bluuebunny/crossref_metadata_2025 huggingface dataset:
The importance of glyoxylate and other glycine precursors in the hepatic and renal conjugation of benzoate in normal and hyperammonemic mice
Authors: Qureshi Ijaz A. , Clermont Paule , Letarte Jacques
Published: April 2011

Benzoate conjugation, represented by hippurate synthesis, was measured in hepatocytes isolated from normal and sparse-fur (spf) mutant mice, with X-linked ornithine transcarbamylase deficiency, to compare the effects of glyoxylate and piridoxylate (a hemiacetal of glyoxylate and pyridoxine), substituted for glycine. Various amino acid precursors of glycine described in the literature, including serine, threonine, glutamine, and glutamate, were studied in a similar manner. The role of glyoxylate and piridoxylate was also assessed in the renal cortex, in comparison with liver homogenates from normal and hyperammonemic mice. The results indicate the importance of glyoxylate and piridoxylate to completely substitute for glycine (96–115%) in isolated hepatocytes of spf/Y mice, as compared with 53–69% (p < 0.05) in normal +/Y controls. The mean value of amino acid precursors to substitute for glycine in spf mice was serine 51%, threonine 29% (p < 0.05), and glutamine 9%. In normal mice, only serine (21%) (p < 0.01) partly substituted for glycine, whereas threonine, glutamine and glutamate gave negative values of net hippurate synthesis. The specific activity of renal cortex for hippurate synthesis from glycine, glyoxylate and piridoxylate was 3–4 times that of liver homogenates (p < 0.01 – < 0.001). A scheme for the transamination of glyoxylate by alanine is presented. Besides alanine, the excess of glycine, serine, and threonine is readily deaminated in the body to take part in gluconeogenic reactions, thus contributing to hyperammonemia. The cumulative effect of benzoate conjugation to drain these ammoniagenic precursors through glycine may be the basis of its therapeutic effect in hyperammonemia.Key words: glycine, glyoxylate, sodium benzoate, hippurate synthesis, spf mice, hepatocytes.
Effect of glucocorticoids on the response of airway smooth muscle to catecholamine and resorcinol β-agonists
Authors: Kolbeck Ralph C. , Chaudhary Bashir A. , Speir William A.
Published: April 2011

The influence of hydrocortisone (11β,17α,21-trihydroxy-pregn-4-ene-3,20-dione) or of methylprednisolone (6α-methyl-11β,17α-21-trihydroxy-1,4-pregnadiene-3,20-dione) on the response of airway smooth muscle to a variety of β-adrenergic bronchodilators was evaluated using incubated guinea pig tracheal rings, preconstricted with histamine. The adrenergic agonists chosen for this study included the nonselective β1- and β2-catecholamine, isoproterenol, the selective β2-catecholamine, rimiterol, and the selective β2-resorcinols, fenoterol and terbutaline. When the incubated rings were pretreated with 10–50 μg/mL of the steroids, there was a significant enhancement in smooth muscle sensitivity and reactivity to rimiterol and isoproterenol. Tracheal response to fenoterol or terbutaline, on the other hand, was not altered by the glucocorticoids. When used alone, neither steroid exerted an inotropic influence on the tracheal smooth muscle. The results of our study indicate that glucocorticoid enhancement of adrenergic bronchodilators is selective for catecholamines, and not for resorcinols.Key words: tracheal smooth muscle, glucocorticoids, β-adrenergic agonists, catecholamines, resorcinols.
Responses of equine trachealis and lung parenchyma to methacholine, histamine, serotonin, prostanoids, and leukotrienes in vitro
Authors: Doucet M. Y. , Jones T. R. , Ford-Hutchinson A. W.
Published: April 2011

The responses of equine trachealis and lung parenchymal strips to a range of contractile agonists were studied. Equine trachealis responded to methacholine > histamine > serotonin as shown by the maximal responses but failed to respond to either leukotrienes (LT), prostaglandin F2α, or U-44069. Equine parenchymal strips showed considerable tonal activity and responded to LTD4[Formula: see text]LTC4 > U-44069 = LTE4 > methacholine [Formula: see text] histamine [Formula: see text] serotonin > prostaglandin F2α as determined through pD2 values. Neither the concentration response curve to LTD4 nor the intrinsic tonal activity of the preparations was modified by pretreatment with either atropine or indomethacin, although the maximal response to LTD4 was reversed by addition of the LTD4 receptor antagonist, MK-571. Thus arachidonic acid metabolites, including LTs, must be considered potential mediators of equine small airway disease, a potential model of human bronchial asthma.Key words: horse, leukotrienes, U-44069, trachea, lung parenchyma.
The influence of renal nerves on electrolyte excretion in conscious and anesthetized rats fed or fasted overnight
Authors: Mercer P. F. , Kline R. L.
Published: April 2011

The role of the renal nerves in the electrolyte excretion of rats fed or fasted overnight was determined in conscious rats and anesthetized (Inactin) and surgically prepared rats. In conscious rats sodium excretion, as measured in a 1-h urine collection period after feeding or fasting overnight, was decreased with fasting with or without renal nerves. Renal nerve activity, as measured by norepinephrine turnover (inhibition of tyrosine hydroxylase by α-methyl-p-tyrosine), was not different between conscious fed or fasted rats and increased to the same extent in fed and fasted rats when anesthetized and surgically prepared. Anesthetized, surgically prepared rats infused with 5.0% glucose showed a denervation natriuresis if rats were fed overnight, but not if they had been fasted overnight. Potassium excretion in conscious and anesthetized rats was lower in fasted rats than fed rats with or without renal nerves. These data suggest (i) renal nerves are not involved in the renal response to an overnight fast in conscious rats, and (ii) in anesthetized, surgically prepared rats renal sympathetic tone is enhanced and denervation natriuresis occurs if rats are fed but not if fasted. Potassium excretion is a reflection of whether rats are fed or fasted and not whether they have renal nerves.Key words: kidney, fasting, sodium, renal nerves.
Influence of opioid peptides on release from vasopressin and oxytocin neurones of the hypothalamoneurohypophyseal system: effects of naloxone in the conscious rat
Authors: Cheng Savio W. T. , O'Connor Edward F. , North William G.
Published: April 2011

