bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of hypoglycemia and diabetes on fuel metabolism by rat brain microvessels
Authors: McCall A. L. , Sussman I. , Tornheim K. , Cordero R. , Ruderman N. B.
Published: December 2017

Glucose and beta-hydroxybutyrate metabolism were compared in isolated cerebral microvessels from chronically diabetic and hypoglycemic rats. As noted previously, glucose oxidation and conversion to lactate are diminished in rats with streptozotocin-induced diabetes. The decrease in glucose metabolism did not result from selective damage to diabetic vessels during isolation, since the ATP level and the ATP/ADP ratio were similar to those of nondiabetic rats, and O2 consumption was increased. In addition, cerebral microvessel oxidation of beta-hydroxybutyrate was enhanced by diabetes. By contrast, microvessels from rats made chronically hypoglycemic by insulinoma engrafting 30 days earlier had a more than twofold increase in glucose oxidation and conversion to lactate, whereas their oxidation of beta-hydroxybutyrate was diminished by 50%. Unlike the insulinoma rats, no consistent increase in glucose metabolism was observed in microvessels from rats made hypoglycemic either by acute insulin administration or by a 4-day infusion of insulin. These results indicate that diabetes, and under some circumstances chronic hypoglycemia, markedly alters fuel metabolism in the cerebral microvasculature.
Phorbol esters, protein kinase C, and thyroxine 5'-deiodinase in brown adipocytes
Authors: Barge R. M. , Mills I. , Silva J. E. , Larsen P. R.
Published: December 2017

Protein kinase C activity has been identified in the rat brown adipocyte. About 60% of this activity is found in the cytosolic fraction under basal conditions, and 12-O-tetradecanoylphorbol 13-acetate (TPA) causes a rapid shift from the cytosol to the particulate fraction. Norepinephrine and phenylephrine cause a similar redistribution that can be blocked by prazosin but not by alprenolol. alpha 1-Adrenergic agonists cause three- to fivefold stimulation of type 2 iodothyronine 5'-deiodinase activity in brown adipocytes. TPA has no effect on basal deiodinase activity and reduces the response of the enzyme to alpha 1-adrenergic agonists. These results suggest that the translocation of protein kinase C from cytosol to particulate fraction is not sufficient to increase deiodinase activity but can modulate the alpha 1-adrenergic agonist-mediated responses in these cells.
Dose-dependent effects of oral and intravenous glucose on insulin secretion and clearance in normal humans
Authors: Tillil H. , Shapiro E. T. , Miller M. A. , Karrison T. , Frank B. H. , Galloway J. A. , Rubenstein A. H. , Polonsky K. S.
Published: December 2017

Insulin secretion and clearance were studied in 2 groups of 7 normal subjects who each received 25, 50, and 100 g of glucose either orally or intravenously (iv) on separate occasions. Insulin secretion rates were calculated during a 1-h base line and for 5 h after glucose administration from a two-compartmental analysis of peripheral C-peptide concentrations using individual kinetic parameters derived after iv bolus injections of biosynthetic human C-peptide. Incremental glucose areas after oral or iv glucose increased as a function of the glucose dose (P = 0.0001). Incremental insulin secretion increased with increasing doses of both oral and iv glucose (P = 0.0001). The metabolic clearance rate (MCR) of endogenous insulin was calculated as the ratio of the total area under the insulin secretion rate curve and the simultaneous peripheral insulin concentration curve. The basal MCR was 1,879.5 +/- 110.5 ml/min (mean +/- SE). The poststimulatory MCR decreased with increasing doses of both oral and iv glucose concomitant with the greater insulin secretory response (P = 0.0014). This decrease in insulin clearance was not significantly different between oral and iv administration of glucose (P = 0.495). In conclusion diminished insulin clearance may be seen after marked stimulation of insulin secretion with larger doses of oral and iv glucose.
Differences in renal metabolism of insulin and cytochrome c
Authors: Herrman J. , Simmons R. E. , Frank B. H. , Rabkin R.
Published: December 2017

Kidneys degrade small proteins such as cytochrome c (CYT c) by the classic lysosomal pathway. However, because alternate routes for the transport and degradation of protein hormones have been identified in other tissues, we set out to determine whether extralysosomal sites might participate in the renal degradation of insulin. First, we compared the effect of the lysosomal inhibitor NH4Cl on insulin and CYT c degradation by isolated perfused rat kidneys. After kidneys were loaded with radiolabeled proteins to allow for absorption and transport to lysosomes, degradation was measured in the presence or absence of inhibitors. Control kidneys degraded 45 +/- 1.5% of the trapped CYT c per hour, and this was inhibited 62 +/- 1.3% by NH4Cl. In contrast, 86 +/- 2.4% of the trapped insulin was degraded per hour, and this was inhibited 26 +/- 4% by NH4Cl. Next we followed the subcellular distribution of 125I-labeled insulin in kidneys exposed to 125I-labeled insulin in vivo or when isolated and perfused. Under both circumstances the distribution of insulin on a linear sucrose gradient differed from that of the lysosomal enzyme N-acetyl-beta-glucosaminidase. In contrast, [14CH3]CYT c, injected in vivo, distributed over a density similar to the lysosomal marker. Thus important differences exist between the renal metabolism of CYT c, which proceeds in lysosomes, and the renal metabolism of insulin. These include rate of degradation, sensitivity to NH4Cl, and subcellular sites of localization. Accordingly, we suggest that insulin degradation may occur, at least in part, in a different compartment from the classic lysosomal site of protein degradation.
Measuring brain glucose phosphorylation with labeled glucose
Authors: Brondsted H. E. , Gjedde A.
Published: December 2017

