bluuebunny/crossref_metadata_2025 huggingface dataset:
Disposal and distribution of rT3 in humans: a new double-tracer kinetic study
Authors: Pilo A. , Iervasi G. , Vitek F. , Turchi S. , Bianchi R.
Published: December 2017

A satisfactory definition of reverse 3,3',5'-triiodothyronine (rT3) kinetics in humans cannot be obtained if the plasma disappearance curve of the injected labeled hormone is the only experimental data available; most of the kinetic parameters can only be bounded within ranges showing unacceptable variabilities. To gain additional experimental data a double-tracer approach is proposed. After simultaneous injection of [125I]rT3 and 131I the following three experimental curves were determined in plasma: 1) the disappearance of [125I]rT3, 2) the disappearance of 131I, and 3) the appearance of 125I generated in vivo from labeled rT3 degradation. Combined analysis of these three curves, based on a complex six-compartment model, was developed and applied to data obtained in a group of normal subjects. Through this new analysis, fractional disposal rates and fractional exchange rates between the plasma compartment and the periphery are uniquely determined. The main physiologically interesting information on the degradation of the hormone that emerges from these studies are 1) all degradative pathways of rT3 generate iodide, being in all cases the [125I]rT3 dose completely recovered as 125I in plasma; and 2) most rT3 is degraded (65–90%) in peripheral tissues rapidly exchanging with the plasma pool. The extended experimental base is not yet sufficient to compute unique values for production rate (PR) and body mass (Qt); the validity of estimates of PR and Qt is based on the assumption that injected [125I]rT3 is able to trace all rT3 peripherally produced (from thyroxine). The new approach yields ranges for PR and Qt (1.12–2.15 micrograms/h and 2.88–8.24 micrograms) much narrower than those computable from the [125I]rT3 disappearance curve only (1.12–5.07 micrograms/h for PR and 2.88-23.7 micrograms for Qt).
Characterization and ontogeny of endothelin receptors in human placenta
Authors: Kilpatrick S. J. , Roberts J. M. , Lykins D. L. , Taylor R. N.
Published: December 2017

Because of the potent mitogenic and vasoactive properties of endothelin-1 (ET-1) and the presence of its receptor in third trimester placenta, we postulated that ET-1 might be involved in human placental growth and vascularization during development. As an initial approach to test this hypothesis, placental ET receptors were characterized and quantified in each trimester of pregnancy. Membrane-rich particulates were prepared from first-, second-, and third-trimester villous human placenta obtained immediately after pregnancy termination or delivery. ET receptors were characterized by radioligand saturation analysis, ligand competition, and reverse transcription-polymerase chain reaction (RT-PCR) to determine the concentration, affinity, and specificity of ET binding sites, and to document the presence of specific ET-receptor subtype mRNA transcripts in placentas from each trimester. Kinetic determinations of 125I-labeled ET-1 binding yielded a Kd = 61 pM, consistent with the equilibrium determinations of 34 +/- 6 pM (n = 11). The concentration of ET receptors decreased significantly from 682 +/- 94 fmol/mg protein (n = 4) in the first trimester to 266 +/- 89 fmol/mg protein (n = 4) in the third trimester. Competition studies with unlabeled ET-1 indicated a single class of binding sites with a Ki = 49 +/- 5 pM (n = 9), whereas competition with ET-3 demonstrated binding sites with two affinities. The predominant sites had a Ki = 84 +/- 14 pM, similar to that for ET-1. The RT-PCR data confirmed that both ETA and ETB receptors mRNA transcripts are expressed in human placenta.(ABSTRACT TRUNCATED AT 250 WORDS)
Pancreatic beta-cell function and glucose metabolism in human segmental pancreas and kidney transplantation
Authors: Christiansen E. , Andersen H. B. , Rasmussen K. , Christensen N. J. , Olgaard K. , Kirkegaard P. , Tronier B. , Volund A. , Damsbo P. , Burcharth F. , et al.
Published: December 2017

beta-Cell function and glucose metabolism were studied in eight insulin-dependent diabetic recipients of combined segmental pancreas and kidney transplant with peripheral insulin delivery (Px), in eight nondiabetic kidney-transplant individuals (Kx), and in eight normal subjects (Ns) after three consecutive mixed meals. All subjects had normal fasting plasma glucose, but increased basal levels of C-peptide were demonstrated in the transplant groups (P < 0.05 relative to Ns). Postprandial hyperglycemia was increased 14% in Kx and 32% in Px (P < 0.05), whereas compared with Ns postprandial C-peptide levels were increased three- and twofold, respectively, in Kx and Px (P < 0.05). Compared with Ns basal insulin secretion rate (combined model) was increased 2-fold in Kx and 1.4-fold in Px (P < 0.05). Maximal insulin secretion rate was reduced 25% in Px compared with Kx (P < 0.05) but not different from that of Ns (P NS). Also, maximal insulin secretion rate occurred later in Px than in controls (Tmax: Px 50 min, Kx 30 min, and Ns 32 min; P < 0.05). The total integrated insulin secretion was increased 1.4-fold in Px compared with Ns (P < 0.05) but decreased 1.4-fold compared with Kx (P < 0.05). Fasting and postprandial proinsulin-to-C-peptide molar ratios were inappropriately increased in Px compared with Kx and Ns. Basal hepatic glucose production was increased 43% in Px and 33% in Kx compared with Ns (P < 0.05). Postprandial total systemic glucose appearance was similar in all three groups, whereas peripheral glucose disposal was 15% reduced in Px (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Postprandial plasma triacylglycerols in rats under alpha 1-adrenergic blockade
Authors: Deshaies Y. , Belahsen R.
Published: December 2017

