart rate, and plasma active renin concentrations throughout experiments. On the other hand, the administration of active renin at the dose of 1, 3, and 10 micrograms ANG I.h-1.kg-1 increased mean blood pressure of Wistar rats by 8 +/- 2, 15 +/- 2, and 27 +/- 4 mmHg, respectively. Similar results were obtained in Wistar rats at 18 h after bilateral nephrectomy. These results confirmed no activation of prorenin in the circulation of normotensive rats. The activation of prorenin was also examined on both stroke-prone spontaneously hypertensive rats (SHRSP) and 18 h-nephrectomized SHRSP. There was no rise in blood pressure or plasma active renin concentrations in both groups of SHRSP after injection of prorenin. Thus the elevated plasma active renin in SHRSP [Shibota, M., A. Nagaoka, A. Shino, and T. Fujita. Am. J. Physiol. 236 (Heart Circ. Physiol. 5): H409-H416, 1979] seems to be caused by the enhanced release of active renin from the kidney rather than the activation of circulating prorenin.
Muscle phosphorus energy state in very-low-birth-weight infants: effect of exercise
Authors: Bertocci L. A. , Mize C. E. , Uauy R.
Published: December 2017

Skeletal muscle hypotonia is a hallmark clinical finding in very-low-birth-weight (VLBW) human infants. Although the biochemical basis for this phenomenon is not completely understood, one hypothesis is that the phosphorylation potential is abnormally low in the skeletal muscle of these infants. Therefore, we used 31P-nuclear magnetic resonance (NMR) spectroscopy to measure phosphorus metabolites in the skeletal muscle of VLBW infants during rest and during reflex-induced muscle contractions. Compared with healthy larger infants or to adults, the total phosphorus NMR signal is lower in VLBW infants. In VLBW infants during rest, [PCr]/([PCr]+[Pi]), where PCr is phosphocreatine and brackets denote concentration, was 89% and [ATP]/[ADP][Pi] was 59% of that found in larger infants (P less than 0.05). During reflex-induced isometric contractions in VLBW infants, [PCr]/([PCr]+[Pi]) declined by 24% and [ATP]/[ADP][Pi] declined by 35% (P less than 0.05 vs. rest). In all conditions, muscle pH remained 7.1. Overall, the differences in skeletal muscle energy state during rest and the corresponding changes in concentration of high-energy phosphates during mild exercise suggest a very limited energy reserve in the hypotonic muscle of VLBW infants.
Flooding with L-[1-13C]leucine stimulates human muscle protein incorporation of continuously infused L-[1-13C]valine
Authors: Smith K. , Barua J. M. , Watt P. W. , Scrimgeour C. M. , Rennie M. J.
Published: December 2017

To investigate why flooding methods give higher rates than constant-infusion methods for muscle protein synthesis, we studied seven healthy postabsorptive male volunteers (20-42 yr; 67-74 kg) during a 7.5-h primed constant infusion of L-[1-13C]valine (99 atoms %, 1.5 mg/kg prime, 1.5 mg.kg-1.h-1); at 6.5 h they were given a flood of L-[1-13C]leucine (20 atoms %, 0.05 g/kg). Musculus tibialis anterior biopsies were taken at 0.5, 6, and 7.5 h, and blood was sampled as appropriate. The enrichment of valine and leucine in muscle protein (isotope ratio mass spectrometry of protein amino acid-derived 13CO2) was compared with the average enrichment of various amino acid pools (gas chromatography-mass spectrometry). During infusion of [13C] valine the rate of muscle protein synthesis measured using alpha-ketoisovalerate (alpha-KIV) as precursor surrogate was 0.043 +/- 0.002%/h (SE). After flooding with leucine, the incorporation rate of [13C]valine increased by 70% (P less than 0.05), i.e., apparent muscle protein synthetic rate (based on alpha-[13C]KIV) increased to 0.065 +/- 0.009%/h (P less than 0.05); the rate calculated from the [13C]leucine flood was 0.060 +/- 0.005%/h (P less than 0.01). The synthetic rates calculated using the constant-infusion method were higher after flooding, irrespective of the precursor chosen, raising serious concern about the validity of the flooding-dose method.
NPY-stimulated Ca2+ mobilization in SK-N-MC cells is enhanced after isoproterenol treatment
Authors: Michel M. C. , Feth F. , Rascher W.
Published: December 2017

