bluuebunny/crossref_metadata_2025 huggingface dataset:
Maitotoxin stimulates hormonal release and calcium flux in rat anterior pituitary cells in vitro
Authors: Schettini G. , Koike K. , Login I. S. , Judd A. M. , Cronin M. J. , Yasumoto T. , MacLeod R. M.
Published: December 2017

The marine dinoflagellate toxin maitotoxin (MTX), an activator of calcium channels, stimulates the release of prolactin (PRL), growth hormone (GH), thyroid-stimulating hormone (TSH), and luteinizing hormone (LH) from monolayers of anterior pituitary cells in a dose-dependent manner. Maitotoxin significantly increased PRL, GH, and LH release within 1.5 min and TSH release within 3.5 min, and the stimulation continued for at least 1 h (P less than 0.01). MTX-stimulated hormonal release was blocked by the calcium channel blocker manganese (P less than 0.01). In freshly dispersed perifused pituitary cells in columns, exposure to MTX for 10 min markedly increased PRL, GH, TSH, and LH release for at least 1 h after withdrawal of the toxin. In other experiments, MTX significantly stimulated 45Ca2+ exchange by dispersed pituitary cells within 30 s, continuing for at least 30 min. We conclude that MTX increases anterior pituitary hormonal release, possibly by activating calcium channels, thereby increasing cellular calcium influx. Thus MTX may be a useful agent for investigating the involvement of Ca2+ in hormonal secretory processes.
Dexamethasone-induced insulin resistance enhances B cell responsiveness to glucose level in normal men
Authors: Beard J. C. , Halter J. B. , Best J. D. , Pfeifer M. A. , Porte D.
Published: December 2017

To determine whether islet adaptation during insulin resistance involves increased responsiveness to the level of plasma glucose, insulin resistance was induced in nine normal men by giving dexamethasone (Dex) (3 mg twice daily for 2 days). Plasma insulin and acute insulin responses (AIR) to isoproterenol were measured at three different glucose levels under control and Dex conditions. During Dex there were elevations above control levels of basal glucose (104 +/- 2 vs. 94 +/- 3 mg/dl) and insulin (21 +/- 3 vs. 13 +/- 2 microU/ml, both P less than 0.03). When glucose levels were raised stepwise by matching amounts using glucose clamps, AIR to isoproterenol rose as a linear function of glucose level under both conditions but rose more steeply during Dex. That is, the potentiating effect of glucose (delta AIR/delta glucose) was greater during Dex: 1.3 +/- 0.2 vs. 0.8 +/- 0.2 (P less than 0.01). Similarly, matched increments in glucose level produced greater increments in prestimulus insulin level during Dex (P less than 0.03). We conclude that 48 h of Dex raises the "gain" of the potentiating effect of glucose. Because the direct effect of glucocorticoids on B cell function has been reported to be inhibitory, the observed stimulation is likely to be a result of the insulin resistance caused by Dex.
Brief decreases in dopamine result in surges of prolactin secretion in monkeys
Authors: Frawley L. S. , Neill J. D.
Published: December 2017

We have reported previously that the amount of dopamine in hypophysial stalk blood was sufficient to account for tonic hypothalamic inhibition of prolactin secretion in rhesus monkeys. In the present study we determined the effect on prolactin secretion of decreases in dopamine. When hypophysial stalk-transected, estrogen-treated monkeys were infused with dopamine at a rate (0.1 microgram X kg-1 X min-1) to achieve peripheral plasma concentrations similar to those previously measured in stalk blood, their elevated serum prolactin levels fell to base line (from 47.6 +/- 4.8 to 9.7 +/- 2.7 ng/ml, mean +/- SE, n = 4). Brief interruptions of the dopamine infusions lasting for 2.5, 5.0, or 7.5 min evoked rapid increases in serum prolactin concentrations (to 27.5 +/- 8.3, 52.9 +/- 3.6, and 58.9 +/- 8.1 ng/ml, respectively, at 10 min). Maximal prolactin levels were attained within 10 to 20 min after dopamine removal and serum prolactin remained elevated for an additional 35 to 150 min. Uninterrupted dopamine infusions of stalk-transected, estrogen-treated monkeys (n = 3) led to continuously suppressed prolactin values. These results demonstrate that brief decreases in dopamine lead to major increases in prolactin secretion. Thus, if a brief decrease in hypothalamic dopamine secretion occurs after a suckling stimulus in monkeys, as it does in rats, a decrease in dopamine secretion alone may account, in part, for suckling-induced prolactin secretion in monkeys.
Reflex inhibition of insulin secretion: vagus nerve involvement via CNS
Authors: Curry D. L.
Published: December 2017

The in situ brain-pancreas experimental model was used to investigate the influence of the vagus nerve during tonic direct central nervous system (CNS) inhibition of insulin secretion. Tonic CNS inhibition of insulin secretion was partially and transiently reversed following bilateral cervical vagotomy, suggesting that this inhibition includes a vagally mediated component. However, a substantial CNS inhibition of insulin secretion still occurred in the vagotomized preparations. This demonstrates that a major component producing tonic CNS inhibition of insulin secretion is independent of the vagus nerve and, furthermore, that it must be via direct sympathetic efferent pathways to the pancreas (because these preparations are functionally parasympathectomized via vagotomy). Further investigation into the vagus nerve involvement was carried out by stimulating either the afferent (central) or efferent (pancreatic) cut end of the vagus nerve of bilaterally vagotomized brain-pancreas preparations. Stimulation of the efferent vagus did not appreciably alter the effect of vagotomy on insulin secretion. However, when the central cut vagus was stimulated, the early transient reversal of tonic inhibition, which occurred in the vagotomized preparations, was totally reversed. This suggests that the vagally mediated early transient component of tonic CNS inhibition of insulin secretion is via afferent (central) neurons in the vagus nerve. These data demonstrate a reflex pathway for inhibition of insulin secretion that is comprised of vagal afferent neurons, the CNS, and sympathetic efferent neurons ending directly on the islets of Langerhans. It is tempting to speculate that gastrointestinal receptors exist that are capable of initiating this reflex inhibition of insulin secretion.
Growth of fetal guinea pig: physical and chemical characteristics
Authors: Sparks J. W. , Girard J. R. , Callikan S. , Battaglia F. C.
Published: December 2017

