bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased bone formation in rat tibiae after a single short period of dynamic loading in vivo
Authors: Forwood M. R. , Owan I. , Takano Y. , Turner C. H.
Published: December 2017

Based on our quantum concept for mechanically adaptive bone formation, we hypothesized that a single bout of loading would increase bone formation at the endosteal surface in rat tibiae, with a maximal response 4-8 days after loading and a stimulus-response relationship for load magnitude. Bending loads were applied to right tibiae of rats at 31, 43, 53, or 65 N for a single bout of 36 or 360 cycles; bone formation was assessed 1-4, 5-8, or 9-12 days after loading. A single loading episode increased lamellar bone formation rate (BFR) in all groups (P<0.05) and was maximal 5-8 days after loading. A distinct dose-response relationship was not evident among all load magnitudes or for duration, but 65 N was significantly more osteogenic than loads of 31-53 N (P<0.05), consistent with a threshold response to loading. There was also evidence for a significant increase in BFR (P<0.05) and double-labeled surface (P<0.01) within 4 days of loading, suggesting that bone-lining cells were activated directly by the stimulus. Thus subtle changes in BFR may occur by modulating the activity of surface cells, but large modeling drifts and anabolic responses require recruitment and differentiation of osteoprogenitor cells near the bone surface.
Increments in skeletal muscle GLUT-1 and GLUT-4 after endurance training in humans
Authors: Phillips S. M. , Han X. X. , Green H. J. , Bonen A.
Published: December 2017

We investigated the time course of training-induced changes in the expression of GLUT-1 and GLUT-4 in human skeletal muscle. Seven healthy males trained for 2 h/day (approximately 60% pretraining VO2peak) for 31 days (31D). Muscle biopsies were obtained before training (PRE) and after 5 (5D) and 31 days (31D) of training. Training resulted in progressive increases in muscle GLUT-4 with increasing training duration (PRE<5D<31D; P<0.01). Muscle GLUT-1 content was also increased (P<0.05) after training; however, the increase was not observed until 31D (131%). Increases in muscle hexokinase (HK) activity were complete by 5D (P<0.01). Muscle malate dehydrogenase activity was not elevated after 5D of training but was increased (+35%; P<0.01) at 31D. Results from this study show that increases in both GLUT-4 and HK represent early training-induced adaptations to prolonged exercise training. As training progresses, further increases in GLUT-4, but not HK, occur in conjunction with an increase in muscle mitochondrial potential and GLUT-1.
Preservation of insulin secretory responses to P2 purinoceptor agonists in Zucker diabetic fatty rats
Authors: Tang J. , Pugh W. , Polonsky K. S. , Zhang H.
Published: December 2017

The role of P2 purinoceptor agonists in regulatory insulin secretion in Zucker diabetic fatty (ZDF) rats was studied using the isolated perfused pancreas and intracellular Ca2+ concentration ([Ca2+]i) microfluorimetry. The relative potency of different purinoceptor agonists to stimulate the insulin secretory process was consistent with the conclusion that responses in [Ca2+]i and insulin secretion are mediated by the P2y subtype of purinoceptors. Additional studies using specific antagonists of the Ca2+ signaling pathway indicated that activation of P2y purinoceptor releases Ca2+ from intracellular stores and promotes Ca2+ entry through voltage-independent rather than voltage-dependent Ca2+ channels on the beta-cell membrane. Perfused pancreas and isolated islets from ZDF rats demonstrated markedly reduced or absent insulin secretion and [Ca2+]i responses to glucose and KCl. In contrast, responses to P2y purinoceptor agonists were normal, indicating that the secretion coupling pathway activated by these agonists is preserved in glucose-unresponsive islets from diabetic animals. These observations raise the possibility that the purinoceptor pathway may play an important role in regulating insulin secretion in hyperinsulinemic non-insulin-dependent diabetes mellitus.
Integrated mathematical model to assess beta-cell activity during the oral glucose test
Authors: Thomaseth K. , Kautzky-Willer A. , Ludvik B. , Prager R. , Pacini G.
Published: December 2017

A model describing beta-cell secretion during an oral glucose tolerance test (OGTT) is introduced. The aim was to quantify beta-cell activity in different pathologies by analyzing peripheral concentration data of insulin, C-peptide, and islet amyloid polypeptide (IAPP). Insulin appearance in periphery is given by the fraction of C-peptide secretion, CPS(t), which accounts for liver degradation. A novelty of this study is the inclusion of IAPP delivery assumed proportional to CPS(t). Although IAPP fractional clearance is estimated in every subject, the clearances of insulin and C-peptide are assigned from a wide set of previous independent studies. Sensitivity analysis was performed to quantify the "error" in the estimated variables due to these assignments. All parameters relating to beta-cell secretion increased in the glucose-intolerant states [integrated CPS(t)=56 +/- 8 nmol/l in 180 min vs. 32 +/- 3 of controls, P<0.05; total IAPP delivery= 83 +/- 21 pmol/l in 180 min vs. 41 +/- 6, P<0.05]. Elevated plasma IAPP concentration of the patients was due to augmented secretion since IAPP clearance was found to be even slightly greater than in controls, (0.053 +/- 0.011 vs. 0.034 +/- 0.004 min-1) and markedly lower than that of insulin (0.14 +/- 0.02, P<0.01). In conclusion, the model introduced here allows the characterization of beta-cell secretory parameters during a simple test such as OGTT.
The hot but not the cold minimal model allows precise assessment of insulin sensitivity in NIDDM subjects
Authors: Avogaro A. , Vicini P. , Valerio A. , Caumo A. , Cobelli C.
Published: December 2017

