bluuebunny/crossref_metadata_2025 huggingface dataset:
Dietary sulfur amino acid modulation of cysteine sulfinic acid decarboxylase
Authors: Jerkins A. A. , Steele R. D.
Published: December 2017

Male rats were fed sulfur and nonsulfur amino acid-supplemented diets, and the response of cysteine sulfinic acid decarboxylase (CSAD) activity was determined. After adaptation to a casein-based basal diet, rats were fed diets containing additions of L-methionine. Hepatic CSAD activity decreased in a dose-dependent manner. Significant depression of CSAD activity in liver was evident within 24 h of feeding rats a methionine-supplemented diet. Depression of enzyme activity was reversed upon refeeding the basal diet. After rats were fed diets supplemented with methionine, cystine, homocystine, S-methyl-L-cysteine, phenylalanine, leucine, or ethionine for 14 days, hepatic CSAD activity in rats fed S-methyl-L-cysteine-, phenylalanine-, or leucine-supplemented diets was not depressed compared with activity in rats fed a basal diet. In contrast, CSAD activity in livers of rats fed cystine-, homocystine-, methionine-, or ethionine-supplemented diets was 60, 40, 40, and 8%, respectively, of the activity in livers from control rats. Immunochemical detection and quantification of CSAD protein in rat liver indicated that CSAD protein concentration was correlated to CSAD activity. CSAD activity may be specifically regulated by sulfur amino acids metabolized by the S-adenosylmethionine-dependent pathway of methionine metabolism.
ATP and phosphocreatine changes in single human muscle fibers after intense electrical stimulation
Authors: Soderlund K. , Hultman E.
Published: December 2017

The recovery pattern of adenine nucleotides and glucolytic intermediates after short-lasting anaerobic exercise was studied. Biopsies were obtained from the vastus lateralis muscle at rest, immediately after intermittent electrical stimulation with occluded circulation (total time 166 s), and after 20 s, 60 s, 5 min, and 15 min of recovery. ATP in single fibers decreased from 23.9 +/- 1.41 to 14.2 +/- 3.20 in type I fibers and from 25.01 +/- 1.20 to 13.1 +/- 2.65 mmol/kg dry muscle in type II fibers postexercise. After 15 min of recovery, ATP was resynthesized to 95 and 76% in type I and type II fibers, respectively. The phosphocreatine (PCr) content in type I fibers at rest was 72.3 +/- 4.50 and 83.3 +/- 9.76 mmol/kg dry muscle in type II fibers. After exercise, PCr was depleted in both fiber types. After the 60 s of recovery the PCr content in type I fibers was significantly higher (P less than 0.05) compared with type II fibers, but, after 5 min of oxidative recovery, the PCr levels were equal in the two fiber types. Fifteen minutes postexercise, type II fibers demonstrated a significantly higher content (97.8 mmol/kg dry muscle) compared with its resting value (P less than 0.05).
Transcriptional and posttranscriptional mechanisms in uncoupling protein mRNA response to cold
Authors: Rehnmark S. , Bianco A. C. , Kieffer J. D. , Silva J. E.
Published: December 2017

Three mechanisms account for the rapid elevation and maintenance of uncoupling protein (UCP) mRNA levels in cold-exposed rats, namely, an increase in the rate of transcription initiation, an increase in the fraction of nascent UCP transcripts undergoing elongation, and stabilization of the mature UCP mRNA. The second mechanism precedes and outlasts the increase in the rate of UCP gene transcription, which is brisk but short lived. After 48 h of cold exposure, mature UCP mRNA levels are maintained elevated solely on the basis of stabilization, since the levels of both transcription initiation and fifth intron-containing transcripts (precursors) have returned to basal. Results in hypothyroid rats given 3,5,3'-triiodothyronine (T3) and in dispersed brown adipocytes show that T3 is involved both in the increase in UCP mRNA precursor level and stabilization of mature UCP mRNA. These mechanisms are rapidly reversed when the rats are returned to thermoneutrality. These coordinated transcriptional and post-transcriptional mechanisms modulating UCP gene expression ensure a rapid increase in the concentration of UCP and prevent further accumulation of the protein as physiologically adequate levels are attained.
Hepatic insulin and EGF receptor phosphorylation and dephosphorylation in fetal rats
Authors: Gruppuso P. A. , Boylan J. M. , Carter P. A. , Madden J. A. , Raven T.
Published: December 2017

Hepatic insulin receptor and epidermal growth factor (EGF) receptor phosphorylation and dephosphorylation were studied in normal and growth-retarded fetal rats. Insulin receptor autophosphorylation at a subsaturating ATP concentration (0.5 microM) increased by 10-fold from day 17 to 21 of gestation and decreased by 50% in term growth-retarded fetuses of fasted mothers. In vitro kinase activation at 0.5 mM ATP did not change with gestation or maternal fasting. EGF receptor autophosphorylation increased in parallel with receptor number with advancing gestation and did not change with maternal fasting. Protein tyrosine phosphatases (PTPases), which might attenuate receptor signaling in livers from growth-retarded fetuses, were measured using polybasic and polyacidic artificial substrates as well as the insulin receptor kinase domain. Fetal membrane PTPase activities were twofold higher than in the adult and declined with advancing gestation. However, activities were similar in normal and growth-retarded fetuses. We conclude that decreased hepatic growth in growth-retarded fetuses may involve decreased insulin receptor tyrosine kinase activation in vivo, as indicated by diminished receptor autophosphorylation at subsaturating ATP concentrations. Changes in EGF receptor kinase activity and PTPases could not be implicated based on our in vitro findings.
Central mineralocorticoid receptor antagonism blocks hypertension in Dahl S/JR rats
Authors: Gomez-Sanchez E. P. , Fort C. , Thwaites D.
Published: December 2017

