bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel effects of insulin secretagogues on capacitation of insulin release and survival of cultured pancreatic islets
Authors: MacDonald M. J. , Fahien L. A. , McKenzie D. I. , Moran S. M.
Published: December 2017

Agents that stimulate insulin release from fresh pancreatic islets were tested for their ability to capacitate pancreatic islets to secrete insulin and to support beta-cell survival in tissue culture. Capacitation was defined as the ability to release insulin after 24 h in culture in the presence of an insulinotropic concentration of a secretagogue. Viable islets that lose glucose-induced insulin release gradually regain it during culture for 24 h in 20 mM glucose. Survival was defined as the ability to regain glucose-induced insulin release. To measure insulin release after culture, islets were incubated with various secretagogues in Krebs-Ringer buffer for 1 h. Examples of the diverse patterns of responses included the following. Glucose was the only secretagogue that capacitated glucose-induced release. Leucine-, leucine plus glutamine-, and glyceraldehyde-induced release remained capacitated after culture with no secretagogue. Culture at high glucose completely inhibited leucine-induced release. Culture at low glucose (1 mM) or at both high leucine and glutamine abolished glucose-induced release. Only leucine and glutamine capacitated monomethyl succinate-induced release. All agents including subinsulinotropic glucose (1 mM), except D-glyceraldehyde, permitted islet survival. Thus the metabolic pathways for initiation, capacitation, and survival are not identical between and within secretagogues. There is a reciprocal relationship between leucine and glucose with respect to capacitation. Capacitation follows a time course, which suggests that it is regulated by enzyme induction.
Hepatic uptake and metabolism of oral galactose in adult fasted rats
Authors: Niewoehner C. B. , Neil B. , Martin T.
Published: December 2017

Galactose is incorporated into glycogen by a different metabolic route than glucose and fructose, the other major dietary monosaccharides. Oral galactose (4 g/kg) was given to 24-h-fasted adult rats to 1) compare quantitatively the disposition of galactose with that of glucose and fructose; 2) examine the effects of galactose on hepatic utilization of other metabolic fuels; and 3) examine circulating and liver galactose concentrations to determine whether net hepatic uptake of galactose, like glucose, occurs against a concentration gradient. Galactose absorption, hepatic blood flow, portal venous, arterial, hepatic venous, and liver concentrations of galactose, glucose, lactate, and alanine, and hepatic glycogen concentrations were measured at intervals up to 240 min. Concentrations entering and exiting the liver, hepatic intracellular concentrations, and net hepatic uptake/output were calculated. Galactose concentration entering the liver increased to a peak of 18.8 +/- 0.8 mumol/ml plasma water at 60 min and then decreased but remained above the control value. Liver galactose concentration increased dramatically from 0.28 +/- 0.04 to 21.2 +/- 1.1 mumol/ml liver water and exceeded plasma concentrations, even during the 1st 120 min when concentration gradients across the liver indicated net galactose extraction. Whole blood galactose concentrations initially were lower and then exceeded plasma concentrations, indicating that erythrocytes maintained galactose concentrations exceeding those in plasma. The data suggest that the hepatic and erythrocyte transport systems for galactose represent active mechanisms. Fifty-one percent of absorbed galactose was lost in urine; 18% of the remaining galactose load could be accounted for by net glycogen accumulation. Net increases in galactose, lactate, and alanine uptake could account for the glycogen synthesized but not for the net hepatic glucose output, which changed very little (6% increase).
Cimaterol reduces cathepsin activities but has no anabolic effect in cultured myotubes
Authors: Bechet D. M. , Listrat A. , Deval C. , Ferrara M. , Quirke J. F.
Published: December 2017

The effect of the beta-adrenergic agonist cimaterol on bovine and chicken primary myotubes was assessed. Cimaterol at 10-100 nM concentrations reduced cathepsin B benzyloxy-carbonyl-Arg-Arg-4-methyl-7-coumarylamide hydrolyzing activity, as well as benzyloxycarbonyl-Phe-Arg-4-methyl-7-coumarylamide hydrolysis, which is a substrate for both cathepsin B and cathepsin L. Maximum effect was observed after 6-16 h treatment. Cathepsin H Arg-4-methyl-7-coumarylamide hydrolyzing activity was low and not significantly affected by cimaterol treatment. Despite decreasing cathepsin activities, cimaterol also increased proteolysis rates but induced no detectable effect on protein synthesis rates. These observations suggest that beta-agonists, as a result of a direct action on muscle, can decrease cathepsin activities but that beta-agonist-induced muscle hypertrophy may not be due to a direct effect on muscle cells.
Thyrotropin-releasing hormone in ovine fetus: ontogeny and effect of thyroid hormone
Authors: Polk D. H. , Reviczky A. , Lam R. W. , Fisher D. A.
Published: December 2017