The present studies evaluated the effect of prazosin, a selective alpha 1-adrenergic antagonist, on some metabolic determinants of triacylglycerol-rich lipoproteins. Plasma triacylglycerols (TG), TG secretion rate, TG removal rate, plasma insulin, and glucose were evaluated postprandially in animals fed a high-sucrose meal. In the fasted state plasma TG, glucose, and insulin concentrations were minimally affected by prazosin. There was a significant postprandial elevation in plasma TG levels that was larger after ingestion of a meal containing corn oil than after intake of a fat-free meal. Prazosin totally blunted the postprandial elevation in plasma TG independently of the presence (P < 0.004) or absence of dietary fat (P < 0.01). In the postprandial phase after ingestion of a fat-free, high-sucrose meal, prazosin decreased the rate of secretion of TG into the circulation (-54%, P < 0.0003) and accelerated twofold the clearance of an injected fat emulsion (P < 0.02). The postprandial elevations in plasma insulin and glucose were significantly potentiated by administration of prazosin before intake of the fat-free meal. These results indicate that prazosin prevented the postprandial elevation in plasma TG that followed the ingestion of a high-sucrose meal. The results also demonstrate that the alpha 1-blocker exerted its action both by decreasing TG secretion and by increasing the rate of removal of circulating TG.
Effects of protein restriction and acute refeeding on leucine and lysine kinetics in young men
Authors: Hoerr R. A. , Matthews D. E. , Bier D. M. , Young V. R.
Published: December 2017

To explore the effects of altered protein intake on the uptake and utilization of dietary amino acids in human subjects, six healthy male Massachusetts Institute of Technology students were studied during three dietary periods each of 9 days, with tracer infusion studies conducted on days 8 and 9. During one period the diet provided a generous protein intake (1.5 g.kg-1.day-1) and during the other two a low-protein intake (0.1 g.kg-1.day-1). Tracer infusions (fed state) were given while subjects received either a liquid formula, supplying the prior protein intake or (on day 9) a generous intake. Combinations of [2H3]Leu and [13C]Leu and of [15N]Lys and [2H4]Lys were given via continuous intravenous or intragastric infusion for 4 h to estimate leucine kinetics and the first-pass splanchnic uptake of tracer. Dietary-induced changes in leucine flux and oxidation were similar irrespective of the tracer and/or route of administration and sampled pool (leucine or KIC) used for calculation. Estimates of absolute changes in the rates of leucine disappearance via nonoxidative metabolism (protein synthesis) and of appearance via protein breakdown depended on the route of [13C]Leu administration. However, it appears that both altered rates of protein synthesis and breakdown contribute to the adaptations required in the body nitrogen economy when protein intakes are restricted and subsequently resupplied. From the intragastric [13C]Leu protocol, the first-pass splanchnic uptake of tracer was the same (approximately 30%) for generous, low-protein, and refed conditions.(ABSTRACT TRUNCATED AT 250 WORDS)
Sleep-promoting effects of growth hormone-releasing hormone in normal men
Authors: Kerkhofs M. , Van Cauter E. , Van Onderbergen A. , Caufriez A. , Thorner M. O. , Copinschi G.
Published: December 2017

Growth hormone-releasing hormone (GHRH) promotes rapid-eye-movement (REM) and non-REM sleep in animals, but there is little direct evidence for a hypnogenic action of GHRH in humans. In the present study, the possible somnogenic effects of intravenous bolus injections of a dose of GHRH eliciting physiological elevations of GH secretion in healthy young men were investigated. GHRH (0.3 micrograms/kg body wt) was given in early sleep [i.e., 1st slow-wave (SW) period], late sleep (i.e., 3rd REM period), and early sleep after sleep deprivation until 0400 h (i.e., 1st SW period). In the absence of sleep deprivation, injection of GHRH in early sleep did not modify SW sleep but increased REM sleep. GHRH administration in the third REM period was followed by a marked decrease of wake and an almost 10-fold increase in SW sleep. When GHRH was administered during the first SW period after sleep deprivation until 0400 h, the duration of wake decreased. Thus GHRH has sleep-promoting effects in young adults, particularly when given at a time of decreased sleep propensity.
Contribution of muscle and liver to glucose-fatty acid cycle in humans
Authors: Saloranta C. , Koivisto V. , Widen E. , Falholt K. , DeFronzo R. A. , Harkonen M. , Groop L.
Published: December 2017

To examine the influence of elevated free fatty acid (FFA) levels on hepatic glucose production (HGP) and oxidative and nonoxidative pathways of glucose metabolism, 12 healthy subjects participated in two euglycemic insulin-clamp studies performed with and without infusion of Intralipid plus heparin. To elucidate the role of skeletal muscle in this putative interaction, we performed muscle biopsies for the measurement of activities of glycogen synthase (GS), pyruvate dehydrogenase (PDH), and carnitine palmitoyltransferase (CPT). Infusion of Intralipid plus heparin caused an increase in plasma FFA concentrations and rate of lipid oxidation (measured by indirect calorimetry) that was not inhibited by insulin. Suppression of HGP by insulin was impaired by elevated plasma FFA levels. Furthermore, the increase in plasma FFA was associated with a 20% reduction in total glucose metabolism (P < 0.01), which was completely accounted for by a reduction in the rate of glucose oxidation. Although the fractional activity of GS was increased by insulin, elevation of plasma FFA had no influence on this key enzyme of glycogen synthesis. In addition, the activities of PDH and CPT were uninfluenced by the elevation of FFA, suggesting that oxidative processes in skeletal muscle were not a major target for the operative glucose-fatty acid cycle under the current conditions. Taken together, the data indicate that the interaction between FFA and glucose metabolism also involves impaired suppression of HGP by insulin.
Amylin and CGRP induce insulin resistance via a receptor distinct from cAMP-coupled CGRP receptor
Authors: Kreutter D. K. , Orena S. J. , Torchia A. J. , Contillo L. G. , Andrews G. C. , Stevenson R. W.
Published: December 2017