The development of hypertension in the S/JR rat is accelerated and exacerbated by a high salt consumption. It has been reported that the intracerebroventricular infusion of RU28318, a selective mineralocorticoid antagonist, at doses that are ineffective when administered subcutaneously, inhibits the development of the hypertension produced by the subcutaneous infusion of aldosterone or deoxycorticosterone in normotensive rats. RU28318 was continuously infused intracerebroventricularly or subcutaneously in Dahl S/JR rats before or after the onset of hypertension induced by a high-salt diet. The centrally infused mineralocorticoid antagonist inhibited the initiation of the increase in blood pressure, when the infusion was started concomitantly with the high-salt diet, and blocked its further increase in rats whose blood pressure had already become significantly elevated with 2 wk of a high-salt diet. The subcutaneously infused mineralocorticoid antagonist had no effect. These data serve to strengthen the hypothesis that the mineralocorticoid receptor in the brain is crucial to the genesis of certain forms of hypertension.
Glycylglutamine: metabolism and effects on organ balances of amino acids in postabsorptive and starved subjects
Authors: Lochs H. , Hubl W. , Gasic S. , Roth E. , Morse E. L. , Adibi S. A.
Published: December 2017

The present study was designed to investigate the metabolism of glycylglutamine and its effects on organ balances of amino acids during intravenous infusion of this dipeptide (100 mumol.h-1.kg-1) in postabsorptive and briefly starved (84-86 h) human subjects. Arterial concentrations of glycylglutamine were not significantly different in postabsorptive (265 +/- 18 microM) and starved (241 +/- 13 microM) subjects. Among the organs examined, kidney predominated in clearance of glycylglutamine from plasma. Moreover, renal clearance of glycylglutamine was reduced by starvation (87 +/- 7 vs. 52 +/- 5 mumol/min, P less than 0.01), whereas neither splanchnic nor muscle clearance was significantly affected. Infusion of glycylglutamine raised plasma concentrations of glycine and glutamine by increasing renal release of these amino acids. In postabsorptive subjects the infusion significantly increased splanchnic balances of glycine and glutamine with little or no effect on the muscle balances; the opposite was found in starved subjects. As far as other amino acids are concerned, the infusion decreased the muscle release of alanine and increased renal release of serine. We conclude that the amino acid residues of glycylglutamine are largely metabolized by the splanchnic organs in postabsorptive subjects and by peripheral organs in starved subjects. The latter results in selective inhibition of muscle release of amino acids.
Cell-dependent posttranslational processing and secretion of recombinant mouse renin-2
Authors: Paul M. , Nakamura N. , Pratt R. E. , Burt D. W. , Dzau V. J.
Published: December 2017

In the DBA/2 mouse submandibular gland (SMG), renin is predominantly the expression product of the renin gene Ren-2d. Prorenin is synthesized and rapidly converted to a constitutively secreted single-chain intermediate, which is then processed to and stored as the mature two-chain (2C) form, which is released by regulated secretion. To evaluate whether the mode of renin processing is cell dependent, renin (Ren-2d) complementary DNA was stably integrated in the genome of Chinese hamster ovary (CHO) cells and a mouse pituitary cell line (AtT-20) by transfection, and renin processing and secretion were examined. Transfected CHO cells secreted exclusively prorenin, whereas transfected AtT-20 cells secreted both prorenin and active renin. AtT-20 cells processed prorenin to the single-chain polypeptide (1C-renin) that was the main storage form and was not further processed to the 2C form of correct size, whose site of generation or function is uncertain at this time. In addition, the conversion of prorenin to 1C-renin was much slower in AtT-20 cells than in the SMG. Thus the patterns of renin biosynthesis and secretion in AtT-20 cells show major differences when compared with these processes in the native SMG, suggesting that cell-dependent characteristics, e.g., the presence of specific processing enzymes, are important factors influencing mouse renin processing.
Developmental regulation of lipoprotein lipase in rats
Authors: Tavangar K. , Murata Y. , Patel S. , Kalinyak J. E. , Pedersen M. E. , Goers J. F. , Hoffman A. R. , Kraemer F. B.
Published: December 2017

To evaluate changes in lipoprotein lipase (LPL) expression during development, levels of LPL mRNA, protein, and enzyme activity were measured in heart, epididymal fat, kidney, and brain of rats, from late gestation through 24 mo. LPL mRNA, protein, and enzyme activity were low in fetal and neonatal hearts. LPL mRNA increased 11-fold by 60 days and remained at this level thereafter; LPL protein and enzyme activity increased 10-fold by weaning, before declining to low values by 3 mo. LPL mRNA levels, protein, and enzyme activity did not change in epididymal fat from 3 wk to 21 mo. In the kidney, LPL mRNA levels were high at the end of gestation but fluctuated during the first month. LPL protein and activity were low at day 1 and rose eightfold to peak values by day 7 before decreasing to low levels by weaning. LPL mRNA levels were relatively high in fetal brains and then fell 60% during the neonatal period. LPL protein peaked at day 7 before falling 95% by weaning. Thus LPL is under complex tissue-specific regulation involving transcriptional and posttranscriptional mechanisms.
Regulation of the purine salvage pathway in rat liver
Authors: Kim Y. A. , King M. T. , Teague W. E. , Rufo G. A. , Veech R. L. , Passonneau J. V.
Published: December 2017