The ontogenesis of hypothalamic and extrahypothalamic thyrotropin-releasing hormone (TRH) and the effect of altered thyroid status on tissue TRH levels were studied in fetal sheep. At 62 days gestation (term = 145 days) TRH was detectable in serum and in hypothalamic, placental, and pancreatic tissues; pancreatic, placental, and serum levels exceeded hypothalamic levels two- to fivefold. Analysis of tissues obtained from 88-day gestation fetuses were comparable: TRH levels in placenta (54 +/- 15 pg/mg tissue protein), pancreas (34 +/- 5 pg/mg protein), and serum (93 +/- 9 pg/ml) exceeded those in hypothalamic extracts (15 +/- 9 pg/mg protein). By 120 days gestation, TRH values in the hypothalamus (610 +/- 52 pg/mg protein) exceeded those in extrahypothalamic sites; values were comparable at 140 days gestation. Fetal thyroidectomy resulted in a 2-fold elevation of hypothalamic TRH concentrations (1,030 +/- 139 vs. 522 +/- 29 pg/mg protein) and 2 to 20-fold elevations of TRH in the placenta (147 +/- 23 vs. 42 +/- 8 pg/mg protein), pancreas (195 +/- 11 vs. 29 +/- 7 pg/mg protein), duodenum (363 +/- 97 vs. 29 +/- 7 pg/mg protein), and serum (2,563 +/- 212 vs. 131 +/- 16 pg/ml). 3, 5, 3'-Triiodothyronine (T3) infusion in thyroidectomized fetuses resulted in elevated serum T3 values (480 +/- 80 ng/dl) and suppressed hypothalamic TRH (249 +/- 68 vs. 522 +/- 29 pg/mg protein) and serum TRH concentrations (30 +/- 4 vs. 131 +/- 156 pg/ml). Placental, pancreatic, and duodenal TRH concentrations in thyroidectomized T3-infused animals were below the level of detection of the assay (5 pg/mg tissue protein).(ABSTRACT TRUNCATED AT 250 WORDS)
Acute effect of L-carnitine on skeletal muscle force tests in dogs
Authors: Dubelaar M. L. , Lucas C. M. , Hulsmann W. C.
Published: December 2017

Using the mixed type musculus latissimus dorsi of the dog in the present work, we show the effect of carnitine on an in situ fatigue test. L-Carnitine appears to improve force of this muscle by 34% while stimulated in situ. This effect of carnitine is acute and (stereo)specific, since neither D-carnitine nor the structural analogue choline (also a tertiary amine) has a positive effect on contractile force. Because skeletal muscle is rich in carnitine and because carnitine transport is slow, its effect must be exerted outside the striated muscle cells. Insulin (with glucose) administration abolished the carnitine effect. It is speculated that facilitation of fatty acid oxidation in the blood vessel wall is the basis for this positive effect of carnitine.
Pathway and carbon sources for hepatic glycogen repletion in dogs
Authors: Mitrakou A. , Jones R. , Okuda Y. , Pena J. , Nurjhan N. , Field J. B. , Gerich J. E.
Published: December 2017

The present studies were undertaken to quantitate the relative contributions of the indirect and direct pathways for hepatic glycogen repletion and to determine the role of splanchnic tissues in provision of C precursors used for the indirect pathway. For this purpose, we administered oral glucose (1.4 g/kg) enriched with [1-14C]glucose to 18-h fasted dogs and measured net hepatic and net gastrointestinal glucose, lactate, and alanine balance, hepatic and gastrointestinal fractional extraction [( 3H]lactate), release and uptake of lactate, as well as the total amount of hepatic glycogen formed from the oral glucose and the 14C labeling pattern of the glycogen-glucose C. Although net hepatic glucose uptake (8.7 +/- 0.6 g, 27% of the oral load) exceeded the amount of glycogen formed from the oral glucose (6.3 +/- 1.1 g), analysis of radioactivity in C-1 of the glycogen glucose indicated that nearly 50% of the glycogen was formed by the indirect pathway. Net hepatic uptake of lactate (1.4 +/- 0.1 g) and alanine (1.5 +/- 0.1 g) could account for greater than 90% of glycogen formed by the indirect pathway if all of the lactate and alanine taken up by the liver had been incorporated into glycogen. Release of lactate and alanine by splanchnic tissues approximated the amount of lactate and alanine taken up by the liver. However, in addition to taking up lactate, the liver also produced nearly as much lactate as the gastrointestinal tract (1.8 +/- 0.2 vs. 2.0 +/- 0.3 g, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of parathyroid hormone secretion by plasma calcium in aging rats
Authors: Fox J.
Published: December 2017

Plasma immunoreactive parathyroid hormone (irPTH) levels increase with aging. This study determined 1) whether NH2-terminal irPTH secretory responses to induced hypocalcemia differ between adult (6-mo-old) and aged (24- to 26-mo-old) male rats and 2) whether a higher set point for irPTH release by Ca is responsible for the elevated irPTH levels with aging. Basal irPTH levels were 68% higher and 1,25-dihydroxyvitamin D3 levels were 44% lower in aged rats. An acutely induced, constant hypocalcemic stimulus [0.32 mM decrement in ionized Ca (Ca2+) for 2 h] was developed in catheterized conscious adult and aged rats by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) infusion using the Ca clamp technique. The initial irPTH secretory response to acute hypocalcemia (5-10 min) was reduced in aged rats (1.9- vs. 3.1-fold increase), suggesting reduced hormone stores. However, higher sustained irPTH levels (30 min to 2 h) were maintained in aged rats, indicating increased irPTH synthesis and release. The EGTA infusion rate necessary to maintain constant hypocalcemia was less in aged rats, suggesting skeletal resistance to PTH. Slow EGTA and Ca infusions were used to determine irPTH secretion at plasma Ca2+ levels from 0.7 to 1.5 mM. In aged rats, irPTH levels were higher at all Ca2+ concentrations, but the set point for irPTH release by Ca2+ was the same as in adult rats. Thus the elevated irPTH secretion in aged rats is not caused by a change in the set point for irPTH release but does result in decreased irPTH stores.
Protein-induced changes in energy expenditure in young and old individuals
Authors: Fukagawa N. K. , Bandini L. G. , Lim P. H. , Roingeard F. , Lee M. A. , Young J. B.
Published: December 2017