We examined the effects of acute and chronic treatments with naloxone on release of vasopressin and oxytocin from the hypothalamoneurohypophyseal system (HNS) in conscious, chronically instrumented Long–Evans rats. Plasma concentrations of vasopressin-associated neurophysin and oxytocin-associated neurophysin were evaluated before and during an intravenous infusion of 18% saline at 100 μL∙kg−1 body weight∙min−1 for 60 min. Acute treatment with naloxone (2.75 μmol/kg, intravenous) did not measurably alter basal plasma osmolality or vasopressin-associated neurophysin concentration, but it caused a three-fold rise in basal plasma oxytocin-associated neurophysin concentration (16 ± 2 to 46 ± 3 fmol/mL, p < 0.005). Chronic treatment with naloxone (13.75 μmol/day, subcutaneous pellets) increased plasma osmolality (292 ± 1 to 300 ± 2 mosmol/kg H2O, p < 0.01) by day 5, but it had no measurable effects on basal vasopressin- or oxytocin-associated neurophysin concentration. There were also no significant differences in plasma sodium concentration (144.8 ± 1.1 vs. 142.2 ± 1.4 mequiv./L) under both conditions. Acute and chronic treatments with naloxone accompanied by salt loading produced a five- and four-fold decrease in the rates that plasma concentration of vasopressin-associated neurophysin changed with plasma osmolality, compared with untreated salt-loaded control rats. For oxytocin secretion from the HNS, both treatments accompanied by salt loading substantially decreased the threshold for changes in relation to plasma osmolality; the rise in plasma concentration of oxytocin-associated neurophysin was similar at all levels of hyperosmotic stimulation. A strongly correlated relationship between plasma oxytocin-associated neurophysin and plasma osmolality (r = 0.739) found for control animals became poorly correlated following treatments (acute, r = 0.173; chronic, r = −0.079). Our results suggest that in conscious rats, endogenous opioid peptides enhance the secretion of vasopressin from neurones of the HNS in response to hyperosmotic stimulation but inhibit both basal and stimulated release of oxytocin.Key words: naloxone, vasopressin, oxytocin, neurophysin, conscious rats.
Electrocardiographic evidence for cocaine cardiotoxicity in cat
Authors: Crumb Jr. William J. , Kadowitz Philip J. , Xu You-Qiu , Clarkson Craig W.
Published: April 2011

Recent case studies suggest that cocaine overdose may produce life-threatening cardiac arrhythmias. We therefore investigated its effects on the electrocardiogram (leads II and V1) and arterial blood pressure in cats anesthetized with pentobarbital. Cocaine was administered by intravenous infusion over a 2-min interval at 1 mg/kg in 10 cats. In 5 out of 10 cats an additional infusion of 3 mg/kg cocaine was also administered after hemodynamic and electrocardiographic parameters had returned to control values (i.e., within 10 min). During and following infusion of 1 mg/kg cocaine, no significant change in heart rate or systolic or diastolic blood pressure were found, however the QRS duration increased by 38% (from 46 ± 5 to 64 ± 12 ms) (p < 0.01). Evidence for bundle branch block and (or) premature ventricular beats was observed in 9 out of 10 cats after 1 mg/kg cocaine. Infusion of a further 3 mg/kg cocaine in five cats significantly lowered diastolic blood pressure (from 98 ± 18 to 64 ± 28 mmHg; 1 mmHg = 133.3 Pa) (p < 0.01), and further prolonged QRS to 79 ± 14 ms, a 75% increase from the mean control value (p < 0.01). In addition, 1st and 2nd degree atrioventricular block, ventricular extrasystoles, and ectopic rhythms (AV junctional or idioventricular) were observed in four out of five cats given 3 mg/kg cocaine. Mean plasma concentrations of cocaine were 1.37 ± 0.39 μg/mL (4.28 ± 1.22 μM) (n = 5) at the end of a 1 mg/kg infusion and 2.93 ± 0.43 μg/mL (9.16 ± 1.34 μM) after a 3 mg/kg infusion (n = 3). These data indicate that doses of cocaine similar to those reported to occur in patients suffering from cocaine cardiotoxicity can produce marked disturbances in cardiac conduction and arrhythmias in an anesthetized cat model.Key words: cocaine, electrocardiography, arrhythmia.
The role of the ileum in the control of food intake and intestinal adaptation
Authors: Koopmans Henry S.
Published: April 2011

