bluuebunny/crossref_metadata_2025 huggingface dataset:
A model system for the study of stimulus - enzyme secretion coupling in rat pancreatic acinar cells
Authors: Guderley Helga , Heisler Seymour
Published: April 2011

A superfusion technique was developed as a model system for the study of stimulus- secretion coupling in collagenase-dispersed rat pancreatic acinar cells. Cells (107) were combined with a slurry of Biogel P-4 beads and the mixture was decanted into a plastic column (1.5 cm × 8.5 cm) and perfused with Krebs-Ringer. Amylase activity was determined in sequentially collected effusate fractions and used to estimate the secretory rate. Carbachol, carbachol plus dibutyryl cyclic AMP, cholecystokinin-pancreozymin, and the ionophore A-23187 all stimulated a rapid increase in the rate of secretion. Cell integrity was unaffected by these stimulants as evidenced microscopically and by the lack of lactate dehydrogenase activity in the effusates. Enzymes secreted in response to secretagogues were collected, concentrated, and isoelectrofocused on polyacrylamide gels. A film detection technique was developed to localize amylase activity. The model system has the following advantages: (1) secreted proteolytic products are removed from the vicinity of cells, thereby preventing direct cellular damage and hydrolysis of peptide agonists; (2) the need to add trypsin inhibitors is eliminated and only a minimal addition of albumin (0.001%) is required, thus allowing the separation and distortion-free analysis of secreted proteins; (3) the perfusion conditions can be changed rapidly without disturbing the cells. The model described is therefore well suited to the study of both molecular and kinetic events involved in the enzyme secretory phenomenon in exocrine pancreas.
Utilization of administered folacin derivatives by rats fed a diet low in methionine and folacin
Authors: Farnworth E. R. , Hill D. C.
Published: April 2011

Rats fed a basal diet low in folacin and methionine or the basal supplemented with 1.5% methionine were injected with either tetrahydrofolic acid, 5-methyltetrahydrofolic acid, 5-formyltetrahydrofolic acid, or folic acid. The level of formiminoglutamic acid (FIGLU) excretion was used as an indicator of the animal's metabolically available folacin. Rats fed the basal diet had no decline in FIGLU excretion after dosing. The methionine-supplemented group had significant decreases in FIGLU excretion after dosing with the folacin derivatives. When rats eating the basal diet were dosed with methionine or homocysteine, FIGLU excretions were again decreased.
Effects of Intraluminal sulfate on electrolyte transfers along the perfused rat nephron
Authors: Quamme Gary A.
Published: April 2011

Superficial nephrons were perfused in vivo to determine the effect of intraluminal sulfate (1–20 mM) on electrolyte reabsorption in the rat with special reference to calcium and magnesium transport. This technique allowed us the opportunity of investigating separate electrolyte transfers without alteration of extrarenal influences. The major amount of perfused sulfate was absorbed in the proximal tubule with little absorption distal to the late proximal collection site. Phosphate transport was not affected by high luminal sulfate concentrations indicating distinct reabsorptive mechanisms for these two anions. Intraluminal sulfate significantly inhibited calcium and magnesium reabsorption in the proximal tubule, loop of Henle, and superficial distal tubule, in distinction to modest effects on sodium transport in these nephron segments. Chloride transport was not altered. The inhibition of divalent cation transfer was not quantitively similar in the different tubule segments. Small amounts of sulfate completely inhibited proximal calcium and magnesium reabsorption with little effect on transport within the loop of Henle. Enhanced distal delivery of sulfate significantly inhibited calcium and magnesium reabsorption in the distal tubule, a site where the sulfate anion is not reabsorbed. These results demonstrate the importance of distal delivery of anionic ligands capable of forming nonreabsorbable complexes. Thus distal calcium and magnesium transport may be greatly modified by proximal control of anion reabsorption.
Initiation of migrating myoelectric complexes in human subjects: role of duodenal acidification and plasma motilin
Authors: Daniel E. E. , Fox J. E. T. , Collins S. M. , Lewis T. D. , Meghji M. , Track N. S.
Published: April 2011