Resting energy expenditure (EE) has recently been shown to be reduced in elderly human subjects even after adjustment for body size and composition. The present study extended this examination of EE in relation to age by comparing the thermic effect of a protein meal in young men (YM 20-26 yr, n = 9), old men (OM 70-89 yr, n = 9), and old women (OW 67-75 yr, n = 6). EE was measured before and from 1 to 6 h after presentation of 60 g protein and of a control noncaloric meal on separate occasions. Despite substantial differences in body size and composition, the protein-induced increment in EE was similar in all groups [maximum increase: YM 0.21 +/- 0.05, OM 0.17 +/- 0.12, and OW 0.17 +/- 0.04 (SE) kcal/min]. Although fasting plasma norepinephrine (NE) levels differed among all three groups (YM less than OM less than OW), NE concentrations were not affected by protein ingestion. Because protein administration acutely promotes synthesis of dopamine (DA) and serotonin (5-HT), which are both capable of stimulating EE, blockade of extraneuronal synthesis of DA and 5-HT with carbidopa, a competitive inhibitor of aromatic-L-amino acid decarboxylase, failed to suppress (and actually increased) postprandial EE. These data demonstrate that not all mechanisms responsible for EE decline with age and that protein-induced changes in EE are more a function of the oral load itself than of the size, age, or antecedent diet of the individual ingesting the protein.
Naloxone augments muscle sympathetic nerve activity during isometric exercise in humans
Authors: Farrell P. A. , Ebert T. J. , Kampine J. P.
Published: December 2017

The influence of an endogenous opioid peptide (EOP) antagonist (naloxone, 1.2 mg iv bolus) on muscle sympathetic nerve activity (MSNA, microneurography) was studied on 19 young male and female volunteers. Isometric handgrip, cold pressor test, and acute baroreceptor unloading with sodium nitroprusside (autonomic stresses) were carried out under two conditions, one group (n = 11) before (control responses) and after naloxone and another group (n = 8) before and after placebo saline. Monitored cardiovascular variables included heart rate, central venous pressure (jugular vein catheter), arterial blood pressure (radial artery catheter), circulating catecholamines, and forearm blood flow. At rest, cardiovascular variables and MSNA were not affected by either naloxone or saline. MSNA (total activity = burst frequency x burst amplitude/100 cardiac cycles) increased during isometric handgrip to a greater extent (30 +/- 6 vs. 16 +/- 5 arbitrary units) after naloxone compared with control trials (P less than 0.05). After naloxone, arterial systolic and diastolic blood pressures were higher during handgrip exercise. These augmented arterial pressures and MSNA responses were not evident during either the cold pressor test or the sodium nitroprusside stress. These data suggest that isometric muscle contraction elicits a sympathetic neural response that may be modified by EOP. This interaction is not evident during two other stresses, when sympathetic responses are equal to or greater than those provoked by isometric handgrip exercise.
Effects of calcium on protein turnover of incubated muscles from mdx mice
Authors: MacLennan P. A. , McArdle A. , Edwards R. H.
Published: December 2017

Mdx mice have a genetic defect similar to that which causes Duchenne muscular dystrophy in humans. The influence of calcium on muscle protein metabolism of mdx and wild type (C57BL/10) mice was examined in vitro. Incubation of mdx muscles in a medium containing calcium at a concentration of 2.0 mM (but not 0.2 mM) resulted in proteolytic rates that were greater than those of C57BL/10 muscles. At 2.0 mM extracellular calcium, mdx muscle proteolysis was attenuated by thiol protease inhibitors but not by the weak base methylamine. Protein synthetic rates were higher in incubated mdx muscles than in incubated C57BL/10 muscles, but no effect of extracellular calcium concentration was observed in either strain. These data suggest that mdx mice have an abnormality of muscle calcium handling, which results in activation of nonlysosomal proteolytic processes but does not exert acute effects on protein synthetic rate.
Regulation of venous alpha-adrenergic responses in older humans
Authors: Supiano M. A. , Hogikyan R. V. , Stoltz A. M. , Orstan N. , Halter J. B.
Published: December 2017

Decreased adrenergic responsiveness in human aging could be a result of downregulation mediated by the age-related increase in sympathetic nervous system (SNS) tone. If so, suppression of SNS tone in elderly subjects should upregulate adrenergic responsiveness into the range observed for younger subjects. To test this hypothesis, we examined alpha 1 (phenylephrine)- and alpha 2 (clonidine)-adrenergic agonist-mediated venoconstriction in a group of 15 older healthy subjects (age 59-73 yr) during placebo and when SNS tone was suppressed by guanadrel (15 mg twice daily for 3 wk). During guanadrel compared with placebo 1) there were decreases in plasma norepinephrine (NE) levels (1.47 +/- 0.07 to 0.80 +/- 0.06 nM; P less than 0.001) and in the extravascular NE release rate derived from [3H]NE kinetics (11.8 +/- 1.4 to 6.1 +/- 1.0 nmol.min-1.m-2; P = 0.01), suggesting suppression of SNS tone; 2) there was an augmented clonidine-mediated venoconstriction response [analysis of variance (ANOVA) P = 0.01]; and 3) there was no detectable change in phenylephrine-mediated venoconstriction (ANOVA P = 0.60). When compared with previous results from young subjects, maximal alpha 2-adrenergic venoconstriction during guanadrel was decreased in the elderly compared with the young, although their response appeared to be appropriately upregulated by the decrease in SNS tone. The lack of an age-related decrease in alpha 1-adrenergic venoconstriction, together with the lack of upregulation of this response during guanadrel, suggests that regulation of this alpha 1-adrenergic response is impaired in the older group.
Glucose consumption decreases throughout the brain only hours after portacaval shunting
Authors: DeJoseph M. R. , Hawkins R. A.
Published: December 2017

