bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation and kinetic analysis of insulin-independent glucose uptake in human subjects
Authors: Gottesman I. , Mandarino L. , Gerich J.
Published: December 2017

Using the glucose clamp technique, glucose uptake was determined isotopically in normal human volunteers at plasma glucose concentrations of congruent to 60, 95, and 160 mg/dl during insulin infusions that increased plasma insulin to congruent to 20, 80, and 160 microU/ml. Because glucose uptake was found to be a linear function of plasma insulin at each plasma glucose concentration (r greater than 0.92, P less than 0.01), glucose uptake at 0 plasma insulin was estimated by linear regression analysis. The values thus derived (1.30, 1.62, and 2.59 mg . kg-1 . min-1 for plasma glucose concentrations of 60, 95, and 160 mg/dl, respectively) produced a linear Eadie-Hofstee plot, suggesting that insulin-independent glucose uptake followed Michaelis-Menten kinetics. The Km for glucose uptake at 0 plasma insulin (congruent to 10 mM) was similar to those observed for glucose uptake at the other plasma insulin concentrations studied (congruent to 9-12 mM), but its Vmax was less (5.2 vs. 6.4, 18.5, and 26.8 mg . kg-1 . min-1 for congruent to 20, 80, and 160 U/ml, respectively). These results indicate that in postabsorptive human subjects 75-85% of glucose uptake is noninsulin-mediated and provide additional support for the concept that insulin may increase glucose uptake merely by providing additional transport sites. The method described herein provides an assessment of insulin-independent glucose uptake in vivo that may prove useful in distinguishing between intrinsic defects of the glucose transport system and those due to defects in insulin action.
Calculation of substrate turnover rate in stable isotope tracer studies
Authors: Tserng K. Y. , Kalhan S. C.
Published: December 2017

The determination of substrate turnover rate with stable isotope-labeled compounds has advantages of being safe and applicable in the study of children and pregnant women. Currently, a majority of these studies has been performed with primed constant-rate infusion technique. The isotope enrichment of the substrate in the plasma is measured by gas chromatography-mass spectrometry (GCMS). The turnover rate is then calculated from steady-state kinetics. A number of different equations have been used by various investigators for this purpose. Based on theoretical consideration and experimental data, it is concluded that the equation P = [(1/E) - 1] I or P = (y/x) I should be used for a correct turnover rate calculation, where P is turnover rate in mumol X kg-1, E the isotope enrichment, I the infusion rate in mumol X kg-1 X min-1, and y/x the mole ratio of tracee to tracers. A GCMS standard curve constructed from isotope enrichment versus isotope peak abundance should be used for the former equation, whereas a standard curve constructed from mole ratio (x/y) versus isotope ratio should be used for the latter equation. Interchange of standard curves or use of other equations will produce erroneous turnover rate. This is especially significant when a low enriched isotope-labeled compound is used as a tracer.
Effects of ketosis on glucose flux in children and adults
Authors: Haymond M. W. , Howard C. , Ben-Galim E. , DeVivo D. C.
Published: December 2017

Sequential glucose flux studies were carried out in five normal and six epileptic children and ten adult volunteers using [6,6-2H2]glucose to determine the effect of ketosis on carbohydrate homeostasis in children and adults. All subjects were studied after 14 and 30-38 h of fasting while consuming a normal diet and the epileptic children under 14 h of fasting while consuming an isocaloric ketogenic diet (75% fat wt/wt). Glucose flux, when expressed per kilogram body weight, was inversely correlated with the degree of ketosis in children (P less than 0.001) and in adults (P less than 0.01), but not when both children and adults were considered together (r = 0.078). When glucose flux was corrected for estimated brain weight, the relationship between glucose flux and ketonemia was linearly related in children (P less than 0.001), in adults (P less than 0.02), and when all subjects were considered together (P less than 0.001). The inverse relationship between ketonemia and glucose flux corrected for estimated brain mass is consistent with a partial replacement of glucose by ketone bodies for cerebral metabolism and may provide a more rational means of expressing glucose flux data to take into account the higher brain-to-body ratio in children.
Differential effects of microtubule-altering agents on beta-cells during development
Authors: Hill R. S. , Rhoten W. B.
Published: December 2017

The effect of microtubule-altering agents on the insulin secretory response to glucose during the perinatal period was investigated with an in vitro perifusion system. Rat pancreatic mince from day 17 of gestation (D17G) to day 6 postnatally (D6PN) were perifused for 60 min in basal glucose followed by 45 min with high glucose (3.5 mg/ml) or with high glucose plus 10 mM arginine (D17G). The two phases of insulin secretion in response to high glucose developed in an age-dependent and asynchronous manner. The first phase matured between D17G and D18G, and maturation of the second phase occurred subsequently. Vinblastine (VB) (20 or 100 microM) had a differential effect on the insulin secretory response. VB did not inhibit stimulated insulin release at D17G. This absence of an inhibitory effect of VB at D17G could not be explained by the absence of polymerized tubulin because microtubules were present in the control beta-cells and, in addition, VB treatment resulted in the formation of paracrystalline deposits. Subsequently in development, and with isolated islets of the adult, VB inhibited stimulated insulin release. Heavy water (deuterium oxide, D2O) inhibited stimulated insulin secretion at D17G but blocked completely insulin release from the near-term beta-cell. The inhibition of insulin secretion by D2O was rapidly reversed when water replaced D2O in the perifusion media. The results indicate that the maturation of the second phase of insulin secretion coincides with the ability of the microtubule-altering agents to modify the insulin secretory response. One possible explanation for these findings is that at D17G the microtubules are not coupled physicochemically to other molecules or structures necessary for their role in insulin secretion to be expressed fully.
Epinephrine sensitivity with respect to metabolic rate and other variables in women
Authors: Sjostrom L. , Schutz Y. , Gudinchet F. , Hegnell L. , Pittet P. G. , Jequier E.
Published: December 2017

