bluuebunny/crossref_metadata_2025 huggingface dataset:
Somatomedin C/insulinlike growth factor I during liver regeneration in the rat
Authors: Russell W. E. , D'Ercole A. J. , Underwood L. E.
Published: December 2017

We measured immunoreactive somatomedin C/insulinlike growth factor I (Sm C/IGF I) in blood and tissues of rats following partial hepatectomy (PH) to determine a possible regulatory role for this growth factor in liver regeneration. From a mean value of 0.66 U/ml +/- 0.19 before PH, the serum Sm C/IGF I rose to 1.09 +/- 0.08 1 h after PH [P less than 0.001 vs. sham-hepatectomized (SH) values]. Concurrently there was a twofold rise in serum aspartate aminotransferase, suggesting that the rise in Sm C/IGF I may be the result of hepatocellular injury rather than a specific secretory event. In the subsequent 22 h, serum Sm C/IGF I of PH rats fell to 0.31 +/- 0.06 U/ml, compared with 0.73 +/- 0.03 in SH rats. During this time, liver concentrations of the peptide declined to 30% of basal, whereas lung and kidney fell to only approximately 60% of basal. As the Sm C/IGF I declined, hepatic DNA synthesis increased 10-fold in PH animals. Our results, therefore, do not support a mitogenic role for Sm C/IGF I in the regulation of liver regulation. Food consumption was markedly depressed in the 22 h after PH (20.8 +/- 2.6 vs. 4.33 +/- 2.9 g/day; P less than 0.001). PH and pair-fed SH rats had serum Sm C/IGF I concentrations that were indistinguishable (0.31 +/- 0.06 vs. 0.35 +/- 0.11 U/ml), although liver tissue concentrations were lower in PH rats (0.04 +/- 0.01 U/g vs. 0.07 +/- 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)
Clearance and metabolism of glandular kallikrein in the rat
Authors: Rabito S. F. , Seto M. , Maitra S. R. , Carretero O. A.
Published: December 2017

This study was undertaken to characterize the clearance of circulating rat glandular kallikrein and to determine the contribution of various organs and the urinary excretion to the removal of glandular kallikrein from the bloodstream. We injected either active 125I-kallikrein or kallikrein inactivated with phenylmethylsulfonyl fluoride (125I-PMSF-kallikrein) intravenously into intact or nephrectomized rats and then studied the disappearance rate of trichloroacetic acid (TCA)-precipitable radioactivity from the circulation. Inactivation by PMSF markedly reduced the binding of kallikrein to plasma protease inhibitors. The removal rate of the acid-precipitable radioactivity fit a biexponential curve for both active and inactive kallikrein. In the intact rats approximately 50% of the radioactivity was removed from the circulation 30 min after the injection of active 125I-kallikrein. Removal of the kidneys did not significantly affect the clearance of active kallikrein. On the other hand, inactive 125I-PMSF-kallikrein was removed from blood faster than active 125I-kallikrein in normal animals. Approximately 50% of the radioactivity was removed from the circulation 8 min after the injection, and the half-life of inactive 125I-PMSF-kallikrein was markedly prolonged by bilateral nephrectomy. Active 125I-kallikrein was taken up by tissues, particularly the liver and the kidney. In urine, less than 2% of the radioactivity was excreted in 60 min as TCA-precipitable material. We concluded that glandular kallikrein is cleared rapidly from the circulation of the rat, probably in the form of a complex with a plasma protease inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)
Ketone body metabolism in normal and diabetic human skeletal muscle
Authors: Nosadini R. , Avogaro A. , Sacca L. , Vigorito C. , de Kreutzenberg S. , Cobelli C. , Toffolo G. , Trevisan R. , Tessari P. , Tiengo A. , et al.
Published: December 2017

Although the liver is considered the major source of ketone bodies (KB) in humans, these compounds may also be formed by nonhepatic tissues. To study this aspect further, 3-[14C]hydroxybutyrate (BOH) or [3-14C]acetoacetate (AcAc) were constantly infused after a priming dose and contemporaneous arterial and venous samples were taken at splanchnic, heart, kidney, and leg sites in eight normal subjects (N) undergoing diagnostic catheterization and at the forearm site in five normal and six ketotic diabetic (D) subjects. After 70 min of infusion, tracer and tracee levels of AcAc and BOH reached a steady state in the artery and vein in both normal and diabetic subjects. The venous-arterial (V-A) difference at the forearm step for cold KB was negligible both in normal and diabetic subjects, whereas for labeled KB it was approximately 10-fold higher in diabetic subjects (V-A AcAc, -31 +/- 7 and -270 +/- 34 dpm/ml in N and D, respectively; V-A BOH, -38 +/- 6 and -344 +/- 126 dpm/ml in N and D, respectively). We assumed that the V-A difference in tracer concentration was consistent with dilution of the tracer by newly synthesized tracee inside the muscle and calculated that the forearm muscle produces KB at a rate of 16.2 +/- 3.3 mumol/min in D and 0.9 +/- 0.9 mumol/min in N. These findings can be accounted for by the hypothesis that the disappearance flux of KB from circulation was replaced by an equivalent flux of KB entering the vein at the muscle step in D but not in N. Moreover, in N KB were not only produced but also utilized by the splanchnic area (39 +/- 9 mumol/min).(ABSTRACT TRUNCATED AT 250 WORDS)
Cardiovascular responses to parathyroid hormone
Authors: Crass M. F. , Moore P. L. , Strickland M. L. , Pang P. K. , Citak M. S.
Published: December 2017

