bluuebunny/crossref_metadata_2025 huggingface dataset:
DOPA, norepinephrine, and dopamine in rat tissues: no effect of sympathectomy on muscle DOPA
Authors: Eldrup E. , Richter E. A. , Christensen N. J.
Published: December 2017

We studied the effect of unilateral sympathectomy on rat quadriceps and gastrocnemius muscle concentrations of endogenous dihydroxyphenylalanine (DOPA), dopamine (DA), and norepinephrine (NE) and assessed the relationships between these catecholamines in several rat tissues. Catecholamines were measured by reverse-phase high-performance liquid chromatography with electrochemical detection. Sympathectomy decreased NE and DA concentrations of muscles to approximately 10% of control values, whereas the DOPA concentration tended to increase. Relatively high concentrations of DOPA were found in the gastrointestinal tract, kidney, and spleen. No correlations were obtained between the tissue concentration of DOPA and NE. A DA-to-NE ratio approximately 1% was observed in liver, muscle, pancreas, spleen, and heart, whereas we found exponentially increasing DA values with increasing NE concentration in tissues obtained from stomach, small and large intestine, kidney, and lung. In conclusion, endogenous DOPA in muscle tissue is not located in sympathetic nerve terminals but probably in muscle cells. DA concentrations in the gastrointestinal tract and in the kidneys were greater than could be ascribed to its role as a precursor in the biosynthesis of NE.
Leucine metabolism in aging humans: effect of insulin and substrate availability
Authors: Fukagawa N. K. , Minaker K. L. , Young V. R. , Matthews D. E. , Bier D. M. , Rowe J. W.
Published: December 2017

To elucidate the relative roles of insulin (I) and amino acid (AA) availability on body protein economy and AA kinetics, we compared whole body leucine kinetic responses, using a 360-min constant infusion of L-[1-13C]leucine, during administration of an L-AA solution to six healthy young (21-25 yr) and six healthy old (72-87 yr) men (study 1) to those when the AA solution was given in conjunction with a euglycemic I clamp (study 2). In study 1, serum I increased significantly (P less than 0.02) by 4 +/- 1 and 4 +/- 2 microU/ml in young (Y) and old (O) men, respectively. In study 2, I was raised to 91 +/- 7 (Y) and 88 +/- 7 (O) microU/ml; the glucose infusion to maintain euglycemia in the Y was significantly greater than in the O (8.0 +/- 0.1 vs. 6.8 +/- 1.9 mg.kg-1.min-1). Leucine flux and oxidation increased significantly in both age groups during the administration of AA. Estimates of leucine released from protein breakdown declined (P less than 0.01) by 18 and 20% in study 1 and 2, respectively, in the young and by 12 and 44%, respectively, in the elderly. Rates of leucine incorporation into protein increased (P less than 0.01) similarly in both age groups and in both studies. These findings emphasize the importance of AA availability in the stimulation of protein synthesis and suggest that insulin's major role in vivo is to repress whole body proteolysis. Furthermore, despite evidence of an age-related decline in glucose disposal, the elderly had similar leucine kinetic responses to hyperaminoacidemia.
AMP and IMP dephosphorylation by soluble high- and low-Km 5'-nucleotidases
Authors: Spychala J. , Madrid-Marina V. , Nowak P. J. , Fox I. H.
Published: December 2017

Three distinct 5'-phosphomonoesterase activities were isolated from soluble fractions of human placenta, cultured human T and B lymphoblasts, and rat liver using 5'-AMP-sepharose 4B affinity chromatography. We define these activities as "low-Km" 5'-nucleotidase, "high-Km" 5'-nucleotidase, and nonspecific phosphatase. High-Km 5'-nucleotidase was eluted with 0.5 M NaCl, low-Km 5'-nucleotidase was eluted with 10 mM ADP, and nonspecific phosphatase was not retained on the column. We have found significant variability in the relative content of high- to low-Km activities in the tissues studied with the ratios ranging from 5.5 to 264. The properties were studied after further purification. The molecular mass of the low-Km enzymes ranged from 72.5 to 209 kDa, optimum pH ranged from 7.4 to 9.0, Km for AMP ranged from 7 to 15 microM, and Km for IMP ranged from 10 to 26 microM. The molecular mass of the high-Km enzymes ranged from 182 to 210 kDa, pH optimum was at 6.5, Km for AMP ranged from 3.0 to 9.4 mM, and the Km for IMP ranged from 0.3 to 0.5 mM. The data indicate that the soluble low- and high-Km 5'-nucleotidase coexist in the mammalian cells and tissues studied. These observations suggest a complex system for the regulation of nucleoside 5'-monophosphate dephosphorylation.
Reversal of the toxic effects of cachectin by concurrent insulin administration
Authors: Fraker D. L. , Merino M. J. , Norton J. A.
Published: December 2017

Rats treated with recombinant human tumor necrosis factor-cachectin, 100 micrograms/kg ip twice daily for 5 consecutive days, had a 56% decrease in food intake, a 54% decrease in nitrogen balance, and a 23-g decrease in body weight gain vs. saline-treated controls. Concurrent neutral protamine hagedorn insulin administration of 2 U/100 g sc twice daily reversed all of these changes to control levels without causing any treatment deaths. The improvement seen with insulin was dose independent. Five days of cachectin treatment caused a severe interstitial pneumonitis, periportal inflammation in the liver, and an increase in wet organ weight in the heart, lungs, kidney, and spleen. Concurrent insulin treatment led to near total reversal of these histopathologic changes. Cachectin treatment did not significantly change blood glucose levels from control values of 130-140 mg/dl, but insulin plus cachectin caused a significant decrease in blood glucose from 1 through 12 h after injection. Administration of high-dose insulin can near totally reverse the nutritional and histopathologic toxicity of sublethal doses of cachectin in rats.
L-leucine or its keto acid potentiate but do not initiate insulin release in chicken
Authors: Rideau N. , Simon J.
Published: December 2017