The cerebral metabolic rate for glucose (CMRGlc) was measured at the level of individual structures 6, 12, 24, and 48 h and 4 wk after the formation of a portacaval shunt in rats, a model of hepatic encephalopathy. A quantitative autoradiographic technique with [6-14C]glucose as tracer was used. After 6 h, CMRGlc was depressed in all areas measured by an average of 16%. By 48 h, CMRGlc fell further and reached a value comparable to that seen in rats shunted for many weeks (25-30% below normal). The decrease in CMRGlc occurred throughout the brain to about the same degree. CMRGlc was also measured with another tracer, deoxy-D-[14C]glucose, 48 h after portacaval shunting. The deoxy-D-glucose results agreed with those obtained with [6-14C]glucose. The decrease in CMRGlc may be interpreted to be a consequence of the decreased activity of brain cells, reflecting the cerebral dysfunction that occurs when liver function is inadequate. The experiments demonstrate that the onset of cerebral dysfunction occurs within hours of portacaval shunting and is fully established within days.
Effect of salivary epidermal growth factor on wound healing of tongue in mice
Authors: Noguchi S. , Ohba Y. , Oka T.
Published: December 2017

The role of salivary epidermal growth factor (EGF) in wound healing of the tongue was studied in mice. Sialoadenectomy (removal of the submandibular glands, which are the major source of salivary EGF) or sham operation was performed 2 wk before infliction of wound on the tongue. Salivary EGF levels were 1.98 +/- 0.47 and 0.20 +/- 0.04 (SE) microgram/ml in sham-operated male and female mice, respectively, whereas sialoadenectomy reduced salivary EGF to undetectable levels in both male and female mice. A circular superficial wound measuring approximately 2 mm in diameter was made in the middle of the tongue by mechanically ablating only the epithelial layer. The rate of wound healing was monitored by a stereomicroscopy. Sialoadenectomized male mice showed a significant delay in wound healing compared with sham-operated controls. Treatment of sialoadenectomized male mice with EGF (1 microgram/ml in drinking water) restored the rate of wound healing to normal levels. Transforming growth factor (1 microgram/ml) was as effective as EGF in the promotion of wound healing, whereas nerve growth factor (1 microgram/ml) was ineffective. Essentially the same results were obtained in female mice. In addition, two classes of EGF binding sites with high and low affinity were demonstrated in the epithelium of the tongue obtained from male and female mice. The maximum binding sites and dissociation constants of the EGF receptors were the same between males and females and were not affected by sialoadenectomy. These results suggest that salivary EGF is involved in the promotion of wound healing of the tongue in both male and female mice.
Energy metabolism in single human muscle fibers during contraction without and with epinephrine infusion
Authors: Greenhaff P. L. , Ren J. M. , Soderlund K. , Hultman E.
Published: December 2017

The concentrations of glycogen, ATP, and phosphocreatine were analyzed in types I and II muscle fibers separated from biopsy samples of the quadriceps femoris muscle in five healthy volunteers. Muscle samples were obtained before and after 64 s of intermittent electrical stimulation. The experiment was carried out without and with epinephrine (Epi) infusion. Before stimulation the glycogen concentration was 11% higher in type II than in type I fibers (P less than 0.05). During electrical stimulation, rapid glycogenolysis occurred in type II fibers with hardly any detectable glycogenolysis in type I fibers. The calculated rates of glycogenolysis were 0.18 +/- 0.14 and 3.54 +/- 0.53 mmol glucose.kg dry muscle-1.s-1 in types I and II fibers, respectively. Epi infusion increased the rate of glycogenolysis during electrical stimulation in type I fibers (10-fold) but did not enhance the rate in type II fibers (P greater than 0.05). It is considered that, during short-term maximal muscle contraction, rapid muscle glycogenolysis occurs predominantly in type II fibers even though types I and II fibers are recruited and that, when Epi stimulation of glycogenolysis occurs, this is predominantly limited to type I fibers.
Insulin stimulates sodium-dependent phosphate transport by osteoblast-like cells
Authors: Kunkler K. J. , Everett L. M. , Breedlove D. K. , Kempson S. A.
Published: December 2017

The rat osteosarcoma cell line UMR-106-01 has an osteoblast-like phenotype. When grown in monolayer culture, these cells transport Pi via a Na(+)-dependent carrier. The Na(+)-Pi cotransport system is stimulated by parathyroid hormone (PTH). Because there are insulin receptors on osteoblast-like cells, we determined possible effects of insulin on Na(+)-Pi cotransport in UMR-106-01 cells. Incubation of cells with 10(-8) M insulin for 3 h produced a 73% increase (P less than 0.025) in Na(+)-Pi cotransport. There was no significant change in Na(+)-L-alanine cotransport or in Na(+)-independent uptake of Pi and alanine. The stimulatory action of insulin on Na(+)-Pi cotransport was present within 2 h and was dose dependent in the range 10(-10) to 10(-7) M. The increase in Na(+)-Pi cotransport was accompanied by an increase in apparent maximal velocity with no change in apparent Michaelis constant for Pi. Use of cycloheximide to block de novo protein synthesis did not interfere with this action of insulin. We conclude that insulin, like PTH, directly stimulates the Na(+)-Pi cotransport system in osteoblast-like cells. The mechanism remains to be determined.
Control of glycogenolysis and blood flow by arterial and portal norepinephrine in perfused liver
Authors: Gardemann A. , Jahns U. , Jungermann K.
Published: December 2017