The synthetic amino terminal fragment of parathyroid hormone, PTH-(1-34), is a potent coronary artery vasodilator in the dog. In the present study, using instrumented open-chest dogs, we have performed the initial characterization of this effect and showed other dose-related cardiovascular effects of the hormone. A near-maximal flow response was obtained after intracoronary injection of 0.024 nmol X kg-1 PTH-(1-34) with minor, if any, concomitant changes in mean blood pressure, contractile force, or heart rate. At higher doses, mean blood pressure decreased while contractile force and heart rate increased in dose-dependent fashion. Infusion of PTH-(1-34) for 20 min showed that the vasodilatory effect could be sustained without a concomitant decrease in mean arterial pressure. Pharmacological characterization showed for the first time that the coronary response to PTH-(1-34) was unaltered in the presence of beta- or alpha-adrenergic, muscarinic, or histaminergic blockades. We conclude that PTH-(1-34), an endogenous circulating calcemic peptide, produces a large increase in coronary blood flow at doses sufficiently low to preclude complicating effects on blood pressure, contractile force, and heart rate. Furthermore, the results suggest that the vasodilatory effects may be specific.
Responses and molecular heterogeneity of IR-GIP after intraduodenal glucose and fat
Authors: Krarup T. , Holst J. J. , Larsen K. L.
Published: December 2017

The plasma responses and molecular heterogeneity of human immunoreactive gastric inhibitory polypeptide (IR-GIP) after intraduodenal administration of equicaloric amounts of glucose (25 g) and fat (10 g) were determined with five different antisera. Two of these do not cross-react with 8 kdaltons (kDa) IR-GIP. In the fasting state plasma IR-GIP concentrations were highest measured with antisera, which detected both 5 and 8 kDa IR-GIP. The total integrated or incremental IR-GIP areas were similar after glucose and fat when determined with the same antiserum. When antisera with similar cross-reactivity with human 5 kDa IR-GIP were compared, no difference in incremental IR-GIP areas after either stimulus was found between antisera that did and did not measure 8 kDa IR-GIP. Gel filtration of plasma showed a consistent increase in 5 kDa IR-GIP 60 min after both glucose and fat but small and inconsistent changes in 8 kDa IR-GIP. Thus fat on a weight and molar basis is more potent than glucose in releasing IR-GIP. Both fat and glucose release predominantly the 5 kDa IR-GIP. Although of importance for the absolute IR-GIP level in plasma, 8 kDa IR-GIP contributes little to the increase in IR-GIP after both stimuli.
Absence of albumin receptor on brain capillaries in vivo or in vitro
Authors: Pardridge W. M. , Eisenberg J. , Cefalu W. T.
Published: December 2017

Hormones and drugs are known to be available for transport into brain and liver in vivo from the circulating albumin-bound pool. An albumin receptor-mediated mechanism is one possible way in which the transport of ligands from the circulating albumin-bound pool into the tissue may be catalyzed. The albumin receptor model was tested for brain in the present studies using both 125I-albumin (labeled by lactoperoxidase) and [3H]albumin (labeled by reductive methylation). The interaction of the labeled albumin with brain capillaries was assessed in vivo with the carotid injection technique in rats and in vitro with isolated bovine brain capillaries. Artifactually high nonspecific binding in both the in vivo and in vitro assays was observed with 125I-albumin. Conversely, the transit time of [3H]albumin through the brain capillaries in vivo was no greater than the transit time of [14C]sucrose. The binding of [3H]albumin to isolated microvessels in vitro was low, less than [3H]inulin and was nonsaturable. In conclusion these studies do not support the albumin receptor model for the transport of albumin-bound ligands into tissues such as brain.
Metabolic changes during maturation of male monkeys: possible signals for onset of puberty
Authors: Cameron J. L. , Koerker D. J. , Steiner R. A.
Published: December 2017

There is a close relationship between the metabolic status of a maturing animal and the timing of puberty onset. However, the signals linking metabolic status to the maturation of the reproductive axis remain unknown. We looked for metabolic differences before and after puberty by comparing plasma profiles of insulin, glucose, amino acids, beta-hydroxybutyrate, and glycerol between juvenile and adult monkeys in fed and fasted states. Thirteen juvenile and 13 adult male crab-eating macaques (Macaca fascicularis) were fed a mixed meal, and blood samples were collected at intervals between 1.5 and 52 h after the meal. Plasma insulin concentrations decreased in a similar manner in both groups during the first 16 h of fasting. By 20 h after a meal, basal insulin levels were significantly lower (P less than 0.025) in juveniles compared with adults and remained so until the end of the fast. Circulating levels of glucose were similar in juveniles and adults immediately after a meal and then decreased significantly (P less than 0.025) in juveniles by 28 h of fasting and in adults by 52 h of fasting. Plasma concentrations of all large neutral amino acids (i.e., tyrosine, tryptophan, phenylalanine, valine, leucine, and isoleucine, LNAA) except tryptophan decreased more precipitously in juveniles than in adults during the first 20 h of fasting. However, the ratios of tyrosine to other LNAA and tryptophan to other LNAA were similar in juveniles and adults at all times. beta-Hydroxybutyrate concentrations were low in both groups until 24 h after a meal, at which time plasma levels increased more rapidly and attained higher values in juveniles compared with adults.(ABSTRACT TRUNCATED AT 250 WORDS)
Theoretical basis for a new in vivo radioreceptor assay for polypeptide hormones
Authors: Whitcomb D. C. , O'Dorisio T. M. , Cataland S. , Nishikawara M. T.
Published: December 2017