Assessment of insulin sensitivity in subjects with non-insulin-dependent diabetes mellitus (NIDDM) is of paramount importance but intrinsically difficult. The standard (hereafter cold) minimal model, in conjunction with an insulin-modified protocol, has been recently proposed, but the estimates of insulin sensitivity showed poor precision (Saad et al. Diabetes 43: 1114-1121, 1994). We propose the tracer (hereafter hot) minimal model as a highly reliable method to estimate insulin sensitivity (SI*) and fractional glucose clearance (SG*), reflecting glucose disposal only, in NIDDM subjects. A [6,6- 2H2] glucose-labeled insulin-modified intravenous glucose tolerance test was performed in seven NIDDM subjects. In particular, SI* was 1.07 +/- 0.34 x10(-4)min(-1).microU-1.ml estimated with an average precision (mean coefficient of variation of 12%, range 4-22%), whereas the cold minimal model SI was 0.96 +/- 0.26 x 10(-4) min-1. microU-1.ml (mean coefficient of variation of 105%, range 3-353%). Another advantage of the hot indexes with respect to the cold indexes is their ability to reflect glucose and insulin effect on glucose disposal only, and not also on hepatic glucose production. Finally, we also studied by simulation the effect of glucose urinary loss on cold and hot minimal model indexes; only cold glucose effectiveness (SG) was significantly affected, resulting in a mean approximately 40% lower. The hot minimal model appears therefore more reliable than the cold model for assessing glucose tolerance in NIDDM subjects. In particular its ability to dissect disposal from production processes, coupled with the very good precision of the estimated metabolic indexes, supports the clinical use of this method in NIDDM subjects.
Role of insulin and IGF-I in activation of muscle protein synthesis after oral feeding
Authors: Svanberg E. , Zachrisson H. , Ohlsson C. , Iresjo B. M. , Lundholm K. G.
Published: December 2017

The aim was to evaluate the role of insulin and insulin-like growth factor I (IGF-I) in activation of muscle protein synthesis after oral feeding. Synthesis rate of globular and myofibrillar proteins in muscle tissue was quantified by a flooding dose of radioactive phenylalanine. Muscle tissue expression of IGF-I mRNA was measured. Normal (C57 Bl) and diabetic mice (type I and type II) were subjected to an overnight fast (18 h) with subsequent refeeding procedures for 3 h with either oral chow intake or provision of insulin, IGF-I, glucose, and amino acids. Anti-insulin and anti-IGF-I were provided intraperitoneally before oral refeeding in some experiments. An overnight fast reduced synthesis of both globular (38 +/- 3%) and myofibrillar proteins (54 +/- 3%) in skeletal muscles, which was reversed by oral refeeding. Muscle protein synthesis, after starvation/ refeeding, was proportional and similar to changes in skeletal muscle IGF-I mRNA expression. Diabetic mice responded quantitatively similarly to starvation/refeeding in muscle protein synthesis compared with normal mice (C57 Bl). Both anti-insulin and anti-IGF-I attenuated significantly the stimulation of muscle protein synthesis in response to oral feeding, whereas exogenous provision of either insulin or IGF-I to overnight-starved and freely fed mice did not clearly stimulate protein synthesis in skeletal muscles. Our results support the suggestion that insulin and IGF-I either induce or facilitate the protein synthesis machinery in skeletal muscles rather than exerting a true stimulation of the biosynthetic process during feeding.
Prolonged bed rest decreases skeletal muscle and whole body protein synthesis
Authors: Ferrando A. A. , Lane H. W. , Stuart C. A. , Davis-Street J. , Wolfe R. R.
Published: December 2017

We sought to determine the extent to which the loss of lean body mass and nitrogen during inactivity was due to alterations in skeletal muscle protein metabolism. Six male subjects were studied during 7 days of diet stabilization and after 14 days of stimulated microgravity (-6 degrees bed rest). Nitrogen balance became more negative (P < 0.03) during the 2nd wk of bed rest. Leg and whole body lean mass decreased after bed rest (P < 0.05). Serum cortisol, insulin, insulin-like growth factor I, and testosterone values did not change. Arteriovenous model calculations based on the infusion of L-[ring-13C6]-phenylalanine in five subjects revealed a 50% decrease in muscle protein synthesis (PS; P < 0.03). Fractional PS by tracer incorporation into muscle protein also decreased by 46% (P < 0.05). The decrease in PS was related to a corresponding decrease in the sum of intracellular amino acid appearance from protein breakdown and inward transport. Whole body protein synthesis determined by [15N]alanine ingestion on six subjects also revealed a 14% decrease (P < 0.01). Neither model-derived nor whole body values for protein breakdown change significantly. These results indicate that the loss of body protein with inactivity is predominantly due to a decrease in muscle PS and that this decrease is reflected in both whole body and skeletal muscle measures.
Long-term GABAA receptor activation increases [Ca2+]i in single lactotrophs
Authors: Lorsignol A. , Taupignon A. , Dufy B.
Published: December 2017

Prolactin (PRL) release by pituitary lactotrophs is inhibited by gamma-aminobutyric acid (GABA). We have investigated the effect of long-lasting activation of GABAA receptors on membrane potential and cytosolic free calcium concentration ([Ca2+]i) in single identified lactotrophs. Membrane potential was recorded using the perforated patch-clamp technique and [Ca2+]i using indo 1 as a fluorescent Ca2+ probe. When cells were bathed in muscimol (10 microM) for 30 min, [Ca2+]i unexpectedly increased in 53% of the lactotrophs. This was due to a Ca2+ influx, since it was inhibited by Ca(2+)-free extracellular medium or by Ca2+ channel blockers such as the dihydropyridine PN 200-110. In cells incubated in muscimol, wash of muscimol from the cell membrane potential and reduced [Ca2+]i to the levels found in control cells. This effect was mimicked by picrotoxin, a GABA-operated Cl- channel blocker, thus supporting the involvement of a muscimol-induced Cl- flux. Conversely, under similar experimental conditions, static assays of PRL release revealed an inhibition of release by muscimol, unaffected by the dihydropyridine PN 200-110. Our observations suggest that GABAA, receptors may not regulate the process of exocytosis within the Ca(2+)- regulated steps.
Effect of nitric oxide synthase inhibitors on bone metabolism in growing rats
Authors: Tsukahara H. , Miura M. , Tsuchida S. , Hata I. , Hata K. , Yamamoto K. , Ishii Y. , Muramatsu I. , Sudo M.
Published: December 2017

