bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of ANG II and AVP receptors in isolated hepatocytes of pregnant rats
Authors: Massicotte G. , Coderre L. , Chiasson J. L. , Thibault G. , Schiffrin E. L. , St-Louis J.
Published: December 2017

Recent evidence suggests that angiotensin II (ANG II) and vasopressin (AVP) act on the liver via specific receptors. We have examined the binding properties of these receptors in isolated rat hepatocytes and studied the regulation of the biological responses to ANG II and AVP during pregnancy in the rat. In contrast to [3H]ANG II, 125I-labeled-[Sar1-Ile8]ANG II was markedly resistant to degradation by isolated liver cells. Displacement and saturation experiments with this iodinated antagonist revealed the presence of a single class of binding sites [2 x 10(5) sites/cell, dissociation constant (KD) = 1.0 nM]. The potency of ANG II analogues to displace 125I-[Sar1-Ile8]-ANG II agrees closely with data reported for vascular smooth muscle cells. Isolated hepatocytes have approximately 8 x 10(4) [3H]AVP binding sites/cell (KD = 1.0 nM) based on saturation experiments. AVP analogues selectively displaced [3H]AVP, suggesting the presence of V1-AVP receptor subtype. The maximum response of [Sar1]ANG II-induced glycogenolysis in the cells was decreased during gestation, whereas the effective concentration producing 50% of maximum response (EC50) was significantly increased (0.15-0.28 nM) when compared with cells from nonpregnant animals. In pregnancy, receptors for 125I-[Sar1-Ile8]ANG II were not changed in affinity (KD) or in density (Bmax). The maximum response and EC50 of AVP on liver glycogenolysis were not significantly decreased during pregnancy, whereas an increased number of AVP binding sites (from 5.0 +/- 0.5 x 10(4) to 11.0 +/- 1.7 x 10(4)) with similar KD was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
Protein and leucine metabolism in maple syrup urine disease
Authors: Thompson G. N. , Bresson J. L. , Pacy P. J. , Bonnefont J. P. , Walter J. H. , Leonard J. V. , Saudubray J. M. , Halliday D.
Published: December 2017

Constant infusions of [13C]leucine and [2H5]phenylalanine were used to trace leucine and protein kinetics, respectively, in seven children with maple syrup urine disease (MSUD) and eleven controls matched for age and dietary protein intake. Despite significant elevations of plasma leucine (mean 351 mumol/l, range 224-477) in MSUD subjects, mean whole body protein synthesis [3.78 +/- 0.42 (SD) g.kg-1. 24 h-1] and catabolism (4.07 +/- 0.46) were similar to control values (3.69 +/- 0.50 and 4.09 +/- 0.50, respectively). The relationship between phenylalanine and leucine fluxes was also similar in MSUD subjects (mean phenylalanine-leucine flux ratio 0.35 +/- 0.07) and previously reported adult controls (0.33 +/- 0.02). Leucine oxidation was undetectable in four of the MSUD subjects and very low in the other three (less than 4 mumol.kg-1.h-1; controls 13-20). These results show that persistent elevation in leucine concentration has no effect on protein synthesis. The marked disturbance in leucine metabolism in MSUD did not alter the relationship between rates of catabolism of protein to phenylalanine and leucine, which provides further support for the validity of the use of a single amino acid to trace whole body protein metabolism. The minimal leucine oxidation in MSUD differs from findings in other inborn metabolic errors and indicates that in patients with classical MSUD there is no significant route of leucine disposal other than through protein synthesis.
PGF2 alpha and PGE2 binding to rat myometrium during gestation, parturition, and postpartum
Authors: Molnar M. , Hertelendy F.
Published: December 2017

The specific binding of prostaglandins (PG) F2 alpha and E2 was studied in a rat myometrial membrane-enriched fraction during the latter part of gestation and parturition, as well as in the postpartal period. Tritiated PGE2 and PGF2 alpha binding was specific, saturable, time dependent, and directly proportional to the amount of membrane protein. Scatchard analysis indicated the presence of high-affinity (Kd2) and low-affinity (Kd2) binding sites for both PGs. The affinity of both binding sites for PGF2 alpha and the apparent Kd2 for PGE2 remained essentially the same throughout gestation and post-partially and were similar to nonpregnant rats. The apparent Kd1 of PGE2, however, increased by 10-fold from day 21 of gestation to 1 day postpartum. Although the maximal binding capacity of the high-affinity (Bmax1) and low-affinity (Bmax2) binding sites of PGF2 alpha showed a nonsignificant increase compared with prepartum values, reaching maximal values 12-24 h postpartum, those of PGE2 showed a significant increase on the third day after delivery. The concentration of prostanoids in uterine venous plasma and amniotic fluid increased significantly with approaching parturition, whereas plasma progesterone decreased, raising the estradiol-progesterone ratio 25-fold. After unilateral fetectomy, the binding sites for PGF2 alpha and PGE2 increased significantly compared with the contralateral pregnant horns. Administration of the PG synthetase inhibitor, indomethacin, also increased two- to threefold both PGF2 alpha and PGE2 binding compared with the placebo group, whereas intrauterine administration of PGF2 alpha and PGE2 significantly reduced it.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of hyperglucagonemia on hepatic glycogenolysis and gluconeogenesis after a prolonged fast
Authors: Hendrick G. K. , Frizzell R. T. , Williams P. E. , Cherrington A. D.
Published: December 2017