In the isolated perfused chicken pancreas, 20 and 40 mM L-leucine or 10–40 mM alpha-ketoisocaproic acid (alpha-KIC) did not initiate insulin release. In the presence of 14 mM glucose (a noninsulinotropic concentration), 20 mM L-leucine and 10 mM alpha-KIC evoked a slight biphasic insulin release. The response to 20 mM L-leucine was further increased when 14 mM glucose was combined with 10 mM L-glutamine (10 mM glutamine alone did not induce insulin release and did not potentiate the response to 10 mM L-leucine). At 1 mM, 8-bromo-adenosine 3',5'-cyclic monophosphate (8-BrcAMP) alone caused a slight and progressive increase in insulin secretion but did not sensitize the pancreas to either 20 mM L-leucine or 10 mM alpha-KIC, whereas it facilitated a marked insulin release in response to 14 mM glucose. On the other hand, 10–40 mM K+ or 20 mM L-arginine induced a rapid monophasic insulin output. In conclusion, L-leucine or alpha-KIC, which do not initiate insulin release alone and are not potentiated by 8-BrcAMP, may not be regarded as primary insulinotropic agents in the chicken. This result, together with the previously documented resistance of the chicken pancreas to glucose alone or to D-glyceraldehyde, strongly suggests that the mechanisms initiating insulin secretion are different in chickens and mammals, whereas potentiating mechanisms (low glucose concentration, arginine, acetylcholine, and cAMP) and membrane depolarization events (K+ and arginine) are present in both chickens and mammals.
Enhanced acute response to corticosterone in genetically obese (ob/ob) mice
Authors: Tokuyama K. , Himms-Hagen J.
Published: December 2017

Our previous work showed that ob/ob mice responded to physiological concentrations of blood corticosterone (maintained by implanted pellets of corticosterone in adrenalectomized mice) by increasing food intake and blood insulin concentration to a much greater extent than did lean mice. The present study sought to determine whether the chronic presence of corticosterone was necessary or whether a single injection would also have these effects. Lean and ob/ob mice were adrenalectomized at 4.5 wk of age, injected with corticosterone at 10.5 wk of age, and killed 6 or 15 h after injection. A markedly exaggerated hyperinsulinemia was seen in ob/ob mice at 15 h. Food intake increased in both lean and obese mice, and brown adipose tissue thermogenesis (as reflected by mitochondrial guanosine 5'-diphosphate binding) was suppressed in both. We conclude that the ob/ob mouse has an excessive central sensitivity and responsiveness to a rapid action of corticosterone that results in neural activation of insulin secretion and suppression of brown adipose tissue thermogenesis. The persistence of some degree of obesity in the adrenalectomized ob/ob mouse is attributed to the remaining slight hyperinsulinemia coupled with reduced energy expenditure due to persistent thermoregulation at a lower than normal body temperature.
Fuel-mediated teratogenesis: biochemical effects of hypoglycemia during neurulation in mouse embryos in vitro
Authors: Hunter E. S. , Sadler T. W.
Published: December 2017

Hypoglycemia has been reported to induce congenital malformations and growth retardation in rodent embryos during the period of neural tube closure in vitro. However, the biochemical alterations responsible for the production of the dysmorphogenic effects have not been evaluated. Therefore, the rates of glucose metabolism by glycolysis, citric acid cycle, oxidative pentose phosphate pathway (PPP), and anabolic utilization were evaluated in mouse embryos and extraembryonic membranes using the whole embryo culture technique. Altered glucose metabolism by glycolysis and oxidative PPP, as well as altered anabolic synthesis, were produced by exposure to hypoglycemia. In embryos exposed to mild hypoglycemia (80 mg/dl) altered metabolism by the PPP and an associated effect on nucleic acid synthesis were in part responsible for the dysmorphogenic effects of this treatment. In contrast, severe hypoglycemia (40 mg/dl) appeared to have an immediate effect on glycolytic metabolism in addition to effects on the PPP and nucleic acid synthesis. Therefore, a multifactorial biochemical mechanism contributes to the induction of malformations by severe hypoglycemia in mouse embryos in vitro. Furthermore, the differential effects of moderate vs. severe hypoglycemia on glycolytic metabolism, and possibly energy production, may account for the differences in the severity of these treatments on embryonic growth and the incidence of malformations.
Beta-endorphin and islet hormone release in humans: evidence for interference with cAMP
Authors: Giugliano D. , Cozzolino D. , Ceriello A. , Salvatore T. , Paolisso G. , Torella R.
Published: December 2017

The present studies were undertaken to characterize further the influence of synthetic human beta-endorphin (0.5 mg/h) on insulin and glucagon responses to intravenous glucose in humans. Infusion of beta-endorphin in 10 normal volunteers caused a clear-cut inhibition of the overall insulin responses to a glucose pulse (0.33 g/kg iv) with values of glucose disappearance rates in the diabetic range [0.89 +/- 0.09 (P less than 0.01) vs. saline 1.82 +/- 0.15%/min]. Glucose-induced glucagon suppression was significantly lower during beta-endorphin, a fact that could have contributed to the reduced glucose utilization rates. The infusion of theophylline (150 mg + 350 mg/h) to increase the intracellular cAMP activity by inhibiting phosphodiesterase completely reversed the inhibitory effect of beta-endorphin on glucose-induced insulin secretion. As a consequence, glucose disappearance rates rose to 1.77 +/- 0.18%/min. Theophylline did not influence significantly the glucagon-releasing effect of beta-endorphin as well as the reduced glucagon suppression. An infusion of exogenous calcium (100 mg as iv bolus + 5 mg/min) to raise serum calcium in the hypercalcemic range (15 mg/dl) and lysine acetylsalicylate (72 mg/min) to block the synthesis of endogenous prostaglandin E did not interfere with the inhibiting effect of beta-endorphin on insulin secretion. These data confirm that beta-endorphin stimulates glucagon and inhibits basal and glucose-stimulated insulin secretion and suggest that the opioid influences the intraislet adenylate cyclase activity.
Effects of ketamine and fentanyl on lung metabolism in perfused rat lungs
Authors: Martin D. C. , Carr A. M. , Livingston R. R. , Watkins C. A.
Published: December 2017

