bluuebunny/crossref_metadata_2025 huggingface dataset:
Insulin-mediated changes in PD and glucose uptake after correction of acidosis in humans with CRF
Authors: Reaich D. , Graham K. A. , Channon S. M. , Hetherington C. , Scrimgeour C. M. , Wilkinson R. , Goodship T. H.
Published: December 2017

To test the hypothesis that acidosis contributes to the insulin resistance of chronic renal failure (CRF) and impairs the action of insulin to decrease protein degradation, eight CRF patients were studied using the combined L-[1–13C]leucine-euglycemic clamp technique before (acid) and after (NaHCO3) 4 wk treatment with NaHCO3 (pH: acid 7.29 +/- 0.01 vs. NaHCO3 7.36 +/- 0.01, P < 0.001). Protein degradation (PD) was estimated sequentially from the kinetics of a primed continuous infusion of L-[1–13C]leucine in the basal state and during a hyperinsulinemic euglycemic clamp. Insulin sensitivity was measured during the clamp. The correction of acidosis significantly increased the glucose infusion rate necessary to maintain euglycemia (acid 6.44 +/- 0.89 vs. bicarbonate 7.38 +/- 0.90 mg.kg-1.min-1, P < 0.01) and significantly decreased PD in the basal state (acid 126.4 +/- 8.1 vs. bicarbonate 100.1 +/- 6.9 mumol.kg-1.h-1, P < 0.001). Hyperinsulinemia decreased PD in both studies (acid basal 126.4 +/- 8.1 vs. clamp 96.5 +/- 7.7, P < 0.001; bicarbonate basal 100.1 +/- 6.9 vs. clamp 88.2 +/- 5.5 mumol.kg-1.h-1, P = 0.06), its effect being unaltered by acidosis, with a reduction of 24% before and 12% after the correction of acidosis. In conclusion, acidosis contributes to the insulin resistance of CRF but does not affect the action of insulin on PD.
Regulation of growth hormone expression in fetal rat pituitary gland by thyroid or glucocorticoid hormone
Authors: Nogami H. , Yokose T. , Tachibana T.
Published: December 2017

The regulation of growth hormone (GH) cell development by thyroid and glucocorticoid hormones in the fetal rat pituitary gland was examined. Dexamethasone (Dex) treatment of dams induced GH and GH mRNA accumulation in the fetal pituitary gland on day 17 or 18 of gestation when substantial GH expression has not yet occurred in the control fetus. The additional thyroxine injections apparently enhanced the effect of Dex, whereas it exhibited no effect when given alone. The reduction of fetal thyroid hormone level by methimazole suppressed either the Dex induction of GH expression on day 18 or the spontaneous onset of GH expression on day 19 of gestation. The results suggest that 1) thyroid hormone exerts its stimulatory action on fetal GH gene expression only in the presence of glucocorticoid, 2) this synergistic action of these two hormones is evident as early as day 17 of gestation, and 3) rapid maturation of GH cells seen on day 19 in the normal fetus is considered to be induced by concomitant increase in both serum thyroid and glucocorticoid hormone levels.
Increased insulin-like growth factor I mRNA expression in rat osteocytes in response to mechanical stimulation
Authors: Lean J. M. , Jagger C. J. , Chambers T. J. , Chow J. W.
Published: December 2017

We recently developed an experimental model whereby a single 10-min episode of mechanical stimulation induces bone formation in the eighth caudal vertebra of 13-wk-old rats. We used this model to relate the kinetics of the bone-forming response, as measured by administration of fluorescent markers, to an in situ hybridization analysis of changes in mRNA for two matrix proteins (type I collagen and osteocalcin) and a growth factor implicated in the regulation of bone formation [insulin-like growth factor I (IGF-I). We found that increased fluorochrome labeling was accompanied by an increase in the proportion of trabecular bone surfaces on which transcripts for collagen type I and osteocalcin were detectable, from < 3 to 25% 72 h after loading. IGF-I expression on trabecular surfaces showed a slightly earlier increase. We also noted intense hybridization for IGF-I in osteocytes in the diaphyseal cortex and in metaphyseal trabeculae. This was observed only in loaded bones, within 6 h of loading, and became undetectable in trabecular osteocytes 48 h and cortical osteocytes 120 h after loading. This is the first identification of a specific mRNA species in osteocytes after mechanical stimulation. Its production before the increase in transcription of matrix protein mRNA, and before the transcription of IGF-I mRNA in bone surface cells, represents persuasive evidence for a role for osteocytes, and for IGF-I, in the osteogenic response of bone to mechanical stimulation.
Effects of ANP receptor antagonists on ANP secretion from adult rat cultured atrial myocytes
Authors: Nachshon S. , Zamir O. , Matsuda Y. , Zamir N.
Published: December 2017

Atrial natriuretic peptide (ANP) is a hormone-secreted predominantly by atrial myocytes. ANP exerts many of its actions via activation of the particulate guanylyl cyclase receptor ANPR-A and the formation of guanosine 3',5'-cyclic monophosphate (cGMP), which serves as a second messenger in the target cells. Using membrane-permeable cGMP analogues (8-bromo-cGMP and dibutyryl- cGMP), we first tested the hypothesis that ANP secretion by adult rat cultured atrial myocytes can be modulated through the second messenger cGMP. Second, we examined the effects of two competitive ANPR-A receptor antagonists, namely HS-142-1 and anantin, on cGMP formation and ANP secretion from cultured atrial myocytes. Cultured atrial myocytes secreted large quantities of immunoreactive (ir) ANP under basal conditions. We found that cGMP analogues inhibited basal irANP secretion from cultured atrial myocytes, whereas HS-142-1 and anantin had stimulating effects. HS-142-1 and anantin reduced cGMP formation in cultured atrial myocytes at basal conditions. These results suggest an autoregulatory mechanism of ANP secretion by atrial myocytes in an autocrine/paracrine fashion.
Early alteration of insulin stimulation of PI 3-kinase in muscle and adipocyte from gold thioglucose obese mice
Authors: Heydrick S. J. , Gautier N. , Olichon-Berthe C. , Van Obberghen E. , Le Marchand-Brustel Y.
Published: December 2017