This study tested whether glucose labeled at the C-6 position generates metabolites that leave brain so rapidly that C-6-labeled glucose cannot be used to measure brain glucose phosphorylation (CMRGlc). In pentobarbital-anesthetized rats, the parietal cortex uptake of [14C]glucose labeled in the C-6 position was followed for times ranging from 10 s to 60 min. We subtracted the observed radioactivity from the radioactivity expected with no loss of labeled metabolites from brain by extrapolation of glucose uptake in an initial period when loss was negligible. The observed radioactivity was a monoexponentially declining function of the total radioactivity expected in the absence of metabolite loss. The constant of decline was 0.0077.min-1 for parietal cortex. Metabolites were lost from the beginning of the experiment. However, with correction for the loss of labeled metabolites, it was possible to determine an average CMRGlc between 4 and 60 min of circulation of 64 +/- 4 (SE; n = 49) mumol.hg-1.min-1.
Hyperglycemia induced by electrical stimulation of lateral part of dorsal parabrachial nucleus
Authors: Fujiwara T. , Nagai K. , Takagi S. , Nakagawa H.
Published: December 2017

Electrical stimulation of the lateral part of the dorsal parabrachial nucleus (PBD) induces hyperglycemia by enhancing glucagon secretion and suppressing insulin secretion in rats. The mechanism of this effect in the light period was examined by use of blockers of the autonomic nervous system. Hexamethonium, a ganglion blocker, and propranolol, a beta-adrenergic blocker, markedly inhibited the hyperglycemic response to stimulation of the lateral part of the PBD (LPBD). In contrast, phenoxybenzamine, an alpha-adrenergic blocker, and atropine methylnitrate, a muscarinic blocker, had no effect. Because previous studies showed that bilateral lesions of the suprachiasmatic nucleus (SCN) eliminated hyperglycemia induced by intracranial injection of 2-deoxy-D-glucose and that blinding largely suppressed the hyperglycemia, the effects of these two treatments on hyperglycemia induced by electrical stimulation of the LPBD were examined. SCN lesions abolished the hyperglycemic response but did not affect the hyperglucagonemic response. Results 4 wk after orbital enucleation were similar to those after SCN lesions. These findings suggest that the SCN and a beta-adrenergic mechanism are involved in the hyperglycemic response to LPBD stimulation.
Allocation of systemic glucose output to cerebral utilization as a function of fetal canine growth
Authors: Huang M. M. , Kliegman R. M. , Trindade C. , Kall D. , Voelker K.
Published: December 2017

To determine whether the neonatal canine brain consumes a major proportion of the systemic glucose production, we investigated the cerebral glucose requirement and hepatic glucose production in beagle pups. Sixteen pups received D-[6-3H]-glucose to determine systemic glucose production. Cerebral blood flow was measured by [N-methyl-14C]antipyrine, and the brain uptake index (BUI) of glucose was determined using 2-[14C]deoxy-D-glucose. Glucose production was 49.6 +/- 11.0 mumol.kg-1.min-1. Cerebral blood flow was 0.83 ml.g-1.min-1; cerebral uptake of glucose was 0.60 +/- 0.15 mumol.g-1.min-1. Of the total glucose production 36.6 +/- 7.9% was accounted for by the cerebral uptake of glucose. Brain-to-body weight and brain-to-liver weight ratios were the greatest in the smallest pups, suggesting brain sparing. The effect of growth status on cerebral substrate availability could not be correlated with cerebral uptake of glucose or oxygen or with systemic glucose production. However, the percentage of systemic glucose production allotted to the cerebral cortex increased with increasing body weight (r = 0.50, P less than 0.05). Cerebral glucose entry measured by BUI was demonstrated to be 0.108 +/- 0.014; BUI inversely correlated with canine birth weight (r = -0.832, P less than 0.001). We conclude that the percentage of glucose production utilized by the neonatal canine brain is not proportionately larger in the smaller pups despite a proportionately larger brain. Because the absolute cerebral glucose utilization may be static, we speculate that BUI (glucose entry) may be less of a rate-limiting factor for cerebral glucose entry in the smallest pups.
Neuroendocrine-gonadal axis in men: frequent sampling of LH, FSH, and testosterone
Authors: Spratt D. I. , O'Dea L. S. , Schoenfeld D. , Butler J. , Rao P. N. , Crowley W. F.
Published: December 2017

Previous studies of episodic hormone secretion of the hypothalamic-pituitary-gonadal axis in normal men have produced conflicting results due to examinations of small cohorts of subjects or to limited sampling techniques. We evaluated gonadotropin and testosterone (T) secretory patterns in 20 normal men by sampling blood at 10-min intervals for luteinizing hormone (LH) and follicle-stimulating hormone (FSH). T concentrations were also analyzed at 20-min intervals in 10 subjects. A previously unappreciated spectrum of gonadotropin and T secretory patterns was observed in normal men. Both mean LH concentrations and mean LH pulse amplitudes varied fourfold between individuals. LH interpulse intervals varied from 30 to 480 min (mean 119 +/- 32). Results also suggested a relative refractory period at the level of the hypothalamus or pituitary. In three subjects, a striking nighttime accentuation of LH pulsations was noted. Through use of Fourier analysis, a diurnal variation in LH was observed in the population (P less than 0.02). Mean FSH levels showed marked variation between individual subjects, with discrete pulses rarely observed. No diurnal variation in FSH secretion was noted. Serum T concentrations determined at 6-h intervals ranged from 105 to 1,316 ng/dl between subjects. When T was measured at 20-min intervals, marked intermittent declines in the T concentrations to levels well below the normal range were observed in 3 of 10 subjects. T secretion was found to lag behind LH secretion by approximately 40 min (P less than 0.02).
Glucagon, not insulin, may play a secondary role in defense against hypoglycemia during exercise
Authors: Tuttle K. R. , Marker J. C. , Dalsky G. P. , Schwartz N. S. , Shah S. D. , Clutter W. E. , Holloszy J. O. , Cryer P. E.
Published: December 2017