Neuropeptide Y (NPY) receptors in the SK-N-MC human neuroblastoma cell line couple to mobilization of intracellular Ca2+ and inhibition of adenylylcyclase. Pretreatment of SK-N-MC cells with isoproterenol enhanced the NPY-stimulated Ca2+ mobilization, mainly by increasing the maximal response to NPY. The enhancement was time-(maximal after 24 h) and concentration-dependent (maximal at 10 microM isoproterenol), blocked by the beta-adrenergic antagonist propranolol, and mimicked by forskolin. Concomitant treatment with cycloheximide prevented the enhancing effect of isoproterenol, suggesting the involvement of protein synthesis. Isoproterenol treatment did not alter the number or affinity of 125I-labeled NPY binding sites, the amount of pertussis toxin substrates, or NPY-mediated inhibition of cAMP accumulation. Similarly, isoproterenol treatment had no effect on basal intracellular Ca2+ and on Ca2+ increases elicited by carbachol, caffeine, or ionomycin. We conclude that isoproterenol treatment can sensitize NPY receptor responsiveness in a way that is specific for Ca2+ mobilization mechanisms used by this hormone.
Trace element movement and oxidative stress in skeletal muscle atrophied by immobilization
Authors: Kondo H. , Miura M. , Nakagaki I. , Sasaki S. , Itokawa Y.
Published: December 2017

The movements of trace elements and the level of oxidative stress in the soleus, a typical slow red muscle which, atrophied by immobilization, were investigated in designated intervals. Male Wistar rats (14 wk old) whose one ankle joints were immobilized in the extended position were killed after 4, 8, and 12 days. Fe, Zn, Mn, and Cu concentrations and the levels of thiobarbituric acid-reactive substance (TBARS) and glutathione were measured. The rate of atrophy increased rapidly until the 8th day and slowly after that. In whole muscle, Fe concentration kept increasing, and Zn and Mn increased temporarily. Their subcellular distributions also changed; especially, the Fe level of the microsomal fraction kept increasing and reached threefold at 12 days. Increased TBARS and glutathione disulfide and decreased total glutathione indicated the increased oxidative stress in atrophy, which might result from an increased Fe level, especially that of the microsomal fraction. Vitamin E injection lessened the rate of atrophy, which showed that oxidative stress accelerated muscle atrophy. This might be mediated by increased intracellular Ca. Also metallothionein was induced in muscle atrophy.
Caffeine ingestion and muscle metabolism during prolonged exercise in humans
Authors: Spriet L. L. , MacLean D. A. , Dyck D. J. , Hultman E. , Cederblad G. , Graham T. E.
Published: December 2017

We examined the effects of a high-caffeine dose on endurance performance and muscle acetyl group metabolism during prolonged exercise. Eight subjects cycled to exhaustion at approximately 80% maximal oxygen uptake (VO2max) 1 h after ingestion of 9 mg/kg body wt dextrose (Pl) or caffeine (Caf). In the Pl trial, muscle biopsies were taken at rest (1 h postingestion) and at 15 min and exhaustion during exercise. The Caf trial followed the same protocol 1 wk later, with an additional biopsy at the time corresponding to Pl exhaustion. The subjects cycled significantly longer during the Caf trial (96.2 +/- 8.8 min) than in the Pl trial (75.8 +/- 4.8 min). Net glycogenolysis during the initial 15 min of cycling was reduced in the Caf vs. Pl trial (4.7 +/- 1.5 vs. 10.6 +/- 1.3 mmol.kg dry muscle-1.min-1; P less than 0.05). Muscle citrate concentration was increased at rest with Caf (0.59 +/- 0.07 vs. 0.37 +/- 0.05 mmol/kg dry muscle; P less than 0.05) but increased to similar values in both trials during cycling. Caf elevated the acetyl-CoA/CoA-SH ratio at rest (0.316 +/- 0.046 vs. 0.201 +/- 0.023; P less than 0.05) but had no effect on the increases in muscle acetyl-CoA and acetylcarnitine during exercise. The results indicate that Caf before exercise decreased muscle glycogenolysis by approximately 55% over the first 15 min of exercise at approximately 80% VO2max. This "spared glycogen" was available late in exercise and coincided with a prolonged time to exhaustion. Increased utilization of intramuscular triacylglycerol and/or extramuscular free fatty acids after caffeine ingestion may inhibit carbohydrate use at rest and early during exercise via elevations in muscle citrate and the acetyl-CoA/CoA-SH ratio. Muscle acetyl-CoA and acetylcarnitine were maintained above resting contents even at exhaustion when muscle glycogen was depleted.
Linear bone growth of oMT1a-oGH transgenic male mice
Authors: Oberbauer A. M. , Currier T. A. , Nancarrow C. D. , Ward K. A. , Murray J. D.
Published: December 2017