Amylin and calcitonin gene-related peptide (CGRP) inhibited insulin-stimulated 2-deoxyglucose uptake in L6 myocytes and isolated soleus muscle. Both peptides were maximally active at 10 pM in L6 cells and inhibited insulin action by 40-50%. In soleus muscle amylin and CGRP inhibited insulin-stimulated uptake by 65-85%. Amylin competed with 125I-CGRP for binding to L6 cells but with 100-fold lower potency than CGRP. Occupancy of the CGRP receptor in L6 cells is coupled to adenylyl cyclase. Amylin increased the cellular content of adenosine 3',5'-cyclic monophosphate (cAMP), but consistent with binding, amylin was 100-fold less potent than CGRP. In soleus muscle, 100 nM amylin, which maximally inhibited 2-deoxyglucose uptake, had no effect cAMP content, whereas CGRP at the same concentration increased cAMP by 50%. The effect of CGRP on cAMP levels was completely suppressed by the competitive antagonist, CGRP-(8-37). In contrast, the suppression of insulin-stimulated glycogen synthesis or 2-deoxyglucose uptake by amylin was unaffected by 1 microM CGRP-(8-37). Our results demonstrate that the inhibition of insulin-stimulated glucose transport by amylin is independent of cAMP and may be mediated by a unique receptor that is distinct from the adenylyl cyclase-coupled CGRP receptor.
Alpha-mediated changes in hepatocyte intracellular calcium in the catfish, Ictalurus melas
Authors: Moon T. W. , Capuzzo A. , Puviani A. C. , Ottolenghi C. , Fabbri E.
Published: December 2017

Adult catfish, Ictalurus melas, hepatocytes respond to alpha-agonists by increasing intracellular free calcium concentrations ([Ca2+]i) in a dose-dependent manner. Basal [Ca2+]i were approximately 78 nM in catfish hepatocytes; this value was increased by 213, 243, 131, and 238 nM in the presence of epinephrine (Epi; 10(-6) M), norepinephrine (NE; 10(-5) M), phenylephrine (PE; 10(-4) M), and isoproterenol (Iso; 10(-4) M), respectively. The binding constants were 3.4 x 10(-8), 2.6 x 10(-7), 9.8 x 10(-7), and 6.1 x 10(-5) M for Epi, NE, PE, and Iso, respectively, which is the same order of potency for these agonists reported for the alpha 1-adrenoceptor system of mammalian hepatocytes. The Epi-induced changes in [Ca2+]i were antagonized equally by phentolamine (PH; 10(-8) M) and yohimbine (10(-8) M) but poorly by propranolol (Prop; 10(-6) M), as indicated by their respective inhibitory constants. Epi (10(-7) M) induced a time-dependent increase in hepatocyte adenosine 3',5'-cyclic monophosphate concentration that was antagonized by Prop but not PH. There were, however, no clear agonist-induced changes in the activities of glycogen phosphorylase (total, a, or %a) under these conditions. These studies provide evidence that Epi and other adrenergic agonists increase [Ca2+]i by an alpha- or alpha 1-like adrenoceptor pathway in catfish hepatocytes, but the biochemical effector system responding to changes in [Ca2+]i has yet to be elucidated.
Insulin resistance is localized to skeletal but not heart muscle in type 1 diabetes
Authors: Nuutila P. , Knuuti J. , Ruotsalainen U. , Koivisto V. A. , Eronen E. , Teras M. , Bergman J. , Haaparanta M. , Voipio-Pulkki L. M. , Viikari J. , et al.
Published: December 2017

To determine the tissue localization of insulin resistance in type 1 diabetic patients, whole body and regional glucose uptake rates were determined under euglycemic hyperinsulinemic conditions. Leg, arm, and heart glucose uptake rates were measured using positron emission tomography-derived 2-deoxy-2-[18F]-fluoro-D-glucose kinetics and the three-compartment model described by Sokoloff et al. (L. Sokoloff, M. Reivich, C. Kennedy, M.C. DesRosiers, C.S. Patlak, K.D. Pettigrew, O. Sakurada, and M. Shinohara. J. Neurochem. 28: 897–916, 1977) in eight type 1 diabetic patients and eight matched normal subjects. Whole body glucose uptake was quantitated by the euglycemic insulin clamp technique. Whole body glucose uptake was approximately 31% lower in the diabetic patients (P < 0.01) than in the normal subjects, thus confirming the presence of whole body insulin resistance. The rate of glucose uptake was approximately 45% lower in leg muscle when measured in the femoral region (55 +/- 7 vs. 102 +/- 13 mumol.kg muscle-1.min-1, diabetic patients vs. normal subjects, P < 0.05) and approximately 27% lower in the arm muscles (66 +/- 4 vs. 90 +/- 13 mumol.kg muscle-1.min-1, respectively, P < 0.05), whereas no difference was observed in heart glucose uptake [789 +/- 80 vs. 763 +/- 58 mumol.kg muscle-1.min-1 not significant (NS)]. Whole body glucose uptake correlated with glucose uptake in femoral (r = 0.93, P < 0.005) and arm muscles (r = 0.66, P < 0.05) but not with glucose uptake in the heart (r = 0.04, NS). We conclude that insulin resistance in type 1 diabetic patients is localized to skeletal muscle, whereas heart glucose uptake is unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)
Skeletal unloading in rat decreases proliferation of rat bone and marrow-derived osteoblastic cells
Authors: Machwate M. , Zerath E. , Holy X. , Hott M. , Modrowski D. , Malouvier A. , Marie P. J.
Published: December 2017

