bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of insulin on whole body and forearm leucine and KIC metabolism in type 1 diabetes
Authors: Tessari P. , Biolo G. , Inchiostro S. , Sacca L. , Nosadini R. , Boscarato M. T. , Trevisan R. , De Kreutzenberg S. V. , Tiengo A.
Published: December 2017

To investigate whole body rates of appearance (Ra) and forearm metabolism of leucine and alpha-ketoisocaproate (KIC) in type 1 diabetes, before and after insulin administration, seven diabetic subjects were studied in the postabsorptive state with primed-constant infusions of L-[4,5-3H]leucine and [1-14C]KIC, and forearm arterial deep-venous catheterization. This combined technique allowed the selective quantitation of the two processes regulating forearm leucine and KIC metabolism (release and uptake) that may occur simultaneously. Before insulin (arterial plasma glucose, 284 +/- 24 mg/dl; leucine, 215 +/- 24 mumol/l; KIC, 42 +/- 3 mumol/l) forearm leucine and KIC release exceeded uptake slightly but significantly (P less than 0.05). During a 180-min insulin infusion, arterial glucose (144 +/- 27 mg/dl) and leucine concentrations (130 +/- 15 mumol/l) decreased (P less than 0.05 or less vs. base line) toward normal, whereas KIC did not change (33 +/- 4 mumol/l, NS). However, no net uptake of either leucine or KIC across the forearm was detected at any time point. In contrast, a significant net release of these substrates occurred throughout the insulin infusion. By the end of the hormone administration, whole body leucine and KIC Ra decreased 17 and 33%, respectively (P less than 0.01). However, forearm uptake and release of leucine and KIC did not significantly change with respect to base line. The fraction of whole body leucine released from estimated total muscle mass did not change (54 to 48%, NS) before vs. after insulin.(ABSTRACT TRUNCATED AT 250 WORDS)
Pancreatic beta-cell somatostatin receptors
Authors: Thermos K. , Meglasson M. D. , Nelson J. , Lounsbury K. M. , Reisine T.
Published: December 2017

The characteristics of somatostatin (SRIF) receptors in rat pancreatic beta-cells were investigated using rat islets and the beta-cell line HIT-T15 (HIT). The biochemical properties of the SRIF receptors were examined with 125I-labeled des-Ala-1,Gly-2-desamino-Cys-3-[Tyr-11]- dicarba3,14-somatostatin (CGP 23996). 125I-CGP 23996 bound to SRIF receptors in HIT cells with high affinity and in a saturable manner. The binding of 125I-CGP 23996 to SRIF receptors was blocked by SRIF analogues with a rank order of potency of somatostatin 28 (SRIF-28) greater than D-Trp-8-somatostatin greater than somatostatin 14 (SRIF-14). To investigate the physical properties of the HIT cell SRIF receptor, the receptor was covalently labeled with 125I-CGP 23996 using photo-cross-linking techniques. 125I-CGP 23996 specifically labeled a protein of 55 kDa in HIT cell membranes. The size of the SRIF receptor in HIT cells is similar to the size of the SRIF receptor labeled with 125I-CGP 23996 in membranes of freshly isolated islets, suggesting that the physical properties of SRIF receptors in HIT cells and rat islet cells are similar. The binding studies suggest that beta-cells predominantly express a SRIF-28-preferring receptor. In freshly isolated islets, glucose- and arginine-stimulated insulin release was effectively blocked by SRIF-28 but not by SRIF-14. SRIF-14 did inhibit arginine-stimulated glucagon secretion from freshly isolated islets. The dissociation of the inhibitory effects of SRIF-28 and SRIF-14 on insulin and glucagon release from freshly isolated islets suggests that the two peptides act through different receptors in islets to regulate hormone secretion.
Distribution and kinetics of glucose in rats analyzed by noncompartmental and compartmental analysis
Authors: Raman M. , Radziuk J. , Hetenyi G.
Published: December 2017

The steady-state kinetics and distribution of glucose were assessed using noncompartmental and various two-compartment models in rats that were infused with insulin (+/- euglycemic clamping), methylprednisolone (MP), or phlorizin (PHL) as well as rats injected with protamine-zinc-insulin (PZI) or rendered diabetic. Decreases in clearance of glucose (PCR) were greatest with insulin infusion, followed by PHL, MP, and PZI treatments. PCR decreased in diabetes to 25% of normal. With hyperinsulinemia and euglycemia, turnover rates were 1.18 times the rate of glucose infusion. In normal rats the ratio of the contents of the two compartments was 0.6-0.8 (depending on the model). Significant increases, of between 2.8 and 5.2, were observed with insulin infusion and between 0.8 and 1.8 with PHL, again depending on the model. Because PHL-induced changes in PCR are renal, these data suggest that variations in glucose distribution depend on changes in PCR as well as insulin. The intercompartmental rate constant decreased, and the noncompartmental volume of distribution increased to reflect the above changes. In non-steady-state studies, glucose release increased in response to insulin but not to PHL in contrast to other species.
Acute effects of insulin-like growth factor I and insulin on glucose metabolism in vivo
Authors: Moxley R. T. , Arner P. , Moss A. , Skottner A. , Fox M. , James D. , Livingston J. N.
Published: December 2017

We have compared the actions of insulin-like growth factor (IGF-I) and insulin on glucose metabolism in vivo, using the glucose clamp technique in rats. Both hormones caused dose-dependent inhibition of hepatic glucose production, stimulation of whole body glucose disposal, and an increase in the glucose metabolic rate of specific muscles. Infusion of IGF-I also decreased the plasma concentration of insulin. An an infusion rate of 0.57 nmol.kg-1.min-1, IGF-I led to stimulation of whole body glucose uptake that was similar to the glucose uptake produced by infusion of 0.01 nmol.kg-1.min-1 insulin. The glucose metabolic rate, as measured by 2-deoxy-D-glucose uptake, was comparable in quadriceps femoris, soleus, and diaphragm muscles during the infusion of 0.57 nmol.kg-1.min-1 IGF-I and 0.01 nmol.kg-1.min-1 insulin. However, at these rates of infusion, IGF-I caused only a 38 +/- 6% inhibition of hepatic glucose output compared with 66 +/- 12% inhibition by insulin (P less than 0.05). Thus, under these conditions, muscle is more responsive than liver to IGF-I, which agrees with the complement of IGF-I receptors in the two tissues.
Dose-dependent effect of insulin on plasma free fatty acid turnover and oxidation in humans
Authors: Bonadonna R. C. , Groop L. C. , Zych K. , Shank M. , DeFronzo R. A.
Published: December 2017