Linear bone growth was studied in male mice possessing a controlled ovine metallothionein 1a promoter-ovine growth hormone (oMT1a-oGH) transgene. Transgene expression was activated at weaning by the addition of 25 mM zinc sulfate to drinking water; transgenic and control mice received the zinc supplementation. The ulna, humerus, and tibia were excised at 10-day intervals until 130 days from control and from mice hemizygous for oMT1a-oGH. Bones from mice overexpressing growth hormone (GH) were 11-20% longer than those from controls (P less than 0.01) at 130 days. Transgenic mice exhibited both an enhanced rate of bone growth and a growth period of greater duration, i.e., the ulna, tibia, and humerus from oMT1a-oGH mice grew at an accelerated rate for an additional 20-40 days relative to the same bones from control mice. The bones from both groups were characterized by isometric growth patterns. Genetic size scaling revealed that the observed differences in bone growth were directly related to the mature size of the bone, suggesting that the bones possess an inherent growth pattern that is followed even in the presence of elevated GH.
Kidney IGF-I and renal hypertrophy in GH-deficient diabetic dwarf rats
Authors: Flyvbjerg A. , Frystyk J. , Osterby R. , Orskov H.
Published: December 2017

Insulin-like growth factor I (IGF-I) has been proposed as a renotropic factor in initial diabetic kidney growth. To examine the effects of an isolated growth hormone (GH) and IGF-I deficiency on diabetic renal hypertrophy, dwarf rats were made diabetic and studied over a period of 7 days. Diabetic dwarf rats treated with human GH (hGH) or insulin and diabetic rats with intact pituitary were used as controls. In diabetic control animals kidney weight had increased by day 2 (P less than 0.01), and the increase amounted to 27% after 7 days, whereas untreated diabetic dwarf rats had a slower and lesser degree of kidney weight increase, reaching significance on day 7 only, amounting to 8%. hGH administration in diabetic dwarf rats increased the kidney weight on day 7 when compared with untreated diabetic dwarf rats (P less than 0.05) and was 19% over that of insulin-treated diabetic dwarf rats. The glomerular volume had increased by 43% in untreated diabetic control rats at day 7, compared with a 29% increase in untreated diabetic dwarf rats (P less than 0.05). hGH administration in diabetic dwarf rats increased the glomerular volume by 46%, comparable to the increase seen in diabetic control animals. Kidney IGF-I was increased on day 2 by 51 and 46% in saline- and hGH-injected diabetic dwarf rats, respectively, but a significantly higher increase in kidney IGF-I amounting to 96% was seen in diabetic control rats.(ABSTRACT TRUNCATED AT 250 WORDS)
Glucose utilization and insulin action in adult rats submitted to prolonged food restriction
Authors: Escriva F. , Rodriguez C. , Cacho J. , Alvarez C. , Portha B. , Pascual-Leone A. M.
Published: December 2017

Glucose tolerance and insulin effects on glucose production and utilization by various tissues were studied in 70-day-old anesthetized rats submitted to food restriction from the fetal stage. Basal and glucose-induced plasma insulin levels were reduced in food-restricted rats without alterations in glucose tolerance. Insulin action was quantified by using the euglycemic-hyperinsulinemic clamp technique. Glucose turnover rates were measured by using D-[6-3H]glucose. Exogenous insulin failed to decrease glucose production in food-restricted rats. Weight-related whole body glucose utilization was higher in restricted rats than in controls both in the basal (21.9 +/- 0.7 vs. 9.4 +/- 0.6 mg.min-1.kg-1) and hyperinsulinemic states (37.5 +/- 1.1 vs. 14.0 +/- 1.2 mg.min-1.kg-1). Local glucose utilization by peripheral tissues was estimated by a 2-deoxy-D-[1-3H]glucose technique. In both basal and hyperinsulinemic conditions glucose utilization was increased in various adipose and muscle tissues of the food-restricted rats as compared with the controls. Thus we conclude that food restriction leads to an increase in the insulin-mediated glucose uptake by various peripheral tissues and to insulin resistance in the liver.
Adrenergic and nonadrenergic cotransmitters inhibit insulin secretion during sympathetic stimulation in dogs
Authors: Lorrain J. , Angel I. , Duval N. , Eon M. T. , Oblin A. , Langer S. Z.
Published: December 2017