In isolated rat liver single pass perfused via both the hepatic artery (80 mmHg, 30% flow) and the portal vein (10 mmHg, 70% flow), norepinephrine (NE) was infused either singly or jointly via the hepatic artery or the portal vein in the absence or presence of the alpha 1-blocker prazosin or the beta 2-blocker butoxamine. Arterial NE caused an increase in glucose output and a shift from lactate uptake to release that was slower in onset and smaller in peak height but longer in duration than the alterations affected by portal NE. The sum of the metabolic changes by arterial and portal NE was not equal to the changes by jointly applied arterial plus portal NE. The metabolic alterations by arterial NE were mediated via alpha 1-receptors, with beta 2-receptors probably having a permissive function, but those by portal NE were transmitted only via alpha 1-receptors. Arterial NE caused a strong decrease in arterial flow and contralaterally also a smaller reduction of portal flow. Portal NE decreased portal flow but did not significantly influence arterial flow. The sum of the alterations in flow by arterial and portal NE was not equal to the changes by jointly applied NE. The hemodynamic alterations in the artery by arterial NE were the results of actions via alpha 1-receptors and counteractions via beta 2-receptors, whereas the changes in the portal vein by arterial NE and portal NE were mediated via alpha 1-receptors. About 65% of arterial and only 30% of portal NE was extracted during a single path. The results indicate that the hepatic artery and the portal vein can function as independent sites of hormonal signal input, which interact by complex but still undefined mechanisms in the regulation of metabolism and hemodynamics.
Molecular cloning of a rat uterine gap junction protein and analysis of gene expression during gestation
Authors: Lang L. M. , Beyer E. C. , Schwartz A. L. , Gitlin J. D.
Published: December 2017

To study the molecular mechanisms controlling the rapid increase in myometrial gap junctions observed in the parturient uterus, we have isolated a full-length cDNA clone corresponding to a rat uterine gap junction protein. Nucleotide sequence analysis of the cDNA clone reveals complete identity of the coding region with that of a previously reported heart gap junction protein (connexin43). Southern blot analysis suggests that the gene encoding this gap junction protein exists as a single copy in the rat haploid genome and contains no introns within the coding region. RNA blot analysis with this gap junction cDNA reveals a single 3.0-kb mRNA in uterine tissue without changes in transcript size throughout gestation. When normalized to the amount of 28S rRNA, the relative abundance of the connexin43 transcript in uterine tissue is quite constant between the nonpregnant state, during gestation, intrapartum, and postpartum. Similar size transcripts are shown by RNA blot analysis to be present in heart, lung, liver, brain, and skeletal muscle, and these transcripts are identified by the same 3'-nontranslated sequence probe. The results of these studies suggest that rat connexin43 is encoded by a single gene that is transcribed to identical transcripts in heart, uterus, and other tissues. They further suggest that changes in the abundance of connexin43 transcript are unlikely to be responsible for the abrupt increase in connexin43-containing myometrial gap junctions at term.
Opiate blockade enhances hypoglycemic counterregulation in normal and insulin-dependent diabetic subjects
Authors: Caprio S. , Gerety G. , Tamborlane W. V. , Jones T. , Diamond M. , Jacob R. , Sherwin R. S.
Published: December 2017

To examine the impact of opiate blockade on glucose counterregulation we performed two hypoglycemic insulin clamp studies with and without naloxone in healthy subjects and well-controlled insulin-dependent (IDDM) patients with defective glucose counterregulation. During both studies plasma glucose fell to 55-60 mg/dl and was then maintained at that level using a variable glucose infusion. In normal subjects, naloxone increased glucose production, thereby reducing the exogenous glucose dose needed to maintain the hypoglycemic plateau. Epinephrine and cortisol responses to hypoglycemia were increased during naloxone plus insulin compared with insulin alone; glucagon responses were unaffected. IDDM patients with suppressed hepatic and hormonal responses to insulin-induced hypoglycemia also demonstrated greater stimulation of glucose production as well as epinephrine, growth hormone, and cortisol release during the naloxone study. In the absence of hypoglycemia, naloxone did not significantly affect glucose production or glucoregulatory hormones. We conclude that opiate blockade augments glucoregulatory responses to insulin-induced hypoglycemia, even in IDDM patients with preexisting defects in glucose counterregulation. This effect is at least in part due to enhanced counterregulatory hormone release during hypoglycemia. Endogenous opiates may modulate hormonal responses during hypoglycemia; their blockade could provide a means of ameliorating defective counterregulation in IDDM patients.
Role of glycogen in control of glycolysis and IMP formation in human muscle during exercise
Authors: Spencer M. K. , Katz A.
Published: December 2017

The effect of prior glycogen depletion on glycolysis [flux through phosphofructokinase (PFK)] and inosine monophosphate (IMP) formation in human skeletal muscle has been investigated. Eight subjects cycled at a work load calculated to elicit 95% of maximal O2 uptake on two occasions, the first to fatigue [5.5 +/- 0.3 (SE) min] and the second at the same workload and for the same duration as the first. Before the first experiment, muscle glycogen stores were lowered by a combination of exercise and diet. Before the second experiment, muscle glycogen stores were supercompensated. In the low-glycogen (LG) state muscle glycogen decreased from 201 +/- 31 mmol glucosyl units/kg dry wt at rest to 105 +/- 28 after exercise, and in the high-glycogen (HG) state from 583 +/- 40 to 460 +/- 49. The accumulation of fructose 6-phosphate (F-6-P; activator of PFK) during exercise was markedly attenuated in the LG state (P less than 0.01), whereas lactate accumulation in muscle was similar between treatments, suggesting that muscle pH was also similar. Glycolysis (estimated from glycogenolysis minus accumulation of hexose monophosphates) was not measurably different between treatments (LG = 88 +/- 17, HG = 106 +/- 43 mmol/kg dry wt; P greater than 0.05). IMP was significantly greater in the LG state after exercise (3.63 +/- 0.85 vs. 1.97 +/- 0.44 mmol/kg dry wt; P less than 0.05). It is concluded that decreased glycogen availability does not measurably alter the rate of muscle glycolysis during intense exercise. It is hypothesized that the attenuated increase in F-6-P in the LG state, which should theoretically decrease glycolysis, is compensated for by increases in free ADP and AMP (activators of PFK) at the enzymatic site during the contraction phase. The greater increase in IMP in the LG state is consistent with this hypothesis, since ADP and AMP are also activators of AMP deaminase.
Nerve blood flow in early experimental diabetes in rats: relation to conduction deficits
Authors: Cameron N. E. , Cotter M. A. , Low P. A.
Published: December 2017