The effects of ketamine and fentanyl on serotonin (5-hydroxytryptamine; 5-HT) metabolism, angiotensin-converting enzyme (ACE), and protein synthesis (PS) were investigated in an isolated lung model. Rat lungs were perfused in situ with a blood-free physiological salt solution. The pulmonary vasculature was exposed to ketamine (0.005-2.1 mM) or fentanyl (1.8-4.5 microM) for up to 2 h. After 1 h, accumulation of 5-[14C]hydroxyindoleacetic acid (5-HIAA) by the lung was monitored as an index of 5-HT metabolism. ACE activity was estimated from hydrolysis of [3H]benzoylphenylalanyl-alanyl-proline, a synthetic substrate for the enzyme. [3H]phenylalanine was added to the perfusate after 1 h, and its incorporation into acid-precipitable lung protein was measured over the subsequent hour. Ketamine inhibited 5-HT uptake in a concentration-related manner. The inhibition was characterized as competitive and reversible. Fentanyl had no effect on lung 5-HIAA accumulation. Neither drug altered ACE activity or protein synthesis over the concentration ranges tested. The results indicate an action by ketamine that inhibits the 5-HT membrane-transport process. The different effects observed by ketamine and fentanyl on this process could contribute to the diverse pharmacological properties of these two drugs.
Importance of ammonium ions in regulating hepatic glutamine synthesis during fasting
Authors: Cersosimo E. , Williams P. , Geer R. , Lairmore T. , Ghishan F. , Abumrad N. N.
Published: December 2017

Four-day fasting in the conscious dog is associated with enhanced ammoniagenesis in both the gut and kidneys and a switch in the hepatic glutamine balance from net uptake to that of net production. In the present study we examined the role that the rise in portal venous ammonium ions plays in regulating nitrogen metabolism in vivo. Three groups of 18- to 24-h fasted conscious dogs with catheters surgically implanted in the femoral artery and in the hepatic, portal, and renal veins for 17-21 days were studied. On the day of the study, one group (n = 6) received intraportal ammonium acetate at 3.0 mumol.kg-1.min-1 intended to result in portal venous ammonium ion levels slightly above those seen in the 4-day fasted dog. Another group (n = 5) received an equimolar infusion of sodium acetate, and a third group (n = 6) received saline (0.9%) and acted as controls. Organ balances across the liver, extrahepatic splanchnic tissues (gut), and kidneys were estimated by the arteriovenous differences multiplied by blood flows. All of the load of ammonium acetate infused intraportally was taken up by the liver. As a result there was an immediate switch in hepatic glutamine balance from that of net uptake to net production similar to that seen in the 4-day fasted dog. Simultaneously, net hepatic production of urea nitrogen doubled. These occurred with no change in acid-base balance or no change in circulating arterial or portal venous levels of insulin and glucagon.(ABSTRACT TRUNCATED AT 250 WORDS)
Regression of white adipose tissue in diabetic rats
Authors: Geloen A. , Roy P. E. , Bukowiecki L. J.
Published: December 2017

The effects of long-term diabetes (4 wk) on the development of parametrial (PWAT) and retroperitoneal (RWAT) white adipose tissues were studied in young Sprague-Dawley rats (170-200 g) injected with a single dose of streptozotocin (75 mg/kg). Diabetes stopped animal growth and totally abolished the normal increases in the wet weight, total protein content, and cellularity (estimated by DNA content) of PWAT and RWAT. Remarkably, the prolonged lack of insulin induced a progressive decrease of the cellularity of RWAT to levels that were lower than those of the initial controls. It also resulted in a marked reduction of adipocyte size. The tiny adipocytes seen in diabetic animals were characterized by the presence of multilocular triglyceride droplets. In general, the decreases in cell number, cell size, and protein content were more pronounced in RWAT than in PWAT. Quantitative cellular frequency studies revealed that adipocytes, and possibly also endothelial cells, contribute to the decrease in RWAT cellularity. The results demonstrate that 1) diabetes inhibits proliferative activity in adipose tissue, 2) total cell number reduction may occur in adipose depot of young growing rats, 3) this effect is depot dependent, and 4) the turnover of adipocytes and endothelial cells is relatively slow (several weeks).
ATP utilization and provision in fast-twitch skeletal muscle during tetanic contractions
Authors: Spriet L. L.
Published: December 2017