Vascular and biochemical responses to pancreatic sympathetic nerve stimulation were investigated in the blood-perfused pancreas of anesthetized dogs. During sympathetic nerve stimulation, pancreatic perfusion pressure and norepinephrine release increased, whereas insulin secretion decreased. The latter effect did not occur after pretreatment with the alpha 2-adrenoceptor antagonist idazoxan. However, after beta-adrenoceptor blockade with propranolol, neither single administration of idazoxan nor the alpha 1-adrenoceptor antagonist prazosin or glibenclamide, a blocker of ATP-modulated K+ channels, affected the decrease in insulin secretion induced by sympathetic nerve stimulation. In contrast, the combination of glibenclamide with idazoxan markedly antagonised the decrease in insulin release evoked by the latter procedure. After depletion of catecholamines with syrosingopine, the stimulation-induced inhibition of insulin secretion remained unchanged even though no increases in pancreas perfusion pressure or norepinephrine release were observed. In this preparation, glibenclamide inhibited the decrease in insulin release by 50%. In animals pretreated with the neuronal blocking agent bretylium, all of the responses to sympathetic nerve stimulation were abolished. These results indicate that the inhibitory effects exerted by the sympathetic nervous system on insulin secretion are mediated not only by the classical neurotransmitter norepinephrine acting on alpha 2-adrenoceptors but also by a nonadrenergic cotransmitter that can maintain transmission under conditions of catecholamine deficiency. The postulated nonadrenergic cotransmitter(s) acts, at least partly, via the opening of ATP-modulated K+ channels blockable by glibenclamide, and its release can be prevented by the neuronal blocking agent bretylium.
Origin and disposal of 1,5-anhydroglucitol, a major polyol in the human body
Authors: Yamanouchi T. , Tachibana Y. , Akanuma H. , Minoda S. , Shinohara T. , Moromizato H. , Miyashita H. , Akaoka I.
Published: December 2017

The origin and disposal of 1,5-anhydro-D-glucitol (AG), one of the main polyols found in the human body, was studied in normal subjects and diabetic patients. AG was detected in various kinds of foods. The mean AG supplement through foods was estimated to be approximately 4.38 mg/day, which was compatible with that calculated in a food analysis (average 0.22 mg AG/100 kcal in Japanese foods) on eight healthy subjects. The mean AG excretion in urine was approximately 4.76 mg/day in these subjects. Excretion into stools was negligible. From observations on the patients without oral supplement of AG, 0.4 mg of daily de novo synthesis of AG was strongly suggested. It was also implied that urinary AG excretion occurred soon after food ingestion and that its amount was closely correlated with daily supplement through foods. Thus the fundamental kinetics of AG were recognized as follows: 1) AG in the body originates mainly from foods and is well absorbed in the intestine, 2) AG is little degraded and metabolized in the body, and 3) an equilibrium exists between oral supplement plus a small but steady amount of de novo synthesis and excretion in urine.
Suppression of muscle protein turnover and amino acid degradation by dietary protein deficiency
Authors: Tawa N. E. , Goldberg A. L.
Published: December 2017

To define the adaptations that conserve amino acids and muscle protein when dietary protein intake is inadequate, rats (60-70 g final wt) were fed a normal or protein-deficient (PD) diet (18 or 1% lactalbumin), and their muscles were studied in vitro. After 7 days on the PD diet, both protein degradation and synthesis fell 30-40% in skeletal muscles and atria. This fall in proteolysis did not result from reduced amino acid supply to the muscle and preceded any clear decrease in plasma amino acids. Oxidation of branched-chain amino acids, glutamine and alanine synthesis, and uptake of alpha-aminoisobutyrate also fell by 30-50% in muscles and adipose tissue of PD rats. After 1 day on the PD diet, muscle protein synthesis and amino acid uptake decreased by 25-40%, and after 3 days proteolysis and leucine oxidation fell 30-45%. Upon refeeding with the normal diet, protein synthesis also rose more rapidly (+30% by 1 day) than proteolysis, which increased significantly after 3 days (+60%). These different time courses suggest distinct endocrine signals for these responses. The high rate of protein synthesis and low rate of proteolysis during the first 3 days of refeeding a normal diet to PD rats contributes to the rapid weight gain ("catch-up growth") of such animals.
Role of FFA-glucose cycle in glucoregulation during exercise in total absence of insulin
Authors: Yamatani K. , Shi Z. Q. , Giacca A. , Gupta R. , Fisher S. , Lickley H. L. , Vranic M.
Published: December 2017