The activation of phosphatidylinositol 3-kinase (PIK) was studied in vivo and in vitro in soleus muscle and adipocytes from young (8 wk) and old (30 wk) gold thioglucose obese mice. Insulin resistance assessed from muscle glucose transport and glycogen synthesis was present both in young and old obese mice. Adipocyte lipid synthesis and muscle glycolysis or glucose oxidation are not defective in young obese mice but become resistant later on. After incubation with 50 nM insulin, muscle antiphosphotyrosine-immunoprecipitable PIK activity was stimulated 5- to 10-fold in both young and old animals. This response was impaired by 56 and 75% in muscles from young and old obese mice, respectively. Insulin stimulation of receptor tyrosine kinase activity was only slightly decreased in muscle of young obese mice, whereas insulin receptor substrate 1 (IRS-1) tyrosine phosphorylation was blunted. The altered PIK stimulation in muscle, which is present both in vivo and in vitro, is thus characterized by a reduced association of PIK activity with IRS-1 and appears to result from a diminished IRS-1 tyrosine phosphorylation. In adipocytes isolated from lean mice, antiphosphotyrosine-immunoprecipitable PIK increased 25-fold within 10 min of incubation with insulin. This stimulation was markedly altered both in young and old obese mice, whereas lipogenesis was insulin resistant only in old obese animals. In adipocytes from young obese mice, insulin's stimulatory effect on the phosphorylation of insulin receptor beta-subunit, pp60, and an exogenous substrate was normal, whereas IRS-1 tyrosine phosphorylation was markedly depressed.(ABSTRACT TRUNCATED AT 250 WORDS)
Skeletal muscle pyruvate dehydrogenase activity during acetate infusion in humans
Authors: Putman C. T. , Spriet L. L. , Hultman E. , Dyck D. J. , Heigenhauser G. J.
Published: December 2017

Pyruvate dehydrogenase activity (PDHa), acetyl group, and citrate accumulation were examined in human skeletal muscle at rest and during cycling exercise while acetate was infused. Eight subjects received 400 mmol of sodium acetate (Ace) at a constant rate during 20 min of rest, 5 min of cycling at 40% maximal O2 uptake (VO2max) and 15 min of cycling at 80% VO2max. Two weeks later experiments were repeated while 400 mmol of sodium bicarbonate was infused in the control condition (CON). Ace infusion increased muscle acetyl-coenzyme A (acetyl-CoA), citrate, and acetylcarnitine. A decline in resting PDHa during 20 min of Ace infusion (0.37 +/- 0.08 vs. 0.16 +/- 0.03 mmol.min-1.kg wet wt-1) coincided with an elevation in the acetyl-CoA-to-free CoA ratio (acetyl-CoA/CoASH; 0.28 +/- 0.04 to 0.73 +/- 0.14). After 20 min of CON infusion, resting PDHa (0.32 +/- 0.06 mmol.min-1.kg wet wt-1) was similar to PDHa before Ace infusion. During exercise, acetyl-CoA, citrate, and acetyl-CoA/CoASH were further elevated, and the differences that existed at rest were resolved. PDHa increased to the same extent in Ace and CON, in which it was 44-47% transformed after 5 min at 40% VO2max and completely transformed after 15 min at 80% VO2max. At rest PDHa was regulated by variations in acetyl-CoA/CoASH secondary to enhanced acetate metabolism. Conversely, during exercise PDHa regulation appeared independent of variations in acetyl-CoA/CoASH. The resting data are consistent with a central role for PDHa and citrate in the regulation of the glucose-fatty acid cycle in skeletal muscle, as classically proposed. However, in the present study Ace infusion was not effective in perturbing the glucose-fatty acid cycle during exercise.
Characterization of type A endothelin receptors in cultured human myometrial cells
Authors: Heluy V. , Breuiller-Fouche M. , Cavaille F. , Fournier T. , Ferre F.
Published: December 2017

The aim of the present study was to characterize endothelin (ET)-receptors in human myometrial cells in culture. 125I-labeled ET-1 binding to myometrial cells was specific and saturable, with a dissociation constant of 64.2 +/- 12.8 pM. Competition binding studies showed the following order of potency: ET-1 > ET-3, which is consistent with the presence of the ETA receptor subtype. FR-139317 and BQ-123, two ETA antagonists, both inhibited 125I-ET-1 binding. BQ-123 only elicited a partial inhibition. The fraction resistant to BQ-123 did not represent the ETB receptor subtype, since no specific 125I-ET-3 binding could be detected. ET-1 and ET-3 were found to stimulate [3H]inositol phosphate (IP) accumulation in cultured myometrial cells, with corresponding half-maximal effective concentration values of 0.26 +/- 0.04 and 87 +/- 17 nM, respectively. Both ETA antagonists inhibited ET-1-induced accumulation of [3H]IP. BQ-123 was only a partial inhibitor, whereas FR-139317 totally suppressed ET-1-stimulated production of [3H]IP. We conclude that human myometrial cells in culture exclusively possess ETA receptor subtypes coupled to phospholipase C.
Triiodothyronine accelerates maturation of bile acid metabolism in infant baboons
Authors: Lewis D. S. , Jackson E. M. , Mott G. E.
Published: December 2017