The sympathochromaffin system, probably sympathetic neural norepinephrine, plays a primary role in the prevention of hypoglycemia during exercise in humans. Our previous data indicated that changes in pancreatic islet hormones are not normally critical but decrements in insulin, increments in glucagon, or both become critical when catecholamine actions are blocked pharmacologically. To distinguish between the role of insulin and that of glucagon in this secondary line of defense against hypoglycemia during exercise in humans, glucoregulation during moderate exercise (approximately 55% of maximum O2 consumption over 60 min) was studied in people who could not decrease insulin but could increase glucagon, i.e., patients with insulin-dependent diabetes mellitus (IDDM). While receiving constant intravenous infusions of regular insulin, in individualized doses shown to result in stable plasma glucose concentrations of approximately 95 mg/dl before exercise, patients with IDDM were studied under two conditions: 1) a control study (n = 13) and 2) an adrenergic blockade study (propranolol infusion, n = 8). In the control study, mean plasma glucose concentrations did not change (from 95 +/- 2 to 100 +/- 11 mg/dl) during exercise despite constant plasma free insulin levels. In the adrenergic blockade study plasma glucose declined (from 96 +/- 2 to 74 +/- 7 mg/dl, P less than 0.01) but stabilized; hypoglycemia did not occur. Exercise-associated increments in plasma glucagon were comparable in the two studies. These data confirm that decrements in insulin are not critical to the prevention of hypoglycemia during moderate exercise in humans and indicate that compensation for deficient catecholamine action does not require decrements in insulin.(ABSTRACT TRUNCATED AT 250 WORDS)
Paradoxical organ-specific adaptations to streptozotocin diabetes mellitus in adult rats
Authors: Pillion D. J. , Jenkins R. L. , Atchison J. A. , Stockard C. R. , Clements R. S. , Grizzle W. E.
Published: December 2017

Adult male Fisher rats injected with streptozotocin (Stz) to produce diabetes mellitus demonstrated a significant loss of total body weight associated with adipose and muscle tissue wasting. Paradoxically, intestinal mass and length were increased in Stz-treated rats despite catabolism of other tissues. Concomitant with increased intestinal mass, food and water intake increased significantly in Stz-diabetic animals. Renal weight was not reduced despite the fall in total body weight. It is proposed that the adult Stz-diabetic rat responds to a loss of available insulin by polyphagia, polydipsia, and catabolism of adipose and muscle tissue and that a large percentage of available synthetic fuel is devoted to the production of additional intestinal tissue.
Regulation of angiotensinogen mRNA accumulation in rat hepatocytes
Authors: Ben-Ari E. T. , Garrison J. C.
Published: December 2017

Experiments were undertaken using isolated rat liver cells to determine whether the stimulation of angiotensinogen synthesis by glucocorticoids, estrogens, and angiotensin II is due to a direct action on the liver and whether these effects involve an increase in angiotensinogen mRNA levels. Dexamethasone and other corticosteroids stimulated angiotensinogen mRNA accumulation in hepatocytes up to 3.5-fold after 2.5-3 h of incubation. The effect of dexamethasone was inhibited competitively by the glucocorticoid antagonist RU486. These results indicate that the stimulation of hepatic angiotensinogen production by glucocorticoids is a direct, receptor-mediated effect and occurs via an increase in angiotensinogen mRNA accumulation. The stimulatory diastereomer of adenosine 3',5'-cyclic phosphorothioate, an active adenosine 3',5'-cyclic monophosphate analogue, caused a 1.8-fold increase in angiotensinogen mRNA accumulation, and this effect was additive with that of dexamethasone, suggesting a distinct mechanism of action. Angiotensin II increased angiotensinogen mRNA levels by only 1.2-fold after 2.5 h, whereas ethinyl estradiol had no effect.
Phenylarsine oxide and denervation effects on hormone-stimulated glucose transport
Authors: Sowell M. O. , Robinson K. A. , Buse M. G.
Published: December 2017

Insulin and insulin-like growth factor I (IGF-I) stimulate glucose transport in skeletal muscle through separate receptors. The proximal postreceptor events in coupling insulin and IGF-I receptors to glucose transport have been suggested to differ. Denervation of skeletal muscle produces a postreceptor insulin resistance presumably at an early step in the signaling cascade. We examined the effects of denervation and phenylarsine oxide (PAO), an agent believed to block insulin action on transport at a postreceptor step, on insulin and IGF-I stimulated 2-deoxy-D-glucose transport in isolated solei. Denervation (24 h) produced severe IGF-I resistance without affecting IGF-I receptor number or affinity. PAO inhibited insulin and IGF-I stimulation of transport in control muscles by approximately 90 and approximately 70%, respectively. In denervated muscle PAO inhibited transport stimulation by both hormones less than in controls. Conclusions are that 1) skeletal muscle insulin and IGF-I receptors signal transport mainly through a PAO-sensitive mechanism, but IGF-I's action involves a larger PAO-resistant component; 2) the denervation-induced postreceptor resistance of glucose transport to both hormones involves primarily the PAO-sensitive pathway.
Short-term energy balance: relationship with protein, carbohydrate, and fat balances
Authors: Abbott W. G. , Howard B. V. , Christin L. , Freymond D. , Lillioja S. , Boyce V. L. , Anderson T. E. , Bogardus C. , Ravussin E.
Published: December 2017