Studies on animals that drastically reduce their food intake after having a jejunoileal bypass or an ileal transposition surgery suggest that the lower ileum may play a major role in the control of daily food intake. In this study, eight rats were given slow continuous infusions of either 18, 28, or 38 mL of their normal liquid diet directly into their upper ileum. They reduced their daily intake in a compensatory way for the two smaller infusions and in a more than compensatory way for the large infusion. The later result suggests that the large infusion may have caused the rats some discomfort, which led to a lower food intake. This was tested in a conditioned aversion paradigm with an ileal infusion of 26 mL of the diet into eight naive rats. These rats showed a strong aversion to the ileal infusion. Infusion of the same amount of diet into the stomach of eight other rats failed to demonstrate an aversion and showed that the procedures of the experiment did not produce the aversion. The infusion of relatively small amounts of liquid diet into the ileum produces an internal signal that reduces intake and is regulatory. A second process in which ileal infusion causes discomfort leads eventually to a more than regulatory decrease in daily intake.Key words: food intake, intestinal infusion, ileal, conditioned aversion.
α1-Adrenergic partial agonists utilize cytosolic Ca2+ more effectively for contraction in aortic smooth muscle
Authors: Takayanagi Issei , Onozuka Shuji
Published: April 2011

Fura 2 loaded thoracic aorta strips from rabbits were used. Norepinephrine, phenylephrine, clonidine, and tizanidine induced an increase in cytosolic Ca2+ concentration ([Ca2+]i) and muscle tension in a concentration-dependent manner. A positive correlation between [Ca2+]i and tension development owing to the agonists was noted. The slope of regression lines between [Ca2+]i and tension development for clonidine and tizanidine, α1-adrenergic partial agonists, were significantly steeper than those for norepinephrine and phenylephrine, α1-adrenergic full agonists. The intrinsic activities of the partial agonists obtained from tension development were greater than those from changes in [Ca2+]i. These results suggest that the partial agonists cause a greater muscle tension than the full agonists at the same level of [Ca2+]i.Key words: cytosolic Ca2+ concentration, tension, partial agonist, full agonist,α1-adrenoceptors.
Training-induced alterations in muscle glycogen utilization in fibre-specific types during prolonged exercise
Authors: Green H. J. , Smith D. , Murphy P. , Fraser I.
Published: April 2011

Using the glycogen depletion technique, we have examined utilization of specific fibre types during prolonged submaximal exercise to investigate the recruitment pattern employed by the central nervous system to sustain force generation in the face of a progressive glycogen depletion. Six male subjects ([Formula: see text] max, 52.8 ± 2.5 mL∙kg−1∙min−1,[Formula: see text]) cycled at 59% of pretraining [Formula: see text] max (the same absolute power output) for 99.5 ± 6 min on two occasions, before training and after 10–12 days of intensive training, involving 2 h of cycling per day. Prior to the training, glycogen concentration during exercise in the type I and type IIA fibres of the vastus lateralis muscle as measured by microphotometric techniques was progressively reduced during exercise. The pattern of depletion in both of these fibre types was parallel and showed an early marked depletion amounting to 51 (p < 0.05) and 35% (p < 0.05) in the type I and type IIA fibres, respectively, during the first 15 min of exercise. At the end of exercise, glycogen levels in type I and type IIA fibres were reduced to 9 and 44% of initial levels, respectively. In contrast, glycogen concentration in type IIB fibres was not significantly (p < 0.05) altered throughout the exercise. Following training, a pronounced glycogen sparing occurred that was conspicuous in only the type I and type IIA fibres, which was most pronounced during the first 15 min of the exercise. Similar to pretraining, glycogen concentrations in type IIB fibres were unaffected by either exercise or training. These results support the hypothesis that the muscle fibre recruitment patterns are established early in exercise and that even in the face of extensive glycogen loss observed late in exercise in the lower threshold type I and type IIA fibres, the higher threshold type IIB fibres are not recruited.Key words: recruitment, fibre types (I, IIA, and IIB), prolonged exercise, glycogen depletion.
Adrenal versus nonadrenal sympathetic preganglionic neurones in the lower thoracic intermediolateral nucleus of the cat: physiological properties
Authors: Backman S. B. , Sequeira-Martinho H. , Henry J. L.
Published: April 2011

Adrenal and nonadrenal sympathetic preganglionic neurones (SPNs) in the intermediolateral nucleus of spinal segments T8–T10 in the cat were compared according to a number of physiological properties. An SPN was classified as "adrenal" (n = 37) if it could be antidromically activated by electrical stimulation of the adrenal medulla. An SPN that could not be activated from the adrenal medulla yet could be antidromically activated by electrical stimulation of the greater splanchnic nerve was classified as "nonadrenal" (n = 123). Approximately 50% of adrenal SPNs (17 out of 37) were activated antidromically by stimulation of both the greater splanchnic nerve and adrenal medulla, suggesting that these neurones projected to the adrenal medulla via the greater splanchnic nerve, with the other adrenal SPNs taking a different route. The mean conduction velocities of adrenal (6.7 ± 1.8 (SD) m/s) and nonadrenal (6.7 ± 1.5 m/s) sympathetic preganglionic axons were similar. Over 80% of adrenal (31 out of 37) and nonadrenal (104 out of 116) SPNs were spontaneously active. The two types of neurone were indistinguishable in terms of the rates and patterns of discharge. Adrenal SPNs discharged with a mean rate of 1.4 ± 1.1 spikes/s, and nonadrenal SPNs discharged with a mean rate of 1.8 ± 1.4 spikes/s. With both types of SPN, the pattern of spontaneous activity was either irregular or phasic. With the latter pattern, periodic bursts of discharge were at the same frequency as oscillations in arterial pressure, frequency of ventilation, or phrenic nerve discharge. These data suggest that adrenal and nonadrenal sympathetic preganglionic neurones in the intermediolateral nucleus in caudal thoracic segments share a number of common physiological properties.Key words: adrenal, sympathetic preganglionic neurone, spinal cord, lateral horn.
Ca2+-activated K+ currents in smooth muscle
Authors: Akbarali H. , Nakajima T. , Wyse D. G. , Giles W.
Published: April 2011