We tested the hypothesis that triiodothyronine (T3) treatment accelerates the early postnatal maturation of bile acid metabolism in the baboon. Infant baboons were implanted with 21-day-release pellets containing T3 (n = 12), a placebo pellet (n = 6), or no pellet (n = 13). T3 treatment increased plasma T3 concentrations from 3.0 to 5.0 nmol/l between birth and 15 wk of age. At 15 wk of age, bile acid pool sizes, fractional turnover rates (FTR), and synthetic rates were determined by an isotope-dilution method with 3H- and 14C-labeled cholic (CA) and chenodeoxycholic acid (CDCA). T3 treatment increased CA pool size by 47% and CA synthetic rate by 37% but did not significantly affect CDCA pool size or synthetic rate. Consequently CA-to-CDCA pool size ratio (0.77 vs. 0.42) and biliary CA-to-CDCA concentration ratio (0.88 vs. 0.46) were higher in the T3-treated infants than in combined placebo-treated and nontreated control infants. T3 treatment did not affect the bile acid glycine-to-taurine conjugate ratio, CA FTR, or CDCA pool size, FTR, and synthetic rate. T3 treatment lowered plasma high-density lipoprotein fraction 2 and 3 cholesterol concentrations by 22 and 40%, respectively. T3 treatment also increased hepatic low-density lipoprotein receptor mRNA levels but did not affect plasma low-density lipoprotein cholesterol concentrations. We conclude that modest elevation of plasma T3 during the preweaning period increases the CA-to-CDCA ratio at the end of the preweaning period to near adult values.
Diet restriction in rhesus monkeys lowers fasting and glucose-stimulated glucoregulatory end points
Authors: Lane M. A. , Ball S. S. , Ingram D. K. , Cutler R. G. , Engel J. , Read V. , Roth G. S.
Published: December 2017

Male rhesus monkeys (Macaca mulatta) of different age groups representing the species life span were fed ad libitum or a 30% reduced calorie diet over a 7-yr period. During the first 2-3 yr of this longitudinal study, glucose and insulin levels were not altered by diet restriction (DR). However, reductions in fasting blood glucose became apparent in DR animals after 3-4 yr. At the end of the 6th yr of study, glycated hemoglobin was measured, and intravenous glucose tolerance tests (IVGTTs) were conducted. Maximum glucose levels reached during IVGTTs increased with age but were lower in DR animals compared with controls. Several measures of the insulin response (baseline, maximum, and integrated areas under curve) increased with age and were lower in DR monkeys. With the exception of glycated hemoglobin, which was not different in monkeys subjected to DR, these findings confirm previous studies in rodents demonstrating that DR alters glucose metabolism and may be related to the antiaging action of this intervention.
Molecular mechanisms underlying regional variations of catecholamine-induced lipolysis in rat adipocytes
Authors: Tavernier G. , Galitzky J. , Valet P. , Remaury A. , Bouloumie A. , Lafontan M. , Langin D.
Published: December 2017

The mechanisms underlying catecholamine control of lipolysis were studied in rat white adipocytes from epididymal, retroperitoneal, and subcutaneous fat depots. Sensitivity of subcutaneous adipocytes to selective beta 3-adrenoceptor agonists was lower than that of internal adipocytes. beta 3-Adrenoceptor mRNA levels were lower in subcutaneous adipocytes. A decreased beta 1/beta 2-adrenoceptor-mediated lipolysis was also observed in these adipocytes, and the number of beta 1/beta 2-adrenoceptors was lower than in the internal adipocytes. The number of alpha 2-adrenoceptors was higher in subcutaneous adipocytes without a marked difference in alpha 2-adrenoceptor-mediated antilipolysis between the depots. Subcutaneous adipocytes were also characterized by a lower maximal lipolytic response to drugs acting at different levels of the lipolytic cascade, suggesting differences at the postreceptor level. Lower hormone-sensitive lipase activity and mRNA levels in subcutaneous adipocytes were in agreement with the lipolysis data. These results suggest that the pattern of expression of the genes of the lipolytic pathway varies with the anatomic location of the fat depot.
Effect of somatotropin and feed restriction on body composition and adipose metabolism in obese Zucker rats
Authors: Azain M. J. , Hausman D. B. , Kasser T. R. , Martin R. J.
Published: December 2017

The objective of the present study was to determine whether exogenous somatotropin (STH) administration in conjunction with feed restriction could alter the composition of gain in the obese rat. Five-week-old female lean and obese Zucker rats were assigned to the following treatments for 6 wk: ad libitum fed (AL), restricted (approximately 75% of AL lean), and restricted with STH (2 mg STH/day). Growth rate was decreased in restricted groups and was normalized to that of the AL lean group in restricted rats treated with STH. In lean rats, restriction decreased protein accretion. Restriction plus STH treatment decreased lipid accretion but increased protein accretion and body weight gain compared with the AL lean group. As expected, feed restriction reduced body size in obese rats, but carcass lipid was maintained at 44%, a level similar to that of the AL obese rats. Lipid accretion rate was decreased with restriction in obese rats and was further reduced, to a level similar to that of the lean group, in the obese rats that were restricted and treated with STH. Protein accretion was decreased in the restricted obese group but was normalized in those treated with STH to a level similar to that in the AL lean group. Basal rates of lipolysis in isolated adipocytes were not affected by STH. However, STH treatment normalized the responsiveness of cells from the obese rats to stimulation of lipolysis by isoproterenol. The results demonstrate that a combination of caloric restriction and STH was effective in normalizing body weight and composition of gain in the obese Zucker rat.
Model of extreme hypoglycemia in dogs made ketotic with (R,S)-1,3-butanediol acetoacetate esters
Authors: Ciraolo S. T. , Previs S. F. , Fernandez C. A. , Agarwal K. C. , David F. , Koshy J. , Lucas D. , Tammaro A. , Stevens M. P. , Tserng K. Y. , et al.
Published: December 2017