The growth of the fetal guinea pig was studied in 32 fetuses in 12 litters, ranging from 39 days gestation to full term (67 days). The wet weight of the fetus was well approximated by an exponential function of gestational age (GA) in days [fetal weight (g) = 0.993 e(0.068 X GA), r = 0.94]. Dry weight increased more rapidly than wet weight [dry weight (g) = 0.039 e(0.102 X GA); r = 0.97], resulting in an increase in percent dry weight from approximately 10% at 40 days gestation to 30% at term. Fat content increased even more rapidly than dry weight [body fat (g) = 0.00123 e(0.136 X GA), r = 0.97], accounting for 33% of dry weight and 11.7% of wet weight at term. Using bomb calorimetric projections of caloric value of 9.3 kcal X g fat-1 X day-1 and 4.6 kcal X g nonfat dry wt-1 X day-1, we estimate that growth of the fetal guinea pig requires 220 kcal X kg fetal wt-1 X day-1 near term. Carbon and nitrogen contents of the fetus increased at different rates, reflecting the changes in fat and nonfat tissues. Amino acids contributed 80% of total body nitrogen and 41% of total body carbon near term. Cysteine concentrations increased and lysine concentrations decreased with gestational age; the concentrations of the other measured amino acids did not change with gestational age. These studies represent the first systematic study of the chemical growth of the fetus in a nonhuman species.
A radioisotopic technique for analysis of free fatty acid reesterification in human adipose tissue
Authors: Leibel R. L. , Hirsch J.
Published: December 2017

Reesterification rates of free fatty acids (FFA) formed by intracellular triglyceride hydrolysis in small fragments of human adipose tissue were measured. Subcutaneous gluteal adipose tissue, obtained by needle biopsy, was incubated in a buffered albumin medium containing [3H]palmitate and [14C]glucose, each of high specific activity. In triglycerides (TG) and diglycerides (DG) synthesized by the tissue, [14C]glucose is incorporated exclusively into the glyceride-glycerol moiety, and 3H appears solely in the esterified fatty acids. Since rates of TG and DG synthesis can be determined from 14C accumulation rates in these molecules, the total amounts of FFA esterified can also be calculated. The difference between this estimate of total FFA esterification and the moles of [3H]palmitate esterified to these molecules represents the amount of unlabeled FFA from ongoing TG hydrolysis that was reesterified during the incubation. FFA recycling by the reesterification pathway is an important mechanism for the control of the quantity and proportions of FFA and glycerol leaving the human adipocyte. Fasting and beta-adrenergic stimulation reduce the fraction of endogenously released FFA that are reesterified from resting values of 30-40% to 8-21%, thereby increasing the molar ratio of FFA to glycerol leaving the adipocyte. The technique described can be employed to monitor sequential changes in this important metabolic cycle in humans under a wide range of nutritional and clinical circumstances.
Dynamics of pancreatic insulin release in young Zucker rats: a heterozygote effect
Authors: Blonz E. R. , Stern J. S. , Curry D. L.
Published: December 2017

Total pancreatic insulin, dynamic insulin response to glucose (325 mg/dl), or tolbutamide (40 mg/dl) using the isolated perfused pancreas preparation and body composition were determined for 2- and 4-wk-old homozygous lean Fa/Fa, heterozygous lean Fa/fa, unknown lean Fa/??, and homozygous obese fa/fa female Zucker rats. At 2-wk, obese rats (body fat greater than 16%) released significantly more insulin than homozygous lean rats during first (min 10–16) and second phases (min 17–70) (61 vs. 30 ng and 637 vs. 255 ng, respectively). Plasma insulinemia was 177 microU/ml in obese, compared with 51 microU/ml in homozygous lean rats. The dynamic response of unknown lean followed the pattern of either the homozygous lean or the obese rats. There was no significant difference in total pancreatic insulin among any of the groups at 2 wk of age (Fa/Fa, 1.72; Fa/??, 2.01; and Fa/Fa, 1.80 micrograms). At 4 wk, the dynamic response by obese (2.98 micrograms) was similar to that of heterozygous (3.31 micrograms), both being significantly greater than the homozygous lean (1.14 micrograms) or unknown lean rats (1.77 microgram). Total pancreatic insulin in 4-wk obese (19.8 micrograms) was greater than homozygous lean rats (14.5 micrograms). Tolbutamide-stimulated insulin release was significantly greater in 4-wk obese than homozygous lean rats. Exposure to tolbutamide reduced by 60% the second-phase insulin release in both obese and homozygous lean rats during a subsequent 40-min glucose (325 mg/dl) perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)
Measurement using tracers of steady-state turnover and metabolic clearance of insulin in dogs
Authors: Morishima T. , Bradshaw C. , Radziuk J.
Published: December 2017