Methodology for measuring plasma free fatty acid (FFA) turnover/oxidation with [1–14C]palmitate was tested in normal subjects. In study 1, two different approaches (720-min tracer infusion without prime vs. 150-min infusion with NaH14CO3 prime) to achieve steady-state conditions of 14CO2 yielded equivalent rates of plasma FFA turnover/oxidation. In study 2, during staircase NaH14CO3 infusion, calculated rates of 14CO2 appearance agreed closely with NaH14CO3 infusion rates. In study 3, 300-min euglycemic insulin clamp documented that full biological effect of insulin on plasma FFA turnover/oxidation was established within 60–120 min. In study 4, plasma insulin concentration was raised to 14 +/- 2, 23 +/- 2, 38 +/- 2, 72 +/- 5, and 215 +/- 10 microU/ml. A dose-dependent insulin suppression of plasma FFA turnover/oxidation was observed. Plasma FFA concentration correlated positively with plasma FFA turnover/oxidation in basal and insulinized states. Total lipid oxidation (indirect calorimetry) was significantly higher than plasma FFA oxidation in the basal state, suggesting that intracellular lipid stores contributed to whole body lipid oxidation. Hepatic glucose production and total glucose disposal showed the expected dose-dependent suppression and stimulation, respectively, by insulin. In conclusion, insulin regulation of plasma FFA turnover/oxidation is maximally manifest at low physiological plasma insulin concentrations, and in the basal state a significant contribution to whole body lipid oxidation originates from lipid pool(s) that are different from plasma FFA.
Mechanisms of starvation diabetes: a study with double tracer and indirect calorimetry
Authors: Fery F. , d'Attellis N. P. , Balasse E. O.
Published: December 2017

To analyze the mechanisms of fasting-induced glucose intolerance, glucose metabolism was studied before and after the ingestion of 75 g glucose in 24 normal subjects fasted for either 14 h (n = 12) or 4 days (n = 12). The techniques included intravenous infusion of [6-3H]glucose and oral administration of [1-14C]glucose combined with indirect calorimetry. Compared with the controls, the starved subjects exhibited the following differences in glucose metabolism during the 5 h after glucose ingestion. 1) Mean incremental levels were fourfold higher for glucose and 40% higher for insulin. 2) Absorption of oral glucose was delayed and prolonged, but total amount reaching systemic circulation in 5 h was identical in the two groups (approximately 63 g). 3) Suppression of hepatic glucose output was reduced (-12 +/- 1 vs. -22 +/- 2 g). 4) Consequently, the increment in peripheral appearance of total glucose (exogenous plus endogenous) was augmented (+ 52 +/- 2 vs. +41 +/- 2 g). 5) Mean glucose clearance increased significantly less (+28 +/- 7 vs. +96 +/- 10 ml/min). 6) Oxidation of oral glucose was reduced (9 +/- 2 vs. 36 +/- 3 g), and nonoxidative disposal (presumably storage) was enhanced (56 +/- 2 vs. 36 +/- 3 g) in the presence of an elevated fat oxidation (35 +/- 2 vs. 22 +/- 4 g). Thus the alterations in glucose homeostasis responsible for the starvation-induced glucose intolerance are located both at the splanchnic (hepatic) and peripheral levels.
Immunolocalization, binding, and biological activity of endothelin in rabbit uterus: effect of ovarian steroids
Authors: Maggi M. , Vannelli G. B. , Peri A. , Brandi M. L. , Fantoni G. , Giannini S. , Torrisi C. , Guardabasso V. , Barni T. , Toscano V. , et al.
Published: December 2017

Specific immunostaining for endothelin 1 (ET-1) was observed in the endometrium but not myometrium of rabbits. The staining was dramatically affected by subacute treatment with ovarian steroids: epithelial cells were predominantly positive in immature rabbits, whereas, in sex steroid-primed rabbits, ET-1 was mainly localized in the stromal compartment. Binding studies were performed in myometrium of estrogen-treated rabbits using labeled ET-1 and ET-3, the corresponding unlabeled peptides, and sarafotoxin b (SRTX). Mathematical modeling of experimental results indicates that two populations of sites are present in myometrium. One site (R1 = 1 pmol/mg protein) shows approximately the same affinity for ET-1, ET-3, and SRTX [dissociation constant (Kd) 100 pM], whereas the second site (R2 = 10 pmol/mg protein) selectively binds ET-1 (Kd 400 pM). According to binding studies, ET-1 was more potent than SRTX in stimulating uterine contraction "in vitro." The subacute administration of increasing concentrations of 17 beta-estradiol (0.2-200 micrograms/kg for 4 days), but not 17 beta-estradiol (200 micrograms/kg for 4 days) plus progesterone (5 mg/kg for 4 days), stimulates a dose-dependent increase in endothelin receptors in myometrium (half-maximal effective dose = 0.7 micrograms/kg for 4 days). However, estrogen treatment does not affect the concentration of endothelin receptors in myometrial cells in primary culture. Conversely, divalent ions like calcium and magnesium enhance the binding of ET-1 to both uterine membranes and cells. Our results indicate that in rabbit uterus endothelin is present in the endometrium, whereas specific receptors are located in myometrium.
Growth hormone acutely stimulates forearm muscle protein synthesis in normal humans
Authors: Fryburg D. A. , Gelfand R. A. , Barrett E. J.
Published: December 2017