The hypothesis that acid, emptied intermittently from the stomach during fasting, might initiate the duodenal phase of the migrating motor complex was tested in normal human subjects, in addition, the relationship between plasma motilin concentrations and the initiation of migrating motor complexes was examined. Migrating complexes occurred spontaneously in the absence of acid in the duodenal bulb and in the presence of duodenal bulb neutralization with sodium bicarbonate. Thus duodenal bulb acidification is not necessary for initiation of the duodenal phase of the migrating motor complexes. Further-more, cyclical increases in plasma motilin concentrations were not closely correlated with the initiation of the gastric phase of maximal activity of the migrating motor complexes. However, motilin concentrations were decreased significantly following onset of the duodenal phase III. We conclude that neither duodenal acidification nor increases in motilin concentration are necessary to initiate migrating motor complexes in man.
Circulatory effects of acute or chronic endotoxemia in rats
Authors: Keeler R. , Barrientos Anamaria , Lee K.
Published: April 2011

A study was made of the effects of acute (4 h) or chronic (4 days) infusion of Escherichia coli endotoxin on cardiovascular function in rats. Rats with acute endotoxemia had a reduced cardiac output but maintained their arterial blood pressure. Fractional distribution of the cardiac output was increased to the liver and reduced to the gastrointestinal tract and skin. No changes in fractional distribution to the kidneys, lungs, or heart were observed although absolute blood flow to these areas was reduced.Rats with chronic endotoxemia had a reduced cardiac output and hypotension with no change in peripheral resistance. Other changes resembled those seen in acute endotoxemia apart from a low renal fraction of the cardiac output. Calculation and interpretation of blood flow changes in these animals was difficult because of a large fall in hematocrit and changes in organ weight.
Renal transport of phosphate: role of alkaline phosphatase
Authors: PetitClerc Claude , Plante Gérard E.
Published: April 2011

A new aspect in the study of mechanisms involved in the renal transport of phosphate, the role of alkaline phosphatase (ALP), was introduced by this laboratory in 1977. The present experiments were designed to examine the effects of levamisole, a known inhibitor of ALP, first on in vitro phosphotransferase activity of rat brush border ALP and second on in vivo transport of phosphate and other ionic species, using both clearance and micropuncture techniques.The results indicate that levamisole inhibits in vitro ALP of brush borders obtained from kidney cortex of dogs and rats by reducing the turnover of orthophosphate on the enzyme. When administered in vivo this drug inhibits the net reabsorption of phosphate in these two different mammalian species. Tubular reabsorption of phosphate falls from 87.0 ± 2.9 to 72.1 ± 3.5% when levamisole is administered in the dog femoral vein (25 mM) and from 85.1 ± 3.4 to 71.3 ± 3.2% when levamisole is infused in the dog renal artery (2.5 mM). In the intact rat this parameter falls from 96.7 ± 1.4 to 46.8 ± 9.8% during levamisole and it also decreases from 98.9 ± 0.8 to 67.4 ± 6.7% in the thyroparathyroidectomized animal. The effect of levamisole on the net tubular transport of phosphate is closely related (r = 0.967) to the amount of the drug reaching the tubular lumen from glomerular filtration: that fraction of administered levamisole which first reaches the early segments of the proximal tubule, where the bulk of filtered phosphate is normally reabsorbed.The effect of levamisole appears to be specific for phosphate as no change in the net transport of other ionic species could be documented in the dog experiments. Levamisole produces a significant decrement in renal plasma flow. The mechanism of this effect is not yet determined but certainly created a situation leading to underestimation of the levamisole effect on the net tubular transport of phosphate.Microinjections of 32P either diluted in isotonic saline or administered with flavone phosphate (0.2 mM), a substrate of ALP, were performed in early segments of superficial proximal tubules of the rat. Urinary 32 P recovery averaged 14 ± 4% and 34 ± 8% following saline and flavone phosphate, respectively.The effect of levamisole does not appear to be mediated by changes in parathyroid hormone secretion or other extrarenal humoral substances as a depression of phosphate reabsorption is seen when the drug is administered in the renal artery. The rapid and reversible effect of flavone phosphate suggests that this compound specifically interacts with ALP of brush border membranes.
Different actions of calcium channel blocking agents on resting membrane conductance in developing skeletal muscle
Authors: Thomson C. M. , Dryden W. F.
Published: April 2011