In nine conscious dogs, the steady-state metabolic clearance rate (MCR) and the systemic appearance rate (Ra) of insulin were determined by the tracer dilution method. [3H-PheB1]insulin ([3H]insulin) was infused as a tracer from time 0 at a constant rate. After tracer equilibration was attained, unlabeled porcine insulin was infused at variable constant rates (10.6–279 mU/min) with somatostatin (0.3 microgram . kg-1 . min-1) to suppress endogenous insulin secretion. Glucose was infused to prevent hypoglycemia. Tritiated and immunoreactive insulin (IRI) concentrations were determined in plasma samples after extraction on a C-18 reverse-phase column. Tracer-determined basal Ra of insulin was 2.39 +/- (SE) 0.61 mU/min. The calculated steady-state Ra of insulin for plasma IRI from 20 to 2,300 microU/ml showed good agreement with insulin infusion rates. The mean ratio of these rates was 0.973 +/- 0.018. The MCR of insulin under basal conditions was 29.9 +/- 3.4 ml . kg-1 . min-1, and it decreased with increasing insulin concentrations. It is concluded that 1) insulin turnover rates can be measured accurately using [3H]insulin as a tracer and 2) insulin kinetics are nonlinear.
Reduced responsiveness of glomerulosa cells after prolonged stimulation with angiotensin II
Authors: Enyedi P. , Szabo B. , Spat A.
Published: December 2017

The purpose of this study was to examine whether sustained exposition to angiotensin modifies the responsiveness of adrenal glomerulosa cells when extra-adrenal factors are eliminated. Isolated rat glomerulosa cells were stimulated for 6 h in a superfusion system with angiotensin II or potassium. Their responsiveness to angiotensin II, potassium, and corticotropin (ACTH) was examined before and after the superfusion. Stimulation of the cells during the superfusion with angiotensin II or with potassium reduced their responsiveness to all three stimuli. The steroid synthesis inhibitor aminoglutethimide, applied during the superfusion, overcame the effect of potassium but failed to influence that of angiotensin. This suggests that the reduced responsiveness after stimulation with potassium is related to the increased steroid production whereas the action of angiotensin is independent of that. The results establish the existence of desensitization to angiotensin in the absence of modifying extra-adrenal factors.
Effect of vitamin D3 metabolites on calcium and phosphorus metabolism in chick embryos
Authors: Hart L. E. , DeLuca H. F.
Published: December 2017

The biochemical nature of the physiological defect found in chick embryos from hens supported on 1,25-dihydroxyvitamin D3 as their sole source of vitamin D is described. Vitamin D-deficient hens (44-wk-old) were divided into six groups of five and dosed daily for 19 wk with either 2.0 micrograms of 25-hydroxyvitamin D3, 2.0 micrograms of 24,24-difluoro-25-hydroxy-vitamin D3, 0.4 micrograms of 1,25-dihydroxyvitamin D3, 2.0 micrograms of 24,25-dihydroxyvitamin D3, 0.4 micrograms of 1,25-dihydroxyvitamin D3 plus 2.0 micrograms of 24,25-dihydroxyvitamin D3, or vehicle only. Normal embryonic development was found in eggs from hens given 25-hydroxyvitamin D3 or 24,24-difluoro-25-hydroxyvitamin D3, whereas embryos from hens given 1,25-dihydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or their combination were abnormal and failed to hatch. Embryos from hens fed 1,25-dihydroxyvitamin D3 and/or 24,25-dihydroxyvitamin D3 had vitamin D deficiency: low bone ash, low plasma calcium, low total body calcium, and extremely high plasma phosphorus. Because the shell is the major source of calcium for the developing embryo, calcium transport from the shell to the embryos across the chorioallantoic membrane apparently fails, giving rise to the observed defects in embryonic development.
Carrier-mediated uptake of methylglyoxal bis(guanylhydrazone) by rat lungs perfused in situ
Authors: Rannels D. E. , Addison J. L. , Pegg A. E.
Published: December 2017

Rat lungs perfused in situ were employed to begin investigations of the pathways by which the tissue takes up circulating polyamines (PA). Uptake kinetics were studied using [14C]methylglyoxal bis(guanylhydrazone) (MGBG), a nonmetabolized substrate analogue thought to enter cells via the PA carrier. Lungs concentrated MGBG from the perfusate at a linear rate for at least 60 min. Uptake was saturable with respect to perfusate MGBG concentration; it exhibited an apparent Km of 12.5 microM and Vmax of 0.6 nmol X g lung-1 X min-1. MGBG (1 microM) uptake was inhibited rapidly and to a similar extent (30-40%) by the naturally occurring PAs spermidine, spermine, or putrescine (50 microM); no additional inhibition of uptake was exerted when all three compounds were present simultaneously (total concentration, 150 microM). No inhibition by 5-hydroxytryptamine was evident. Spermidine produced a half-maximal inhibitory effect at a perfusate concentration of 1.9 microM (vs. 1 microM MGBG). The spermidine-insensitive component of MGBG uptake operated at a Vmax similar to that of the control (total), 1.2 nmol X g-1 X min-1, but the apparent Km was increased 3.5-fold to 44 microM. These observations indicate that MGBG is taken up from the pulmonary circulation by a high-affinity, carrier-mediated, concentrative uptake process that is inhibited, at least in part, by naturally occurring polyamines.
Carbachol modulates GIP-mediated insulin release from rat pancreatic lobules in vitro
Authors: McCullough A. J. , Marshall J. B. , Bingham C. P. , Rice B. L. , Manning L. D. , Kalhan S. C.
Published: December 2017