To date the in vivo identification and quantitation of specific hormone receptors has been difficult, time consuming, and lacking in sensitivity. We present the theory underlying a new in vivo radioreceptor assay for polypeptide hormones based on receptor theory derived from in vitro investigations and in vivo kinetic and autoradiographic studies. The assay was developed from a tissue model and a theory of hormone distribution. Measuring the labeled hormone distributed between the plasma and interstitial space in the presence or absence of excess unlabeled hormone permits the accurate determination of hormone specifically bound to receptors. This approach eliminates the problem of nonspecific binding due to free tracer, hormone degradation products, or labeled non-hormone molecules. A receptor compartment and specific binding of hormone are calculated from only four measured parameters: total tissue labeled hormone, tissue albumin, plasma labeled hormone, and plasma albumin. The method is applicable to most tissues and hormones under a variety of conditions and permits simultaneous comparison of multiple tissues in the same animal under identical conditions.
Vasoactive intestinal peptide inhibits insulin-stimulated glucose transport in rat adipocytes
Authors: Green A. , Alvarez I. M. , Misbin R. I.
Published: December 2017

Patients with tumors secreting vasoactive intestinal peptide (VIP) often develop hyperglycemia and glucose intolerance. Although VIP has been reported to increase glucose output by the liver, the concentration required for this effect greatly exceeds that observed clinically. We therefore investigated the effects of VIP on insulin-stimulated glucose transport in isolated adipocytes. Inhibition of insulin action was observed at a concentration of 1 ng/ml VIP with half-maximal inhibition at approximately 20 ng/ml. 125I-VIP bound to specific high-affinity sites on the adipocytes. Fifty percent inhibition of binding occurred at a concentration of unlabeled VIP of approximately 10 ng/ml and was not affected by insulin, glucagon, or growth hormone. As we have observed previously with glucagon and catecholamines, inhibition of insulin action by VIP was observed only when accumulation of adenosine in the incubation medium was prevented by addition of adenosine deaminase. Under these conditions VIP markedly increased cellular cAMP levels. A good correlation was observed among VIP binding, inhibition of insulin-stimulated glucose transport, and cellular concentrations of cAMP. The results suggest that inhibition of insulin action in adipose tissue contributes to the hyperglycemic effect of VIP. Together, with our published findings on glucagon and catecholamines, these results support the hypothesis that counterregulatory hormones inhibit insulin action by increasing cellular concentrations of cAMP.
Renal cAMP and 1,25(OH)2D3 synthesis in estrogen-treated chick embryos and hens
Authors: Martz A. , Forte L. R. , Langeluttig S. G.
Published: December 2017

Onset of sexual maturity in female chickens or administration of estrogen to mature males or to juveniles of either sex results in increased parathyroid hormone (PTH)-dependent adenylate cyclase activity and increased 25-hydroxyvitamin D3-1-hydroxylase activity in kidney. The relationship between estrogen-mediated alterations of these two enzyme systems was investigated in embryonic and mature, egg-laying chickens treated in vivo with 17 beta-estradiol (E2). Basal and PTH- and forskolin-stimulated adenylate cyclase activity in kidney plasma membrane preparations was not affected by E2 treatment of 19-day-old chick embryos or of 41-wk-old egg-laying females. High, possibly maximal, levels of catalytic activity in control embryos and hens may have precluded further stimulation by E2. In contrast, E2 significantly enhanced 25-hydroxyvitamin D3-1-hydroxylase activity of embryonic kidney up to 10-fold (P less than 0.005). In mature females, E2 caused cessation of egg laying accompanied by a significant reduction (P less than 0.005) of 25-hydroxyvitamin D3-1-hydroxylase activity. These results indicate that the PTH-dependent adenylate cyclase and the 25-hydroxyvitamin D3-1-hydroxylase systems of avian kidney can be regulated independently and suggest that factors in addition to estrogen are involved in their regulation.
Pituitary and adrenal hormone responses to naloxone in euhydrated and dehydrated dogs
Authors: Wade C. E.
Published: December 2017

To assess the role of endogenous opioids in the secretion of pituitary and adrenal hormones, we injected intravenously the antagonist naloxone (1 mg/kg) into six dogs, euhydrated or dehydrated. Plasma renin activity (PRA), osmolality, and concentrations of adrenocorticotropic hormone (ACTH), cortisol, aldosterone, vasopressin, Na+, and K+ were measured. Dehydration elevated (P less than 0.05) PRA, vasopressin, osmolality, and Na+. Thirty minutes after injection of naloxone, osmolality, Na+, K+, hematocrit, and plasma protein were not altered. Naloxone-induced elevations of ACTH (25 +/- 10 and 22 +/- 4 pg/ml) and cortisol (4.8 +/- 1.0 and 5.1 +/- 1.0 micrograms/dl) were similar during euhydration and dehydration, respectively. The increase in aldosterone due to naloxone was greater after euhydration (7.7 +/- 3 ng/dl) than during dehydration (2.3 +/- 0.8 ng/dl). Naloxone increased vasopressin by (5.3 +/- 2.8 microU/ml) during dehydration but not during euhydration. Intravenous hypertonic saline infusions showed that naloxone potentiates the osmotic release of vasopressin. Our results indicated that dehydration did not alter the inhibitory role of opioids in regulation of ACTH and cortisol but suppressed the inhibition of aldosterone secretion. Our findings also showed that opioids inhibit secretion of vasopressin during dehydration by decreased responsiveness to osmotic stimulation.
Rat lung metabolism after 3 days of continuous exposure to 0.6 ppm ozone
Authors: Bassett D. J. , Bowen-Kelly E.
Published: December 2017