A reduction in nerve blood flow in chronic experimental diabetes has been linked to impaired conduction. Recently, there have been reports that this is preceded by a period of functional hyperemia. The present investigation explored early changes in sciatic nerve endoneurial blood flow and function in streptozocin-treated rats with durations of diabetes from 1 wk to 4 mo. Blood flow was monitored by microelectrode polarography and hydrogen clearance in thiobutabarbital (Inactin)-anesthetized animals. It was reduced by 41% as early as 1 wk after diabetes induction. There was no evidence of an early functional hyperemia, flow remaining 44% depressed up to 4 mo. In another investigation, similar reductions in blood flow were acutely induced in normal rats rendered hyperglycemic by glucose infusion. In diabetic animals, conduction velocity in sciatic branches supplying gastrocnemius and tibialis anterior muscles was correlated with blood flow. The link was further tested using a group of 2-mo diabetic rats treated with guanethidine. Treatment caused a functional adrenergic sympathectomy, and blood flow increased to within the normal range. Conduction velocity, depressed by 26% with diabetes, was normalized by treatment. These observations support the hypothesis that hyperglycemia-induced blood flow reductions and resultant endoneurial hypoxia are important factors underlying nerve conduction deficits early in the development of diabetic neuropathy.
Release of galanin from isolated perfused porcine adrenal glands: role of splanchnic nerves
Authors: Holst J. J. , Ehrhart-Bornstein M. , Messell T. , Poulsen S. S. , Harling H.
Published: December 2017

We found a high concentration of galanin in extracts of porcine adrenal glands (114 pmol/g). By immunohistochemistry, galanin was localized to groups of medullary cells previously shown to produce norepinephrine. To study mechanisms for the release of galanin, we developed the following in vitro model: isolated perfused porcine adrenals with intact splanchnic nerve supply. When the nerves were electrically stimulated, epinephrine and norepinephrine secretion increased 276- and 291-fold, respectively, and galanin release increased up to 1,300-fold. Acetylcholine at 10(-6) M stimulated galanin release, and hexamethonium almost abolished the response to nerve stimulation. Galanin infusions had no effect on epinephrine and norepinephrine secretion in concentrations of 10(-8) and 10(-7) M, but increased both cortisol and aldosterone secretion (P less than 0.05). Splanchnic nerve stimulation in anesthetized pigs increased the concentration of galanin in the caval vein but not in arterial plasma. It is concluded that galanin, coreleased with catecholamines from the adrenal glands, may have endocrine functions but that galanin may also have local regulatory functions in the adrenals.
Muscle insulin resistance in uremic humans: glucose transport, glucose transporters, and insulin receptors
Authors: Friedman J. E. , Dohm G. L. , Elton C. W. , Rovira A. , Chen J. J. , Leggett-Frazier N. , Atkinson S. M. , Thomas F. T. , Long S. D. , Caro J. F.
Published: December 2017

To determine the cellular basis for insulin resistance observed in patients with uremia, we investigated insulin action in vivo and in vitro using skeletal muscle obtained from patients with chronic renal failure. Uremic subjects had significantly reduced rates of insulin-stimulated glucose disposal, as determined by a 3-h intravenous glucose tolerance test and using the hyperinsulinemic euglycemic clamp technique. Hepatic glucose production was similar before (control, 76.2 +/- 6.3 vs. uremic, 74.2 +/- 6.9 mg.kg-1.min-1) and during insulin infusion at 40 mU.m-2.min-1 (control, -60.9 +/- 6.6 vs. uremic, -53.9 +/- 6.3 mg.kg-1.min-1). In incubated human skeletal muscle fiber strips, basal 2-deoxy-D-glucose transport was unchanged in uremic subjects compared with controls. However, the increase in insulin-stimulated glucose transport was significantly reduced by 50% in muscles from uremic patients (P = 0.012). In partially purified insulin receptors prepared from skeletal muscle, 125I-labeled insulin binding, beta-subunit receptor autophosphorylation, and tyrosine kinase activity were all unchanged in uremic subjects. The abundance of insulin-sensitive (muscle/fat, GLUT-4) glucose transporter protein measured by Western blot using Mab 1F8 or polyclonal antisera was similar in muscles of control and uremic patients. These findings suggest that the insulin resistance observed in skeletal muscle of uremic patients cannot be attributed to defects in insulin receptor function or depletion of the GLUT-4 glucose transporter protein. An alternative step in insulin-dependent activation of the glucose transport process may be involved.
Uptake of glucose carbon in muscle glycogen and adipose tissue triglycerides in vivo in humans
Authors: Marin P. , Hogh-Kristiansen I. , Jansson S. , Krotkiewski M. , Holm G. , Bjorntorp P.
Published: December 2017