The effects of Co2+, Mn2+, and La3+ (2 mM) and verapamil (5 × 10−6 M) on membrane conductance (Gm) and resting potential (Em) were studied in chick skeletal muscle fibres developing in culture. Cobalt and manganese had no effect on Gm at any time during myogenesis but verapamil caused a decrease in Gm in immature myotubes. This effect diminished with time and was absent by 3 days after myoblast fusion. Lanthanum caused an increase in Gm at all stages of development. All the agents studied caused a significant depolarization of Em. It is concluded that there is no resting calcium conductance in developing skeletal muscle but that there may be a resting sodium conductance which declines with maturation. Lanthanum may increase Gm by displacing membrane-bound calcium and destabilizing membrane structure. All the agents studied were thought to induce depolarization by an inhibitory action on (Na+ + K+)-ATPase.
Influence of temperature and external Ca2+ concentration upon dantrolene action on excitation–contraction coupling in frog skeletal muscle
Authors: Oba Toshiharu
Published: April 2011

Effects of dantrolene (DAN) on electrical and mechanical responses in frog skeletal muscle were studied at various Ca2+ concentrations and temperatures to elucidate the mechanism of action of DAN. The following results were obtained. (a) Twitch tension of a DAN-injected fiber, elicited by intracellular stimulation, increased transiently and then decreased whereas extracellular DAN always depressed the tension. (b) Lowering the external Ca2+ concentration resulted in the potentiation of twitch tension. The addition of DAN, however, reduced the tension significantly (p < 0.05). (c) Extracellular DAN caused a transient reduction and subsequent elevation of the threshold current; however intracellular DAN caused only elevation of threshold. (d) DAN prevented the slow depolarization of the membrane in low Ca2+ medium. (e) These effects of the drug were temperature dependent, the effect being more pronounced at higher temperatures. These findings suggest that DAN may manifest its effects by replacement of Ca2+ from its binding sites on the membrane and that this occupation of the Ca2+ sites by DAN is temperature dependent.
Ionic composition (Na+, K+, Ca2+, and Mg2+) of cerebrospinal fluid and feeding behavior in sheep
Authors: Seoane J. R.
Published: April 2011

Concentrations of Na+, K+, Ca2+, and Mg2+ were measured in the cerebrospinal fluid from the lateral ventricles of hungry and satiated sheep. The concentrations of those ions and the ratios between them varied little before and after a meal. Concentrations were, in milliequivalents per litre: Na+, 156.6 ± 1.5; K+, 2.94 ± 0.02; Ca2+, 2.37 ± 0.04; and Mg2+, 2.18 ± 0.03.
Aminopyrine metabolism in cryopreserved isolated rat hepatocytes
Authors: Inaba T. , Makowka L. , Rotstein L. , Mahon W. A. , Falk R. E. , Falk J. E. , Phillips M. J.
Published: April 2011

The method to preserve isolated rat hepatocytes under cryogenic conditions (−70 °C) is described. Aminopyrine N-demethylase activity in the frozen–thawed cells was 10–50% that of freshly prepared hepatocytes and was dependent on the storage time.
Liberation of cyclic AMP and catecholamine from the heart during left stellate stimulation in the anesthetized dog
Authors: Lavallée M. , Laurencin C. , Champlain J. de , Nadeau R. A.
Published: April 2011