Muscle contraction in vitro increases glucose uptake (GU), independent of insulin, but in vivo, the exercise-induced increase in GU is impaired in insulin-deficient diabetic dogs. We wished to determine whether, in vivo, suppression of the free fatty acid (FFA)-glucose cycle with methylpalmoxirate (MP, inhibitor of FFA oxidation) alone or combined with propranolol (PRO, beta-blocker) could improve GU during exercise in the absence of insulin. We performed four groups of exercise experiments (6 km/h, 10% slope) in depancreatized insulin-deprived dogs: 1) control (n = 6); 2) MP treated (5 oral doses of 10 mg/kg, twice daily, n = 6); 3) treated with MP+octanoate (OCT; oxidation unaffected by MP, 27 mumol.kg-1.min-1 iv during exercise; n = 5); and 4) MP+PRO treated (5 micrograms.kg-1.min-1 iv during exercise, n = 6). MP abolished ketosis (inhibition of hepatic FFA oxidation), decreased basal glucose production (GP), and increased metabolic clearance of glucose (MCR). During exercise, MP attenuated the increment in GP (P < 0.01), which was reversed by OCT. MP did not affect the exercise-induced increase in GU and MCR. With MP+PRO, FFAs decreased and lactate did not rise during exercise. GP was not further suppressed, but GU and MCR were increased (P < 0.01) to 89 and 31% of normal, respectively. In insulin-deprived depancreatized dogs, glucose cycling was increased to a greater extent than GP, as in type II diabetes. By the end of exercise, glucose cycling increased (P < 0.05), but to a similar extent as GP.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of streptozotocin-induced diabetes on rough endoplasmic reticulum and lysosomes of rat liver
Authors: Lenk S. E. , Bhat D. , Blakeney W. , Dunn W. A.
Published: December 2017

In the absence of amino acids and insulin, ribosome-free regions of the rough endoplasmic reticulum (RER) invaginate to form an autophagosome, which matures into an autolysosome (W. A. Dunn, Jr., J. Cell Biol. 110: 1923-1933, 1990). In this study, biochemical and morphological methods were used to examine the structure and integrity of the RER and the lysosome-vacuolar system in livers of untreated (normal serum insulin) and streptozotocin (STZ)-treated (depressed serum insulin) fed and fasted rats. Degradation of endogenous proteins was increased by 70% in STZ-treated animals. Proteolysis was further enhanced when these animals were deprived of food for 24 h. These alterations in protein turnover were accompanied by increases in the fractional volume of autophagic vacuoles and in the hepatic amounts of three lysosomal hydrolases. These effects of STZ were prevented on administration of insulin. In addition, there was an insulin-dependent 50% loss of RER surface area in livers from STZ-treated rats. This loss of structural RER was accompanied by comparable decreases in the cellular amounts of two RER membrane proteins and one luminal protein, suggesting that the RER was degraded as a unit. Additional losses of RER were observed when STZ-treated rats were fasted. Furthermore, the hepatic amounts of two serum proteins decreased, suggesting the functional capacity of the RER was reduced. Combined, the data suggest that in STZ-induced diabetes the losses in RER are related to enhanced autophagy.
Fasting and postmeal phenylalanine metabolism in mild type 2 diabetes
Authors: Biolo G. , Tessari P. , Inchiostro S. , Bruttomesso D. , Sabadin L. , Fongher C. , Panebianco G. , Fratton M. G. , Tiengo A.
Published: December 2017

We have investigated postabsorptive and postprandial phenylalanine kinetics in non-obese type 2 diabetic patients [non-insulin-dependent diabetes mellitus (NIDDM)], using a double-isotope technique and the constant oral administration of a synthetic mixed meal. Fasting and postmeal glucose levels were increased (P < 0.01) in NIDDM (165 +/- 16 to 226 +/- 24 mg/dl), with respect to normal controls (85 +/- 3 to 102 +/- 6 mg/dl). Fasting insulin concentrations were comparable in NIDDM (13 +/- 2 microU/ml) and in normals (12 +/- 2 microU/ml), but after the meal it increased less (P < 0.07) in NIDDM vs. normals (to 36 +/- 5 vs. 56 +/- 12 microU/ml, respectively; P < 0.01 vs. basal for both). Postabsorptive phenylalanine rate of appearance (R(a)) in NIDDM (0.63 +/- 0.08 mumol.kg-1 x min-1) was comparable to that of controls (0.73 +/- 0.05 mumol.kg-1 x min-1, not significant). During the meal, total and endogenous phenylalanine R(a), splanchnic uptake, oxidation, and nonoxidative disposal of the ingested phenylalanine were also comparable in the two groups. These data indicate that fasting and postprandial kinetics of the essential amino acid phenylalanine are normal in NIDDM.
Early metabolic consequences of epidermal growth factor administration to neonatal rats
Authors: Donnelly M. M. , Hoath S. B. , Pickens W. F.
Published: December 2017