Glucose disposal into muscle glycogen has previously been directly studied after intravenous, but not after physiological, oral administration. In this study 100 g glucose, containing 50 microCi [U-14C]glucose, were taken orally by premenopausal women in the overnight fasting state or after a carbohydrate-rich meal. After 4 h, biopsies were taken from the vastus lateralis muscle and abdominal and femoral subcutaneous adipose tissue for determinations of label in isolated glycogen and triglycerides, respectively. Uptake of administered glucose carbon in muscle glycogen was estimated to be approximately 20 g in the fasting and approximately 9 g in the carbohydrate-fed groups, respectively. Total uptake in adipose tissue triglycerides was approximately 2 g. Glucose carbon uptake in muscle glycogen correlated positively with glucose infusion rates during euglycemic hyperinsulinemic glucose clamps, glycogen synthase activity in vitro, and type I muscle fiber distribution and fiber area. Negative correlations were found between glucose uptake in adipose tissue triglycerides, type II fiber distribution and fiber area, as well as the waist-to-hip circumference ratio and degree of obesity. It was concluded that muscle glycogen is probably not a major pathway for disposal of oral glucose carbon in the sedentary condition.
Single umbilical artery ligation-induced fetal growth retardation: effect on postnatal adaptation
Authors: Oyama K. , Padbury J. , Chappell B. , Martinez A. , Stein H. , Humme J.
Published: December 2017

To assess whether prolonged intrauterine stress and resultant fetal growth retardation result in depletion of adrenal catecholamines and alter the adrenergic signal transduction system, we studied newborn sheep after single umbilical artery ligation (SUAL)-induced growth retardation. The animals were delivered at term, and postnatal cardiovascular, pulmonary, endocrine, and metabolic responses were measured. We also evaluated the status of myocardial and pulmonary beta-adrenergic receptor number and function. SUAL caused significant growth retardation but relative preservation of brain and adrenal gland weight and adrenal catecholamine content. Blood pressure, plasma free fatty acid, and glucose responses at birth were blunted in SUAL animals. The plasma epinephrine (Epi) and norepinephrine levels were comparable in both groups for the first 2 h of age. By 4 h, both plasma concentration and plasma appearance rate of Epi were reduced to 40% of control in SUAL animals (P less than 0.05). Neither beta-receptor density, affinity, nor adenylate cyclase activity were altered by SUAL in either cardiac or pulmonary membranes. These results suggest that, rather than overt depletion, there is relative sparing of initial adrenal medullary function that later waned. This response and preservation of the beta-adrenergic signal transduction system may represent partial compensation for the physiological stress induced by SUAL.
Role of eicosanoids in vasopressin-induced calcium mobilization in A7r5 vascular smooth muscle cells
Authors: Thibonnier M. , Bayer A. L. , Laethem C. L. , Koop D. R. , Simonson M. S.
Published: December 2017

The role of arachidonic acid (AA) and its metabolites in vasopressin (AVP)-induced calcium mobilization in A7r5 aortic smooth muscle cells was explored by intracellular calcium monitoring, [14C]AA labeling, and high-performance liquid chromatography (HPLC) techniques. In fura 2-loaded A7r5 cells, AA potentiated AVP-stimulated increase in intracellular free Ca2+ ([Ca2+]i). The cyclooxygenase inhibitor indomethacin reduced both the AA- and AVP-induced influx of extracellular Ca2+. AVP-induced [Ca2+]i transients were not altered by lipoxygenase inhibitors but were reduced in a dose-dependent fashion by ketoconazole, an inhibitor of cytochrome P-450 monooxygenases. Among several epoxygenase metabolites of AA tested, 5,6-epoxyeicosatrienoic acid potentiated AVP-induced [Ca2+]i transients. Reverse-phase HPLC analysis of lipid extracts from A7r5 cells prelabeled with [14C]AA isolated a radioactive peak that did not coelute with established products of cyclooxygenase-, lipoxygenase-, or cytochrome P-450-catalyzed oxidations of AA. This peak was significantly increased after AVP stimulation and was completely blocked by preincubation with ketoconazole. Thus the stimulation of V1-vascular AVP receptors of A7r5 cells triggers several cytoplasmic signaling pathways involving AA metabolite formation through the cyclooxygenase and epoxygenase pathways.
Clenbuterol mimics effects of innervation on myogenic regulatory factor expression
Authors: Maltin C. A. , Delday M. I. , Campbell G. P. , Hesketh J. E.
Published: December 2017

The amelioration of denervation atrophy by the beta-adrenoceptor agonist clenbuterol has led to the suggestion that the drug mimics or stimulates production of neurotrophic factors. Neurotrophic factors have profound effects on muscle growth, but the precise mechanisms through which this influence is exerted are unknown. The expression of myoD and myogenin, proteins that in turn regulate the transcription of tissue-specific genes during skeletal muscle differentiation, is controlled by innervation. In muscle undergoing denervation-induced atrophy, myoD and myogenin mRNAs increase. However, this is only partially reversed by electrical activity, thus implicating neurotrophic factors in regulation of these genes. Here we demonstrate that clenbuterol represses myoD and myogenin expression and decreases the levels of acetylcholine receptors in denervated muscles. The data provide the first evidence that the action of clenbuterol is directed through the neural axis.
Free and conjugated catecholamines and serotonin in canine thoracic duct lymph: effects of feeding
Authors: Chen Y. K. , Richter H. M. , Go V. L. , Tyce G. M.
Published: December 2017