The aim of this study was to determine if glucagon can stimulate hepatic glucose production in prolonged fasted (7 days) animals. Two protocols were used; in one ("hormone replacement"; n = 4), intraportal basal replacement amounts of insulin and glucagon were given during a somatostatin infusion, whereas, in the other ("glucagon excess"; n = 5) basal insulin was given along with somatostatin and excess glucagon. Plasma insulin levels were similar and constant throughout both protocols (6 +/- 1 microU/ml). The plasma glucagon was basal in the hormone-replacement protocol (49 +/- 9 pg/ml) but rose from 46 +/- 7 to 448 +/- 35 pg/ml (P less than 0.05) in the other protocol. Plasma glucose levels and the rates of glucose production were unchanged during hormone replacement but rose from 100 +/- 5 to 199 +/- 28 mg/dl and from 1.5 +/- 0.1 to a peak of 5.6 +/- 0.2 mg.kg-1.min-1 at 15 min (P less than 0.05) and an eventual plateau of 2.7 +/- 0.2 mg.kg-1.min-1 (P less than 0.05) in response to glucagon excess. Because of the sluggish increase in gluconeogenic parameters, the early marked rise in glucose production was attributable to increased glycogenolysis. Eventually, however, the gluconeogenic rate rose, with net hepatic uptake of alanine increasing 50% and fractional alanine extraction doubling. Gluconeogenic efficiency and conversion increased in response to glucagon excess by 0.30 +/- 0.05 and 159 +/- 48%, respectively, although it should be noted that these parameters rose 0.15 +/- 0.06 and 150 +/- 49% in the hormone-replacement protocol. In conclusion, even after a prolonged fast physiological glucagon can cause hyperglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of epinephrine on amino acid and energy metabolism in humans
Authors: Matthews D. E. , Pesola G. , Campbell R. G.
Published: December 2017

Epinephrine was infused for 8.5 h into five normal, healthy, young adult men on four different occasions at 0, 0.5, 1, and 2 micrograms/min to elevate circulating levels of epinephrine into the high physiological range as seen in stress and trauma. Energy expenditure, heart rate, and blood pressure were measured at hourly intervals. [1-13C]leucine, [ring-2H5]phenylalanine, and [2-15N]glutamine were infused during the last 3.5 h to follow essential amino acid and glutamine kinetics. This design was adapted to study the effects of epinephrine on energy and protein metabolism after acute and temporary metabolic responses to epinephrine had occurred. Plasma glucose was significantly increased by approximately 20 mg/dl from 83 mg/dl (saline infusion) at all levels of epinephrine infusion. Amino acid levels were depressed with epinephrine infusion, with the largest drop occurring for the essential amino acids (-27% at the 2.0-micrograms/min dose). Energy expenditure was increased with epinephrine infusion in a dose-dependent fashion (+17% increase at 2.0 micrograms/min infusion). These effects were sustained for the duration of 8.5 h epinephrine infusion. There was no significant change in leucine or phenylalanine flux, indicative of protein breakdown, or in leucine oxidation. Glutamine flux was significantly (but modestly, +7%) increased at only the 2.0-micrograms/min infusion rate. Changes in kinetics that altered amino acid levels were not apparent by 7 h of epinephrine infusion (the beginning of the plateau period for the tracer infusion study). Although epinephrine can produce long-term elevations of metabolic rate, its effects on protein metabolism are minimal beyond acute changes affecting amino acid levels.
Early establishment of cerebral dysfunction after portacaval shunting
Authors: Mans A. M. , DeJoseph M. R. , Davis D. W. , Vina J. R. , Hawkins R. A.
Published: December 2017

Portacaval shunting in rats results in brain dysfunction, as indicated by reduced energy metabolism and behavioral abnormalities, as well as many biochemical changes in plasma and brain. No etiological connections have been made between these findings, which have been studied mainly 2 wk or more after shunting. To determine how soon the various abnormalities occur and which are associated temporally with the decrease in brain glucose use, we studied shunted and sham-operated rats between 6 h and 11 days after surgery. Six hours after portacaval shunting, plasma aromatic amino acids, brain glutamine, aromatic amino acids, 5-hydroxyindoleacetic acid, and tryptophan transport into the brain were all significantly higher than normal. Brain glucose use showed a downward trend and was fully depressed within 1 day. Plasma branched-chain amino acids and threonine were decreased, and brain serotonin and norepinephrine content increased only after 2 days; these changes were therefore dissociated from the other abnormalities that developed in a shorter period. The results showed that the cerebral dysfunction characteristic of portacaval shunting began within hours and was fully established by 2 days.
Splanchnic control of vasopressin secretion in conscious rats
Authors: Choi-Kwon S. , McCarty R. , Baertschi A. J.
Published: December 2017

Saline solutions (NaCl, 2 ml, pH 7.4, 10-598 mosmol/kgH2O) were infused over 4 min in conscious rats, via tail artery catheter or intragastric tube. Intragastric infusions of hyper- and hypotonic solutions caused, within 14.4 +/- 2.2 min, a maximal increase and decrease, respectively, of plasma vasopressin (AVP) relative to time controls (r = 0.97; P less than 0.00001) without affecting systemic plasma osmolality (r = -0.09; P less than 0.92). Mean changes of plasma AVP between 11 and 21 min were also correlated with the osmolality of gastric infusion (r = 0.72; P less than 0.000001), whereas systemic osmolality was unchanged (r = 0.14; P less than 0.42). Systemic infusions caused within 9.0 +/- 2.0 min a maximal change in both plasma AVP (r = 0.82; P less than 0.00001) and systemic osmolality (r = 0.97; P less than 0.00001). However, mean changes of plasma AVP between 11 and 21 min weakly correlated with the osmolality of systemic infusions (r = 0.27; P less than 0.20), although correlations between mean changes of systemic osmolality and the osmolality of systemic infusions were significant (r = 0.72; P less than 0.00001). Lack of correlations with mean arterial pressure and heart rate suggest that hemodynamic changes did not mediate the AVP responses. Pretreatment with atropine methyl bromate (2 mg/kg) abolished the AVP response to gastric but not systemic infusions of hypertonic saline. These results indicate that a splanchnic cholinergic receptor mechanism modulates AVP secretion during a moderate gastric intake of salt or water.
Selective reduction of alpha 2-adrenergic responsiveness in hamster adipose tissue during prolonged starvation
Authors: Carpene C. , Galitzky J. , Saulnier-Blache J. S. , Lafontan M.
Published: December 2017