Continuous exposure of rats to low concentrations of ozone has previously been associated with enhanced metabolic enzyme activities, when measured in lung homogenates. In this study, metabolic rates were measured in intact perfused lungs with altered pathology brought about by 3 days continuous exposure to 0.6 ppm ozone. Increased metabolism of ozone-exposed lungs was indicated by a twofold enhancement in glucose utilization, associated with a 62% increase in lactate formation and a 166% increase in the rate of 14CO2 production from D-[U-14C]glucose from control values of 5.2 +/- 0.5 mumol lactate and 4.4 +/- 0.6 mumol 14CO2/h per lung (+/- SE, n = 4), respectively. Mitochondrial metabolism was separately assessed by measurements of 14CO2 production from [U-14C]-pyruvate, which was found not to be significantly altered by ozone exposure, although homogenate oxygen uptake in the presence of succinate was significantly enhanced by 57%. These changes in intermediary metabolism could be correlated with increased glucose carbon incorporation into lipid and elevated activity of glucose-6-phosphate dehydrogenase. The observed elevated metabolic rates were consistent with the energy and synthetic needs of a lung during repair of ozone-induced damage.
Insulin processing by cultured hepatocytes
Authors: Blackard W. G. , Smith R. M. , Jarett L.
Published: December 2017

The chloroquine-sensitive and chloroquine-insensitive steps in insulin degradation by cultured hepatocytes have been explored by employing low temperature to retard processing. Under standard conditions (90 min association and 60 min dissociation) chloroquine inhibited insulin degradation at 15 degrees C but not at 37 degrees C. However, if the association and dissociation periods were short so that only early degradation was examined, marked inhibition of insulin degradation by chloroquine could also be observed at 37 degrees C. This inhibitory effect was observed only during the first 15 min, being masked by increased insulin degradation subsequently. An increase in slowly dissociable insulin, as well as a twofold increase in volume density of multivesicular bodies (MVB), occurred in the presence of chloroquine at both 37 and 15 degrees C. Rapid insulin processing from the slowly dissociable compartment at 37 degrees C masked chloroquine's effect on insulin processing under usual conditions at that temperature. At physiological temperature the chloroquine-sensitive step is not obligatory for insulin degradation by hepatocytes.
Effect of valinomycin on thyroid iodide transport and TSH-stimulated cAMP formation
Authors: Sherwin J. R. , Seaford J. W.
Published: December 2017

The K+ ionophore valinomycin, in concentrations as low as 0.1 microM, induces an inhibition of thyroid-stimulating hormone (TSH)-stimulated cAMP formation in cat and pig thyroid slices and isolated, trypsin-collagenase-dispersed beef thyroid cells. Valinomycin was also shown to inhibit histamine and prostaglandin E1 stimulation of thyroid cAMP formation. The inhibitory effect of valinomycin could be partially overcome by elevated (81 mM) K+ concentrations. In the absence of valinomycin, the ability of TSH to stimulate thyroid cAMP formation was dependent on extracellular K+. Chronic removal or addition of K+ to medium bathing thyroid sections was accompanied by inhibition of TSH-stimulated cAMP formation. Maximum TSH stimulation was observed at an extracellular K+ of 2.7 mM. Valinomycin had no significant effect on thyroid ATP content but did reduce the ATP-to-ADP ratio. However, chronic removal of K+ had no effect on either ATP or the ATP-to-ADP ratio. Varying extracellular Na+ from 26 to 144 mM or addition of tetrodotoxin did not affect TSH action. Valinomycin addition to thyroid slices was associated with a reduction in iodide transport as measured by the ratio of tissue to extracellular iodide concentrations. The effect of valinomycin on iodide transport was accompanied by an increase in iodide efflux that was not greater than that observed with perchlorate ion, suggesting a reduced recirculation of released iodide in valinomycin-treated tissue. These findings suggest that alterations in thyroid cell K+ permeability or intracellular K+ concentration may be accompanied by changes in TSH-induced stimulation of thyroid cAMP formation.
Insulin resistance in acromegaly: defects in both hepatic and extrahepatic insulin action
Authors: Hansen I. , Tsalikian E. , Beaufrere B. , Gerich J. , Haymond M. , Rizza R.
Published: December 2017

Short-term growth hormone excess is associated with impaired hepatic and extrahepatic responses to insulin in the absence of a change in insulin binding. To determine whether similar defects occur after chronic growth hormone excess, insulin dose-response curves for stimulation of glucose utilization and suppression of glucose production and monocyte and erythrocyte insulin binding were determined in five acromegalic patients and six healthy volunteers of comparable age, sex, and obesity. During infusion of insulin, glucose infusion rates required to maintain euglycemia were significantly lower (P less than 0.02 all) in the acromegalic patients than in the control subjects. Suppression of glucose production was impaired in the acromegalic subjects at insulin concentrations in the physiological range but not at insulin concentrations in the supraphysiological range. In contrast stimulation of glucose utilization was decreased in the acromegalic subjects at both physiological and supraphysiological insulin concentrations. Neither monocyte nor erythrocyte insulin binding differed significantly in the acromegalic and control subjects. These data indicate that chronic growth hormone excess is associated with a defect in both hepatic and extrahepatic insulin action. The decrease in glucose utilization at supraphysiological insulin concentrations in the acromegalic subjects and the normal monocyte and erythrocyte insulin binding suggest a postbinding alteration in insulin action.
Response to glucose infusion in humans: role of changes in insulin concentration
Authors: Wolfe R. R. , Shaw J. H. , Jahoor F. , Herndon D. N. , Wolfe M. H.
Published: December 2017