Calcium-activated potassium currents have been described in a wide variety of cell types. This report summarizes some important properties of these currents in smooth muscle and provides examples from our recent single channel recordings from human cystic artery.Key words: calcium-activated K currents, smooth muscle, human cystic artery, voltage clamp.
Effect of adenosine and glucagon on hepatic blood volume responses to sympathetic nerves
Authors: Lautt W. Wayne , Schafer Joshua , Legare Dallas J.
Published: April 2011

Hepatic blood volume responses were studied in cats using in vivo plethysmography. The maximal response (Rmax) to sympathetic nerve stimulation and to infusions of norepinephrine into the hepatic artery or portal vein was similar (12–14 mL expelled per liver in 2.9-kg cats; average liver weight, 76.8 ± 6.8 g). The ED50 for norepinephrine intraportal (0.44 ± 0.13) and intrahepatic arterial infusions (0.33 ± 0.08 μg∙kg−1∙min−1) were similar indicating equal access of both blood supplies to the capacitance vessels. Adenosine (2.0 mg∙kg−1∙min−1) did not cause significant volume changes but produced a mild (27%) suppression of Rmax due to nerve stimulation with no change in the frequency (3.4 Hz) needed to produce 50% of Rmax. Rmax tended (not statistically significant) to decrease during glucagon (1.0 μg∙kg−1∙min−1) infusion but the nerve frequency needed to produce 50% of Rmax rose to 5.6 Hz. Thus both adenosine and glucagon produced modulation of sympathetic nerve-induced capacitance responses without having significant effects on basal blood volume. Adenosine, by virtue of its marked effects on arterial resistance vessels (at substantially lower doses than those used here) and the relative lack of effect on venous capacitance vessels, may be useful for producing clinical afterload reduction without venous pooling.Key words: blood volume, capacitance, sympathetic nerves, adenosine, glucagon.
Vital marker for muscle nuclei in myoblast transfer
Authors: Fang Qiuwen , Chen Ming , Li Hua-ju , Goodwin Tena G. , Law Peter K.
Published: April 2011

A new method is developed using Fluoro-Gold (FG) as a vital stain to label the nuclei of donor myoblasts in myoblast transfer studies. In vitro incubation with 0.01% FG for 16 h resulted in 100% nuclei labelling. Intensive fluorescence persisted following 9 days of subculture, when the human myoblasts were injected into the quadriceps of mouse recipients immunosuppressed with cyclosporine. Injected muscles showed mosaicism of host and donor nuclei 25 days after injection, indicating (i) survival and fusion among donor myoblasts, and (ii) fusion between host and donor cells. FG labelling was not observed in control muscles injected with an equal volume of FG-labelled dead myoblasts, 0.01% FG medium, or phosphate-buffered saline.Key words: Fluoro-Gold, nucleus vital stain, myoblast culture and transplant.
Measurement of starch fermentation in the human large intestine
Authors: Cummings J. H. , Englyst H. N.
Published: April 2011

Starch, not fibre, is probably the major substrate for fermentation in the human colon. However, quantitating the amount of starch that resists pancreatic amylase and thus escapes digestion in the small bowel is difficult. A number of techniques have been employed in man and are reviewed here, including direct intubation of the ileum, the ileostomy model, and breath studies. The results of a series of studies of the digestion of starch from potato and banana are reported. When fed to ileostomy patients, 3% of hot potato starch and 12% of cold potato starch were resistant to digestion, as was 75% of banana starch. In feeding experiments with healthy volunteers none of the starch was recoverable in faeces, indicating its complete fermentation in the colon. Breath H2 measurements after test meals of these starches indicated that only 2–5% of potato starch and 7–12% of banana starch was fermented. A single blood acetate measurement timed to coincide with peak breath H2 was not useful. However, a number of problems with breath H2 studies are discussed, and it is suggested that either ileal intubation or the ileostomy model are the most reliable techniques presently available, with serial blood acetate determinations also potentially valuable. Overall on Western diets, approximately 10% of all starch is probably resistant starch.Key words: starch, large intestine, fermentation, breath.
Effects of epinephrine on the net hepatic uptake of lactate, pyruvate, and glycerol in sheep
Authors: Brockman Ronald P.
Published: April 2011

Epinephrine causes hyperglycemia in part by increasing gluconeogenesis. However, the mechanism of its gluconeogenic effects has not been studied in ruminants. This study was undertaken to examine the effect of epinephrine on the net hepatic uptake of selected glucose precursors in sheep. The major abdominal blood vessels of the sheep were catheterized in normal and alloxan diabetic sheep. Glucose production, metabolic clearance of glucose, and the hepatic removal of certain glucose precursors were determined before, during, and after epinephrine infusion. Epinephrine increased the hepatic glucose output, the concentrations of lactate and glycerol in plasma, and the net hepatic uptake and fractional hepatic extraction of lactate and glycerol. These effects were independent of changes in the concentrations of insulin and glucagon in plasma. These results show that epinephrine directly stimulates hepatic gluconeogenesis in sheep.Key words: epinephrine, hepatic gluconeogenesis, sheep.
Effect of chloride on renal blood flow in angiotensin II induced hypertension
Authors: Passmore John C. , Jimenez Agnes E.
Published: April 2011