A test for determination of epinephrine sensitivity has been worked out using six healthy young women. Variables considered were metabolic rate, heart rate, respiratory frequency, blood pressure, blood glucose, plasma insulin, glycerol, free fatty acids, and lactate. After established basal conditions, epinephrine was infused at rates of 0.01, 0.03, and 0.1 microgram X kg fat-free mass-1 X min-1. Most variables responded to epinephrine in a dose-dependent manner. Physiological threshold plasma concentrations of epinephrine ranged from 95 to 250 pg/ml for different variables. Calculated maximal responses ranged from approximately -15% to +900% of basal values and infusion rates giving half-maximal responses from approximately 15 to 190 ng X kg fat-free mass-1 X min-1. On an average, metabolic rate increased by 8, 16, and 29%, respectively, at the three infusion rates, and the maximal metabolic response was calculated to be approximately 35%. The error in determining epinephrine-induced increments in metabolic rate was 7% of the response. As calculated from nonprotein RQ, carbohydrate oxidation increased and lipid oxidation decreased rapidly during the first 10 min of epinephrine infusion. Later, fat oxidation became more important. Results on epinephrine plasma metabolic clearance rate agreed with earlier results in the literature.
Effects of beta-adrenergic blockade on lateral hypothalamic lesion-induced thermogenesis
Authors: Corbett S. W. , Kaufman L. N. , Keesey R. E.
Published: December 2017

Oxygen consumption is markedly elevated in rats with lesions of the lateral hypothalamus (LH), a response typically associated with hyperactivity. To test for involvement of adrenergic systems in this hypermetabolic state, propranolol was administered before and immediately after LH lesions. Propranolol attenuated both the lesion-induced rise in oxygen consumption and activity in the 12 h after surgery. A second experiment evaluated the contribution of activity to this thermic response by lesioning rats immobilized by a continuous barbiturate infusion. The persistence of lesion-induced increases in oxygen consumption in the absence of activity and the attenuation of this response by propranolol demonstrated that 1) LH lesions directly alter metabolic heat production, and 2) this effect is at least partly mediated by beta-adrenergic systems. The functional significance of increased energy expenditure after LH lesions is discussed in light of the known effects of this lesion on the level of regulated body weight.
Human pancreatic GRF stimulates phosphatidylinositol labeling in cultured anterior pituitary cells
Authors: Canonico P. L. , Cronin M. J. , Thorner M. O. , MacLeod R. M.
Published: December 2017

The effects of natural and synthetic human pancreatic growth hormone-releasing factor (hpGRF) on 32P incorporation into phospholipids were studied in cultured rat anterior pituitary cells. Natural hpGRF (1:30 dilution) significantly (P less than 0.01) stimulated phosphatidylinositol labeling at all times studied (15, 30, and 60 min). Synthetic hpGRF-(1–40)OH also significantly (P less than 0.05; P less than 0.01) increased 32P incorporation into phosphatidylinositol in a dose-related (1–30 nM) and time-dependent (5, 10, and 30 min) manner. In contrast, phosphatidylcholine and phosphatidylethanolamine labeling was not affected at any time studied. Somatostatin (30 nM) did not affect basal or hpGRF-stimulated phosphatidylinositol labeling but inhibited the hpGRF stimulation of cyclic AMP accumulation and growth hormone release. These results suggest that the phosphatidylinositol cycle may be involved in the mechanism of action of hpGRF in the anterior pituitary gland.
Cation-dependent vitamin D activation of human renal cortical guanylate cyclase
Authors: Vesely D. L. , Juan D.
Published: December 2017

The objective of this investigation was to determine whether physiological levels of vitamin D and its metabolites have part of their mechanisms of action through stimulation of guanylate cyclase (EC 4.6.1.2). These sterols enhanced both soluble and particulate guanylate cyclase activities as well as cGMP levels two- to threefold in human and rat tissues. At a concentration of 1 nM, 1,25(OH)2D3 greater than 25(OH)D3 greater than vitamin D3 greater than 24,25(OH)2D3 = 25,26(OH)2D3 = vitamin D2. Dose-response curves revealed that maximal stimulation of guanylate cyclase by these sterols was at 1 nM and that there was no augmented guanylate cyclase activity at 0.01 nM. The precursors of vitamin D, cholesterol and 7-dehydrocholesterol, had no effect on guanylate cyclase activity. The activation of guanylate cyclase activity by the vitamin D sterols required the presence of manganese ion. Calcium was not as efficient as manganese in optimizing basal or hormone-stimulated guanylate cyclase activity. Vitamin D and its metabolites failed to stimulate adenylate cyclase (EC 4.6.1.1) activity. The data in this investigation suggest that guanylate cyclase may play a role in the mechanism of action of vitamin D at the cellular level.
Skeletal muscle beta-adrenergic receptors: variations due to fiber type and training
Authors: Williams R. S. , Caron M. G. , Daniel K.
Published: December 2017