We have used the primed-constant infusion of stable isotopes of glucose ([6,6-d2]glucose), alanine([3-13C] alanine), and urea ([15N2]urea) to investigate their kinetic interrelationships in normal volunteers in the postabsorptive state and during the infusion of unlabeled glucose at two rates. Each glucose infusion was tested with and without the simultaneous infusion of somatostatin (S), insulin (I), and glucagon (G) to clamp those hormonal levels. When glucose was infused at 1 mg X kg-1 X min-1, endogenous glucose production was suppressed almost exactly 1 mg X kg-1 X min-1, regardless of whether S plus I plus G were infused. The 4 mg X kg-1 X min-1 glucose infusion suppressed endogenous glucose production, both with and without hormonal control. The plasma concentration of glucose also increased to the same extent during the 4 mg X kg-1 X min-1 infusion in both protocols, which indicated that the spontaneous insulin response to the glucose infusion (an increase from 11 +/- 2 to 24 +/- 3 microU/ml) did not stimulate the peripheral clearance of glucose. The high rate of glucose infusion, both with or without hormonal control, stimulated alanine flux and inhibited urea production. These results indicate that glucose, per se, is an important direct controller of normal metabolic interactions of endogenous alanine, glucose, and urea kinetics.
Correction by insulin of disturbed TG-rich LP metabolism in rats with chronic renal failure
Authors: Roullet J. B. , Lacour B. , Yvert J. P. , Drueke T.
Published: December 2017

To define the role of insulin in lipid disturbances of chronic renal failure, chronically uremic rats (U+) were supplemented by continuous insulin infusion over a 35-day experimental period and compared with control ad libitum-fed rats (C) and uremic rats without insulin (U). Uremic rats were characterized by hypoinsulinemia, an increase in both circulating very low-density lipoprotein (VLDL) and their cholesterol concentration, a normal hepatic triglyceride secretion rate (TGSR) determined with Triton WR 1339, and a low adipose tissue lipoprotein lipase (LPL) activity. Chronic insulin infusion at low rate (0.5 IU/24 h) to U+ rats normalized serum insulin (from 17.0 +/- 0.6 mU/l in U rats to 23.4 +/- 1.7 mU/l in U+ rats), serum VLDL triglycerides (from 804 +/- 65 to 410 +/- 36 mg/l), and serum VLDL cholesterol (from 43 +/- 8 to 16 +/- 3 mg/l). Hepatic TGSR decreased significantly after insulin treatment (from 0.58 +/- 0.03 to 0.44 +/- 0.03 mumol/min). Moreover, adipose tissue LPL was restored to normal by insulin supplementation (from 460 +/- 60 to 860 +/- 150 mU per total epididymal fat in U and U+ rats, respectively). Correction of the disturbed VLDL metabolism was associated with multiple actions of insulin including 1) a decrease of peripheral lipolysis, 2) a decrease of hepatic TGSR, and 3) an increase of adipose tissue LPL activity. Because cholesterol-rich VLDL are potentially atherogenic, their normalization with insulin treatment in this animal model suggests a viable area of investigation for the prevention of accelerated atherogenesis in chronic renal failure.
Oxygen cost of twitch and tetanic isometric contractions of rat skeletal muscle
Authors: Hood D. A. , Gorski J. , Terjung R. L.
Published: December 2017

The distal muscles of a rat single hindlimb preparation, perfused at 14-15 ml/min, were stimulated sequentially for 10-min intervals at 12, 24, 36, 48, 60, 75, and 120 twitch/min (8 V, 0.05 ms) or at 7.5, 15, 30, 45, 60, 75, and 90 tetani/min (100-ms train, 100 Hz). Oxygen consumption (VO2) of the whole muscle increased up to 6- and 10-fold over rest during twitch and tetanic conditions, respectively. Tension development during each stimulation interval decreased sequentially at the higher contraction frequencies. VO2, corrected for this loss in tension development, increased linearly with contraction frequency with a slope of 0.037 +/- 0.003 mumol O2 X g-1 X twitch contraction-1 and 0.260 +/- 0.034 mumol O2 X g-1 X tetanic contraction-1. This sevenfold difference in slopes, which represent the O2 cost of a single contraction without fatigue, corresponds to the difference in developed tension between twitch and tetanic contractions. Anaerobic metabolism was negligible during tetanic contractions, but was significant during some twitch conditions. These values probably represent the O2 cost for fast-twitch muscle, since this is the predominant type (greater than 90%) in the rat hindlimb. However, an approximate fourfold difference in blood flow (determined with microspheres) between the white and red gastrocnemius sections (predominantly fast-twitch white and fast-twitch red, respectively) suggested a disparity in metabolic response. Estimates of the peak VO2 for each fiber type, for our perfusion conditions, are 6- and 30-fold above rest, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of interorganal glutamine flow in metabolic acidosis
Authors: Welbourne T. C. , Phromphetcharat V. , Givens G. , Joshi S.
Published: December 2017

Metabolic acidosis redirects interorgan glutamine flow from hepatic utilization to renal ammoniagenesis at the expense of ureagenesis. The roles of arterial glutamine load and organ glutaminase capacity in the regulation of glutamine balance across the gut, liver, and kidneys were studied in control and chronically acidotic rats. In control rats these organs combined to remove 733 nmol glutamine X min-1 X 100 g-1 in agreement with their respective glutaminase content, gut greater than liver greater than kidneys. In chronic metabolic acidosis renal glutamine extraction alone increased to 1,158 nmol X min-1 X 100 g-1 associated with an increased glutaminase capacity. However, the total glutamine deficit across these organs rose to only 1,043 nmol glutamine consumed X min-1 X 100 g-1 as a consequence of hepatic glutamine uptake reversing to net release. This reversal was not dependent on increased hepatic glutamine synthetase capacity, but rather appears to be dependent on the combined effect of reduced portal venous glutamine load and increased ammonia load. The reduction in portal glutamine load is, in turn, a consequence of renal glutamine extraction and reduced arterial glutamine concentration in metabolic acidosis as well as maintained gut glutamine extraction. Elevating arterial glutamine concentration in metabolic acidosis has no effect on renal uptake, but enhances splanchnic bed extraction with the restoration of ureagenesis. Thus the interorgan flow of glutamine and deposition of N into either urea or ammonia appears to be dependent on arterial glutamine concentration and hence glutamine availability in chronic metabolic acidosis in the rat.
Pituitary-dependent and -independent secretion of CS caused by bacterial endotoxin in rats
Authors: Suzuki S. , Oh C. , Nakano K.
Published: December 2017