In open-chest pentothal–chloralose anesthetized dogs, plasma catecholamine and cyclic AMP levels were evaluated in the aortic and coronary sinus blood, during stimulations of the left ansa subclavia (1, 2, and 4 Hz). Basal aortic and coronary sinus catecholamine levels were respectively 0.373 ± 0.090 and 0.259 ± 0.048 ng/mL and cyclic AMP levels averaged 21.4 ± 1.4 and 20.9 ± 1.6 pmol/mL. Statistically significant increases in cyclic AMP levels were induced by sympathetic stimulations at 1 Hz (2.0 ± 0.6 pmol/mL, 2 Hz (2.5 ± 1.2 pmol/mL) and 4 Hz (6.5 ± 1.5 pmol/mL), concomitantly with elevations of coronary sinus catecholamine levels. Sotalol (5 mg/kg) abolished the increases in coronary sinus cyclic AMP levels induced by 4-Hz stimulations. In five dogs in which the coronary sinus blood flow was evaluated, the stimulation-induced increases in coronary sinus cyclic AMP output averaged 282 ± 30 pmol/min (1 Hz), 662 ± 160 pmol/min (2 Hz), and 1679 ± 242 pmol/min (4 Hz). Sympathetically induced cyclic AMP output (4 Hz) was blunted by sotalol (−81 ± 14 pmol/min). Aortic cyclic AMP levels were not significantly influenced by stellate stimulation. Intense correlations were found between increases in coronary sinus plasma catecholamines and cyclic AMP concentration levels (r = 0.81, slope = 1.45, ordinate = −1.42, n = 15) as well as between Δ cyclic AMP output versus Δ catecholamine output values in the coronary sinus (r = 0.93, slope = 2.82, ordinate = 216, n = 15). Δ Max dP/dt and Δ coronary sinus blood flow were also intensely related to Δ cyclic AMP output levels. Intracoronary infusion of phenylephrine (10 μg/min) or nitroprusside (200 μg/min) had no influence on cyclic AMP plasma levels whereas aortic and coronary sinus levels were respectively increased by 5.5 ± 1.9 and 7.3 ± 1.4 pmol/mL during the administration of isoproterenol (5 μg/min). These data suggested that plasma cyclic AMP constitutes a sensitive index of cardiac β-adrenergic activity elicited by the release of endogenous catecholamine during stellate stimulations.
Inactivation of substance P and its C-terminal fragments in rat plasma and its inhibition by Captopril
Authors: Couture R. , Regoli D.
Published: April 2011

The metabolic degradation of substance P(SP), some of its C-terminal fragments, and some analogues by rat plasma has been evaluated from the disappearance of the biological activities of these peptides on the guinea pig isolated ileum. The experiments were performed by dissolving each peptide in saline and by adding 20% (v/v) of rat plasma for incubation at 37 °C for various periods of time.It was found that SP and octapeptide 4–11 are inactivated quite rapidly and at approximately the same rate whereas SP-free acid, heptapeptide 5–11, hexapeptide 6–11, and [D-Trp8]-SP are inactivated more slowly. The replacement of Phe7 by D-Trp does not protect the undecapeptide SP from inactivation.The degradation of SP and of all the C-terminal fragments was completely blocked by Captopril at a concentration of 10 μg/mL of plasma. Under these conditions, Captopril also slightly reduced the rate of inactivation of bradykinin and of SP-free acid.These results were interpreted as indicative of the presence in rat plasma of an endopeptidase that hydrolyses a peptide bond in the C-terminal pentapeptide sequence of SP. This endopeptidase is completely inactivated by Captopril, which thus appears to be not as specific for the angiotensin-converting enzyme as it was thought to be.
Comment: On functions of the "cerebellar circuit" in movement control
Authors: Brooks V. B.
Published: April 2011

Unsolved problems are raised about the roles of the ventrolateral nucleus of the thalamus in relation to those of the "cerebellar circuit" in movement control. The circuit consists of the cerebellum and the parts of the brain to which it is connected.
Diuretic and cardiovascular effects of furosemide in rats
Authors: Leenen Frans H. H.
Published: April 2011

