bluuebunny/crossref_metadata_2025 huggingface dataset:
The in vivo gastrointestinal absorption in rats of the intact cyclo(L-leucylglycine) dipeptide
Authors: Gallo-Torres Hugo E. , Heimer Edgar P. , Witt Constance , Miller O. Neal , Meienhofer Johannes , Cheeseman C. I.
Published: April 2011

Unanesthetized rats with catheterized portal veins were administered, intragastrically, a saline solution of the diketopiperazine cyclo(L-leucyl-[U-14C]glycine) (cyclo(L-Leu-[14C]Gly)) at a dose of 47.9 nmol. The appearance of this cyclic dipeptide in portal vein plasma was followed chromatographically using a microcolumn of Sephadex G-25 complexed with copper. Further identification was done by thin-layer chromatography. Net absorption was evaluated by the balance method. The intestinal site of maximal absorptive capacity for cyclo(L-Leu-[14C]Gly) was also investigated. The gastric emptying rate was 98% in 15 min. After intragastric administration, cyclo(L-Leu-[14C]Gly) was absorbed (peak at 2.5 min) into the portal vein. The balance method showed that the efficiency of absorption was 94% within the first 10 min and was completed after 20 min. This compound was absorbed intact and remained unmetabolized in the portal vein of the rat and seemed to be absorbed throughout the length of the small intestine. Shortly after administration (1- to 5-min period), the greatest absorption of the diketopiperazine occurred at the level of the duodenum; however, the absorption maximum appeared to move down the gut and after 10 min the highest uptake took place in the jejunum, but never seemed to reach the ileum to a significant degree. Only negligible amounts of the cyclic dipeptide were excreted with the feces. Cyclo(L-Leu-[14C]Gly) is thus an example of a low molecular weight peptide which is rapidly and completely absorbed, after its intragastric administration at low concentration and is enzymatically stable during the process of absorption. In vitro experiments determined that this peptide apparently traverses the intestinal wall passively and does not use the carrier-mediated mechanisms for linear peptides.
A comparison of the local anaesthetic effects of cationic, anionic, and neutral amphipathic agents in frog skeletal muscle
Authors: Foulks James G. , Morishita Lillian
Published: April 2011

Impermeant alkyl amphipathic agents reduced the excitability of frog twitch muscle fibers, indicating that local anaesthesia can be produced by perturbations within the external lamina of the sarcolemma. Cationic (n-alkyl trimethylammonium) and anionic (n-alkyl sulfonate) as well as permeant neutral (n-alkanol) agents have been compared with regard to their local anaesthetic potency. Small impermeant agents (fewer than six carbon atoms) alone were ineffective. Within each series the concentration required to reduce excitability was proportional to the length (hydrophobicity) of the hydrocarbon chain attached to the polar group. However, corresponding members of these three series of compounds differed considerably in their local anaesthetic potency. Hence, charged groups as well as apolar moieties can influence local anaesthetic efficacy. The supra-additive character of the local anaesthesia produced by combining impermeant alkyl anions and cations indicates that these two types of amphipaths may produce their similar effects by perturbations at different membrane sites.
Triazene metabolism. III. In vitro cytotoxicity towards M21 cells and in vivo antitumour activity of the proposed metabolites of the antitumour 1-aryl-3,3-dimethyltriazenes
Authors: Kohlsmith Douglas J. , Vaughan Keith , Luner Stephen J.
Published: April 2011

In vitro cytotoxicity of a series of antitumour triazenes towards the M21 melanoma cell line has been studied. Dimethyltriazenes are structural analogues of 5-(3,3-dimethyl-1-triazeno-)imidazole-4-carboxamide (Dacarbazine) and are inactive, which is consistent with the requirement for metabolic activation. Monomethyltriazenes and hydroxymethyltriazenes, the proposed metabolites of the dimethyltriazenes, are cytotoxic to the M21 cell line. A new series of 4-hydroxy-1,2,3-benzotriazines has been tested for in vitro cytotoxicity. A series of monoalkyltriazenes (Ar∙N=N∙NHR) has been tested for antitumour activity against the P388 lymphoma in vivo. Only monomethyltriazenes had significant antitumour activity, which supports the hypothesis that the monomethyltriazene is the active metabolite of the antitumour dimethyltriazenes. The activity of monomethyltriazenes in vivo is correlated with the chemical stability and t1/2 measurements in pH 7.5 phosphate buffer.
Control of spontaneous and deoxycorticosterone–salt hypertension and polyuria by nitrendipine pellets
Authors: Hall Charles E. , Hungerford Shirley
Published: April 2011

Weekly subcutaneous implantation of 25-mg nitrendipine pellets prevented onset of both spontaneous and deoxycorticosterone–salt hypertension in rats. Discontinuance of implantation led to reappearance of hypertension after about 2 weeks in the former and led to rising though still normotensive pressures after about 3 weeks in the latter. A new implant caused blood pressures in both to drop within a day or two to normotensive levels in the case of spontaneously hypertensive rats. Nitrendipine prevented cardiac hypertrophy in steroid hypertensive rats, but not in spontaneous hypertensives. A nitrendipine pellet given 1 day before or a 30 mg/kg injection given 1 h prior to the administration of a water, Na+, and K+ load, prevented the diabetes insipidus-like syndrome resulting from deoxycorticosterone–salt treatment, and lowered sodium but not potassium excretion. Nitrendipine did not affect steroid-induced hypernatremia and hypokalemia.
Fade of the responses of the isolated, blood-perfused dog atrium to cholinergic interventions
Authors: Furukawa Yasuyuki , Martin Paul , Levy Matthew N.
Published: April 2011

