bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of hepatic glucose production by insulin in vivo in rats: contribution of glycolysis
Authors: Terrettaz J. , Assimacopoulos-Jeannet F. , Jeanrenaud B.
Published: December 2017

The action of insulin on hepatic glucose production (HGP) has been studied in fed anesthetized rats during a euglycemic hyperinsulinemic clamp. At the end of the clamp, the liver was rapidly removed, frozen, and enzyme activities and metabolites were measured. When insulin totally suppressed HGP, it did not modify glycogen phosphorylase or synthase activity, nor did it "spare" or increase glycogen content. Insulin decreased glucose 6-phosphate while increasing glycolytic intermediates (fructose 1,6-bisphosphate, alpha-glycerophosphate, lactate, and pyruvate) as well as fructose 2,6-bisphosphate, the potent effector of 6-phosphofructo-1-kinase. Insulin also increased pyruvate kinase activity of low substrate concentration. Lipogenesis measured with 3H2O incorporation into fatty acids was increased four-to fivefold by insulin. The data suggest that in normal rat liver, when glycemia is maintained at constant basal level, insulin promotes no change in glycogen metabolism, whereas the hormone stimulates the glycolytic pathway. This action contributes to the suppression of hepatic glucose production observed after the addition of the hormone.
Genotype dependency of adaptation in adipose tissue metabolism after short-term overfeeding
Authors: Poehlman E. T. , Despres J. P. , Marcotte M. , Tremblay A. , Theriault G. , Bouchard C.
Published: December 2017

The present study investigated the interaction of genotype and short-term overfeeding on adipose tissue metabolism of six pairs of male monozygotic twins. The sedentary nonobese twins were submitted to a 22-day overfeeding period in which their normal daily intake was supplemented by an additional 1,000 kcal/day. A fat tissue biopsy was performed in the suprailiac region before and after overfeeding to determine fat cell diameter and basal and maximal stimulated epinephrine, norepinephrine, and isoproterenol lipolysis from collagenase-isolated fat cells. Fat cell basal and maximal insulin-stimulated glucose conversion into triglycerides (basal and stimulated lipogenesis) were measured using [14C]glucose. Adipose tissue heparin-releasable lipoprotein lipase activity (LPL) was also determined. A repeated measures analysis of variance revealed overfeeding induced significant elevations in basal lipogenesis (P less than 0.05) and fat cell diameter (P less than 0.05). No significant group changes were noted in basal, epinephrine-, norepinephrine-, and isoproterenol-stimulated lipolysis, insulin-stimulated lipogenesis, and LPL activity due to large individual variation in the response to overfeeding. However, significant intrapair resemblance was noted in the changes of the aforementioned variables, suggesting a coherent within-twin pair response, despite large between-pair variation in response. Less within-pair similarity was noted in changes in basal lipogenesis and fat cell diameter. The results of the present study suggest that overfeeding induced a large range of adipose tissue metabolic responses and that the genotype plays a role in determining the sensitivity of adipose tissue adaptation to caloric affluence.
Kinetics of zinc uptake and exchange by primary cultures of rat hepatocytes
Authors: Pattison S. E. , Cousins R. J.
Published: December 2017

The kinetics of 65Zn2+ uptake and exchange by hepatocytes in primary culture have been examined in detail to provide a basis for analyzing hormonal regulation of hepatic zinc metabolism. 65Zn2+ uptake was found to be a biphasic process. The slow phase represents an exchange between Zn2+ in the medium and preexisting, intracellular zinc pools. This exchange rate was saturable with a medium zinc concentration of 9.5 microM eliciting one-half the maximum exchange rate and a maximum exchange rate of 9.9 pmol Zn2+ . min-1 . mg protein-1 in the presence of bovine serum albumin. In the absence of albumin, a secondary, nonsaturable uptake rate was observed. The slow phase was relatively selective, and of the divalent transition metal ions tested, only Cd2+ and Mn2+ caused inhibition. The rate of exchange suggests total hepatocyte zinc has a turnover rate of approximately 30 h. The fast phase of 65Zn2+ reflects net Zn2+ accumulation into a labile pool. The initial rates for this process were too fast to be measured accurately, but steady-state measurements allowed determination of the labile pool size. The pool dimensions saturated in the presence [Kapp = 28.6 microM; pool capacity = 0.44 nmol Zn2+/mg protein] and absence [Kapp = 11.8 microM; pool capacity = 0.34 nmol Zn2+/mg protein] of bovine serum albumin. Kinetics and equilibria of Zn2+ uptake into the labile pool suggest that the latter acts as a source of Zn2+ for the slow-exchange phase. Dexamethasone stimulated slow Zn2+ exchange and also increased the labile pool size. The data suggest physiological factors alter hepatic zinc metabolism by influencing both intracellular Zn2+ pools.
Epinephrine is not critical to prevention of hypoglycemia during exercise in humans
Authors: Hoelzer D. R. , Dalsky G. P. , Schwartz N. S. , Clutter W. E. , Shah S. D. , Holloszy J. O. , Cryer P. E.
Published: December 2017

We documented stability of plasma glucose concentrations and glucose production and utilization rates, and levels of other metabolic substrates and regulatory factors, during the islet clamp (somatostatin infusion with glucagon and insulin replacement) in the absence of an intervention in five normal humans and further applied this technique to the study of glucoregulation during moderate exercise. Based on previous evidence that sympathochromaffin activation plays a primary role in the prevention of hypoglycemia during exercise, the role of adrenomedullary catecholamines was assessed by exercise (60% of maximum oxygen consumption for 60 min) studies in four bilaterally adrenalectomized, epinephrine-deficient humans under two conditions: control (saline infusion) and islet clamp. Increased glucose utilization and production rates were matched and plasma glucose was unchanged during exercise under both conditions. Thus adrenomedullary catecholamines including epinephrine are not critical to glucoregulation during moderate exercise in humans even when changes in insulin and glucagon are prevented. These findings provide further support for the suggestion that sympathetic neural norepinephrine is the operative catecholamine in the prevention of hypoglycemia during exercise in humans.
Galanin: a novel pancreatic neuropeptide
Authors: Dunning B. E. , Ahren B. , Veith R. C. , Bottcher G. , Sundler F. , Taborsky G. J.
Published: December 2017