Dose–response relationships of furiosmide to its duretic and cardiovascular actions and its effects on plasma renin activity (PRA) were evaluated in unanesthetized rats. A dose of 1 mg∙kg−1 i.v. induced a small diuretic effect with no change in PRA. Furosemide at 5 mg∙kg−1 provoked a clear diuretic effect (about 75% of the maximal effect) accompanied by a 20–25% plasma volume deficit but by only a twofold rise in PRA. Higher doses (10 and 40 mg∙kg−1) induced a somewhat larger diuresis without further increases in plasma volume deficit or in PRA. Compared with the marked diuretic effect and plasma volume deficit, water intake increased only slightly (2 mL compared with a diuresis of 10 mL). Furosemide did not induce significant changes in blood pressure and heart rate, but it did alter the renin dependency of the blood pressure as assessed by Saralasin.These results indicate that furosemide has a steep dose–response curve for its effects on plasma volume and PRA; the relation is somewhat less steep for the diuretic action. Considering the large diuresis and plasma volume deficit, the changes in PRA and water intake induced by furosemide appear inappropriately small and suggest an inhibitory effect of furosemide on these parameters.
A comparison of antigen-induced and calcium ionophore A23187 induced contraction of isolated guinea pig trachea
Authors: Burka John F. , Paterson Nigel A. M.
Published: April 2011

Ovalbumin (OA) and the calcium ionophore A23187 induced a dose-dependent contraction of guinea pig tracheal strips. The OA-induced contraction (of sensitized trachea) consisted of an initial peak contraction, maximal between 5 and 10 min, followed by a very gradual decline from the peak. On the other hand, A23187 induced a sustained contraction of the trachea with a more gradual onset. Both antigen- and A23187-induced contractions required the presence of extracellular calcium. The response was not reduced by delaying (up to 10 min) the addition of calcium, suggesting that the mechanism of antigen-induced contraction differs from that of antigen-induced histamine secretion from rat mast cells and human basophils. The 1st min of the OA-induced contraction was inhibited significantly by mepyramine (10−5 M) suggesting that histamine contributed to the contraction at this time point. In contrast, A23187-induced contraction was unaffected by mepyramine. On the other hand, both the A23187-induced contraction and the prolonged phase of the OA-induced contraction were enhanced by indomethacin, a cyclooxygenase inhibitor, and inhibited by phenidone, a cyclooxygenase–lipoxygenase inhibitor. This suggests that a product of the lipoxygenase pathway of arachidonic acid metabolism contributes to OA- and A23187-induced contraction of the guinea pig trachea.
The influence of altered thyroid hormone levels on guinea pig cardiac adrenoceptors and histamine receptors
Authors: MacLeod K. M. , McNeill J. H.
Published: April 2011

Responses to adrenoceptor and histamine H2 receptor agonists were tested in cardiac preparations from hypothyroid and hyperthyroid guinea pigs. The inotropic and chronotropic potencies of the β-adrenoceptor agonist isoproterenol were significantly enhanced in right atria, left atria, and papillary muscles from hyperthyroid animals, and were significantly reduced in these preparations from hypothyroid animals, compared with their respective euthyroid controls. However, the log dose-ratio for propranolol antagonism of the isoproterenol response was not significantly different from the control in any of these preparations from hypo- or hyper-thyroid animals. No α-adrenoceptor mediated chronotropic response could be detected in right atria from animals in any thyroid state. The α-agonist methoxamine produced a small positive inotropic response in euthyroid left atria but not in papillary muscles. The maximum response to methoxamine was diminished in hypothyroid left atria and enhanced in hyperthyroid left atria, as was the maximum response to phenylephrine in the presence of propranolol. The potency of methoxamine was unchanged or slightly reduced in hypothyroid left atria, while the potencies of both methoxamine and phenylephrine, as well as the log dose-ratio for phentolamine antagonism of the phenylephrine response, were significantly reduced in hyperthyroid left atria.Neither the potency nor the maximum response to the specific H2 agonist 4-methylhistamine was significantly different from control in hypothyroid or hyperthyroid right atria or in hyperthyroid papillary muscles. Both the maximum response and the potency of this agonist were significantly reduced in hypothyroid papillary muscles.These results demonstrate that responses to adrenoceptor, but not histamine H2 receptor agonists can be specifically altered in guinea pig myocardium by changes in thyroid state. The results cannot be explained by the adrenoceptor interconversion hypothesis, although the mechanism responsible for these changes is not apparent at present.
Steady state glucose kinetics and their relation to plasma glucose concentration in the premature and full term neonatal piglet
Authors: Flecknell P. A. , Wootton R. , John Muriel , Royston J. P.
Published: April 2011