Energy balance (energy intake-energy expenditure) is known to vary considerably on a day-to-day basis in free-living individuals. The extent to which stores of protein, carbohydrate, and fat are used to store short-term surpluses of energy and the extent to which these stores are used to make up temporary energy deficits are incompletely known. We have measured body energy balance as well as carbohydrate, fat, and protein balances in 27 Caucasian men and 27 Caucasian women over a 24-h period in a respiratory chamber. An estimated weight-maintenance diet was fed to each subject. Because of individual differences in family background, body composition, activity, and the failure of some subjects to eat all of their food, these estimates are not exact, and energy balance is rarely achieved. Energy balance was correlated with fat balance in men (r = 0.79, P less than 0.0001) and women (r = 0.72, P less than 0.0001), and the slope of this relationship was not distinguishable from unity in men (1.16 +/- 0.18) or women (0.80 +/- 0.15). There were no correlations between energy balance and either carbohydrate or protein balances. This study demonstrates that carbohydrate and protein stores are closely regulated by adjusting oxidation to intake. Thus fat, rather than carbohydrate or protein, is almost exclusively used or stored in response to day-to-day fluctuations in energy balance.
Gonadotropin-releasing hormone sensitivity in underfed prepubertal female rats
Authors: Lively K. M. , Piacsek B. E.
Published: December 2017

Studies were conducted to investigate the effect of reduced food intake on pituitary gonadotropin-releasing hormone (GnRH) sensitivity as a possible link in the delay of puberty by underfeeding. Immature female rats (30-32 days old at the start of each experiment) were used throughout the study. Rats on reduced food intake (R) received 60% of normal food intake beginning at the age of 21 days, whereas control (C) animals were fed ad libitum. In ovariectomized (OVX), estradiol benzoate-progesterone-treated R rats, low doses (less than 5 ng/100 g body wt) of GnRH injected intravenously produced higher serum luteinizing hormone (LH) concentration than in comparable C rats. No difference was found at 5 ng GnRH but response to high doses (15 and 45 ng/100 g body wt) was sharply reduced in R rats. No difference in serum follicle-stimulating hormone concentrations was found. In contrast to the OVX-steroid treated animals, in intact R rats, GnRH evoked higher serum LH concentrations at both low and high doses. These studies indicate that reduced caloric intake can affect pituitary GnRH sensitivity and that the effect depends on both the dose of GnRH and the internal, gonadal steroid hormone milieu.
Verapamil induces PTH resistance but increases duodenal calcium absorption in rats
Authors: Fox J.
Published: December 2017

In vitro, verapamil inhibits duodenal Ca absorption, parathyroid hormone (PTH) secretion, and PTH-stimulated bone resorption. This study was designed to determine if any effects of chronic oral verapamil treatment on PTH secretion-action are reflected by changes in vitamin D metabolism, duodenal Ca absorption, and bone Ca content. Rats (100 g) received verapamil in the drinking water at doses of 4, 20, or 100 mumol.kg-1.day-1 for 2 wk. Verapamil administration did not significantly affect growth, plasma Ca or phosphate, or bone Ca content. However, verapamil treatment was associated with a dose-dependent 90% increase in plasma PTH levels. The elevated PTH was accompanied by a 22% decrease in 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels, such that there was a significant negative correlation (r = -0.52; P less than 0.01) between PTH and 1,25(OH)2D3 levels. Despite the decreased plasma 1,25(OH)2D3 levels, verapamil treatment was associated with a dose-dependent increase in duodenal Ca absorption. The increased Ca absorption did not seem to be caused by a verapamil-induced increased intestinal sensitivity to 1,25(OH)2D3, since verapamil-treated vitamin D-deficient rats showed the same absorptive response to administered 1,25(OH)2D3 as untreated rats. Thus chronic oral verapamil treatment induces an apparent PTH resistance but does not appear to have major effects on overall Ca homeostasis in young male rats.
Rapid and transitory stimulation of 3-O-methylglucose transport by growth hormone
Authors: Carter-Su C. , Rozsa F. W. , Wang X. , Stubbart J. R.
Published: December 2017

The regulation of hexose transport by growth hormone (GH) was investigated using isolated rat adipocytes. GH caused a rapid (less than 3 min) rise in rates of 3-O-methylglucose transport that reached a maximum of two to six times the basal rates in 10-30 min. The stimulation of transport was transitory, and rates of transport started to decline 15-30 min after GH was added. Transport stimulation required a period of preincubation; no stimulation was observed in freshly isolated cells. GH stimulated hexose transport between 100 and 5,000 ng/ml, with a 50% effective dose between 200 and 300 ng/ml. Depletion of cellular ATP by 2,4-dinitrophenol blocked the ability of GH to stimulate transport but not the decline of transport rates following stimulation by GH. In contrast, an inhibitor of RNA synthesis, actinomycin D, had no effect on either the initial stimulation by GH or the initial subsequent decline of transport when added simultaneously or 15 min prior to GH. Actinomycin D did, however, cause a second rise in hexose transport at approximately 120 min that was blocked by 2,4-dinitrophenol. These results suggest that changes in glucose transport contribute to the effects of GH on carbohydrate and lipid metabolism in adipose tissue. These changes are rapid, of substantial magnitude, and of a complex nature, suggesting that regulation of glucose transport by GH most likely involves multiple mechanisms.
A novel general biophysical model for simulating episodic endocrine gland signaling
Authors: Veldhuis J. D. , Johnson M. L.
Published: December 2017