Rat fast-twitch muscles were tetanically stimulated in situ with an occluded circulation to examine ATP utilization and provision during isometric tension production. Plantaris (PL) and gastrocnemius (G) muscles were stimulated for 60 s in four conditions: A) 1.0-Hz train rate, 200-ms train duration at 80 Hz, B) 1.0 Hz (100 ms, 80 Hz), C) 0.5 Hz (100 ms, 80 Hz), and D) 1.0 Hz (200 ms, 40 Hz). Muscles were sampled pre- and post-stimulation for pH, high-energy phosphates, and glycolytic intermediates. Contributions to total ATP utilization (all muscles and conditions) were 64-67% glycolysis, 24-28% phosphocreatine, and 8-9% endogenous ATP. Glycogenolysis and glycolysis were greatest in white G (WG), 40% lower in red G (RG), and intermediate in PL muscles. Average energy costs in conditions A and D were approximately 0.60 mumol ATP/(N.s). Decreasing the train duration to 100 ms in B and the number of tetani to 30 in C increased energy costs to 0.93 +/- 0.05 and 1.26 +/- 0.07 mumol ATP/(N.s). Despite a lower pH, WG glycogenolytic (phosphorylase) activity was constant during condition A, whereas RG activity decreased in the final 30 contractions. Larger accumulations of Pi and inosine monophosphate may account for the maintained phosphorylase activity. Glycolytic (phosphofructokinase, PFK) activity was highest in WG and associated with higher fructose 6-phosphate concentration, greater depletion of ATP and, in later contractions, a higher NH4+ concentration. During tetanic in situ stimulation of fast-twitch muscle, the H+ profiles of phosphorylase and PFK are extended beyond in vitro predictions via the accumulation of positive modulators. This permits significant anaerobic ATP production via the glycolytic pathway despite increasing [H+]. The findings also suggest that lengthening the duration of tetani, generating lower peak tensions, and prolonging relaxation time all contribute to lower energy costs in fast-twitch muscle.
Interaction of vasopressin and angiotensin II in stimulation of prostacyclin synthesis in vascular smooth muscle cells
Authors: Vallotton M. B. , Gerber-Wicht C. , Dolci W. , Wuthrich R. P.
Published: December 2017

The effect of angiotensin II (ANG II) and arginine vasopressin (AVP) on prostacyclin production by vascular smooth muscle cells (VSMC) has been examined. Cultured rat aortic VSMC were studied during either static incubation in multiwell plates or during dynamic incubation in superfusion columns. Prostacyclin synthesis was assessed by radioimmunoassaying one of its stable metabolites, 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). Both ANG II and AVP stimulated the biosynthesis of prostacyclin in a concentration-dependent manner (10(-10) to 10(-5) M). ANG II (ED50 = 3 nM) displayed a higher potency than AVP (ED50 = 10 nM). ANG II was 4.4 times more potent than AVP at 10(-8) M. The effect of both peptides was inhibited selectively by antagonists. In the case of AVP (10(-8) M), a pure V1 antagonist (dEt2AVP) and the V2 agonist dDAVP, both at 10(-6) M, completely blocked the production of prostacyclin induced by AVP, whereas a mixed V1-V2 antagonist [d(CH2)5-D-Leu-VAVP] at 10(-6) M displaced the concentration-response curve by approximately two orders of magnitude to the right. Superfusion with a calcium-free medium containing ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid inhibited 89 +/- 3% of the ANG II- and 70 +/- 8% of the AVP-induced prostacyclin production, whereas nifedipine (10(-6) M) had no effect. A potentiating effect was observed when the stimulation with either ANG II or AVP was repeated two or three times. An even more marked potentiation resulted when the stimulation by ANG II (10(-8) M) followed stimulation by AVP (10(-8) M).(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of ketone body flux in septic patients
Authors: Beylot M. , Guiraud M. , Grau G. , Bouletreau P.
Published: December 2017

To assess the effect of sepsis on ketone body (KB) kinetics in humans, we measured in normal and septic subjects KB appearance rate (Ra) before (initial state) and during a rise of free fatty acids (FFA) level (intravenous infusion of a triglycerides emulsion). We studied normal subjects in postabsorptive state and septic patients when receiving an hypocaloric intravenous infusion of glucose and amino acids or 12 h after its interruption. When receiving glucose and amino acids infusion, septic patients had higher glucose and insulin levels than normal subjects, and despite lower FFA concentrations (255 +/- 44 vs. 480 +/- 51 mumol/l, P less than 0.05) comparable initial KB Ra (2.50 +/- 0.10 vs. 2.48 +/- 0.30 mumol.kg-1.min-1). Triglyceride infusion increased FFA to comparable values (septic 780 +/- 130, normal 730 +/- 45 mumol/l), but KB Ra rose in septic patients only to 3.7 +/- 1.1 instead of 7.7 +/- 1.1 mumol.kg-1.min-1 as in normal subjects (P less than 0.05). Somatostatin infusion decreased the hyperinsulinemia of septic patients but did not restore a normal ketogenesis. After interruption of nutriment infusion, septic patients had normal FFA levels and only mild hyperglycemia and hyperinsulinemia. Their initial KB Ra was not modified. However, their response of KB Ra (increase to 6.27 +/- 2.0 mumol.kg-1.min-1) to raised FFA levels (842 +/- 170 mumol/l) was comparable to the response of normal subjects. In conclusion, although septic patients receiving an hypocaloric parenteral nutrition had a depressed ketogenesis they were able to restore a normal ketogenic capacity after a short-time caloric deprivation. Glucose and/or insulin appears to have a major role in this modulation of hepatic ketogenesis.
Amino acids augment insulin's suppression of whole body proteolysis
Authors: Flakoll P. J. , Kulaylat M. , Frexes-Steed M. , Hourani H. , Brown L. L. , Hill J. O. , Abumrad N. N.
Published: December 2017