In the isolated, blood-perfused, canine right atrium, intramural parasympathetic nerve stimulation and intra-arterial infusions of acetylcholine induced substantial negative chronotropic and inotropic responses. The responses to parasympathetic stimulation reached their maximum values quickly, and then usually faded back toward control levels over the next 1 or 2 min of stimulation. The fade of the responses at high stimulation frequencies (≥30 Hz) was significantly greater than that at lower frequencies. The inotropic responses to acetylcholine infusion (1 μg/min) faded slightly but significantly, whereas the chronotropic responses did not fade at all. These results suggest that the fade of the cardiac responses to parasympathetic stimulation is mainly ascribable to a progressive reduction in the rate of acetylcholine release from the nerve endings, especially at higher stimulation frequencies. The fade of the inotropic responses was more pronounced and had a longer time course than that of the chronotropic responses. Furthermore, the fade of the inotropic responses diminished significantly as the response magnitude was augmented by an increase in stimulation voltage. Conversely, the fade of chronotropic responses was not significantly affected by this intervention. These differences in the inotropic and chronotropic responses to neural stimulation, and the occurrence of a slight fade of the inotropic response to acetylcholine infusion, suggest that in addition to the predominant prejunctional mechanism, a postjunctional phenomenon may also be partly responsible for the fade of the inotropic response to cholinergic interventions.
Mechanism of action of arachidonic acid in the isolated perfused rat heart
Authors: Shaffer Joel E. , Malik Kafait U.
Published: April 2011

The purpose of this study was to elucidate the mechanism of action of arachidonic acid in the isolated rat heart perfused with Krebs solution at a constant flow. Administration of arachidonic acid, 3.3–33 nmol, into the heart caused a small transient increase followed by a pronounced decrease in coronary perfusion pressure and increased myocardial tension, heart rate, and the output of prostaglandins (6-keto-PGF1α, PGE2, and PGF2α). Administration of structurally similar fatty acids, dihomo-γ-linolenic acid, and 8,14,17-eicosatrienoic acid, produced vasoconstriction and decreased myocardial tension without affecting heart rate or the output of prostaglandins. Infusion of PGI2, PGF2α, or PGE2 produced coronary vasodilation and increased myocardial tension, whereas PGF2α increased heart rate, an effect which was not prevented by propranolol. Indomethacin blocked the effect of arachidonic acid on myocardial tension and heart rate, but only reduced the duration of coronary vasodilation. The initial component of arachidonic acid induced coronary vasodilation which was unaffected by indomethacin and also remained unaltered during the infusion of three structurally dissimilar lipoxygenase inhibitors, eicosatetraynoic acid, nordihydroguaiaretic acid, and 1-phenyl-3-pyrazolidone. Indomethacin did not alter the effects of the exogenously administered prostaglandins on perfusion pressure or myocardial tension; however, it blocked the effect of PGF2α on heart rate. The effect of arachidonic acid or PGF2α to increase heart rate was not blocked by thromboxane synthetase inhibitors, imidazole, or OKY-1581. We conclude that the cardiac effects of arachidonic acid are mediated primarily through its conversion to cyclooxygenase products. However, the initial biphasic component of the coronary vascular response, vasoconstriction, and subsequent vasodilation produced during the first 3-min period following arachidonic acid administration appears to be unrelated to prostaglandins, whereas the duration of the coronary vasodilation depends upon the formation of cyclooxygenase products.
Effects of moderate hypoxia on premature action potentials of rabbit papillary muscle
Authors: Alvarez Julio , Dorticós Francisco , Morlans Jesús
Published: April 2011

Experiments were performed to study the effects of hypoxia on the characteristics of premature action potentials of rabbit papillary muscles. At normal resting potential, the duration of the premature action potential at the shortest coupling intervals was always greater than that of the control response. As the coupling interval was increased beyond 150 ms, the duration of the premature action potential regained control values. In cells depolarized to −70 mV by KCl, early lengthening of the premature response was attenuated. After 60 min of hypoxia, recovery of action potential duration at normal and reduced resting potentials was accelerated. The maximum rate of depolarization and its reactivation time constant were not affected by 60 min of hypoxia. It is suggested that intracellular free Ca is important in the control of action potential duration via the outward background potassium current.
Effects of intraventricular injections of gamma-aminobutyric acid and related substances on feeding behavior in satiated sheep
Authors: Seoane J. R. , Dumont F. , Girard C. L. , Bédard L. , Matte J. J.
Published: April 2011

Feed intake was measured following injections of gamma-aminobutyric acid (GABA), muscimol (a GABA agonist), and picrotoxin (a GABA antagonist) into the lateral ventricles of satiated sheep. Doses ranging from 0.20 to 3200 nmol of GABA did not affect feeding behavior at 15, 30, 60, and 120 min postinjection. A dose of 160 nmol of muscimol induced a marked increase in feeding, comparable to that provoked by an injection of 78 μmol of pentobarbital. Muscimol-induced feeding was blocked effectively by a preinjection of picrotoxin. These observations implicate that neurons sensitive to gamma-aminobutyric acid may be involved in the control of feeding behavior in ruminants.
The 3β-hydroxysteroid dehydrogenase activity of cultured porcine Leydig cells in primary culture
Authors: Bernier M. , Gibb W. , Saez J. M. , Collu R. , Ducharme J. -R.
Published: April 2011

