bluuebunny/crossref_metadata_2025 huggingface dataset:
Serum thyroid hormones and tissue 5'-monodeiodinase activity in acutely thyroidectomized newborn lambs
Authors: Polk D. H. , Wu S. Y. , Fisher D. A.
Published: December 2017

After either total thyroidectomy or sham operation in full-term fetal sheep, fetuses were delivered and serial blood samples were obtained for measurements of thyroxine (T4), triiodothyronine (T3), and catecholamines. Despite comparable serum T4 values (T4 means +/- SE, sham 7.1 +/- 0.6 micrograms/dl, thyroidectomized 6.8 +/- 0.7 micrograms/dl at 60 min after birth), serum T3 values were lower in the thyroidectomized animals (T3 means +/- SE, thyroidectomized 39 +/- 4.8 ng/dl, sham 153 +/- 20.1 ng/dl at 60 min after birth). Four hours after birth, the animals were killed with an intravenous overdose of barbiturate. Brain, thyroid, liver, kidney, and brown adipose tissues were dissected and analyzed for thyroxine 5'-monodeiodinase (5'-MDI) activity in vitro. 5'-MDI activity was comparable in all tissues from sham-operated and thyroidectomized lambs. Plasma epinephrine and norepinephrine concentrations, mean arterial pressure, mean pulse, rectal temperature, and arterial blood gas values were similar in the two groups of animals. These data support the hypothesis that the thyroid gland is the major source of T3 for the T3 surge in the immediate newborn period. They also indicate that the neonatal T3 surge has limited immediate metabolic significance in euthyroid newborns.
Effects of caloric deprivation on thyroid hormone tissue uptake and generation of low-T3 syndrome
Authors: van der Heyden J. T. , Docter R. , van Toor H. , Wilson J. H. , Hennemann G. , Krenning E. P.
Published: December 2017

Changes in thyroid hormone metabolism in the low-3,5,3'-triiodothyronine (T3) syndrome cannot be fully explained in all conditions by a decrease in 5'-deiodinase activity. Recent observations showed that in rat hepatocytes iodothyronines are taken up by an active transport mechanism. To investigate whether regulation, i.e., inhibition of active transmembraneous transport for iodothyronines in humans may contribute to the generation of the low-T3 syndrome, tracer thyroxine (T4) and T3 kinetic studies were performed in 10 obese subjects before and after 7 days on a 240 kcal diet. Kinetics analyses were performed according to a three-pool model of distribution and metabolism for both T4 and T3. For T4 kinetics, during caloric deprivation serum total T4 and plasma pool did not change and production rate and metabolic clearance rate (MCR) were significantly lower. Despite a significantly higher serum free T4, the mass transfer rate to the rapidly equilibrating pool (REP) and the slowly equilibrating pool (SEP) diminished significantly, leading to smaller tissue pools. For T3 kinetics, both serum total T3, free T3, plasma pool, and production rate diminished significantly, while MCR remained unchanged. Mass transfer rates to the REP and the SEP were lowered by approximately 50%, leading to smaller tissue pools. These changes cannot be fully explained by a similar decrease of serum free T3 (only 25%), indicating a diminished transport efficiency for T3. In conclusion, during caloric restriction, transport of T4 and T3 into tissues is diminished, and this phenomenon is much more pronounced for T4 than for T3.(ABSTRACT TRUNCATED AT 250 WORDS)
Activation of protein kinase C inhibits synthesis and release of decidual prolactin
Authors: Harman I. , Costello A. , Ganong B. , Bell R. M. , Handwerger S.
Published: December 2017

Activation of calcium-activated, phospholipid-dependent protein kinase C by diacylglycerol and phorbol esters has been shown to mediate release of hormones in many systems. To determine whether protein kinase C activation is also involved in the regulation of prolactin release from human decidua, we have examined the effects of various acylglycerols and phorbol esters on the synthesis and release of prolactin from cultured human decidual cells. sn-1,2-Dioctanoylglycerol (diC8), which is known to stimulate protein kinase C in other systems, inhibited prolactin release in a dose-dependent manner with maximal inhibition of 53.1% (P less than 0.01) at 100 microM. Diolein (100 microM), which also stimulates protein kinase C activity in some systems, inhibited prolactin release by 21.3% (P less than 0.05). Distearin and dipalmitin, which are much less effective in activating protein kinase C, and monopalmitin and tripalmitin, which do not activate protein kinase C, had no significant effect on prolactin release. Phorbol 12-myristate 13-acetate (PMA), phorbol 12,13-didecanoate, and 4 beta-phorbol 12,13-dibutyrate, which activate protein kinase C in other systems, also inhibited the release of prolactin, while the protein kinase C inactivate 4 alpha-phorbol-12,13-didecanoate was without effect. The inhibition of prolactin release was secondary to a decrease in prolactin synthesis. The amounts of prolactin synthesized by cells exposed to diC8 (300 microM) or PMA (10(-7) M) for 30 min were 56.3 and 50.0% less than that synthesized by control cells (P less than 0.01 in each instance).(ABSTRACT TRUNCATED AT 250 WORDS)
A dual-isotope technique for determination of in vivo ketone body kinetics
Authors: Miles J. M. , Schwenk W. F. , McClean K. L. , Haymond M. W.
Published: December 2017