The short-term effects of growth hormone (GH) on skeletal muscle protein synthesis and degradation in normal humans are unknown. We studied seven postabsorptive healthy men (age 18-23 yr) who received GH (0.014 micrograms.kg-1.min-1) via intrabrachial artery infusion for 6 h. The effects of GH on forearm amino acid and glucose balances and on forearm amino acid kinetics [( 3H]Phe and [14C]Leu) were determined after 3 and 6 h of the GH infusion. Forearm deep vein GH rose to 35 +/- 6 ng/ml in response to GH, whereas systemic levels of GH, insulin, and insulin-like growth factor I (IGF-I) were unchanged. Forearm glucose uptake did not change during the study. After 6 h, GH suppressed forearm net release (3 vs. 6 h) of Phe (P less than 0.05), Leu (P less than 0.01), total branched-chain amino acids (P less than 0.025), and essential neutral amino acids (0.05 less than P less than 0.1). The effect on the net balance of Phe and Leu was due to an increase in the tissue uptake for Phe (71%, P less than 0.05) and Leu (37%, P less than 0.005) in the absence of any significant change in release of Phe or Leu from tissue. In the absence of any change in systemic GH, IGF-I, or insulin, these findings suggest that locally infused GH stimulates skeletal muscle protein synthesis. These findings have important physiological implications for both the role of daily GH pulses and the mechanisms through which GH can promote protein anabolism.
Compensatory changes in thyroid blood flow are only partially mediated by thyrotropin
Authors: Michalkiewicz M. , Connors J. M. , Huffman L. J. , Pietrzyk Z. , Hedge G. A.
Published: December 2017

It has been shown that the compensatory growth of the thyroid gland and the compensatory increase in hormone secretion that occur after hemithyroidectomy are preceded by a dramatic increase in thyroid blood flow (BF). These alterations in the thyroid remnant may be due to the concomitant increase in plasma thyrotropin (TSH) concentrations. It has been suggested, however, that the compensatory thyroid growth may also involve a neural reflex. In this study we have investigated the role of TSH in mediating the compensatory alterations in thyroid BF and mass after subtotal thyroidectomy. Male Sprague-Dawley rats were anesthetized with ether for surgical or sham hemithyroidectomy. One-half of the hemithyroidectomized rats (HTX) received no further treatment; in the other one-half of the HTX rats (Clamp), plasma TSH levels were maintained at levels comparable with those in sham-operated animals by initiating constant thyroid hormone replacement beginning at the time of hemithyroidectomy. Plasma samples for TSH, 3,5,3'-triiodothyronine, and thyroxine radioimmunoassays were obtained 2, 7, 14, and 21 days after surgery. Thyroid BF was determined at 1, 2, and 3 wk after surgery by the reference sample version of the radioactive microsphere technique (141Ce, 15 microns diameter). Plasma TSH levels and thyroid lobe weight were significantly elevated in HTX rats but not in Clamp rats. Thyroid BF was markedly increased in HTX rats. Thyroid BF was also significantly increased in Clamp rats despite the suppression of the rise in plasma TSH concentration, but this increase was less than that in HTX rats. Neither hemithyroidectomy nor Clamp treatments had any effect on arterial blood pressure or BF to other tissues (e.g., kidney).(ABSTRACT TRUNCATED AT 250 WORDS)
Neuroendocrine rhythms and sleep in aging men
Authors: van Coevorden A. , Mockel J. , Laurent E. , Kerkhofs M. , L'Hermite-Baleriaux M. , Decoster C. , Neve P. , Van Cauter E.
Published: December 2017

To delineate the physiological effects of aging on basal levels and temporal patterns of neuroendocrine secretions, the 24-h profiles of cortisol, thyroid-stimulating hormone (TSH), melatonin, prolactin, and growth hormone (GH) levels were simultaneously obtained at frequent intervals in eight healthy, active elderly men, age 67-84 yr and in eight young male adults, age 20-27 yr. The study was preceded by an extended period of habituation to laboratory conditions, and sleep was polygraphically recorded. Mean cortisol levels in the elderly were normal, but the amplitude of the circadian rhythm was reduced. Circulating levels of daytime and nighttime levels of both TSH and GH were greatly diminished in old age. In contrast, prolactin and melatonin concentrations were decreased during the nighttime only. The circadian rises of cortisol, TSH, and melatonin occurred 1-1.5 h earlier in elderly subjects, and the distribution of rapid-eye-movement stages during sleep was similarly advanced, suggesting that circadian timekeeping is modified during normal senescence. Despite perturbations of sleep, sleep-related release of GH and prolactin occurred in all elderly men. Age-related decreases in hormonal levels were associated with a decrease in the amplitude, but not the frequency, of secretory pulses. These findings demonstrate that the normal process of aging involves alterations in the central mechanisms controlling the temporal organization of endocrine release in addition to a reduction of secretory outputs.
Effects of growth hormone on fuel utilization and muscle glycogen synthase activity in normal humans
Authors: Bak J. F. , Moller N. , Schmitz O.
Published: December 2017

To examine the insulin antagonistic effects of growth hormone (GH), seven healthy subjects underwent, in random order, two 5-h euglycemic clamp studies with moderate hyperinsulinemia. A GH infusion (45 ng.kg-1.min-1) was given throughout one of the studies. GH inhibited the insulin-stimulated glucose disposal by 27% from 4.4 +/- 0.7 to 3.3 +/- 0.4 mg.kg-1.min-1 (P less than 0.02) and raised the nonprotein energy expenditures (NPEE) from 18.7 +/- 0.5 to 20.5 +/- 0.3 kcal.kg-1.24 h-1 (P less than 0.03). Lipid oxidation contributed 71.7 +/- 5.6% of NPEE during the GH infusion as compared with 48.7 +/- 5.2% during the control clamp (P less than 0.02). In skeletal muscle biopsies, insulin binding to wheat germ agglutinin-purified insulin receptors and insulin receptor kinase activity were unaffected by GH infusion. Glycogen synthase activation by insulin was inhibited by 41% during the GH clamp (fractional velocity 14.1 +/- 2.5 vs. 8.3 +/- 1.4%, P less than 0.03). In conclusion, GH 1) increases energy expenditures and inhibits glucose oxidation in favor of an increased lipid oxidation, and 2) inhibits insulin-mediated activation of the glycogen synthase in skeletal muscle biopsies by a mechanism distal to insulin receptor binding and kinase activity.
Whole body and hepatic insulin action in normal, starved, and diabetic rats
Authors: Koopmans S. J. , de Boer S. F. , Sips H. C. , Radder J. K. , Frolich M. , Krans H. M.
Published: December 2017