The regulation of purine metabolism in rat liver has been examined under conditions that alter the flux through the pathway. Rats were given intraperitoneal injections of ethanol, sodium acetate, or sodium phosphate to attain body water concentrations of approximately 70, 20, and 10 mM, respectively. The livers were freeze-clamped after 30 min, and extracts were made for the analysis of metabolites, cofactors, purine bases, and nucleosides; homogenates were made for the measurement of the activities and kinetic parameters of seven enzymes that participate in purine salvage. The values of the equilibrium constants of nine reactions were determined in vitro and compared with the ratios of the reactants measured in liver. The changes in phosphoribosylpyrophosphate (PRPP), a key intermediate in both the de novo and salvage pathways of purine metabolism, were directly correlated with the changes in ribose 5-phosphate (ribose-5-P); ([PRPP] = 1.7[ribose-5-P] - 7.4 mumol/kg). Ribose-5-P concentrations in turn could be predicted from the liver content of fructose 6-phosphate and glyceraldehyde 3-phosphate by calculation from the known equilibria. The maximum velocities in the tissue of the seven enzymes measured were calculated from the measured substrate values in the liver and with consideration of other effectors of enzyme activity. PRPP synthetase was the least active of the enzymes measured, indicating a possible rate-limiting step. The delta G of the enzyme steps differed from equilibrium values by factors ranging from 4 (nucleoside phosphorylase) to 10(5) (PRPP synthetase and purine transferase reactions). The regulation of purine salvage appeared to depend on the levels of PRPP and ribose-5-P.
Mechanism of regulation of glucose production by lipolysis in humans
Authors: Jahoor F. , Klein S. , Wolfe R.
Published: December 2017

The relationship between the rate of lipolysis and rate of glucose production (Ra) was investigated in 14- and 86-h fasted humans. [6,6-2H]glucose and [2H]5glycerol were infused to measure glucose and glycerol Ra in response to infusions of nicotinic acid in 14- and 86-h fasted subjects (protocol 1). The response of glucose Ra to nicotinic acid alone and nicotinic acid plus unlabeled glycerol was also measured in 86-h fasted subjects (protocol 2). After a 14-h fast, nicotinic acid caused a 30% decrease in plasma insulin levels and a marked (66%) decrease in plasma free fatty acid levels but did not have any significant effect on glucose Ra and concentration. After 86 h of fasting, nicotinic acid decreased glycerol Ra and hence lipolytic rate by approximately 60%. This caused a significant decrease (P less than 0.05) of 16-20% in glucose Ra and uptake. This decrease in glucose Ra was abolished when unlabeled glycerol was also infused with nicotinic acid to maintain glycerol Ra. These findings suggest that, in normal humans, a decrease in the rate of lipolysis regulates glucose Ra via its effect on the availability of glycerol for gluconeogenesis.
Metabolism of 25-hydroxyvitamin D3 in rats: low-calcium diet vs. calcitriol infusion
Authors: Bolt M. J. , Jensen W. E. , Sitrin M. D.
Published: December 2017

It has been proposed that the decreased serum level of 25-hydroxyvitamin D [25(OH)D] observed with dietary Ca restriction is mediated by an increase in circulating 1,25-dihydroxyvitamin D [1,25(OH)2D]. We compared the effects of endogenous and exogenous elevations in serum 1,25(OH)2D on the production rate (PR), metabolic clearance rate (MCR), and excretory pathways of [3H]25(OH)D3 in rats, with the use of steady-state techniques. Low-Ca diet and 1,25(OH)2D3 infusion caused comparable reductions in serum 25(OH)D and elevations in 1,25(OH)2D. Low-Ca diet lowered serum 25(OH)D by increasing MCR from 21.8 +/- 3.2 to 29.1 +/- 5.4 (SD) microliters.min-1.kg-1 (P less than or equal to 0.005) and decreasing PR from 944 +/- 161 to 663 +/- 163 pg.Ain-1.kg-1 (P less than or equal to 0.001). In contrast, 1,25(OH)2D3 infusion produced a dramatic rise in the MCR of 25(OH)D from 23.4 +/- 4.5 to 62.8 +/- 13.7 microliters.min-1.kg-1 (P less than or equal to 0.001) and also increased the PR from 943 +/- 165 to 1,500 +/- 337 pg.min-1.kg-1 (P less than or equal to 0.001). With 1,25(OH)2D3 infusion, urinary excretion of metabolites of [3H]25(OH)D3 rose rapidly, and kidney homogenates from these rats demonstrated vigorous side-chain oxidation of [3H]25(OH)D3. With low-Ca diet, urinary tritium excretion increased more gradually, and no direct side-chain oxidation of [3H]25(OH)D3 occurred in vitro. The increased MCR of 25(OH)D3 with low-Ca diet could be accounted for by enhanced synthesis of 1,25(OH)2D3 and subsequent degradation in target tissues.
Dissociation of phosphaturia and 25(OH)D-1 alpha-hydroxylase trophism using a novel analogue of parathyroid hormone
Authors: Carpenter T. O. , McPhee M. D. , Bort R. , Mitnick M. A. , Carnes D. L.
Published: December 2017

Certain parathyroid hormone (PTH) analogues have been shown to selectively impair some but not all physiological actions of PTH. In this study, transaminated rat (r) PTH [TA-rPTH-(1-34)], a PTH analogue that differs from the rPTH-(1-34) fragment in that the NH2-terminal alanine is converted to pyruvate, was infused into mice to determine its properties in vivo and specifically to determine whether stimulation of 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase) activity was more dependent on concomitant renal handling of phosphate or on generation of adenosine 3',5'-cyclic monophosphate (cAMP). High-performance liquid chromatography-purified TA-rPTH-(1-34) was infused into C57BL mice at 10 or 30 pmol/h for 24 h. At 30 pmol/h, TA-rPTH-(1-34) was comparable with rPTH-(1-34) in its hypophosphatemic and phosphaturic effects but was less potent than rPTH-(1-34) in raising serum calcium. TA-rPTH-(1-34) was markedly less effective in stimulating renal 1 alpha-hydroxylase than rPTH-(1-34). Stimulation of urinary cAMP excretion occurred after infusion with TA-rPTH-(1-34), but this effect was significantly less than that seen with rPTH-(1-34). These findings indicate that PTH-induced hypophosphatemia and phosphaturia can be uncoupled from PTH stimulation of 1 alpha-hydroxylase. Furthermore, cAMP-related signal transduction appears to be more significant in regulation of 1 alpha-hydroxylase than mechanisms that mediate PTH-sensitive phosphate transport, independent of cAMP.
DIMSUM: an expert system for multiexponential model discrimination
Authors: Marino A. T. , Distefano J. J. , Landaw E. M.
Published: December 2017