Rat pancreatic lobules were used to investigate the interaction of gastric inhibitory polypeptide (GIP), carbachol, glucose, and an amino acid mixture on insulin secretion. At 5 mM glucose, GIP (1.1 ng/ml) did not augment insulin secretion in the presence or absence of carbachol (5 X 10(-5)M) during a 210-min incubation. However, at 11 mM glucose, GIP did augment insulin secretion in the presence (342.5 +/- 62.0 vs. 212.5 +/- 50.5 microU . ml-1 . mg tissue-1, mean +/- SE; P less than 0.01) but not the absence (217.0 +/- 45.5 vs. 205.8 +/- 35.0 microU . ml-1 . mg tissue-1) of carbachol. During subsequent 30-min incubations, GIP was increased to a supra-physiological concentration of 11 ng/ml and again augmented insulin secretion with (65.8 +/- 10.8 vs. 27.8 +/- 2.4 microU . ml-1 . mg tissue-1 . h-1; P less than 0.001) but not without (37.2 +/- 1.8 vs. 30.2 +/- 2 microU . ml-1 . mg-1 tissue-1 . h-1) carbachol present. This GIP-mediated insulin secretion was blocked by atropine (34.8 to 1.8 vs. 37.6 +/- 1.6 microU . ml-1 . mg tissue-1 . h-1). At amino acid concentrations of 21 and 211 mM, but not 2.1 mM, GIP augmented insulin release but again only with carbachol present. In conclusion, porcine GIP augments amino acid as well as glucose-mediated insulin secretion in vitro. Furthermore, this biological action is dependent on an, as yet, unidentified cholinergic mechanism. The pathophysiological significance of the neural-hormonal interaction deserves further investigation.
Abnormal oral glucose tolerance in genetically obese (fa/fa) rats
Authors: Ionescu E. , Sauter J. F. , Jeanrenaud B.
Published: December 2017

The effect of intravenous glucose or tolbutamide administration on plasma glucose and insulin levels was compared with that following spontaneous ingestion of glucose in freely moving 6- to 7-wk- and 13- to 14-wk-old lean and obese (fa/fa) rats. Irrespective of age, the obese rats had a normal blood glucose tolerance when glucose or tolbutamide load was given intravenously, whereas the glucose ingestion [oral glucose tolerance test (OGTT) caused a marked glucose intolerance that became more pronounced with the duration of the syndrome. This suggests that factors other than insulin resistance could play a role in the occurrence of abnormal OGTT in obese rats. When blood insulin levels were expressed as percent change over base line and when compared with age-matched normal rats, the 6- to 7-wk obese rats showed a normal and even higher beta-cell responsiveness to intravenous or oral glucose as well as to tolbutamide. In contrast, the 13- to 14-wk obese rats presented a decreased beta-cell responsiveness to all such stimuli. Thus the beta-cell function of obese rats worsens with time. Inasmuch as 13- to 14-wk-old obese fa/fa rats have insulin resistance, high basal glycemia, and abnormal oral glucose tolerance, they can be viewed as a potential model of type II diabetes.
Role of intrapancreatic ganglia in regulation of periodic insular secretions
Authors: Stagner J. I. , Samols E.
Published: December 2017

The regulatory system responsible for insulin oscillations from the in vitro pancreas is unknown. To test the hypothesis that intrapancreatic ganglia are the pacemaker or driver of the oscillations, combined nicotinic, muscarinic, and adrenergic antagonists were infused. Combined muscarinic, alpha- and beta-adrenergic, and presynaptic nicotinic receptor blockade (beta-bungarotoxin) was without effect on oscillations. The infusion of the postsynaptic nicotinic receptor antagonists, hexamethonium, alpha-bungarotoxin (ATX), or curarine, significantly altered the preinfusion oscillatory pattern of insulin release by reducing the period. Nicotine-stimulated insulin release was inhibited by ATX on a background of atropine, phentolamine, and beta-bungarotoxin. Propranolol decreased nicotine-stimulated insulin release, which was further reduced by ATX. These data support the theory that nicotinic receptors may be present pre- and postsynaptically at the ganglionic level and presynaptically on sympathetic nerve axons. We propose that ganglionic nicotinic receptors may be regulatory and that ganglia may serve as the pacemaker to regulate pancreatic hormone oscillations.
Diabetes enhances activity of alanine transport in liver plasma membrane vesicles
Authors: Rosenthal N. R. , Jacob R. , Barrett E.
Published: December 2017

In the present study plasma membrane vesicles were prepared from livers of control and alloxan-induced diabetic rats and the substrate specificity and kinetic characteristics of alanine transport determined in both groups. Sodium-dependent alanine uptake at physiological alanine concentrations (100 microM) was enhanced threefold in diabetic as compared with control animals (0.31 +/- 0.04 vs. 0.11 +/- 0.01 nmol X mg protein-1 X 10 s-1). This accelerated influx corresponded to a three- to fourfold increase in the Vmax of alanine transport in diabetic versus control group (7.1 +/- 2.1 vs. 1.6 +/- 0.2 nmol X mg protein-1 X 10 s-1, P less than 0.05), whereas the Km of alanine uptake was unchanged (2.8 +/- 1.2 vs. 1.4 +/- 0.1 mM). Other neutral amino acids (20 mM) inhibited alanine transport to a similar degree in both groups. The sodium-dependent influx of glutamine (100 microM) was similar in diabetic and control groups (0.17 +/- 0.03 and 0.14 +/- 0.02 nmol X mg protein-1 X 10 s-1, respectively). The initial velocity of 22Na uptake (80 mM) into vesicles and half-maximal stimulation of alanine transport was achieved at essentially identical sodium concentrations (approximately 40 mM) in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanisms involved in alpha-adrenergic phenomena
Authors: Exton J. H.
Published: December 2017