In normal (N), 3-days starved (S), and streptozotocin-treated (65 mg/kg) 3-days diabetic (D) rats we examined the in vivo dose-response relationship between plasma insulin levels vs. whole body glucose uptake (BGU) and inhibition of hepatic glucose production (HGP) in conscious rats, as determined with the four-step sequential hyperinsulinemic euglycemic clamp technique, combined with [3-3H]glucose infusion. Twelve-hour fasting (basal) HGP was 3.0 +/- 0.2, 2.1 +/- 0.2, and 5.4 +/- 0.5 mg/min in N, S, and D rats, respectively. Next, all rats were clamped at matched glycemia (6 mM). Lowering plasma glucose in D rats from +/- 20 to 6.0 mM did not increase plasma norepinephrine, epinephrine, glucagon, and corticosterone levels. For BGU, insulin sensitivity was increased (70 +/- 11 microU/ml) in S and unchanged (113 +/- 21 microU/ml) in D compared with N rats (105 +/- 10 microU/ml). Insulin responsiveness was unchanged (12.4 +/- 0.8 mg/min) in S and decreased (8.5 +/- 0.8 mg/min) in D compared with N rats (12.3 +/- 0.7 mg/min). For HGP, insulin sensitivity was unchanged (68 +/- 10 microU/ml) in S and decreased (157 +/- 21 microU/ml) in D compared with N rats (71 +/- 5 microU/ml). Insulin responsiveness was identical among N, S, and D rats (complete suppression of HGP). In summary, 1) insulin resistance in D rats is caused by hepatic insensitivity and by a reduction in BGU responsiveness. 2) S rats show normal hepatic insulin action, but insulin sensitivity for BGU is increased. Therefore, S and D rats both suffering from a comparable catabolic state (10-15% body wt loss in 3 days) show opposite effects on in vivo insulin action. This indicates that in vivo insulin resistance in D rats is not caused by the catabolic state per se.
Fraction of hepatic cytosolic acetyl-CoA derived from glucose in vivo: relation to PDH phosphorylation state
Authors: Kaempfer S. , Blackham M. , Christiansen M. , Wu K. , Cesar D. , Vary T. , Hellerstein M. K.
Published: December 2017

We measured the contribution of glucose to hepatic cytosolic acetyl-CoA in vivo in rats and compared it with the phosphorylation state of a potentially regulatory enzyme complex [pyruvate dehydrogenase (PDH)]. Xenobiotic probes were used to sample hepatic cytosolic acetyl-CoA [acetylated sulfamethoxazole (SMX)] and UDP-glucose (glucuronidated acetaminophen) in vivo during [U-14C]glucose infusions. Percent active (dephosphorylated) form of PDH (PDHa) was determined on freeze-clamped liver. First, we confirmed using liver cell elutriation that acetylation of SMX occurs in parenchymal hepatocytes. Next, the fraction of cytosolic acetyl-CoA derived from [14C]glucose in vivo was shown to depend on dietary state. Specific activity of acetyl-CoA relative to plasma glucose or hepatic UDP-glucose was lower after 48 h fasting than after overnight fasting, and glucose refeeding (25 mg.kg-1.min-1 iv) maximally increased [14C]-glucose fractional contribution to acetyl-CoA within 2 h in the overnight-fasted but not in the prolonged fasted group. Hepatic PDHa demonstrated a similar but not identical pattern. The isotopic and enzymatic parameters showed significant correlations (r2 = 0.61 in 48-h fasted-refed group, r2 = 0.28 in overnight-fasted refed group), although [14C]glucose contribution to acetyl-CoA increased disproportionately compared with PDHa as refeeding progressed. The indirect pathway of UDP-glucose synthesis correlated inversely with the fractional contribution of glucose to acetyl-CoA. In summary, the fraction of hepatic acetyl-CoA derived from glucose in vivo is influenced by acute and chronic dietary factors and is only partially explained by PDHa. Regulation of the carbon source of hepatic acetyl-CoA in vivo and interactions suggested by these results (e.g., glucose-fatty acid cycle; branch-point regulation of glucose recycling) can be addressed in a quantitative fashion using this experimental framework.
Adrenal steroid receptor activation in vivo and immune function
Authors: Miller A. H. , Spencer R. L. , Trestman R. L. , Kim C. , McEwen B. S. , Stein M.
Published: December 2017

Recent studies have indicated significant differences among immune and other tissues in in vivo adrenal steroid receptor activation after a given hormone exposure. Nevertheless, the relationship between in vivo receptor activation and functional measures of the immune response has not been determined. Type I and type II adrenal steroid receptor binding in conjunction with mitogen-induced T-cell proliferative responses were measured in the spleens of Sprague-Dawley rats that were administered various concentrations of dexamethasone (DEX). A linear relationship between type II receptor binding and splenocyte proliferation was found, with decreases in measurable type II receptors (indicating in vivo receptor activation) being highly correlated with decreases in immune function. There was no evidence of spare type II receptors. In vitro studies using the type II receptor antagonist RU 486 confirmed that the inhibitory effect of DEX on splenocyte proliferation was mediated via the type II receptor. These findings provide a foundation for future studies evaluating glucocorticoid effects on immune system function and suggest that evidence of in vivo receptor activation may be critical for predicting when and in which tissues adrenal steroid hormones may be capable of modulating the immune response.
Interactions between insulin and glucocorticoids in the maintenance of genetic obesity
Authors: Dubuc P. U.
Published: December 2017