DIMSUM is a highly automated, rule-based expert system designed to fit multiexponential models of increasing dimension to time series data, followed by selection of the best candidate model based on a user-modifiable and weighted decision tree of statistical criteria for model discrimination. The major features of DIMSUM are 1) an interactive and friendly user interface; 2) options for incorporating prior information about the parameters, the data, and/or the system from which the data were collected, in the form of equality and inequality constraints; 3) a built-in algorithm for automatically obtaining starting values for parameter estimation; 4) a robust weighted least-squares parameter estimation algorithm operating in an adaptive, user-adjustable search space; 5) comprehensive statistical results comparing different order candidate models fitted to the data; and 6) a novel, user-modifiable (learning) rule-based advisory subsystem providing an “expert's” interpretation of these statistical results and an explanation of all advice.
Glucoregulation during rest and exercise in depancreatized dogs: role of the acute presence of insulin
Authors: Wasserman D. H. , Bupp J. L. , Johnson J. L. , Bracy D. , Lacy D. B.
Published: December 2017

To determine the effects of the presence of insulin in poorly controlled diabetes, depancreatized (PX) dogs (n = 5) were studied during rest and 150 min of exercise in paired experiments in which saline alone was infused (IDEF) and in which insulin was replaced intraportally (200 microU.kg-1.min-1) with glucose clamped at the levels in IDEF (IR+G). PX dogs (n = 4) were also studied with insulin, but glucose was allowed to fall (IR). Insulin was not detectable, 6 +/- 1 and 6 +/- 2 microU/ml in IDEF, IR+G, and IR. Plasma glucose was 470 +/- 47, 480 +/- 48, and 372 +/- 35 mg/dl at rest in IDEF, IR+G, and IR, respectively. Levels were unchanged with exercise in IDEF and IR+G, but fell by 139 +/- 13 mg/dl in IR. Basal glucose rate of appearance (Ra) was 7.0 +/- 0.9, 1.3 +/- 1.1, and 6.0 +/- 0.7 mg.kg-1.min-1 in IDEF, IR+G, and IR, respectively. Exercise elicited a rise in Ra in only IDEF. The rises in Rd and metabolic clearance rate in IDEF were reduced (delta 2.6 +/- 0.7 and delta 0.8 +/- 0.3 ml.kg-1.min-1 at 150 min) compared with IR+G (delta 5.3 +/- 1.9 and delta 1.7 +/- 0.2 ml.kg-1.min-1 at 150 min) and IR (delta 3.7 +/- 1.2 and delta 2.4 +/- 0.8 ml.kg-1.min-1). The insulin sensitivity of glucose utilization (Rd) was elevated by approximately 75% at 150 min. Basal glycerol was similar in IDEF and IR but was reduced by approximately 70% in IR+G. Glycerol rose similarly with exercise in IDEF and IR.(ABSTRACT TRUNCATED AT 250 WORDS)
A substantial part of GLUT-1 in crude membranes from muscle originates from perineurial sheaths
Authors: Handberg A. , Kayser L. , Hoyer P. E. , Vinten J.
Published: December 2017

The distribution of GLUT-1 and GLUT-4 in cryosections of rat skeletal muscles was investigated immunocytochemically. Intense labeling of GLUT-1 was found in the perineurial sheaths of intramuscular nerves, whereas only a very faint signal was associated with the sarcolemma, and labeling of extraneural vessels was not detectable. The majority of the GLUT-4 reactivity was located at the periphery of muscle cells in nonuniform patches, and GLUT-4 was absent in vessels and nerves. In sections of femoral nerve GLUT-1 was confined to the perineurial sheath and endoneurial vessels. The contribution of GLUT-1 from intramuscular perineurial sheaths to total GLUT-1 in a muscle was determined from immunoblots of crude membranes isolated from mixtures of homogenates of excised nerves and muscles. The recovery of GLUT-1 increased linearly with the amount of nerve added, and it was calculated that GLUT-1 from intramuscular perineurial sheaths accounted for approximately 60% of the GLUT-1 content in a membrane fraction from soleus muscle or red gastrocnemius. The remaining 40% of GLUT-1 is likely to originate from the sarcolemma.
Interactions between ANG II, sympathetic nervous system, and baroreceptor reflexes in regulation of blood pressure
Authors: Reid I. A.
Published: December 2017

The renin-angiotensin system plays an important role in the regulation of arterial blood pressure and in the development of some forms of clinical and experimental hypertension. It is an important blood pressure control system in its own right but also interacts extensively with other blood pressure control systems, including the sympathetic nervous system and the baroreceptor reflexes. Angiotensin (ANG) II exerts several actions on the sympathetic nervous system. These include a central action to increase sympathetic outflow, stimulatory effects on sympathetic ganglia and the adrenal medulla, and actions at sympathetic nerve endings that serve to facilitate sympathetic neurotransmission. ANG II also interacts with baroreceptor reflexes. For example, it acts centrally to modulate the baroreflex control of heart rate, and this accounts for its ability to increase blood pressure without causing a reflex bradycardia. The physiological significance of these actions of ANG II is not fully understood. Most evidence indicates that the actions of ANG to enhance sympathetic activity do not contribute significantly to the pressor response to exogenous ANG II. On the other hand, there is considerable evidence that the actions of endogenous ANG II on the sympathetic nervous system enhance the cardiovascular responses elicited by activation of the sympathetic nervous system.
C-25 hydroxylation of vitamin D3 in periportal and perivenous region of hepatic acinus
Authors: Gascon-Barre M. , Vallieres S. , Benbrahim N. , Huet P. M.
Published: December 2017