The influence of fasting on the dual adrenergic control of adipose tissue lipolysis was investigated in hamsters because in this species the adipocytes exhibit both beta-stimulatory and alpha 2-inhibitory adrenergic responses. In adipocytes from fed animals, the number of alpha 2-receptors (identified with [3H]clonidine and [3H]RX 821002) was greater than that of beta-receptors. As in humans, the alpha 2-adrenoceptor number was greater in adipocyte membranes from subcutaneous (inguinal and popliteal) than from internal (perirenal and epididymal) adipose tissues. Despite this difference in alpha 2-adrenoceptor number, the antilipolytic responses to the alpha 2-agonists clonidine and UK 14304 were similar in the two tissues. Food deprivation for a period of 1-6 days induced a net depletion of both adipose tissues. In 6-day starved animals the number of adipocyte alpha 2-adrenoceptors and the maximal antilipolytic effect of UK 14304 were less than 50% of those in fed controls. In contrast, the antilipolytic responses to phenylisopropyladenosine or prostaglandin E1 remained unchanged. Starvation induced a decrease in alpha 2-adrenoceptor number and an increase in beta-adrenergic sensitivity that were greater in adipocytes from subcutaneous than from internal fad pads. The data suggest that the adipocyte beta- and alpha 2-adrenoceptors are independently regulated during starvation. In the adipocyte, the alpha 2-antilipolytic responses and the alpha 2-adrenoceptor levels are dependent on the extent of the adipose mass; they are particularly reduced in emaciated hamsters.
Platelet catecholamine contents are cumulative indexes of sympathoadrenal activity
Authors: Chamberlain K. G. , Pestell R. G. , Best J. D.
Published: December 2017

Blood platelets continually accumulate catecholamines (CA) from plasma. Plasma CA levels fluctuate rapidly, but platelet CA appear to have a slower turnover, making them potentially useful as long-term indexes of sympathoadrenal activity. We measured the effect of different types of human physical exertion on epinephrine (E), norepinephrine (NE), and dopamine (DA) and their sulfoconjugates in both plasma and washed platelets using a radioenzymatic assay. Acute strenuous exercise caused only a small (26%) rise in unconjugated plus sulfated platelet E, but regular training (140 +/- 30 km/wk) was associated with levels of platelet CA or CA sulfates 39-112% higher than controls. After completion of an ultramarathon (607-1,020 km in 6-8 days), platelet CA and CA sulfates were 139-405% higher than controls. Platelet CA declined over several days postrace, and the loss of platelet NE was significantly slower than the loss of platelet E. Plasma CA sulfates were significantly elevated in the runners, whereas plasma CA were normal apart from a transient elevation in NE postrace. Platelet CA levels provide a useful index of chronic sympathoadrenal activity but may be affected by changes in platelet turnover or activation.
Thermogenesis following meal feeding, isoproterenol, and cold in rats with LH lesions
Authors: Corbett S. W. , Roland B. , Keesey R. E.
Published: December 2017

Responses to several thermogenic stimuli were measured in rats maintaining stable but reduced body weights following lateral hypothalamic (LH) lesions. Oxygen consumption was monitored in open-circuit respirometers before and after exposure to cold (16.5 degrees C), intubation of a meal, and isoproterenol injection (40 micrograms/kg 0.75). Observations were made in both warm- (28 degrees C) and cold-acclimated (9 degrees C) LH-lesioned rats. Cold exposure, intubation, and drug injection each caused marked increases in heat production in sham- and LH-lesioned rats. This thermogenic response was similar in magnitude and form for both groups. Acclimation to 9 degrees C caused increased baseline levels of heat production when measured at 28 degrees C. Subsequent exposure to thermogenic stimuli revealed an exaggerated response to isoproterenol but not intubation in cold-acclimated groups. The LH-lesioned cold-acclimated rats responded in the same manner as sham-lesioned cold-acclimated rats. These findings are in contrast to the immediate postlesion period when rats show enhanced thermogenic activity. At reduced body weights LH-lesioned rats show normal rates of heat production and make normal responses to thermogenic stimuli. Enhanced thermogenesis does not appear to play a role in the maintenance of chronically reduced body mass in LH-lesioned rats.
Low ratio of fat to carbohydrate oxidation as predictor of weight gain: study of 24-h RQ
Authors: Zurlo F. , Lillioja S. , Esposito-Del Puente A. , Nyomba B. L. , Raz I. , Saad M. F. , Swinburn B. A. , Knowler W. C. , Bogardus C. , Ravussin E.
Published: December 2017

Reduced oxidation of fat leading to a positive fat balance could be a factor in the development of obesity. Twenty-four-hour respiratory quotient (RQ) was measured in 152 nondiabetic Pima Indians fed a weight-maintenance diet [87 males and 65 females; 27 +/- 6 yr (mean +/- SD); 93.9 +/- 22.9 kg; 32 +/- 9% fat]. Twenty-four-hour RQ varied from 0.799 to 0.903. Prior change in body weight, 24-h energy balance, sex, and percent body fat explained 18% of the variance in 24-h RQ (P less than 0.001). In a subgroup of 66 siblings from 28 families, family membership explained 28% of the remaining variance in 24-h RQ (P less than 0.05). In 111 subjects for whom follow-up data (25 +/- 11 mo) were available, 24-h RQ was correlated with subsequent changes in body weight and fat mass (r = 0.27, P less than 0.01 and r = 0.19, P less than 0.05, respectively). Subjects with higher 24-h RQ (90th percentile) independent of 24-h energy expenditure were at 2.5 times higher risk of gaining greater than or equal to 5 kg body weight than those with lower 24-h RQ (10th percentile). We conclude that in Pima Indians fed a standard diet 1) family membership is the principal determinant of the ratio of fat to carbohydrate oxidation, and 2) a low ratio of fat to carbohydrate oxidation is associated with subsequent weight gain independent of low energy expenditure and may contribute to the familial aggregation of obesity.
Tumor necrosis factor-alpha and interferon-gamma reduce prolactin release in vitro
Authors: Walton P. E. , Cronin M. J.
Published: December 2017