Injection of bacterial endotoxin [lipopolysaccharide (LPS)] or immobilization stress increased serum levels of ACTH with a concomitant increase in the levels or corticosterone (CS) of rats. LPS also caused a significant increase in the serum CS levels of hypophysectomized rats. In contrast, immobilization stress-induced CS release was abolished completely in these rats. Injection of histamine, a possible mediator of LPS-induced CS secretion, provoked a significant increase in the serum CS levels of hypophysectomized rats. Neither histamine nor LPS had any appreciable effect on production or release of CS by cultured adrenal cells. These results suggest that LPS-induced CS secretion is largely dependent on hypophysial ACTH release but it also depends, in part, on an extrapituitary mechanism and that the LPS-induced pituitary-independent secretion of CS is mediated by histamine produced in the peripheral tissues. On the other hand, stress-provoked CS secretion is absolutely dependent on the pituitary-adrenocortical system.
Rapid effects of insulin on in vitro translational activity of specific mRNA in diabetic rat heart
Authors: Shanker R. , Neeley W. E. , Dillmann W. H.
Published: December 2017

We studied the time course of response of specific cardiac mRNA after administration of insulin to diabetic rats. The primary aim was to identify specific cardiac mRNA, which show a rapid response to insulin administration. Diabetic rats were injected with 2 U of regular insulin intravenously, and total cardiac RNA was prepared 0.5, 1.5, 3, 5, 12, and 24 h later. RNA was translated in vitro in the presence of [35S]methionine and the translational products separated by two-dimensional electrophoresis and quantitated by digital matrix photometry. A rapid change in the translational activity of five specific mRNA species was observed within 0.5 h after administration of insulin to the diabetic animal. One translational product exhibits a more delayed response at 1.5 h. The predominance of three of these products was increased, while that of three was decreased. Two specific mRNA coding for translation products designated as spots 97 and 106 show the most significant change, with a dramatic decrease of 15-fold and 6.5-fold, respectively, within 0.5 h after insulin administration. The change in levels of these specific mRNA species could result from effects of insulin at various sites of mRNA synthesis or degradation. However, the rapidity of the response is compatible with a direct effect of insulin on gene expression. The very quick response of these specific mRNA species to insulin could thus serve as a useful model system to examine the molecular mechanisms of insulin action in the heart.
Oscillations enhance the efficiency and stability of glucose disposal
Authors: Marsh B. D. , Marsh D. J. , Bergman R. N.
Published: December 2017

Oscillations in plasma concentrations of glucose and insulin as well as the rates of glucose disposal by liver and periphery have been observed in dogs during states of net glucose anabolism. To examine whether the existence of oscillations is important for efficient disposal of nutrients, we compared constant glucose infusion (with plasma glucose and insulin oscillations) to experiments in which glucose oscillations were suppressed using the glucose clamp. Mean glucose levels attained were the same for the two protocols (142 +/- 2 for constant glucose infusion at 10.8 +/- 0.4 mg X kg-1 X min-1, 144 +/- 1 mg/dl for clamps, P = 0.35). Despite matched mean glucose, integrated plasma insulin was 36.3 +/- 3.2 mU X ml-1 X 600 min in controls but higher in clamps (53.8 +/- 9.1 mU X ml-1 X 600 min, P = 0.017). Despite 48% higher insulin, total glucose disposed during the 10-h clamps was not greater than during constant glucose infusion (clamps, 162.1 +/- 10.7 g/600 min; infusions, 154.4 +/- 7.5 g/600 min; P = 0.19). These studies demonstrate that the presence of coordinated oscillations in glucose and insulin, during glucose infusion, are associated with more efficient disposal of glucose than when oscillations are suppressed. The results suggest that oscillations may play an important role in the efficient disposal of administered nutrient and may be an important component of normal glucose tolerance.
Desensitization and redistribution of beta-adrenergic receptors on human mononuclear leukocytes
Authors: Motulsky H. J. , Cunningham E. M. , DeBlasi A. , Insel P. A.
Published: December 2017

We have used intact human mononuclear leukocytes (MNL) to examine desensitization of beta-adrenergic receptors in normal mammalian cells. MNL were prepared and radioligand binding experiments were performed at 4 degrees C. At this temperature the ligand [125I]iodocyanopindolol ([125I]ICYP) identified the same number of receptors as at 37 degrees C, and the agonist isoproterenol competed for this binding with high affinity (dissociation constant, Ki = 20 nM). At 37 degrees C, results were similar when the binding incubation was terminated after 1 min, but the apparent affinity of the receptors for isoproterenol was several 100-fold lower when the incubation was allowed to reach steady state. In desensitized MNL (prepared by incubating whole blood with 10 microM isoproterenol at 37 degrees C for 10 min, and then isolating and washing the MNL at 4 degrees C), isoproterenol-stimulated cAMP accumulation was reduced 63 +/- 4%. After desensitization, the total number of beta-receptors was unchanged, but isoproterenol and the hydrophilic antagonist CGP-12177 were able to compete with [125I]ICYP for binding to only 18 +/- 6% of these sites. Direct binding with [3H]CGP-12177 yielded similar results. These results demonstrate that isoproterenol promotes a rapid desensitization of beta-adrenergic receptors on MNL and a concomitant redistribution of receptors into a cellular compartment to which some ligands (including catecholamines) have restricted access. The findings demonstrate that redistribution of beta-receptors may be a mechanism mediating desensitization to catecholamines in normal mammalian cells.
Estimation of insulin sensitivity and glucose clearance from minimal model: new insights from labeled IVGTT
Authors: Cobelli C. , Pacini G. , Toffolo G. , Sacca L.
Published: December 2017