Immunofluorescent staining for galanin in canine pancreatic tissue was performed together with an evaluation of the effects of synthetic galanin on pancreatic output of glucagon, somatostatin, and insulin in pentobarbital-anesthetized dogs. A dense network of galaninlike immunoreactive nerve fibers was visualized in association with the islets of Langerhans and occasional galanin immunoreactive fibers were seen to course through the exocrine parenchyma of dog pancreas. During intravenous infusion of synthetic porcine galanin (25 pmol X kg-1 X min-1) pancreatic glucagon output rapidly doubled, and the output of both somatostatin and insulin decreased by 70%. Because arterial and pancreatic venous catecholamine levels remained unchanged, the effects on hormone secretion were not secondary to activation of the sympathetic nervous system. The direct pancreatic action of galanin was confirmed by infusing a peripherally ineffective dose of galanin (0.25 pmol X kg-1 X min-1) into the pancreatic artery, which also stimulated glucagon (+90%) and suppressed somatostatin (-50%) and insulin (-70%) release. The presence of galaninlike immunoreactive neurons in dog islets, together with the direct action of galanin on pancreatic hormone release, suggest that this recently discovered peptide could serve as an important neuromodulator of endocrine pancreatic function.
Glucose carbon recycling and oxidation in human newborns
Authors: Denne S. C. , Kalhan S. C.
Published: December 2017

Total carbohydrate oxidation, plasma glucose oxidation, and glucose carbon recycling were measured in 11 fasting newborns using a constant infusion of D-[U-13C]glucose combined with respiratory calorimetry. The "true" rate of glucose appearance (Ra) was quantified from the enrichment of the nonrecycling tracer species (m + 6), while the "apparent" rate of glucose appearance was quantified from the enrichment of glucose C - 1. The plasma glucose concentration remained constant at approximately 50 mg/dl (2.8 mM) throughout the study. The true rate of glucose production was 5.02 +/- 0.41 mg X kg-1 X min-1, (means +/- SD). Glucose was oxidized at a rate of 2.67 +/- 0.34 mg X kg-1 X min-1 and represented 53% of the glucose turnover. Recycling of glucose carbon represented 36% of the glucose production rate, or 1.87 +/- 0.74 mg X kg-1 X min-1. The oxidation of plasma glucose provided 15.8 +/- 2.0 kcal X kg-1 X day-1, whereas total carbohydrate oxidation (measured by respiratory calorimetry) provided 19.9 +/- 6.6 kcal X kg X day. The data indicate that 1) recycling of glucose carbon accounts for about one-third of glucose production, demonstrating active gluconeogenesis in the fasting newborn; 2) the oxidation of plasma glucose represents only 80% of total carbohydrate oxidation, the remaining 20% possibly representing the local oxidation of tissue glycogen stores; and 3) as the measured rate of glucose oxidation will be insufficient to supply the entire calculated cerebral metabolic requirements, these data suggest that fuels in addition to glucose may be important for cerebral metabolism in the fasting human newborn.
Thyroxine 5'-deiodinase in brown adipose tissue of myopathic hamsters
Authors: Kopecky J. , Sigurdson L. , Park I. R. , Himms-Hagen J.
Published: December 2017

Myopathic Syrian hamsters (BIO 14.6) have less brown adipose tissue (BAT) than normal. The trophic response of this tissue to cold is smaller than normal and trophic responses to diet and to photoperiod are absent. The objective was to find out whether activity of thyroxine 5'-deiodinase in their BAT was increased normally in response to cold and thus whether a defect in endogenous production of 3,5,3'-triiodothyronine might underlie the attenuated trophic response. The effect of feeding a high-fat diet on activity of 5'-deiodinase was also studied. Cold acclimation increased thyroxine 5'-deiodinase activity in BAT of the myopathic hamster, but the total remained smaller than normal because of the smaller size. The cold-induced increase in concentration of mitochondrial uncoupling protein was also smaller than normal. The level of serum 3,5,3'-triiodothyronine was low in myopathic hamsters and remained lower than normal when they were cold-exposed or cold acclimated. Feeding the high-fat diet to myopathic hamsters resulted in a greater than normal suppression of thyroxine 5'-deiodinase activity than in normal hamsters; the normal increases in protein content and in concentration of mitochondrial uncoupling protein were absent. We conclude that the defective trophic response of BAT of the myopathic hamster is not secondary to defective regulation of its thyroxine 5'-deiodinase activity because this activity does not appear to be obligatorily linked to hypertrophy of BAT. The low level of serum 3,5,3'-triiodothyronine in the myopathic hamster may be secondary to reduced capacity for peripheral thyroxine deiodination in its BAT.
Effects of serum calcium and phosphorus on skeletal mineralization in vitamin D-deficient rats
Authors: Holtrop M. E. , Cox K. A. , Carnes D. L. , Holick M. F.
Published: December 2017