"Total ketone body specific activity" has been widely used in studies of ketone body metabolism to circumvent so-called "isotope disequilibrium" between the two major ketone body pools, acetoacetate and beta-hydroxybutyrate. Recently, this approach has been criticized on theoretical grounds. In the present studies, [13C]acetoacetate and beta-[14C]hydroxybutyrate were simultaneously infused in nine mongrel dogs before and during an infusion of either unlabeled sodium acetoacetate or unlabeled sodium beta-hydroxybutyrate. Ketone body turnover was determined using total ketone body specific activity, total ketone body moles % enrichment, and an open two-pool model, both before and during the exogenous infusion of unlabeled ketone bodies. Basal ketone body turnover rates were significantly higher using [13C]acetoacetate than with either beta-[14C]hydroxybutyrate alone or the dual-isotope model (3.6 +/- 0.5 vs. 2.2 +/- 0.2 and 2.7 +/- 0.2 mumol X kg-1 X min-1, respectively, P less than 0.05). During exogenous infusion of unlabeled sodium acetoacetate, the dual-isotope model provided the best estimate of ketone body inflow, whereas 14C specific activity underestimated the known rate of acetoacetate infusion by 55% (P less than 0.02). During sodium beta-hydroxybutyrate infusion, [13C]-acetoacetate overestimated ketone body inflow by 55% (P = NS), while better results were obtained with 14C beta-hydroxybutyrate alone and the two-pool model. Ketone body interconversion as estimated by the dual-isotope technique increased markedly during exogenous ketone body infusion. In conclusion, significant errors in estimation of ketone body inflow were made using single-isotope techniques, whereas a dual-isotope model provided reasonably accurate estimates of ketone body inflow during infusion of exogenous acetoacetate and beta-hydroxybutyrate.(ABSTRACT TRUNCATED AT 250 WORDS)
Glucose turnover in response to exercise during high- and low-FIO2 breathing in man
Authors: Cooper D. M. , Wasserman D. H. , Vranic M. , Wasserman K.
Published: December 2017

The purpose of this study was to assess whether breathing high or low concentrations of O2 could affect glucose turnover during exercise in man. Ten healthy subjects performed two constant work-rate exercise tests, one when the fraction of inspired O2 (FIO2) was 0.15 and the other at the same work rate but when the FIO2 was 0.80. The work rate for each subject was chosen so that blood lactate would be elevated during hypoxia, but would be lower during hyperoxia. Glucose appearance (Ra) and disappearance (Rd) were measured using the primed, constant infusion of [3-3H]glucose. Although the work rate was the same during hypoxia and hyperoxia in each subject, hypoxic exercise was accompanied by a significantly larger rest to exercise increase in Rd (delta Rd) compared with hyperoxia by 265%. Similarly, delta Ra was greater during hypoxia than during hyperoxia by 188%. Lactate to pyruvate ratios were significantly higher during hypoxic exercise suggesting a shift in the cell redox to a more reduced state. Insulin and glucagon were not affected by the FIO2, but both epinephrine and norepinephrine were increased during hypoxic exercise, which may explain the increase in Ra. The regulation of blood glucose during exercise in vivo appears to be dependent on the availability of oxygen to the working muscle cells.
Effect of sulfonylureas on hepatic fatty acid oxidation
Authors: Patel T. B.
Published: December 2017

In isolated rat livers perfused with oleic acid (0.1 mM), infusion of tolbutamide or glyburide decreased the rate of ketogenesis in a dose-dependent manner. The inhibition of fatty acid oxidation was maximal at 2.0 mM and 10 microM concentrations of tolbutamide and glyburide, respectively. Neither tolbutamide nor glyburide inhibited ketogenesis in livers perfused with octanoate. The inhibition of hepatic ketogenesis by sulfonylureas was independent of perfusate oleic acid concentration. Additionally, in rat livers perfused with oleic acid in the presence of L-(-)-carnitine (10 mM), submaximal concentrations of tolbutamide and glyburide did not inhibit hepatic ketogenesis. Finally, glyburide infusion into livers perfused with [U-14C]oleic acid (0.1 mM) increased the rate of 14C label incorporation into hepatic triglycerides by 2.5-fold. These data suggest that both tolbutamide and glyburide inhibit long-chain fatty acid oxidation by inhibiting the key regulatory enzyme, carnitine palmitoyltransferase I, most probably by competing with L-(-)-carnitine.
Lipoprotein lipase in adipose tissues of exercise-trained, cold-acclimated rats
Authors: Deshaies Y. , Richard D. , Arnold J.
Published: December 2017

The combined effects of exercise training and cold acclimation on serum lipids and on the activity of lipoprotein lipase (LPL) in epididymal white (WAT) and interscapular brown adipose tissues (BAT) of the rat were evaluated. Sedentary and exercise-trained (treadmill) rats were housed and trained at either 24 or 4 degrees C for 45 days. Although neither treatment given alone influenced serum total cholesterol, exercise training in the cold resulted in a 54% increase in this variable. Serum triglycerides were lowered to 80% of control values by exercise training and to 44% of control by cold acclimation. Both treatments resulted in lower insulin and thyroxine concentrations, while triiodothyronine levels were unaffected. Total LPL activity in WAT was increased twofold by exercise training at both temperatures, whereas cold acclimation stimulated WAT LPL activity to a lesser extent. Exercise training had no overall effect on LPL activity of BAT, whereas cold acclimation increased the latter in both sedentary (217%) and trained (420%) animals. These results emphasize the potential importance of LPL-mediated lipid assimilation in the metabolic events that lead to energy production in response to environmental stresses and lend support to the notion that the regulation of LPL activity is tissue specific.
Dose-response curves of effects of insulin on leucine kinetics in humans
Authors: Tessari P. , Trevisan R. , Inchiostro S. , Biolo G. , Nosadini R. , De Kreutzenberg S. V. , Duner E. , Tiengo A. , Crepaldi G.
Published: December 2017