Prolactin binds to lymphocytes and monocytes and can modulate immune cell function. It was postulated that proteins released from activated macrophages and lymphocytes could directly influence prolactin release and thus form an endocrine control loop during infection, tumor invasion, or inflammation. This hypothesis was tested by exposing cultured rat anterior pituitary cells to murine tumor necrosis factor-alpha (TNF-alpha) and/or interferon-gamma (IFN-gamma) for 24 h before a 4-h test of cell function. Overall prolactin accumulation during this first 24 h was inhibited by TNF-alpha and markedly reduced by TNF-alpha plus IFN-gamma. In contrast, thyroid-stimulating hormone levels were unchanged in these same media. During the subsequent 4-h challenge, both cytokines reduced thyrotropin-releasing hormone-stimulated prolactin release but had no effect on inhibited prolactin release mediated by dopamine and somatostatin receptors. Cellular viability (assessed by trypan blue and chromium release assays) and prolactin cell content were unchanged after TNF-alpha or IFN-gamma treatment. We conclude that both TNF-alpha and IFN-gamma have the potential to act directly on anterior pituitary cells to slow the rate of prolactin release.
Food deprivation alters liver glycogen metabolism and endocrine responses to hemorrhage
Authors: Ljungqvist O. , Boija P. O. , Esahili H. , Larsson M. , Ware J.
Published: December 2017

Liver glycogen content, blood glucose, insulin, glucagon, and epinephrine were determined during 1 h hemorrhagic hypotension at 60 mmHg and 23 h thereafter in fed and two groups of 24-h food-deprived rats receiving either no infusion or 30% glucose intravenously during hemorrhage. Liver glycogen content was reduced by greater than 90% after 24-h food deprivation. Fed and food-deprived rats given glucose developed similar and substantial elevations of blood glucose during hemorrhage, whereas changes in blood glucose were modest in food-deprived rats given no infusion. In fed rats, liver glycogen was reduced by 60% during the 1-h bleed, but within 2 h after hemorrhage repletion of liver glycogen content commenced. By 6 h, approximately 75% of the glycogen lost during hemorrhage had been restored, and 23 h after hemorrhage liver glycogen content was six times greater compared with nonbled controls. Although glycogen levels increased after hemorrhage in food-deprived animals, the increase was negligible compared with that found in fed rats. Infusion of glucose during hemorrhage or adrenergic blockade after hemorrhage did not alter glycogen repletion in food-deprived rats. Posthemorrhage fed animals had high levels of insulin, glucagon, and epinephrine during hemorrhage, whereas insulin levels remained low in food-deprived rats despite exogenously induced hyperglycemia. It is concluded that rapid and substantial glycogen repletion can occur even immediately poststress. The conditions seem to be related to the nutritional state at the time of the insult.
Osmoregulation of vasopressin in diabetic ketoacidosis
Authors: Durr J. A. , Hoffman W. H. , Hensen J. , Sklar A. H. , el Gammal T. , Steinhart C. M.
Published: December 2017

Osmoregulation of arginine vasopressin (AVP) is altered in diabetic ketoacidosis (DKA). With hyperglycemia, the AVP-plasma sodium (PNa) curve is displaced to the left, whereas the AVP-osmolality (Posm) curve is displaced to the right. The shift in the Na curve is explained by either resetting of the Na set point or by glucose acting as a nonpermeable solute, substituting for Na. Conversely, putative unmeasured solutes that, like urea, fail to affect AVP have been postulated to account for the right shift in the AVP-Posm curve. Therefore the respective roles of Posm = sigma [Xi] and plasma tonicity (Pton = sigma [sigmaiXi]), i.e., the sum of concentrations of all solutes [Xi] corrected (Pton) or not (Posm) for their relative cell permeability (sigma i), were studied in DKA. Indeed, Posm = sigma [Xi] exceeds Pton = sigma [sigma iXi] in DKA, since sigma i less than 1 for glucose. Potential determinants of AVP release (Posm, Pton, and PNa) were monitored in 7 patients with DKA. Conventional correlation analysis and two-dimensional (2D) graphs reproduced the paradox of an opposite shift in PNa and Posm set points for AVP release. However, by using the concept of tonicity instead of osmolality, 3D plots instead of 2D graphs, and multiple regressions instead of correlations, the AVP-PNa and AVP-Pton curves did not appear displaced. The concept of tonicity resolved the paradox of both osmolality and Na thresholds reset in opposite directions. Indeed, in states where a solute like glucose (with sigma less than 1) contributes substantially to plasma osmolality, Posm measured in vitro by the osmometer greatly exceeds Pton perceived in vivo by the osmoreceptor.
Reconstitution of solubilized V1 vasopressin receptors of human platelets
Authors: Thibonnier M. , Bayer A. L. , Simonson M. S. , Snajdar R. M.
Published: December 2017