Daily administration of epidermal growth factor (EGF) to neonatal rodents elicits a classic morphogenetic syndrome. In this study, we examined the early (minutes to hours) consequences of EGF treatment in the neonatal rat (age 0–72 h). Significant findings included a rapid reduction in resting heart rate 4 h after EGF treatment accompanied by a sensitive dose- and age-dependent decrease in systemic oxygen consumption (VO2). Midscapular skin temperature (MST) was measured as a putative noninvasive indicator of brown adipose tissue thermogenesis. As little as 10 ng EGF/g body wt elicited a significant reduction in MST. Both the decrease in VO2 evoked by EGF and the MST response were potentiated by environmental cold exposure. EGF treatment also resulted in rapid (90 min) reductions in circulating levels of glycerol, triglyceride, and cholesterol while increasing serum glucose and arachidonic acid. Other free fatty acids were unaffected. Serum lactate levels were increased by EGF with the same time course as the reduction in VO2. These results provide new biochemical data on the pharmacological actions of EGF and further characterize the EGF-treated neonatal rodent as an intriguing in vivo model of growth factor action.
Mass isotopomer distribution analysis: a technique for measuring biosynthesis and turnover of polymers
Authors: Hellerstein M. K. , Neese R. A.
Published: December 2017

Mass isotopomer distribution analysis (MIDA) is a technique for measuring biosynthesis and turnover of polymers in vivo. A stable isotopically enriched precursor is administered, and the relative abundances of different mass isotopomers in the polymer of interest are measured by mass spectrometry (MS). By comparison of statistical distributions predicted from the binomial or multinomial expansion to the pattern of excess isotopomer frequencies observed in the polymer, the enrichment of the biosynthetic precursor subunits (p) for newly synthesized polymers is calculated. MIDA thereby provides a solution to the problem of determining the isotope content in the actual precursor molecules that entered a particular polymeric product (the “true” precursor). The fraction of polymer molecules in a mixture that were newly synthesized during an isotopic experiment (fractional synthesis) can then be calculated. We describe some mathematical characteristics of MIDA and point out certain advantageous features. For example, mathematical estimates of p remain valid even if there does not exist a single anatomic or functional precursor pool. The interpretation of decay curves of endogenously labeled polymers may be improved by the use of higher mass isotopomers, which better fulfill the assumption of flash labeling. By combining fractional synthesis values with rate constants of decay, absolute endogenous synthesis rates can be calculated. Thus, by using probability logic combined with MS analysis, MIDA allows dynamic measurements to be made through analyses on a polymer alone during both isotopic incorporation and decay phases. The method has been applied to fatty acids, cholesterol, and glucose and is potentially applicable to nucleic acids, porphyrins, perhaps proteins, and many other classes of polymers.
Glucose counterregulation: prevention and correction of hypoglycemia in humans
Authors: Cryer P. E.
Published: December 2017

The prevention or correction of hypoglycemia in humans is the result of both dissipation of insulin and activation of glucose counterregulatory (glucose-raising) systems. Whereas insulin is the dominant glucose-lowering factor, there are redundant glucose counterregulatory factors. Furthermore, there is a hierarchy among the glucoregulatory factors. The first defense against a decrement in plasma glucose is decreased insulin secretion; this occurs with glucose decrements within the physiological range at a glycemic threshold of 4.6 +/- 0.2 mmol/l. However, biological glucose recovery from hypoglycemia can occur despite mild (approximately 2-fold) peripheral hyperinsulinemia and can occur in the absence of portal hypoinsulinemia. Thus additional (glucose counterregulatory) factors must be involved. Critical glucose counterregulatory systems are activated at glycemic thresholds of approximately 3.8 mmol/l (the level at which brain glucose uptake is first measurably reduced), well above the thresholds for symptoms of hypoglycemia (approximately 3.0 mmol/l) and those for cognitive dysfunction resulting from neuroglycopenia (approximately 2.7 mmol/l). Among the glucose counterregulatory factors, glucagon plays a primary role. Indeed, it may be that hypoglycemia does not occur if the secretion and actions of both glucagon and insulin, among the glucoregulatory hormones, are normal. Epinephrine is not normally critical, but it becomes critical to glucose counterregulation when glucagon is deficient. Because hypoglycemia develops or progresses when both glucagon and epinephrine are deficient and insulin is present, these three hormones stand high in the hierarchy of redundant glucoregulatory factors.(ABSTRACT TRUNCATED AT 250 WORDS)
Increased proliferation of osteoblast precursor cells in estrogen-deficient rats
Authors: Modrowski D. , Miravet L. , Feuga M. , Marie P. J.
Published: December 2017