The effects of skeletal unloading on osteoblastic cells were evaluated in tail-suspended rats. Hindlimb elevation for 14 days induced osteopenia, decreased histomorphometric indexes of bone formation in tibial metaphysis, and reduced plasma osteocalcin and alkaline phosphatase (ALP) levels compared with controls. The in vitro proliferation of osteoblastic cells isolated from the endosteal bone surface of suspended tibias was decreased by 42 and 31% at 2 and 4 days of culture, respectively, compared with controls, as shown by [3H]thymidine labeling and cell number. The proliferation of ALP-positive marrow stromal cells was also decreased by 20–24% at 1 and 2 days of culture. However, ALP activity in bone-derived cells and marrow stromal cells was not different in unloaded and control rats, and the number of bone cells synthesizing osteocalcin, osteonectin, and type I or type III collagen was identical in the two groups. The results indicate that the inhibition of bone formation induced by skeletal unloading is related to a decreased proliferation of putative osteoblast precursor cells present along the endosteal bone surface and in the marrow stroma.
Impaired epidermal growth factor production in genetically obese ob/ob mice
Authors: Serrero G. , Lepak N. M. , Hayashi J. , Goodrich S. P.
Published: December 2017

Epidermal growth factor (EGF) is a potent inhibitor of adipose differentiation in vitro and delays adipose tissue development in vivo. Here we show that in the homozygous male obese mice the level of EGF in the submaxillary gland and plasma is significantly lower than in the glands and plasma of age-matched control littermates. This EGF deficiency in ob/ob mice was observed as early as 5 wk of age when obesity had just become apparent and was also found in adult mice. The level of prepro-EGF mRNA expression in the submaxillary gland was also lower in obese mice than in control littermates. However, the level of kidney prepro-EGF mRNA was the same in mice with both phenotypes, suggesting that the regulation of prepro-EGF mRNA expression is different in both tissues. These results indicate that genetic obesity in mice is accompanied by a decrease in the production of EGF.
Effect of chronic intracerebroventricular dexamethasone on blood pressure in normotensive rats
Authors: Tonolo G. , Soro A. , Madeddu P. , Troffa C. , Melis M. G. , Patteri G. , Parpaglia P. P. , Sabino G. , Maioli M. , Glorioso N.
Published: December 2017

We report herein the effects of long-term intracerebroventricular (icv) dexamethasone in normotensive rats. Dexamethasone (0.002, 0.02, 0.2, and 2.0 micrograms/day) or its vehicle (0 microgram/day, n = 8 each group) was infused icv via subcutaneous miniosmotic pumps (Alzet 2002) for 24 days in male conscious Wistar rats (weight range 190-240 g). Eighteen Wistar rats (weight range 200-230 g) received either vehicle or dexamethasone (0.2 and 2 micrograms/day) subcutaneously (sc) for 24 days. Systolic blood pressure (SBP, tail cuff) and body weight were recorded two times a week in the trained conscious rats. Dexamethasone (0.2 micrograms/day icv) exerted a progressive significant decrease in SBP over 24 days compared with both rats receiving vehicle and to pretreatment values (108 +/- 4 vs. 122 +/- 4 and 120 +/- 2 mmHg, P < 0.01). As previously reported, a significant increase in SBP was observed after 6 days in rats given 2 micrograms/day sc dexamethasone compared with both rats receiving vehicle and to pretreatment values (150 +/- 4 vs. 122 +/- 2 and 120 +/- 2 mmHg, P < 0.01 for both). Thereafter, SBP remained at plateau for the entire experiment. A similar significant decrease in body weight gain with age was observed in rats given icv or sc dexamethasone. Our data suggest that the glucocorticoid receptors exert opposite effects on blood pressure when stimulated at the brain level instead of at the peripheral vascular level.
Parathyroidectomy abolishes the increase of renal 25-hydroxyvitamin D-1 alpha-hydroxylase in lactating rats
Authors: Lobaugh B. , Garner S. C. , Lovdal J. A. , Boass A. , Toverud S. U.
Published: December 2017

Serum ionized calcium (Ca), but not inorganic phosphorus or immunoreactive parathyroid hormone, negatively correlates with renal 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase) and serum 1,25-dihydroxyvitamin D in intact lactating rats. The present study tested the hypothesis that the presumed stimulation of renal 1 alpha-hydroxylase by hypocalcemia requires the presence of intact parathyroid glands. Lactating and nonlactating rats were surgically parathyroidectomized (PTX) or sham-operated (sham) at 9-10 days of lactation. Later (24 h) the rats were bled, nephrectomized, and killed. In lactating PTX rats, serum ionized Ca decreased to 50% of the level of sham rats, and serum 1,25-dihydroxyvitamin D fell to 37 +/- 5.0 pg/ml compared with 82 +/- 13.0 pg/ml for sham lactating rats but was still 2.5 times the value for nonlactating PTX rats (15 +/- 0.8 pg/ml). In contrast to the still elevated serum 1,25-dihydroxyvitamin D concentration in lactating PTX rats, renal 1 alpha-hydroxylase was suppressed to the same low level as in nonlactating PTX rats, suggesting the existence of extrarenal synthesis of 1,25-dihydroxyvitamin D in lactation. A curvilinear relationship was revealed between serum ionized Ca and renal 1 alpha-hydroxylase in sham lactating and nonlactating rats (r2 = 0.71, P < 0.0001). However, in PTX rats, decreasing ionized Ca did not lead to any increase in 1 alpha-hydroxylase above the low baseline values seen at ionized Ca concentrations between 1.3 and 1.5 mM. We therefore conclude that intact parathyroid glands are required for hypocalcemia to activate renal 1 alpha-hydroxylase in female rats.
Bioactive-to-immunoreactive ACTH activity changes with severity of stress in late-gestation ovine fetus
Authors: Castro M. I. , Valego N. K. , Zehnder T. J. , Rose J. C.
Published: December 2017