We describe the reconstitution of solubilized human platelet arginine vasopressin (AVP) receptors into phospholipid vesicles. Purified platelet plasma membranes enriched in AVP receptors [binding equilibrium dissociation constant (Kd) = 1.87 +/- 0.14 nM, maximum number of binding sites (Bmax) = 261 +/- 10 fmol/mg protein] were solubilized with 20 mM sodium cholate. Phospholipid vesicles made of 10% cholesterol, 20% egg phosphatidylcholine, and 70% egg phosphatidylserine were formed by bath sonication. Solubilized AVP receptors were incorporated into the vesicles while the detergent was removed by filtration through Sephadex G-100. The reconstituted receptors retained a high affinity for [3H]AVP (Kd = 3.19 +/- 0.13 nM, Bmax = 257 +/- 9 fmol/mg). Competition experiments with different AVP analogues confirmed the V1 vascular nature of the reconstituted receptors. Saturation experiments carried out with the agonist [3H]AVP and the V1 antagonist [3H]d(CH2)5Tyr(Me)AVP revealed that agonist binding to the reconstituted receptors was divalent cation dependent, whereas antagonist binding was not. Moreover, the affinity of the agonist [3H]AVP for the reconstituted receptors was modulated by the nonhydrolyzable guanine nucleotide analogue guanosine 5'-[gamma-thio]triphosphate (GTP gamma S), whereas [3H]d(CH2)5Tyr(Me)AVP binding affinity was not. The phospholipid vesicles could be loaded with free fura-2 and displayed an enhanced fluorescence caused by calcium entry after addition of ionomycin. However, stimulation by AVP did not induce an increase of free calcium inside the vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)
Interpretation of isotopomer patterns in tracing glycogen synthesis and glucose recycling using [13C6]glucose
Authors: Des Rosiers C. , Landau B. R. , Brunengraber H.
Published: December 2017

Tracing glycogen synthesis with [U-13C]glucose involves determination of isotopomer patterns in precursors and products. The contribution of the direct pathway to glycogen synthesis has been estimated from the ratio (R) of the number of glycogen glucose molecules having six 13C atoms to the total number of glucose molecules having one to six 13C atoms. Using theoretical examples, we show that the equation to calculate R underestimates the contribution of the direct pathway. We derive a correct stoichiometric expression for R. Also, we show how to correct these estimates for 1) recondensation of two M+3 three-carbon intermediates into M+6 glucose 6-phosphate, and 2) the increasing enrichment of arterial glucose in various isotopomers arising from the indirect pathway. Finally, using the developed formulas we recalculate data from the literature. Similar considerations apply to investigations of glucose recycling using [U-13C6]glucose.
Characterization of insulin receptor kinase activity and autophosphorylation in different skeletal muscle types
Authors: Azhar S. , Butte J. C. , Santos R. F. , Mondon C. E. , Reaven G. M.
Published: December 2017

We have examined insulin binding, autophosphorylation, and tyrosine kinase activity in detergent-solubilized and wheat germ agglutinin-purified insulin receptor preparations from four rat muscles of different fiber composition (i.e., tensor fascia latae, soleus, vastus intermedius, and plantaris). Insulin binding activity was similar in three of the four muscles but lower in tensor fascia latae. No significant differences were noted in the affinity of insulin for its receptor from various muscle types. Insulin receptor tyrosine kinase activity measured in the absence (basal) and presence of insulin (0.3-300 nM) was comparable in all muscle types (normalized to the amount of insulin bound). Insulin sensitivity, measured as the dose of insulin required for half-maximal activation of kinase activity, was also similar in all muscle types. Likewise, incubation of receptor preparations with [gamma-32P]ATP, Mn2+, and insulin (0.25-100 nM) resulted in a dose-dependent autophosphorylation of the beta-subunit (relative molecular weight approximately 95 kDa) with similar kinetics in all muscle types. In conclusion, these results show that the functional behavior of the insulin receptor autophosphorylation-kinase system (in vitro) is not changed by alterations in muscle fiber composition, indicating that differences in insulin sensitivity between different skeletal muscle types is probably not due to modulation of the insulin receptor phosphorylation system.
Temporal structure of in vivo growth hormone secretory events in humans
Authors: Hartman M. L. , Faria A. C. , Vance M. L. , Johnson M. L. , Thorner M. O. , Veldhuis J. D.
Published: December 2017

The time course of spontaneous growth hormone (GH) secretion was studied in 12 normal men by analyzing serum GH concentrations measured in blood collected at 5-min intervals over 24 h with a multiple-parameter deconvolution model to simultaneously resolve endogenous GH secretory and clearance rates. Twenty-four-hour profiles of serum GH concentrations were accounted for by an average of 12 +/- 1.2 (SE) discrete GH secretory bursts having a mean half-duration (duration at half-maximal amplitude) of 25 +/- 2.3 min, indicating that 95% of daily GH secretion occurred in 8.8 h. The majority (96%) of GH was secreted in volleys composed of multiple (4.0 +/- 0.4) discrete secretory bursts. Such volleys of GH secretion were separated by 171 +/- 19 min, whereas their constituent individual secretory events occurred every 36 +/- 1.7 min (P = 0.0001). Between secretory volleys, calculated GH secretory rates fell asymptotically to zero. Significant positive and negative autocorrelations were observed for the series consisting of successive GH secretory burst mass and interburst intervals, respectively. Linear regression analysis revealed significant negative correlations between the mass of GH secreted per burst and both the preceding and following interburst intervals. Estimates of the half-life of endogenous GH (17 +/- 1.7 min) and of the endogenous GH production rate (0.25 +/- 0.033 mg/m2 for an assumed distribution volume of 7.9% body wt) agreed well with earlier independent measurements. We conclude that the human pituitary gland secretes GH in volleys consisting of multiple secretory bursts, without measurable intervening tonic secretion. This pattern of in vivo GH release in normal humans is consistent with a model of high-frequency GH-releasing hormone secretory events superimposed on low-frequency episodes of somatostatin withdrawal.
Effect of systemic hyperinsulinemia on amino acid flux across human legs in postabsorptive state
Authors: Arfvidsson B. , Zachrisson H. , Moller-Loswick A. C. , Hyltander A. , Sandstrom R. , Lundholm K.
Published: December 2017