We have evaluated the in vivo and in vitro changes in osteoblast characteristics induced by estrogen deficiency and 17 beta-estradiol (E2) treatment in ovariectomized (OVX) rats. Estrogen deficiency induced osteopenia and increased bone turnover, as evidenced by bone histomorphometry at 1, 3, and 6 mo postovariectomy. Bone surface osteoblastic cells (OB) isolated from tibias of OVX rats, OVX rats treated with E2 (10 micrograms/kg body wt), and sham rats showed no difference in alkaline phosphatase activity and osteocalcin production in vitro. In contrast the proliferation rate of OB cells was higher in OVX rats compared with sham rats at all time points post-surgery, as shown by [3H]thymidine incorporation and cell number. The proliferation rate of alkaline phosphatase-positive marrow cells was also higher in OVX rats compared with sham rats. E2 treatment of OVX rats corrected histologic indexes of bone resorption and formation and normalized OB cell proliferation. induced by estrogen deficiency in OVX rats is related to an increased proliferation of osteoblast precursor cells present in the marrow stroma and along the endosteal bone surface.
Characterization of a common VIP-PACAP receptor in human small intestinal epithelium
Authors: Salomon R. , Couvineau A. , Rouyer-Fessard C. , Voisin T. , Lavallee D. , Blais A. , Darmoul D. , Laburthe M.
Published: December 2017

Vasoactive intestinal peptide (VIP) receptors were characterized in epithelial plasma membranes from human small intestine. Native VIP inhibited the binding of 125I-labeled VIP to jejunal membranes, and Scatchard analysis of these data was consistent with the existence of one class of receptor with a dissociation constant of 42 pM and a maximal binding of 256 fmol/mg membrane protein. VIP stimulated adenylyl cyclase activity in human jejunal membranes in the 0.01 nM-1 microM range [half-maximal effective dose = 0.7 nM]. Coupling of VIP receptors with a Gs protein was further assessed by the ability of GTP (10(-8) to 10(-3) M) to inhibit 125I-VIP binding to membranes. 125I-VIP binding was seven to eight times higher in villus cells than in crypt cells. Finally, 125I-VIP binding was detectable throughout the small and large intestines with the highest binding in jejunum. Among the natural peptides structurally related to VIP, some inhibited 125I-VIP binding with the following order of potency: VIP = pituitary adenylate cyclase-activating peptide (PACAP)-27 = PACAP-38 > helodermin >> peptide histidine methionineamide = human growth hormone-releasing factor > secretin. The same order of potency of peptides for inhibiting 125I-VIP or 125I-labeled PACAP was observed, supporting that the two tracers bound to a common VIP-PACAP receptor site. This order of potency was also observed for the stimulation of adenylyl cyclase activity by these peptides. 125I-VIP was cross-linked to membranes using disuccinimidyl suberate. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, one single band of 70,000 mol wt was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
Respiratory, ionic, and functional effects of succinate esters in pancreatic islets
Authors: Malaisse W. J. , Rasschaert J. , Villanueva-Penacarrillo M. L. , Valverde I.
Published: December 2017

The methyl esters of succinic acid were introduced a few years ago as new potent insulin secretagogues. In the present study, they were found to increase O2 uptake by rat islets incubated in the absence or presence of D-glucose; to decrease 86Rb outflow from prelabeled islets; to stimulate biosynthetic activity in the islets, with a preferential effect on the synthesis of proinsulin; to inhibit 45Ca efflux from prelabeled islets perifused in the absence of extracellular Ca2+ but to augment 45Ca net uptake and to cause a biphasic stimulation of 45Ca outflow in islets incubated or perifused in the presence of extracellular Ca2+; and to evoke a biphasic stimulation of insulin release. The insulinotropic action of these methyl esters coincided with a shift to the left of the sigmoidal relationship between insulin output and D-glucose concentration, was concentration related in the 2-10 mM range, failed to be duplicated by succinic acid, displayed both Ca2+ dependency and resistance to a lowering of extracellular pH, and was operative in the absence of D-glucose whether or not the islets were stimulated by non-nutrient secretagogues. It is concluded that the respiratory, cationic, biosynthetic, and secretory responses of the islets to succinate methyl esters display the characteristic features usually encountered in the process of nutrient-stimulated insulin release.
Parathyroid hormone-related protein increases cAMP production in mammary epithelial cells
Authors: Ferrari S. , Rizzoli R. , Chaponnier C. , Gabbiani G. , Bonjour J. P.
Published: December 2017