A multiple-parameter convolution integral is used to define and generate waveforms that quantitatively and qualitatively resemble the experimentally observed behavior of episodic endocrine signals. Our formulation of the convolution integral in terms of multiple distinct parameters with statistically bounded values allows investigators to quantitatively model variations in the duration, amplitude, frequency, and/or contour of the hormone secretory pulse, as well as alterations in rates of endogenous hormone clearance. Here we demonstrate the applicability of this new concept of endocrine gland signaling to experimentally observed (physiological) endocrine data, parameter sensitivity analysis, the evaluation of statistical errors in hormone peak detection, and the estimation of random-pulse coincidence rates between two independent endocrine series.
Exercise regulation of triiodothyronine metabolism
Authors: Katzeff H. L. , Bovbjerg D. , Mark D. A.
Published: December 2017

Negative caloric balance reduces triiodothyronine (T3) production in both humans and rodents. The effects of chronic voluntary exercise and various levels of caloric intake and balance on T3 metabolism were studied in adult male C57/BL6 mice to determine if exercise had any direct effects on T3 production in vivo and in vitro. Chronic voluntary exercise was induced by the addition of running wheels to cages for 28 days. Ad libitum-fed exercising mice ingested 20% greater calories (P less than 0.02), maintained body weight, and increased T3 production (53.1 +/- 5.3 vs. 42.3 +/- 3.4 ng.h-1.100 mg body wt-1; P less than 0.01). Exercising animals pair fed to sedentary ad libitum-fed controls decreased their body mass to an equivalent degree as underfed sedentary animals (caloric intake 75% of ad libitum-fed controls) but had increased T3 clearance compared with weight-matched underfed sedentary control (P less than 0.05). Animals that were underfed and exercised decreased their body weight to a greater extent (P less than 0.01) compared with the sedentary underfed group, but T3 production rates were equal. Activity of liver 5'-deiodinase activity was decreased almost 50% (P less than 0.01) during both exercise plus pair feeding and exercise plus caloric restriction but decreased only 28% during caloric restriction alone (P less than 0.01). T3 metabolic clearance and production rates in vivo were correlated to caloric intake (r = 0.73, P less than 0.01), but an interaction between exercise and caloric balance was observed. Chronic voluntary exercise modulates T3 metabolism via several mechanisms. Exercise has an apparent stimulatory effect independent of caloric intake, but also there are regulatory effects dependent on the absolute level of caloric intake and relative caloric balance.(ABSTRACT TRUNCATED AT 250 WORDS)
Changes in GDP binding to brown adipose tissue mitochondria and the uncoupling protein
Authors: Swick A. G. , Swick R. W.
Published: December 2017

Incubation in vitro of brown adipose tissue (BAT) mitochondria with divalent cations, spermine, or alkaline phosphatase led to a marked increase in the binding of [3H]GDP. The effect of Mg2+ appeared to be the most specific and led to the largest increase in GDP binding. A simplified method was developed for measuring GDP binding to purified uncoupling protein from rat BAT mitochondria. Application of this method indicates that uncoupling protein from cold-acclimated rats binds twice as much GDP as uncoupling protein from cold-acclimated rats that were briefly returned to thermoneutrality, paralleling changes in GDP binding to the mitochondria. Incubation of BAT mitochondria with Mg2+ led to a smaller increase in GDP binding to the subsequently purified uncoupling protein, suggesting that divalent cations may somehow participate in the regulation of the activity of the uncoupling protein.
Time-dependent involvement of autonomic nervous system in hyperglycemia due to 2-deoxy-D-glucose
Authors: Yamamoto H. , Nagai K. , Nakagawa H.
Published: December 2017

To determine the mechanism of time-dependent hyperglycemia due to intracranial injection of 2-deoxy-D-glucose (2DG), we examined the effects of various blockers of the autonomic nervous system on the hyperglycemia and hyperglucagonemia induced by intracranial injection of 2DG in male Wistar rats in light and dark periods. Hexamethonium inhibited the hyperglycemia in both light and dark periods but did not block the hyperglucagonemia in either period. Intracranial injection of 2DG did not affect the plasma insulin concentration in saline-treated control rats, but hexamethonium caused an increase in the basal plasma insulin concentration and further increase in the plasma concentration after 2DG injection in the light period. Phenoxybenzamine, an alpha-adrenergic blocker, inhibited the hyperglycemia only in the light period and the hyperglucagonemia only in the dark period and slightly stimulated the basal concentrations of insulin and glucagon only in the light period. Propranolol, a beta-adrenergic blocker, blocked the hyperglycemia and hyperglucagonemia and also lowered the basal plasma glucagon concentration in both periods. Atropine sulfate and atropine methyl nitrate, muscarinic blockers, inhibited hyperglycemia only in the light and dark period, respectively. In contrast, both drugs blocked the hyperglucagonemia in both periods. These findings suggest that the autonomic nervous system is involved time dependently in the hyperglycemia and hyperglucagonemia due to intracranial 2DG injection.
Effect of CCK-8 on pentose phosphate shunt activity, pyridine nucleotides, and glucokinase of rat islets
Authors: Verspohl E. J. , Breuning I. , Ammon H. P.
Published: December 2017