Glucoregulation and body composition were examined in 3-mo-old C57BL/6 ob/ob mice 6 wk after streptozotocin (STZ) or STZ plus adrenalectomy. STZ depressed somatic growth in ob/ob mice but did not cause hyperglycemia until immunoreactive insulin (IRI) was 40% (100 microU/ml) that of intact ob/ob mice. When IRI approached that of lean mice (40 microU/ml), ob/ob mice displayed severe hyperglycemia (800+ mg/dl) and other sequelae of type I diabetes but still maintained the same 50% body fat as untreated obese mice. In contrast, STZ diabetes in lean mice caused disproportionate reductions in body fat. Adrenalectomy before STZ led to the same insulinopenia, depressed growth, and hyperglycemia as STZ alone, but, after combined treatment, percent body fat declined in proportion to IRI. Thus a subgroup of severely diabetic adrenalectomized STZ obese mice with very low IRI (20 microU/ml) had body fat contents and fat-free masses equal to those of weight-matched lean mice. The data suggest that hypercorticoidism rather than hyperinsulinemia is largely responsible for obesity in ob/ob mice. However, in the absence of adrenal glucocorticoids, or perhaps with just their normalization, hyperinsulinemia appears necessary for maintaining excessive body energy stores.
Effect of hypophysectomy on plasma catecholamines and enkephalins in fetal sheep
Authors: Coulter C. L. , Young I. R. , Simonetta G. , McMillen I. C.
Published: December 2017

The aim of this study was to determine the effect of fetal hypophysectomy on the plasma concentrations of catecholamines and enkephalins in the fetal sheep between 120 and 140 days gestation under basal and hypoxic conditions. During basal conditions, there was no difference in the plasma concentrations of norepinephrine and epinephrine between intact and hypophysectomized groups. Fetal plasma norepinephrine concentrations were significantly increased during hypoxia in intact fetal sheep (7.2 +/- 2.2 pmol/ml, -15 min; 20.2 +/- 7.7 pmol/ml, 30 min) between 130 and 140 days, but after fetal hypophysectomy there was no significant norepinephrine response to hypoxia at this gestational age (4.7 +/- 1.3 pmol/ml, -15 min; 8.8 +/- 2.8 pmol/ml, 30 min). In contrast, fetal plasma epinephrine concentrations were significantly increased during hypoxia in both the intact (1.5 +/- 0.5 pmol/ml, -15 min; 3.3 +/- 1.7 pmol/ml, 30 min) and hypophysectomized groups (1.8 +/- 0.6 pmol/ml, -15 min; 6.8 +/- 4.1 pmol/ml, 30 min) between 130 and 140 days. During basal conditions, plasma concentrations of free Met-Enk were significantly less in hypophysectomized fetal sheep (170.8 +/- 34.3 pg/ml; 120-140 days) than in intact fetal sheep (305.6 +/- 47.3 pg/ml). There were no differences, however, in the fetal plasma concentrations of total Met-Enk between the intact (18.0 +/- 1.9 ng/ml) and hypophysectomized (16.9 +/- 2.6 ng/ml) groups. During hypoxia, there were no changes in the fetal plasma concentrations of either free or total Met-Enk in the intact or hypophysectomized groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of brown adipose tissue lipogenesis by thyroid hormone and the sympathetic nervous system
Authors: Yeh W. J. , Leahy P. , Freake H. C.
Published: December 2017

Thyroid hormone regulates lipogenesis differently in rat liver and brown adipose tissue (BAT). In the hypothyroid state, lipogenesis is suppressed in liver but enhanced in BAT. Here we investigated the mechanisms underlying increased lipogenesis in hypothyroid BAT. Housing the animals at 28 degrees C decreased lipogenesis in hypothyroid BAT to euthyroid levels. Denervation resulted in a 90% reduction in lipogenesis in hypothyroid BAT such that levels were lower than in euthyroid tissue. Thyroid hormone treatment of hypothyroid rats stimulated fatty acid synthesis in denervated BAT, as in liver, but decreased it in intact BAT. Steady-state levels of mRNA encoding acetyl-CoA carboxylase, fatty-acid synthase, and spor 14 were measured in similar animals by Northern analysis. The expression of these mRNAs mirrored the lipogenic data, showing that both thyroid hormone and the sympathetic nervous system work at a pretranslational level in this tissue. These data suggest that the increased BAT lipogenesis found with hypothyroidism is mediated by the sympathetic nervous system to counter the reduction in metabolic rate in these animals.
Impact of chronic stress hormone infusion on hepatic carbohydrate metabolism in the conscious dog
Authors: McGuinness O. P. , Fugiwara T. , Murrell S. , Bracy D. , Neal D. , O'Connor D. , Cherrington A. D.
Published: December 2017

The effects of chronic administration of counterregulatory hormones on hepatic glycogenolysis and gluconeogenesis were investigated. We studied 14 20-h fasted conscious dogs prior to (day 0) and after a 70-h stress hormone (SHI, n = 7) or saline (n = 7) infusion (day 3). Glucose production and gluconeogenesis were assessed using tracer and arteriovenous difference techniques. SHI increased plasma glucagon, cortisol, epinephrine, and norepinephrine levels approximately fivefold. SHI increased the arterial plasma glucose and insulin concentrations (110 +/- 2 to 204 +/- 19 mg/dl and 13 +/- 2 to 36 +/- 3 microU/ml on day 3). Tracer-determined glucose appearance and net hepatic glucose output were increased 80 and 60%, respectively. Net hepatic lactate uptake and fractional extraction were increased by 11.2 +/- 3.8 and 0.51 +/- 0.18 mumol.kg-1 x min-1, respectively, as was net hepatic glycerol uptake (1.0 +/- 0.6 mumol.kg-1 x min-1). Net hepatic fractional alanine extraction was also increased by 0.37 +/- 0.03 mumol.kg-1 x min-1; however, net hepatic alanine uptake was not altered. The efficiency of alanine conversion to glucose almost doubled (0.33 +/- 0.05 to 0.59 +/- 0.09). Renal glucose production was also increased, accounting for 33% of the increase in glucose turnover. This increase was paralleled by an increase in renal gluconeogenic precursor uptake. In conclusion, SHI created marked hyperglycemia and hyperinsulinemia and elevated glucose production from both the liver and the kidney, with gluconeogenesis accounting for approximately 70% of the response.
Systemic and uterine responses to chronic infusion of estradiol-17 beta
Authors: Magness R. R. , Parker C. R. , Rosenfeld C. R.
Published: December 2017