Parathyroid hormone-related protein (PTHrP) is a major cause of malignant hypercalcemia but has been found in many nontumoral tissues as well. Thus it is produced by the mammary gland during lactation and released into milk. Whether PTHrP directly affects breast tissue is however not known. We investigated the effects of PTHrP on adenosine 3',5'-cyclic monophosphate (cAMP) production in primary cultures of mammary epithelial cells isolated from lactating rats. On the 7th day in culture, synthetic PTHrP-(1-34), recombinant (r) PTHrP-(1-108), and rPTHrP-(1-141) stimulated cAMP production in a concentration-dependent manner. Thus PTHrP-(1-34) induced a 1.92 +/- 0.04-fold stimulation of cAMP production (mean +/- SE, n = 5 separate experiments, P < 0.001). At the time of maximal responsiveness to PTHrP, a significant proportion of the cells was characterized by an elongated shape and a positive immunofluorescent staining for both prekeratin and alpha-smooth muscle actin 1, compatible with a myoepithelial phenotype. It therefore appears that PTHrP can stimulate the production of cAMP in mammary cells, suggesting a possible autocrine/paracrine regulatory function for PTHrP in breast tissue.
Whole body and splanchnic oxygen consumption and blood flow after oral ingestion of fructose or glucose
Authors: Brundin T. , Wahren J.
Published: December 2017

The contribution of the splanchnic tissues to the initial 2-h rise in whole body energy expenditure after ingestion of glucose or fructose was examined in healthy subjects. Indirect calorimetry and catheter techniques were employed to determine pulmonary gas exchange, cardiac output, splanchnic blood flow, splanchnic oxygen uptake, and blood temperatures before and for 2 h after ingestion of 75 g of either fructose or glucose in water solution or of water only. Fructose ingestion was found to increase total oxygen uptake by an average of 9.5% above basal levels; the corresponding increase for glucose was 8.8% and for water only 2.5%. The respiratory exchange ratio increased from 0.84 in the basal state to 0.97 at 45 min after fructose ingestion and rose gradually after glucose to 0.86 after 120 min. The average 2-h thermic effect, expressed as percent of ingested energy, was 5.0% for fructose and 3.7% for glucose (not significant). Splanchnic oxygen consumption did not increase measurably after ingestion of either fructose or glucose. The arterial concentration of lactate rose, arterial pH fell, and PCO2 remained essentially unchanged after fructose ingestion. Glucose, but not fructose, elicited increases in cardiac output (28%) and splanchnic blood flow (56%). Fructose, but not glucose, increased arterial blood temperature significantly. It is concluded that both fructose and glucose-induced thermogenesis occurs exclusively in extrasplanchnic tissues. Compared with glucose, fructose ingestion is accompanied by a more marked rise in CO2 production, possibly reflecting an increased extrasplanchnic oxidation of lactate and an accumulation of heat in the body.
Carbonic anhydrase III in obese Zucker rats
Authors: Lynch C. J. , Brennan W. A. , Vary T. C. , Carter N. , Dodgson S. J.
Published: December 2017

Proteins from 5- to 7-wk-old lean and obese Zucker rats were separated by one-dimensional sodium dodecyl sulfate (SDS) and two-dimensional SDS-isoelectric focusing-polyacrylamide gel electrophoresis. Laser densitometry revealed an obesity-related decrease in the concentration of a 28-kDa cytosolic adipocyte protein, the most abundant protein in adipocytes from lean Zucker rats. Microsequencing revealed the identity of this protein to be carbonic anhydrase III (CA III). The identity and obesity-related decrease was further confirmed using isoform-specific antisera and CA III enzyme activity measurements made by 18O mass spectrometry. Immunoblotting studies also revealed that CA III is present in at least two charge isoforms in adipocytes. Our data indicate that lean Zucker rat adipocytes may represent the richest source of CA III in nature (24% of the cytosolic protein content). An obesity-related decrease in both the concentration and activity of CA III was observed in two lipogenic tissues, liver and white fat, but not in soleus muscle. Adipocyte CA III activity was no longer depressed when hyperinsulinemic obese rats were made insulin deficient by streptozotocin injection. This suggests that the obesity-related decrease in CA III may be related to the hyperinsulinemia as well as to the insulin hyperresponsiveness that adipocytes from obese Zucker rats of this age display.