The rationale behind this study is that controlled starvation of poorly differentiated (anaplastic) fast-growing tumor cells, but not host cells, might be possible in vivo. The energy metabolism of anaplastic tumor cells, but not host cells, is largely dependent on carbohydrate metabolism at all times. Therefore depleting plasma of carbohydrate fuels could place these tumor cells at a significant metabolic disadvantage. Hence an animal model was developed in which all cells would be required to oxidize fatty acids, ketoacids, and/or 1,3-butanediol to satisfy their energy needs. To achieve this aim, one would need ketosis, severe hypoglycemia, and low lactatemia. Anesthetized normal dogs were infused with somatostatin and a mixture of (R,S)-1,3-butanediol monoacetoacetate and (R,S)-1,3-butanediol diacetoacetate; these latter compounds are nonionized precursors of ketoacids. They were infused at 90% of the dog's caloric requirement. After establishment of a moderate ketosis (2-3 mM) over < 100 min, a severe degree of hypoglycemia (close to 0.5 mM) without rebound and without hyperlactatemia was induced by infusing insulin and dichloroacetate. Tracer kinetic measurements showed 1) a 20% decrease in the rate of appearance of glucose, 2) 50 and 62% increases in glycerol and nonesterified fatty acid rates of appearance, reflecting stimulation of lipolysis, and 3) no change in the rate of glutamine appearance. We suggest that this model may prove useful for selectively starving those cancer cells that are unable to utilize fat-derived fuels while preserving nutrient supply to vital organs.
Atrial natriuretic peptide induces acrosomal exocytosis in bovine spermatozoa
Authors: Zamir N. , Barkan D. , Keynan N. , Naor Z. , Breitbart H.
Published: December 2017

The induction of acrosomal exocytosis in capacitated bull spermatozoa by atrial natriuretic peptide (ANP) was studied in vitro. ANP markedly stimulated acrosomal exocytosis in a calcium-dependent manner. Typically, ANP exerts its action via activation of the ANP receptor (ANPR-A), a particulate guanylyl cyclase-linked receptor, and subsequent formation of guanosine 3',5'-cyclic monophosphate (cGMP). We found that the ANP-induced acrosome reaction was inhibited by the competitive ANPR-A receptor antagonist-anantin, indicating a receptor-mediated effect. We could mimic the effect of ANP on the acrosome reaction by using 8-bromo-cGMP, suggesting that cGMP may serve as a signal transducer mediating the acrosome reaction. Indeed, the ANP-induced acrosome reaction was associated with elevation of cGMP levels. cGMP can also be formed by activation of the soluble form of guanylyl cyclase. Sodium nitroprusside (SNP) stimulated cGMP accumulation and acrosome reaction of capacitated spermatozoa. Thus ANP and the nitric oxide-releasing compound SNP, via activation of guanylyl cyclase (the former activating the particulate and the latter activating the soluble form of the enzyme), may play a significant role in the induction of the acrosome reaction.
Effect of intravenous glucose and lipid on proteolysis and glucose production in normal newborns
Authors: Denne S. C. , Karn C. A. , Wang J. , Liechty E. A.
Published: December 2017

To determine whether nonprotein substrate can suppress proteolysis in normal newborns and to assess the effect of this substrate on glucose production, the rates of appearance (Ra) of leucine (reflecting proteolysis) and glucose were measured in healthy 2-day-old full-term newborns during fasting, an intravenous glucose infusion (5.5 mg.kg-1.min-1), an intravenous lipid infusion (2.5 mg.kg-1.min-1), and a combined glucose plus lipid infusion (5.5 mg.kg-1.min-1 glucose + 2.5 mg.kg-1.min-1 lipid). Leucine RA was not reduced from fasting values during any of the substrate infusions. Intravenous lipid infusion alone neither suppressed nor increased glucose production. In contrast, glucose production was nearly completely suppressed (approximately 90%) during intravenous infusions of glucose provided either alone or in combination with lipid; this suppression was achieved at glucose concentrations of approximately 90 mg/dl and insulin concentrations of approximately 6 microU/ml. Thus normal newborns respond to intravenous glucose with sustained nearly complete suppression of glucose production, even at moderate levels of glycemia and at low insulin concentrations; however, nonprotein substrate infusion does not result in suppression of proteolysis. It remains unclear to what extent any potential regulator can suppress proteolysis in this population.
Tumor-related selection of calcium signals in vasopressin-stimulated human adenomatous corticotrophs
Authors: Corcuff J. B. , Guerineau N. C. , Tabarin A. , Mollard P.
Published: December 2017

The action of arginine vasopressin (AVP) on cytosolic free calcium concentration ([Ca2+]i) was studied at the single-cell level in corticotrophs cultured from pituitary adenoma fragments removed from eight patients with Cushing's disease. AVP evoked distinct [Ca2+]i responses with regard to the tumor origin. In cells from two tumors, AVP consistently evoked a series of characteristic elevations of [Ca2+]i (transient pattern) that depended on Ca2+ entry. In cells from the other tumors, AVP triggered different patterns of [Ca2+]i rise, which consisted of low-amplitude slow monophasic increases at low AVP concentration and a high-amplitude spike increase followed by a sustained plateau (spike-plateau pattern) at higher concentration of AVP. Slow monophasic increases and the spike of spike-plateau responses were due to calcium release from internal stores, whereas the plateau was a consequence of calcium entry. These two patterns (transient vs. spike-plateau) resemble those observed in subpopulations of corticotrophs from healthy rat pituitary glands (Corcuff et al., J. Biol. Chem. 268: 22313-22321, 1993), suggesting that tumorigenesis can lead in pituitary tissues to a selection rather than alteration of AVP [Ca2+]i signals.
Role of glucagon in maintenance of euglycemia in fed and fasted rats
Authors: Brand C. L. , Jorgensen P. N. , Knigge U. , Warberg J. , Svendsen I. , Kristensen J. S. , Holst J. J.
Published: December 2017