In the present study, we have evaluated the role of calcium and phosphorus concentrations in serum on the mineralization of bone in the absence of vitamin D. This was accomplished by feeding mother rats and subsequently their pups vitamin D-deficient diets varying in calcium, phosphorus, and lactose content. After 5-7 wk on these diets, serum concentrations of 25-hydroxyvitamin D [25(OH)D] and 1,25-hydroxyvitamin D [1,25(OH)2D] were undetectable. Rats fed a vitamin D-deficient diet containing 0.44% calcium and 0.3% phosphorus showed a serum calcium of 4.9-5.9 mg/dl and a serum phosphorus of 7.3-8.2 mg/dl; rickets (wide epiphysial plates) had developed as well as osteomalacia (wide osteoid seams). Rats maintained on a vitamin D-deficient diet containing 3% calcium and 0.65% phosphorus had normal serum calcium, low serum phosphorus, and severe rickets, but osteomalacia was not seen. Rats fed a diet containing 20% lactose, 4% calcium, and 1% phosphorus showed normal serum calcium, somewhat low serum phosphorus, normal serum PTH, normal width of the epiphysial plate, normal volume density of trabecular bone, and normal volume density of osteoid seams. These data confirm the findings of others, using a different experimental model, that serum calcium and phosphorus concentrations are the determining factors in mineralization defects and not the absence of 25(OH)D or 1,25(OH)2D. In these rats thyroparathyroidectomy is well tolerated, which makes for an ideal model for the study of the effects of calcium-regulating hormones on bone histology, cytology, and biochemistry.
Heterogeneity of insulin action in muscle: influence of blood flow
Authors: James D. E. , Burleigh K. M. , Storlien L. H. , Bennett S. P. , Kraegen E. W.
Published: December 2017

The influence of blood flow (BF) and basal neuromotor tone on in vivo insulin-stimulated glucose uptake (Rg') in muscle was examined using the euglycemic clamp plus deoxyglucose/glucose tracer (insulin action) and labeled microsphere (BF) techniques. Anesthesia was used to produce perturbations in BF and/or activity compared with conscious rats. An index of muscle glycolytic flux (Gf) was estimated from Rg' in excess of glycogen synthesis. Gf and glycogen synthesis were significantly increased in soleus and red gastrocnemius (RG) during insulin infusion (150 mU/l) in conscious rats. Rg' was related to muscle BF in conscious rats (r = 0.92). In anesthetized rats, Rg' and BF were reduced in soleus, RG, red quadriceps, and plantaris (e.g., soleus 69%, P less than 0.001, and 80%, P less than 0.001, respectively). However, it is unlikely that Rg' and BF are causally related because fractional extraction of glucose by muscle was low (approximately 9%); fractional extraction increased during anesthesia (17%, P less than 0.01); BF but not Rg' was reduced by anesthesia in extensor digitorum longus, white gastrocnemius, and white quadriceps; and reduced Rg' during anesthesia in soleus and RG was mainly due to reduced GF. In conclusion, BF is not a major contributor to the heterogeneity in insulin-stimulated glucose uptake among individual muscles under basal conditions. These data suggest that neuromotor tone may indirectly influence the magnitude of muscle glucose uptake during insulin elevation via a substrate switching effect. This may give rise to a significant increase in glycolytic flux of glucose in those muscles that exhibit elevated activity even at rest (e.g., soleus).(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of fetal insulin infusion on glucose kinetics in pregnant sheep: a compartmental analysis
Authors: Bloch C. A. , Banach W. , Landt K. , Devaskar S. , Sperling M. A.
Published: December 2017

A three-compartment model, consisting of fetus (F), uteroplacenta, and mother (M) was applied to quantitate the effects of fetal hyperinsulinemia on glucose kinetics in pregnant sheep late in gestation. The approach combines the Fick principle with isotope dilution of differentially labeled glucose isotopes, infused simultaneously to F [U-14C]- and M [2-3H]glucose. In the basal state, rates of umbilical glucose uptake (8.37 +/- 0.98 mg/kg per min) and fetal glucose utilization (7.38 +/- 1.13) were equivalent (mean +/- SE; n = 12). When fetal insulin was increased from 13.7 +/- 2.2 to a plateau of approximately 100 microU/ml, arterial glucose decreased from 18.9 +/- 0.8 to a new steady state of approximately 13 mg/dl (P less than 0.001). Whereas umbilical glucose uptake increased at 90 min and remained elevated thereafter (P less than 0.01), fetal glucose utilization increased only transiently at 60 min by 1.9 +/- 0.8 mg/kg per min (26%; P less than 0.05) and then returned to base line. Insulin's persistent effect, however, was evident from the sustained doubling of the glucose clearance rate from 39.3 +/- 5.9 to 66.6 +/- 10.5 ml/kg per min (P less than 0.005). No endogenous fetal glucose production was evident throughout the experiments. Maternal glucose production and utilization remained unchanged, although there was a small decline in M glucose concentration and an increase in glucose transfer from M to the uteroplacenta and F, from 33.9 +/- 8.1 to 48.1 +/- 7.0 mg/min at 60 min (P less than 0.01 by paired analysis). We conclude that fetal hyperinsulinemia initially lowers glucose concentration by transiently increasing fetal glucose utilization.(ABSTRACT TRUNCATED AT 250 WORDS)
Atrial natriuretic factor and vasopressin during dehydration and rehydration in rats
Authors: Januszewicz P. , Thibault G. , Gutkowska J. , Garcia R. , Mercure C. , Jolicoeur F. , Genest J. , Cantin M.
Published: December 2017