Previous studies have shown that there is a spontaneous progressive increase in human chorionic gonadotropin (HCG)-stimulated testosterone (T) production by immature porcine Leydig cells during primary culture for 3 days, whereas basal T production is unaltered. Preliminary data indicated that during this time, there was an increase in the activity of the 3β-hydroxysteroid dehydrogenase (3β-HSD). The purpose of the present study was to further characterize this increase. 3β-HSD was assayed by measuring the conversion of tritiated dehydroepiandrosterone (DHEA) to androstenedione in the presence of NAD+. A ninefold increase in activity occurred between days 1 and 2 and only twofold between days 2 and 3. A 5- to 20-fold increase of the apparent maximum velocity of the enzyme was observed after 3 days of culture while the apparent Km remained unchanged. Cycloheximide treatment (150 ng/mL) completely abolished this spontaneous increase in enzyme activity. In parallel experiments, the stimulatory effect of HCG on T and DHEA production was inhibited by cycloheximide treatment by 90% and 60%, respectively, whereas basal T production was not affected. These results suggest that the spontaneous increase of 33-HSD activity in primary cultures of porcine Leydig cells is secondary to de novo protein synthesis and that this phenomenon may be partially responsible for the increased responsiveness of these cells to HCG during the culture period.
Biointeraction of dietary T-2 toxin and zinc in mice
Authors: Chanin B. E. , Hamilton D. L. , Hancock D. S. , Schiefer H. B.
Published: April 2011

The effect of varying dietary levels of zinc was evaluated in mice fed T-2 toxin. A semipurified diet was used to produce a low zinc (< 2 parts per million (ppm)), a zinc replete (100 ppm), and a high zinc (2500 ppm) diet. T-2 toxin was added to the three zinc diets at a concentration of 10 ppm. The mice were fed one of the six diets ad libitum for up to 28 days. Mice from each diet were submitted for necropsy after 14 and 28 days and after 14 days zinc absorption and retention was measured in mice from each of the low and replete zinc diets, with and without T-2 toxin. Animals receiving a low zinc diet with T-2 toxin had reduced weight gains. The high zinc diet did not depress growth and did not influence T-2 depression of growth. The diets produced significant hematological changes without evidence of a T-2 toxin – zinc interaction. While zinc absorption was greater in mice fed the low zinc diet than those fed the replete zinc diet, T-2 toxin decreased absorption of zinc in the low zinc group and increased absorption in the replete zinc group. T-2 toxin did not influence the biological half-life of retained zinc in either the low or replete zinc groups. The biological half-life of zinc was significantly increased in the mice fed the low zinc diet relative to the replete zinc diet. Splenic follicle necrosis was observed microscopically by day 14 in all animals fed T-2 toxin, regardless of dietary zinc concentrations; however, erythroid cell regeneration was seen in most of the animals fed the replete and high zinc diets. By day 28, animals receiving T-2 toxin had splenic follicle necrosis in the low and replete zinc groups but not in the high zinc group. The results demonstrate significant interactions between dietary zinc levels and T-2 toxin with regard to growth, zinc absorption, and microscopic lesions. The high zinc diet was not particularly toxic to mice and appeared to reduce the toxicity of T-2 toxin.
The effect of propranolol on blood viscosity changes induced by experimental coronary occlusion
Authors: Biro G. P. , Beresford-Kroeger Diana
Published: April 2011

The effect of propranolol treatment was investigated in the myocardial ischemia-induced hyperviscosity state in anesthetized dogs. In untreated control dogs, low shear blood viscosity rose progressively, following an acute occlusion of the left anterior descending coronary artery; this effect was partially but significantly reduced by intravenously administered propranolol (0.2 mg/kg). The effect of the in vitro addition of propranolol was also determined upon viscosity of blood samples obtained at hourly intervals from dogs subjected to similar coronary ligation. The in vitro addition of propranolol did not produce a similar reversal of the hyperviscosity state observed in the blood obtained from dogs after coronary ligation.
Flow and pressure responses of coronary arteries and veins to vasodilating agents
Authors: Sylven J. C. H. , Armour J. A. , Klassen G. A.
Published: April 2011

The response to a bolus injection of nitroglycerine, adenosine, nifedipine, and dipyridamole of the canine systemic as well as coronary artery and venous circulations was observed and contrasted. Particular attention was paid to the time of change of pressures and flows and to changes in oxygen extraction by the myocardium induced by the pharmacological agents. The dosages of vasodilators used were selected so that no significant change in aortic blood flow occurred. Nitroglycerine and adenosine caused a rapid and similar vasodilation in the coronary circulation. Oxygen extraction was not altered by nitroglycerine, but was decreased by adenosine. The onset time of the vasodilation produced by either nifedipine or dipyridamole was similar, but the time to peak action was much slower for dipyridamole. As well, the effect of dipyridamole on intramyocardial and left intraventricular pressures was more delayed than that following the injection of the other agents. Oxygen extraction was reduced by nifedipine and dipyridamole. These results indicate that pharmacological vasodilating agents can affect coronary arteries, coronary veins, and myocardial oxygen extraction differently.
Inotropic effect of amrinone in rabbit papillary muscle: reversal of the myocardial depressant effect of halothane
Authors: Komai Hirochika , Rusy Ben F.
Published: April 2011