Many biotransformation activities have absolute or modulated localization within the hepatic acinus. To investigate the intrahepatic acinar zonation of vitamin D3 (D3) metabolism, hepatic D3 extraction was investigated by antegrade or retrograde perfusion of normal livers and livers bearing selective periportal (PP) or perivenous (PV) destruction; D3 C-25 hydroxylation was studied after selective harvesting of PP or PV hepatocytes by digitonin-collagenase perfusion. Data indicate that hepatic D3 extraction is not regioselective and not perturbed by destruction of the proximal (PP) or distal (PV) part of the acinus, indicating that D3 extraction takes place in the most proximal hepatocytes being perfused. These observations suggest that, in vivo, D3 extraction will take place according to its concentration gradient within the hepatic acinus, thus resulting in a preferential PP extraction of the vitamin. D3 C-25 hydroxylation was higher in PP than in PV hepatocytes in the presence of 1.9 mM Ca2+, with 25-hydroxyvitamin D3 [25(OH)D3] formation of 34.6 +/- 3.9 and 24.4 +/- 1.1 fmol.h-1.(10(6) hepatocytes)-1, respectively (P less than 0.05). Modulators of extracellular [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)] or intracellular Ca2+ (parathyroid hormone, A23187), however, significantly influenced 25(OH)D3 formation with similar decreases in the PP (31%) and PV (26%) areas in the presence of EGTA but with increases in the presence of Ca2+ ionophore A23187 of 189 +/- 16% in PP and of 260 +/- 20% in PV hepatocytes, resulting in similar production in both regions of the acinus.(ABSTRACT TRUNCATED AT 250 WORDS)
Insulin-like growth factor I-dependent tyrosine kinase activity in stromal cells of human endometrium in vitro
Authors: Von Eye Corleta H. , Strowitzki T. , Kellerer M. , Haring H. U.
Published: December 2017

The study was undertaken to identify and characterize insulin-like growth factor I (IGF-I) receptors in human endometrial stromal cells in culture and to examine whether these receptors are modulated by estradiol (E2) and/or progesterone (P). We found that partially purified plasma membrane proteins from these cells contain specific high-affinity binding sites for IGF-I (10 fmol/micrograms protein). Chemical cross-linking with 125I-labeled IGF-I and autophosphorylation with [32P]ATP-labeled proteins of relative molecular weight 135,000 and 95,000 correspond to the known Mr values of the alpha- and the beta-subunits of IGF-I receptors. Receptor autophosphorylation and phosphorylation of the substrate poly(Glu,Na4Tyr1) was stimulated in vitro by IGF-I (half-maximally at 1 nM, maximally at 100 nM). After stimulation of intact cells with IGF-I (5 nM) and subsequent partial purification of receptors in the presence of phosphatase inhibitors, a 2.5- to 3.6-fold stimulation of the kinase activity toward poly(Glu,Na4Tyr1) was found. Preincubation of the cells for 16 h with E2, P, and E2 + P did not modify the IGF-I binding characteristics nor the effect of IGF-I (5 nM) on tyrosine kinase stimulation in intact cells. This suggests that, in isolated humans, endometrial cell modulation of IGF-I receptor function by estrogen and P does not occur.
Kinetics of 1,25-dihydroxyvitamin D metabolism in the aging rat
Authors: Wada L. , Daly R. , Kern D. , Halloran B.
Published: December 2017

To determine whether postmaturational aging influences the kinetics of 1,25-dihydroxyvitamin D [1,25(OH)2D] metabolism in the rat, we measured the metabolic clearance (MCR) and production (PR) rates of 1,25(OH)2D in 6-, 12-, 18-, and 24-mo-old Fischer 344 rats using the constant infusion method. Plasma calcium, phosphorus, and parathyroid hormone (PTH), urinary calcium and phosphorus, and glomerular filtration rate (GFR) were also measured. MCR and PR increased 57 and 91%, respectively (when expressed per rat), and 32 and 39%, respectively (when expressed per kg body wt), between 6 and 24 mo of age, with the greatest increase occurring between 18 and 24 mo. The plasma concentration of 1,25(OH)2D remained unchanged. Plasma PTH, when compared with 6-mo-old animals, was significantly elevated at 18 mo (147%) and even higher at 24 mo (240%). GFR (51Cr-labeled EDTA clearance) remained unchanged through 18 mo but tended to be reduced at 24 mo. Plasma phosphorus tended to decrease with age, whereas plasma calcium, urinary calcium, and urinary phosphorus did not differ among the age groups. These data indicate that both clearance and production of 1,25(OH)2D increase with postmaturational aging in the rat. They also suggest that the early age-related rise in plasma PTH is neither a consequence of low plasma calcium nor of renal insufficiency.
Effect of hyperinsulinemia on whole body and skeletal muscle leucine carbon kinetics in humans
Authors: Heslin M. J. , Newman E. , Wolf R. F. , Pisters P. W. , Brennan M. F.
Published: December 2017

Data documenting the isolated effect of systemic hyperinsulinemia on whole body and skeletal muscle leucine carbon kinetics in humans are limited. Using steady-state [14C]leucine kinetics, 10 normal volunteers were studied in the baseline postabsorptive state and then under euglycemic, hyperinsulinemic (71 +/- 5 microU/ml), and euleucinemic conditions. Systemic hyperinsulinemia resulted in a significant decrease in whole body and forearm leucine rate of appearance (Ra) by 17 and 37%, respectively, (P less than 0.0003, 0.03), without a significant change in the nonoxidized rate of disappearance for either (P = 0.23, 0.66). The baseline contribution of total body skeletal muscle (TBSM) leucine Ra and rate of disappearance (Rd) to whole body leucine Ra and Rd was 27 +/- 6 and 24 +/- 5%, respectively. During hyperinsulinemia TBSM Ra decreased by 34%, whereas whole body Ra decreased by 16%. We conclude that the primary effect of insulin in the whole body and skeletal muscle is to decrease leucine release from protein without a significant effect on leucine incorporation into protein. This antiproteolytic effect of insulin is more pronounced in skeletal muscle than in other tissues in the body.
Relationship between aerobic fitness level and daily energy expenditure in weight-stable humans
Authors: Sharp T. A. , Reed G. W. , Sun M. , Abumrad N. N. , Hill J. O.
Published: December 2017