The effect of selective dietary sodium and (or) chloride loading on blood pressure and renal blood flow (RBF) in the rat angiotensin II (AII) model of hypertension was determined. AII (200 ng/min) or saline was infused intraperitoneally. Diets were provided with either high or low concentrations of sodium, chloride or both ions for 22 days. The blood pressure of saline-treated animals was not increased by the high sodium chloride diet. Animals on a high sodium, high chloride diet had a significantly greater increase of blood pressure at 8, 15, 18, and 22 days of AII infusion compared with AII-treated animals on a low sodium, low chloride diet (p < 0.05). Selective dietary loading of either high sodium or chloride in AII-treated rats produced no greater elevation of blood pressure than AII with the low sodium, low chloride diet. Selective high dietary chloride was associated with a lower RBF in AII- and vehicle-treated rats compared with low dietary chloride. The chloride effect on RBF was greater in AII-treated animals. In conclusion, both sodium and chloride are necessary to produce the maximum increase of blood pressure in AII animals. AII enhances the decreased RBF induced by dietary chloride.Key words: angiotensin II, sodium chloride, blood pressure.
Effects of endothelin 3 on diastolic blood pressure of pithed Sprague–Dawley, Wistar–Kyoto, and spontaneously hypertensive rats before and after pretreatment with nifedipine
Authors: Tabrizchi Reza , Triggle Christopher R.
Published: April 2011

Pressor actions of endothelin 3 (ET3) were examined in pithed Sprague–Dawley (SD), Wistar-Kyoto (WKY), and spontaneously hypertensive (SH) rats before and after the administration of the calcium channel antagonist, nifedipine. Systolic and diastolic blood pressures were recorded via an intra-arterial catheter from sodium pentobarbital anaesthized rats prior to pithing. The systolic and diastolic blood pressures recorded from SH rats were significantly greater than those of SD and WKY rats; however, after pithing there were no significant differences between the diastolic blood pressures among the various strains. Administration of nifedipine significantly reduced the diastolic blood pressure of pithed rats to an equal extent in all three strains. The infusion of ET3 produced a dose-dependent increase in diastolic blood pressure of SD, WKY, and SH rats, but neither vascular sensitivity nor reactivity to ET3 was altered in SH rats. Nifedipine was more effective at inhibiting the vasoactive actions of ET3 in SD and WKY than in SH rats. It was therefore concluded that the pressor actions of ET3 in SH rats may be less dependent on the influx of calcium through a dihydropyridine-sensitive calcium channel as compared with WKY and SD rats.Key words: endothelin 3, calcium antagonist, diastolic blood pressure, spontaneously hypertensive, pithed rats.
Disparate effects of fenfluramine on thermogenesis in brown adipose tissue in the rat
Authors: Ma Stephanie W. Y. , Preston Edward
Published: April 2011

It has been suggested that fenfluramine, a clinically used appetite suppressant, can also promote weight loss by augmenting energy expenditure, as indicated by increased whole-body O2 consumption [Formula: see text] and mitochondrial GDP binding in brown adipose tissue (BAT) of fenfluramine-treated rats. To further investigate a possible involvement of BAT in the drug's metabolic effects, 113Sn-labelled microspheres were injected into the left cardiac ventricle of conscious rats 70–80 min after intraperitoneal delivery of 20 mg/kg fenfluramine (DL-mixture) or saline vehicle. At 28 °C ambient temperature, fenfluramine augmented resting whole-body [Formula: see text] and increased the microsphere entrapment in BAT, indicating enhanced blood flow and metabolism. At 20 °C ambient temperature, the expected increase in BAT blood flow associated with nonshivering thermogenesis was observed in control rats, but in fenfluramine-treated rats the increase in BAT blood flow was severely attenuated, and [Formula: see text] and body temperature were reduced. The stimulatory effect of fenfluramine on BAT metabolism was not prevented by urethane anesthesia but did not occur if the tissue was denervated. These blood flow measurements corroborate previous reports, based on GDP-binding assays, that fenfluramine treatment can augment thermogenesis in BAT by effects mediated through the innervation of the tissue. However, the data also indicate that this calorigenic effect is dependent on ambient temperature being near thermoneutrality and that in a cool environment the drug inhibits BAT thermogenesis.Key words: fenfluramine, brown adipose tissue, thermogenesis.
Characterization of gonadotropin-releasing hormone (GnRH) receptors in the ovary of common carp (Cyprinus carpio)
Authors: Pati Debananda , Habibi Hamid R.
Published: April 2011

Gonadotropin-releasing hormone (GnRH) binding sites have been characterized in the fully mature common carp ovary, using an analog of salmon GnRH ([D-Arg6,Trp7,Leu8,Pro9-NEt]-GnRH; sGnRH-A) as a labeled ligand. Binding of sGnRH-A to carp follicular membrane preparation was found to be time-, temperature-, and pH-dependent. Optimal binding was achieved after 40 min of incubation at 4 °C at pH 7.6; binding was found to be unstable at room temperature. Binding of radioligand was a function of tissue concentration, with a linear correlation over the range of 8.0–40.0 μg membrane protein per tube. Incubation of membrane preparations with increasing levels of [125I]sGnRH-A revealed saturable binding at radioligand concentrations greater than 400 nM. The binding of [125I]sGnRH-A to the carp ovary was also found to be reversible; addition of unlabeled sGnRH-A (10−6 M) after reaching equilibrium resulted in complete dissociation of [125I]sGnRH-A within 30 min, and the log dissociation plot indicated the existence of a single class of binding sites. Addition of unlabeled sGnRH-A displaced the bound [125I]sGnRH-A in a dose-related manner. Hill plot as well as Scatchard analysis suggested the presence of one class of high affinity GnRH binding sites. Bound [125I]sGnRH-A was also found to be displaceable by other GnRH peptides, including sGnRH ([Trp7,Leu8]-GnRH), cGnRH-II ([His5,Trp7,Tyr8]-GnRH) and a GnRH antagonist ([D-pGlu1,D-Phe2,D-Trp3,6]-GnRH; GnRH-ANT) in a parallel fashion, indicating that these peptides bind to the same class of binding sites. sGnRH-A and cGnRH-II were found to bind with greater affinities than sGnRH and GnRH-ANT to the carp ovarian binding sites. These results provide for the first time characterization of GnRH binding sites in the ovary of a teleost species, Cyprinus carpio.Key words: gonadotropin-releasing hormone, luteinizing hormone releasing hormone, receptor, ovary, carp, Cyprinus carpio.
Effect of pressure on circumferential order of adventitial collagen in human brain arteries
Authors: Canham Peter B. , Whittaker Peter , Barwick Sharon E. , Schwab Monika E.
Published: April 2011