Human and ovine pregnancies are associated with increases in plasma levels of estrogens and angiotensin II (ANG II), cardiac output (CO), blood volume (BV), and uterine blood flow (UBF), as well as attenuated ANG II pressor responses. We hypothesized that, in nonpregnant animals, prolonged estradiol-17 beta (E2 beta) treatment would reproduce these endocrine and hemodynamic alterations. Nonpregnant ovariectomized ewes (n = 5) received 5 microgram E2 beta/kg iv followed by 220 micrograms/day for 14 days. Plasma E2 beta increased from 36 +/- 6 to 269 +/- 79 (SE) pg/ml (P < 0.05) during E2 beta treatment, returning to control values 4 days posttreatment. By 3 days of E2 beta, mean arterial pressure (MAP) and systemic vascular resistance (SVR) fell 9 +/- 1 and 29 +/- 1%, whereas heart rate (HR) and CO increased 20 +/- 5 and 26 +/- 1% (P < 0.05). Stroke volume (SV), BV, and plasma volume were unchanged until 7 days of E2 beta, with values rising 17 +/- 5, 13 +/- 3, and 14 +/- 4, respectively (P < 0.05). Although MAP remained similarly depressed (-11 +/- 1%) during week 2 of E2 beta, SVR decreased further (-37 +/- 3%) and was associated with additional increases (P < 0.05) in CO to 44 +/- 5%, reflecting rises in SV (21 +/- 2%) but not HR. Increases in BV correlated with rises in CO (r = 0.55) and SV (r = 0.64) but not HR (r = -0.04).(ABSTRACT TRUNCATED AT 250 WORDS)
Acute hyperglycemia enhances proteolysis in normal man
Authors: Flakoll P. J. , Hill J. O. , Abumrad N. N.
Published: December 2017

The influence of hyperinsulinemic-hyperglycemia on protein and carbohydrate homeostasis was assessed using L-[1-13C]-leucine and [3-3H]glucose combined with open-circuit indirect calorimetry. After a 30-min basal period, healthy human volunteers were subjected to two sequential experimental periods (150 min each) during which insulin was continuously infused at a rate to elicit maximal effects (10.0 mU.kg-1 x min-1, resulting in 220-fold basal levels) in conjunction with an infusion of L-amino acids to maintain euleucinemia. Plasma glucose was maintained near basal (94 +/- 2 mg/dl) during period I and at twofold basal (191 +/- 4 mg/dl) during period II. The endogenous rate of leucine appearance (index of proteolysis in mumol.kg-1 x h-1) dropped by 80% from basal during period I (P < 0.01) but only by 44% during period II. Although hyperglycemia stimulated the rate of proteolysis threefold (18.0 +/- 10.2 to 49.8 +/- 7.2, P < 0.001), neither leucine oxidation nor nonoxidative leucine rate of disappearance (an estimate of protein synthesis) was altered. During both glycemic conditions, the rates of hepatic glucose production were completely suppressed, and this was accompanied by 3- and 11-fold increases in the estimated rates of protein and carbohydrate oxidation, respectively, and an 80% decrease in the rate of lipid oxidation. The estimated rate of glucose storage was increased fourfold during period I and by an additional 2.3-fold (to approximately 10-fold basal) in period II. The present study demonstrates that, during hyperinsulinemia, acute elevations of plasma glucose to two times basal levels result in a marked stimulation of whole body proteolysis during hyperinsulinemia.
Glutamine carbon disposal and net glutamine uptake in fetuses of fed and fasted ewes
Authors: Levitsky L. L. , Stonestreet B. S. , Mink K. , Zheng Q.
Published: December 2017

We have traced ovine fetal glutamine carbon uptake and disposal in 7 chronically catheterized fetuses of fed ewes and 10 fetuses of 48-h fasted ewes. Net fetal glutamine uptake (Fick principle, antipyrine blood flow) was 10.0 +/- 2.0 mumol.kg-1 x min-1 in fed fetuses and 6.4 +/- 1.4 mumol.kg-1 x min-1 in fasted fetuses [not significant (NS)]. However, net fetal glutamine uptake was linearly related to the umbilical vein glutamine level (P < 0.05) in fed and fasted fetuses. In contrast, fetal glutamate transfer to the placenta was 4.0 +/- 0.8 mumol.kg-1.min-1 in the fed state and 2.7 +/- 0.1 mumol.kg-1 x min-1 in the fasted state. Net fetal glutamine uptake and fetal glutamate transfer to the placenta were directly correlated (P < 0.05). Fetal glutamine carbon disposal was measured using a primed continuous infusion of [U-14C]-glutamine over a 3-h period and blood sampling during the last hour of infusion (steady state). Disposal was 20.9 +/- 2.6 mumol.kg-1 x min-1 in the fed state and 18.6 +/- 2.3 mumol.kg-1 x min-1 in the maternal fasted state (NS). Glutamine carbon disposal did not correlate with fetal arterial glutamine levels and was not influenced by maternal nutritional state.
Advances in kinetic analysis of insulin-stimulated GLUT-4 translocation in adipose cells
Authors: Quon M. J.
Published: December 2017