To determine the effect of water deprivation (mixed volume and osmotic stimulus) on the secretion of atrial natriuretic factor (ANF) and arginine vasopressin (AVP), plasma immunoreactive ANF (IR-ANF), and plasma AVP were measured in normal conscious Sprague-Dawley rats. IR-ANF was decreased to 19.9 +/- 3.6 pg/ml (24 h dehydration), 9.8 +/- 2.5 pg/ml (48 h dehydration), and undetectable level (72 h dehydration) from the control level of 62.4 +/- 2.4 pg/ml. These decreases were accompanied by significant increase in plasma AVP, serum Na+, osmolality (osm), and hematocrit (Hct). In animals deprived of water for 3 days the secretion of ANF and AVP was monitored at seven time points during the 1st h after voluntary rehydration with tap water. After rehydration, IR-ANF was elevated dramatically within 3 min and gradually for up to 1 h after water was offered; AVP decreased within 3 min of rehydration and stayed at the water-repleted level during the next 1 h. Na+, osm, and Hct did not change until 15, 9, and 30 min after rehydration, respectively. The rapid modifications in plasma IR-ANF and AVP were accompanied by a transient but significant increase in arterial blood pressure for up to 15 min after water consumption. These results indicate that oropharyngeal-gastric stimuli contribute to the release of both ANF and AVP.
Characterization of glutamine transport by liver plasma membrane vesicles
Authors: Jacob R. , Rosenthal N. , Barrett E. J.
Published: December 2017

Plasma membrane vesicles were prepared from livers of fed normal and diabetic rats and used to characterize the membrane transport process responsible for glutamine uptake by the liver cell. In vesicles from normal rats the initial velocity of glutamine uptake was fourfold more rapid (0.20 +/- 0.02 vs. 0.05 +/- 0.02 nmol X mg protein-1 X 10 s-1) when Na+ replaced K+ in the extravesicular buffer. In the presence of a Na+-gradient glutamine uptake by vesicles was saturable, with a Km of 1.3 +/- 0.5 mM and a Vmax of 10 +/- 2.3 nmol X mg-1 X min-1. Lithium could fully substitute for Na+ in stimulating glutamine entry. In the presence of an imposed K+-gradient glutamine uptake was a linear function of its extravesicular concentration. In accord with the sodium-stimulated uptake of glutamine occurring via a sodium symport process, we observed that glutamine stimulated the initial rate of 22Na+ entry into vesicles by four- to fivefold. We further observed that glutamine entry was more rapid when lipophilic anions accompanied sodium in the incubation buffer, suggesting that Na+-glutamine flux is electrogenic. Preloading of vesicles with glutamine did not effect subsequent entry of labeled glutamine (no transstimulation), whereas intravesicular alanine did enhance alanine but not glutamine entry. Alloxan diabetes, which is known to stimulate the Na+-alanine cotransporter in these vesicles did not increase glutamine entry at any concentration tested.(ABSTRACT TRUNCATED AT 250 WORDS)
Turnover and excretion of copper in rats as measured with 67Cu
Authors: Linder M. C. , Roboz M.
Published: December 2017

We have examined the whole-body turnover and excretion of copper in rats, using 67Cu. Female Fischer rats, 3-4 mo of age, were injected intraperitoneally with tracer doses of 67CuCl2, and whole-body radioactivity was monitored over the next 3-6 days. The rate of loss was exponential and biphasic, with a half-life of 67 h for the first 70 h, followed by a much slower rate over the following days. A small percentage (2-7%) of the early loss was in the urine, the rest in the feces. In sexually immature animals, turnover was slower in the first and faster in the second phases. Pretreatment of rats with a large dose of copper had no significant effect on the initial turnover rate. Ligation of the common bile duct cut the rate in half, but did not block turnover. It is concluded that there are at least two pools of copper in the rat that turn over at different rates and that excretion of copper occurs via the bile and also by other intestinal routes.
Calculation of metabolic fluxes with anatomically separated sources of tracer and tracee
Authors: Norwich K. H. , Wasserman D. H.
Published: December 2017

Traditional calculations of metabolic fluxes using isotope dilution are based on the assumption that tracer and tracee enter the distribution space through effectively identical ports. If the tracer infusion site is not identical with the site of endogenous release of the tracee, the traditional equations for calculating rate of appearance (Ra) of a metabolite may give rise to appreciable errors due to the presence of gradients in specific activity. When tracer and tracee enter by means of anatomically disparate sites, such as may be encountered in the study of metabolite (e.g., lactate, alanine, and glycerol) or free fatty acid turnover, one must employ a modification of the traditional specific activity. This modified specific activity is obtained as the ratio of tracer concentration "near" (in the same compartment as) the source of tracee to the concentration of tracee near the source of tracer infusion. This concept is employed to derive equations for calculating metabolic turnover in both steady- and non-steady-state conditions when entry sites of tracer and tracee are dissimilar.
Pulsatile hyperglucagonemia fails to increase hepatic glucose production in normal man
Authors: Paolisso G. , Scheen A. J. , Luyckx A. S. , Lefebvre P. J.
Published: December 2017

To study the metabolic effects of pulsatile glucagon administration, six male volunteers were submitted to a 260-min glucose-controlled glucose intravenous infusion using the Biostator. The endogenous secretion of the pancreatic hormones was inhibited by somatostatin (100 micrograms X h-1), basal insulin secretion was replaced by a continuous insulin infusion (0.2 mU X kg-1 X min-1), and glucagon was infused intravenously in two conditions at random: either continuously (125 ng X min-1) or intermittently (812.5 ng X min-1, with a switching on/off length of 2/11 min). Blood glucose levels and glucose infusion rate were monitored continuously by the Biostator, and classical methodology using a D-[3-3H]glucose infusion allowed us to study glucose turnover. While basal plasma glucagon levels were similar in both conditions (122 +/- 31 vs. 115 +/- 18 pg X ml-1), they plateaued at 189 +/- 38 pg X ml-1 during continuous infusion and varied between 95 and 501 pg X ml-1 during pulsatile infusion. When compared with continuous administration, pulsatile glucagon infusion initially induced a similar increase in endogenous (hepatic) glucose production and blood glucose, did not prevent the so-called “evanescent” effect of glucagon on blood glucose, and after 3 h tended to reduce rather than increase hepatic glucose production. In conclusion, in vivo pulsatile hyperglucagonemia in normal man fails to increase hepatic glucose production.
Uptake of exogenous spermidine by rat lungs perfused in situ
Authors: Rannels D. E. , Addison J. L.
Published: December 2017