To determine the relationship between oxidative capacity and characteristics of beta-adrenergic receptors (beta AR) in skeletal muscle, selected biochemical variables were quantitated in particulate preparations from soleus and gastrocnemius muscle from rats subjected to 10 wk of treadmill running and from three control groups: free-fed, sedentary controls; food-restricted, pair-weighted controls; and animals trained by swimming. Beta AR density and isoproterenol-stimulated adenylate cyclase activity were considerably greater in the slow-twitch oxidative soleus muscle than in the mixed fiber type gastrocnemius in animals from each group (P less than 0.005). Succinic dehydrogenase (SDH) activity of gastrocnemius was increased 23-42% (P less than 0.05) in runners over each of the control groups, concommitantly with a 15-27% increase (P less than 0.05) in beta AR density (Bmax for binding of 125I-cyanopindolol). In 24 animals from all four treatment groups, there was a significant correlation between SDH activity and beta AR density (r = 0.68; P less than 0.001). We conclude that BAR density correlates positively with oxidative capacity in skeletal muscle, but further studies are required to determine the physiological importance of these differences.
Comparison of glucose, LCT, and LCT plus MCT as calorie sources for parenterally nourished rats
Authors: Stein T. P. , Presti M. E. , Leskiw M. J. , Torosian M. E. , Settle R. G. , Buzby G. P. , Schluter M. D.
Published: December 2017

Protein and fat metabolism were studied in fed and protein-depleted rats. The rats were given one of three isocaloric, isonitrogenous nutrient mixes parenterally. The nutritional regimens differed in the source of nonprotein calories: i) glucose, ii) an emulsion containing long-chain fatty acid triglyceride esters (LCT), and iii) an emulsion containing both LCTs and medium-chain fatty acid triglycerides (MCT). Nitrogen balance, protein synthesis and breakdown, fat deposition in the liver, and the periuterine fat pads were measured using [15N]glycine as the tracer for the protein metabolism and deuterium for the lipid studies. Results are as follows. i) Nitrogen retention and protein synthesis were greater in the fed rats treated with glucose than with LCT. ii) Nitrogen fluxes were lower with LCT than with glucose. iii) Extensive lipogenesis in the liver was only found with the glucose-treated rats. iv) None of the caloric regimens promoted lipogenesis in the periuterine fat pads. v) With the two lipid-containing regimens there was a relative depletion of the depot fat in the periuterine fat pads relative to their glucose-treated counterparts. v) Although the MCT-containing emulsion did not cause hepatomegaly, its apparent caloric effectiveness was lower than that of either glucose or LCT. vi) Chain elongation is not a major pathway for MCT metabolism in parenterally nourished rats.
Distribution of sodium in cellular and luminal compartments of turtle thyroid glands
Authors: Yen-Chow Y. C. , Chow S. Y. , Woodbury D. M.
Published: December 2017

Sodium distribution in luminal and cellular compartments of turtle thyroid was studied by measurements of radiosodium uptakes into whole thyroid and luminal fluid, sampled with micropipettes, and of Na+ activities in the luminal and cellular fluids of thyroid follicles with a liquid ion-exchange microelectrode. Thyroid water and electrolyte contents were also determined chemically. Radiosodium uptake by both the whole thyroid and by the luminal fluid of control and thyrotropin (TSH)-treated turtles did not reach maximal levels until 16-24h after injection of the radioisotope. In control animals, the volumes of distribution of radiosodium in the whole thyroid and the luminal fluid were much smaller than those calculated from the chemical analysis data for the corresponding tissues. TSH increased the radiosodium spaces to values almost equal to those of the chemically determined sodium spaces. Luminal fluid sodium concentration increased after TSH and decreased after ouabain and furosemide treatments. Intracellular sodium concentration markedly increased after ouabain and decreased after TSH and furosemide. These and our previous results suggest a Na+-I- cotransport mechanism in the thyroid.
Influence of adrenalectomy and steroid replacement on heart citrate synthase levels
Authors: Marver D.
Published: December 2017

Aldosterone-dependent changes in citrate synthase (CS) activity have been used as an index of mineralocorticoid target sites. However, adrenalectomy (ADX) resulted in a fall in activity of CS and several other enzymes in rabbit heart, a tissue with glucocorticoid-but not mineralocorticoid-specific receptors. The enzymes included CS (2.03-1.36 U/mg protein, normal----ADX, P less than 0.001), isocitrate dehydrogenase-NADP+ (1.10-0.80 U/mg, P less than 0.002), isocitrate dehydrogenase-NAD+ (0.034-0.020 U/mg, P less than 0.01), and hydroxymethylglutaryl-CoA lyase (0.072 to 0.035 U/mg, P less than 0.001); in contrast, mitochondrial malate dehydrogenase levels were not significantly reduced by adrenal loss. There was also a decrease after surgery in sarcolemmal Na-K-(17.30-12.31 mumol Pi . mg protein-1 . h-1, P less than 0.002) and Mg-ATPase activities (14.16-12.11 mumol Pi . mg protein-1 . h-1, P less than 0.05). However, ADX did not result in a significant change in heart weight per kilogram body weight or recovery of mitochondrial protein per gram heart. CS was also assayed in hearts from ADX animals following acute (90 min) and chronic (3 day) steroid replacement. Although neither acute intravenous aldosterone (10 micrograms/kg) nor dexamethasone (100 micrograms/kg) increased activity, exposure to multiple subcutaneous injections of either steroid over a 3-day period significantly elevated CS above ADX values. The coordinate changes in the levels of several myocardial enzymes associated with energy metabolism is discussed in terms of an adaptation to chronic alterations in energy demands as opposed to specific mineralocorticoid or glucocorticoid receptor-mediated processes.
Enhanced muscle glucose metabolism after exercise: modulation by local factors
Authors: Richter E. A. , Garetto L. P. , Goodman M. N. , Ruderman N. B.
Published: December 2017