To determine the effects of physiological and pharmacological insulin concentrations on leucine-carbon kinetics in vivo, eight postabsorptive normal volunteers were infused with L-[4,5-3H]leucine and alpha-[1-14C]ketoisocaproate (KIC). Insulin concentrations were sequentially raised from 8 +/- 1 to 43 +/- 6 and 101 +/- 14 and to 1,487 +/- 190 microU/ml, while maintaining euglycemia with adequate glucose infusions. At the end of each 140-min insulin-infusion period, steady-state estimates of leucine and KIC rates of appearance (Ra), KIC (approximately leucine-carbon) oxidation, nonoxidized leucine-carbon flux [an index of leucine incorporation into protein (Leu----P)], and leucine and KIC interconversion rates were obtained. After the three insulin infusions, leucine Ra decreased by a maximum of approximately 20%. KIC Ra decreased by a maximum of approximately 50%. The sum of leucine plus KIC Ra in the basal state was 2.59 +/- 0.24 mumol X kg-1 X min-1 and decreased by approximately 30% at the maximal insulin concentrations. KIC oxidation decreased by a maximum of approximately 65%. Leu----P did not increase after hyperinsulinemia. Interconversion rates were promptly and markedly suppressed by 50-70%. Leucine clearance increased by approximately 120%. We conclude that euglycemic hyperinsulinemia, at physiological and pharmacological concentrations, decreased leucine and KIC concentrations, leucine-carbon turnover and oxidation, and leucine and KIC interconversions in a dose-dependent manner in vivo.
Trioctanoin infusion increases in vivo leucine oxidation: a lesson in isotope modeling
Authors: Rodriguez N. , Schwenk W. F. , Beaufrere B. , Miles J. M. , Haymond M. W.
Published: December 2017

We have reported that infusion of trioctanoin in conscious dogs had little effect on leucine oxidation but decreased the rate of appearance (Ra) and interconversion of leucine and its alpha-keto acid, alpha-ketoisocaproate (KIC). To verify that these conclusions were independent of the leucine tracers and isotope models employed, the studies were repeated using [1-14C]leucine and [4,5-3H]KIC rather than [1-14C]KIC and [4,5-3H]leucine. In the present study, leucine oxidation calculated using the plasma [14C]leucine or [14C]KIC specific activities (SA) increased nearly twofold (P less than 0.001) during trioctanoin infusion in direct contrast to our previous results. When the data from either study were analyzed using the plasma SA of the leucine moiety reciprocal to the infused tracer as a potential indicator of the intracellular leucine SA, similar conclusions were obtained from either study: trioctanoin infusion in conscious dogs appears to increase whole-body leucine oxidation and does not decrease proteolysis. These studies challenge the validity of previously used isotope models of leucine metabolism and suggest that the plasma KIC SA during infusion of labeled leucine may most accurately reflect changes in whole-body leucine metabolism.
Effect of insulin on uptake of metabolic substrates by the sheep fetus
Authors: Milley J. R. , Papacostas J. S. , Tabata B. K.
Published: December 2017

To measure the effect of fetal hyperinsulinemia on fetal oxidative metabolic rate and the uptake of fetal oxidative substrates, we operated on 12 near-term ewes under spinal anesthesia and placed catheters in the fetus under local anesthesia. Four days after surgery, we began an 18-h insulin infusion, at the end of which we drew blood samples for analysis of oxygen, glucose, lactate, amino-nitrogen concentrations, blood gases, pH, hematocrit, and plasma insulin concentrations, then injected radiolabeled microspheres to measure umbilical blood flow. Three to five infusions were given to each fetus. Fetal plasma insulin concentrations varied from 0.3 to 60 microU/ml. As fetal plasma insulin concentration rose, the blood concentrations of oxygen, glucose, lactate, and amino-nitrogen fell, but the fetal uptakes of oxygen, glucose, and amino-nitrogen rose. The rise of fetal oxygen uptake occurred by increasing oxygen extraction, resulting in arterial hypoxemia. The increase of the glucose uptake was sufficient to account for an increased fraction of oxidative metabolism, allowing the increased uptake of amino acids to be used for either synthetic or oxidative purposes.
Increased rate of purine biosynthesis in rat liver after bilateral adrenalectomy
Authors: Itakura M. , Maeda N. , Yamashita K.
Published: December 2017

In bilaterally adrenalectomized rat liver the increased rate of de novo purine synthesis was shown by the increased [14C]glycine incorporation into hepatic acid-soluble purines with unchanged rapidly miscible glycine pool size and its turnover rate and by the increased rate of chasing of radiolabeled purines. At 24 h after adrenalectomy, the rate of de novo purine synthesis increased by 70%, 5-phosphoribosyl-1-pyrophosphate (PRPP) content increased by 200%, the specific activity of amidophosphoribosyltransferase (EC 2.4.2. 14; ATase) did not change, ATP and GTP showed a 33 and 24% decrease, and AMP and ADP showed a 245 and 38% increase. Combined, the metabolic pool size data reflected an unchanged total inhibitory potential on ATase. Replacement with corticosterone acetate for 24 h partially restored some of these abnormalities. These results suggest that the increase in the rate of de novo purine synthesis in adrenalectomized rat liver is secondary to increased catabolism of purine ribonucleotides and mediated by increased PRPP concentrations.
Protein degradation in skeletal muscles after evisceration of fed or fasted rats
Authors: Smith O. L.
Published: December 2017

To test the rate of protein degradation in muscles under more physiological conditions, in vitro methods were adapted for use in rats whose skeletal muscles had been isolated intact by an evisceration procedure. Under pentobarbital anesthesia the vessels to the gastrointestinal tract were ligated, the organs removed, and the liver left in situ. Normal rectal temperature was maintained, glucose was given to prevent hypoglycemia and the animals were studied for a 2-h period. For the present experiments, evisceration was carried out after protein synthesis was blocked with cycloheximide so that the accumulation of the amino acid tyrosine (not metabolized) in the plasma of the preparation could be used to indicate the rate protein was degraded in the peripheral tissues. When normal fed rats (270 g) were eviscerated, the concentration of plasma tyrosine increased postoperatively, but, if the rats were fasted 20 h and then eviscerated, tyrosine accumulation was significantly enhanced. After 2 h, it was 50% greater than in the fed controls. Refeeding for 3 h completely prevented this effect. The results suggest that the rate of overall skeletal muscle protein degradation can be measured by the use of eviscerated rats and that this rate is sensitive to short periods of food deprivation.
Effects of alanine on malate-aspartate shuttle in perfused livers from cold-exposed rats
Authors: Sugano T. , Ohta T. , Tarui A. , Miyamae Y.
Published: December 2017