The "minimal model" of glucose disappearance provides noninvasive estimates of insulin sensitivity and glucose effectiveness from an intravenous glucose tolerance test (IVGTT). However, this model does not allow the separation of glucose production from utilization. To overcome this limitation, labeled glucose was injected along with cold glucose in six normal dogs, and both cold and labeled glucose time courses were monitored along with insulin concentration. A revised minimal model was fitted to tracer data to obtain new measures of insulin sensitivity (SI* = 6.41 +/- 0.91 10(-4) min-1 X microU-1 X ml-1) and fractional glucose clearance (SG* = 0.0092 +/- 0.0009 min-1). SG* was compared with a direct measure obtained by a hepatic arterial-venous difference technique, which yielded a value of 0.0097 +/- 0.0002, virtually identical to SG*, thereby validating the model estimate. When the original minimal model was identified from cold data, we obtained S1 = 4.52 +/- 1.39 and SG = 0.042 +/- 0.009. SI* and SG* were different from SI and SG, respectively. In particular SG overestimates fractional glucose clearance by approximately five times. The revised minimal model yields glucose disposal parameters SI* and SG* that are not affected by the confounding effect of insulin and glucose inhibition of glucose production. Limitations inherent in cold IVGTT and original minimal model are overcome by labeled IVGTT and the revised minimal model, while test simplicity remains.
Stimulation of corticosterone secretion in vitro by brief ACTH exposure
Authors: Keith L. D. , Tam B. , Greer M. A.
Published: December 2017

We examined the relationship between ACTH concentration and exposure duration on stimulation of corticosterone (B) secretion in vitro using perifused enzymatically dispersed rat adrenocortical cells. A modular perifusion apparatus was used that permitted evaluation of 20-24 cell chambers per experimental session. In expt 1, 20-1000 pg/ml concentrations of synthetic ACTH-(1-24) were presented to cells for 1 min. In expt 2, 100 pg ACTH-(1-24) was presented to adrenal cells in five dose-duration regimens ranging from 5 pg/min for 20 min to 100 pg/min for 1 min. Perifusal rate was 1 ml/min in all sessions. B was determined by radioimmunoassay. In expt 1 (constant-duration paradigm), 1-min presentation of ACTH-(1-24) produced log-linear dose-response effects across these concentrations (r = 0.926, P less than 0.01). In expt 2 (constant-mass paradigm), identical masses administered in different dose-duration regimens had different steroidogenic efficacies (P less than 0.02): low-dose long-duration regimens provoked greater total release than high-dose short-duration regimens. Overall, every dose-duration regimen was associated with stimulation of B secretion. These results indicate that very brief exposure to physiological concentrations of ACTH-(1-24) is a significant stimulus for corticosteroid secretion; variations in the dose-duration regimen over the physiological range modifies both the maximum rate of secretion and the duration of secretion, but not the response latency; and ACTH-(1-24) presentation mass is not the sole determinant of B secretion.
Effect of infusing epinephrine on liver and muscle glycogenolysis during exercise in rats
Authors: Arnall D. A. , Marker J. C. , Conlee R. K. , Winder W. W.
Published: December 2017

To determine the possibility of a threshold concentration of plasma epinephrine that stimulates liver glycogenolysis during exercise, adrenodemedullated (ADM) and sham-operated (SHAM) rats were infused with saline or epinephrine at rates that produced plasma concentrations ranging between 0.01 ng/ml (0.06 nM) and 4.3 ng/ml (23.7 nM). During the infusion rats were run on a rodent treadmill for 0, 30, or 60 min at 21 m/min up a 15% grade. Liver glycogen decreased at similar rates in all exercising rats regardless of plasma epinephrine concentration. Epinephrine infusion stimulated significant muscle glycogen depletion in the soleus and red and white vastus lateralis muscles. ADM saline-infused animals exhibited the least muscle glycogen depletion. Blood glucose and lactate in exercising ADM rats increased as the epinephrine infusion concentration increased. During exercise, there was no epinephrine concentration that stimulated liver glycogenolysis more effectively than physiological saline.
Effect of free fatty acids on blood amino acid levels in human
Authors: Ferrannini E. , Barrett E. J. , Bevilacqua S. , Jacob R. , Walesky M. , Sherwin R. S. , DeFronzo R. A.
Published: December 2017

Raised plasma free fatty acid (FFA) levels effectively impede glucose uptake in vivo, thereby conserving plasma glucose and sparing glycogen. To test whether FFA have any effect on blood amino acid levels, we infused Intralipid plus heparin or saline into healthy volunteers under four different experimental conditions: A) overnight fast; B) euglycemic hyperinsulinemia (approximately 100 microU/ml); C) hyperglycemic (approximately 200 mg/100 ml) hyperinsulinemia (approximately 50 microU/ml); and D) hyperglycemic (approximately 300 mg/100 ml) normoinsulinemia (approximately 20 microU/ml). In the fasting state (A), lipid infusion was associated with lower blood levels of most amino acids, both branched chain and glucogenic. This effect, however, could not be ascribed to lipid infusion alone, because plasma insulin levels were also stimulated. The clamp studies (B, C, and D) allowed to assess the influence of lipid on blood amino acid levels at similar plasma insulin and glucose levels. It was thus observed that lipid infusion has a significant hypoaminoacidemic effect of its own under both euglycemic (B) and hyperglycemic (C) conditions; this effect involved many glucogenic amino acids (alanine, glycine, phenylalanine, serine, threonine, and cystine) but none of the branched-chain amino acids (leucine, isoleucine, and valine). In marked contrast, normoinsulinemic hyperglycemia (D), with or without lipid infusion, caused no change in the blood level of any measured amino acid. We conclude that lipid infusion has a hypoaminoacidemic action. We also suggest that this action is permitted by insulin and may involve specific metabolic interactions (e.g., reduced availability of glucose-derived pyruvate or glycerophosphate) as well as enhanced uptake by the liver.
Thyroxine 5'-deiodinase in hamster and rat brown adipose tissue: effect of cold and diet
Authors: Kopecky J. , Sigurdson L. , Park I. R. , Himms-Hagen J.
Published: December 2017