In rabbit papillary muscles, the pronounced inotropic effect of amrinone (0.4–0.8 mg/mL) observed at low stimulation frequencies (0.1–0.5 Hz) diminished as the frequency was increased to 1.0–2.0 Hz. Reversal of the negative inotropic effect of halothane (1%) by amrinone (0.8 mg/mL) was similarly dependent on stimulation frequency. The contractile response to paired-pulse stimulation in the presence of amrinone (0.8 mg/mL) was summation rather than postextrasystolic potentiation. Amrinone (0.8 mg/mL) was not effective in reversing the negative inotropic effect of halothane (1%) on potentiated state contraction generated by paired-pulse stimulation. These results suggest that amrinone increases the influx of extracellular Ca2+ across the sarcolemma but not the availability of cellular Ca2+ which accumulates, most likely in sarcoplasmic reticulum, under the condition of potentiation.
Influence of hypoxemia and respiratory acidosis on the plasma kinetics and tissue distribution of digoxin in the conscious dog
Authors: Souich Patrick Du , Clozel Jean-Paul , Saunier Claude , Ong Huy , Hartemann Denise , Garcia-Carmona Teresa , Sadoul Paul
Published: April 2011

The aim of the present study was to investigate the influence of hypoxemia combined with respiratory acidosis on the kinetics of digoxin in conscious dogs. One group of three beagles was exposed to air and 7 days later to 10% O2, 10% CO2, and 80% N2. In a second group of three dogs, the order of exposure to the two atmospheric conditions was reversed. The dogs received 25 μg/kg digoxin and blood and urine samples were collected over the next 29 h. At the conclusion of the second treatment, the dogs were sacrificed to determine digoxin concentrations in the left ventricle, liver, renal cortex, and skeletal muscle. Digoxin total body clearance increased from 6.2 ± 0.9 in control to 9.0 ± 1.0 mL min−1 kg−1 in hypoxemic and hypercapnic dogs (p < 0.05). The digoxin apparent volume of distribution at steady state (Vss) was increased in the dogs with hypoxemia and hypercapnia (11.63 ± 1.11 vs. 8.62 ± 0.41 L/kg in the controls, p < 0.05). As a consequence the digoxin plasma half-life remained unchanged (18.6 ± 1.5 h in hypoxemic and hypercapnic dogs versus 20.1 ± 2.8 h in the controls). In dogs with hypoxemia and hypercapnia, the ratio of tissue to plasma digoxin concentrations tended to increase in the liver, in the renal cortex, and in the left ventricle and remained unchanged in the left hind leg muscle. In vitro studies showed that the digoxin total binding to erythrocyte membranes was slightly increased in the dogs with hypoxemia and hypercapnia, resulting from an increase in the apparent intrinsic association constant for digoxin (p < 0.003). It is concluded that hypoxemia combined with respiratory acidosis changes digoxin disposition in the conscious dog and is the cause of a digoxin redistribution into the tissues.
Unusual potassium channels mediate nonadrenergic noncholinergic nerve-mediated inhibition in opossum esophagus
Authors: Jury J. , Jager L. P. , Daniel E. E.
Published: April 2011

Field stimulation of the circular muscle of the opossum esophagus produces a transient hyperpolarization (inhibitory junction potential, IJP) followed by an "off" depolarization. A similar nonadrenergic, noncholinergic (NANC) response in guinea pig taenia caecum has been shown to be due to an increase in the potassium ion permeability of the smooth muscle cell membrane. Double sucrose gap studies showed a decrease in resistance during the IJP, and a reversal at an estimated membrane potential of about −90 mV (4 mM K+). The reversal potential was dependent on the extracellular potassium concentration, shifting to −75 mV when the potassium in the superfusion medium was increased to 10 mM. The IJP in the opossum esophageal circular smooth muscle is therefore like the IJP of the guinea pig taenia caecum in that it is probably due to a selective increase in potassium ion permeability. Potassium conductance blocking agents, tetraethylammonium chloride (TEA, 20 mM) and 4-aminopyridine (4-AP, 5 mM) both caused a depolarization of the smooth muscle cell membrane, but TEA increased the membrane resistance, whereas 4-AP did not affect the membrane conductance in a consistent way. A decrease in IJP amplitude owing to these agents was not apparent. Apamin (10 μM) did not affect the membrane potential, the membrane resistance, or the IJP. Quinine (0.1 mM) produced effects quantitatively similar to those of TEA. Quinine (1 mM) did abolish the IJP, however, this was likely due to a blockade of impulse transmission of the intramural nerves. These results suggest that the receptor-operated channels opened by the NANC-nerve mediator in this tissue are unusual in that they are different from those functioning to maintain the resting membrane potential and they differ from those involved in the IJP in the guinea pig taenia caecum.
Ventilation and respiratory pattern and timing in resting awake cats
Authors: Jennings D. B. , Szlyk P. C.
Published: April 2011

The purpose of this study was to characterize the variability and patterns of spontaneous respiratory behaviour in awake cats. Respiration was measured in six cats over 80 or 90 min by the plethysmographic technique. In three cats, arterial blood gases were measured. Breath frequency (f) and tidal volume (VT) varied considerably breath-to-breath, although on average, these measurements as well as average ventilation remained relatively constant. The incidence of breath ventilation (VT × 60/TTOT) and VT were distributed unimodally but the incidence of breath f had a bimodal distribution. In the low f range, average f was 22.5 breaths/min, and in the high f range, average f was 41.6 breaths/min. The latter range appeared to be associated with purring. Inspiratory duration (TI) was less than expiratory duration (TE) at low f but exceeded TE at high f. For a given breath ventilation there was a predictable f and VT. At shorter TI (higher f) mean inspiratory flow, an index of central respiratory drive, increased but VT decreased. This study indicates that "normal" control respiratory behaviour in awake cats is better described by the range and pattern of breathing than by average values.
Thoracoabdominal motion during hypercapnia, hypoxia, and exercise
Authors: Chapman K. R. , Perl A. , Zamel N. , Rebuck A. S.
Published: April 2011