Studies in the rat suggest that after voluntary exercise there are two phases of glycogen repletion in skeletal muscle (preceding study). In phase I glucose utilization and glycogen synthesis are enhanced both in the presence and absence of insulin, whereas in phase II only the increase in the presence of insulin is found. To determine whether these alterations and in particular those mediated by insulin are due to local or systemic factors, one hindlimb of an anesthetized rat was electrically stimulated, and both hindlimbs were perfused immediately thereafter. Glucose and glycogen metabolism in the stimulated leg closely mimicked that observed previously after voluntary exercise on a treadmill. With no insulin added to the perfusate, glucose incorporation into glycogen was markedly enhanced in muscles that were glycogen depleted as were the uptake of 2-deoxyglucose and 3-O-methylglucose. Likewise, the stimulation of these processes by insulin was enhanced and continued to be so 2 h later when the muscles of the stimulated leg had substantially repleted their glycogen stores. The results suggest that the increases in insulin-mediated glucose utilization and glycogen synthesis in muscle after exercise are modulated by local contraction-induced factors.
Measurement of urea kinetics in humans: a validation of stable isotope tracer methods
Authors: Matthews D. E. , Downey R. S.
Published: December 2017

To define the importance of an accurate priming dose for measurement of urea production using a primed, short-duration (e.g., 4 h) infusion of labeled urea, [18O]- and [13C]ureas were infused simultaneously at two different prime-to-infusion (P/I) doses into five young adult men. The measured mean (+/-SE) urea production rates were 261 +/- 12 and 509 +/- 25 mumol X kg-1 X h-1 for P/I = 12.6-h and 5.0-h priming doses, respectively. In a second series of studies, a single dose of [18O]urea tracer was administered intravenously to four subjects, and the urea production rate was determined from the plasma urea tracer disappearance curve obtained over the following 6 h by fitting the data to a two-exponent curve. The mean urea production rate was 224 +/- 14 mumol X kg-1 X h-1. Because the fractional turnover of the body urea pool is slow, the priming dose strongly influences the "apparent" plasma urea enrichment plateau and, therefore, the measured urea production rate during short-duration infusions. Alternatively, the single-dose protocol can be applied to measure human urea production accurately in periods as short as 6 h.
A new technique for hepatic portal vein catheterization in freely moving rats
Authors: Helman A. , Castaing D. , Morin J. , Pfister-Lemaire N. , Assan R.
Published: December 2017

To perform kinetic studies of pancreatic hormones in freely moving rats, we have designed a new technique for hepatic portal vein catheterization through the left branch of the portal vein. Rats were followed up for 14-38 days. Catheter patency allowed blood sampling in 86% of rats on postoperative day 8 and in 55% on day 12. Rat growth, liver functions, and regional blood flows (measured with radiolabeled microspheres) were normal. In freely moving rats fasted for 16 h, portal venous concentrations in the basal state were: glucose, 112 +/- 4 mg/dl; insulin, 67 +/- 10 microU/ml; and glucagon, 480 +/- 74 pg/ml. These values remained stable for a 1-h period. Intravenous glucose infusion induced a biphasic insulin release, significant from the 1st min of infusion on, and a significant decline in glucagon level. Intravenous arginine stimulated both A and B cells. The portoperipheral hormone concentration gradient, which was detected in the basal state, increased during arginine infusion, particularly in regard to insulin. Ingestion of a mixed meal induced an early glucagon release and a sustained rise in insulin and glucose concentrations.
Fetal fuels. VII. Ketone bodies inhibit synthesis of purines in fetal rat brain
Authors: Shambaugh G. E. , Angulo M. C. , Koehler R. R.
Published: December 2017

Maternal starvation in late gestation results in ketonemia and a lowered DNA content in fetal rat brain. Because purines are needed for formation of new RNA and DNA, we examined the de novo pathway for purine biosynthesis in fetal rat brain slices by measuring the incorporation of [14C]formate into [14C]adenine. Maternal starvation days 18-20 resulted in a slight but nonsignificant fall in purine biosynthesis from 0.230 +/- 0.006 to 0.216 +/- 0.006 mumol X g-1 X 2 h-1. Graded concentrations of DL-3-hydroxybutyrate (3OHB) produced a progressive inhibition of formate incorporation in fetal brain slices, and rates of purine biosynthesis in the presence of 5.4 mM 3OHB were significantly lower (P less than 0.01) in fetal brain slices from both fed and starved mothers, i.e., 0.199 +/- 0.006 and 0.189 +/- 0.006 mumol X g-1 X 2 h-1, respectively. Acetoacetate caused an inhibition similar in magnitude to 3OHB. That 3OHB did not act via a protein biosynthetic step was evidenced by unimpaired biosynthesis of purines and sustained 3OHB inhibition in the presence of 1 mM cycloheximide. Unlike the de novo pathway, the salvage pathway measured by incorporation of [8-14C]adenine into labeled nucleotides was not significantly inhibited even by supraphysiological levels of 3OHB (21.6 mM). Serial measurements of the de novo and salvage pathways in neonatal brain slices showed a maintenance of salvage activity during the first 2 wk but a progressive fall in activity of the de novo pathway. Thus ketone bodies could act to restrain the synthesis of purine nucleotide building blocks for new cell formation in fetal but not in neonatal rat brain.
Catecholamine measurements by high-performance liquid chromatography
Authors: Hjemdahl P.
Published: December 2017