Steady state glucose kinetics were measured in 19 premature and 16 full-term piglets. Bodyweight, plasma glucose concentration, total body glucose turnover rate, and glucose pool size were not significantly different between the two groups. This suggests that the premature piglet is capable of maintaining glucose homeostasis during the first 24 h of life. Although there appeared to be a correlation between glucose turnover and plasma glucose concentration, analysis of covariance showed that it was spurious, suggesting that glucose utilization proceeds independently of the glucose concentration in plasma.Glucose turnover rate in the premature piglet is closely comparable with that reported in the premature human infant. These findings encourage the use of the neonatal piglet as an animal model for the study of the problems of the neonatal human.
Dibutyryl cyclic GMP, a competitive inhibitor of cholecystokinin/pancreozymin and related peptides in the gallbladder and ileum
Authors: Davison J. S. , Najafi-Farashah A.
Published: April 2011

Dibutyryl cyclic GMP (dbcGMP), a known selective inhibitor of the effects of cholecystokinin/pancreozymin (CCK/Pz) in the pancreas, shows a similar selective antagonism of the motor-stimulating actions of CCK/Pz in guinea pig gallbladder and ileum. The inhibition is reversible and competitive. Hence, dbcGMP could be used to identify physiological mechanisms which utilize CCK/Pz. Since dbcGMP abolished the peristaltic reflex it is suggested that CCK/Pz may be utilized as a transmitter in the nerve pathways of the reflex.
Effect of disopyramide and disobutamide on conduction in perfused rabbit hearts
Authors: Dresel Peter E. , Cameron Keith D.
Published: April 2011

The effects of disopyramide (DP) and a new antiarrhythmic agent, disobutamide (DB) on cardiac conduction were studied using His bundle recording from modified rabbit Langendorff preparations electrically driven at 3 and 4 Hz. Both disopyramide (4–16 μg/mL) and disobutamide (1–30 μg/ml) slowed conduction throughout the atrioventricular conduction system, i.e., SA, AH, and HV intervals were increased in a dose-related manner. Conversion of the conduction time changes to percent changes indicates that disobutamide has a relatively equal effect on each part of the system whereas disopyramide exhibited significantly less effect on AV nodal conduction. Slowing of conduction in the AV node by DP was clearly related to rate. Changes in SA and HV intervals were rate related to a lesser degree. No such rate-related effect was evident with disobutamide. Block of atrial conduction occurred in two out of six hearts when the rate was increased at 8 μg/mL of DP and in three additional hearts at 16 μg/mL. This was interpreted to indicate a change in atrial excitability such that 2 × threshold currents no longer excited the tissues. This was not observed at any concentration of DB.
The effects of nucleotides on the response of the isolated guinea pig urinary bladder to nonadrenergic, noncholinergic nerve stimulation
Authors: Lukacsko P. , Krell R. D.
Published: April 2011