We measured, in 11 healthy volunteers, the contributions of rib cage and abdomen–diaphragm compartments to increased ventilation caused by hypercapnia, hypoxia, and exercise to determine whether different stimuli produce similar or different patterns of ventilation with respect to the motion of rib cage and abdominal compartments. Progressive hypcroxic hypercapnia and progressive isocapnic hypoxia were induced by rebreathing methods and graded exercise performed on a treadmill, and compartmental tidal volume (VT) was measured by respiratory inductive plethysmography. For each stimulus, the wide range of VT responses among individuals was determined primarily by the range of rib cage contributions to VT, the abdominal compartment VT response slopes accounting for less of this range. There were no significant differences between hypercapnia and hypoxia in either rib cage or abdominal contributions to ventilation (for both, p < 0.3). However, exercise rib cage and abdominal contributions to ventilation were significantly different from those during chemically driven breathing: for the rib cage compartment, p < 0.0001 and for the abdominal compartment, p < 0.05. Whereas, in 8 of 10 subjects the rib cage contribution to VT during exercise was similar to or exceeded that during rebreathing, in 7 of 10 subjects the abdomen–diaphragm contribution fell below that measured during both hypercapnia and hypoxia. There was a significant correlation between hypercapnia and hypoxia in the VT contribution of each compartment at equivalent levels of ventilation (rib cage, p < 0.0001; abdomen, p < 0.0005), but there was no significant correlation in the VT contribution of either compartment between exercise and hypercapnia or exercise and hypoxia. The pattern of compartmental contributions to ventilation during treadmill exercise differs significantly from that observed during chemically driven breathing.
Assessing the pressure at zero flow in canine epigastric skin flaps
Authors: Clarke Howard M. , McKee Nancy H.
Published: April 2011

The pressure at zero flow was examined using three independent techniques in island epigastric skin flaps in dogs under sodium pentobarbital anesthesia. (i) The flap was perfused from a reservoir which was varied in height to supply a range of pressures. The corresponding flows were measured by electromagnetic blood flowmetry and the pressure at zero flow was determined by extrapolation to zero flow. (ii) Arterial inflows as low as 2.2 μL/min were delivered by a Harvard pump and corresponding pressures were measured. The pressure at zero flow was determined by inspection. (iii) The artery supplying the flap was occluded with a microclip and the plateau following the decay of pressure was read as the pressure at zero flow. The pressure decay technique was the simplest, most reproducible method and was verified by the other two methods. It gave a pressure at zero flow of 5.8 ± 0.4 mmHg (0.77 ± 0.05 kPa). The critical closing pressure is discussed and related to the pressure at zero flow.
Resistance of the diabetic rat nerve to ischemic inactivation
Authors: Jaramillo J. , Simard-Duquesne N. , Dvornik D.
Published: April 2011

The resistance of the action potential to ischemic inactivation observed in diabetic patients has been reproduced in vivo in rat rendered diabetic with streptozotocin and, acutely, in normal rats given p.o. a load of glucose. The resistance phenomenon was not detected in galactosemic rats. The preservation of the action potential was reversed by the administration of insulin, but not by treatment with an aldose reductase (AR) inhibitor. The ischemic resistance is attributed to the metabolic availability of excess glucose to the nerve. AR does not appear to be involved in the phenomenon.
Measurements of transmitter action: the problem of voltage dependence
Authors: MacDonald J. F.
Published: April 2011

Conventional intracellular recordings, from central mammalian neurones, are used to assess the actions of putative transmitters on neuronal membrane parameters such as input conductance and to determine reversal potentials. Ohm's Law and constant current methods can be employed to accurately assess such parameters provided the putative transmitter activates a voltage-independent response. However, several likely transmitter candidates act via voltage-dependent mechanisms to alter neuronal excitability; as a consequence, results from this method of analysis must be cautiously interpreted. Under this constraint of possible voltage dependence, constant current methods can lead to spurious conclusions about the physiological and pharmacological characterization of the response.
Modulation of inhibition in the hippocampus in vivo
Authors: Ropert Nicole
Published: April 2011

The nature and mechanisms of septohippocampal transmission have been elucidated by taking advantage of an in situ preparation in experiments with Sprague–Dawley rats under urethane. Both extracellular field potentials and intracellular recordings were made in CA1–3 regions of the hippocampus; and the hippocampal commissure and medial septum stimulated to evoke synaptic activity. Using muscarinic and nicotinic agonists and antagonists it was shown that both acetylcholine and medial septal activity can increase the excitability of pyramidal cells, mainly through muscarinic receptors. The effect of septal stimulation was enhanced by local application of physostigmine and reduced by intraventricular injections of hemicholinium. It was also shown that acetylcholine, when applied in the stratum pyramidale, can reduce the voltage and conductance changes observed during evoked inhibitory postsynaptic potentials (IPSP) without affecting the action of γ-aminobutyric acid on membrane conductance and voltage. It is therefore proposed that acetylcholine can reduce evoked IPSPs through presynaptic inhibition. Evidence is also presented that medial septal stimulation can reduce the efficacy of evoked IPSPs. These observations provide further support for the existence of a cholinergic septohippocampal pathway.
Organization of medial elastin at aortic junctions in sheep and lambs
Authors: van Baardwijk Charles , Barwick Sharon E. , Roach Margot R.
Published: April 2011