Epinephrine and norepinephrine exert many important actions by interacting with alpha 1- and alpha 2-adrenergic receptors in their target cells. Activation of alpha 2-adrenergic receptors causes platelet aggregation and other inhibitory cellular responses. Some of these responses are attributable to a decrease in cAMP due to inhibition of adenylate cyclase. Activation of alpha 2-adrenergic receptors promotes their coupling to an inhibitory guanine nucleotide binding protein (Ni). This coupling promotes the binding of GTP to Ni, causing it to dissociate into subunits. This results in inhibition of the catalytic component of adenylate cyclase. Activation of alpha 1-adrenergic receptors stimulates the contraction of most smooth muscles and alters secretion and metabolism in several tissues. The primary event is a breakdown of phosphatidylinositol-4,5-bisphosphate in the plasma membrane to produce two intracellular "messengers": myo-inositol-1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol (DAG). IP3 causes the release of Ca2+ from endoplasmic reticulum, producing a rapid rise in cytosolic Ca2+. Ca2+ binds to the regulatory protein calmodulin, and the resulting complex interacts with specific or multifunctional calmodulin-dependent protein kinases and other calmodulin-responsive proteins, altering their activities and thereby producing a variety of physiological responses. DAG also produces effects by activating a Ca2+-phospholipid-dependent protein kinase (protein kinase C) that phosphorylates and alters the activity of certain cellular proteins. Frequently there is synergism between the IP3 and DAG mechanisms.
Effects of growth hormone on lipogenic enzyme activities in cultured rat hepatocytes
Authors: Schaffer W. T.
Published: December 2017

The presence of cloned methionyl human growth hormone at 1 microgram/ml medium for the final 5 days of a 6-day culture period decreased the activity of malic enzyme (EC 1.1.1.40) 45% from 202 to 112, fatty acid synthetase 52% from 26 to 12, and ATP citrate lyase (EC 4.1.3.8) 20% from 192 to 154 nmol NADPH.min-1.mg-1 supernatant protein in rat hepatocytes maintained in serum-free primary culture. Also, the activity of mitochondrial glycerol-3-phosphate dehydrogenase (EC 1.1.99.5) decreased 52% from 20 to 9 nmol.min-1.mg-1 mitochondrial protein. In the same cells, no changes were observed in the activity of 6-phosphogluconate dehydrogenase (EC 1.1.1.44) and lactate dehydrogenase (EC 1.1.1.27). Glucose-6-phosphate dehydrogenase (EC 1.1.1.49) was increased 2.4-fold from 70 to 183 nmol.min-1.mg-1 protein, indicating the activity of this enzyme was paradoxically increased, whereas other enzymes involved in lipogenesis were decreased. Half-maximal decrease of malic enzyme activity and increase of glucose-6-phosphate dehydrogenase activity occurred at 10 and 3 ng methionyl human growth hormone per milliliter medium, respectively. These values are within the range of normal circulating growth hormone concentrations in the rat. The effects on malic enzyme and glucose-6-phosphate dehydrogenase appeared after 3-day exposure to growth hormone. These findings are consistent with the hypothesis that growth hormone antagonizes the action of agents that stimulate the activity of malic enzyme while concomitantly increasing the extractable activity of glucose-6-phosphate dehydrogenase.
Insulin action on membrane potential and glucose uptake: effects of high potassium
Authors: Zierler K. , Rogus E. M. , Scherer R. W. , Wu F. S.
Published: December 2017

These experiments were designed to test the hypothesis that insulin-induced hyperpolarization is a link in the chain of events leading to stimulation of glucose transport. External potassium concentration, [K+]o, was increased by equimolar substitution of KCl for NaCl, a method known to cause cell swelling, and by substitution of [K+]o for [Na+]o with maintenance of constant [K+]o X [Cl-]o product, a method that does not cause cell swelling. When there was constant KCl product, even at 76.8 meq [K+]o insulin continued to hyperpolarize, although by only approximately 44% as much as in normal [K+]o, and insulin-stimulated 2-deoxyglucose uptake was only approximately 60% of that at normal [K+]o. With equimolar substitution of KCl for NaCl: electrical potential difference across cell membranes of surface fibers of rat caudofemoralis muscle decreased with logarithm [K+]o, in the presence or absence of insulin. Insulin-induced hyperpolarization decreased as [K+]o increased and disappeared at 36 mM [K+]o. The amount of insulin bound to its receptors in 1 h was not affected by [K+]o over the range studied. Insulin effects on membrane potential and on 2-deoxyglucose uptake, as both were altered by [K+]o, correlated well. As the probe moved in depth through the first six fibers there was stepwise decrease in depolarization in high [K+]o in the absence of insulin. Insulin hyperpolarized the deepest of these fibers, even when it did not hyperpolarize the outermost. The decrease in insulin-induced hyperpolarization as [K+]o increases is consistent with the hypothesis that insulin hyperpolarizes by decreasing the ratio PNa/PK.
Time course of changes in gluconeogenic enzyme activities during exercise and recovery
Authors: Dohm G. L. , Kasperek G. J. , Barakat H. A.
Published: December 2017

Gluconeogenic enzymes were assayed after varying periods of exercise and recovery to determine how rapidly changes occur and whether they persist after the cessation of exercise. Untrained male rats (250 g) ran on a treadmill at 28 m/min and were killed after varying periods of exercise and recovery. Livers were quickly removed and analyzed for maximal enzyme activities (saturating levels of substrate) and submaximal activities (low-substrate concentrations). The most significant enzyme changes during exercise were increased maximal activity of phosphoenolpyruvate carboxykinase (PEPCK) and decreased submaximal activity of phosphofructokinase (PFK). Submaximal PFK activity was decreased by 30 min of exercise and remained at that low level up to exhaustion (172 +/- 16 min). Changes in submaximal PFK activity are in response to decreased concentrations of fructose-2,6-bisphosphate that were decreased to approximately one-tenth the control value after 30 min of exercise and remained low throughout exercise and 1 h of recovery. The PEPCK activity progressively increased during exercise and was highest at exhaustion. The cAMP level was significantly elevated in liver of rats exercised for 30 min and continued to rise with duration. Six hours after exercise PEPCK and submaximal PFK activities were the same in control and exercised-rested rats. The change in PEPCK activity is consistent with an increase in the rate of enzyme synthesis and/or a decrease in enzyme degradation during exercise, whereas the lowered activity of PFK likely reflects covalent modification of 6-phospho-fructo-2-kinase/fructose-2,6-bisphosphatase.
Metabolic adaptation to reduced muscle blood flow. I. Enzyme and metabolite alterations
Authors: Elander A. , Idstrom J. P. , Schersten T. , Bylund-Fellenius A. C.
Published: December 2017