The role of glucagon in the regulation of blood glucose in fed and fasted anesthetized rats was studied by injecting intravenously 4 ml/kg of a high-capacity (40 nmol/ml) high-affinity (0.6 x 10(11) mol/l) monoclonal glucagon antibody. Blood glucose was lowered by the antibody by 2 mmol/l in fed rats but remained unchanged in 10- and 48-h-fasted rats. Antibody injection significantly reduced plasma insulin in both fed and 10-h-fasted rats. In 10-h-fasted rats, propranolol injection decreased blood glucose by 0.6 mmol/l, and combined with antibody administration, a decrease by 1.1 mmol/l was observed. Blood glucose was never < 3.3 mmol/l. Thus glucagon is partly responsible for maintenance of euglycemia in fed rats, whereas during fasting it plays a limited role. However, immunoneutralization of glucagon reduces insulin secretion irrespective of blood glucose. Additional mechanisms seem to be responsible for the maintenance of blood glucose in the fasting state when glucagon and the sympathoadrenergic system are blocked.
Splanchnic and muscle metabolism during exercise in NIDDM patients
Authors: Martin I. K. , Katz A. , Wahren J.
Published: December 2017

To characterize splanchnic and muscle metabolism during exercise in non-insulin-dependent diabetes mellitus (NIDDM), eight male nonobese patients and seven healthy control subjects (CON) were studied during 40 min of bicycle exercise at 60% of maximal oxygen uptake. Biopsies were obtained from the quadriceps femoris muscle at rest and immediately after exercise. Arterial glucose concentration in NIDDM had declined by 10% (P < 0.01) at the end of exercise, whereas in CON it had risen by 21% (P < 0.05). Leg glucose uptake rose from 0.19 +/- 0.06 mmol/min at rest to 2.25 +/- 0.61 mmol/min at the end of exercise in NIDDM and from 0.13 +/- 0.05 to 1.17 +/- 0.34 mmol/min in CON. Splanchnic glucose output increased from 0.52 +/- 0.06 to 2.37 +/- 0.26 mmol/min in NIDDM and from 0.79 +/- 0.12 to 2.44 +/- 0.38 mmol/min in CON. Leg lactate output during exercise was twofold higher in NIDDM. Muscle contents of lactate and glycogen were similar in both groups at rest, whereas after exercise lactate tended to be higher (19.5 +/- 1.7 vs. 12.7 +/- 5.9 mmol/kg dry wt) and glycogen lower (154 +/- 35 vs. 251 +/- 41 mmol glucosyl units/kg dry wt) in NIDDM. Whole body respiratory exchange ratio during exercise was higher in NIDDM (0.84 +/- 0.02 vs. 0.78 +/- 0.02, P < 0.05). Exercise-induced changes in other muscle metabolites were similar in NIDDM and CON. These data indicate that the decline in blood glucose during exercise in nonobese NIDDM is due to enhanced peripheral glucose utilization rather than to an attenuated increase in splanchnic glucose output.
Gene-targeting and transgenic approaches to IGF and IGF binding protein function
Authors: Wood T. L.
Published: December 2017

The ability to manipulate genetic information in the germ line of mice has provided powerful approaches to study gene function in vivo. These approaches have included the establishment of mouse lines in which a specified gene or genes are overexpressed, ectopically expressed, or deleted. Transgenic and gene-targeted mouse lines have been used extensively to study the function of the insulin-like growth factors (IGF), IGF-I and IGF-II, and their receptors and binding proteins. In the IGF system, these technologies have elucidated the roles of the IGFs in fetal and somatic growth and have demonstrated a critical role for this system in transformation and tumorigenesis. Analysis of combinatorial crosses of gene-targeted mouse lines also has suggested the existence of an as yet unidentified IGF receptor that regulates fetal growth. Similar approaches using transgenic and gene-targeted mouse models have been initiated to study the in vivo functions of the IGF binding proteins. These mouse models provide important tools to test specific functional questions in vivo as well as to study the long-term physiological consequences of chronic gene alterations.
A new correction factor for use in tracer estimations of plasma fatty acid oxidation
Authors: Sidossis L. S. , Coggan A. R. , Gastaldelli A. , Wolfe R. R.
Published: December 2017

The purpose of this study was to acquire a new correction factor for use in tracer estimations of plasma fatty acid oxidation that would fully account for label fixation during the infusion of fatty acid tracers. Thus volunteers were infused with 13C-labeled fatty acids and [1-14C]acetate in the basal state, during hyperinsulinemia-hyperglycemia (clamp), and during 1 h of cycling exercise. The fractional recovery of acetate label (i.e., the acetate correction factor) was 0.56 +/- 0.02, 0.50 +/- 0.03, and 0.80 +/- 0.03 in the basal state and during the clamp and exercise, respectively. Isotopically determined plasma fatty acid oxidation rates (mumol.kg-1.min-1) were 1.7 +/- 0.2, 0.8 +/- 0.2, and 6.4 +/- 0.5 (no correction); 2.1 +/- 0.2, 1.0 +/- 0.2, and 6.7 +/- 0.5 (bicarbonate correction); and 3.1 +/- 0.2, 1.5 +/- 0.2, and 8.2 +/- 0.4 (acetate correction). We conclude that use of the acetate correction factor in place of the bicarbonate correction factor should improve the accuracy of isotopic measurements of plasma fatty acid oxidation, because it accounts for label fixation that might occur at any step between the entrance of labeled acetyl-CoA into the tricarboxylic acid cycle until the recovery of label in breath CO2.
Response of glutamine metabolism to exogenous glutamine in humans
Authors: Hankard R. G. , Darmaun D. , Sager B. K. , D'Amore D. , Parsons W. R. , Haymond M.
Published: December 2017