Aortas from four sheep and three fetal lambs were fixed at physiological pressure in 10% neutral buffered formalin. The regions with branches were serially sectioned in either cross or longitudinal section at 7-μm intervals and stained for elastin with Gomori–aldehyde–fuchsin. A large model of one aortointercostal junction was made from Plexiglas to show that bundles of elastin appeared to be continuous from the aorta into the branch. These bundles were then studied from large photomicrographs of the other junctions. At the intercostals and lumbars, the elastin lamellae ran continuously from the outer third of the media into the branch. There was often an added "pad" of elastin and other acellular material on the flow divider (distal lip). The large muscular branches which arose from the abdominal aorta have much less elastin than the intercostals. In them the aortic elastin appears to merge into a raphe on the proximal and lateral sides of the junction, with a very abrupt transition. A "tongue" of muscle from the branch often penetrated into the media of the aorta distally. Occasionally a small acellular cap was seen on the apex of the flow divider. There were few significant differences between the lambs and the sheep, probably because embryologically the arteries develop very early. The proximal and distal lips of all junctions were easily distinguished from each other, and the small and large branches were also different. We suspect these regions may respond differently to pressure, but we did not test this hypothesis.
Limitation of theophylline elimination by reduced oxygen availability in mouse hepatocytes and rat isolated livers
Authors: Nakatsu Kanji
Published: April 2011

The effect of oxygen availability on theophylline metabolism by mouse hepatocytes and rat isolated livers was examined. The elimination of theophylline by mouse hepatocytes and the metabolism of theophylline to dimethyluric acid by isolated, perfused rat livers was seriously impaired when the gas mixture supplied contained less than 28% oxygen. The correlation coefficients relating oxygen supply and the concentration of theophylline remaining in mouse hepatocyte suspensions were −0.74 to −0.84. In the isolated, perfused rat liver experiments, the correlation coefficient relating oxygen availability and dimethyluric acid production was 0.87. These observations are interpreted as supporting the hypothesis that oxygen availability per se is an important factor in determining the rate of theophylline metabolism.
Inactivation of the β-adrenergic receptor in cardiac muscle by dithiols
Authors: Prior Trevor I. , Patel Vandana , Drummond G. I.
Published: April 2011

The effect of sulfhydryl reagents on binding of the β-adrenergic antagonist (−)-[3H]dihydroalprenolol hydrochloride ((−)-[3H]DHA) to a microsomal fraction of rabbit ventricular muscle was studied. Incubation with the disulfide reducing agents dithiothreitol (DTT), 2-mercaptocthanol, and reduced glutathione resulted in loss of (−)-[3H]DHA binding. At 500 μM DTT, less than 50% of specific binding activity remained; at 100 mM, binding was completely eliminated. 2-Mercaptoethanol and reduced glutathione were less effective than DTT at inhibiting binding activity. The total binding capacity (Bmax) decreased from 155.4 fmol mg−1 of protein, in the absence of DTT, to 92.4 and 77.5 fmol mg−1 at 0.25 and 0.7 mM DTT, respectively. The equilibrium dissociation constant (KD) increased from 7.6 nM, in the absence of DTT, to 10.3 nM at 0.25 mM DTT and to 20.8 nM at 0.7 mM DTT. Thus, DTT-induced decline in (−)-[3H]DHA binding results from a decrease in both the number and affinity of membrane binding sites for the tracer. Receptors could be protected from DTT inactivation by preincubation with β-adrenergic ligands. Oxidants could not reverse inactivation, with the exception of o-iodosobenzoate which was only partially effective. Thus, the β-adrenergic receptor of rabbit ventricular muscle contains essential disulfide moietie(s) which can be inactivated by reducing thiols.
Structure–desensitization relationships of angiotensin analogues in the rat isolated uterus
Authors: Moore Graham J. , Franklin Kevin J. , Nystrom Diana M. , Goghari Mahesh H.
Published: April 2011

The desensitizing potencies of angiotensin II (ANG II) analogues modified at positions 1, 2, 4, 7, and 8 have been examined in the rat isolated uterus assay by determining the time of recovery of the half-maximal concentration (EC50) response to angiotensin II after treatment of the tissues with a high dose (10−5 M) of each analogue for 2 min. The magnitude of the desensitization effect was substituent dependent in the following manner: position 1, sarcosine (Sar) > Asp > des-Asp; position 2, Arg > Sar; position 4, Tyr > Tyr(Me) ~ Phe; position 7, 3,4-dehydroproline (Dpr) > Pro > thioproline (Tpr) > Sar; position 8, Ile > D-Trp > Ala > Phe. The "additivity" rule applied to these structure–desensitization relationships and the most potent desensitizer, requiring 3 h for reestablishment of the EC50 response, was [Sar1,Dpr7,Ile8]-ANG II. The desensitizing potencies of these analogues did not correlate with agonist or antagonist activities and demonstrated that the angiotensin-mediated tissue desensitization process has unique structural determinants. Methylation or elimination of the tyrosine hydroxyl group of strong desensitizers virtually eliminated the desensitization effect, implicating the phenoxyl moiety in the mechanism of desensitization. The initial phase of recovery of angiotensin responsiveness after desensitization by several analogues appeared to obey first-order kinetics. The results are discussed in the contexts of both one- and two-site receptor models.
Isolation and characterization of calcineurin from bovine brain
Authors: Gupta Ramesh C. , Khandelwal Ramji L. , Sulakhe Prakash V.
Published: April 2011