The effect of physiological hyperinsulinemia (approximately 110 mU/l) on leg tissue protein balance was investigated in eight weight-stable healthy individuals. A primed constant infusion of L-[U-14C]tyrosine was used to measure the disposal and release of tyrosine across the leg before and during 2 h of euglycemic clamp studies. The leg exchange of 3-methyl-L-histidine (3-MH) and all amino acids in blood were measured before and during insulinization, including the muscle tissue content of amino acids. Hyperinsulinemia decreased whole body tyrosine flux from 52 +/- 2 to 35 +/- 1 mumol/min (P less than 0.0001), whereas neither disposal (53 +/- 9 vs. 45 +/- 9 nmol.min-1.100 g-1) nor release of tyrosine across the leg (76 +/- 11 vs. 66 +/- 10 nmol X min-1 X 100 g-1) was significantly influenced. The arterial concentration and the leg exchange of 3-MH were not significantly affected by 2 h of hyperinsulinemia, but the sum of all amino acids declined significantly. The net leg balance of tyrosine was not affected at all by hyperinsulinemia, whereas the balance of the branched-chain amino acids and methionine were switched from efflux toward influx. Phenylalanine efflux from the leg only showed a trend to a significant effect by insulin. The muscle tissue concentration of six individual amino acids decreased significantly during hyperinsulinemia, particularly the branched-chain amino acids. The leg exchange of glucose, free fatty acids, and glycerol immediately changed significantly, as expected in response to insulinization.(ABSTRACT TRUNCATED AT 250 WORDS)
Muscle mitochondrial morphology, body composition, and energy expenditure in sedentary individuals
Authors: Kirkwood S. P. , Zurlo F. , Larson K. , Ravussin E.
Published: December 2017

To investigate whether differences in metabolic rate are related to differences in muscle mitochondrial morphology and/or to differences in in vitro muscle respiration, we studied 17 healthy Caucasians, covering a wide range of body weight and composition [9 males, 8 females; body wt 96 +/- 37 (SD) kg; body fat = 28 +/- 10%]. Central and peripheral mitochondrial volume density (Vmit c and Vmit p, respectively) and the ratio of mitochondrial outer surface to volume of mitochondria (SVmit c in center and SVmit p at periphery) were determined by stereological analyses of transmission electron micrographs from samples of the vastus lateralis. There was no relationship between mitochondrial morphology or muscle respiration and 24-h energy expenditure, basal metabolic rate, or sleeping energy expenditure adjusted for differences in fat-free mass, fat mass, age, and sex. Although total body fat was not associated with muscle cell morphology, central distribution of body fat [waist-to-thigh circumference ratio (W/T)] correlated negatively with Vmit c (r = -0.58, P = 0.01), SVmit c (r = -0.59, P = 0.01), and SVmit p (r = -0.48, P = 0.05). W/T was also negatively related to muscle respiration (r = -0.59, P = 0.01). Despite the lack of relationship between metabolic rate and muscle mitochondrial morphology, central distribution of body fat is associated with lower mitochondrial density and larger mitochondria in skeletal muscle and is associated with a decreased oxidative capacity of muscle.
Ovarian hydroxyeicosatetraenoic acids compared with prostanoids and steroids during ovulation in rats
Authors: Espey L. L. , Tanaka N. , Adams R. F. , Okamura H.
Published: December 2017

Hydroxyeicosatetraenoic acid methyl esters (HETEs) are lipoxygenase products of arachidonic acid that are generated along with prostaglandins (PGs) during acute inflammatory reactions. Whereas it is well known that ovarian PG levels increase during the ovulatory process, little is known about ovarian HETEs. This report compares the ovarian changes in 5-, 12-, and 15-HETE with ovarian PGE and PGF, along with progesterone, 17 alpha-hydroxyprogesterone, 4-androstene-3,17-dione, testosterone, and 17 beta-estradiol. Ovulation was induced in immature Wistar rats by sequential treatment with pregnant mare's serum gonadotropin and human chorionic gonadotropin (hCG). Follicles began rupturing 10 h after hCG treatment. The greatest correlation was among 12-HETE, 15-HETE, and progesterone, which increased to peak levels at 10 h after hCG. In contrast, the ovarian levels of 5-HETE, 17 alpha-hydroxyprogesterone, testosterone, and 17 beta-estradiol all declined sharply beginning 4 h after hCG. 2 alpha,4 alpha,7-4,5-Epoxy-17-hydroxy-4,17-dimethyl-3-oxo-androstane-2- carbonitrile (epostane), a potent inhibitor of steroid synthesis and ovulation, sharply reduced the synthesis of all five steroids within 30 min after its injection at 3 h after hCG. Among the five eicosanoids, epostane mainly inhibited 15-HETE. The results suggest that 15-HETE, along with progesterone, may have an important role in ovulation.
IGF-I and the truncated analogue des-(1-3)IGF-I enhance growth in rats after gut resection
Authors: Lemmey A. B. , Martin A. A. , Read L. C. , Tomas F. M. , Owens P. C. , Ballard F. J.
Published: December 2017