To determine whether exogenous glutamine affects whole body glutamine metabolism, preliminary experiments were performed to verify that L-[1-13C]-, L-[U-14C]-, and L-[3,4-3H]glutamine given simultaneously by vein provided similar estimates of glutamine appearance rates [Ra; 355 +/- 24, 373 +/- 19, and 393 +/- 24 (SE) mumol.kg-1.h-1, respectively, P = NS] in six healthy men; glutamine oxidation accounted for 32 +/- 3 and 51 +/- 5% (P < 0.01) of glutamine Ra when it was measured using L-[U-14C]- and L-[1-13C]glutamine, respectively. Five subjects received two 5-h intravenous infusions of L-[3,4-3H]glutamine and a simultaneous nasogastric infusion of L-[1-13C]glutamine on 2 separate days in the postabsorptive state, along with saline on 1 day and natural L-glutamine (856 +/- 45 mumol.kg-1.h-1) on another day in a randomized order. Splanchnic glutamine extraction (determined from [13C]glutamine appearance into systemic blood) reached 74 +/- 4 and 53 +/- 5% during the enteral infusion of tracer alone and in combination with a large load of glutamine, respectively. Glutamine infusion was associated with increased plasma glutamine concentration (from 630 +/- 50 to 1,297 +/- 75 microM), Ra (from 258 +/- 20 to 589 +/- 45 mumol.kg-1.h-1), and oxidation (from 179 +/- 20 to 477 +/- 47 mumol.kg-1.h-1, all P < 0.01), no change in glutamine release from proteolysis, and a decline in glutamine de novo synthesis (from 156 +/- 15 to 93 +/- 13 mumol.kg-1.h-1).(ABSTRACT TRUNCATED AT 250 WORDS)
Magnesium supplementation reduces development of diabetes in a rat model of spontaneous NIDDM
Authors: Balon T. W. , Gu J. L. , Tokuyama Y. , Jasman A. P. , Nadler J. L.
Published: December 2017

We examined the effects of a magnesium-supplemented (Mg-S) diet in the male obese Zucker diabetic fatty rat, a model of non-insulin-dependent diabetes mellitus (NIDDM). Obese rats were maintained on either a control (0.20% Mg) or magnesium-supplemented (Mg-S; 1% Mg) diet for 6 wk beginning at 6 wk of age. The rats maintained on the Mg-S diet had markedly lower fasting and fed-state blood glucose concentrations and an improved glucose disposal. By 12 wk of age, all of the eight animals on the control diet became diabetic, whereas diabetes developed in only one of eight animals on the Mg-S diet. Insulin and C-peptide concentrations, in addition to pancreatic GLUT-2 and insulin mRNA expression, were higher in the male obese Mg-S rats than in their control-fed counterparts. A subgroup of rats on the control diet with established diabetes was switched to a Mg-S diet for an additional 4 wk. The Mg-S diet did not reverse diabetes once already established. These data indicate that an increased dietary Mg intake in male obese rats prevents deterioration of glucose tolerance, thus delaying the development of spontaneous NIDDM.
Interleukin-1 beta-induced anorexia and pyrexia in rat: relationship to hypothalamic neuropeptide Y
Authors: McCarthy H. D. , Dryden S. , Williams G.
Published: December 2017

We investigated the effect of recombinant human interleukin-1 beta (rhIL-1 beta)-induced anorexia and pyrexia on the hypothalamic neuropeptide Y (NPY)-ergic system, which stimulates feeding and reduces thermogenesis. In meal-fed rats, food intake decreased by 83%, 90 min after IL-1 beta treatment (1.3 micrograms/100 g ip; n - 8) vs. controls. NPY concentrations were significantly higher in the medial preoptic area (MPO), paraventricular (PVN), ventromedial (VMN), and dorsomedial (DMN) nuclei but unchanged in the arcuate nucleus (ARC) in both IL-1 beta-treated and pair-fed groups. Indomethacin (0.25 mg/100 g ip) reduced IL-1 beta-induced anorexia and tended to normalize NPY concentrations. In study 2, IL-1 beta increased core temperature by 1.1 degrees C above preinjection values (P < 0.001) and significantly raised NPY concentrations in the MPO, PVN, VMN, and DMN compared with controls, 60 min postinjection. Indomethacin prevented the pyrexia and normalized hypothalamic NPY levels. As NPY concentrations were not increased in the ARC (the hypothalamic site of synthesis), we suggest that the increased NPY levels may result from blocked release, which would be in accord with the known experimental effects of NPY.
Glucocorticoid deprivation alters in vivo glucose uptake by muscle and adipose tissues of GTG-obese mice
Authors: Blair S. C. , Caterson I. D. , Cooney G. J.
Published: December 2017

The effect of 1 wk of glucocorticoid deprivation by surgical adrenalectomy (ADX) on tissue 2-deoxy(-)[U-14C]glucose (2-DG) uptake and hepatic glucose production (HGP) was assessed in conscious, catheterized mice 5 wk after the induction of obesity with gold thioglucose (GTG). Despite the prevailing hyperglycemia and hyperinsulinemia, glucose uptake by heart, quadriceps muscle, and interscapular brown adipose tissue (BAT) of GTG-obese mice was unchanged compared with controls, suggesting that the hyperglycemia of GTG-obese mice is able to compensate for the insulin resistance of these tissues. In contrast, epididymal white adipose tissue (WAT) of GTG-obese mice showed increased glucose uptake with hyperglycemia and hyperinsulinemia. ADX decreased the hyperglycemia and lowered the elevated glycogen content of the liver of GTG-obese mice. ADX reduced glucose uptake by heart and WAT of control and GTG-obese mice, consistent with the concomitant decrease in insulinemia. Glucose uptake by muscle of control and GTG-obese mice was not significantly decreased after ADX despite the decrease in insulin, and ADX increased glucose uptake by BAT of GTG-obese mice, suggesting increased sympathetically mediated thermogenesis in this tissue. HGP was increased in GTG-obese mice compared with controls, and ADX significantly reduced HGP in both GTG-obese and control mice. These results suggest that the improved glucose tolerance of ADX GTG-obese mice and ADX control mice is due to a decrease in HGP rather than an increase in peripheral glucose uptake.
Suppression of circulating calcitriol and duodenal active Ca transport by ketoconazole in pregnant rats
Authors: Boass A. , Toverud S. U.
Published: December 2017