Calcineurin was isolated from bovine cerebrum extracts by sequential chromatography on Affi-Gel blue and calmodulin affinity columns. Calcineurin so isolated was ~90% pure and was composed of equimolar amounts of subunit A (Mr = 61 000 – 63 000) and subunit B (Mr = 15 000 – 17 000) when examined by sodium dodecyl sulfate gel electrophoresis. A polypeptide (<10%) with Mr = 71 000 whose function and role remains to be investigated, was routinely detected in the calcineurin preparation. Both inhibitory activity (towards calmodulin-dependent cAMP phosphodiesterase) and phosphatase activity (with 32P-labelled myelin basic protein as substrate) were associated with calcineurin as evidenced by (i) coelution from Affi-Gel blue, Affi-Gel calmodulin, diethythaminoethyl-Sepharose, and Sephacryl S-200 chromatography columns; (ii) association with the same protein band on nondenaturing gels; (iii) similar stability upon storage at 4 °C and with repeated freezing and thawing; and (iv) parallel heat inactivation. Phosphatase activity of calcineurin was maximal with 32P-labelled myelin basic protein as the substrate. Using this substrate, enzyme activity was generally stimulated 5- to 10-fold in the presence of Ca2+ and calmodulin; half-maximal activation (A0.5) was observed with 25 nM calmodulin. Calmodulin increased the Vmax of the reaction without affecting the Km for the substrate. Optimum temperature and pH for the reaction were 45 °C and 7, respectively, in both the absence and presence of Ca2+ and calmodulin. The presence of sodium dodecyl sulfate in the assay mixtures caused a decrease in Ca2+ –calmodulin dependent phosphatase but an increase in Mn2+ –calmodulin dependent phosphatase; inhibitory activity was decreased, although to a lesser extent. When A and B subunits of calcineurin were resolved by polyacrylamide gel electrophoresis in the presence of MnCl2 and a low concentration of sodium dodecyl sulfate, the phosphatase activity was found to be associated with subunit A and was stimulated by MnCl2 or MnCl2 + calmodulin.
Action of insulin modulated by pertussis toxin in rat adipocytes
Authors: Goren H. Joseph , Northup John K. , Hollenberg Morley D.
Published: April 2011

We studied the effect of pertussis toxin (PT) treatment on the ability of insulin to inhibit lipolysis and to stimulate glucose oxidation in isolated rat adipocytes. In cells maximally modified by PT (100% ADP ribosylation of a 41-kdalton protein in membranes), the ability of insulin to inhibit lipolysis stimulated either by PT alone or in combination with a catecholamine was abolished. In cells wherein ADP ribosylation was submaximal (about 67% modification), a small but variable antilipolytic action of insulin could still be detected. In cells maximally modified by PT, both basal and insulin-stimulated glucose oxidation were markedly reduced (to 10–15% of control levels). However, relative to the basal oxidation level, the fold stimulation by insulin in PT-treated cells was equivalent to the fold stimulation in control cells. Nonetheless, PT treatment caused a rightward shift in the dose–response curve for insulin-stimulated glucose oxidation as well as a small reduction in insulin binding. Our results point strongly not only to a link between the inhibitory guanine nucleotide regulatory complex (Gi) and the antilipolytic action of insulin but also to a link between the Gi complex and the overall regulation of glucose metabolism in adipocytes.
The physiologic reserve in oxygen carrying capacity: studies in experimental hemodilution
Authors: Chapler C. K. , Cain S. M.
Published: April 2011

The mechanisms by which the body attempts to avoid tissue hypoxia when total body oxygen delivery is compromised during acute anemia are reviewed. When the hematocrit is reduced by isovolemic hemodilution the compensatory adjustments include an increase in cardiac output, redistribution of blood flow to some tissues, and an increase in the whole body oxygen extraction ratio. These responses permit whole body oxygen uptake to be maintained until the hematocrit has been lowered to about 10%. Several factors are discussed which contribute to the increase in cardiac output during acute anemia including the reduction in blood viscosity, sympathetic innervation of the heart, and increased venomotor tone. The latter has been shown to be dependent on intact aortic chemoreceptors. With respect to peripheral vascular responses, the rise in coronary and cerebral blood flows which occur following hemodilution is proportionally greater than the increase in cardiac output while the opposite is true for kidney, liver, spleen, and intestine. Skeletal muscle does not contribute to a redistribution of blood flow to more vital areas during acute anemia despite its relatively large anaerobic capacity. Overall, peripheral compensatory adjustments result in an increased oxygen extraction ratio during acute anemia which reflects a better matching of the limited oxygen supply to tissue oxygen demands. However, some areas such as muscle are relatively overperfused which limits an even more efficient utilization of the reduced oxygen supply. Studies of the response of the microcirculation and the extent to which sympathetic vascular controls are involved in peripheral blood flow regulation are necessary to further appreciate the complex pattern of physiological responses which help ensure survival of the organism during acute anemia.
Activity of in situ stellate ganglion neurons of dogs recorded extracellularly
Authors: Armour J. A.
Published: April 2011