The late-gestation ovine fetus (> 130 days, 0.90 gestation, full term 145 days) is capable of increased pituitary-adrenal activity following a variety of stressors. To examine the relationship between plasma immunoreactive adrenocorticotropic hormone (iACTH) and bioactive ACTH-like activity (bACTH), late-gestation fetuses were studied under nonstress (group I, chronically catheterized), “mild” stress (group II, acutely exteriorized), or marked stress (group III, acutely exteriorized and hemorrhaged 30% of blood volume). Plasma iACTH was determined by standard radioimmunoassay. Plasma bACTH was determined by a bioassay that utilized dispersed rat adrenal cells. Plasma iACTH was lower in group I than in groups II or III (78.4 +/- 16.3 vs. 320 +/- 116 and 622 +/- 144 pg/ml, respectively, mean +/- SE, P < 0.05 group I vs. III). Plasma bACTH was significantly lower in groups I and II than in group III (13.8 +/- 2.7 and 52 +/- 22 vs. 601 +/- 106 pg/ml, respectively, P < 0.05). The ratio of bACTH to iACTH was low in groups I and II but elevated in group III (0.188 +/- 0.028 and 0.091 +/- 0.07 vs. 0.996 +/- 0.122, P < 0.05). We conclude that the amount of bACTH compared with iACTH in the late-gestation fetus is low under nonstress states or mild stress and that bACTH increases disproportionately compared with iACTH after marked stress. This suggests that a change in ACTH processing and/or secretion is associated with stimulus intensity in the late-gestation ovine fetus.
IGF-I and pamidronate increase bone mineral density in ovariectomized adult rats
Authors: Ammann P. , Rizzoli R. , Muller K. , Slosman D. , Bonjour J. P.
Published: December 2017

Effects induced by insulin-like growth factor I (IGF-I) and/or the bisphosphonate pamidronate (APD) on bone mineral density (BMD) of the lumbar spine and proximal and midshaft tibia were studied in adult rats made osteopenic by ovariectomy, using dual-energy X-ray absorptiometry. IGF-I, which was administered by osmotic minipumps implanted subcutaneously for 6 wk, caused a dose-dependent increase of BMD at the three investigated sites. A 4-wk course of IGF-I, followed by intermittent cyclical APD administration, induced significant increases of BMD at the levels of spine and proximal tibia. At midshaft tibia, where cortical bone predominates, BMD was increased by IGF-I only. In conclusion, IGF-I increased BMD at sites with trabecular and/or cortical bone, whereas the APD influence was mainly detectable in the former site only.
Experimental approaches in muscle metabolism: hindlimb perfusion and isolated muscle incubations
Authors: Bonen A. , Clark M. G. , Henriksen E. J.
Published: December 2017

The perfusion of rat hindlimb muscles and the isolated in vitro muscle preparation are usually the preferred methods for investigating muscle metabolism. In light of recent concerns about the incubated muscle preparation, we have examined the problems, the advantages, and the viability of these two experimental techniques, with focus on glucose metabolism. A major advantage of the hindlimb perfusion system is that it maintains its metabolic viability very well, and perfusions in resting muscles can be achieved successfully with cell-free media. However, variations in the perfused rat hindlimb procedures result in considerable differences in perfusate flow among muscles, making quantitative comparisons among perfusion procedures difficult. Metabolic viability has been identified as a problem in some isolated in vitro muscle preparations. We have provided criteria to avoid muscle hypoxia. Minimum levels of insulin seem to be a key requirement to maintaining the muscle's viability, and essential amino acids are required to retard an increase in the basal rate of glucose and amino acid uptake. Under such conditions metabolic viability can be maintained during prolonged incubations (9-30 h). Both the isolated in vitro muscle preparation and the hindlimb perfusion preparation are viable models for the study of muscle metabolism.
Effect of cortisol on energy expenditure and amino acid metabolism in humans
Authors: Brillon D. J. , Zheng B. , Campbell R. G. , Matthews D. E.
Published: December 2017

Hydrocortisone was infused overnight into nine normal healthy adults on three occasions at 0, 80, and 200 micrograms.kg-1.h-1, producing plasma cortisol concentrations of 10.6 +/- 1.2, 34.0 +/- 2.0, and 64.9 +/- 4.3 micrograms/dl, respectively. L-[1-13C]leucine, L-[phenyl-2H5]phenylalanine, and L-[2-15N]glutamine were infused during the last 7 h of hypercortisolemia to measure amino acid kinetics. During the last 3.5 h, somatostatin, glucagon, and insulin were infused to reduce the cortisol-induced elevation in plasma insulin to basal. Hypercortisolemia increased plasma glucose, free fatty acid (FFA), and insulin concentrations. Institution of the somatostatin clamp returned insulin to basal but increased glucose and FFA. Acute hypercortisolemia increased protein breakdown 5-20%, as measured by increases in leucine and phenylalanine appearance rates. Normalizing insulin during hypercortisolemia did not alter phenylalanine flux but enhanced leucine appearance rate, the latter result indicating that insulin was affecting leucine metabolism during hypercortisolemia. The fraction of the leucine flux that was oxidized was not significantly increased with hypercortisolemia, but disposal by the nonoxidative route of leucine uptake for protein synthesis was increased. Hypercortisolemia increased cycling of amino acids by increasing protein breakdown and synthesis, but the increase in this process could have increased resting energy expenditure (REE) only 1-2%. Hypercortisolemia increased glutamine flux in a dose-dependent fashion through an increase in de novo synthesis, which presumably reflects increased release from skeletal muscle. Hypercortisolemia increased REE 9-15% at the 80 and 200 micrograms.kg-1.h-1 infusion rates. Respiratory quotient did not rise with cortisol infusion but tended to decrease, suggesting that the increase in REE was fueled by increased oxidation of fat. These data demonstrate that hypercortisolemia increases metabolic rate and may be in part responsible for the hypermetabolic state in injury.
Chloroquine does not exert insulin-like actions on human forearm muscle metabolism
Authors: Barrett E. J. , Jahn L. A. , Oliveras D. M. , Fryburg D. A.
Published: December 2017