In rat pancreatic islets the effects of cholecystokinin octapeptide (CCK-8) on pentose phosphate shunt (PPS) activity, glucokinase and hexokinase activity, and NADPH, NADP+, NADH, and NAD+ were studied. By elevating the glucose concentration from 3.0 to 8.3 and 16.7 mM the oxidation of [1-14C]- and [6-14C]glucose and the calculated PPS activity were increased in a concentration-dependent manner; 10 nM CCK-8 enhanced selectively the effect on [1-14C]glucose oxidation thereby increasing the PPS activity but only at an intermediate glucose concentration (8.3 mM). CCK-8 had no effect on glucokinase or hexokinase activity and CCK-8 did not influence glucose utilization. By elevating the glucose concentration, total NADPH and NADH were increased and total NADP+ and NAD+ were decreased. CCK-8 (10 nM) increased selectively NADPH and decreased NADP+ but did not change NADH or NAD+; the effect of CCK-8 on NADPH and NADH was only observed in the presence of an intermediate stimulatory glucose concentration (8.3 mM) but not at either a substimulatory glucose concentration or a maximally stimulatory glucose concentration for insulin release (3.0 or 16.7 mM). The data indicate first that CCK-8 does not act on glucose phosphorylation or glucose utilization and second that CCK-8 increases PPS activity and NADPH levels in rat pancreatic islets. Since the concentrations of glucose necessary for these CCK-8 effects are in the range of 8.3 mM and parallel with those necessary for insulin release as shown in earlier observations, glucose oxidation via pentose phosphate shunt and NADPH are suggested to be related to the CCK-8-modulated insulin release.
Hypothalamic noradrenergic and sympathoadrenal control of glycemia after stress
Authors: Smythe G. A. , Pascoe W. S. , Storlien L. H.
Published: December 2017

Central noradrenergic pathways play a significant role in mediating blood glucose levels after neuroglycopenia. To further investigate hypothalamic noradrenergic neuronal activity (NNA) and sympathoadrenal influences in glucoregulation, we studied the effects of acute stress on glycemia and insulin release in normal and adrenalectomized (ADRX) rats. Within 5 min of exposure of rats to ether or cold-swim stress, significant positive correlations were evident between hypothalamic NNA and serum glucose levels (r = 0.70, P less than 0.001; at 15 min r = 0.78, P less than 0.0001). Five minutes after stress in the intact rat, insulin release was inhibited and serum insulin levels inversely correlated to hypothalamic NNA (r = 0.45, P less than 0.05). This relationship between insulin and NNA was no longer present 15 min after stress, but the levels of insulin remained inappropriately low with respect to the elevated serum glucose levels (approximately 30% above basal). Blockade of sympathetic noradrenergic pathways by treatment of intact rats with guanethidine prevented the rise in glucose after cold-swim stress but did not prevent the inhibition of insulin release. Fifteen minutes after exposure of ADRX rats to cold-swim stress their hypothalamic NNA and serum glucose levels were similar to intact animals. However, in contrast to their intact counterparts, serum insulin levels were significantly elevated (P less than 0.01). These data are consistent with central noradrenergic neural pathways directly mediating hepatic glucose release and indirectly inhibiting pancreatic insulin release via activation of adrenal medullary catecholamines.
In vitro correction of impaired Na+-K+-ATPase in diabetic nerve by protein kinase C agonists
Authors: Lattimer S. A. , Sima A. A. , Greene D. A.
Published: December 2017

Diminished Na+-K+-ATPase activity in diabetic peripheral nerve plays a central role in the early electrophysiological, metabolic, and morphological abnormalities of experimental diabetic neuropathy. The defect in Na+-K+-adenosinetriphosphatase (ATPase) regulation in diabetic nerve is linked experimentally to glucose- and sorbitol-induced depletion of nerve myo-inositol but is not fully understood at a molecular level. Therefore, regulation of nerve Na+-K+-ATPase activity by phosphoinositide-derived diacylglycerol was explored as the putative link between myo-inositol depletion and the Na+-K+-ATPase impairment responsible for slowed saltatory conduction in diabetic animal models. In vitro exposure of endoneurial preparations from alloxan-diabetic rabbits to two protein kinase C agonists, 4 beta-phorbol 12 beta-myristate 13 alpha-acetate and 1,2-(but not 1,3-) dioctanoyl-sn-glycerol, for as little as 1 min completely and specifically corrected the 40% decreased enzymatically measured ouabain-sensitive ATPase activity. Neither of these agonists affected ouabain-sensitive ATPase activity in endoneurial preparations derived from nondiabetic controls. These observations are compatible with the hypothesis that metabolites of electrically stimulated phosphoinositide turnover such as diacylglycerol acutely regulate nerve Na+-K+-ATPase activity, probably via protein kinase C, thereby tightly coupling energy-dependent Na+-K+-antiport with impulse conduction in peripheral nerve. Glucose-induced depletion of myo-inositol presumably limits phosphoinositide turnover and diacylglycerol production, thereby disrupting this putative regulatory mechanism for Na+-K+-ATPase in diabetic peripheral nerve.
Central effects of beta-endorphins on glucose homeostasis in the conscious dog
Authors: Radosevich P. M. , Lacy D. B. , Brown L. L. , Williams P. E. , Abumrad N. N.
Published: December 2017

The effects of centrally administered beta-endorphins on glucose homeostasis in the conscious dog were studied. Intracerebroventricular administration of beta-endorphin (0.2 mg/h) caused a 70% increase in plasma glucose. The mechanism of the hyperglycemia was twofold: there was an early increase in glucose production and a late inhibition of glucose clearance. These changes are explained by marked increases in plasma epinephrine (30-fold) and norepinephrine (6-fold) that occurred during infusion of beta-endorphin. Central administration of beta-endorphin also resulted in increased levels of adrenocorticotropic hormone and cortisol. In addition there was an increase in plasma insulin but no increase in plasma glucagon. Intravenous administration of beta-endorphin did not alter glucose homeostasis. Intracerebroventricular administration of acetylated beta-endorphin did not perturb glucose kinetics or any of the hormones that changed during infusion of the unacetylated peptide. We conclude that beta-endorphin acts centrally to cause hyperglycemia by stimulating sympathetic outflow and the pituitary-adrenal axis. Acetylation of beta-endorphin abolishes the in vivo activity of the peptide.
Food intake, body and heart composition, and heart rate in T3 plus atenolol-treated rats
Authors: Burgi U. , Burgi-Saville M. E. , Ziegler F. , Krahenbuhl L. , Huber G. , Schoch C.
Published: December 2017