Activity was recorded from 145 neurons in the in situ stellate ganglia of 36 dogs. The activity of 28 of these neurons, most of them located in the ganglia's cranial medial region, was related to the cardiac cycle primarily during systole. The activity of 16 of these cardiovascular-related neurons was modified by gentle mechanical distortion of the superior vena cava (1), heart (4), or thoracic aorta (11). Forty-one of the neurons were modified by respiration, with 17 being phase-locked to the respiratory cycle. Other neurons were activated by gentle mechanical distortion of localized regions of the thoracic wall (21% of all neurons), neck (18%), skin of the left foreleg (10%), or the mediastinum adjacent to the stellate ganglion (3%). Acutely decentralizing the stellate ganglion abolished the spontaneous activity of some, but not all, of these neurons including the respiratory or cardiovascular-related neurons. In the intact or acutely decentralized stellate ganglion, few neurons were activated by single short duration (1 – 4 ms) stimuli delivered to nerves attached directly or indirectly to the ganglion; however, most were activated by brief high frequency stimuli delivered in trains of 20–200 ms, or by single stimuli lasting 20–200 ms. As most cardiovascular, respiratory, or neck-related neurons in the stellate ganglion were not activated by single brief stimuli delivered to the cardiopulmonary nerves or vagosympathetic trunks, presumably they did not project their axons into the neck or thoracic organs. Thus, they were considered to be interneurons. It is postulated that interneurons in stellate ganglia can be modified by afferent receptors located in tissues of the neck, lungs, heart, or great thoracic vessels, whether the ganglion is intact or acutely decentralized. In addition, neurons in the stellate ganglion can be modified by mechanoreceptors located in the thoracic wall, abdominal wall, foreleg, or adjacent mediastinum. The majority of these neurons are activated by trains of impulses rather than single short duration impulses.
Attenuation of the responses to repeated cholinergic interventions in the isolated dog atrium
Authors: Furukawa Yasuyuki , Martin Paul
Published: April 2011

In the isolated, blood-perfused canine right atrium, which was pretreated with propranolol, negative chronotropic and inotropic responses were evoked by stimulation of the intramural parasympathetic nerve fibers or by intra-arterial infusion of acetylcholine (ACh). Successive cholinergic interventions were applied; first, a conditioning intervention for 2 min was given, then this was followed by a test intervention for 4 min. The two interventions were separated by a rest period that varied from 15 to 240 s. The cardiac responses to the conditioning parasympathetic nerve stimulation quickly reached maximum levels, and then they "faded" or progressively diminished back toward the control level. The inotropic responses to the conditioning infusion of ACh (1 μg/min) faded slightly but the chronotropic response did not. After the rest period, the test nerve stimulation evoked responses that also gradually faded with time. The maximal amplitude of the responses to the test simuli were less than those to the conditioning stimuli. This reduction in the maximal amplitude of the cardiac responses to the test stimuli was more pronounced with high frequency stimulation (30 Hz) than with low frequency stimulation (5 Hz). The decrement was also more pronounced the shorter the rest period, and it was greater at earlier times after beginning the stimulation. Conversely, the maximal cardiac responses to test infusions of ACh were not appreciably less than the responses to the conditioning infusions. We conclude, therefore, that the diminution of the cardiac responses to the second test stimulation of the parasympathetic nerve fibers was mainly ascribable to a prejunctional rather than to a postjunctional mechanism.
Steroid metabolism by cells from human chorion laeve isolated on Percoll gradients
Authors: Gibb William , Lavoie Jean-Claude
Published: April 2011

Collagenase-dispersed cells from human chorion laeve were examined on Percoll gradients. The 3β-hydroxysteroid dehydrogenase (a trophoblast marker) and steroid sulfatase activities of the cells were measured and a system was developed to isolate enriched preparations of the trophoblast cells. No cells were found to sediment at Percoll concentrations greater than 50%, and using continuous gradients of Percoll there appeared to be cells with different 3β-hydroxy steroid dehydrogenase (3βHSD): steroid sulfatase ratios sedimenting in different regions of the gradient. Cells with a high ratio were found in the denser region of the gradient. Continuous gradients provided inadequate separations of distinct populations of cells, thus to obtain a more reproducible system to isolate cells, discontinuous gradients of Percoll were studied. A discontinuous gradient composed of 5, 20, 40, and 60% Percoll was developed and three bands of cells were found sedimenting at the 20, 40 and 60% interfaces, respectively. The number and appearance of cells at the 20 and 60% interfaces varied from tissue to tissue. In contrast, the cells sedimenting at the 40% interface were less variable, a substantial number was found to be present in every tissue studied, they were similar in appearance to the trophoblast cells and had high 3βHSD:sulfatase ratios.
Role of thyroxine and insulin on the development of the fetal mouse duodenum in organ culture
Authors: Beaulieu Jean-François , Calvert Raymond
Published: April 2011

The role of thyroxine and insulin in the regulation of proliferation and differentiation of the immature duodenal epithelium of the fetal mouse was investigated using an organ culture method with a serum-free medium. Thyroxine (10 nM) stimulates specifically the activity of maltase. Insulin (125 mU/mL) remains without effect on the maturation of all hydrolytic functions studied. Each hormone significantly increases the percentages of brush border enzyme activities liberated in the medium and reduces the amount of glucose released in the medium. In the presence of dexamethasone (76 nM) the effect of thyroxine on maltase activity is still observed. Finally, thyroxine and insulin do not modify the labelling index in the duodenal crypts of the explants in the presence or absence of dexamethasone. These findings indicate that thyroxine and insulin can act directly on the development of the fetal mouse duodenum at the end of gestation. Nevertheless, their implication in prenatal development of the gut functions appears to be of minor importance.