Insulin's anabolic action on skeletal muscle and whole body protein is attributable to its action to slow tissue proteolysis. The antimalarial chloroquine inhibits lysosomal proteolysis and is reported to improve glycemia in poorly controlled diabetic patients. We infused chloroquine into the brachial artery of seven healthy postabsorptive volunteers over 3 h during a steady-state infusion of L-[ring-2,6-3H]phenylalanine (Phe) to study its effect on muscle glucose and protein turnover. Compared with basal, chloroquine increased forearm blood flow (P < 0.01) but did not change glucose uptake or lactate release. Neither Phe released from muscle by proteolysis (78 +/- 15 vs. 94 +/- 16 nmol Phe.min-1.100 ml-1) nor Phe balance (-37 +/- 7 vs. -50 +/- 6 nmol.min-1.100 ml-1) was reduced from basal. We conclude that in postabsorptive human skeletal muscle: 1) lysosomal proteolysis does not make a major contribution to proteolysis; and 2) chloroquine does not cause an acute increase in glucose uptake. These findings suggest that the inhibition of postabsorptive muscle protein degradation provoked by physiological increases in plasma insulin is likely mediated by a nonlysosomal proteolytic pathway.
Secretion and clearance of immunoreactive ACTH by fetal lung
Authors: Cudd T. A. , Wood C. E.
Published: December 2017

We have previously reported the presence of immunoreactive adrenocorticotropic hormone (irACTH) in fetal and adult ovine lung and secretion of the irACTH into the pulmonary venous blood during surgical stress. The aim of the present experiments was to determine whether the fetal lung secretes irACTH during less stressful conditions. Seven fetal sheep were chronically prepared with systemic, pulmonary arterial, and pulmonary venous catheters. After recovery from surgery, paired samples were obtained from the pulmonary arterial and venous catheters. In 51 pairs of samples, we quantified the arteriovenous (A-V) difference in plasma irACTH concentration. Pulmonary A-V difference in plasma irACTH was significantly related to the arterial plasma concentration of irACTH but not to fetal blood gases, pH, or gestational age. Regression analysis revealed that, at arterial plasma concentrations of irACTH less than approximately 200 pg/ml, the lung releases irACTH into plasma and that, at higher concentrations, the lung clears irACTH from the plasma. We conclude that the lung independently secretes and clears irACTH into and from plasma.
Excitatory cholinergic innervation in canine portal and mesenteric veins
Authors: Yoshioka K. , Furuta T. , Hayakawa A. , Ishikawa N. , Shigei T.
Published: December 2017

A possibility that the canine portal and mesenteric veins may have an excitatory cholinergic innervation similar to that observed in the middle segment of the inferior vena cava (IVC) was investigated. After adrenergic blockade with prazosin, contractile responses of isolated longitudinal strips of the portal and mesenteric veins to transmural electrical stimulation were greatly diminished. Subsequent anticholinesterase (neostigmine or physostigmine) treatment, however, revealed in the nerve-evoked contraction a component that was antagonized by atropine. The same phenomenon was also observed in circular strips of the portal and mesenteric veins but was absent in those of the external jugular, saphenous, and splenic veins. In accord with the results of nerve stimulation, concentration-response curves of acetylcholine-induced contraction were shifted leftward by neostigmine in strips of the portal and mesenteric veins as well as of the middle segment of IVC. In contrast, no shift was observed in 12 other different sites of the venous system. Cholinesterase staining demonstrated positively stained smooth muscle and nerve fibers in the portal and mesenteric veins and in the middle segment of IVC. These findings indicate the existence of excitatory cholinergic innervation in the portal and mesenteric veins, which may reflect the common embryological origin of smooth muscle of these veins with the intestinal muscle.
Hyperthermia increases cerebral metabolic rate and blood flow in neonatal pigs
Authors: Busija D. W. , Leffler C. W. , Pourcyrous M.
Published: December 2017

We examined effects of hyperthermia on cerebral metabolic rate for oxygen (CMRO2) and cerebral blood flow (CBF) in anesthetized, newborn pigs (2–5 days old). CBF and CMRO2 were measured during normothermia (38 degrees C) and during hyperthermia induced by body heating (42 degrees C). During normothermia, total CBF was 32 +/- 3 ml.min-1.100 g-1 (n = 9), and CMRO2 was 1.34 +/- 0.08 ml O2.100 g-1.min-1 (n = 7). During hyperthermia, total CBF increased by 97 +/- 23% and CMRO2 by 65 +/- 24%. We also examined whether cerebral resistance vessels were responsive under these conditions. During hyperthermia, total CBF was 63 +/- 6 ml.min-1.100 g-1, and CMRO2 was 2.13 +/- 0.27 ml O2.100 g-1.min-1. During sustained hyperthermia, intravenous injection of 5 mg/kg of indomethacin decreased total CBF by 45 +/- 7% (n = 9), and CMRO2 fell by 55 +/- 10% (n = 5). We conclude that 1) hyperthermia increases CBF and CMRO2, and 2) the dilated cerebrovascular bed during hyperthermia still is responsive to a constrictor stimulus.
Ca-activated K channel in cultured smooth muscle cells of rat aortic media
Authors: Sadoshima J. , Akaike N. , Tomoike H. , Kanaide H. , Nakamura M.
Published: December 2017