Active Ca transport in the duodenum and the circulating level of calcitriol are elevated during pregnancy and lactation in the rat. Because calcitriol stimulates Ca transport in nonmated rats, we investigated its contribution to the increased transport during pregnancy and lactation. Rapid suppression of calcitriol from 28 +/- 3 to 8 +/- 0.4 pg/ml with the steroid hydroxylase inhibitor ketoconazole resulted in a 34% suppression of Ca transport in nonmated rats. At the end of pregnancy, when calcitriol concentration was suppressed from 64 +/- 7 to 12 +/- 2 pg/ml, the transport ratio decreased by 44%. Ca transport did not correlate with calcitriol levels between 40 and 80 pg/ml, suggesting a threshold level for maximal Ca transport stimulation. During lactation at even higher calcitriol levels, ketoconazole treatment again resulted in marked reduction in calcitriol from 124 +/- 1 to 71 +/- 12 pg/ml, but without any concurrent reduction in Ca transport in the duodenum. We conclude that in the vitamin D-replete rat the pregnancy-mediated, and probably also the lactation-mediated, increase in active Ca transport capacity is dependent on an increase in circulating calcitriol up to a certain threshold level.
Effects of aging on glucose regulation during wakefulness and sleep
Authors: Frank S. A. , Roland D. C. , Sturis J. , Byrne M. M. , Refetoff S. , Polonsky K. S. , Van Cauter E.
Published: December 2017

Glucose intolerance, reduced sleep efficiency, and disturbed circadian rhythmicity occur in aging. In normal young subjects, glucose regulation is modulated by sleep and circadian rhythmicity. To examine age-related alterations in the temporal pattern of glucose tolerance and insulin secretion, eight modestly overweight healthy older men, eight weight-matched young men, and six young lean men were studied during constant glucose infusion for 53 h. Levels of glucose, insulin, C-peptide, and growth hormone (GH) were measured every 20 min. Rates of insulin and GH secretion were calculated by deconvolution. In older volunteers, sleep ws shallow and more fragmented than in young subjects but was nevertheless associated with robust glucose elevations. However, postsleep increases of insulin secretion were markedly dampened. During wakefulness, the normal morning-to-evening increase in glucose was preserved in the elderly, but insulin secretion failed to increase proportionately. Thus decreased glucose tolerance in aging is associated with insulin resistance and also with a relative insensitivity of the beta-cell to the modulation of glucose regulation by sleep and circadian rhythmicity.
Impact of sampling technique on appraisal of pulsatile insulin secretion by deconvolution and cluster analysis
Authors: Porksen N. , Munn S. , Steers J. , Veldhuis J. D. , Butler P. C.
Published: December 2017

Little is known about the optimal experimental conditions for assessing pulsatile insulin secretion in vivo. To address this, we employed a recently validated canine model (n = 12) to determine the consequences of 1) sampling from the systemic circulation (SC) vs. the portal vein (PV), 2) sampling intensity and duration, and 3) deconvolution vs. cluster analysis on assessing pulsatile insulin secretion. PV vs. SC sampling resulted in a approximately 40% higher pulse frequency by deconvolution (9.0 +/- 0.5 vs. 6.6 +/- 0.9 pulses/h, P < 0.02) and cluster analysis (7.5 +/- 0.3 vs. 5.6 +/- 0.6 pulses/h, P < 0.01) due to a higher signal-to-noise ratio (19 +/- 4.8 PV vs. 12 +/- 1.8 SC). PV sampling also disclosed a higher calculated contribution of the pulsatile vs. nonpulsatile mode of delivery to total insulin secretion (57 +/- 4 vs. 28 +/- 5%, P < 0.001). Analysis of the relevance of sampling intensity revealed that 1-min data yielded a markedly higher estimate of pulse frequency with PV sampling than 2-min data (9.0 +/- 0.5 vs. 5.4 +/- 0.5, P < 0.02, deconvolution; 7.5 +/- 0.3 vs. 4.3 +/- 0.6 pulses/h, P < 0.001, cluster). Optimal sampling duration was shown to be 40 min or more. We conclude that the resolving power of the analytical tool, the anatomic site of blood withdrawal, the frequency of blood sampling, and the duration of the total observation interval all significantly influence estimated insulin secretory pulse frequency and the fraction of insulin secreted in pulses. With the assumption that PV 1-min insulin data constitute the "gold standard," our in vivo inferences of 7.5-9.0 insulin pulses/h closely recapitulate in vitro islet secretory activity.
Females secrete growth hormone with more process irregularity than males in both humans and rats
Authors: Pincus S. M. , Gevers E. F. , Robinson I. C. , van den Berg G. , Roelfsema F. , Hartman M. L. , Veldhuis J. D.
Published: December 2017

In humans, serum growth hormone (GH) concentrations are significantly higher in women than in men, but the neuroendocrine mechanisms that underlie such gender differences are not known. We compared normal episodic GH secretion in males and females in three distinct settings: two human studies employing quite different assay techniques (immunoradiometric assay and a high-sensitivity immunofluorimetric method) and a rat study. To quantify the amount of regularity in data, we utilized approximate entropy (ApEn), a scale- and model-independent statistic. In each study, females exhibited significantly greater statistical irregularity in GH concentration series than their male counterparts (P < 10(-3) for each human study, P < 10(-6) for the rat study), implying that mass and mode of GH secretion are regulated differently in males and females. The regularity comparisons indicated complete gender separation (100% specificity and sensitivity) for the rat study and nearly complete separation for the immunofluorimetric assay study. The consistency and statistical significance of these findings suggest that this gender difference may be broadly based within higher animals and that this may be readily evaluated objectively by analysis of ApEn.
Upregulation of adipocyte metabolism by agouti protein: possible paracrine actions in yellow mouse obesity
Authors: Jones B. H. , Kim J. H. , Zemel M. B. , Woychik R. P. , Michaud E. J. , Wilkison W. O. , Moustaid N.
Published: December 2017