The role of glucocorticoids in the increase by cold-exposure of the effect of alanine on the malate-aspartate shuttle was studied in perfused rat liver. The capacity of the shuttle was evaluated by measurement of changes in both the rate of glucose production from sorbitol and the ratio of lactate to pyruvate during ethanol oxidation (Biomed. Res. 6, Suppl., 1986). The effect of alanine on the shuttle capacity was decreased by adrenalectomy. When 1.5 mg/kg dexamethasone sulfate was administrated to adrenalectomized rats kept at 24 or 4 degrees C, once daily for 5 days, the effect of alanine on the shuttle increased its capacity to the level of sham-operated rats that had been exposed to 4 degrees C for 5 days. The effects of dexamethasone were blocked by the coadministration of tetracycline with the agent. Cold exposure and steroid replacement had little effect on the alanine-induced elevation of the levels of aspartate, glutamate, and alpha-ketoglutarate in liver cells. The increase of the effect of alanine could not be explained only by changes in the activity of NAD+ malate dehydrogenase and aspartate aminotransferase. The results suggest that cold exposure and replacement treatment with glucocorticoids modulate equally the effect of alanine on the capacity of the malate-aspartate shuttle.
In vivo inhibition of tyrosine uptake into rat retina by large neutral but not acidic amino acids
Authors: Fernstrom M. H. , Volk E. A. , Fernstrom J. D.
Published: December 2017

The uptake of tyrosine into rat retina and brain was studied in vivo after its peripheral injection alone or in combination with other amino acids. Both retinal and brain tyrosine levels increased monotonically for at least 60 min after tyrosine administration. When tyrosine was injected along with branched-chain amino acids, but not with acidic amino acids, such increments in retinal and brain tyrosine levels were significantly attenuated. The postinjection tyrosine levels in retina and brain paralleled better the serum ratio of tyrosine to the sum of the other large neutral amino acids (which include the branched-chain amino acids) than the serum tyrosine level alone. These results suggest that tyrosine uptake into rat retina, like that into brain, is mediated by a competitive transport system shared among the large neutral amino acids.
Glucose and fructose 6-phosphate cycle in humans
Authors: Karlander S. , Roovete A. , Vranic M. , Efendic S.
Published: December 2017

We have determined the rate of glucose cycling by comparing turnovers of [2-3H]- and [6-3H]glucose under basal conditions and during a glucose infusion. Moreover, the activity of the fructose 6-phosphate cycle was assessed by comparing [3-3H]- and [6-3H]glucose. The study included eight lean subjects with normal glucose tolerance. They participated in two randomly performed investigations. In one experiment [2-3H]- and [6-3H]glucose were given simultaneously, while in the other only [3-3H]glucose was given. The basal rate of glucose cycling was 0.32 +/- 0.08 mg X kg-1 X min-1 or 17% of basal glucose production (P less than 0.005). During glucose infusion the activity of endogenous glucose cycling did not change but since glucose production was suppressed it amounted to 130% of glucose production. The basal fructose 6-phosphate cycle could be detected only in three subjects and was suppressed during glucose infusion. In conclusion, the glucose cycle is active in healthy humans both in basal conditions and during moderate hyperglycemia. In some subjects, the fructose 6-phosphate cycle also appears to be active. Thus it is preferable to use [6-3H]glucose rather than [3-3H]glucose when measuring glucose production and particularly when assessing glucose cycle.
Effect of charge on hepatic specific nature of vesicle encapsulated insulin in conscious dogs
Authors: Spangler R. S. , Triebwasser K. C. , Wilson M. L.
Published: December 2017

Positively [(+)-VEI] and negatively [(-)-VEI] charged formulations of vesicle encapsulated insulin (VEI) were compared with insulin on the basis of their ability to suppress hepatic glucose production (hepatic Ra) and stimulate glucose utilization (Rd) in conscious dogs. Our results indicate that (-)-VEI and insulin have an equivalent capacity to suppress hepatic glucose production at dose levels of 0.2, 1.2, and 2.4 mU X kg-1 X min-1. (+)-VEI is less effective at suppressing hepatic Ra than both insulin and (-)-VEI at dose levels of 1.2 and 2.4 mU X kg-1 X min-1. Both (+)-VEI and (-)-VEI induced significantly less glucose utilization than a comparable amount of insulin at dose levels of 1.2 and 2.4 mU X kg-1 X min-1. The amount of glucose utilization stimulated by (+)-VEI was significantly less than that induced by insulin at 0.6 mU X kg-1 X min-1. This difference was not evident with (-)-VEI. These results suggest that the insulin contained in (+)-VEI is less bioavailable than that contained in (-)-VEI. This difference in bioavailability is believed to be the result of greater serum stability of (+)-VEI vesicles when compared with that of (-)-VEI. In conclusion, both (+)-VEI and (-)-VEI have the capacity to shield encapsulated insulin from interacting with peripheral tissues and deliver insulin selectively to the liver. Both formulations afford one an opportunity to expand the therapeutic window for hepatically active compounds where their utility is limited by systemic toxicity.
Insulin but not GH directly stimulates growth of transplanted fetal rat paws
Authors: Cooke P. S. , Higa L. , Nicoll C. S.
Published: December 2017