A key factor in the contribution of collagen fibres to tissue mechanics is the alignment of the fibres, which we studied in brain arteries, focussing on alignment changes with distending pressure. Arteries from autopsy were cannulated and fixed at different distending pressures from 0 to 200 mmHg (1 mmHg = 133.32 Pa), alcohol dehydrated, paraffin embedded, sectioned, and stained for birefringent enhancement. The polarized light microscope was set for extinction and fibre orientations were precisely determined at the rotational position of extinction for 200 positions around the artery wall. Results from 22 arterial cross sections revealed, with fixation pressure, a significant but incomplete straightening of collagen (even at 200 mmHg). The mean angular deviation of alignment of fibres was ±30° for arteries fixed at zero transmural pressure, which in contrast was ±7° for the inner and ±13° for the mid-adventitia for arteries fixed at 200 mmHg transmural pressure. We verified on vessels fixed at low pressure, by using a full wave plate in conjunction with the specificity of the interference colours, that the measurements were correct and not confused with angles at 90° to the morphological axis. Alternative tissue processing was done with two arteries fixed at 120 mmHg and processed for frozen sections; the results showed diminished variability in alignment but within the range of measurements for wax embedded tissue. We concluded that the collagen fabric could contribute to the mechanics of brain arteries but that it would be with sinusoidal rather than straightened fibres of collagen.Key words: brain artery, adventitia, collagen, organization, polarized light.
Characterization of intestinal smooth muscle responses and binding sites for endothelin
Authors: Bolger Gordon T. , Liard Francine , Garneau Michel , Jaramillo Jorge
Published: April 2011

The contractile activity of and binding sites for endothelin-1 (ET-1) were investigated in isolated guinea-pig ileal longitudinal smooth muscle (GPILM). ET-1 produced concentration-dependent contractions of GPILM that either slowly subsided in the continued presence of ET-1 or rapidly subsided following washing of the tissue. The ED50 value for ET-1 contractions was 4.2 ± 1.3 × 10−9 M. The removal of extracellular calcium or pretreatment with nifedipine produced a complete inhibition of the contractions to ET-1. The IC50 value of nifedipine for inhibition of ET-1 mediated contractions was 3.0 ± 0.8 × 10−8 M. ET-1 produced a marked prolonged homologous desensitization of its contractile response but did not affect the responses mediated by carbachol, histamine, serotonin, substance P, and PLA2. High-affinity binding sites for 125I-labelled ET-1 were identified on microsomal membranes prepared from GPILM with Kd and Bmax values obtained by Scatchard analysis of 3.5 ± 0.6 × 10−10 M and 2138 ± 159 fmol/mg protein, respectively. The binding of 125I-labelled ET-1 to GPILM microsomes was characterized by a rapid association (kob value of 0.077 min−1 at a radioligand concentration of 0.45 nM and an extremely slow dissociation (kl value of 0.011 min−1; t1/2 value of 793 min). The binding was unaffected by the calcium channel antagonists nifedipine, verapamil, and diltiazem (10−6 M); the receptor antagonists phenoxybenzamine, atropine, and naloxone (10−6 M) and propranolol; and the peripheral benzodiazepine receptor antagonists Ro 5-4864 and PK 11195 and psychotomimetic drug phencyclidine (10−5 M). Incubation of GPILM with ET-1 (2 × 10−8 M) for 10 min followed by washing of the tissue for 1 h resulted in a significant (p < 0.05 unpaired Student's t-test) reduction (33%) of 125I-labelled ET-1 binding that partially recovered following 2 h of washing the tissue. These results demonstrate that ET-1 is an intestinal smooth muscle spasmogen that produces its pharmacologic effects by a mechanism(s) that is not shared by other major intestinal neurotransmitters. Furthermore, intestinal smooth muscle contains specific high-affinity binding sites that likely mediate the contractile responses to ET-1.Key words: intestine, smooth muscle, endothelin, calcium channels, contraction.
Functional sensitivity of the native skeletal Ca2+-release channel to divalent cations and the Mg–ATP complex
Authors: Rousseau Eric , Pinkos Janet , Savaria Diane
Published: April 2011