Leucine (LEU) kinetics were assessed using a primed-continuous infusion of L-[1-14C]LEU in normal overnight-fasted male volunteers during a basal period and an experimental period where insulin (INS) was infused at either 0.6, 1.2, 2.5, 5.0, 10, or 20 mU.kg-1.min-1 with euglycemia maintained. Two protocols were used: 1) subjects were allowed to develop hypoaminoacidemia or 2) plasma essential amino acids (AA) were maintained near basal levels by frequently monitoring plasma LEU in conjunction with variable infusions of an AA solution (LEU infused = 0.41, 0.72, 0.93, 1.03, 1.31, and 1.35 mumol.kg-1.min-1 at escalating INS doses, respectively). Basal rates of LEU appearance (Ra), nonoxidative disappearance (NORd) and oxidative disappearance (OXRd) were similar in both protocols (means = 1.74, 1.40, and 0.36 mumol.kg-1.min-1, respectively). INS infusions without AA resulted in a progressive decrement in LEU Ra (14 to 45%), NORd (16-41%), and OXRd (3-56%) compared with basal values. The infusion of AA resulted in an additional reduction in endogenous Ra (P less than 0.01; approximately 100% suppression achieved at plasma INS greater than 1,000 microU/ml) and a blunting of NORd reduction (P less than 0.05) at each dose of INS. Observed differences in INS's suppression of LEU Ra between the two protocols suggests the existence of a component of whole body proteolysis that is highly dependent on circulating plasma AA. Therefore, hypoaminoacidemia associated with INS treatment would appear to blunt the responsiveness of INS's suppression of protein breakdown and in the presence of near basal plasma AA, proteolytic suppression by INS is enhanced.
Atrial natriuretic factor in the elderly: diminished response to epinephrine
Authors: Morrow L. A. , Morganroth G. S. , Hill T. J. , Sanfield J. A. , Rosen S. G. , Grekin R. J. , Halter J. B.
Published: December 2017

We have previously found that epinephrine (EPI) increases plasma immunoreactive atrial natriuretic factor (irANF) in young human subjects. Because elderly humans have decreased sensitivity to adrenergic stimulation, we compared plasma irANF responses to intravenous infusion of EPI, 5 micrograms/min for 80 min in six young (ages 20-29) and nine old (ages 62-75) healthy subjects. In addition, we measured plasma irANF responses of the nine old subjects to 1 liter of normal saline infused over 30 min. Young and old subjects had similar basal EPI levels [108 +/- 18 vs. 106 +/- 10 (SE) pg/ml], but basal irANF levels tended to be higher in the old (32 +/- 7 vs. 50 +/- 8 pmol/l, P = 0.15). The young subjects had a significant increase in irANF levels after the EPI infusion (32 +/- 7 vs. 59 +/- 11 pmol/l, P less than 0.02), but there was no change in irANF in the old (50 +/- 8 vs. 48 +/- 7 pmol/l) despite similar plasma EPI levels in young and old (1,125 +/- 57 vs. 1,183 +/- 52 pg/ml). In contrast, the irANF response of the old subjects to saline infusion was striking: all nine subjects demonstrated a rise in irANF (P less than 0.01); mean levels increased from 54 +/- 4 pmol/l to a peak of 122 +/- 23 pmol/l. We conclude that healthy elderly subjects have a defect in EPI-stimulated ANF secretion, a finding compatible with other evidence for diminished sensitivity to adrenergic stimulation in aging.(ABSTRACT TRUNCATED AT 250 WORDS)
Enzymes of glutamine metabolism in inflammation associated with skeletal muscle hypertrophy
Authors: Kelso T. B. , Shear C. R. , Max S. R.
Published: December 2017

Glutamine synthesis and utilization were studied in the plantaris muscle after removal of its functional synergists, the soleus and gastrocnemius muscles. Rat plantaris muscle was compared with unoperated controls at 7, 14, and 30 days after synergist ablation and induction of hypertrophy. Glutamine synthetase activity increased from 6.17 +/- 1.77 to 33.92 +/- 2.23 nmol.h-1.mg protein-1, and glutaminase activities increased from 98.63 +/- 23.05 to 478.70 +/- 64.17 nmol.h-1.mg protein-1 7 days after surgery and remained elevated at 14 and 30 days. Sham-operated controls examined 7 days after surgery did not exhibit significantly increased glutamine synthetase activity. Histological examination revealed a large proliferation of connective tissue cells, as well as cells involved in tissue repair and inflammation; this influx was maximal 1 wk after surgery. The activity of the oxidative enzymes of the pentose phosphate pathway increased from 3.08 +/- 4.31 to 20.86 +/- 1.13 nmol.min-1.mg protein-1 1 wk after surgery. The time course of changes in pentose phosphate pathway enzymes was similar to that of the increases in glutamine synthetase, glutaminase, and cellular infiltration. Increases in muscle wet weight followed a different time course than changes in glutamine synthetase, glutaminase, and pentose phosphate pathway activities. It is concluded that the initial increases in plantaris muscle weight are probably due to edema, connective tissue proliferation, and cells involved in tissue repair and inflammation. The increase in glutamine synthetase activity appears to occur in skeletal muscle, whereas the changes in glutaminase and pentose phosphate pathway activities appear to represent infiltrating inflammatory cells. Furthermore, the increase in glutamine synthetase activity may serve to support the infiltrating cells, which appear to lack substantial capacity for glutamine production. These results represent a functional relationship between skeletal muscle glutamine synthesis and utilization by cells mediating inflammation and connective tissue repair and synthesis.
Estimation of whole body protein synthesis from oxidation of infused [1-14C]leucine
Authors: Yagi M. , Walser M.
Published: December 2017