We have investigated whether insulin or growth hormone (GH) can affect growth of transplanted fetal rat paws by direct and/or indirect actions. Paws from 15-day rat fetuses were transplanted under the kidney capsule of adult female hosts, and grown for 7 days. In hypophysectomized (HX) or diabetic hosts their growth was reduced by 65% and 35%, respectively. The direct effects of insulin and GH were studied by inserting a catheter connected to an osmotic minipump into the left renal artery. Thus transplants on the left (infused) kidney were exposed directly to much higher concentrations of hormone than were those on the right (uninfused) side. In HX hosts, infusion of GH (0.1 microgram X g body wt-1 X day-1) had no effect on growth of paws on either kidney. At 0.3 or 1.0 microgram X g body wt-1 X day-1 GH caused a dose-related restoration of transplant growth that was equivalent on both sides. In diabetic hosts infusion of insulin (2 U X kg body wt-1 X day-1) partially restored growth of paws on the infused kidney without affecting those on the right. Insulin at 6 U X kg body wt-1 X day-1 caused full restoration of growth of the paws on the left and a partial increase in those on the right. At 9 U X kg body wt-1 X day-1 insulin caused full restoration of transplant growth on both kidneys. These results indicate that insulin promotes normal growth of transplanted fetal paws by direct and possibly indirect mechanisms, but the effects of GH are apparently only indirect.
Hormonal regulation of iodothyronine 5'-deiodinase in rat brown adipose tissue
Authors: Silva J. E. , Larsen P. R.
Published: December 2017

Norepinephrine, isoproterenol, insulin, and glucagon increase the type II (low Km) iodothyronine 5'-deiodinase (5'-D) in the brown adipose tissue (BAT) of intact rats. Cycloheximide or actinomycin D blocks the increase after norepinephrine, suggesting new mRNA synthesis is required for this effect. The 3- to 10-fold increase in BAT 5'-D after insulin administration was also blocked by cycloheximide. The effects of all stimulators are blunted by fasting or streptozotocin-induced diabetes. While all these hormones have the potential for stimulating BAT 5'-D, the dose-response relationships suggest that norepinephrine and insulin are the most potent. These and our earlier studies showing additional effects of thyroid and growth hormones on BAT 5'-D point to the complex regulation of this enzyme, suggesting that the triiodothyronine produced from its action has an important role in the thermogenic response of this tissue.
Somatostatin potentiation of insulin-induced glucose uptake in normal individuals
Authors: Wu M. S. , Ho L. T. , Chen J. J. , Chen Y. D. , Reaven G. M.
Published: December 2017

The ability of somatostatin (SRIF) to enhance insulin-stimulated glucose uptake was evaluated during clamp studies in normal individuals and patients with non-insulin-dependent diabetes mellitus (NIDDM). The results demonstrated that glucose uptake at insulin levels of approximately 100 microU/ml was significantly greater (P less than 0.001) in normal individuals in response to insulin plus SRIF as compared with insulin alone. In contrast, SRIF did not enhance insulin-stimulated glucose uptake in patients with NIDDM. Measurements were also made of the relative ability of insulin as compared with insulin plus SRIF to suppress C-peptide and glucagon concentrations during the clamp studies. The results of these experiments showed that SRIF did not potentiate the ability of insulin to suppress C-peptide concentrations in normal subjects but did in patients with NIDDM. However, plasma glucagon levels were reduced to a greater degree when SRIF was added to insulin in both normal and diabetic individuals.
Expression of a cholecystokinin precursor-related peptide in vertebrate and invertebrate tissues
Authors: Schneider B. S. , Maimon J. , Friedman J.
Published: December 2017

We have developed a radioimmunoassay for the nonapeptide predicted by cDNA sequence analysis to reside at the extreme C-terminus of the mouse cholecystokinin (CCK) precursor. Sensitivity of the assay is 1 pg synthetic CCK precursor-related peptide (CCK-PRP)/ml. The antibody has no cross-reactivity with cholecystokinin, gastrin, or a variety of other known neuropeptides. We have employed this assay to demonstrate the presence, in rodent brain, gut, and peripheral plasma, of peptides with immunological properties that are identical to, and gel filtration characteristics that are very similar to, those of the synthetic CCK-PRP. We have also detected a similar peptide in the culture media of a human CCK-producing tumor. The molar ratios of immunoreactive CCK-PRP/CCK vary widely among tissues of origin and during ontogeny, suggesting regional and developmental differences in the turnover rates or in posttranslational modification of the two peptides. Our studies suggest that peptides very similar to intact CCK-PRP are posttranslationally liberated from the cholecystokinin precursor in a variety of tissues and may have neurotransmitter and/or hormonal functions distinct from those of CCK. Relatively high quantities of material immunologically indistinguishable from CCK-PRP were also found in several coelenterate species, indicating that this epitope arose as early in evolution as did CCK.
Thermic effects of food and exercise in lean and obese men of similar lean body mass
Authors: Segal K. R. , Gutin B. , Albu J. , Pi-Sunyer F. X.
Published: December 2017