We examined the effects of chronic nitric oxide (NO) blockade on bone mineral status in growing rats. Oral administration of NG-nitro-L-arginine methyl ester (L-NAME) for 4 wk caused hypertension and a significant reduction in urinary NO2- and NO3- excretion. Four-week oral aminoguanidine (AG, 400 mg/dl of drinking water) did not alter blood pressure but caused a significant decrease in urinary NO2- and NO3-. Rats treated with L-NAME at doses of 20 and 50 mg/dl had normal bone mineral mass in the lumbar spine, but the highest dose (80 mg/dl) caused a slight decrease in bone mass. Chronic AG induced a significant spine osteopenia. This effect of AG was abolished by the simultaneous administration of L-arginine (2.0 g/dl). AG-induced osteopenia was associated with a significant increase in urine excretion of collagen cross-links with normal serum osteocalcin. These findings indicate that chronic AG administration can cause an imbalance between bone resorption and formation, resulting in a decrease in bone mass in growing rats, and suggest that NO produced by inducible NO synthase plays an important role in basal osteoclast bone degradation activity in vivo.
Paracrine stimulation of preadipocyte-enriched cell cultures by mature adipocytes
Authors: Considine R. V. , Nyce M. R. , Morales L. M. , Magosin S. A. , Sinha M. K. , Bauer T. L. , Rosato E. L. , Colberg J. , Caro J. F.
Published: December 2017

We developed a double-chamber system in which to examine the effects of mature adipocytes on the growth and differentiation of preadipocytes and other cells in the adipose tissue. In the present study we found that mature adipocytes from both lean and obese subjects release a factor that stimulates the growth of preadipocyte-enriched and dedifferentiated adipocyte-enriched cell cultures. This growth stimulation was dependent on both time of exposure to mature cells and the number of mature cells in the coculture. Proliferation of the preadipocyte-enriched (n = 4) and dedifferentiated adipocyte-enriched cultures (n = 5) in the presence of mature adipocytes from obese subjects [body mass index (BMI) > 35] was 4.1- and 2.9-fold more (P < 0.05) than that in the presence of adipocytes from lean subjects (BMI < or = 25). There was no difference in the growth of cultures enriched in preadipocytes or dedifferentiated adipocytes from lean or obese subjects in the absence of mature adipocytes. These observations demonstrate that mature adipocytes from obese patients stimulate the growth of preadipocyte-enriched cultures to a greater extent than those from lean individuals.
Physical fitness, muscle morphology, and insulin-stimulated limb blood flow in normal subjects
Authors: Utriainen T. , Holmang A. , Bjorntorp P. , Makimattila S. , Sovijarvi A. , Lindholm H. , Yki-Jarvinen H.
Published: December 2017

The response of limb blood flow to insulin is highly variable even in normal subjects. We examined whether physical fitness or differences in muscle morphology contribute to this variation. Maximal aerobic power, muscle fiber composition and capillarization, and the response of forearm glucose extraction and blood flow to a sequential hyperinsulinemic euglycemic clamp (serum insulin 374 +/- 10, 816 +/- 23, and 2,768 +/- 78 pmol/l) were determined in 16 normal males (age 25 +/- 1 yr, body mass index 24 +/- 1 kg/m2). Maximal aerobic power correlated positively with the proportion of type I fibers (r = 0.67, P < 0.01) and negatively with the proportion of type IIb fibers (r = -0.73, P < 0.01). Fiber composition but not blood flow correlated significantly with forearm and whole body glucose uptake. All doses of insulin significantly increased forearm blood flow, maximally by 123 +/- 21%. The ratio of capillaries per fiber was significantly correlated with basal and insulin-stimulated blood flow (0.58∑ 0.76, P < 0.05∑0.01). Mean arterial blood pressure and the insulin∑induced increase in blood flow were inversely correlated (r = ∑0.59, P < 0.05). We conclude that variation in glucose extraction is significantly determined by muscle fiber composition, whereas variation in insulin-stimulated blood flow is closely associated with muscle capillarization.
Effects of pulsatile delivery of basal growth hormone on lipolysis in humans
Authors: Cersosimo E. , Danou F. , Persson M. , Miles J. M.
Published: December 2017

Growth hormone (GH) excess stimulates lipolysis, but its role in the hierarchy of lipolysis regulation is not clear. We studied whether pulsatile GH delivery is required for its lipolytic effect. With use of the pancreatic clamp, eight subjects were randomized to three protocols: protocol A, GH deficiency; protocol B, constant GH infusion; protocol C, pulsatile GH delivery (same total GH as protocol B). Pulsatile GH was given in four consecutive bursts, with symmetric peak width (60 min), amplitude of 10.7 (men) and 15 (women) ng.kg-1.min-1, and peak width at half-height of 15 min. Palmitate flux (PF) was measured at baseline and in the last hour of each study with [3H]palmitate. GH (ng/ml) decreased from approximately 3.5 to 2.0 in protocol A (P < 0.05), it remained between 3.2 and 4.0 in protocol B (P < 0.05), but in protocol C it fluctuated between approximately 2.7 and approximately 5.0 (P < 0.05). Palmitate concentration (in mumol/l) was approximately 150 at baseline; it did not change in protocols A and B (137 +/- 17 and 136 +/- 12, respectively) but increased to 198 +/- 16 (P < 0.05) in protocol C. PF (mumol.kg-1.min-1) was approximately 2.7 at baseline and did not change in protocol B (2.4 +/- 0.2); it decreased to 2.2 +/- 0.1 in protocol A (P < 0.05); it increased to 3.1 +/- 0.3 (P < 0.05) in protocol C. These experiments provide evidence that pulsatile secretion of GH is required for its lipolytic effect.
Galanin gene expression in radiothyroidectomy-induced thyrotroph adenomas
Authors: Hyde J. F. , Moore J. P. , Drake K. W. , Morrison D. G.
Published: December 2017