Thyroid hormones and beta-blockers both affect energy balance and the heart. The interaction of 3,5,3'-triiodothyronine (T3) and the beta-blocker atenolol on some cardiac and energy balance parameters was therefore investigated. Stock-fed male Wistar rats (approximately 400 g) received 5 micrograms (expt 1) or 1.5 micrograms (expt 2) T3.100 g body wt-1.day-1 for 3 wk, with or without atenolol. In expt 3, rats were overfed with a "cafeteria" diet before and during the experiment and otherwise treated as in experiment 2. Compared with stock-fed (expt 1 and 2) or overfed (expt 3) controls, T3 caused an increase in food intake in experiments 1 and 2 but not in experiment 3. There was a large loss of body fat in all experiments, disproportionately greater than the body weight loss. Protein loss was significant only in experiment 1 and negligible in cafeteria rats. Heart rate and weight were increased, although heart composition remained unchanged. Atenolol, in a dose that abolished T3-induced tachycardia, did not modify any of the other T3 effects investigated, including the hypertrophy of the heart. These results indicate that T3-induced tachycardia can be abolished by concomitant treatment with a beta-blocker without altering parameters connected with energy balance, whereas protein loss caused by T3 can be attenuated by lowering the dose of T3 used and can be further blunted by dietary manipulation (cafeteria overfeeding).
Interpulse interval of GnRH stimulation independently modulates LH secretion
Authors: O'Dea L. S. , Finkelstein J. S. , Schoenfeld D. A. , Butler J. P. , Crowley W. F.
Published: December 2017

To examine the importance of the interpulse interval of gonadotropin-releasing hormone (GnRH) stimulation in modulating gonadotroph responsiveness, a fixed individualized dose of GnRH was administered to eight GnRH-deficient men at intervals selected randomly from the distribution of luteinizing hormone (LH) interpulse intervals of normal men. The responses were compared with data derived from a study of LH pulses in 20 normal men. A positive relationship was found between LH pulse amplitude and the preceding interpulse interval both in the GnRH-deficient (P less than 0.05) and in the normal (P less than 0.003) men. The distributions of LH pulse amplitudes appeared to differ between the two groups with failure of the study paradigm to reproduce the distribution of low-amplitude pulses of the normal men in the GnRH-deficient men. There was significantly more variability about the line that related interpulse interval and LH amplitude in the normal men (P less than 0.004) in whom the amount of GnRH could vary physiologically. This difference remained significant both for pulses with amplitudes below (P less than 0.01) or above (P less than 0.03) the mean of the normal men. These studies demonstrate that the GnRH interpulse interval is an independent determinant of pituitary responsiveness and that alterations in the amount of GnRH secreted from the hypothalamus are an important determinant of LH pulse amplitude in men.
Postreceptor defect in insulin action in streptozotocin-induced diabetic rats
Authors: Nishimura H. , Kuzuya H. , Okamoto M. , Yamada K. , Kosaki A. , Kakehi T. , Inoue G. , Kono S. , Imura H.
Published: December 2017

To clarify the mechanism(s) responsible for the insulin resistance in streptozotocin (STZ)-treated diabetic rats, we studied insulin-induced glucose disposal by using the glucose clamp technique and measured insulin receptor and glucose transporter of muscles. The insulin dose-response curve of the metabolic clearance rate (MCR) of glucose revealed a decrease of the maximal response without a rightward shift in STZ rats. Maximal MCR was even lower when clamped at 300 rather than 150 mg/dl of blood glucose levels. Insulin binding to the crude plasma membrane of muscles from STZ rats was increased compared with controls. The number of glucose transporter of the plasma and microsomal membranes were significantly decreased in STZ rats. These in vivo and in vitro studies using skeletal muscles suggest that in STZ-treated diabetic rats 1) a defect or defects exist in the signal transduction mechanism of insulin in postbinding steps, 2) the decreased maximal MCR is related at least partly to the decrease of glucose transporter numbers, and 3) a defect in glucose metabolism (postglucose transport defect) is also present.
Polymyxin B inhibits stimulation of glucose transport in muscle by hypoxia or contractions
Authors: Henriksen E. J. , Sleeper M. D. , Zierath J. R. , Holloszy J. O.
Published: December 2017

Glucose transport can be stimulated via two separate pathways in muscle. One is activated by insulin, the other by contractile activity and hypoxia. Polymyxin B, a cationic antibiotic that displaces Ca2+ from anionic phospholipids, is reported to selectively inhibit the stimulation of glucose transport by insulin in muscle. A purpose of the present study was to determine whether the inhibition by polymyxin B is actually restricted to insulin. We found that polymyxin B (250 micrograms/ml) significantly inhibited the stimulation of glucose transport in rat skeletal muscles not only by insulin and vanadate but also by hypoxia, electrical stimulation, and K+. Polymyxin B also decreased the tension developed in response to electrical stimulation or K+. Although polymyxin B inhibited the increase in sugar transport activity induced by insulin and hypoxia, it had no inhibitory effect on sugar transport after it had been stimulated by these agents. These results show that the inhibitory effect of polymyxin B on the stimulation of glucose transport is not specific for insulin action. They suggest that polymyxin B inhibits a step that is common to the two pathways for stimulating glucose transport in skeletal muscle.
Disposition of a glucose load in fed rats and rats adapted to a high-carbohydrate diet
Authors: Niewoehner C. B. , Nuttall F. Q.
Published: December 2017