The thermic effect of food at rest, during 30 min of cycle exercise, and postexercise with two sequences of exercise and meal (before or after exercise) was compared in eight lean (mean +/- SE, 12.8 +/- 0.7% body fat) and eight obese men (29.7 +/- 0.6% fat) to determine whether exercise before or after a meal enhances thermogenesis. The groups were matched for age, height, and lean body mass (LBM) in order to study the relationship between thermogenesis and body fat independent of LBM. Metabolic rate was measured by indirect calorimetry on five mornings, in randomized order, after an overnight fast. Treatments on respective days were 1) 3-h rest, no meal; 2) 3-h rest after a 750-kcal mixed meal (14% protein, 31% fat, 55% carbohydrate); 3) during and 3 h after 30 min of cycling, no meal; 4) during and 3 h after 30 min of cycling, meal 30 min before exercise; and 5) 3 h after 30 min of cycling, meal immediately after exercise. The thermic effect of food, which is the fed minus fasted caloric expenditure, was significantly greater for the lean than the obese men under the resting (mean +/- SE 53 +/- 5 vs. 26 +/- 5 kcal over 3 h for the lean and obese groups, P less than 0.01), exercise (26 +/- 4 vs. 4 +/- 2 kcal over 30 min, P less than 0.01), and both postexercise conditions. However, for the lean men the thermic effect of food was significantly greater for the meal-before-exercise than the resting and the meal-after-exercise conditions.(ABSTRACT TRUNCATED AT 250 WORDS)
Vital microscopy of islet blood flow: catecholamine effects in normal and ob/ob mice
Authors: Rooth P. , Taljedal I. B.
Published: December 2017

The pancreatic microcirculation in noninbred ob/ob mice and normal controls was visualized in a fluorescence microscope and examined for responses to intravenous infusions of epinephrine or norepinephrine. Evaluations of coded video recordings revealed a smooth dose-response relationship and validated a semiquantitative method of analysis. In ob/ob mice the islet microcirculation was markedly and reversibly inhibited by 0.14–4 micrograms of epinephrine X min-1 X kg body wt-1; the flow was almost totally stopped at the highest infusion rates. Capillary flow in the exocrine pancreas appeared unaffected, except for some inhibition at 4.0 micrograms X min-1 X kg-1. Norepinephrine was less potent an inhibitor of islet blood flow. Normal lean mice exhibited minor responses to 1–11.3 micrograms of epinephrine X min-1 X kg-1; in most cases there was no visible effect. It is concluded that there is a selective regulation of blood flow through the endocrine portion of the pancreas and that the islet microcirculation is hypersensitive to catecholamines in noninbred ob/ob mice. A defective inhibitory influence from the brain may play a role in the development of excessive hyperinsulinemia in ob/ob mice.
Insulin and islet cell transplants: effects on diabetic rat cardiac myofibril ATPase
Authors: MacLean I. M. , Rajotte R. V. , Belcastro A. N.
Published: December 2017

Streptozotocin-induced diabetes results in depression of growth rate, cardiac myofibril ATPase activity, and elevated plasma glucose levels. Reversibility of these changes with daily insulin injections and pancreatic islet cell transplants was investigated and compared. Cardiac myofibril ATPase activities (mumol Pi X mg-1 X min-1) were depressed in the uncontrolled diabetic (D) group over the complete range of Ca2+ concentrations tested (e.g., 0.057 +/- 0.017 at 10 microM free Ca2+) with respect to the control (C) group (0.113 +/- 0.009). Neither the transplanted (T) group (0.128 +/- 0.017) nor the insulin injected (I) group (0.111 +/- 0.014) was significantly different from the C animals. Normal growth rates were restored in both I and T groups, whereas in the D group weight gains were negligible in comparison. Cardiac myofibril protein yields (in mg/g wet wt) were not significantly different among groups. These findings indicate that both islet cell transplants and daily insulin injections are capable of normalizing plasma glucose levels, cardiac myofibril ATPase activity, and growth rates in STZ-diabetic rats.
Cortisol-induced inhibition of ovine renin and aldosterone responses to hypotension
Authors: Wood C. E. , Silbiger J.
Published: December 2017

Previous studies from this laboratory have demonstrated that in preterm fetal sheep increases in plasma cortisol (F) concentration equal in amplitude to fetal F stress responses suppress plasma renin activity (PRA). The purpose of this study was to investigate the possibility that this negative interaction exists in adult sheep. Five conscious ewes with chronically prepared carotid arterial loops were infused intravenously with F (6 micrograms X kg-1 X min-1) or vehicle (5% ethanol in 0.9% saline) for 5 h. One hour after the end of F or vehicle infusion, renin secretion was stimulated by hypotension produced by infusion of sodium nitroprusside (20 micrograms X kg-1 X min-1, iv). F infusion increased plasma F from 26 +/- 3 to 46 +/- 8 ng/ml; during vehicle infusion plasma F did not change from 20 +/- 4 ng/ml. F infusion decreased hematocrit from 29 +/- 2 to 26 +/- 1%. Basal PRA in vehicle- and F-infused groups were 0.4 +/- 0 and 0.2 +/- 0.1 ng angiotensin I X ml-1 X h-1 and did not change. In vehicle-infused ewes, PRA increased from 0.4 +/- 0 and 0.2 +/- 0.1 ng angiotensin I X ml-1 X h-1 and did not change. In vehicle-infused ewes, PRA increased from 0.4 +/- 0 to 4.6 +/- 0.4 and plasma aldosterone from 26.0 +/- 1.0 to 173.1 +/- 21.8 pg/ml, while, in F-infused ewes, PRA increased from 0.2 +/- 1 to 3.3 +/- 0.4 ng angiotensin I X ml-1 X h-1 and aldosterone from 25.0 +/- 0 to 48.2 +/- 23.2 pg/ml, significantly smaller responses.(ABSTRACT TRUNCATED AT 250 WORDS)
A model-free approach to estimation of relative potency in dose-response curve analysis
Authors: Guardabasso V. , Rodbard D. , Munson P. J.
Published: December 2017

We have developed a new, general approach to analysis of dose-response curves from bioassay, immunoassay (including radioimmunoassay, immunoradiouretic assay, enzyme-linked immunosorbent assay), and other experimental procedures. It provides a test for parallelism, similarity of shape, and a measure of relative potency for any set of two or more curves. The method uses a constrained smoothing spline function to estimate the curve shape, together with a nonlinear least-squares fitting technique to estimate parameters for relative potency and slope. The use of “constrained splines” permits the analysis of nonlinear dose-response curves that cannot be described by a simple model or equation such as the symmetric four-parameter logistic. A microcomputer program is used for the analysis, providing relative potencies and their SE and evaluation of goodness of fit
Effect of diet on insulin binding and glucose transport in rat sarcolemmal vesicles
Authors: Grimditch G. K. , Barnard R. J. , Sternlicht E. , Whitson R. H. , Kaplan S. A.
Published: December 2017