Galanin gene expression is markedly increased in the anterior pituitary glands of estrogen-treated rats (lactotroph hyperplasia) as well as human growth hormone-releasing hormone transgenic mice (somatotroph hyperplasia). The objective of this study was to examine galanin in a mouse model of thyrotroph adenoma formation. Male mice were radiothyroidectomized by use of iodine-131 (131I), and galanin peptide levels were assessed in the hypothalamic-pituitary axis. Immunoreactive galanin concentrations in the anterior pituitaries of 131I-treated mice were decreased 80% at 3, 6, 9, and 12 mo after radiothyroidectomy. Galanin peptide levels in the hypothalamus were decreased 20-25% at these times. Treatment with either estradiol or 3,3',5-triiodo-L-thyronine increased galanin peptide concentrations in the anterior pituitaries of 131I-treated mice, but neither treatment restored galanin concentrations. Galanin mRNA levels were decreased > 80% 1 yr after radiothyroidectomy. We conclude that, unlike animal models of lactotroph and somatotroph hyperplasia, galanin gene expression is suppressed throughout the development of thyrotroph adenomas, suggesting that galanin does not have a stimulatory role in the proliferation of thyrotrophs. Moreover, these data show that thyroid hormones are important positive regulators of galanin gene expression in the mouse and that estrogen may stimulate galanin gene expression in the absence of thyroid hormones.
Metabolic response of type I and II muscle fibers during repeated bouts of maximal exercise in humans
Authors: Casey A. , Constantin-Teodosiu D. , Howell S. , Hultman E. , Greenhaff P. L.
Published: December 2017

Nine male subjects performed two bouts of 30-s maximal isokinetic cycling. Each bout of exercise was performed at 80 revolutions/min and was separated by 4 min of recovery. Mixed-muscle phosphocreatine (PCr) resynthesis during recovery (88.1 +/- 6.1%) was positively correlated with the restoration of total work production during bout 2 (r = 0.80, P < 0.05). During bout 1, ATP and PCr utilization were greater in type II compared with type I fibers (P < 0.01 and P < 0.05, respectively). The subsequent 4-min period of recovery was insufficient to allow total restoration of ATP and PCr in type II fibers, but restoration of ATP and PCr in type I fibers was almost complete. During the second bout of exercise, ATP and PCr utilization were reduced in type II fibers (P < 0.01), without a corresponding change in type I fibers, and performance was also significantly reduced. The reduction in work capacity observed during bout 2 may have been related to a slower resynthesis, and consequently a reduced availability, of ATP and PCr in type II fibers.
Kinetic aspects of acetate metabolism in healthy humans using [1-13C] acetate
Authors: Pouteau E. , Piloquet H. , Maugeais P. , Champ M. , Dumon H. , Nguyen P. , Krempf M.
Published: December 2017

Acetate metabolism in humans is not well known. Kinetic aspects of acetate were investigated in the postabsorptive state on healthy subjects. In a first study, six subjects were infused with a primed constant infusion of [1-13C]acetate for 3 h and a prime of NaH13CO3. No difference was found between arterialized and venous tracer enrichments from the arm, although arterialized acetate concentrations were higher (74 +/- 12 vs. 59 +/- 14 mumol/l, P <0.05), suggesting that the hand muscles used but did not produce acetate in the postabsorptive state. Total body flux of acetate was 8.4 +/- 0.6 mumol.kg-1.min-1, of which 69 +/- 5% was oxidized. Acetate contributed to 6.5 +/- 0.4% of the basal energy expenditure. In a second study, five volunteers were submitted to a gastric infusion for 3 h followed by an intravenous infusion of [1-13C]acetate for 3 h. Higher fluxes were observed with the tracer gastric infusion, and the first-pass removal of acetate within the splanchnic bed was 60 +/- 7%. Acetate contributes significantly to the energy supply of the body. It is mainly used by the liver when produced in the gut.
Perfused skeletal muscle contraction and metabolism improved by angiotensin II-mediated vasoconstriction
Authors: Rattigan S. , Dora K. A. , Tong A. C. , Clark M. G.
Published: December 2017

In the present study, the effects of angiotensin II (ANG II) on tension development and associated metabolism during twitch and tetanic stimulation via the sciatic nerve of the gastrocnemius-plantaris-soleus muscle group of the perfused rat hindlimb were investigated. Rat hindlimbs were perfused at constant flow with an erythrocyte-containing medium equilibrated with 95% air-5% CO2 at 37 degrees C, and determinations of oxygen and glucose uptake, lactate and glycerol release, and 2-deoxy-D-[1-3H]glucose uptake (Rg') into individual muscles were carried out. ANG II (1 nM) infusion alone caused vasoconstriction with increased oxygen (55%) and glucose (98%) uptake and lactate (37%) and glycerol (64%) release. ANG II infusion during muscle contraction gave less vasoconstriction but increased the tension development during tetanic stimulation by 80% and increased the contraction-induced oxygen uptake and Rg' by plantaris and gastrocnemius red and white muscles. These effects of ANG II may have been due to increased nutritive flow to contracting muscles or to redirection of flow from noncontracting and type I fiber muscles to the type II fiber contracting muscles in the hindlimb. The results indicate that the regulation of flow by the vasculature is an important regulator of muscle contraction and metabolism.
Neural and pancreatic influences on net hepatic glucose uptake and glycogen synthesis
Authors: Moore M. C. , Rossetti L. , Pagliassotti M. J. , Monahan M. , Venable C. , Neal D. , Cherrington A. D.
Published: December 2017