Uptake of the polyamine spermidine (SPD) from the pulmonary circulation was characterized by using ventilated rat lungs perfused in situ with Krebs-Henseleit-bicarbonate buffer containing 4.5% bovine serum albumin, 5.6 mM glucose, and 20 amino acids at plasma levels. [14C]SPD was accumulated by the lungs in a time- and concentration-dependent manner. The pathway of SPD uptake exhibited saturation kinetics with an apparent Km in the range of 1 microM and a Vmax of 450–540 pmol/g lung min. SPD uptake was inhibited by the naturally occurring polyamines putrescine and spermine (SPM) and by the inhibitor of polyamine synthesis, methyglyoxal bis(guanylhydrazone) (MGBG). Inhibition of SPD uptake by SPM followed competitive kinetics; although MGBG was also a competitive inhibitor of SPD uptake, MGBG was less effective than SPM. These observations indicate that SPD is taken up from the pulmonary circulation by a carrier-mediated pathway that is inhibited by other natural polyamines and by MGBG and exhibits substrate affinity in the range of plasma SPD concentrations.
Mineralocorticoid specificity of renal type I receptors: in vivo binding studies
Authors: Sheppard K. , Funder J. W.
Published: December 2017

We have injected rats with [3H]aldosterone or [3H]corticosterone, plus 100-fold excess of the highly specific glucocorticoid RU 28362, with or without excess unlabeled aldosterone or corticosterone and compared type I receptor occupancy in kidney and hippocampus. Thirty minutes after subcutaneous injection [3H]aldosterone was well retained in renal papilla-inner medulla, renal cortex-outer medulla, and hippocampus; in contrast, [3H]corticosterone was well retained only in hippocampus. Competition studies for [3H]aldosterone binding sites showed corticosterone to be a poor competitor in the kidney compared with hippocampus. Time-course studies, with rats killed 10-180 min after tracer administration, showed very low uptake/retention of [3H]corticosterone by kidney; in hippocampus [3H]corticosterone retention was similar to that of [3H]aldosterone in kidney, and retention of [3H]aldosterone by hippocampus was much more prolonged than of either tracer in any other tissue. Studies in 10-day-old rats, with very low levels of corticosteroid binding globulin (CBG), showed a high degree of aldosterone selectivity in both zones of the kidney, whereas [3H]aldosterone and [3H]corticosterone were equivalently bound in hippocampus. We interpret these data as evidence for a mechanism unrelated to extravascular CBG conferring mineralocorticoid specificity on renal type I receptors and propose two models derived from our findings consistent with such differential selectivity.
Effects of D-amino acid substituents on degradation of LHRH analogues by proximal tubule
Authors: Flouret G. , Majewski T. , Peterson D. R. , Kenny A. J. , Carone F. A.
Published: December 2017

Less than Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2, the luteinizing hormone-releasing hormone, LHRH, is degraded in renal proximal tubules (PT) in vivo (rat) and in vitro (rabbit) to less than Glu-His (2), less than Glu-His-Trp (3), and less than Glu-His-Trp-Ser (4). LHRH may be cleaved by endopeptidases simultaneously at multiple bonds, or initially at Ser4-Tyr5 followed by carboxypeptidase hydrolysis of 4 to 3 and then 2. To distinguish between these mechanisms, [3H]LHRH analogues were incubated with rabbit renal brush-border membranes (BBM), microinfused into PT in vivo or in vitro, and products were analyzed by HPLC. [D-Ser4]LHRH was not cleaved at D Ser4-Tyr5 but yielded less than Glu-His-Trp-D-Ser-Tyr-Gly as the major metabolite plus 2 and 3. [D-Trp6]LHRH was cleaved by BBM and PT to 2 and 3, but not to 4. [D-Ser4, D-Trp6]LHRH was not cleaved by BBM, but was degraded to 2 by PT in vivo. Thus, D-amino acid substituents altered the expected cleavage pattern of these analogues. [3H]LHRH was cleaved by BBM or by endopeptidase-24.11 from porcine PT to metabolites 2, 4, small amounts of 3, and less than Glu-His-Trp-Ser-Tyr-Gly, but cleavage was strongly inhibited by the specific inhibitor phosphoramidon. Thus, normally LHRH may be cleaved in PT by endopeptidase-24.11 to 2 and 4, and by angiotensin I-converting enzyme to 3, its known cleavage site.
Effect of fetal growth on maternal protein metabolism in postabsorptive rat
Authors: Ling P. R. , Bistrian B. R. , Blackburn G. L. , Istfan N.
Published: December 2017

Rates of protein synthesis were measured in whole fetuses and maternal tissues at 17 and 20 days of gestation in postabsorptive rats using continuous infusion of L-[1–14C]leucine. Fetal protein degradation rates were derived from the fractional rates of synthesis and growth. Whole-body (plasma) leucine kinetics in the mother showed a significant reduction of the fraction of plasma leucine oxidized in the mothers bearing older fetuses, a slight increase in the plasma flux, with total leucine oxidation and incorporation into protein remaining similar at the two gestational ages. Estimates of fractional protein synthesis in maternal tissues revealed an increase in placental and hepatic rates at 20 days of gestation, whereas the fractional synthetic rate in muscle remained unchanged. A model for estimation of the redistribution of leucine between plasma and tissues is described in detail. This model revealed a more efficient utilization of leucine in fetal protein synthesis in comparison with other maternal tissues, a greater dependency of the fetus on plasma supply of leucine, and a significant increase (2-fold) in the release of leucine from maternal muscle as the fetal requirements increased proportionately with its size. The latter conclusion, supported by nitrogen analysis and the ratio of bound-to-free leucine in maternal tissues, confirms the importance of maternal stores in maintaining the homeostasis of essential amino acids during late pregnancy.
Role of calcium in effects of atrial natriuretic peptide on aldosterone production in adrenal glomerulosa cells
Authors: Chartier L. , Schiffrin E. L.
Published: December 2017