The purpose of this study was to compare the effects of a high-fat, high-sucrose diet (HFS) and a low-fat, high-complex carbohydrate diet (LFC) on glucose tolerance, insulin binding, and glucose transport in rat skeletal muscle. During the intravenous glucose tolerance test, peak glucose values at 5 min were significantly higher in the HFS group; 0-, 20-, and 60-min values were similar. Insulin values were significantly higher in the HFS group at all time points (except 60 min), indicating whole-body insulin resistance. Skeletal muscle was responsible, in part, for this insulin resistance, because specific D-glucose transport in isolated sarcolemmal (SL) vesicles under basal conditions was similar between LFC and HFS rats (35 +/- 5 vs. 32 +/- 4 pmol/mg protein), despite the higher plasma insulin levels. Scatchard analyses of insulin binding curves to sarcolemmal vesicles revealed that the Ka of the high-affinity binding sites was significantly reduced by the HFS diet (0.63 +/- 0.09 vs. 0.35 +/- 0.05 X 10(9) M-1); no other binding changes were noted. Specific D-glucose transport in SL vesicles after maximum insulin stimulation (1 U/kg) was significantly depressed in the HFS group (87 +/- 7 vs. 58 +/- 7 pmol/mg protein), indicating that HFS feeding also caused a postbinding defect. These results indicate that the insulin resistance in skeletal muscle associated with a HFS diet is due to both a decrease in the Ka of the high-affinity insulin receptors and a postbinding defect.
Halothane anesthesia does not suppress sympathetic activation produced by neuroglucopenia
Authors: Havel P. J. , Flatness D. E. , Halter J. B. , Best J. D. , Veith R. C. , Taborsky G. J.
Published: December 2017

To determine the suitability of halothane anesthesia for studies of sympathetic control of the endocrine pancreas in dogs, we assessed the effect of halothane anesthesia (0.8% inspired concentration) on the sympathetic response to central neuroglucopenia. In dogs anesthetized with halothane, intravenous administration of the neuroglucopenic agent, 2-deoxy-D-glucose (2-DG; 100 mg/kg), produced increases of both systemic plasma epinephrine (EPI; delta = 269 +/- 86 pg/ml, P less than 0.025) and norepinephrine (NE; delta = 157 +/- 55 pg/ml, P less than 0.025) equivalent to those previously observed in conscious dogs. Measurement of plasma NE kinetics revealed that the plasma NE response to 2-DG during halothane was due to an increase in the rate of NE appearance that was identical to that of conscious dogs, rather than to an impairment of NE clearance. In contrast, 2-DG at this dose did not increase plasma EPI or NE levels in dogs anesthetized with pentobarbital sodium (30 mg/kg). Plasma glucose increased modestly after 2-DG (100 mg/kg) in both conscious and halothane-anesthetized dogs but not in the pentobarbital-anesthetized dogs. Although 2-DG at a threefold higher dose (300 mg/kg) caused plasma EPI, NE, and glucose (delta = 12 +/- 3 mg/dl, P less than 0.001) to increase in pentobarbital-anesthetized dogs, the responses to this higher dose of 2-DG were all significantly larger in halothane-anesthetized dogs (delta of plasma glucose = 30 +/- 8 mg/dl, P less than 0.005; P less than 0.0025 vs. pentobarbital).(ABSTRACT TRUNCATED AT 250 WORDS)
Evidence for cAMP as a mediator of gonadotropin secretion from male pituitaries
Authors: Bourne G. A. , Baldwin D. M.
Published: December 2017

The purpose of this study was to use sodium flufenamate, a compound that inhibits gonadotropin-releasing hormone (GnRH)-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) production in the pituitary, to evaluate the potential role of cAMP as a mediator of GnRH-stimulated gonadotropin secretion from male pituitaries. Quartered male pituitaries were perifused at 37 degrees C and sequential effluent fractions collected every 10 min. Infusions of GnRH resulted in a twofold increase in luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion. Cycloheximide, 5 microM, completely inhibited the GnRH-stimulated LH and FSH secretion. Infusions of 0.1 mM flufenamate had similar effects on gonadotropin secretion as cycloheximide, whereas the administration of 5 mM dibutyryl cAMP in combination with GnRH and flufenamate restored the secretory responses of both hormones. The flufenamate-inhibited GnRH stimulated LH and FSH release, which was restored by DBcAMP and appeared to be protein synthesis dependent and specific for cAMP. These results suggest an indirect role for cAMP as a mediator of gonadotropin secretion from male pituitaries. However, in contrast to female pituitaries, the secretion of these hormones from male pituitaries is completely dependent on cAMP and de novo protein synthesis.
Neuroanatomic localization of the inhibitory effect of TRH on growth hormone secretion
Authors: Ishikawa K. , Katakami H. , Frohman L. A.
Published: December 2017