The relationship between exercise and energy expenditure is unclear, with some suggestions that exercise leads to increased energy expenditure over and beyond the increase due to the exercise itself. In this cross-sectional study, we examined the relationships among aerobic fitness level, body composition, and total daily energy expenditure in 78 subjects. Daily energy expenditure (determined in a whole room calorimeter) was significantly correlated with both fat-free mass (FFM) and aerobic fitness (estimated from maximum aerobic capacity or VO2max). However, multiple-regression analysis demonstrated that, after accounting for FFM, VO2max did not explain a significant amount of the remaining variation in energy expenditure. In addition, the relationship between resting metabolic rate and both FFM and VO2max was evaluated using data from 214 weight-stable subjects analyzed retrospectively. The results were identical with the results obtained from the 78 subjects in that VO2max did not have effects independent of FFM on energy expenditure. We conclude that aerobic fitness does not have a direct effect on energy expenditure. However, it may have effects that are mediated through body composition, since in both populations studied here, VO2max was positively correlated with FFM and negatively correlated with adiposity.
Atrial natriuretic peptide-induced inhibition of aldosterone secretion: a quest for mediator(s)
Authors: Ganguly A.
Published: December 2017

Atrial natriuretic peptide (ANP) inhibits aldosterone secretion evoked by its physiological secretagogues by a mechanism(s) likely to involve intracellular messengers. When one examines the results of various investigations so far, this premise, although not definitive yet, seems to be supported. Therefore a brief perspective on the cellular messengers of the various secretagogues is provided before the inquiry into the possible mechanism of action of ANP. The receptors of ANP in the adrenal cells have been identified and characterized. ANP inhibits adenylate cyclase in various tissues through an inhibitory G protein, which appears to explain in part the inhibitory effect of ANP on adrenocorticotropin-induced aldosterone secretion. However, there could be other possible effects of ANP as discussed. ANP probably inhibits aldosterone secretion evoked by angiotensin II and potassium by interfering with the appropriate changes in calcium flux and cell calcium concentration, concomitants of stimulation by these secretagogues. The potential modes of these effects are probed. The role of guanosine 3',5'-cyclic monophosphate, which is increased by receptor activation of guanylate cyclase by ANP and is thought to play a major role in the biological effects of ANP in some other tissues, remains controversial in the aldosterone-lowering effect of ANP, and this is also discussed extensively in this review.
Enhanced degradation of collagen within apical vs. basal wall of ovulatory ovine follicle
Authors: Murdoch W. J. , McCormick R. J.
Published: December 2017

Electron microscopic examination of ovulatory ovine follicles indicated that dissolution of thecal collagen was enhanced along the follicular circumference adjacent to the ovarian serosa. Concentrations of hydroxyproline were correspondingly lower within apical than basal tissues. Collagenolytic activity of tissue homogenates and extracts was assessed by monitoring radioactive peptide release from cocultured collagen fibrils. Collagenase inhibitors were separated from enzyme by sequential extraction of follicular homogenates with detergent and heating. Enzymatic activities of homogenates and heat extracts of apical and basal tissues increased toward ovulation. A distinction between apex and base was not attributed to significant differences in homogenates; however, collagenolytic activity of heat extracts of apical tissue was selectively elevated (i.e., extraction was evidently required to effectively dissociate collagenase from thecal fibrils, making more enzyme available for substrate digestion). Activity of detergent extracts was restored by dithiothreitol and iodoacetamide (which inactivate tissue inhibitors of metalloproteinases), and collagenolysis induced by heat extracts was augmented by aminophenylmercuric acetate (a stimulator of latent collagenases). Nonetheless, variations between apex and base invoked by these compounds were relative. It therefore appears that active collagenase is more tightly bound within the extracellular matrix of the follicular apex than enzyme associated with basal tissue. This phenomenon might serve to preferentially favor enzymatic catabolism of collagen in that region, thereby dictating the ovarian site of follicular rupture.
Forearm ketone body metabolism in normal and in insulin-dependent diabetic patients
Authors: Avogaro A. , Doria A. , Gnudi L. , Carraro A. , Duner E. , Brocco E. , Tiengo A. , Crepaldi G. , Bier D. M. , Nosadini R.
Published: December 2017

In insulin deficiency, there is excessive arterial delivery of free fatty acid (FFA) to muscles where they are converted to acetoacetyl-CoA and acetyl-CoA. These intermediates may be metabolized further to acetoacetate and beta-hydroxybutyrate, which can be released into the venous circulation. When ketone body (KB) tracers are infused in vivo, they are diluted across muscle tissue. This dilution may be due to 1) KB newly formed within muscle (ketogenesis); 2) exchange of tracer between labeled and unlabeled acetyl-CoA and acetoacetyl-CoA, intermediates common to the metabolism of both FFA and KB (pseudoketogenesis). Thus this study assessed whether such label exchange could be detected across the human forearm and whether an increased delivery of FFA in insulin-sufficient controls provoked dilution of labeled KB tracer comparable to that observed in insulin-deficient diabetics. Five normal and five insulin-dependent diabetic (IDDM) subjects were infused with labeled [3,4-13C2]-acetoacetate. [13C]KB enrichments were lower in forearm vein than in the artery, and dilution of labeled KB was always higher than that which could be explained by arterial-venous differences of unlabeled KB. When arterial FFA concentrations in normals were raised (Intralipid+heparin) to values comparable to those of the diabetics, no additional increase in forearm arteriovenous dilution of labeled KB was observed. Neither in the basal state nor under conditions of increased plasma FFA were we able to detect venous appearance of KB labeled in the first and in the second carbon atoms, a necessary consequence of pseudoketogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)
Selective reduction of creatine kinase subunit mRNAs in striated muscle of diabetic rats
Authors: Su C. Y. , Payne M. , Strauss A. W. , Dillmann W. H.
Published: December 2017