Atrial natriuretic peptide (ANP) inhibits the stimulation of aldosterone secretion by isolated adrenal glomerulosa cells produced by angiotensin II (ANG II), ACTH, and potassium. The effect of ANP on the dose-response curve of aldosterone stimulated by ANG II, ACTH, and potassium on isolated rat adrenal glomerulosa cells was studied. In the presence of ANP the maximal response of aldosterone output stimulated by ANG II or potassium decreased and the half-maximum (EC50) of the response to ACTH was displaced to the right. Because these effects resemble those of calcium-channel blockers, we investigated the effect of different concentrations of nifedipine, a dihydropyridine calcium-channel blocker, on the dose-response curve of aldosterone stimulated by ANG II, ACTH, and potassium. Nifedipine produced effects similar to ANP. The maximal response of aldosterone stimulated by ANG II and potassium was decreased and the dose-response curve to ACTH was displaced to the right. ANP decreased the maximal response of aldosterone to the dihydropyridine derivative BAY K8644, a calcium-channel "activator," without change in its EC50. In contrast, nifedipine displaced the dose-response curve to BAY K8644 to the right as expected of a competitive inhibitor. The effect of ANP and nifedipine on basal and stimulated 45Ca influx into isolated rat adrenal glomerulosa cells was studied. Basal calcium influx was not significantly affected by ANP or nifedipine. Angiotensin II-, ACTH-, potassium-, and BAY K8644-stimulated calcium influx were significantly decreased by 1 nM ANP or 30 microM nifedipine. ANP may act on the rat adrenal glomerulosa cells at least in part by interference with calcium entry.
Brown adipose tissue metabolism in ob/ob mice: effects of a high-fat diet and adrenalectomy
Authors: Kim H. K. , Romsos D. R.
Published: December 2017

Adrenalectomy prevents development of obesity in ob/ob mice fed high-carbohydrate stock diets partly by stimulating the low thermogenic capacity of their brown adipose tissue (BAT). Adrenalectomy, however, fails to prevent development of obesity in ob/ob mice fed a high-fat diet. Effects of adrenalectomy on BAT metabolism in ob/ob mice fed a high-fat diet were thus examined. ob/ob mice fed the high-fat diet developed gross obesity despite normal BAT metabolism, as assessed by rates of norepinephrine turnover in BAT, GDP binding to BAT mitochondria, and GDP-inhibitable, chloride-induced mitochondrial swelling. Adrenalectomy failed to arrest the development of obesity or to influence BAT metabolism in ob/ob mice fed the high-fat diet. Development of obesity in ob/ob mice fed a high-fat diet is not associated with low thermogenic capacity of BAT or with adrenal secretions, as it is in ob/ob mice fed high-carbohydrate stock diets.
Characterization by microdialysis of intracellular glucose level in subcutaneous tissue in humans
Authors: Jansson P. A. , Fowelin J. , Smith U. , Lonnroth P.
Published: December 2017

The subcutaneous intercellular glucose concentration was measured with a microdialysis method in 14 healthy volunteers and compared with that in venous blood. Under steady-state fasting conditions the intercellular glucose concentration was similar to that in the blood. During an oral glucose tolerance test the absorption phase was slightly delayed (approximately 2 min) in the intercellular space compared with the blood. However, the kinetics for the decline in glucose was similar in the two compartments. The interstitial glucose concentration was similar to that in venous blood during both a eu- and a hyperglycemic clamp. However, a rapid change from euglycemia to hyperglycemia was associated with a significant delay (approximately 8 min) in the intercellular glucose. The data demonstrate that the subcutaneous tissue glucose concentration under non-steady-state conditions closely resembles that in venous blood.
Acute inhibition of rat heart protein synthesis in vitro during beta-adrenergic stimulation or hypoxia
Authors: Fuller S. J. , Sugden P. H.
Published: December 2017

In the anterogradely perfused rat heart with glucose as fuel, 1 microM isoproterenol (ISO) inhibited the insulin (INS) plus adenosine deaminase (AdoDA) stimulation of ventricular protein synthesis by 72%. ISO (1 microM) alone had no effect on ventricular protein synthesis but inhibited atrial protein synthesis by 20%. The concentration dependence of the ISO inhibition was similar to the stimulation of glucose uptake by ISO. Inhibition could not be overcome by increasing INS concentrations. The effects of ISO were diminished by propranolol and could be partially mimicked by forskolin (FSK) or 8-(4-chlorophenylthio-)adenosine 3',5'-cyclic monophosphate (CPT-cAMP). The stimulation of protein synthesis by noncarbohydrate fuels was antagonized by ISO. Hypoxia (PO2 = 50%) also antagonized the INS stimulation of ventricular protein synthesis but did not affect basal rates. ATP contents were decreased by ISO but not by a PO2 of 50%. Both manipulations increased lactate output. The inhibition of protein synthesis by ISO could possibly be explained by indirect effects of ISO on cardiac "energy status." Furthermore, inhibition may thus represent purely an in vitro phenomenon and may not occur in vivo. However, the possibility that there are more direct effects of ISO on the machinery of protein synthesis has not been excluded. The inhibition of protein synthesis by hypoxia cannot be explained by changes in energy status and may result from intracellular lactoacidosis.
Glucocorticoids and inhibition of bone formation induced by skeletal unloading
Authors: Halloran B. P. , Bikle D. D. , Cone C. M. , Morey-Holton E.
Published: December 2017