The role of the liver nerves in the disposition of peripherally administered glucose was examined in seven hepatic innervated (HI) and nine hepatic denervated (HD) 42-h-fasted conscious dogs. After a 40-min basal period, there was a 4-h experimental period during which the hepatic glucose load was increased twofold via peripheral glucose infusion. Somatostatin was infused to suppress pancreatic endocrine secretion, and insulin and glucagon were infused intraportally to produce a fourfold increase in insulin and a gradual decrease (approximately 25%) in glucagon. The area under the curve of net hepatic glucose uptake (NHGU) during the glucose infusion period totaled 483 +/- 82 and 335 +/- 32 mg/kg in HD and HI, respectively (P < 0.05). The area under the curve of the hepatic fractional extraction of glucose was 27% greater in HD (P < 0.05). Net hepatic lactate output was similar in the two groups, and net hepatic glycogen synthesis was 3.8 +/- 0.8 vs. 2.7 +/- 0.5 mg.kg dog wt-1.min-1 in HD and HI, respectively (P = 0.13). The direct pathway of glycogen synthesis was responsible for 54-58% of net hepatic glycogen synthesis in both HI and HD (n = 6 for both). In summary 1) NHGU in response to peripheral glucose infusion was approximately 44% greater in HD than in HI, 2) net hepatic glycogen synthesis was enhanced by 41% in HD although the probability of this change was 0.13, and 3) the contribution of the direct pathway to glycogen synthesis was the same in HD and HI. These data are consistent with a role for the liver nerves in regulating the magnitude of NHGU in response to glucose administration. They also indicate that the absence of liver nerves may reduce glycogen turnover during glucose infusion.
Regulation of type II adenylyl cyclase mRNA in rabbit skeletal muscle by chronic motor nerve pacing
Authors: Torgan C. E. , Kraus W. E.
Published: December 2017

Skeletal muscle exhibits a wide range in functional phenotype in response to changes in physiological demands. We have observed that, in response to changes in work patterns, alterations in gene expression of some proteins coincide with changes in adenylyl cyclase (AC) activity [Kraus, W.E., J.P. Longabaugh, and S. B. Liggett. Am. J. Physiol 263 (Endocrinol. Metab. 26): E266-E230, 1992]. We now examine AC isoform transcript prevalence in various rabbit skeletal muscles and in response to changing work demands. Using reverse transcriptase-polymerase chain reaction, we detected type II AC isoform transcripts in rabbit skeletal muscle. Ribonuclease protection analyses revealed that expression of the type II isoform significantly correlated with the percentage of fast-twitch type IIb/IId fibers (r2 = 0.765, P < 0.01). When a fast-twitch muscle was converted to a slow-twitch muscle via chronic electrical pacing, expression of type II AC mRNA significantly decreased. This response occurred 3 days after the onset of stimulation (78% decrease) and was still present after 21 days of stimulation (76% decrease). As type II AC is relatively insensitive to calcium regulation while sensitive to protein kinase C (PKC) signaling, these data provide further impetus for investigations of protein kinase A and PKC cross-talk signaling mechanisms in the regulation of gene expression.
Gastric antisecretory effect of serotonin: quantitation of release and site of action
Authors: Lepard K. J. , Chi J. , Mohammed J. R. , Gidener S. , Stephens R. L.
Published: December 2017

Despite many reports that serotonin (5-HT) inhibits gastric acid output, the role and mechanism of action of endogenous 5-HT to modulate gastric secretion remain unclear. Vagal stimulation enhanced the basal rate of 5-HT release into both the gastric lumen (600%) and the portal circulation (265%) of the rat. The peak rate of 5-HT release into the portal circulation was 1,000-fold higher that luminal release (12 micrograms/min and 1.2 ng/min, respectively). To elucidate site(s) of action of 5-HT to inhibit acid secretion, several approaches were taken. Intraluminal perfusion of exogenous 5-HT to encompass enhanced levels seen after vagal stimulation did not reduce gastric acid output. In contrast, administration of systemic 5-HT, which raised portal venous 5-HT to similar levels as vagal stimulation, had a marked antisecretory effect. Chemical or surgical ablation of enteric or sympathetic nerves innervating the stomach did not attenuate the inhibitory effect of exogenous 5-HT on gastric acid output. The antisecretory effect of systemic 5-HT was insensitive to pretreatment with piroxicam, doxantrazole, close gastric intra-arterial sodium nitroprusside, somatostatin monoclonal antibody, or bilateral adrenalectomy. The results suggest that 5-HT is released from endogenous stores into the portal circulation in sufficient quantities after vagal stimulation to alter gastric physiology and that its action is independent of the autonomic nervous system, gastric mucosal prostaglandins or somatostatin, mucosal mast cell or adrenal constituents, or changes in gastric mucosal blood flow.
Enhancement of Ca2+ currents by GHRH and its relation to PKA and [Ca2+]i in human GH-secreting adenoma cells
Authors: Takei T. , Takano K. , Yasufuku-Takano J. , Fujita T. , Yamashita N.
Published: December 2017