In rats infused with NaH14CO3, 14CO2 exhalation approached an asymptotic rate equal to 96.0 +/- 1.3 (SD) % of the infusion rate of 14C in a monoexponential manner with a half-time of 20 min. In rats infused with [1-14C]leucine, 14CO2 exhalation (/0.96) approached an asymptotic value, (1-F), of 16-25% of 14C infusion rate (mean 20.4%) in a monoexponential manner with a half-time of approximately 31 min. Whole body protein synthesis (S) was calculated from 1-F and urea N plus ammonia N excretion (C) as S = CF/(1-F). S was a uniform function of body weight in these rats, in six additional rats in which S was measured 6 h after single intravenous injection of [1-14C]leucine and also in previously reported rats given single injections. The relationship was S (mg.100 g-1.h-1) = 11-0.143 body wt (g) +/- 8.3. In six of these rats, S was also estimated from the plateau specific activity of plasma leucine or plasma 2-ketoisocaproate (KIC); the former estimate of S was significantly lower (by an average of 17%), but S was the same when specific activity of KIC was employed. These results support the validity of the expired 14CO2 technique for measuring S.
Endurance training, not acute exercise, differentially alters beta-receptors and cyclase in skeletal fiber types
Authors: Buckenmeyer P. J. , Goldfarb A. H. , Partilla J. S. , Pineyro M. A. , Dax E. M.
Published: December 2017

beta-Adrenergic receptor binding characteristics and adenylate cyclase activity were examined in rat skeletal muscle membranes to determine if acute exercise or endurance training altered beta-receptors or adenylate cyclase activity in different muscle fiber types. Binding characteristics and adenylate cyclase activity were examined in type IIA [red fast-twitch, red vastus (RV)], type IIB [white fast-twitch, white vastus (WV)], and type I [red slow-twitch, soleus (S)] muscles. Acute exercise involved a 20-min run on a treadmill at 20 m/min and did not alter beta-receptor density or adenylate cyclase activity in any of the fiber types examined. Endurance training consisted of a progressive treadmill protocol that involved increasing intensity and duration of exercise for 18 wk. beta-Adrenergic receptor density increased in skeletal muscle fiber types primarily recruited during submaximal training (types I and IIA), whereas nonreceptor-mediated adenylate cyclase activity was altered in the three fiber types. Endurance training significantly increased beta-receptor density in RV by 25% and in S by 19% (P less than 0.05), whereas in WV beta-receptor density was not altered. Basal adenylate cyclase activity in RV was increased approximately 2.5 fold by endurance training. Nonreceptor-mediated adenylate cyclase activity, stimulated by NaF and forskolin, increased by approximately twofold in both RV and WV as a result of endurance training. The data support and extend previous observations to show greater effects of endurance training in types I and IIA fibers with respect to alterations in beta-receptor density and alterations in adenylate cyclase activity in each fiber type. Acute exercise did not alter these parameters either in trained or untrained rats.
Effect of insulin on protein synthesis and degradation in skeletal muscle after exercise
Authors: Balon T. W. , Zorzano A. , Treadway J. L. , Goodman M. N. , Ruderman N. B.
Published: December 2017

This study examined whether insulin stimulation of protein synthesis and inhibition of protein degradation is enhanced after exercise. The isolated perfused rat hindquarter preparation was used to evaluate net protein breakdown, myofibrillar protein degradation, and protein synthesis. Thirty minutes after treadmill exercise of high and moderate intensity, rates of tyrosine release were increased by 58 and 25%, respectively. Insulin at 75 microU/ml had no effect on these increases after intense exercise; however, 20,000 microU/ml of insulin totally inhibited this increase. Cycloheximide increased the tyrosine release in both control and exercised rat muscle. It also abolished the difference between them, suggesting that the increase in tyrosine release after exercise is caused by an inhibition of protein synthesis. Phenylalanine incorporation into protein was marginally depressed (22%, P = NS) in the white gastrocnemius muscle after intense exercise. Insulin at 200 microU/ml stimulated protein synthesis in these rats, but no more than it did in a nonexercised control group. Failure to observe a greater effect of insulin on protein metabolism was also noted when rat muscle was studied 150 min after intense exercise and after contractions induced by electrical stimulation of the sciatic nerve. These findings suggest that after exercise or electrically induced contractions the enhanced ability of insulin to stimulate hexose and amino acid transport is not paralleled by an increase in its ability to stimulate protein synthesis or inhibit protein degradation.
Growth-promoting properties of the internal milieu of pregnant and lactating rats
Authors: Chiang M. , Russell S. M. , Nicoll C. S.
Published: December 2017

The growth-promoting properties of the internal milieu of pregnant and lactating rats were investigated using transplanted whole rat embryos or fetal paws. When placed under the kidney capsule of intact nonpregnant hosts and incubated for 12 days, such transplants grow rapidly, and tissues differentiate normally. Thus they provide an accurate means of assessing the growth-promoting properties of the internal environment of host animals in different physiological states. Transplant growth during days 0-11 of pregnancy was similar to that observed in age-matched virgin control hosts during an equivalent 12-day period. However, growth of transplants was decreased by 40% in hosts during days 10-22 of pregnancy and by approximately 30% in hosts during days 1-13 or days 11-23 of lactation. Increase in tail length, which was used as an index of maternal skeletal growth, was reduced by 50% during the second half of pregnancy and the early and late periods of lactation compared with age-matched virgin females. No such inhibition was recorded during the first half of pregnancy. Compared with virgins, serum insulin-like growth factor I (IGF-I) levels were reduced by approximately 20% on days 6 and 10 of pregnancy, and by 63-66% during the second half of gestation. Serum IGF-I levels rose during lactation to reach prepregnancy levels by day 12, but a second decline occurred by day 18 postpartum.(ABSTRACT TRUNCATED AT 250 WORDS)
Neuroendocrine and gastric myoelectrical responses to illusory self-motion in humans
Authors: Koch K. L. , Stern R. M. , Vasey M. W. , Seaton J. F. , Demers L. M. , Harrison T. S.
Published: December 2017