The inhibitory effect of centrally administered thyrotropin-releasing hormone (TRH) on the plasma growth hormone (GH) response to GH-releasing hormone (GHRH) in the rat was studied in relation to the anatomic loci involved. Experiments were performed in animals with bilateral electrolytic lesions in the medial preoptic (MPO) area or with anterolateral hypothalamic deafferentation and in sham-operated controls. Blood samples were obtained every 10 to 20 min from and drugs were injected into freely moving animals with indwelling cannulas in the right atrium and lateral cerebral ventricle. In control animals, the plasma GH response to GHRH, 1 microgram iv, was almost completely inhibited by TRH, 1 microgram icv, injected 5 min previously. In animals with either MPO lesions or anterolateral hypothalamic deafferentation in which median eminence somatostatin immunochemical staining was almost completely eliminated, the GH response to GHRH was enhanced and TRH did not exhibit any inhibitory effect. These results, together with the previous observation that the inhibitory effect of TRH is blocked by prior treatment with anti-somatostatin serum, suggest that the effect of TRH is mediated by stimulation of somatostatin-containing neurons in the periventricular nucleus of the MPO area.
Comparative assessments of objective peak-detection algorithms. II. Studies in men
Authors: Urban R. J. , Kaiser D. L. , van Cauter E. , Johnson M. L. , Veldhuis J. D.
Published: December 2017

The performances of eight currently available computerized pulse-detection algorithms were compared on signal-free noise and physiological luteinizing hormone (LH) time series. Signal-free noise was made to vary from 4 to 36% for Gaussian and empirical distributions. Physiological LH data were obtained by immunoassay of blood samples withdrawn every 5 min for 24 h in 8 healthy men, so that the data sets could be emended to simulate varying sampling intensities. Whenever possible, programs were tested at a presumptive 1% false-positive rate. In relation to signal-free noise, the Santen and Bardin program and its modification manifested elevated false-positive rates when the intraseries coefficients of variation increased. The Regional Dual-Threshold program yielded a 1% false-positive rate except on simulated series with high variance. The Cluster and Detect programs both approximated a 1% false-positive rate and the Ultra program approximated a 2.3% false-positive rate throughout the entire range of variance tested. In regard to physiological LH data, all algorithms disclosed a significant impact of sampling intensity on estimates of LH pulse frequency. Sampling-intensity dependent estimates of LH peak frequency by three of the eight programs (Ultra, Cluster, and Detect) were statistically indistinguishable from each other but distinct from the five other programs tested. Furthermore, when judged in relation to their ability to identify individual peaks, the three congruent programs were minimally distinguishable (McNemar's test). Rather, these programs identified the same particular peaks (as defined by concordance of peak maxima) at least 72% of the time.
Diabetes and low Ca-P diet have opposite effects on adult and fetal bone mineral metabolism
Authors: Verhaeghe J. , Bouillon R. , Lissens W. , Visser W. J. , Van Assche F. A.
Published: December 2017

The effect of diabetes on maternal bone mineral metabolism and fetal mineralization was studied in nonpregnant and pregnant BB rats fed two diets (0.85% calcium-0.7% phosphorus and 0.2% calcium-phosphorus). Non-pregnant female diabetic rats had normal total bone mineral content (BMC), despite decreased trabecular bone volume density (TBVD). Nondiabetic rats on the low calcium-phosphorus diet showed decreased TBVD, signs of increased bone turnover, and decreased BMC; plasma 1,25-dihydroxyvitamin D3 [1,25 (OH)2D3] was increased and urinary calcium excretion was decreased. A similar response was observed in diabetic rats with a further decrease in TBVD. Nondiabetic 21-day pregnant rats on high and low calcium-phosphorus diets had higher 1,25(OH)2D3 than nonpregnant rats (98 vs. 58 and 328 vs. 147 pg/ml, respectively). Maternal BMC did not change during pregnancy but was decreased by the low calcium-phosphorus diet; fetal mineral content was not influenced by the low calcium-phosphorus regime. No increase in 1,25(OH)2D3 was observed in pregnant diabetic rats (57 vs. 52 and 112 vs. 128 pg/ml in high and low calcium-phosphorus diet groups). Fetal mineralization was severely impaired in diabetes but was not further decreased by the low calcium-phosphorus diet. Thus nonpregnant diabetic rats respond normally to a low calcium-phosphorus diet, but pregnant diabetic rats do not show increased 1,25(OH)2D3 levels due to impairment of fetal mineralization.
Glucoregulatory function of thyroid hormones: role of pancreatic hormones
Authors: Muller M. J. , Burger A. G. , Ferrannini E. , Jequier E. , Acheson K. J.
Published: December 2017

Glucose metabolism was investigated in humans before and 14 days after 300 micrograms L-thyroxine (T4)/day using a sequential clamp protocol during short-term somatostatin infusion (500 micrograms/h, 0-6 h) at euglycemia (0-2.5 h), at 165 mg/dl (2.5-6 h), and during insulin infusion (1.0 mU.kg-1.min-1, 4.5-6 h). T4 treatment increased plasma T4 (+96%) and 3,5,3'-triiodothyronine (T3, +50%), energy expenditure (+8%), glucose turnover (+32%), and glucose oxidation (Glucox +87%) but decreased thyroid-stimulating hormone (-96%) and nonoxidative glucose metabolism (Glucnonox, -30%) at unchanged lipid oxidation (Lipox). During somatostatin and euglycemia glucose production (Ra, -67%) and disposal (Rd, -28%) both decreased in euthyroid subjects but remained at -22% and -5%, respectively, after T4 treatment. Glucox (control, -20%; +T4, -25%) fell and Lipox increased (control, +42%; +T4, +45%) in both groups, whereas Glucnonox decreased before (-36%) but increased after T4 (+57%). During somatostatin infusion and hyperglycemia Rd (control, +144%; +T4, +84%) and Glucnonox (control, +326%; +T4, +233%) increased, whereas Glucox and Lipox remained unchanged. Insulin further increased Rd (+76%), Glucox (+155%), and Glucnonox (+50%) but decreased Ra (-43%) and Lipox (-43%). All these effects were enhanced by T4 (Rd, +38%; Glucox, +45%; Glucnonox, +35%; Ra, +40%; Lipox, +11%). Our data provide evidence that, in humans, T3 stimulates Ra and Rd, which is in part independent of pancreatic hormones.