The development of sensitive detectors has allowed the use of high-performance liquid chromatography (HPLC) for measurements of catecholamines in extracts of plasma, urine, and tissue samples. Separation of the catecholamines may be effected by reversed phase chromatography or cation-exchange chromatography and quantitation by electrochemical detection (EC) or by fluorometry coupled with postcolumn derivatization according to the trihydroxyindole (THI) method. EC has a somewhat lower sensitivity than the THI method for norepinephrine (NE) and epinephrine (E). The THI method is insensitive to dopamine (DA). Basal plasma E levels of 0.1 nM (20 pg/ml) or less may be measured in sample volumes of 1-2 ml with EC. Sensitivity and reproducibility of an assay is not necessarily a guarantee of accuracy. It is argued that new methods and modifications of old methods should be validated against accepted methodology. This is rarely the case. Cation exchange HPLC with EC has been adequately validated, but only one of the reversed phase methods has been compared with radioenzymatic methodology. HPLC has the advantages of economy, speed, and more stimulating laboratory work, as compared with radioenzymatic methodology.
Effects of surgical stress and insulin on cardiovascular function and norepinephrine kinetics
Authors: Christensen N. J. , Hilsted J. , Hegedus L. , Madsbad S.
Published: December 2017

In resting supine subjects the whole-body clearance of norepinephrine (NE) based on arterial and venous sampling averaged 1.4 and 2.5 liters/min, respectively (P less than 0.02). The difference in clearance values was due to a peripheral uptake of NE averaging 45%. The calculation of plasma NE clearance based on venous sampling results in values that are too high. The plasma appearance rate of NE increased considerably after surgery, whereas the arterial blood pressure remained unchanged. This suggests that the sensitivity to NE is reduced postsurgery. Insulin has certain acute effects on cardiovascular function and plasma NE kinetics that are unrelated to the counterregulatory response to decrements in plasma glucose concentration. Insulin may both induce antagonism to the action of NE and increase the release of NE from sympathetic nerves. Intravenous insulin decreases the plasma volume and increases the hematocrit by an adrenergic mechanism. Plasma NE increases in normal subjects after an oral glucose load. This response may be of importance because in sympathectomized patients both oral glucose and insulin administration decreases the arterial blood pressure. During an oral glucose load insulin-dependent diabetics show abnormalities in the regulation of cardiovascular function and sympathetic nervous activity that may be related to the lack of rise in endogenous insulin in these patients. These results suggest that insulin may be of importance for the normal function of the cardiovascular system.
Methods of plasma catecholamine measurement including radioimmunoassay
Authors: Raum W. J.
Published: December 2017

Fluorometric and radioenzymatic assays are presently the most widely used techniques for the estimation of plasma, urine, and tissue catecholamines. The fluorometric assay lacks specificity and sensitivity. The radioenzymatic assay is significantly more sensitive and specific but is technically very complex, time consuming, and expensive. A newer methodology has been developed by modification of a 125I radioimmunoassay for metanephrine. The assay utilizes an antibody that specifically binds metanephrine. Plasma and urinary epinephrine and norepinephrine are detected by conversion to metanephrine with the enzymes catechol-O-methyl-transferase (COMT) and phenylethanolamine-N-methyltransferase (PNMT). The major advantages of the radioimmunoassay are the savings in cost and time. The radioenzymatic assay utilizes an expensive tritium-labeled compound, S-adenosylmethionine, and requires multiple organic solvent-extraction steps, thin-layer chromatography, and liquid scintillation counting. The radioimmunoassay requires only one extraction with alumina to aid in specificity and to concentrate the catecholamines. Sample detection is by gamma counting. The radioenzymatic assay is presently the reference method for catecholamines and is best suited for small numbers of samples where sample volume is limited and exquisite sensitivity is required. The radioimmunoassay is rapid, has sufficient sensitivity, specificity, and precision for most applications and is best applied to the analysis of large numbers of samples.
Fetal-perinatal catecholamine secretion: role in perinatal glucose homeostasis
Authors: Sperling M. A. , Ganguli S. , Leslie N. , Landt K.
Published: December 2017

Secretion of catecholamines may play an important role in several of the adaptations that characterize the transition from intra- to extrauterine life including cardiovascular, respiratory, and metabolic events, specifically the initiation of endogenous glucose production following curtailment of the transplancental maternal supply of glucose. Maturation of neural and enzymatic pathways involved in catecholamine secretion occurs late in gestation; fetal hypoxia can produce a 20- and 125-fold increase in plasma epinephrine (E) and norepinephrine (NE), respectively. Estimates of turnover (approximately 2,000 pg X kg-1 X min-1) and metabolic clearance rates (20-40 ml X kg-1 X min-1) indicate active secretion and metabolism of E from fetal sources with negligible transfer from the mother. Simultaneously, there is maturation of functional alpha- and beta-adrenergic receptors. At birth, plasma E and NE rise three- to tenfold; plasma levels are higher in hypoxic infants and lower in prematures. Concurrently, glucagon increases three- to fivefold; cortisol and growth hormone also are high, whereas insulin remains low and poorly responsive to stimuli; the number of glucagon receptors increases, whereas that of insulin decreases. Acting in concert these hormonal changes activate glycogenolysis, gluconeogenesis, lypolysis, and ketogenesis. Glucose production and gluconeogenesis, absent in utero, become evident within hours of birth in both humans and sheep. The spontaneous surge in catecholamine secretion at birth may be the key event because infusion of E or NE to fetal sheep in late gestation simulates the metabolic and hormonal profile of glucagon and insulin as well as glucose production that normally only occur with separation of the placenta.
Mechanisms of catecholamine effects on ketogenesis
Authors: Bahnsen M. , Burrin J. M. , Johnston D. G. , Pernet A. , Walker M. , Alberti K. G.
Published: December 2017