The source and fate of sulfoconjugated catecholamines present in plasma are not known. Sulfated norepinephrine has been shown to overflow together with free norepinephrine from a typical peripheral neuroeffector junction. Some released free norepinephrine is removed via the lymphatic system, but it is not known whether sulfated catecholamines are removed similarly. Serotonin, another biogenic amine, is released from the enterochromaffin cells into portal blood. The aims of the present study were to determine whether conjugated catecholamines and serotonin could be detected in thoracic duct lymph of dogs and to compare concentrations in lymph with those in samples of portal blood collected before and after the dogs were fed. A method is described for the extraction and purification of free and conjugated catecholamines and serotonin from lymph. In lymph and in plasma, there were similar concentrations of free (0.2-0.4 ng/ml) and conjugated (0.1-0.2 ng/ml) norepinephrine and of conjugated dopamine (0.2-1.0 ng/ml). The concentrations of free serotonin were much lower in lymph (0.1-0.2 ng/ml) than in portal blood (100-200 ng/ml). Small amounts of conjugated serotonin (0.1-0.4 ng/ml) were detected in lymph but were not detected in plasma. Feeding caused increases in concentration of conjugated dopamine in lymph and in plasma and small increases in the output of free norepinephrine and free and conjugated serotonin in lymph.
Direct measurement of change in muscle glycogen concentration after a mixed meal in normal subjects
Authors: Taylor R. , Price T. B. , Katz L. D. , Shulman R. G. , Shulman G. I.
Published: December 2017

Postprandial storage of carbohydrate as glycogen in muscle was quantitated in normal subjects (n = 8) by natural abundance 13C-nuclear magnetic resonance spectroscopy with proton decoupling in a 4.7-tesla magnet. After an overnight fast three basal measurements of gastrocnemius muscle glycogen were made and a mixed meal was given. Muscle glycogen concentration rose from 83.3 +/- 5.2 to a maximum of 100.2 +/- 6.7 mmol/l muscle at 4.9 h (P < 0.01) and fell thereafter to 90.6 +/- 5.9 mmol/l muscle at 7 h postprandially (P < 0.006). The meal brought about an increase in plasma glucose from 5.4 +/- 0.2 to 7.3 +/- 0.4 mmol/l at 30 min but this was followed by a rapid fall to 6.2 +/- 0.4 mmol/l at 75 min. Plasma insulin rose from 62.4 +/- 11.4 to 900 +/- 216 pmol/l at 30 min and declined steadily thereafter. It was calculated from total muscle mass measurements and estimation of carbohydrate absorption rates that at peak muscle glycogen concentrations between 26 and 35% of the absorbed carbohydrate was stored as muscle glycogen. These data quantitate the role of skeletal muscle glycogen synthesis in postprandial carbohydrate storage and demonstrate that this tissue acts as a dynamic buffer to maintain glucose homeostasis during postprandial substrate storage.
Metabolic acidosis inhibits growth hormone secretion in rats: mechanism of growth retardation
Authors: Challa A. , Krieg R. J. , Thabet M. A. , Veldhuis J. D. , Chan J. C.
Published: December 2017

To test the hypothesis that growth retardation in nonanion gap acidosis may be associated with impairment of growth hormone (GH) secretory patterns, we examined GH secretion in rats made acidotic with ammonium chloride ingestion. Considerable growth retardation was demonstrated in pair-fed and acidotic rats after 1 wk of ammonium chloride ingestion compared with control. With stable metabolic acidosis sustained on the 8th day of experiment, pulsatile secretion of GH was evaluated by blood samples drawn every 10 min for 6 h. Using deconvolution analysis to quantitate in vivo GH secretory rates, we found significant inhibition of pulsatile GH secretion in acidotic rats. Changes in amplitude of GH pulses and mean mass of GH pulses correlated with changes in body weight. These studies showed that chronic metabolic acidosis causes growth impairment, reduced food efficiency, and amplitude-specific inhibition of pulsatile secretion of GH. We propose that this GH axis suppression, whether mediated by decreased nutrients or not, contributes significantly to growth failure in children with renal tubular acidosis. Because a similar degree of inhibition of GH secretion was seen in pair-fed rats, we infer that insufficient calorie intake in metabolic acidosis may contribute to disruption of normal GH secretion patterns. These changes in GH secretion were specific, because acidotic rats were different from pair-fed controls in that they showed no change in either half-life of GH in circulation or in pulse frequency. Such observations offer a rationale for more detailed clinical investigations into the impact of metabolic acidosis on physiological regulation of pulsatile GH secretion in humans.
Creatine kinase isoenzymes are highly regulated during pregnancy in rat uterus and placenta
Authors: Payne R. M. , Friedman D. L. , Grant J. W. , Perryman M. B. , Strauss A. W.
Published: December 2017

Creatine kinase (CK) isoenzymes play a central role in energy transfer. Expression of CK isoenzymes in rat uterus and placenta was analyzed to evaluate their contribution to energy metabolism during pregnancy and delivery. Tissue from the uterine horns and placentas of pregnant rats from day 14 of gestation to 17 days postpartum was analyzed for expression of “brain” CK (BCK) and ubiquitous mitochondrial CK (uMtCK) mRNA, protein, and enzyme activity. uMtCK mRNA expression is high in prepartum uterus, but rapidly falls (> 10-fold) after delivery to a nadir at 7 days postpartum. Prepartum BCK mRNA expression is coordinate with uMtCK but has a 15-fold greater expression than uMtCK. Both CK mRNAs rise by 17 days postpartum. Both BCK and uMtCK mRNA expressions are strongly induced in placenta at 20 days gestation with a rapid fall (> 6-fold) immediately before delivery. Protein expression of BCK and uMtCK is also coordinate. However, analysis of mRNA and protein expression indicates that significant posttranscriptional regulation of both kinds of CK also occurs. CK activity in uterus and placenta reflects BCK expression. By immunohistochemistry, BCK and uMtCK protein expression is highly localized in the placenta and endometrium of prepartum uterus. This expression shifts entirely to the uterine smooth muscle by 17 days postpartum. uMtCK mRNA expression is rapidly induced by beta-estradiol in vitro (> 6-fold), demonstrating estrogen-responsive elements in the uMtCK nuclear gene. Thus a second isoenzyme of CK, uMtCK, is expressed in rat uterus and placenta and is highly regulated with BCK. These results suggest an important role for CK in the maintenance and termination of pregnancy.