A rat model was developed in which the adaptive effects of exposing skeletal muscle tissue to a reduced blood flow during muscle contractions could be studied. The common iliac artery was ligated in one hindlimb, using the other as control. This procedure reduced the exercise blood flow to the individual muscles of the lower limb by 76-93%, evaluated with the microsphere technique. Muscle contractions were induced by electrical stimulation of the sciatic nerves in both legs. After intermittent stimulation for 6 days, a significant increase in citrate synthase and cytochrome c oxidase activities was found in the soleus (26%) and extensor digitorum longus (EDL, 20%) muscles of the ligated legs compared with the control legs. Resting metabolite concentrations were also measured, and a reduction of the ATP level (soleus 35%, EDL 14%) and an increased glycogen content (55-71%) were found. These results demonstrate that a reduced blood flow during muscle contractions provokes an adaptive increase of the oxidative enzyme capacity as well as altered resting levels of intracellular metabolites.
Decreased in vitro secretion of LH, FSH, and free alpha-subunits by pituitary cells from old male rats
Authors: Blackman M. R. , Mukherjee A. , Tsitouras P. D. , Harman S. M.
Published: December 2017

Various in vivo and in vitro pituitary-Leydig cell functions were examined in mature (5-8 mo) vs. old (22-25 mo) male Wistar rats. Old rats exhibited decreased serum concentrations of testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) (P less than 0.0025) but similar levels of prolactin (P less than 0.01) both before and 4 wk after castration. The in vitro release of LH, FSH, and free alpha-subunits was measured in primary cultures of dispersed anterior pituitary cells from both intact and castrated rats. During 48 h of incubation, basal secretion rates of the glycoproteins were decreased (P less than 0.001) from cells of both intact and castrated old rats. After stimulation with LH-releasing hormone (LRH) in single (10(-8) M) or multiple (10(-10) - 10(-7) M) doses, the total amounts of the glycoproteins secreted were also less from cells of both intact and castrated old rats. However, repeated measures analysis of variance revealed age-related hyporesponsivity to LRH stimulation only for LH secretion by cells from intact rats. The basal molar ratios of alpha/(LH + FSH) secreted by cells from intact but not castrated old rats were lower than those from cells of the corresponding mature rats. Moreover, after LRH stimulation (10(-10) - 10(-7) M), molar secretory ratios of alpha/(LH + FSH) decreased from cells of intact mature rats but increased from cells of intact old rats. These in vitro data suggest that the reduced serum LH and FSH levels in intact and castrated old male rats result in part from decreased secretion of these glycoproteins.(ABSTRACT TRUNCATED AT 250 WORDS)
Selective insulinization of liver in conscious diabetic dogs
Authors: Spangler R. S.
Published: December 2017

Insulin encapsulated in lipid vesicles and targeted to hepatocytes by means of a digalactosyl diglyceride moiety [(designated vesicle encapsulated insulin (VEI)] was administered intravenously to conscious catheterized diabetic dogs to determine the effects of hepatic and extrahepatic glucose utilization. Our results indicate that VEI administered intravenously to diabetic dogs over a dose range of 0.5 to 2.0 mU X kg-1 X min-1 reduces hepatic glucose output or induces hepatic glucose uptake without causing any significant alteration in the rate of extrahepatic glucose utilization. Steady-state comparisons of 1.0 mU X kg-1 X min-1 VEI with intraportal and peripherally administered insulin revealed that VEI and intraportal insulin result in significantly less extrahepatic glucose utilization than does an equivalent dose of peripherally administered insulin (6.36 +/- 1.21 and 5.08 +/- 0.97 vs. 8.82 +/- 1.61 mg X kg-1 X min-1; P less than 0.03). Through the use of VEI, we were able to significantly alter the deposition of intravenously administered glucose from 11% hepatic and 89% extrahepatic noted with peripheral insulin to 35% hepatic and 65% extrahepatic with VEI (P less than 0.03). Thus, by encapsulating insulin into a lipid carrier specifically targeted to the liver, selective hepatic insulinization can be achieved. As a result of this approach, one can alter the distribution of a glucose load to favor hepatic deposition.
Role of serotonin type 2 receptors in regulation of aldosterone production
Authors: Matsuoka H. , Ishii M. , Goto A. , Sugimoto T.
Published: December 2017