Ketogenesis may be controlled at several sites. Lipolysis with release of plasma nonesterified fatty acid (NEFA) substrate is the first step. Plasma NEFA are taken up by the liver in a concentration-dependent fashion and, after conversion to the acyl-CoA derivative, may either be reesterified or enter the mitochondria via the carnitine shuttle. After beta-oxidation the resultant acetyl-CoA may either be converted to ketone bodies that are then released into the circulation or be condensed with oxaloacetate and enter the tricarboxylic acid cycle, the third potential control point. In humans, infusion of epinephrine causes a transient two- to threefold increase in fatty acids, glycerol, and ketone bodies. Insulin levels show a small absolute increase. Norepinephrine has similar effects, although insulin levels tend to be suppressed and glucagon levels rise somewhat. If somatostatin is added simultaneously, the lipolytic and ketogenic effects are accentuated and prolonged. Dopamine, in a high dose, has no effect on ketone bodies alone but shows small increases in NEFA and ketone bodies in the presence of somatostatin and may play a modulatory role in ketogenesis. The ketogenic effect of catecholamines could thus be in the adipocyte or in the liver. Studies with perfused liver or hepatocytes showed only trivial effects on ketogenesis even with supraphysiological doses of catecholamines. Furthermore infusion studies in rats showed decreased rather than increased ketogenesis with no change in NEFA levels. The data suggest that a) there are species differences, and b) in humans epinephrine- and norepinephrine-induced increases in ketogenesis are secondary to increases in NEFA substrate supply.
Mediation of endotoxin-induced changes in zinc metabolism in rats
Authors: DiSilvestro R. A. , Cousins R. J.
Published: December 2017

A further characterization of endotoxin-induced changes in zinc metabolism provided insight into the possible mediation processes involved. Endotoxin reduced serum zinc levels while elevating zinc associated with hepatic metallothionein (Zn-MT) in control, fasted, and zinc-depleted rats. Unlike zinc, copper in the serum and that associated with metallothionein showed little response to endotoxin. In vitro translation of liver mRNA demonstrated that metallothionein mRNA levels were increased after endotoxin administration to either control or zinc-depleted rats. Cycloheximide fully blocked endotoxin-induced alterations in serum and metallothionein zinc, but actinomycin D was only partially inhibitory. Glucagon might act as the primary mediator for these actinomycin D-insensitive changes. Glucocorticoids might be responsible for the remaining alterations in zinc metabolism because dexamethasone increased 65Zn accumulation in cultured hepatocytes, whereas endotoxin did not. In endotoxin-treated rats, the kidney as well as liver showed increases in metallothionein-zinc and metallothionein-mRNA. Virtually all the effects of endotoxin were mimicked by leukocytic endogenous mediator, implying that it probably represents the initial mediator of endotoxin action on zinc metabolism.
Interaction between stimulus intensity and corticosteroid feedback in control of ACTH
Authors: Keller-Wood M. , Shinsako J. , Dallman M. F.
Published: December 2017

These studies were performed to examine the relationship between stimulus intensity and corticosteroid feedback on ACTH secretion. We have measured the ACTH responses in five dogs to each of three levels of hypoglycemia induced by injection of three doses of insulin after production of each of four levels of corticosteroid feedback induced by the infusion of saline or three rates of ACTH. Both the peak and integrated ACTH responses were related to the degree of hypoglycemia in saline-infused dogs (P less than 0.01). ACTH infusions did not affect the hypoglycemia induced by insulin; however, the lower two infusion rates (20 and 50 ng/min for 40 min) inhibited the peak ACTH responses to hypoglycemia by mean values of 45 and 75%, respectively, and the integrated ACTH responses by about 60 and 90%, respectively. The high infusion rate of ACTH (500 ng/min for 40 min) abolished the subsequent ACTH responses to hypoglycemia (103% inhibition). Therefore, the degree (%) of inhibition was the same for a given prior corticosteroid level at all intensities of hypoglycemia. The plasma ACTH response was a function of both stimulus intensity and prior corticosteroid levels and was proportional to the stimulus intensity divided by the feedback dose. Thus, corticosteroids exert a modulatory rather than a simple subtractive effect on the secretion of ACTH.
Metabolic effects of oral fructose in the liver of fasted rats
Authors: Niewoehner C. B. , Gilboe D. P. , Nuttall G. A. , Nuttall F. Q.
Published: December 2017