Creatine kinase (CK) is important for energy transfer and is composed of mitochondrial (mitCK), muscle (MCK), and brain (BCK) subunits, each being the product of separate nuclear genes. The concentrations of MCK and BCK mRNAs have been shown to decrease in streptozotocin-hypoinsulinemic rat hearts, and in this report, we examined in detail the diabetic effect on CK gene expression in cardiac muscle and in two types of skeletal muscle. The level of sarcomeric mitCK mRNA was not altered in the diabetic myocardium, but was reduced by 86 and 67% in diabetic slow-twitch soleus muscle and fast-twitch extensor digitorum longus (EDL) muscle, respectively. MCK mRNA was also lowered in diabetic soleus muscle by 56%, while it remained at control levels in diabetic EDL. In both skeletal muscles, at either state, BCK mRNA was not detectable. There was a 33% decrease in total CK activity in diabetic cardiac and soleus muscle, but not in EDL. Diabetes thus exerts a widespread, muscle type-dependent adverse effect on CK expression that we found to be insulin therapy revertible. This study adds to our understanding of defective energy transduction in diabetic muscle.
Tissue-specific expression of bone proteins in femora of growing rats
Authors: Turner R. T. , Kapelner S. N. , Spelsberg T. C.
Published: December 2017

Total cellular RNA was extracted from bone cells of three different femoral compartments of 2-mo-old rats. The intact femora were first incubated with collagenase to obtain periosteal cells. The bisected periosteum-free diaphyses and metaphyses were then incubated with collagenase to obtain enriched populations of endosteal and cancellous bone cells, respectively. The total cellular RNA from these three tissues was separated by size using agarose gel electrophoresis, transferred to nylon filters, hybridized to 32P-labeled cDNA probes for glyceraldehyde-3-phosphate dehydrogenase (GAP), pre-pro-alpha (I) type I collagen (collagen), osteocalcin (BGP), and alkaline phosphatase (AP), and the cDNA/mRNA hybrids were visualized by radioautography. Bone matrix deposition was measured in each tissue compartment by tetracycline-based dynamic bone histomorphometry. The bone formation and apposition rates were greatest in the periosteum and least in metaphysis. Mean mRNA levels for collagen and BGP were positively correlated with mean bone formation and mineral apposition rates. Interestingly, mean AP mRNA levels were not correlated with indexes of bone formation. These results demonstrate that the steady-state mRNA levels for bone matrix proteins in femora show pronounced site specificity and correlate with the rates of bone matrix deposition.
Hypertension and insulin resistance: role of sympathetic nervous system activity
Authors: Supiano M. A. , Hogikyan R. V. , Morrow L. A. , Ortiz-Alonso F. J. , Herman W. H. , Bergman R. N. , Halter J. B.
Published: December 2017

he purpose of this study was to test the hypothesis that heightened sympathetic nervous system (SNS) activity contributes to the mechanism by which hypertension is associated with insulin resistance in humans. We performed frequently sampled intravenous glucose tolerance tests to determine tissue sensitivity to metabolic effects of insulin (SI) and measured plasma norepinephrine (NE) levels in 21 normotensive and 14 hypertensive Caucasian subjects. Compared with the normotensive subjects, hypertensive subjects had decreased SI (5.4 +/- 0.5 vs. 4.0 +/- 0.7 x 10(-5) x min-1 x pM-1; P = 0.03) but similar plasma NE levels (normotensive: 1.82 +/- 0.12 vs. hypertensive: 1.73 +/- 0.16 nM; P = 0.23). In a multiple regression model, only body mass index (BMI) and mean arterial blood pressure (MABP) were significant independent predictors of SI [SI = (-0.513)(BMI) + (-0.058)(MABP) + 23.6; r = 0.748; P = 0.0001]; age, plasma glucose, epinephrine, and NE level did not enter this model. As an additional test of this hypothesis, seven hypertensive subjects were restudied after 10 days of guanadrel therapy to determine whether SI would increase during suppression of SNS activity by guanadrel. Despite a significant reduction in plasma NE levels with guanadrel (baseline: 1.63 +/- 0.18 vs. guanadrel: 0.99 +/- 0.14 nM; P = 0.01), there was no significant change in SI (baseline: 2.97 +/- 0.78 vs. guanadrel: 2.41 +/- 0.54 x 10(-5).min-1 x pM-1; analysis of variance P = 0.57). We conclude that, in the Caucasian population we studied, heightened SNS activity is not essential for the insulin resistance observed in hypertensive humans.
Influence of growth hormone on glucose-glucose 6-phosphate cycle and insulin action in normal humans
Authors: Neely R. D. , Rooney D. P. , Bell P. M. , Bell N. P. , Sheridan B. , Atkinson A. B. , Trimble E. R.
Published: December 2017

Increased activity of the hepatic glucose-glucose 6-phosphate (G/G-6-P) cycle is associated with hepatic and peripheral insulin resistance in acromegaly. To determine whether a similar association occurs after short-term growth hormone (GH) elevation within the physiological range, two-step euglycemic hyperinsulinemic clamps were performed in normal human males after 12-h GH (2.2 ng.kg-1 x h-1) and control infusions. G/G-6-P cycle activity and endogenous glucose production (EGP) were determined by [2-3H]- and [6-3H]-glucose using labeled exogenous glucose infusions and selective enzymatic detritiation. GH increased levels of circulating lipid intermediates despite a twofold increase in basal insulin (P < 0.005), but plasma glucose, EGP, and G/G-6-P cycle activity were unchanged. GH impaired insulin suppression of EGP and lipid intermediates and impaired insulin stimulation of glucose disposal, but G/G-6-P cycle activity was unchanged. We conclude that increased activity of the G/G-6-P cycle does not contribute to the hepatic insulin resistance induced by GH under these conditions but that changes in fatty acid metabolism may be partly responsible for the impairment in hepatic and peripheral insulin action.
Role of alpha- and beta-adrenoceptors in sympathetically mediated thermogenesis
Authors: Blaak E. E. , van Baak M. A. , Kempen K. P. , Saris W. H.
Published: December 2017