Effects of insulin-like growth factor I (IGF-I) administration and that of the truncated analogue des-(1-3)IGF-I have been examined in 170-g rats over a 7-day period after surgery to remove 80% of the jejunum plus ileum. The doses administered via osmotic infusion pumps were 0.96 and 2.4 mg.kg-1.day-1 IGF-I and 0.96 mg.kg-1.day-1 des-(1-3)IGF-I. All groups lost weight on the day after surgery, but over the next 3 days the des-(1-3)IGF-I and high-dose IGF-I groups stabilized better and subsequently gained significantly (P less than 0.05) more weight than the vehicle or low-dose IGF-I groups over the last 3 days. The weight gains (mean +/- SE) for the groups over this last 3-day period were 14.0 +/- 1.7, 14.4 +/- 2.9, 21.9 +/- 1.7, and 20.8 +/- 1.0 g for the vehicle, low-dose IGF-I, high-dose IGF-I, and des-(1-3)IGF-I groups, respectively. The nitrogen balances over the last 3 days for the high-dose IGF-I and des-(1-3)IGF-I groups, at 242 +/- 14 and 217 +/- 13 mg/d, respectively, were significantly (P less than 0.05) more positive than the control group at 153 +/- 21 mg/d. These differences could at least partially be explained by changes in muscle protein breakdown, as assessed by 3-methyl-L-histidine excretion. The kidneys were heavier in all treatment groups and the thymus after administration of des-(1-3)IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)
Influence of a mixed meal on splanchnic and interscapular energy expenditure in humans
Authors: Brundin T. , Wahren J.
Published: December 2017

Pulmonary, splanchnic, and interscapular O2 uptake was studied in 14 male volunteers before and for 90 min after a mixed meal. Thermistor catheters were inserted into a hepatic vein, the azygous vein, the pulmonary artery, and the aorta. Systemic and regional blood flows were determined during indirect calorimetry measurements and recordings of blood temperature. After the meal, pulmonary O2 uptake rose by 33-49 ml/min and splanchnic O2 uptake increased by 16-25 ml/min. In the azygous region O2 uptake did not increase significantly. Cardiac output increased after the meal by 1.1-1.5 l/min and splanchnic blood flow rose by 0.4-0.9 l/min. Azygous venous blood flow increased from 130 +/- 19 ml/min to 163 +/- 23 ml/min. In relation to splanchnic O2 uptake, the blood-drained splanchnic heat was low, 11 +/- 1 J/ml, and decreased to 7 +/- 1 J/ml after the meal. We conclude that after a mixed meal approximately one-half of the rise in O2 uptake occurs in the splanchnic organs; azygous-drained tissues, including possible interscapular brown adipose tissue, contribute minimally. The amount of heat drained with blood from the splanchnic region was low in relation to the splanchnic O2 uptake, indicating that splanchnic heat may be dissipated by routes other than the perfusing blood.
Effect of a new mineralocorticoid antagonist mespirenone on aldosterone-induced hypertension
Authors: Opoku J. , Kalimi M. , Agarwal M. , Qureshi D.
Published: December 2017

The effects of the mineralocorticoid antagonist mespirenone on the development and maintenance of aldosterone-induced hypertension in Sprague-Dawley rats has been studied. Uninephrectomized saline-drinking male Sprague-Dawley rats were injected with either 0.2 ml olive oil, 50 g aldosterone, 1 mg mespirenone, 50 g aldosterone plus 500 g mespirenone, or 50 g aldosterone plus 1 mg mespirenone, each dissolved in 0.2 ml olive oil. Administration of aldosterone alone significantly increased the systolic blood pressure (SBP) from a control value of 114 +/- 3.6 to 162 +/- 4 mmHg by the end of the 3-wk experimental period. Mespirenone given alone had no effect on SBP. However, mespirenone given in combination with aldosterone reversed the hypertension caused by aldosterone in a dose-dependent manner. Saline consumption and urinary output were slightly increased in aldosterone-treated rats compared with the other groups, but the body and organ weights were comparable in all groups. Microscopic examination of kidney and heart showed no abnormalities due to mespirenone. These results suggest that in vivo administration of mespirenone to Sprague-Dawley rats effectively prevents the aldosterone-induced hypertension.
Role of leucine as a precursor of glutamine alpha-amino nitrogen in vivo in humans
Authors: Darmaun D. , Dechelotte P.
Published: December 2017

To assess the role of leucine as a precursor of glutamine alpha-amino N in vivo, five healthy men received primed continuous intravenous infusions of L-[15N]leucine, L-[15N]alanine, and L-[2-15N]glutamine in the postabsorptive state on three separate days and over 7, 4, and 4 h, respectively. A steady state in isotopic enrichment was observed in every amino acid during the last hour of each isotope infusion and was used to calculate the rates of amino acid appearance (Ra) and interconversion. Leucine, alanine, and glutamine Ra values were 137 +/- 18, 234 +/- 42, and 320 +/- 18 (SD) mumol.kg-1.h-1, respectively. Rates of N transfer from leucine to glutamine and alanine were 29 +/- 9 and 29 +/- 11 mumol.kg-1.h-1, respectively; these rates represented 21 +/- 8 and 21 +/- 12%, respectively, of leucine's N and 9 +/- 3 and 13 +/- 4% of glutamine's alpha-amino N and alanine N, respectively. These results suggest that the endogenous branched-chain amino acids released by protein breakdown are major precursors of both glutamine and alanine de novo synthesis in postabsorptive humans.
Dose-related effects of epinephrine on glucose production in conscious dogs
Authors: Stevenson R. W. , Steiner K. E. , Connolly C. C. , Fuchs H. , Alberti K. G. , Williams P. E. , Cherrington A. D.
Published: December 2017