We compared gastric myoelectrical activity and endogenous neuroendocrine responses in subjects with and without motion sickness elicited by illusory self-motion or vection. Rotating a drum with black and white vertical stripes around seated stationary subjects (n = 22) produced vection. Gastric myoelectrical activity was recorded with cutaneous electrodes. Thirteen subjects developed gastric dysrhythmias [4- to 9-cycles/min (cpm) signals] and motion sickness during vection, whereas nine subjects maintained normal 3-cpm gastric rhythms and remained symptom free. Base-line plasma cortisol and beta-endorphin levels were significantly greater (P less than 0.01) in the subjects who would develop gastric dysrhythmias and nausea compared with the subjects who would not develop motion sickness. Norepinephrine levels increased in the nauseated group immediately after vection ceased (354.6 +/- 41.1 pg/ml) compared with the symptom-free subjects (223.1 +/- 22.8 pg/ml, P less than 0.05). Epinephrine increased significantly (P less than 0.05) after vection only in the nauseated subjects, whereas dopamine levels were not altered by vection in either group. We conclude that 1) anticipatory increases in plasma cortisol and beta-endorphin occurred in subjects who would develop nausea and gastric tachyarrhythmias during vection; 2) endogenous epinephrine and norepinephrine were increased in subjects who had vection-induced nausea and gastric dysrhythmias; and 3) vection stimulates brain-gut interactions, resulting in gastric tachyarrhythmias and complex neuroendocrine responses in subjects with motion sickness.
Pancreatic and extrapancreatic galanin release during sympathetic neural activation
Authors: Dunning B. E. , Havel P. J. , Veith R. C. , Taborsky G. J.
Published: December 2017

To address the hypothesis that the neutropeptide, galanin, functions as a sympathetic neurotransmitter in the endocrine pancreas, we sought to determine if galanin is released from pancreatic sympathetic nerves during their direct electrical stimulation in halothane-anesthetized dogs. During bilateral thoracic splanchnic nerve stimulation (BTSNS), both peripheral arterial and pancreatic venous levels of galanin-like immunoreactivity (GLIR) increased (delta at 10 min = +92 +/- 31 and +88 +/- 25 fmol/ml, respectively). Systemic infusions of synthetic galanin demonstrated that 1) the increment of arterial GLIR observed during BTSNS was sufficient to modestly restrain basal insulin secretion and 2) only 25% of any given increment of arterial GLIR appears in the pancreatic vein, suggesting that the pancreas extracts galanin, as it does other neurotransmitters. By use of 75% for pancreatic extraction of circulating galanin, it was calculated that pancreatic galanin spillover (output) increased by 410 +/- 110 fmol/min during BTSNS. To reinforce the conclusion that pancreatic sympathetic nerves release galanin, GLIR spillover was next measured during direct local stimulation of the pancreatic sympathetic input produced by electrical stimulation of the mixed autonomic pancreatic nerves (MPNS) in the presence of the ganglionic blocker, hexamethonium. During this local pancreatic sympathetic nerve stimulation, arterial GLIR remained unchanged, but pancreatic venous GLIR increased by 123 +/- 34 fmol/ml. Thus pancreatic GLIR spillover increased by 420 +/- 110 fmol/min during MPNS in the presence of hexamethonium. We conclude that galanin is released from both pancreatic and extrapancreatic sources during sympathetic neural activation in dogs.
Model of the distribution and metabolism of a GnRH superagonist in dogs
Authors: Lacoste D. , Candas B. , Normand M. , Labrie F.
Published: December 2017

The plasma kinetics of [D-Trp6, des-Gly-NH2(10)]gonadotropin-releasing hormone (GnRH) ethylamide was assessed in eight dogs over a period of 8 h after rapid intravenous or subcutaneous injection. Each animal received doses of 0.2, 2, and 20 micrograms/kg body wt iv and 1 and 10 micrograms/kg body wt sc. A two-compartment structure, to which a source compartment was added to represent the subcutaneous route, adequately fits the five kinetics when the apparent volume of distribution follows a plasma concentration-dependent sigmoid function. Despite the nonlinearity, the apparent volume of distribution can be approximated by a constant value of 280 ml/kg body wt for the dynamics corresponding to the three lowest and more physiological doses. The metabolic clearance rate is 4.63 ml.min-1.kg body wt-1. The two exponential components that characterize the two-compartment structure are equal to 0.0348 +/- 0.0053 and 0.00470 +/- 0.00060 min-1, respectively. The agonist injected subcutaneously diffuses to plasma at a fractional rate of 0.0265 +/- 0.0029 min-1. Disposal occurs at a maximal rate of 0.017 and 0.0055 min-1 of the amount of agonist present in the central and peripheral compartments, respectively. The highest fractional exchange rate between compartments reaches 0.01 min-1. As simulated with the model, a continuous infusion of 4.63 ng.min-1.kg body wt-1 leads to a steady state of 1 ng/ml plasma; 90% of that level is reached 7 h after the onset of the subcutaneous input signal. The kinetics of plasma [D-Trp6, des-Gly-NH2(10)]GnRH ethylamide is many times slower than that of the native hormone and of the other GnRH agonists.
Voltage-dependent calcium currents in rat gonadotropes separated by centrifugal elutriation
Authors: Marchetti C. , Childs G. V. , Brown A. M.
Published: December 2017

Centrifugal elutriation of rat pituitary cells yielded two functionally active fractions (6 and 7) that contained 30-40 and 50-60% gonadotropes, respectively. We studied the membrane ionic currents of these cells with the whole cell patch-clamp method. In physiological solution, cells from the enriched fractions displayed a tetrodotoxin-sensitive sodium current. In 20 mM external calcium and zero sodium, the inward current contained two components that were different in threshold, steady-state inactivation, and deactivation. One component was half activated at approximately -25 mV, half inactivated from a holding potential of -61 mV, and deactivated with a time constant of 3 ms. The second component was half activated at 6 mV and deactivated with a time constant of 0.35 ms. These two currents resembled the high-voltage-activated and low-voltage-activated calcium current described in many preparations, including clonal and primary pituitary cells. Bath application of 20 nM gonadotropin-releasing hormone caused a transient and reversible decrease of the calcium current at depolarized voltages and a negative shift of 10 mV in the activation curve. Both effects were observed in a percentage of cells that closely matches the percentage of gonadotropes in the fraction. The shift appeared to affect both components of the current and can partially account for the increased activity of Ca2+ channels at potentials close to the resting value.
Metabolism of neurotensin by isolated perfused rat kidney
Authors: Gillatt D. J. , Shulkes A. , Read D. M. , Hardy K. J.
Published: December 2017