This study was intended to investigate the role of alpha- and beta-adrenoceptor populations in the sympathetically mediated thermogenesis in healthy lean males. In the first study, the beta 1-, beta 2-, and beta 3-agonist isoprenaline was infused in increasing doses with and without simultaneous infusion of the beta 1-blocker atenolol (Iso and Iso+AT, respectively). There was an increase in whole body energy expenditure (EE) after infusing Iso+AT (P < 0.001) and an almost twofold higher increase after infusion of Iso only (P < 0.001). Stimulation of the beta 2-adrenoceptors by a specific agonist (salbutamol) resulted in a significant increase in EE (P < 0.001). The effect of stimulation of alpha 1-adrenoceptors on EE was measured by infusing increasing doses of the alpha 1-agonist phenylephrine. EE did not change, whereas blood pressure (BP) increased (P < 0.001) and heart rate decreased (P < 0.01). In addition to this study, the alpha 1-, alpha 2-, beta 1-, beta 2-, and beta 3-agonists norepinephrine and epinephrine were infused with simultaneous infusion of the beta 1- and beta 2-blocker propranolol. In both studies, there was no effect on EE, whereas BP increased (P < 0.01). In conclusion, in healthy male lean volunteers both beta 1- and beta 2-adrenoceptors are involved in the sympathetically mediated thermogenesis, whereas the alpha 1-, alpha 2-, and beta 3-adrenoceptors do not play a role.
Measurement of endogenous synthesis of plasma cholesterol in rats and humans using MIDA
Authors: Neese R. A. , Faix D. , Kletke C. , Wu K. , Wang A. C. , Shackleton C. H. , Hellerstein M. K.
Published: December 2017

We used the mass isotopomer distribution analysis (MIDA) technique to measure endogenous synthesis of plasma cholesterol in vivo in rats and normal human subjects. Sodium [1-13C]- or [2-13C]acetate was infused, and plasma free cholesterol was analyzed by gas chromatography-mass spectrometry. Frequencies of mass isotopomers M0-M4 (mass-to-charge ratio 368-372) were quantified. The enrichment of the true precursor for cholesterol synthesis (acetyl-coenzyme A in contributing tissues) was determined using the MIDA method. This technique remains mathematically valid even if more than one tissue contributes to circulating free cholesterol. The fractional contribution (f) from endogenous synthesis to free cholesterol in normal women (n = 5) was 2.48 +/- 0.39% after 7 h in the postabsorptive state and 1.27 +/- 0.41% after 8 h of refeeding. In ad libitum-fed rats (n = 12), f was 2.89 +/- 0.44% after 12 h, whereas administration of recombinant tumor necrosis factor increased this value fourfold. Next, the rate constant (k) for removal of labeled free cholesterol from plasma was calculated. Higher masses (M2-M4) were followed to avoid the problem of persistent label incorporation. During the 60 h after cessation of [13C]acetate infusions, k was 0.02490 +/- 0.00298/h in humans. Using these values of k and f, absolute cholesterogenesis was 568 +/- 55 mg/day in normal women (follicular menstrual phase), similar to prior estimates based on whole body sterol balances. Women also exhibited a diurnal variation for endogenous cholesterol synthesis (34.6 +/- 5.4 mg/h nighttime vs. 15.9 +/- 5.2 mg/h daytime) consistent with current knowledge about rhythms in cholesterogenesis. Checks on the model were internally consistent (e.g., comparisons among different isotopomers for calculating precursor enrichment). We conclude that fractional and absolute endogenous cholesterol synthesis can be measured using stable isotopes in vivo by the MIDA technique.
Effects of thyroparathyroidectomy, parathyroid hormone, and PTHrP on kidneys of ovine fetuses
Authors: MacIsaac R. J. , Horne R. S. , Caple I. W. , Martin T. J. , Wintour E. M.
Published: December 2017

The fetal parathyroid glands and parathyroid hormone-related protein (PTHrP) have been shown to be important regulators of fetal calcium metabolism through their actions on the placenta and bone. This study examined the effects of fetal thyroparathyroidectomy (with thyroxine replacement) and exogenous infusion of human parathyroid hormone [PTH-(1–34)], PTHrP-(1–34), and PTHrP-(1–141) on the urinary excretion of calcium in chronically cannulated ovine fetuses during the last one-fifth of gestation. Fetal plasma total and ionized calcium concentrations were significantly lower in thyroparathyroidectomized (TxPTx) fetuses when compared with intact fetuses, but there were no significant differences in urinary excretion rates of total calcium. However, TxPTx produced a significant increase in the fractional excretion rate of total calcium and a significant decrease in the excretion of adenosine 3',5'-cyclic monophosphate (cAMP) compared with intact fetuses. Infusions of PTH-(1–34), PTHrP-(1–34), and PTHrP-(1–141) into the jugular vein of TxPTx fetuses (n = 5) at the rate of 1 nmol/h for 2 h, after a 1-nmol loading dose, significantly decreased the excretion rate of total calcium and increased the excretion rate of cAMP in fetal urine. Infusions of all three peptides resulted in significant increases in the concentration of total calcium in fetal plasma but had no effect on the plasma concentrations or urinary excretion rates of phosphate. Infusion of either PTH-(1–34), PTHrP-(1–34), or PTHrP-(1–141) also resulted in an increase in fetal urine osmolality and pH and a decrease in free water clearance in TxPTx fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)