Current evidence suggests that, during the transition from the fasted to the fed state, liver glycogen is synthesized primarily from gluconeogenic precursors rather than from glucose unless the circulating glucose concentration is high. In the fed state the glucose concentration already is elevated. We aimed to determine whether administration of an additional oral glucose load (4 g/kg) to chow- or high-carbohydrate diet-adapted (CHO) rats would further increase the glucose concentration and result in increased direct glucose uptake. In the chow- and CHO-fed rats, 70 and 98% of the administered glucose was absorbed by 120 min. In the chow-fed rats the glucose concentration entering the liver increased by only 1.0 mM from 8.0 to 9.0 mM; no net hepatic glucose uptake was observed. In the CHO-adapted rats the entering glucose concentration increased transiently by 3.5 mM from 8.0 to 11.5 mM. This was associated with net glucose uptake, which continued until the entering glucose concentration fell below 9.5 mM, the entering glucose concentration threshold above which net glucose uptake was observed previously in fasted rats. Net hepatic glucose uptake could not be correlated with insulin or hepatic intracellular glucose concentrations. Net glycogen synthesis did not occur in either group. We could not account for the absorbed glucose by the rise in portal glucose concentrations or by increased muscle glycogen deposition. The fate of much of the absorbed glucose remains unknown.
Effect of short- and long-term beta-adrenergic blockade on lipolysis during fasting in humans
Authors: Klein S. , Peters E. J. , Holland O. B. , Wolfe R. R.
Published: December 2017

Stable isotope tracers and indirect calorimetry were used to evaluate the importance of beta-adrenergic stimulation of lipolysis and triglyceride-fatty acid cycling during fasting in healthy human volunteers. Each subject was studied after 12 and 84 h of fasting both with and without propranolol infusion (protocol 1) and when oral propranolol treatment was given throughout fasting (protocol 2). In protocol 1, the rates of appearance of glycerol and palmitic acid increased from 3.04 +/- 0.19 and 1.78 +/- 0.17 mumol.kg lean body mass-1.min-1, respectively, after 12 h of fasting to 5.28 +/- 0.31 and 3.47 +/- 0.15 mumol.kg lean body mass-1.min-1, respectively, after 84 h of fasting (P less than 0.005). The rate of triglyceride-fatty acid cycling increased from 97 +/- 8 to 169 +/- 5 mumol/min (P less than 0.005). Intravenous propranolol infusion decreased the rate of lipolysis after both 12 and 84 h of fasting, but the magnitude of the antilipolytic effect was much greater after 84 h (P less than 0.005). In protocol 2, the rate of lipolysis and triglyceride-fatty acid cycling was still increased by fasting despite beta-adrenergic blockade with oral propranolol. This study demonstrates that beta-adrenergic stimulation contributes to the mobilization of fat during fasting. However, other mechanism(s) can increase lipolysis and triglyceride-fatty acid cycling when beta-adrenergic receptors are continuously blocked.
Phosphorylase synthesis in diabetic hepatocytes and cardiomyocytes
Authors: Rulfs J. , Jaspers S. R. , Garnache A. K. , Miller T. B.
Published: December 2017

Whereas total cardiac glycogen phosphorylase activity appears to be unaffected by severe insulin deficiency, a diabetes-induced decreased in hepatic glycogen phosphorylase activity has been demonstrated by our laboratory and others using liver extracts, isolated perfused liver, and cultured hepatocytes. The loss of activity in diabetic liver can be correlated with a drop in protein levels. Using primary cultures of cells from normal and diabetic rats and phosphorylase specific antibodies, we found a corresponding decrease in phosphorylase synthesis in diabetic hepatocytes cultured for 2 days in a serum-free, chemically defined medium. When hepatocytes are cultured in the presence of insulin, triiodothyronine, and cortisol, there is a significant recovery in the rate of phosphorylase synthesis after 3 days. Over the 3-day time period, there is no significant difference in the rate of phosphorylase degradation in normal compared with diabetic hepatocytes. Total protein synthesis in both hepatocytes and cardiomyocytes is unaffected by diabetes, as is phosphorylase synthesis in cultured cardiomyocytes.
In vivo insulin secretion and action in hyperglycemic rat
Authors: Laury M. C. , Penicaud L. , Ktorza A. , Benhaiem H. , Bihoreau M. T. , Picon L.
Published: December 2017

This work was designed to study the effects of insulin secretion and action in vivo of moderate hyperglycemia induced by glucose infusion during 4 days in unrestrained rats. The maintenance of a glycemia around 170 mg/dl throughout the infusion time necessitated a gradual increase of glucose infusion rate from 11.5 to 19 g/day. Throughout the infusion period, plasma insulin-to-glucose ratio remained much higher in hyperglycemic rats (HG) than in controls. Glucose tolerance and insulin secretion tests were performed 2 h after the end of the infusion, when glycemia and insulinemia were back to basal values. Incremental plasma glucose values were significantly lower in HG than in control rats without significant changes in incremental plasma insulin concentrations, suggesting an increased insulin efficiency. At the same insulin level, glucose utilization was higher in HG than in control rats during euglycemic-hyperinsulinemic clamps. These data show that short-term hyperglycemia and hyperinsulinemia do not induce a defect in insulin secretion in vivo and do increase tissue sensitivity to insulin.