The effects of human growth hormone-releasing hormone (hGHRH) on Ca2+ channels were examined in human growth hormone-producing adenoma cells using the perforated whole cell clamp technique. These cells exhibited T- and L-type Ca2+ channel currents, and application of 10(-8) M hGHRH increased the amplitude of both currents. Application of 10(-5) M 8-bromoadenosine 3',5'-cyclic monophosphate also increased T- and L-type currents. Additional application of 10(-8) M hGHRH did not further increase the current amplitudes. Treatment with the Rp diastereomer of adenosine 3',5'-cyclic monophosphothioate (10(-5) M) or H-89 (10(-5) M) inhibited the enhancement of Ca2+ channel currents by hGHRH, as did intracellular injection of protein kinase A (PKA) inhibitor peptide [PKI-(5-24)], indicating that hGHRH increased the amplitude of Ca2+ channel currents through the activation of the adenosine 3',5'-cyclic monophosphate (cAMP)-PKA system. When intracellular Ca2+ concentration ([Ca2+]i) was chelated to < 30 nM with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTAAM), hGHRH failed to increase the Ca2+ channel currents. In this condition, hGHRH activated nonselective cation channels, which revealed that the cAMP-PKA system operated after treatment with BAPTA-AM and that the site of low [Ca2+]i-induced inhibition of hGHRH effects on Ca2+ channels was at a step after PKA activation.
Extracellular glucose distribution is not altered by insulin: analysis of plasma and interstitial L-glucose kinetics
Authors: Steil G. M. , Richey J. , Kim J. K. , Wi J. K. , Rebrin K. , Bergman R. N. , Youn J. H.
Published: December 2017

We examined the effects of insulin on leg blood flow, whole body extracellular glucose distribution, and glucose diffusion into the interstitial fluid (ISF) surrounding skeletal muscle cells in anesthetized dogs. Extracellular glucose distribution and glucose diffusion into the muscle ISF were assessed by studying the kinetics of L-[1-14C]glucose in plasma and hindlimb lymph. Femoral artery blood flow was not increased with insulin (7.9 +/- 0.7 vs. 7.1 +/- 1.4 ml.min-1.kg-1; P = 0.54). Plasma and lymph dynamics of L-glucose after intravenous administration were superimposable between saline and insulin infusion experiments, indicating that insulin did not affect L-glucose disappearance from plasma or appearance in muscle ISF. Plasma L-glucose kinetics were best described by a four-compartment model, and one of the remote pools (intermediate) predicted the lymph L-glucose dynamics well. Estimation of maximum glucose diffusion capacity indicated that this pool, rather than the slowest pool, represents insulin-sensitive tissues. In conclusion, our data indicate that insulin does not increase transcapillary glucose diffusion to insulin-sensitive cells. In addition, hindlimb lymph represents primarily skeletal muscle ISF, which is represented by an intermediate, rather than the slowest, remote pool from whole body compartmental analysis.
Exercise during pregnancy and maternal and fetal plasma corticosterone and androstenedione in rats
Authors: Carlberg K. A. , Alvin B. L. , Gwosdow A. R.
Published: December 2017

Adrenocortical glucocorticoid and androgen secretion is stimulated by exercise. Excesses of these hormones in fetuses can cause abnormalities in development. We measured maternal and fetal plasma corticosterone and androstenedione concentrations in Sprague-Dawley rats immediately after maternal exercise in exercise-trained mothers and at rest in sedentary mothers. To do this, we developed a technique for fetal blood sampling and assessed its effect on maternal and fetal plasma corticosterone concentrations. Under halothane anesthesia, maternal blood was collected by cardiac puncture and fetal blood was collected from carotid and jugular vessels. Corticosterone was not affected by the blood collection procedure. Corticosterone was significantly higher in exercised mothers and their fetuses after 30 min of running than in sedentary mothers and their fetuses at rest. Androstenedione was significantly higher in exercised mothers after 30 min of running than in sedentary mothers at rest, but fetal androstenedione was not different between groups. We conclude that this maternal exercise protocol elevates plasma corticosterone but not androstenedione concentrations in fetal rats.
Measurement of interstitial muscle glucose and lactate concentrations during an oral glucose tolerance test
Authors: Muller M. , Holmang A. , Andersson O. K. , Eichler H. G. , Lonnroth P.
Published: December 2017

To study the relationship between blood flow rate and muscle metabolism, muscle microdialysis was performed in nine human subjects (5 females and 4 males) after an oral glucose load (75 g). Two microdialysis probes were inserted into the medial femoral muscle for estimation of glucose and lactate concentrations in the interstitial fluid, and the muscle blood flow was measured concomitantly with strain-gauge plethysmography. After subjects fasted overnight, their glucose concentration in arterial plasma and interstitial fluid was 4.6 +/- 0.13 vs. 3.8 +/- 0.23 mmol/l (P < 0.05), and the corresponding lactate concentrations were 0.60 +/- 0.07 vs. 0.83 +/- 0.07 mmol/l (P < 0.05). Muscle blood flow was 5.2 +/- 0.7 and 7.5 +/- 1.4 ml.100 g-1.min-1 (P < 0.05) at 0 and 90 min after oral glucose, respectively. The arterial-interstitial concentration differences of glucose increased after oral glucose [at 0 min 0.73 +/- 0.24 vs. 2.19 +/- 0.60 mmol/l at 90 min (P < 0.001)]. The corresponding values for lactate were -0.23 +/- 0.10 at 0 min vs.-0.26 +/- 0.18 mmol/l at 90 min (not significant). The data show that 1) the capillary wall is partly rate limiting for glucose uptake, and 2) after oral glucose, the glucose concentration gradient over the capillary wall increases despite a limited increase in blood flow rate, which then mediates approximately 10-20% of total enhancement of glucose uptake in muscle.
Glutamine synthetase induction by glucocorticoids is preserved in skeletal muscle of aged rats
Authors: Meynial-Denis D. , Mignon M. , Miri A. , Imbert J. , Aurousseau E. , Taillandier D. , Attaix D. , Arnal M. , Grizard J.
Published: December 2017