Sarcoplasmic reticulum (SR) vesicles, prepared from rabbit skeletal muscle, were characterized by functional and binding assays and incorporated into planar lipid bilayers. Single-channel activity was recorded in an asymmetric calcium buffer system and studied under voltage clamp conditions. Under these experimental conditions, a large conductance (100 pS in 50 mM Ca2+trans) divalent cation selective channel displaying high ruthenium red and low Ca2+ sensitivity was identified. This pathway has been previously described as the Ca2+-release channel of the SR of skeletal muscle. We now report that in the presence of a Mg–ATP complex, the Ca2+ sensitivity of the open probability of this channel is increased. Furthermore, we show that micromolar cis Sr2+ concentrations also activated the Ca2+-release channel. The open probability of the Sr2+-activated channel was increased in the presence of a 2 mM Mg–ATP complex and adenine nucleotides on the cytoplasmic face of the Ca2+-release channel. These results were confirmed by isotopic flux measurements using passively 45Ca2+-loaded vesicles. In the latter case, the presence of extra vesicular AMP-PCP (the nonhydroly sable ATP analog) enhanced the percentage of 45Ca2+ release induced either by Ca2+ or Sr2+ activation. In conclusion our findings emphasize the fact that the divalent cation activation of the Ca2+-release channel may be induced by Ca2+ and Sr2+, but not by Ba2+, in the presence of adenine nucleotides. Furthermore, they support the view that in situ Ca2+ and Mg–ATP complexes are involved in modulating the gating mechanism of this specific pathway.Key words: Ca2+ release, sarcoplasmic reticulum, planar lipid bilayer, strontium.
Vascular actions of thrombin receptor peptide
Authors: Muramatsu Ikunobu , Laniyonu Adebayo , Moore Graham J. , Hollenberg Morley D.
Published: April 2011

We have examined the action of the thrombin receptor-derived polypeptide, S42FLLRNPNDKYEPF55 (TRP42–55), in rat and guinea pig aortic rings and helical arterial strips, and we have compared the actions of the peptide with those of thrombin. In rat preparations, both TRP 42–55 and thrombin caused a concentration-dependent endothelium-dependent relaxation that was blocked by Nω-nitro-L-arginine methyl ester; the relaxation response of the intact rat aortic strip preparation to concentrations of the peptide in the range 30–60 μg/mL (17–34 μM) was equivalent to the response to 0.03–0.1 U/mL of thrombin (about 0.3–0.9 nM), yielding a potency ratio (TRP 42–55:thrombin) of about 38 000: 1. In contrast with the complete desensitization of thrombin-treated rat aortic preparations to a second administration of the enzyme, the rat aortic tissue was not desensitized by repeated exposures to TRP 42–55 and remained responsive to the peptide even after treatment of the tissue by thrombin. In contrast with the rat aortic tissue, in either intact or endothelium-free guinea pig aortic preparations both TRP 42–55 and thrombin caused a concentration-dependent endothelium-independent contraction. The contractile action of 60 μg/mL of receptor peptide (34 μM) in guinea pig aortic strip preparations was equivalent to the contractile action of 0.1–0.3 U/mL thrombin (0.9–3 nM), yielding a potency ratio of about 17 000: 1. In guinea pig aortic preparations with an intact endothelium that were precontracted with noradrenaline, neither thrombin nor TRP 42–55 caused relaxation, whereas substance P did so. As with the rat aortic preparation, thrombin treatment of the guinea pig aorta rendered the tissue refractory to a second exposure to the enzyme, whereas treatment with the receptor peptide did not desensitize the tissue to a subsequent exposure to thrombin. Nonetheless, as opposed to the rat aortic preparation, wherein repeated exposure to the peptide yielded a constant response, repeat doses of TRP 42–55 caused a modest desensitization of its contractile action in the guinea pig aortic strip preparation. None of the effects of TRP 42–55 were affected by the thrombin inhibitor hirudin, which blocked the action of thrombin in both the rat and guinea pig aortic preparations. We conclude that the distinct effects of TRP 42–55 in both rat and guinea pig aortic tissue, which mimic the actions of thrombin in both preparations, are due to the presence of a thrombin receptor in these tissues, akin to the one previously characterized in platelet tissue. Further, the data indicating different TRP 42–55:thrombin potency ratios and different desensitizing properties in the rat and guinea pig aortic tissue support the notion that there may be distinct thrombin receptor signal transduction systems that regulate vascular contractility either directly by acting on smooth muscle elements or indirectly via an action on endothelial cells.Key words: thrombin, thrombin receptor, vasoconstriction, vasorelaxation, aorta, endothelium.
Renal adrenergic receptors: localization of [125I]prazosin binding sites along the microdissected rat nephron
Authors: Cohen Herbert T. , Takemoto Fumi , Satoh Takeo , Katz Adrian I.
Published: April 2011

Norepinephrine stimulates renal tubular sodium reabsorption, probably through an α1-adrenoceptor-mediated mechanism. Although the distribution of α1-adrenoceptors in the kidney has been studied with autoradiography, the precise location of these receptors in isolated nephron segments is unclear. Using a microassay we determined the specific binding of [125I]iodoarylazidoprazosin ([125I]prazosin), a high specific radioactivity analog of the selective α1-antagonist prazosin, to microdissected glomeruli and tubule segments. Specific binding of [125I]prazosin (3 nM) in the proximal convoluted tubule was time- and concentration-dependent, saturable, and reversible. In this segment the apparent KD by association and dissociation rate constants of [125I]prazosin binding was 0.47 nM, and the maximum receptor density was ~ 0.19 fmol/mm, or 720 fmol/mg protein. Binding specificity was verified in competition studies with excess (3 μM) unlabeled prazosin and probes for α2- (yohimbine), β- (propranolol), dopamine1- (SCH23390), and dopamine2- (S-sulpiride) receptors. [125I]Prazosin binding was inhibited significantly only by unlabeled prazosin. Mapping of prazosin binding along the nephron revealed that the highest density was in the proximal convoluted tubule, followed by the proximal straight tubule. Lesser binding was found in the thick ascending limb and in the distal convoluted tubule, whereas in the cortical and outer medullary collecting duct and in glomeruli, binding was not significantly different from zero. These results demonstrate specific prazosin binding sites in the proximal and early distal nephron where direct innervation by monoaminergic nerves is most abundant, and suggest that portions of the nephron beyond the proximal tubule, specifically the diluting segment, may also be under α1-agonist influence.Key words: α1-adrenoceptor, prazosin, isolated tubule, glomerulus, catecholamine.
Hemodynamic and plasma atrial natriuretic factor responses to cardiac volume loading in young versus older normotensive humans
Authors: Legault Louis , Nguyen Paul van , Holliwell Donna L. , Leenen Frans H. H.
Published: April 2011