Skeletal unloading or loss of normal weight bearing in the growing animal inhibits bone formation and reduces bone calcium. To determine whether the inhibition of bone formation induced by skeletal unloading is a consequence of an increase in plasma glucocorticoids and/or an increase in bone sensitivity to glucocorticoids, we measured plasma corticosterone throughout the day in unloaded and normally loaded rats (hindlimb elevation model) and examined the effect of adrenalectomy on the response of bone to skeletal unloading. Plasma corticosterone levels were similar in normally loaded and unloaded rats at all times. Skeletal unloading in sham-adrenalectomized animals reduced tibial and vertebral calcium by 11.5 and 11.1%, respectively, and in adrenalectomized animals by 15.3 and 20.3%, respectively. Uptake of 45Ca and [3H]proline in the tibia was reduced by 8 and 14%, respectively, in the sham-adrenalectomized animals and by 13 and 19% in the adrenalectomized animals. Bone formation and apposition rates were reduced to the same level in sham- and adrenalectomized animals. These results suggest that the inhibition of bone formation induced by skeletal unloading is not a consequence of increased plasma glucocorticoids or an increase in bone sensitivity to the glucocorticoids but, rather, point to a local mediator in bone that senses mechanical load and transmits that information to the bone-forming cells directly.
Reciprocal changes of muscle oxidases and liver enzymes with recovery from iron deficiency
Authors: Azevedo J. L. , Willis W. T. , Turcotte L. P. , Rovner A. S. , Dallman P. R. , Brooks G. A.
Published: December 2017

We determined the recovery time courses of muscle oxidases and liver enzymes after iron administration to iron-deficient rats. Female 21-day-old Sprague-Dawley rats were fed an iron-deficient (3 mg Fe/kg) or a control (50 mg Fe/kg) diet for 3 wk. The deficient rats were then injected with 50 mg Fe as iron dextran/kg body wt (Fe-T) or saline (Fe-) intraperitoneally. At 16, 40, 64, 112, and 180 h after injection, blood and tissue samples were taken to determine hemoglobin concentration (Hb), gastrocnemius glycolytic enzyme and oxidase activities, and liver amino acid catabolic enzyme activities. No changes were observed in any parameter across time in either the Fe- or control (Fe+) rats. In the Fe- rats, Hb, pyruvate + malate (P + M), 2-oxoglutarate (2-OG), and succinate oxidases (SO) were depressed to 33, 36, 44, and 7% of Fe+, respectively (P less than 0.05). At 16 h, Fe-T values were significantly elevated compared with Fe- rats but still only 40, 48, 55 and 10% of controls, respectively. Glutamate dehydrogenase (GDH) and alanine aminotransferase (AAT) of Fe- rats were 174 and 134% of control values (P less than 0.05). By the 180-h time point, Hb, P + M, 2-OG, and SO of Fe-T rats increased to 99, 84, 89, and 43% of Fe+ values, whereas GDH and AAT activities declined to 111 and 106% of controls. Glycolytic enzymes showed no systematic changes with iron deficiency or after iron administration.(ABSTRACT TRUNCATED AT 250 WORDS)
Major thermogenic defect associated with insulin resistance in brown adipose tissue of obese diabetic SHR/N-cp rats
Authors: Marette A. , Deshaies Y. , Collet A. J. , Tulp O. , Bukowiecki L. J.
Published: December 2017

The effects of norepinephrine and insulin on thermogenesis were investigated in adipocytes isolated from brown adipose tissue (BAT) of obese non-diabetic LA/N-cp rats (obese LA), obese diabetic SHR/N-cp rats (obese SHR), and their corresponding lean controls. The maximal calorigenic response (Vmax) and the sensitivity [50% effective concentration (EC50)] to norepinephrine (1 microM) were markedly reduced in brown adipocytes from obese SHR rats compared with their lean controls (3- to 4-fold decrease in the Vmax and 50% increase in the EC50 value). In the same cells, there was a similar decrease in the respiratory response to dibutyryl adenosine 3',5'-cyclic monophosphate, indicating the presence of a major postreceptor defect. Remarkably, total BAT cytochrome oxidase activity (an index of cellular mitochondrial content) was also diminished three to four times in obese SHR rats, suggesting that a reduced BAT mitochondrial content is responsible for the decreased thermogenesis. Ultrastructural studies revealed that the cytoplasm of brown adipocytes from obese SHR rats contained a large lipid droplet, numerous tiny droplets, and few atypical mitochondria with loosely packed cristae. Adipocytes from obese SHR rats were also characterized by a significant resistance to the antithermogenic effect of insulin but not to that of the nonmetabolizable adenosine analogue N6-phenylisopropyl adenosine. In contrast, all the above biochemical parameters were normal in obese LA rats. These results demonstrate that the marked insulin resistance in BAT of obese SHR rats is associated with a decreased responsiveness and sensitivity to norepinephrine, indicating the presence of receptor and postreceptor defects. It is suggested that insulin resistance and/or diabetes in SHR/N-cp rats lead to a decreased mitochondriogenesis in BAT, which results in a reduced thermogenic capacity, thereby contributing to the development of obesity.
Cut set analysis of compartmental models with applications to experiment design
Authors: Feng D. , Distefano J. J.
Published: December 2017