Glutamine synthetase (GS) is a glucocorticoid-inducible enzyme that has a key role for glutamine synthesis in muscle. We hypothesized that the glucocorticoid induction of GS could be altered in aged rats, because alterations in the responsiveness of some genes to glucocorticoids were reported in aging. We compared the glucocorticoid-induced GS in fast-twitch and slow-twitch skeletal muscles (tibialis anterior and soleus, respectively) and heart from adult (age 6-8 mo) and aged (age 22 mo) female rats. All animals received dexamethasone (Dex) in their drinking water (0.77 +/- 0.10 and 0.80 +/- 0.08 mg/day per adult and aged rat, respectively) for 5 days. Dex caused an increase in both GS activity and GS mRNA in fast-twitch and slow-twitch skeletal muscles from adult and aged rats. In contrast, Dex increased GS activity in heart of adult rats, without any concomitant change in GS mRNA levels. Furthermore, Dex did not affect GS activity in aged heart. Thus the responsiveness of GS to an excess of glucocorticoids is preserved in skeletal muscle but not in heart from aged animals.
Acute postprandial changes in leucine metabolism as assessed with an intrinsically labeled milk protein
Authors: Boirie Y. , Gachon P. , Corny S. , Fauquant J. , Maubois J. L. , Beaufrere B.
Published: December 2017

Mechanisms of protein gain during protein feeding have been investigated using a combination of oral and intravenous labeled leucine in healthy young men. The oral labeled leucine was administered as a free oral tracer ([13C]- or [2H3]leucine) added to unlabeled whey protein or as whey protein intrinsically labeled with L-[1-13C]leucine. When the oral tracer was free leucine, it appeared in the plasma more rapidly than the unlabeled leucine derived from the whey protein, and this resulted in an artifactual 88% decrease of protein breakdown. When the oral tracer was protein bound, protein breakdown did not change significantly after the meal. In contrast, nonoxidative leucine disposal (i.e., protein synthesis) was stimulated by 63% by the meal. In conclusion, 1) an intrinsically labeled protein is more appropriate than an oral free tracer to study postprandial leucine kinetics under non-steady-state conditions and 2) protein gain after a single whey protein meal results solely from an increased protein synthesis with no modification of protein breakdown.
Different physiological traits underlying increased body fat of fatty (fa/fa) and heterozygous (+/fa) rats
Authors: Schwarzer K. , Doring H. , Schmidt I.
Published: December 2017

To find out whether the most characteristic physiological traits distinguishing suckling-age fa/fa pups from lean littermates also differ between +/+ and +/fa littermates, we analyzed the body composition and cold defense of 7- and 16-day-old pups and the plasma concentrations of insulin, glucose, triglycerides, and free fatty acids in 16-day-old pups. Zucker rat x Brown Norway hybrid pups were genotyped by using a molecular marker within 0.5 cM of the fa gene. At both ages the +/fa pups had significantly more body fat than their +/+ littermates. At 7 days this difference was as large as that between +/fa and fa/fa pups, but at 16 days it was only one-seventh of the fa/fa vs. +/fa difference. In contrast, there were no heterozygote differences for three parameters that show crucial abnormalities in the fa/fa pups: thermoregulatory thermogenesis and plasma concentrations of insulin and triglycerides. The physiological mechanisms underlying the increased fat content of +/fa pups thus differ from those known to fuel most of the excessive fat deposition of their fa/fa littermates.
Glucose utilization and glucose transporter proteins GLUT-1 and GLUT-3 in brains of diabetic (db/db) mice
Authors: Vannucci S. J. , Gibbs E. M. , Simpson I. A.
Published: December 2017

This study describes the effects of diabetes on brain growth, cerebral glucose utilization (CGU), and the glucose transporter proteins GLUT-1 and GLUT-3 in the genetically diabetic db/db mouse. Mice were studied at 5 and 10 wk of age and compared with age-matched nondiabetic littermates. At 5 wk, db/db mice were not yet hyperglycemic, but their body weights were 27.5% greater than those of their nondiabetic littermates. By 10 wk, db/db mice were both hyperglycemic (blood glucose values of 39.3 +/- 4.3 vs. 12.1 +/- 2.1 mmol/l for db/db and control, respectively) and obese, with a twofold increase in body weight. Significant reductions in brain weight were observed at 5 wk (15% decrease in brain wet wt), and no further brain growth was observed, such that by 10 wk, brains of db/db mice were 25% smaller than those of control mice; brain wet weight-to-dry weight ratios were slightly reduced. Global rates of CGU, as determined with 2-[14C]deoxyglucose, were significantly reduced in the 10-wk diabetic mice. Levels of brain glucose and brain-to-blood glucose ratios were increased in 5- and 10-wk db/db mice, reflecting adequate glucose delivery to the brain. Blood-brain barrier GLUT-1 levels were unchanged, and mRNA levels were regionally increased. The expression of the neuronal glucose transporter GLUT-3 was not reduced to a significant extent in brains of db/db mice. The results of this study indicate that the db/db mouse has markedly decelerated brain growth accompanied by global reductions in glucose metabolism that are not due to reductions in glucose transport capacity.
Ovine fetal leucine kinetics and protein metabolism during acute metabolic acidosis
Authors: Milley J. R.
Published: December 2017

Fetal acidosis is associated with poor fetal growth. Because protein accretion is an important component of fetal growth, we used seven chronically prepared fetal lambs (10-16 days postoperation) to find whether fetal metabolic acidosis affected fetal protein accretion, and, if so, whether such effects were due to decreased synthesis or increased breakdown of proteins. Fetal leucine kinetics were measured during infusion of [1-(14)C]leucine by the reciprocal pool method. After control measurements, metabolic acidosis was induced by fetal infusion of 0.5 N HCl, and the measurements were repeated. Although fetal leucine concentration rose (164 +/- 11 vs. 216 +/- 15 microM; P < 0.001), fetal leucine uptake fell during acidosis (3.33 +/- 0.30 vs. 1.43 +/- 0.35 micromol x kg(-1) x min(-1); P < 0.05). However, the influx of leucine from protein breakdown increased (12.6 +/- 2.6 vs. 14.7 +/- 2.6 micromol x kg(-1) x min(-1); P < 0.02). The incorporation of leucine into fetal protein was unaffected by acidosis, so that fetal protein accretion fell (0.48 +/- 1.04 vs. -2.32 +/- 1.53 micromol x kg(-1) x min(-1); P < 0.001). Fetal leucine decarboxylation increased during acidosis (2.85 +/- 0.33 vs. 3.75 +/- 0.61 micromol x kg(-1) x min(-1); P < 0.05). We conclude that fetal metabolic acidosis stimulates pathways to degrade both protein and at least one of the subsequently derived amino acids, leucine. The consequence of such changes induced by acidosis is decreased protein accretion, a finding incompatible with normal fetal growth.
Persistently enhanced sensitivity of pancreatic islets from ob/ob mice to PKC-stimulated insulin secretion
Authors: Chen N. G. , Romsos D. R.
Published: December 2017