Mutations leading to ectopic expression of the murine agouti gene (a) result in progressive obesity. To further characterize this model, we analyzed adipose and hepatic mRNA levels for fatty acid synthase (FAS) and stearoyl-CoA desaturase (SCD), two key enzymes in de novo fatty acid synthesis and desaturation, respectively. FAS and SCD mRNA in both tissues of obese (Avy) mice were dramatically increased relative to lean (ala) controls. Excessive expression of these genes in this model could be due to direct effects of the agouti gene product; to test this possibility we treated 3T3-L1 adipocytes in vitro with recombinant agouti protein. Agouti treatment increased FAS and SCD mRNA levels by 1.5- and 4-fold, respectively. In addition, FAS activity and triglyceride content were 3-fold higher in agoutitreated 3T3-L1 cells relative to controls; these effects were attenuated by simultaneous treatment with a calcium channel blocker (nitrendipine). These data demonstrate that the agouti protein can directly increase lipogenesis in adipocytes and suggest that these effects are mediated through an intracellular calcium-dependent mechanism.
Interaction of carbohydrate and fat fuels in human skeletal muscle: impact of obesity and NIDDM
Authors: Mandarino L. J. , Consoli A. , Jain A. , Kelley D. E.
Published: December 2017

The current study was undertaken to examine the impact that obesity and non-insulin-dependent diabetes mellitus (NIDDM) have on the ability of glucose to stimulate its own uptake and oxidation in muscle. Euglycemic and hyperglycemic clamp experiments were performed with somatostatin infusions so that insulin could be replaced to basal levels or to physiological hyperinsulinemia. Arteriovenous leg balance methods were used to measure the pathways of leg muscle glucose uptake, oxidation, and storage. Percutaneous biopsies of the vastus lateralis muscle were taken to determine the pyruvate dehydrogenase complex or glycogen synthase activities. During basal insulin replacement, obese compared with lean nondiabetic subjects had higher values for glucose uptake, respiratory quotient, and glucose oxidation (all P<0.05) and a higher proportion of leg energy expenditure derived from glucose. Obese NIDD patients had a greater reliance on fat calories than lean diabetics during basal insulin replacement (P< 0.05). Hyperinsulinemia increased leg glucose metabolism (P<0.001) in all groups, but obese NIDD patients were significantly more insulin resistant. Hyperglycemia in NIDDM compensated for insulin resistance to the extent that rates of glucose metabolism were the same as those for nondiabetics studied at euglycemia. When nondiabetics were studied at hyperglycemia matched to the diabetics, the insulin resistance was still readily apparent.
Interaction between nitric oxide and prostaglandin E2 pathways in pregnant rat uteri
Authors: Dong Y. L. , Yallampalli C.
Published: December 2017

We examined the possible interrelationship between nitric oxide (NO) and cyclooxygenase (COX) products in the uterus during pregnancy and labor. Results indicate that 1) rat uteri during labor, at term, demonstrated a 69% decrease in nitrite production and a 217% increase in prostaglandin E2 (PGE2) production compared with day 18 of pregnancy; 2) interleukin-1 beta (IL-1 beta) induced a pronounced elevation of both nitrites and PGE2 in rat uteri; 3) diethylenetriamine/NO, a donor of NO, induced a significant increase of PGE2 production by the uterus in a dose-dependent manner; 4) NG-nitro-L-arginine methyl ester, an inhibitor of NO synthesis, markedly inhibited IL-1 beta-induced nitrite and PGE2 in rat uteri; this inhibitory action was reversed by coincubation with L-arginine; 5)exogenous PGE2 significantly inhibited IL-1 beta-induced, but not constitutive, nitrite production; and 6) inhibition of endogenous PGE2 by indomethacin substantially increased IL-1 beta-induced nitrite production. Thus the interaction between NO and COX pathways might be important in the regulation of uterine contractility during pregnancy and labor.
Chronic desensitization of the glucose-dependent insulinotropic polypeptide receptor in diabetic rats
Authors: Tseng C. C. , Boylan M. O. , Jarboe L. A. , Usdin T. B. , Wolfe M. M.
Published: December 2017

Rats were rendered diabetic by streptozotocin, after which serum glucose-dependent insulinotropic polypeptide (GIP) levels, duodenal mucosal GIP content, and GIP mRNA levels were nine times, 50% and 80%, respectively, greater than in control rats. To determine whether an increase in GIP gene expression might induce chronic desensitization of its receptor, normal rats were subjected to continuous intravenous GIP infusion. Serum GIP levels increased gradually in GIP-infused rats, and by 4 h a threefold increase was detected. In response to GIP infusion, the serum insulin concentration increased at 30 min, followed by a gradual decrease, and at 4 h, no increase in insulin levels was detected despite a sustained elevated serum GIP level. The response to glucagon-like peptide-1 (GLP-1) was preserved, a reporter cell line (LGIPR2) stably transfected with rat GIP receptor cDNA was studied. GIP stimulated adenosine 3', 5'-cyclic monophosphate (cAMP) production in LGIPR2 cells, which was first detected after 1 h of stimulation, reached maximum level at 4 h, and returned to basal concentrations by 16 h. Additional stimulation with GIP at 16 h did not affect cAMP generation, indicating desensitization of the GIP receptor by the ligand. In contrast, a response to prostaglandin E1 or forskolin in GIP-desensitization was a receptor-specific process. The results of these studies indicate that GIP gene expression is enhanced in diabetic animals and that elevated serum GIP level induces chronic desensitization of the GIP receptor in vivo and in a stably transfected cell line.