It is well recognized that serotonin stimulates aldosterone production by the adrenal glands. To investigate the possible roles of serotonin type 1 and 2 receptors in the regulation of aldosterone production, we examined the effects of cyproheptadine (a serotonin antagonist that inhibits both type 1 and 2 receptors) and ketanserin (a serotonin type 2 selective antagonist) on aldosterone and cAMP production in collagenase dispersed rat adrenal capsular cells. Serotonin, ranging in concentration from 10(-9) to 10(-3) M, significantly increased aldosterone production in a dose-dependent fashion after 2 h of incubation at 37 degrees C. Cyproheptadine and ketanserin showed comparable inhibitory effects on basal aldosterone production. These serotonin antagonists preferentially inhibited serotonin-induced aldosterone production. Serotonin significantly increased cAMP production at a dose of 10(-6) M. Both cyproheptadine and ketanserin significantly decreased basal cAMP production at doses of 10(-5) M. These serotonin antagonists preferentially inhibited serotonin-stimulated cAMP production. These results suggest that adrenal serotonin type 2 receptors may be coupled with adenylate cyclase activity and that these receptors are involved in the regulation of aldosterone production. Whether serotonin plays an important role in the regulation of aldosterone secretion in vivo remains to be elucidated.
Glucocorticoid receptors in sheep brain tissues during development
Authors: Rose J. C. , Kute T. E. , Winkler L.
Published: December 2017

In this study we describe changes in the number of glucocorticoid binding sites that occur in cytosols of pituitary, hypothalamic, and hippocampal tissue obtained from fetal, newborn, and adult sheep. We observed specific, saturable binding of [3H]triamcinolone acetonide by cytosols of all three tissues. There were both age-related and tissue-related differences in the number of binding sites observed. By midgestation (70 days) significant quantities of binding sites were present in pituitary and brain tissues, and the number remained relatively constant throughout gestation and in the neonatal period. The number of binding sites declined markedly in cytosols from adult tissues. At all ages there were more binding sites present in pituitary cytosols than in cytosols of hypothalamus and hippocampus. The sucrose density gradient profile of the radioactive ligand-binding site complex is characteristic of a glucocorticoid receptor. Thus, by midgestation at least a portion of the biochemical machinery mediating glucocorticoid effects is present in the fetal pituitary and in specific brain tissues considered important in the modulation of ACTH secretion by corticosteroids.
Altered aortic and cremaster muscle prostaglandin synthesis in diabetic rats
Authors: Myers T. O. , Messina E. J. , Rodrigues A. M. , Gerritsen M. E.
Published: December 2017

Alterations in the synthesis and release of prostaglandins have been reported in humans and animal models of diabetes mellitus. In the present study synthesis and release of prostaglandins by thoracic aorta and cremaster muscle of rats with streptozotocin-induced diabetes of 8 wk duration was compared with age-matched controls. Prostaglandin synthesis was assessed by the measurement of immunoreactive prostaglandin E2 (PGE2) and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) release and by quantifying metabolism of exogenous [1-14C]arachidonic acid by thoracic aortic rings and minced cremaster muscle.The cremaster muscles from diabetic rats released significantly greater quantities of PGE2 and 6-keto-PGF1 alpha and PGE2. In contrast, the aortas from diabetic rats released smaller quantities of 6-keto-PGF1 alpha and PGE2 and exhibited reduced 6-[1-14C]keto-PGF1 alpha. These studies indicate that diminished prostacyclin (PGI2) and/or PGE2 production is not a general feature of all diabetic vascular tissues, suggesting that large and small blood vessels may not be similarly affected by diabetes in regard to the metabolism of exogenous arachidonic acid and the synthesis and release of prostaglandins. Furthermore, the vascular changes often observed in conjunction with diabetes, i.e., alterations in vascular reactivity and microangiopathy in small blood vessels and atherosclerosis of large blood vessels may be related in some way to the segmental differences observed in prostaglandin synthesis.
Effects of ovine maternal hyperglycemia on fetal regional blood flows and metabolism
Authors: Crandell S. S. , Fisher D. J. , Morriss F. H.
Published: December 2017

Fetal combined ventricular output (CVO) and regional distribution of blood flow were measured in 12 ewes in late gestation by the radiolabeled microsphere method. Three sets of determinations were made in sequence beginning with a control study and repeating the measurements after the ewe had received intravenous glucose at 0.35 g X min-1 for 90 min and again after the ewe had received glucose at 0.85 g X min-1 for a second 90-min period. Maternal whole blood glucose concentrations were 2.98 +/- 0.18 (means +/- SE), 10.43 +/- 0.45, and 21.59 +/- 0.90 mM during the respective study periods. Fetal CVO did not change during maternal hyperglycemia; however, it was redistributed, with a decrease in umbilical blood flow to the placenta from 43.5% of CVO to 31.9 and 30.8%, respectively. The fetal carcass, heart, intestines, kidneys, liver, and adrenals each received increased percent CVO; these increases equaled the decrease in placental blood flow. Fetuses became hypoxemic and developed a mixed acidemia during induced maternal hyperglycemia, but oxygen delivery to the heart, brain, and kidneys was unchanged. These observations indicate that maternal hyperglycemia results in previously unsuspected fetal cardiovascular responses.
Meal-induced brown fat thermogenesis and thyroid hormone metabolism in rats
Authors: Glick Z. , Wu S. Y. , Lupien J. , Reggio R. , Bray G. A. , Fisher D. A.
Published: December 2017

The relationship between the meal-induced increase in brown adipose tissue (BAT) thermogenesis, determined by the level of GDP binding to BAT mitochondria, and thyroid hormone metabolism have been examined. A single low-protein, high-carbohydrate meal resulted in a significant increase in the thermogenic activity of BAT. This effect on BAT thermogenesis was accompanied by significant increases in activity of thyroxine 5'-monodeiodinase in the BAT (P less than 0.05) and liver (P less than 0.02) but not with any significant changes in serum concentrations of the thyroid hormones. The stimulatory effects of the meal on BAT thermogenesis and hepatic thyroxine (T4) to triiodothyronine (T3) conversion persisted at least as late as 24 h after meal onset. Food deprivation for 40 h was associated with large reductions in serum concentrations of T3 (P less than 0.01) and T4 (P less than 0.001), but deprivation for 18 h had no significant effect on serum T3 and T4 concentrations. Our data indicate that the meal-induced increase in BAT thermogenesis can be independent from changes in serum concentrations of thyroid hormones and suggest that T3 produced in BAT in response to feeding may play a role in the thermic response of this tissue to meals.
Testosterone transport in brain: primary role of plasma protein-bound hormone
Authors: Pardridge W. M. , Landaw E. M.
Published: December 2017