Islets from 2-wk-old ob/ob and lean littermate mice were cultured for 4-12 days and then perifused or statically incubated to identify early-onset differences in their regulation of insulin secretion. Islets from these young ob/ob and lean mice increased insulin secretion similarly in response to glucose (10 or 20 mM), whereas responsiveness to glucose plus acetylcholine (10 microM) was greater in islets from ob/ob mice than lean mice. This phenotype-specific effect of acetylcholine was mimicked by phorbol 12-myristate 13-acetate (PMA, 100 nM), a protein kinase C (PKC) agonist, whereas prior downregulation of PKC abolished this phenotype-specific effect of acetylcholine. A high concentration of PMA (1 microM) equally and substantially increased insulin secretion from islets of ob/ob and lean mice, suggesting an enhanced regulatory sensitivity rather than altered responsiveness of the PKC system in islets of ob/ob mice. Addition of BAY K 8644, a Ca2+ channel agonist, to the perifusate enhanced acetylcholine-induced insulin secretion from islets of lean mice to attain the high rates observed in islets from ob/ob mice exposed to acetylcholine alone. We propose that acetylcholine-induced PKC regulation of insulin secretion is altered in islets from ob/ob mice, that this alteration may directly or indirectly involve Ca2+ channels, and that it persists even when islets are cultured for up to 12 days.
IGF-I inhibits burst mass of pulsatile insulin secretion at supraphysiological and low IGF-I infusion rates
Authors: Porksen N. , Hussain M. A. , Bianda T. L. , Nyholm B. , Christiansen J. S. , Butler P. C. , Veldhuis J. D. , Froesch E. R. , Schmitz O.
Published: December 2017

Insulin-like growth factor I (IGF-I) shares structural and functional features with insulin, affects carbohydrate metabolism, and inhibits insulin secretion. Insulin secretion is pulsatile, and it is regulated by changing frequency and/or mass of secretory bursts. To examine the mechanism of IGF-I's inhibition of insulin secretion, eight healthy volunteers were studied three times. During glucose infusion (2.5 mg x kg(-1) x min(-1)) blood was sampled minutely at time 75-200 min for triplicate insulin concentration measurements by enzyme-linked immunosorbent assay (ELISA; coefficient of variation 2.1%). Time 125 min infusion of saline, low-dose IGF-I (0.025 microg x kg(-1) x min(-1)) or high-dose IGF-I (0.15 microg x kg(-1) x min(-1)) was commenced and continued until 200 min. Data were compared before (75-125 min) vs. during infusion (150-200 min). Insulin concentration time series were deconvolved, using validated pulse-detection criteria, to assess insulin secretory burst mass and frequency. During saline infusion no time effect occurred. After IGF-I infusion, serum C-peptide decreased (582 +/- 85 vs. 481 +/- 82 pM, low-dose IGF-I, P < 0.05; 539 +/- 84 vs. 427 +/- 69 pM, high-dose IGF-I, P < 0.01). Total insulin secretion rates decreased by 17 and 21%, respectively, via specific inhibition of the insulin secretory burst mass (31 +/- 8 vs. 20 +/- 4 pmol/ml, low-dose IGF-I, P = 0.06; 22 +/- 4 vs. 17 +/- 3 pmol/ml, high-dose IGF-I, P < 0.05), whereas the frequency was not affected (10.5 +/- 1.3 vs. 10.7 +/- 1.3 pulses/h, low-dose IGF-I, P = 0.85; 8.7 +/- 1.0 vs. 11.1 +/- 1.2 min/pulse, high-dose IGF-I, P = 0.15). We conclude that IGF-I inhibits pulsatile insulin secretion by specific inhibition of mass but not frequency of secretory bursts.
Carnitine effects on coenzyme A profiles in rat liver with hypoglycin inhibition of multiple dehydrogenases
Authors: Lieu Y. K. , Hsu B. Y. , Price W. A. , Corkey B. E. , Stanley C. A.
Published: December 2017

To examine the changes in coenzyme A profile and the possible corrective effects of carnitine supplementation in the genetic disorders of mitochondrial beta-oxidation, we carried out experiments using an inhibitor of multiple acyl-CoA dehydrogenase enzymes, methylenecyclopropaneacetic acid (MCPA), in rat hepatocytes. MCPA irreversibly inhibited ketone synthesis from straight-chain fatty acids (butyrate, octanoate, palmitate) and branched-chain fatty acids (alpha-ketoisocaproate) with a parallel 70-90% reduction of hepatocyte acetyl-CoA levels. Alone, MCPA or substrates halved free CoA levels to 15% of total CoA and doubled short- and medium-chain acyl-CoA levels to 30% of total CoA. With MCPA plus substrates combined, free CoA levels were 10% of total CoA, and short- and medium-chain acyl-CoA levels were 45% of total CoA. Comparable changes in CoA profiles were found in a patient with a severe genetic defect in beta-oxidation. Neither the suppression of ketogenesis nor the alterations in CoA profiles induced by MCPA inhibition could be corrected by carnitine supplementation.