Twenty-four-hour-fasted rats were given fructose (4 g/kg) by gavage. Fructose absorption and the portal vein, aorta, and hepatic vein plasma fructose, glucose, lactate, and insulin concentrations as well as liver fructose and fructose 1-P, glucose, glucose 6-P, UDPglucose, lactate, pyruvate, ATP, ADP, AMP, inorganic phosphate (Pi), cAMP, and Mg2+, and glycogen synthase I and phosphorylase alpha were measured at 10, 20, 30, 40, 60 and 120 min after gavage. Liver and muscle glycogen and serum uric acid and triglycerides also were measured. Fifty-nine percent of the fructose was absorbed in 2 h. There were modest increases in plasma and hepatic fructose, glucose, and lactate and in plasma insulin. Concentrations in the portal vein, aorta, and hepatic vein plasma indicate rapid removal of fructose and lactate by the liver and a modest increase in production of glucose. The source of the increase in plasma lactate is uncertain. Hepatic glucose 6-P increased twofold; UDPglucose rose transiently and then decreased below the control level. Fructose 1-P increased linearly to a concentration of 3.3 mumol/g wet wt by 120 min. There was no change in ATP, ADP, AMP, cAMP, Pi, or Mg2+. Serum triglycerides and uric acid were unchanged. Glycogen synthase was activated by 20 min without a change in phosphorylase alpha. This occurred with a fructose dose that did not significantly increase either the liver glucose or fructose concentrations. Liver glycogen increased linearly after 20 min, and glycogen storage was equal in liver (38.4%) and muscle (36.5%).(ABSTRACT TRUNCATED AT 250 WORDS)
Pulsatile glucagon delivery enhances glucose production by perifused rat hepatocytes
Authors: Weigle D. S. , Koerker D. J. , Goodner C. J.
Published: December 2017

We have compared the effects of pulsatile and continuous glucagon administration on hepatocyte glucose production in order to clarify the physiological role of pulsatile hormone secretion. Two identical columns containing freshly isolated rat hepatocytes mixed with polyacrylamide gel beads were perifused with oxygenated tissue culture medium. A fixed total amount of glucagon was delivered to one column as a continuous 90-min infusion and to the other column as a series of six 3-min pulses. A 15-min interpulse interval was chosen in order to approximate the 10- to 12-min interval observed in primates while permitting the resolution of individual hepatocyte responses. With this protocol, the EC50 values for pulsatile and continuous glucagon administration were 186 +/- 41 and 884 +/- 190 (SD) pg/ml, respectively. For glucagon concentrations less than 1,000 pg/ml, pulsatile administration always led to greater hepatocyte glucose production than continuous administration (P = 0.008) and, in the dose range equivalent to concentrations in portal plasma, pulsed glucagon enhanced glucose production twofold. The data suggest that pulsatile secretion is the more efficient means for islet A cells to stimulate hepatic glucose production.
Reduced and S-carboxymethylated human growth hormone: a probe for diabetogenic action
Authors: Cameron C. M. , Kostyo J. L. , Rillema J. A. , Gennick S. E.
Published: December 2017

The biological activity profile of reduced and S-carboxymethylated human growth hormone (RCM-hGH) was determined to establish its suitability for study of the diabetogenic property of hGH. RCM-hGH was found to have greatly attenuated in vivo growth-promoting activity in the 9-day weight-gain test in hypophysectomized rats (approximately 1%) and to have a similar low order of in vitro activity in stimulating amino acid incorporation into the protein of the isolated rat diaphragm. RCM-hGH also only had approximately 1% of the in vitro insulin-like activity of the native hormone on isolated adipose tissue from hypophysectomized rats. In contrast, RCM-hGH retained substantial in vivo diabetogenic activity in the ob/ob mouse, appearing to have approximately 50% of the activity of the native hormone. RCM-hGH was also found to retain significant, although attenuated (25%), in vitro lactogenic activity when tested for the ability to stimulate amino acid incorporation into a casein-rich protein fraction in mouse mammary gland explants. Because RCM-hGH exhibits a high degree of diabetogenic activity, although lacking significant anabolic or insulin-like activities, it will be useful as a "monovalent" probe for the study of the molecular mechanism of the diabetogenic action of GH.
Prolactin stimulation of parathyroid hormone secretion in bovine parathyroid cells
Authors: Magliola L. , Forte L. R.
Published: December 2017

Previous studies have suggested that prolactin (PRL) may affect calcium (Ca) homeostasis by an action on vitamin D metabolism. In this study, the effects of PRL on parathyroid hormone (PTH) secretion were investigated in dispersed bovine parathyroid cells (PTC). PRL (0.013-1.3 microM) caused concentration-dependent increases in PTH secretion. PRL-stimulated PTH release was apparent as early as 1 h and was progressive thereafter for up to 3 h. PRL enhanced PTH release over a wide range of ambient Ca concentrations (0.5-2.0 microM). Ovine and rat PRL were more effective than bovine PRL in stimulating PTH secretion. This effect was apparently specific for PRL because neither ovine nor bovine growth hormone stimulated PTH secretion. PRL-stimulated PTH release was not mediated through the beta-adrenergic or dopaminergic receptor systems of PTC and was not associated with increased adenosine 3',5'-cyclic monophosphate (cAMP) levels. This study demonstrated a direct effect of PRL to stimulate PTH secretion in vitro. Although these data do not provide evidence for an effect of PRL in vivo, we suggest a mechanism by which PRL may influence parathyroid function and Ca homeostasis in the bovine species.
Mobilization of 45Ca from insulin-producing RINm5F cells attached to microcarriers
Authors: Abrahamsson H. , Berggren P. O. , Hellman B.
Published: December 2017

A technique was designed allowing studies of 45Ca efflux from insulin-releasing cells of a clonal cell line (RINm5F) attached to fibronectin-coated plastic beads. Supporting the existence of Ca2+-Ca2+ and Na+-Ca2+ exchange mechanisms, the efflux of 45Ca in a Ca2+-deficient perifusion medium was increased after introduction of Ca2+ and decreased after removal of Na+. The washout of radioactivity was similar to that from pancreatic islets in also being inhibited by glucose in the presence of low concentrations of extracellular Ca2+. During perifusion with a medium containing 2.56 mM Ca2+, increasing the K+ concentration resulted in an increased 45Ca efflux, a process counteracted by D-600. Also, exposure to tolbutamide resulted in a distinct stimulatory peak. Glucose was a poor stimulator of 45Ca efflux, suggesting that this sugar lacks the ability to depolarize the RINm5F cells sufficiently to induce normal opening of the voltage-dependent channels in the plasma membrane. Such a defect might well explain why the RINm5F cells do not respond to glucose with stimulation of insulin release.
Hepatic and extrahepatic lactate metabolism in sheep: effects of lactate loading and pH
Authors: Naylor J. M. , Kronfeld D. S. , Freeman D. E. , Richardson D.
Published: December 2017