Electrical and pharmacological properties of the single Ca-activated K channel in cultured smooth muscle cells (SMC) of the rat aorta were studied with the patch-clamp technique. The Ca-activated K channel had a slope conductance (gamma K) of 135 +/- 2 pS (mean +/- SE; n = 5) in symmetrical 142 mM K solutions. The reversal potentials show a 56-mV change for a 10-fold change in the external K concentration. Probability of the channel opening increased when the intracellular Ca concentration ([Ca]i) was increased over 10(-7) M or the membrane was depolarized. The channel was blocked by either external tetraethylammonium (TEA, 10–30 mM) or by internal Ba (1–5 mM). Channel activities were characterized by burst-like openings. Open-time histogram was fitted with a single exponential (tau = 1.3 ms at +10 mV and 10(-7) M [Ca]i), whereas the closed-time histogram was fitted with two exponentials (tau 1 = 0.7 ms and tau 2 = 111 ms). The permeability ratio for monovalent cations calculated with the Goldman-Hodgkin-Katz equation was K:Rb:Na = 1:0.7: less than 0.01. We conclude from these observations that the Ca-activated K channel in cultured SMC of the rat aorta is characterized by a middle size gamma K, activation by [Ca]i increase and depolarization, relatively low sensitivity to TEA, and high selectivity for K ions.
Time course of sympathetic denervation supersensitivity in canine ventricular recovery
Authors: Martins J. B.
Published: December 2017

We studied the timing of the electrophysiological effects of sympathetic supersensitivity with chronically implanted electrodes in the anterior and posterior left ventricular free wall in 10 dogs. We produced denervation of the anterior wall in six dogs by application of phenol surrounding the anterior electrode. Drug infusions that were performed under pentobarbital sodium anesthesia included norepinephrine, isoproterenol, and methoxamine. In four controls there was no difference in response of the two sites. Presynaptic supersensitivity was manifest as early as 2 days and as late as 64 days by a parallel left shift (greater than or equal to 8.3 ms) in the norepinephrine dose to effective refractory period shortening response curve in the anterior compared with posterior left ventricle, P less than 0.01. The isoproterenol dose-response curve was also shifted to the left by 5.6 ms (P less than 0.01) but was manifest only after 10 days and only until 28 days from the denervation procedure. Local repolarization in the denervated areas shortened more than the innervated areas with both drugs. The methoxamine dose-response curve was flat, and the anterior-denervated area was not different than the posterior-innervated area. We conclude that recovery properties in ventricular muscle demonstrate evidence of supersensitivity, which is neurotransmitter and beta- but not alpha-receptor specific.
Desensitization of myocardial but not coronary VIP receptor-mediated responses in dogs
Authors: Anderson F. L. , Kralios A. C. , Hershberger R. , Bristow M. R.
Published: December 2017

Desensitization to the hemodynamic effects of vasoactive intestinal polypeptide (VIP) was examined in 12 anesthetized, open-chest dogs in which cardiac output, systemic arterial resistance, and heart rate were fixed. VIP was administered by intracoronary infusion, and the effects were compared with isoproterenol and forskolin. Measurements of left ventricular maximum rate of pressure development (dP/dt), coronary blood flow, and myocardial oxygen consumption were made before and after a 90-min infusion of either isoproterenol (6 dogs) or VIP (6 dogs). After isoproterenol infusion, there was a significant decrease in the effect of isoproterenol on left ventricular dP/dt and coronary blood flow. The effects of VIP and forskolin were not changed. After VIP infusion, there was a significant decrease in the effect of VIP on left ventricular dP/dt with no change in the effects of isoproterenol and forskolin. In this group, a significant increase in coronary blood flow with minimal change in myocardial oxygen could still be elicited by VIP injection after VIP infusion. The agonist infusion time to achieve a decrease in inotropic effect was less for VIP when compared with isoproterenol. Thus these data demonstrate acute homologous desensitization of myocardial VIP and beta-adrenergic receptors in canine myocardium with no development of heterologous desensitization, desensitization involving the catalytic subunit of adenylate cyclase, or desensitization of the VIP-mediated primary coronary vasodilator response.
Dynamic fluid redistribution in hyperosmotic resuscitation of hypovolemic hemorrhage
Authors: Mazzoni M. C. , Borgstrom P. , Arfors K. E. , Intaglietta M.
Published: December 2017

A mathematical description of blood volume restoration after hemorrhage with resuscitative fluids, particularly hyperosmotic solutions, is presented. It is based on irreversible thermodynamic transport equations and known physiological data. The model shows that after a 20% hemorrhage, the rapid addition of a hypertonic (7.5% NaCl)-hyperoncotic (6% Dextran 70) solution amounting to one-seventh of the shed blood volume reestablishes blood volume within 1 min. Measurements of systemic hematocrit, hemoglobin concentration, and plasma osmolality taken from 13 experiments on anesthetized rabbits verify this prediction. The model shows that immediately after hyperosmotic infusion, water shifts into the plasma first from red blood cells and endothelium and then from the interstitium and tissue cells. The increase in blood volume is transitory; however, it occurs in a fraction of the time compared with isoosmotic fluids at the same infusion rate and is partially sustained by Dextran 70. We theorize that the concurrent hemodilution and endothelial cell shrinkage during hyperosmotic infusion lead to a decreased capillary hydraulic resistance, an effect that is even more significant in capillaries with swollen endothelium. Our results support the significant role of an osmotic mechanism during hyperosmotic resuscitation in quickly restoring blood volume with the added benefit of improved tissue perfusion.
Effect of albumin on the width of water channels in venous endothelium
Authors: Sanabria P. , Vargas F. F.
Published: December 2017

The effect of bovine and dog albumin and plasma was measured on the hydraulic conductivity (Lp) and electrical resistance (R) across the endothelium of the dog vena cava. An estimate of changes in size of transendothelial water channels was then obtained by combining Lp and R values. Dogs were anesthetized with pentobarbital sodium to surgically remove their thoracic inferior vena cava. Lp was measured by a gravimetric method at constant vessel volume. R was obtained from the transvascular voltage changes caused by current pulses. Lp measured at the beginning of the experiments was 0.97 +/- 0.17 X 10(-7) cm.s-1.cmH2O-1 in plasma and 2.75 +/- 0.48 X 10(-7) cm.s-1.cmH2O-1 in Ringer solution. Bovine albumin produced an 18% reduction in Lp relative to its value in Ringer solution. Dog albumin and plasma lowered Lp 50 and 54%, respectively. The differences were statistically significant with P less than 0.05. R increased from 15.17 +/- 7.0 to 26.5 +/- 16.0 omega.cm2 in dog albumin and 27.4 +/- 9.6 omega.cm2 in dog plasma. Calculations using a model for the transendothelial channel and equations for Lp and R showed a decrease in channel width of 172 A due to the protein. This could be accounted for by the thickness of a monolayer of albumin absorbed to the channel walls. Results suggest that the permeability response to plasma proteins is a general property of vascular endothelium.
Venomotor responses during central and local hypoxia
Authors: Rowell L. B. , Blackmon J. R.
Published: December 2017