GLUT-4 is the major insulin-sensitive glucose transporter in muscle and adipose tissue. Regulation of GLUT-4 is an important component of whole body glucose homeostasis. Abnormalities in the regulation of insulin-stimulated reversible translocation of glucose transporters have been observed in various pathological states, including diabetes. Recently, the development of specific photolabels for glucose transporters and the availability of antibodies against the various transporter isoforms have presented the opportunity for detailed kinetic analysis of GLUT-4 regulation. A kinetic analysis of some of the most recent data is presented to demonstrate how this approach can advance the understanding of GLUT-4 regulation. Some areas in which the currently available data limit the ability to resolve certain mechanistic questions are noted. Using a two-compartment model, we show that the mechanism of insulin-stimulated GLUT-4 translocation is likely to involve a large increase in the exocytosis rate of GLUT-4 with a minimal decrease in the endocytosis rate. Mathematical models based on these kinetic analyses are helpful for testing hypotheses and designing experiments to elucidate the molecular and cellular mechanisms of GLUT-4 regulation under normal and pathological conditions. This type of approach may be useful for evaluating the contribution of GLUT-4 regulation to the pathogenesis of diabetes.
Production of glutamine and utilization of glutamate by rat subcutaneous adipose tissue in vivo
Authors: Kowalski T. J. , Watford M.
Published: December 2017

Information about adipose tissue amino acid metabolism is limited, with most data derived from studies in vitro. The purpose of this study was to further characterize the role of adipose tissue in glutamine metabolism in the rat in vivo. The extracellular concentrations of glutamine, glutamate, alanine, and ammonia were measured in the rat inguinal fat pad using a microdialysis sampling technique. A calibration method was used to accurately assess the extracellular levels of metabolites, and a comparison of these concentrations with those in arterial blood allowed determination of the net flux of each compound. The adipose tissue-arterial blood concentration differences were 122 +/- 19, 54 +/- 37, -61 +/- 21, and -28 +/- 13 microM for glutamine, alanine, glutamate, and ammonia, respectively, indicating a production of glutamine and an uptake of glutamate by subcutaneous adipose tissue. The magnitude of glutamine production suggests that adipose tissue may play a significant role in whole body glutamine homeostasis.
Low-density lipoprotein receptors in rat adipocytes: regulation with fasting
Authors: Kraemer F. B. , Laane C. , Park B. , Sztalryd C.
Published: December 2017

Adipose tissue metabolism is exquisitely sensitive to caloric intake. With increasing adiposity more triglyceride and cholesterol are stored within increasingly large adipocytes, whereas less triglyceride and cholesterol are stored as the size of the fat cell decreases. A portion of the uptake of cholesterol by adipocytes is mediated by low-density lipoprotein (LDL) receptors. The present studies addressed whether LDL receptors are differentially regulated in adipose tissue and the liver during fasting in the rat. Two days of fasting caused a reduction in body weight with an approximately 40% decrease in the epididymal fat depot and fat cell size. No changes in serum cholesterol were noted, but serum triglycerides fell approximately 55% with fasting. LDL receptors detected by immunoblotting decreased progressively with fasting to levels that were 95% below controls in adipocytes isolated from epididymal fat pads by 2-3 days. In contrast, hepatic LDL receptor expression was unaltered by fasting. After 2 days of fasting, the rate of synthesis of LDL receptors in isolated adipose cells was decreased approximately 35%, whereas levels of LDL receptor mRNA were diminished approximately 55%. It is concluded that the expression of LDL receptors in rat adipocytes is markedly downregulated during fasting through transcriptional and posttranscriptional mechanisms. Furthermore, LDL receptor expression is differentially regulated in adipose tissue and liver during fasting in the rat.
Rat skeletal muscle hexokinase II mRNA and activity are increased by a single bout of acute exercise
Authors: O'Doherty R. M. , Bracy D. P. , Osawa H. , Wasserman D. H. , Granner D. K.
Published: December 2017

This study addresses the potential role of skeletal muscle hexokinase (HK) II in the regulation of glucose uptake and metabolism in vivo. Male rats undertook a single bout of treadmill exercise and were then killed immediately or after a predetermined recovery period. Three muscles [soleus (Sol), gastrocnemius/plantaris (Gc), and white vastus] were excised, and HK II mRNA, GLUT-4 mRNA, total HK (HK I and HK II) and heat-stable HK (predominantly HK I) activities were assessed. Three hours after the cessation of a single bout of exhaustive exercise, HK II mRNA was significantly increased in all three muscles. Ninety or thirty minutes of exercise, with a 3-h recovery, increased Gc HK II mRNA to the same extent as exhaustive exercise, but 15 min of exercise had no effect. Gc HK II mRNA continued to increase up to 8 h after the cessation of 90 min of exercise but returned to basal by 24 h postexercise. In contrast to HK II mRNA, Gc GLUT-4 mRNA was unchanged at 0, 3, 8, and 24 h after the cessation of 90 min of exercise. Total HK activity was significantly increased in Sol and Gc, 8 and 24 h after the cessation of 90 min of exercise. Heat-stable HK activity was unchanged in all three muscles. The increase in total HK activity, inferred to be an increase of HK II, may be important in the persistence of the postexercise increase in insulin action.
Regulation of eukaryotic initiation factor-2 expression during sepsis
Authors: Vary T. C. , Jurasinski C. V. , Karinch A. M. , Kimball S. R.
Published: December 2017

Protein synthesis is stimulated at the level of peptide chain initiation in livers from rats with a sterile or septic abscess. In contrast, peptide chain initiation is inhibited in fast-twitch skeletal muscles from septic rats. We investigated the possible mechanisms responsible for these differential changes in peptide chain initiation between liver and skeletal muscle during sepsis by measuring the cellular content of eukaryotic initiation factor-2 (eIF-2), the extent of phosphorylation of the alpha-subunit of eIF-2, and the activity of eIF-2B. In skeletal muscle, neither the eIF-2 content nor the extent of phosphorylation of eIF-2 alpha was altered during sepsis. However, a significant decrease (P < 0.001) in eIF-2B activity was observed in fast-twitch muscles. In liver, neither the extent of phosphorylation of eIF-2 alpha nor the activity of eIF-2B was different in rats with a sterile or septic abscess compared with control. However, the amount of eIF-2 in liver was increased in both sterile inflammation and sepsis. The relative abundance of eIF-2 alpha mRNA was not increased in either condition compared with control. Analysis of the distribution of eIF-2 alpha mRNA from control rats revealed that only approximately 40% of the message was associated with polysomes. Sterile inflammation or sepsis caused a 50% increase in the proportion of eIF-2 alpha mRNA associated with the polysomes compared with control.(ABSTRACT TRUNCATED AT 250 WORDS)
11 beta-Hydroxysteroid dehydrogenase in the rat inner ear
Authors: Ten Cate W. J. , Monder C. , Marandici A. , Rarey K. E.
Published: December 2017