Conventional compartmental analysis typically involves equations derived from mass-rate balance considerations for each compartment (pool), with each equation associated with a single pool. However, alternative mathematical descriptions, which effectively group pools into various other configurations, facilitate model analysis in certain applications, e.g., for kinetic experiment design or analysis. Such equivalent models are usually obtained using (often) complex matrix operations. An alternative approach, cut set analysis, can be applied directly to the graph of the compartmental model to readily generate alternative mathematical descriptions in which the needed equivalence transformations are easily performed graphically. This graphical transformation is developed here for linear, time-invariant multicompartmental models in which particular parameter values are the experimental objective. The method potentially provides greater flexibility in analyzing complex compartmental models in theory and practice, and it is exemplified here by application to the design of steady-state kinetic endocrine system studies in experimental animals.
Effect of glycemia and nonesterified fatty acids on forearm glucose uptake in normal humans
Authors: Walker M. , Fulcher G. R. , Sum C. F. , Orskov H. , Alberti K. G.
Published: December 2017

The purpose of this study was to examine the effect of physiological plasma nonesterified fatty acid (NEFA) levels on insulin-stimulated forearm and whole body glucose uptake and substrate oxidation during euglycemia and hyperglycemia. Seven healthy men received Intralipid and heparin for 210 min in two studies, with saline as control in two further studies. Insulin (0.05 U.kg-1.h-1) was infused from 60 min, and euglycemia was maintained during lipid (EL) and control (EC) studies, and hyperglycemia was maintained in the other studies (HL and HC). Forearm NEFA uptake was comparable in the lipid studies (+61 +/- 10 and +52 +/- 8 nmol.100 ml forearm-1.min-1, EL and HL) and was suppressed in the controls. With Intralipid, forearm glucose uptake decreased during euglycemia but not during hyperglycemia (+3.85 +/- 0.34 vs. +3.34 +/- 0.25 mumol.100 ml forearm-1.min-1, EC vs. EL, P less than 0.02), with comparable changes in whole body glucose uptake. Glucose oxidation and forearm alanine release decreased with Intralipid at both blood glucose levels, with no significant change in the rates of nonoxidative glucose disposal. These observations support the operation of the glucose-fatty acid cycle at physiological plasma NEFA levels at both blood glucose concentrations, but this was associated with a decrease in peripheral insulin sensitivity only during euglycemia.
Does intracarotid PGE2 increase plasma ACTH concentration in conscious adult ewes?
Authors: Cudd T. A. , Wood C. E.
Published: December 2017

The hypothesis that prostaglandin E2 (PGE2) is a circulating mediator of adrenocorticotropic hormone (ACTH) secretion in sheep was tested in conscious adult ewes using 30-min carotid artery infusions of 0, 5, 10, 100, and 500 ng.kg-1. min-1 PGE2 in saline. ACTH, cortisol, and aldosterone were significantly increased during the 500 ng.kg-1.min-1 infusion (166 +/- 61 to 233 +/- 38 pg/ml, 27 +/- 5 to 45 +/- 2 ng/ml, and 52 +/- 11 to 85 +/- 25 pg/ml, respectively). PGE2 infusions of 100 ng.kg-1.min-1 increased ACTH from 104 +/- 31 to 168 +/- 31 pg/ml and cortisol from 18 +/- 5 to 42 +/- 2 ng/ml. PGE2 infusions did not increase arginine vasopressin, plasma renin activity, or hematocrit. Heart rate and mean arterial pressure were minimally but significantly increased during the 500 ng.kg-1.min-1 infusion, from 84.9 +/- 2.8 to 99.3 +/- 5.4 beats/min and 95.5 +/- 1.8 to 101.0 +/- 3.4 mmHg, respectively. In a second study to test whether lower infusion rates of PGE2 increase plasma ACTH in sheep with lower resting hormone concentrations, sheep were infused and sampled through a tether system, preventing any disturbances due to human contact the day of an experiment. For all infusion rates ACTH baselines were less than or equal to 55 +/- 17 pg/ml, and cortisol baselines were less than or equal to 6 +/- 3 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)
Kinetics of equilibration of radioiodide in individual mouse thyroid follicles in vivo
Authors: Andros G. , Wollman S. H.
Published: December 2017

Microdensitometric measurements were made on autoradiographs of radioiodide localized in mouse thyroids subjected to various degrees of stimulation, in which the formation of organic radioiodide was acutely blocked. Estimates were made of the relative concentrations of radioiodide in lumens and cells of follicles and in the nearby blood vessels. Simple models were introduced to interpret the data. Analysis of the ratio of radioiodide concentrations in the lumen and cells of follicles as a function of follicles size and time after injection indicated that smaller follicles equilibrated faster than larger follicles, that the equilibration was faster the more active the gland was, and that the release of radioiodide from follicles in the less active glands must be characterized by a time-dependent exit rate constant. Analysis of the relative concentration of luminal radioiodide as a function of follicle size at short time intervals and in the steady state indicated that the transport properties of the average epithelial cell were generally independent of follicle size.
Mechanisms of early and late hypermetabolism and fever after localized tissue injury in rats
Authors: Cooper A. L. , Rothwell N. J.
Published: December 2017

Inflammation and localized tissue injury were induced in rats by intramuscular injection of turpentine. This caused rapid and sustained (2-24 h) increases in colonic temperature (Tc; up by 2.5 degrees C) and oxygen consumption (VO2; up by 30%) as well as hypophagia (57%). The early responses (0-2 h) were attenuated by anesthesia, C-fiber deafferentation, peripheral but not central injection of a cyclooxygenase inhibitor, or central injection of a neutralizing antibody to corticotropin-releasing factor (CRF). In contrast, the later (18-20 h) changes in Tc and VO2 were unaffected by anesthesia, C-fiber deafferentation, or central injection of a CRF antibody but were inhibited by either peripheral or central administration of a cyclooxygenase inhibitor. beta-Adrenoceptor blockade reduced both phases of the response, and brown adipose tissue activity was significantly elevated from 4 to 24 h after turpentine injection. These data suggest that different mechanisms mediate the metabolic response to localized tissue injury, the early phase involving neural mechanisms characteristic of stress and inflammation, whereas the later phase appears to depend on humoral factors that are commonly associated with infection.