Studies in humans and conscious animals have established that the kidney is a key organ involved in the clearance of the brain-gut peptide neurotensin (NT). However, these in vivo studies cannot determine the mechanisms involved in the renal elimination of NT. We have therefore used the isolated perfused rat kidney preparation, which enables renal elimination to be studied in isolation from other organs. NT was measured with both COOH-terminal (biologically active end) and NH2-terminal (biologically active end) directed antisera. NT was stable in control perfusions (no kidney) with a disappearance half-life of greater than 250 min. The disappearance half-life in filtering kidneys was 52 +/- 3 min (COOH terminal) and 67 +/- 3 min (NH2-terminal). High-performance liquid chromatography of perfusate revealed a pattern similar to that seen in vivo with the NT being metabolized to NH2-terminal fragments. When the kidneys were rendered nonfiltering, NH2-terminal clearance was abolished, whereas COOH-terminal clearance was reduced by 75%. There was no release of NT peptidases into the perfusate. These data demonstrate that NT is metabolized directly by the kidney, predominantly by a filtration and reabsorption mechanism and with only a minor role for peritubular metabolism.
Medium-chain triglycerides induce alterations in carnitine metabolism
Authors: Rossle C. , Carpentier Y. A. , Richelle M. , Dahlan W. , D'Attellis N. P. , Furst P. , Elwyn D. H.
Published: December 2017

Medium-chain triglycerides are generally assumed to be metabolized independently of carnitine. The effects of infusing medium-chain triglycerides on plasma concentrations of carnitine derivatives and beta-hydroxybutyrate were studied in four healthy male adults. Glucose and amino acids were infused alone for 3 h, then continued for another 5.5 h together with a lipid emulsion containing only long-chain triglycerides or a 50:50% (wt/wt) mixture of medium-chain and long-chain triglycerides. During the fat-free infusion, the concentration of free carnitine rose, whereas the level of acylcarnitines decreased. Infusion of the mixed emulsion over 5.5 h reduced free carnitine to lower values (32.4 +/- 4.7 mumols/l) than long-chain triglycerides infusion (44.4 +/- 2.7 mumol/l). By contrast, the plasma concentrations of short-chain acylcarnitine (12.1 +/- 3.3 vs. 5.4 +/- 1.9 mumols/l; P less than 0.01) and of beta-hydroxybutyrate (93 +/- 32 vs. 47 +/- 14 mumols/l; P less than 0.01) became significantly higher with the mixed emulsion than with long-chain triglycerides. This suggests that intravenous medium-chain triglycerides are not metabolized independently of carnitine. Carnitine may play an important role in removing acyl and acetyl groups from mitochondria and in restoring the intramitochondrial CoA level. Fat substrates are converted into compounds that might be utilized by tissues that do not normally oxidize fatty acids, creating an interorgan energy cycle.
Peptide transport systems for opiates across the blood-brain barrier
Authors: Banks W. A. , Kastin A. J.
Published: December 2017

Opiate peptides administered on one side of the blood-brain barrier can exert powerful effects on processes occurring on the other side. There is evidence for direct passage of opiate peptides and their analogues across this barrier. Beta-Endorphin can enter the cerebrospinal fluid after systemic administration, but its entry into brain tissue has been more difficult to demonstrate, even though analogues enter at a modest rate. Enkephalins enter and exit the central nervous system as intact molecules by a combination of saturable and nonsaturable mechanisms. A family of transport systems may exist with varying affinities for the opiate enkephalins, antiopiates like tyrosine melanocyte-stimulating hormone inhibitory factor 1 (Tyr-MIF-1), and related peptides. The major system transporting these peptides, termed Peptide transport system 1, can be influenced by several factors with entry and exit rates affected by aging, drugs, amino acids, monoamines, aluminum, stress, and ethanol addiction and withdrawal. The homeostatic role of the blood-brain barrier thus extends to the regulation of the bidirectional transport of informational peptides such as the opiates.
Mechanism of clearance of dipeptides by perfused hindquarters: sarcolemmal hydrolysis of peptides
Authors: Raghunath M. , Morse E. L. , Adibi S. A.
Published: December 2017

The objective of the present experiment was to investigate the mechanism of clearance of a load of dipeptides (10 mumols) by perfused hindquarters of rats. The clearance was progressive over 60 min and was significantly (P less than 0.01) greater for glycylleucine than for glycylglycine (99 vs. 58% disappearance from the medium). Insulin had no significant effect on clearance of these dipeptides but stimulated the net uptake of their constituent amino acids. Investigation of the fate of peptides considered resistant to membrane hydrolysis showed a modest (24%) clearance for glycylsarcosine but a substantial one (89%) for glycylproline. Investigation of hydrolysis by sarcolemmal vesicles of skeletal muscle showed hydrolase activity against glycylglycine and glycylleucine but none against glycylsarcosine and glycylproline. Investigation of hydrolysis in the medium previously used to perfuse hindquarters for 60 min showed considerable activity against glycylleucine and glycylproline but none against glycylglycine and glycylsarcosine. These activities were entirely abolished by p-hydroxymercuribenzoate, an inhibitor of cytoplasmic peptide hydrolases. In conclusion, our data show that the mechanism of clearance of dipeptides by the perfused hindquarters is largely by hydrolysis, and the site of this hydrolysis differs for different dipeptides; hydrolysis is mediated either by plasma membrane enzymes, cytoplasmic enzymes released into the medium, or a combination of both.