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD) was demonstrated specifically in the spiral ligament of the cochlear membranous labyrinth by enzyme assay, Western blotting, and immunocytochemistry. Other cochlear regions and the vestibular membranous labyrinth were devoid of 11 beta-HSD. Spiral ligament 11 beta-HSD exerted predominantly an oxidative activity and was NADP specific, which is similar to 11 beta-HSD in most other tissues. 11 beta-HSD was colocalized with mineralocorticoid and glucocorticoid steroid receptors in the spiral ligament. 11 beta-HSD may control steroid binding to these inner ear steroid receptors and, in addition, may regulate steroid receptor binding in the adjacent stria vascularis in paracrine fashion.
Adipose tissue metabolism in humans determined by vein catheterization and microdialysis techniques
Authors: Simonsen L. , Bulow J. , Madsen J.
Published: December 2017

A technique for catheterization of a vein draining abdominal subcutaneous tissue and a microdialysis technique that allows measurements of intercellular water concentrations in adipose tissue in humans have recently been described. In the present study, we compare the two techniques during an oral glucose load. In addition a technique using microdialysis for measurement of tissue oxygen and carbon dioxide tensions is described. Microdialysis and vein catheterization were performed in the same region on the abdomen, and the subcutaneous adipose tissue blood flow was measured by the local 133Xe washout method. The results show that subcutaneous adipose tissue gas tensions are on level with gas tensions measured in abdominal venous blood. Comparison of metabolite concentrations measured in the venous blood and venous blood concentrations calculated from microdialysis data shows that there is good agreement between the concentrations obtained by the two techniques with respect to glucose and glycerol, whereas lactate concentrations are very different. With regard to substrate fluxes calculated by Fick's principle, the catheterization technique is probably the most reliable, considering the numerous assumptions on which calculations of venous concentrations from microdialysis data are based. Advantages and disadvantages of the two techniques are discussed.
Role of glucagon in the metabolic response to stress hormone infusion in the conscious dog
Authors: McGuinness O. P. , Burgin K. , Moran C. , Bracy D. , Cherrington A. D.
Published: December 2017

The impact of the absence of an increase in glucagon on the metabolic response to stress hormone infusion was investigated. We studied 11 conscious dogs fasted for 20 h before (day 0) and after (day 3) a 70-h stress hormone infusion containing glucagon, cortisol, epinephrine, and norepinephrine that increased their respective levels approximately sixfold. Five additional dogs were studied on day 0 and were then infused with the same stress hormone infusion but without glucagon. Glucose production and gluconeogenesis were assessed using tracer and arteriovenous difference techniques. The absence of an increase in glucagon during stress hormone infusion attenuated the increase in arterial plasma glucose concentration (delta 81 +/- 16 vs. delta 28 +/- 6 mg/dl) but did not significantly alter the increase in the rate of glucose appearance (delta 1.7 +/- 0.3 vs. delta 1.1 +/- 0.4 mg.kg-1.min-1). However, it eliminated the increase in net hepatic glucose output (delta 0.7 +/- 0.3 vs. delta 0.0 +/- 0.4 mg.kg-1.min-1) primarily because of an increase in hepatic glucose uptake. In addition, the stress hormone-induced increase in net hepatic gluconeogenic precursor uptake (delta 0.7 +/- 0.3 vs. delta 0.2 +/- 0.1 mg of glucose.kg-1.min-1) and the efficiency of gluconeogenesis (delta 0.19 +/- 0.07 vs. delta 0.01 +/- 0.05) were attenuated. Glucagon thus plays a pivotal role in the metabolic response to stress hormone infusion by sustaining gluconeogenesis through a stimulatory effect on the hepatic gluconeogenic precursor uptake as well as on the efficiency of gluconeogenesis within the liver.
Free fatty acid and glucose metabolism in human aging: evidence for operation of the Randle cycle
Authors: Bonadonna R. C. , Groop L. C. , Simonson D. C. , DeFronzo R. A.
Published: December 2017

We assessed insulin effects on plasma free fatty acid (FFA) and glucose metabolism in seven elderly (71 +/- 2 yr) and in seven younger (21 +/- 1 yr) subjects matched for body weight and body mass index but not for percent body fat (32.4 +/- 3.8% in elderly vs. 20.4 +/- 3.5% in young, P < 0.05), by performing sequential euglycemic clamps at five insulin doses (0.6, 1.5, 3, 6, and 15 pmol.min-1.kg-1) in combination with indirect calorimetry and [1-14C]palmitate plus [3-3H]glucose infusion. At baseline, plasma FFA concentration, turnover infusion. At baseline, plasma FFA concentration, turnover and oxidation, and total lipid oxidation were all increased in the elderly (897 +/- 107 vs. 412 +/- 50 mumol/l and 11.2 +/- 1.4 vs. 5.14 +/- 0.86, 3.45 +/- 0.65 vs. 1.37 +/- 0.25, and 4.63 +/- 0.72 vs. 3.01 +/- 0.33 mumol.min-1.kg-1 lean body mass, P < 0.05 for all comparisons), whereas glucose turnover was similar as a result of decreased glucose oxidation (8.2 +/- 1.4 vs. 13 +/- 1.9 mumol.min-1.kg-1 lean body mass, P < 0.05) and increased glucose storage (6.6 +/- 1.4 vs. 1.7 +/- 1.3 mmol.min-1.kg-1 lean body mass, P < 0.05). At all insulin infusions, plasma FFA concentration, turnover and oxidation, and total lipid oxidation were higher in the elderly than in the younger group (P < 0.05). However, if normalized per fat mass, all FFA and lipid metabolic fluxes, both in the postabsorptive state and during hyperinsulinemia, were comparable in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)