Physiologically based mathematical modeling is used to predict the steady-state concentration of intracellular free and bound testosterone in brain. On the basis of previous in vivo tracer kinetic studies of blood-to-brain and brain-to-blood transport of testosterone in the rat, values are assigned to various physiological parameters (hormone association and dissociation reactions with plasma and cytosolic binding proteins, capillary transit time, and membrane transport). The model does not adhere to the restrictions of the free hormone hypothesis and allows for the enhanced transport of hormone from the plasma protein-bound pool into the tissue extravascular space. This process is believed to occur via an endothelial inhibition of ligand binding to the plasma protein without the protein crossing the endothelial wall. The model predicts that the steady-state concentration of intracellular free hormone changes in parallel more closely to changes in the concentration of plasma protein-bound hormone as measured in vitro and not the free hormone as measured in vitro.
Pentobarbital suppresses basal and reflexive pancreatic polypeptide release in dogs
Authors: Taborsky G. J. , Paquette T. L. , Pfeifer M. A. , Gingerich R. L.
Published: December 2017

We sought to determine in overnight-fasted dogs whether basal or 2-deoxy-D-glucose (2-DG)-stimulated levels of pancreatic polypeptide (PP) could be reliably used as an index of cholinergic activity at the pancreas and thereby determine the effect of pentobarbital anesthesia on this cholinergic outflow. At low basal PP levels, either atropine or pentobarbital had a small effect on PP levels; at higher basal levels, both atropine and pentobarbital had a larger effect. Thus both drugs decreased PP in proportion to its initial basal level, suggesting that basal PP levels have a variable cholinergic component. Atropine abolished the PP response to intravenous 2-DG, confirming in our animal model that the PP response to neuroglucopenia is entirely cholinergically mediated. Pentobarbital also abolished the PP response to 2-DG, suggesting that anesthesia either suppresses cholinergic outflow to the pancreas or the response of the pancreatic F-cell to it. To test the latter hypothesis, the acetylcholine analogue bethanechol was administered before and during pentobarbital anesthesia. The PP response to direct cholinergic stimulation was not abolished by pentobarbital, although it was reduced modestly. We conclude that only part of the basal level of PP is under cholinergic control; all of the PP response to 2-DG is cholinergically mediated; pentobarbital anesthesia abolishes the cholinergic input to the pancreas; and if the endogenous cholinergic input influences certain pancreatic endocrine and exocrine responses, then its contribution would be seriously underestimated when studied in pentobarbital-anesthetized animals.
Effect of chronic alcohol intake on muscle composition and metabolic balance of calcium and phosphate in rats
Authors: Adler A. J. , Fillipone E. J. , Berlyne G. M.
Published: December 2017

Chronic alcoholism is associated with abnormalities of serum and muscle mineral metabolism. Decreased muscle phosphate and magnesium and increased muscle calcium have been proposed as significant factors in the development of alcoholic myopathy. As the mechanisms producing these abnormalities remain unknown, we sought to reexamine these findings and investigate the extent to which the kidney and gastrointestinal tract contribute to their pathogenesis. Serum and muscle from rats receiving 20% of their caloric intake as ethyl alcohol were analyzed for PO4, Ca, Mg, Na, and K at 0 and 20 wk and compared with isocalorically fed normals. In addition, individual metabolic balance studies were carried out over 72 h for Ca and PO4 in normal and alcohol-fed rats. The results of serum and muscle analyses did not reveal any differences among the groups for any of the minerals examined. Metabolic balance studies demonstrated that despite a significantly lower Ca and PO4 intake in the alcoholic rats (P less than 0.003) net balance remained the same as in controls. This was due to the retention of a significantly larger proportion of the ingested mineral and was achieved for both Ca (P less than 0.05) and PO4 (P less than 0.03) by means of greater gastrointestinal absorption and additionally for PO4 by a reduction in renal excretion (P less than 0.005). We conclude that in the rat chronic alcohol ingestion is not associated with abnormalities in serum or muscle mineral concentrations, normal adaptive mechanisms by the kidney and gastrointestinal tract compensate appropriately for differences in dietary Ca and PO4, and the rat may not be a suitable species for the study of metabolic effects of chronic alcoholism.
Occupied and unoccupied estrogen receptor during estrous cycle and pregnancy
Authors: Leavitt W. W. , Okulicz W. C.
Published: December 2017

Occupied and unoccupied forms of estrogen receptor (Re) were measured in hamster uterus during the estrous cycle and pseudopregnancy with a new assay method employing pyridoxal 5'-phosphate. In the cycle, occupied Re increased in cytosol and nuclear fractions in parallel with increasing serum estradiol during the follicular phase and then dropped sharply in both compartments during preovulatory progesterone secretion. Unoccupied Re occurred primarily in cytosol with low levels present in nuclei. It is pertinent that similar concentrations of occupied Re accumulate in cytosol and nuclear fractions, suggesting that occupied Re is distributed between these compartments according to an equilibrium model. Progesterone disrupts Re distribution through a selective action on the nucleus to downregulate occupied Re as was shown by progesterone treatment of the proestrous hamster. Re is chronically downregulated in the progesterone-dominated uterus, and the occupied form of Re recovers rapidly after progesterone withdrawal. Thus progesterone downregulates the Re system under physiological conditions by a selective action on the occupied form of Re in the target cell nucleus.