To assess the effects of age on responsiveness of atrial natriuretic factor (ANF) release, and the possible contribution of cardiac sympathetic activity, in young (n = 8) and older normotensives (n = 7), the effects of cardiac volume load on plasma ANF, central venous pressure, and general hemodynamics were evaluated. Studies were performed after pretreatment with placebo or 80 mg propranolol. Cardiac volume loading increased central venous pressure by 3–5 mmHg (1 mmHg = 133.3 Pa); β-blockade did not affect this response. Cardiac volume load caused significant increases in heart rate (10–15 beats/min) and cardiac index (by 0.7–0.8 L∙min−1∙m−2) and decreases in plasma catecholamines. Propranolol attenuated the increases in heart rate and cardiac index. These hemodynamic responses did not differ significantly between the two groups of subjects. Cardiac volume load significantly increased plasma ANF, by 87 ± 21 pg/mL in the young normotensives and by 212 ± 33 pg/mL in the older normotensives (p < 0.01, young vs. older). β-Blockade did not affect this different response. Our results show that the plasma ANF response to volume loading is potentiated by aging. Although differences in atrial stretch cannot be excluded, this effect may relate to the decrease in clearance of plasma ANF occurring with aging.Key words: cardiac volume load, atrial natriuretic factor, aging, β-blockade.
Modulation of lipoprotein lipase activity in the rat by the β2-adrenergic agonist clenbuterol
Authors: Belahsen Rekia , Deshaies Yves
Published: April 2011

This study evaluated the effects of β2-adrenoceptor stimulation on some determinants of triglyceride metabolism. Male Sprague–Dawley rats were injected twice daily with clenbuterol (30 μg∙kg−1) for 7 days, or with an equivalent volume of vehicle. Serum triglycerides, hepatic triglyceride secretion rate, and lipoprotein lipase activity in white and brown adipose tissues as well as in red vastus lateralis muscle and heart were evaluated in the fasting state and following a fat-free, high-sucrose meal, 3 h after the last agonist injection. In rats killed in the fasting and postprandial states, clenbuterol reduced the mass of white adipose tissue (−25 and −12%, respectively; p < 0.02), whereas it increased the mass of vastus lateralis muscle (+11 and +7%; p < 0.002) and heart (+13 and +10%; p < 0.0001). In vehicle-injected animals, the fasting state was associated with lower lipoprotein lipase activity in white and brown adipose tissues, and higher enzyme activity in vastus lateralis and heart, compared with the postprandial state. Postprandially, treatment with clenbuterol reduced lipoprotein lipase activity in white adipose (−24%), whereas it increased enzyme activity in brown adipose (+107%) as well as in vastus lateralis (+35%). In fasted animals, no significant variation of enzyme activity in these tissues was observed following clenbuterol treatment, whereas in the heart, a decrease of lipoprotein lipase activity was observed (−22%). Clenbuterol lowered serum triglycerides significantly (−23%), but not their rate of secretion, whereas the agonist decreased the insulin to glucagon ratio only in the postprandial state. These results suggest that modulation of triglyceride-rich lipoprotein metabolism, particularly tissue-specific alterations in lipoprotein lipase activity, may be one of the pathways through which clenbuterol affects partitioning of lipid substrates.Key words: triglyceride, lipoprotein lipase, tissue specificity, meal intake, β2 agonist.
Oxytocin actions on voltage-dependent ionic channels in pregnant rat uterine smooth muscle cells
Authors: Inoue Yoshihito , Shimamura Keiichi , Sperelakis Nicholas
Published: April 2011

The effects of oxytocin, a uterotonic polypeptide hormone, on the voltage-dependent slow calcium, fast sodium, and potassium channel currents were studied using whole-cell voltage clamp of freshly isolated cells from late pregnant (18–21 day) rat myometrium. The calcium current was rapidly inhibited by oxytocin (about 25% inhibition at 20 nM) in a dose-dependent manner, and this inhibitory effect was completely reversible by washout. However, inhibition was not observed when barium was used as the charge carrier. Sodium current and potassium current were not modified by oxytocin, thus sodium and potassium currents may not play important roles in oxytocin-induced augmentation of uterine contraction. It is concluded that oxytocin stimulates uterine contraction by mechanisms other than augmentation of the voltage-dependent calcium current, e.g., by release of Ca from sarcoplasmic reticulum (by inositol trisphosphate) or by activation of a receptor-operated Ca channel. The inhibition of the slow calcium current may be induced by the elevation of [Ca]i.Key words: oxytocin, ionic channels, uterine smooth muscle, whole-cell voltage clamp, pregnant rat myometrium.