Venomotor responses, measured as the pressure rise in occluded forearm veins, were used in a two-part experiment to test presence or absence of sympathetic neuroeffector mechanisms in 10 men made moderately to severely hypoxemic. In part I, forearm venoconstriction was induced by ice water on the contralateral forearm (a spinal reflex) in eight supine, resting men who breathed air, 10.3% oxygen or 7.7% oxygen. Large reflex venoconstrictions persisted during hypoxia. In part II (seven men), venoconstriction was centrally induced by exercise while subjects were 1) normoxic; 2) arm hypoxic, body normoxic; 3) arm hyperoxic (or normoxic), body hypoxic; or 4) both arm and body hypoxic. Arm vs. body oxygen tensions were separated by occluding the arm as one gas mixture was breathed, then switching the subject to another mixture as the arm remained occluded. Strong venoconstrictor responses to moderate exercise (100-150 W) persisted during both local and central hypoxemia. We conclude that moderate to severe hypoxemia does not block, pre- or postjunctionally, sympathetic venoconstriction that originates from spinal reflexes (cold). Venoconstriction in exercise (presumably originating in higher centers) was not blocked by moderate hypoxemia; severe hypoxemia was not studied.
Oxygen free radicals abolish endothelium-dependent relaxation in diabetic rat aorta
Authors: Pieper G. M. , Gross G. J.
Published: December 2017

The present experiments were conducted to determine whether endothelium-dependent relaxation is impaired in chronic (10-12 wk), streptozotocin-induced diabetic rat aortas and to determine the specificity and sensitivity of diabetic vasculature to oxygen-derived free radicals. Endothelium-dependent relaxation by acetylcholine and ADP was severely impaired in diabetic rat aorta, whereas endothelium-independent relaxation by nitroglycerin or papaverine was not impaired. Exposure to a free radical-generating system of xanthine plus xanthine oxidase caused a marked and prolonged relaxation in diabetic but not control vessels. Relaxation could not be prevented by the cyclooxygenase inhibitor indomethacin or the lipoxygenase inhibitor nordihydroguaiaretic acid but was attenuated or blocked by catalase. After free radical exposure, aortic rings were washed, reequilibrated, and contracted with a submaximal concentration of norepinephrine. In free radical-exposed vessels, endothelium-dependent relaxation by acetylcholine was reduced by 50% in nondiabetic vessels and abolished in diabetic vessels. Nevertheless, diabetic vessels could still be fully relaxed by nitroglycerin or papaverine. These results suggest selective impairment of endothelium-dependent relaxation in chronic diabetic rat aortas with particular sensitivity to free radical-induced damage.
Pulmonary inflation reflex: its lack of physiological significance in coronary circulation of humans
Authors: Wilson R. F. , Marcus M. L. , White C. W.
Published: December 2017

In awake dogs, voluntary deep inspiration results in a marked, reflex-mediated increase in coronary blood flow. To study this reflex in humans, we subselectively measured coronary blood flow velocity (CBFV) with a 3-F coronary Doppler catheter in 12 subjects with angiographically normal coronary arteries. In each subject, intracoronary papaverine increased CBFV to 4.8 +/- 0.2 X resting CBFV and reduced coronary resistance to 0.20 +/- 0.01 X resting coronary resistance, demonstrating normal vasodilator reserve in the vessel under study. Valsalva maneuver reduced CBFV to 0.67 +/- 0.09 X resting CBFV and increased coronary resistance to 1.37 +/- 0.20 X resting coronary resistance (P less than 0.05 vs. control). Maximum voluntary inspiration, however, did not significantly change CBFV (peak response 1.03 +/- 0.05 X resting CBFV) or coronary resistance (0.96 +/- 0.04 X resting). To determine whether augmentation of resting alpha-adrenergic tone would potentiate the reflex, eight patients performed a sustained 33% maximal handgrip for 2 min. Maximal deep inspiration during handgrip failed to result in any significant change in CBFV or coronary resistance. These studies demonstrate that the canine pulmonary inflation reflex has little or no physiological significance in the coronary circulation of conscious humans. Additionally, these data suggest that the magnitude of reflex control of the coronary circulation may vary considerably between dogs and humans.
Arterial pressure control after chronic carotid sinus denervation
Authors: O'Leary D. S. , Scher A. M.
Published: December 2017

This study examines the control of arterial blood pressure in conscious, instrumented dogs with atrioventricular block before and greater than or equal to 9 days after carotid sinus baroreceptor denervation. Strength of reflex control of blood pressure was quantitated by measuring the changes in peripheral resistance and atrial rate after square wave changes in cardiac output. Surprisingly, nine or more days after carotid denervation, the strength of baroreflex control of peripheral resistance and atrial rate were not different (P greater than 0.05) from the values before denervation. This was not due to a change in the base-line levels of arterial pressure, atrial rate, cardiac output, or peripheral resistance. Bilateral vagal block after carotid denervation removed reflex effects from remaining baroreceptors and virtually eliminated changes in peripheral resistance in response to changes in arterial pressure. Therefore, the compensatory responses observed after carotid denervation were mediated by the remaining baroreceptors. Thus, after chronic carotid sinus denervation, there is no decrease in the strength of baroreflex control of peripheral resistance or heart rate.