The effects of increases in plasma epinephrine from 78 +/- 32 to 447 +/- 75, 1,812 +/- 97, or 2,495 +/- 427 pg/ml on glucose production, including gluconeogenesis, were determined in the conscious, overnight-fasted dog, using a combination of tracer [( 3-3H]glucose and [U-14C]alanine) and arteriovenous difference techniques. Insulin and glucagon were fixed at basal levels using a pancreatic clamp. Plasma glucose levels rose during the 180-min epinephrine infusion by 47 +/- 7, 42 +/- 22, and 74 +/- 25 mg/dl, respectively, in association with increases in hepatic glucose output of 1.04 +/- 0.22, 1.87 +/- 0.23, and 3.70 +/- 0.83 mg.kg-1.min-1 (at 15 min). Blood lactate levels rose by 1.52 +/- 0.24, 4.29 +/- 0.49, and 4.60 +/- 0.45 mmol/l, respectively, by 180 min, despite increases in hepatic uptake of lactate of 3.47 +/- 5.73, 12.83 +/- 3.46, and 37.00 +/- 4.20 mumol.kg-1.min-1. The intrahepatic gluconeogenic efficiency with which the liver converted the incoming alanine to glucose had risen by 84 +/- 40, 77 +/- 24, and 136 +/- 34% at 180 min, respectively. The latter effect plus the effect on net hepatic lactate uptake point to an intrahepatic action of high levels of the hormone in vivo. In conclusion, epinephrine produces dose-dependent increments in overall glucose production, which involve a progressive stimulation of both glycogenolysis (as assessed by glucose production at 15 min) and gluconeogenesis (assessed in the last 30 min of the study). The latter involves a peripheral action of the catecholamine to increase gluconeogenic substrate supply to the liver and may also involve a hepatic effect when high epinephrine levels are present.
Binding and degradation of NH2-terminal parathyroid hormone by opossum kidney cells
Authors: Brown R. C. , Silver A. C. , Woodhead J. S.
Published: December 2017

The binding and cellular processing of NH2-terminal parathyroid (PTH) hormone by confluent monolayers of opossum kidney (OK) cells was characterized using radiolabeled PTH peptide analogues. Time- and temperature-dependent specific binding of 125I-labeled (Nle-8,18, Tyr-34)-NH2-bovine(b)PTH-(1-34) was accompanied by the appearance of degraded radiolabel in the cell medium. Degrading activity was observed to be a specific consequence of binding by PTH receptors. Degrading activity was inhibited by monensin, chloroquine, and NH4+ but not by chymotrypsin inhibitors. Acid washing demonstrated that greater than 80% of total cell-associated specific binding at equilibrium was located in a rapidly internalized (acid-resistant) pool. Monensin pretreatment led to increased acid-resistant binding, presumably through inhibition of turnover of internalized receptor ligand and indicated that the degradation of radiolabel was probably associated with processing of the receptor-ligand complex. Release of intact radiolabel from the acid-resistant pool indicated that some of the internalized peptide was recycled out of the cell in an undegraded form (retroendocytosis). Acid-resistant binding and degradation of 125I-(Nle-8,18, Tyr-34)-NH2-bPTH-(3-34) was minimal, indicating that this ligand was not internalized. It is concluded that the binding and internalization of PTH-(1-34) fragment by confluent OK cells is a specific receptor-mediated process. Cellular processing of PTH-(1-34) conforms to established models of internalization by receptor-mediated endocytosis.
Plasma pool source for fibrinogen synthesis in postabsorptive conscious dogs
Authors: Bennet W. M. , Haymond M. W.
Published: December 2017

To assess the contributions of leucine and alpha-ketoisocaproate (KIC) derived from the portal vein vs. hepatic artery for hepatic protein synthesis, 14-postabsorptive dogs were infused simultaneously with [1-14C]- and [4,5-3H]leucine or [1-14C]- and [4,5-3H]KIC. On one occasion one tracer was infused via a leg vein and the other via mesenteric infusion catheters, and dogs were restudied with both tracers infused systemically. The ratios of systemically to portally infused tracers in portal and arterial plasma leucine were used as indexes of the radioactivity in the potential precursor pools and in fibrinogen-bound leucine as a paradigm of hepatic protein synthesis. In the dogs given leucine tracers, the relative proportions of systemically to portally infused radioactivity in portal free leucine (0.50 +/- 0.06) were lower (P less than 0.001) than in arterial free leucine (1.22 +/- 0.03) and not different from that bound in fibrinogen (0.43 +/- 0.02). In the dogs infused intraportally with KIC, these values were 0.81 +/- 0.04, 0.97 +/- 0.05, and 0.74 +/- 0.05, respectively. In the control studies these ratios were not significantly different from the expected value of 1.0. The results suggest that, in postabsorptive dogs, fibrinogen is exclusively synthesized from portally delivered leucine with little or no contribution from the hepatic artery, whereas portally delivered KIC contributes little directly to fibrinogen synthesis. These data are consistent with zonation of hepatic amino acid metabolism and/or protein synthesis.
Increased sarcolemmal Ca2+ transport activity in skeletal muscle of diabetic rats
Authors: Taira Y. , Hata T. , Ganguly P. K. , Elimban V. , Dhalla N. S.
Published: December 2017

Sarcolemmal membranes were isolated from skeletal muscle by a sucrose density gradient method from rats with diabetes induced by a streptozotocin injection (65 mg/kg iv). The activities of Na(+)-dependent Ca2+ uptake and Ca2(+)-stimulated adenosine-triphosphatase (ATPase) in the sarcolemmal fraction from diabetic rats was higher than those from the control animals. These changes were apparent at various times of incubation (1-10 min) as well as at different concentrations of free Ca2+ (10(-7) to 10(-5) M) and developed during the third and/or fourth weeks after streptozotocin injection. ATP-dependent Ca2+ uptake in the sarcolemmal vesicles was also increased at 28 and 56 days after inducing diabetes. Treatment of diabetic animals with insulin for 14 days reversed the changes in Ca2+ transport activities toward the control levels. Sarcolemmal Mg2(+)-ATPase and Na(+)-K(+)-ATPase activities remained unchanged in diabetic preparations. Furthermore, no difference in the sarcolemmal phospholipid composition and sodium dodecyl sulfate-gel electrophoretic pattern was evident between the control and experimental groups. These results indicate a higher activity of the sarcolemmal Ca2+ transport, which may be associated with hyperfunction of the skeletal muscle in diabetic rats.