Thyroxine 5'-deiodinase (type II) is present in a microsomal fraction of brown adipose tissue (BAT) of Syrian hamsters. Cold exposure increased specific activity in homogenates after a lag period of approximately 2 h to reach a maximum by 1-3 days. Total activity increased 80 times in cold-acclimated hamsters. During deacclimation, a rapid decrease occurred again after a lag period of approximately 2 h. The increase did not parallel increases in protein or in thermogenic state of mitochondria (mitochondrial GDP binding), which occurred more slowly. Changes in serum 3,5,3'-triiodothyronine concentration paralleled changes in BAT 5'-deiodinase during both acclimation to cold and deacclimation. The cold-induced increase in BAT 5'-deiodinase activity occurred more slowly but was much larger in hamsters than in rats. Eating a palatable diet increased BAT protein content and thermogenic activity in both hamsters and rats but did not alter total 5'-deiodinase activity in either species. We conclude that the trophic response of brown adipose tissue to cold in both hamsters and rats is accompanied by an enhanced endogenous production of triiodothyronine that may play a role in control of tissue growth. The trophic response to a palatable diet differs in that enhanced endogenous production of triiodothyronine is not an obligatory accompaniment. Specific stimulation of 5'-deiodinase by cold might modify thermogenesis in tissues other than BAT by providing triiodothyronine and be of greater significance in hamsters than in rats.
Angiotensin II receptor alterations during pregnancy in rabbits
Authors: Brown G. P. , Venuto R. C.
Published: December 2017

Despite activation of the renin-angiotensin system during pregnancy, renal and peripheral vascular blood flows increase, and the systemic blood pressure and the pressor response to exogenous angiotensin II (Ang II) fall. Gestational alterations in Ang II receptors could contribute to these changes. Ang II binding parameters were determined utilizing 125I-Ang II in vascular (glomeruli and mesenteric arteries) and nonvascular (adrenal glomerulosa) tissues from 24- to 28-day pregnant rabbits. Comparisons were made utilizing tissues from nonpregnant rabbits. Binding site concentrations (N) and dissociation constants (Kd) were obtained by Scatchard analyses of binding inhibition data. In glomeruli from nonpregnant and pregnant rabbits, N was 515 +/- 84 and 300 +/- 54 fmol X mg-1 protein (P less than 0.005; n = 8), respectively. Kd did not differ (P greater than 0.05). In mesenteric artery membranes from nonpregnant (n = 3) and pregnant (n = 4) rabbits, N was 304 +/- 21 and 112 +/- 23 fmol X mg-1 (P less than 0.005), respectively. Kd did not differ. Neither N nor Kd differed in adrenal glomerulosa tissues (n = 6). Meclofenamate (M) inhibits prostaglandin synthesis, reduces plasma renin activity, and enhances the pressor response to infused Ang II in pregnant rabbits. Administration of M to pregnant rabbits increased N in glomerular and in mesenteric artery membranes from 298 +/- 16 to 381 +/- 8 fmol X mg-1 (n = 3) and from 144 +/- 13 to 218 +/- 13 fmol X mg-1 (n = 4), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Inhibition by proinsulin of endogenous C-peptide release in healthy man
Authors: Waldhausl W. K. , Bratusch-Marrain P. , Gasic S. , Komjati M. , Heding L.
Published: December 2017

To determine the role of proinsulin on endogenous insulin release, splanchnic output and arterial concentrations of C-peptide were measured in healthy subjects before and during infusion of human (HPI) and porcine (PPI) proinsulin at increasing rates for 70 min each (HPI, 328 and 656 micrograms X m-2 X h-1; PPI, 54, 134, and 268 micrograms/m-2 X h-1), while euglycemia was maintained by variable glucose infusion. By using this approach splanchnic C-peptide output was reduced by human proinsulin infusion from 143 +/- 16 (mean +/- SE) pmol/min to 111 +/- 18 and 75 +/- 11 pmol/min (P = 0.01). Simultaneously, arterial concentrations of C-peptide decreased from 716 +/- 40 pmol/l by 23 and 32%. Similar inhibition was induced by porcine PPI of splanchnic C-peptide output at an infusion rate of 268 micrograms X m-2 X h-1. Mean metabolic clearance rate was 2.7 and 3.7 ml X kg-1 X min-1 for HPI and PPI, respectively. Splanchnic glucose output was almost completely suppressed by human and porcine proinsulin at maximal infusion rates. This effect preceded both inhibition by proinsulin of splanchnic C-peptide output and stimulation of peripheral glucose utilization. We conclude that human and porcine proinsulin suppress endogenous insulin secretion at pharmacological concentrations. The observed constancy of the metabolic clearance rate of HPI demonstrates that its clearance remains a nonsaturable process up to supraphysiological HPI concentrations, while clearance of PPI appears to be subject to saturation. Furthermore, it appears that splanchnic glucose output responds earlier to proinsulin exposure than suppression of C-peptide release or stimulation of peripheral glucose utilization.