Hepatic lactate metabolism was studied in five sheep receiving infusions of either lactic acid or sodium lactate using an arteriovenous difference technique. Hepatic uptake of lactate was a saturable process with second order (Michaelis-Menten) kinetics. Although lactic acid infusion decreased blood pH, hepatic saturation of lactate uptake occurred before changes in pH could influence hepatic lactate metabolism. The Vmax for hepatic lactate metabolism is 5.72 mmol X kg-0.75 X h-1 and the Km 3.06 mmol/l. These findings have therapeutic relevance. In acidosis, the hepatic response to therapeutic administration of sodium lactate during fluid therapy will be variable. If plasma lactate is low, lactated fluids may increase hepatic uptake and produce an alkalizing effect. If plasma lactate is already high, hepatic lactate metabolism is nearly saturated, and additional lactate will not produce a hepatic alkalizing response. Extrahepatic tissues switch from lactate production to lactate utilization under conditions of lactate loading. They remove more lactate than liver at high plasma lactate concentrations. Muscle may be important in lactate removal in certain types of exercise.
Transient development and function of rabbit corpora lutea after hypophysectomy
Authors: Yuh K. C. , Bill C. H. , Keyes P. L.
Published: December 2017

The requirement of the pituitary gland and the role of 17 beta-estradiol in the early development of the corpus luteum was investigated in rabbits hypophysectomized the day after sterile mating (day 1). Serum progesterone in hypophysectomized rabbits was normal for 2 days after hypophysectomy. Luteal tissue from hypophysectomized and sham-hypophysectomized rabbits had similar wet weight (4.0 +/- 0.4 vs. 5.3 +/- 0.2 mg/corpus luteum) and similar concentrations of available cytoplasmic estrogen receptor (1.2 +/- 0.2 vs. 1.5 +/- 0.3 fmol/micrograms DNA) and luteinizing hormone (LH) receptor (4.0 +/- 0.2 vs. 6.1 +/- 1.4 fmol/micrograms DNA) on day 4 of pseudopregnancy. Serum progesterone in hypophysectomized rabbits began to decline on day 4 and was undetectable by day 6. Estrogen receptor and luteal weight in hypophysectomized animals also declined after day 4 to low values by day 6, and serum estradiol was undetectable. However, if estradiol was administered by Silastic capsule implanted subcutaneously at the time of hypophysectomy or 3 days after hypophysectomy, serum progesterone, luteal weight, estrogen receptor, and LH receptor were maintained on day 6 of pseudopregnancy. These results indicate that after a preovulatory gonadotropin surge, the function of newly formed corpora lutea is normal for 3–4 days in the absence of pituitary hormones. However, by 4 days after ovulation, estradiol is required to sustain the structural and functional integrity of corpora lutea.
How laboratory dogs accommodate meals of different size but similar composition
Authors: Nomura M. , Greenberg G. R. , Bahoric A. , Zinman B. , Albisser A. M.
Published: December 2017

Healthy laboratory dogs appear to absorb a mixed meal from the gut at a constant rate. This rate is apparently not affected by meal size. If this is the case, then duration of absorption should depend on total or integrated meal size, whereas metabolite and hormonal levels would be independent of the number of feedings. To explore these hypotheses further, we compared the metabolite and hormonal responses with a single mixed meal and one divided in two halves, provided in two feedings 4 h apart. We detected no effect of the second meal in the metabolic response levels of glucose, lactate, pyruvate, alanine, free fatty acids, or 3-hydroxybutyrate or the hormonal responses of insulin, pancretic glucagon, gastrin, or secretin. Only minor differences were detectable in the hormonal response levels of pancreatic polypeptide, gastric inhibitory peptide, and enteroglucagon, consistent with a response to a second meal. We conclude that the observed change in circulating metabolite or hormone concentration is independent of the size of meal eaten, but the duration of the excursion depends on meal size. Thus, during the bulk phase of nutrient uptake, the absorption mechanism of the laboratory dog appears to be saturated.
Blood glucose homeostasis in rats with a deficiency of liver phosphorylase kinase
Authors: Conaglen J. C. , Williams A. B. , Malthus R. S. , Glover D. , Sneyd J. G.
Published: December 2017

The glycogen storage disorder (gsd/gsd) rat has little or no phosphorylase kinase activity in the liver and is unable to break down liver glycogen on fasting. Nevertheless, gsd/gsd rats do not become hypoglycaemic on fasting. Gsd/gsd rats showed a decreased rate of glucose turnover measured with [6-3H]glucose. Perfused livers from gsd/gsd rats showed decreased rates of gluconeogenesis from lactate and alanine when the results were expressed per gram of liver, but the total glucose produced per liver was normal. Measurement of gluconeogenesis in vivo using [14C]-bicarbonate showed that gsd/gsd rats had a decreased rate of glucose production from substrates that enter the gluconeogenic pathway before pyruvate. We conclude that gsd/gsd rats have adapted to unavailability of liver glycogen by decreasing peripheral uptake of glucose and not by increasing gluconeogenesis.