The ability of adenosine 5′-triphosphate (ATP) to suppress the contractile response of guinea pig urinary bladder to nonadrenergic, noncholinergic nerve stimulation was investigated. Strips of guinea pig urinary bladder were incubated for 1 h at 37 °C in a modified Krebs solution containing atropine (2 × 10−7 M), guanethidine (1 × 10−6 M), and indomethacin (5.5 × 10−6 M). Four successive administrations of ATP, guanosine 5′-triphosphate (GTP), or cytidine 5′-triphosphate (CTP), each at 5 × 10−4 M, in the absence of washout resulted in complete desensitization of the tissue to the contractile effect of the nucleotide. Strips desensitized to GTP or CTP were also nonresponsive to ATP. The response of the strips to electrical stimulation (100 V, 0.1-ms pulse, 5-s train at 3 Hz) was markedly reduced following desensitization with ATP but only slightly with GTP or CTP. Under similar conditions, adenosine 5′-monophosphate (AMP) or diphosphate (ADP) or adenosine (A) also reduced the response of the strips to intramural nerve stimulation, but guanosine.5′-monophosphate (GMP) or diphosphate (GDP), guanosine (G), cytidine 5′-monophosphate (CMP) or diphosphate (CDP), or cytidine (C) did not. The present data suggest that desensitization of smooth muscle to exogenous ATP may be predominantly the result of its conversion to metabolic products rather than inactivation of "purinergic" receptors per se.
Metabolism of [3H]noradrenaline by the isolated rat uterus
Authors: Fernández-Pardal Julio , Gimeno Martha F. , Gimeno Alvaro L.
Published: April 2011

The metabolism of [3H]noradrenaline by uterine horns from estrous, ovariectomized, and ovariectomized and estrogen-treated rats was explored. Uterine strips are able to take up [3H]noradrenaline and store it for up to 85 min after the isotope incubation. The major compounds retained in the tissue from rats either ovariectomized or during estrus were [3H]noradrenaline and 3H-labelled O-methylated deaminate metabolites. The [3H]3,4-dihydroxyphenylglycol ([3H]DOPEG) and 3,4-dihydroxymandelic acid ([3H]DOMA) fractions were higher in tissues from ovariectomized rats than during estrus. Ovariectomy also increased significantly the spontaneous efflux of [3H]DOPEG and [3H]DOMA. The metabolic pattern of [3H]noradrenaline both in the tissue and in the efflux from ovariectomized rats was changed by estrogen treatment and became similar to those obtained during estrus. These data suggest a possible modulation of the noradrenaline metabolism by estrogens on the isolated rat uterus.
Positive inotropic responses in cardiac muscles: influence of stimulation frequency and species
Authors: Siegl Peter K. S. , McNeill John H.
Published: April 2011

Inotropic responses to cumulative additions of methoxaminc (10−7 to 3 × 10−4 M), isoproterenol (10−9 to 10−5 M), or calcium (2 to 32 mM) were measured in isolated rat left atria and papillary muscles and rabbit right ventricular papillary muscles at three stimulation frequencies. Cardiac muscles were incubated in oxygenated Chenoweth–Koelle solution (2 mM calcium) at 37 °C. The basal developed force (BDF) before and maximum developed force (MDF) after challenge with methoxamine and isoproterenol were inversely related to stimulation frequency in rat preparations. BDF was directly related to stimulation rate in rabbit papillary muscles while MDF was independent of the rate. Drug-induced increases in force (MDF – BDF) were independent of stimulation frequency in rat and inversely related to stimulation frequency in rabbit. Responses to calcium were similar to the observed adrenergic responses. Also, force–frequency relationships of the rat and rabbit preparations were not similar in the absence and presence of these agonists. These data show that inotropic responses by rat and rabbit hearts are not affected similarly by stimulation frequency and this may reflect a species difference in the utilization of extracellular calcium for contraction.
Peripheral nerve autografts increase soleos muscle hydrolase activity
Authors: Boegman Roland J. , Scarth Brenda
Published: April 2011

A peripheral nerve autograft placed on the surface of a normally innervated muscle has been shown to induce acetylcholine hypersensitivity and myofibrillar degeneration. Using a similar preparation, we determined the acid protease, alkaline protease, and N-acetylglucosaminidase activity in rat soleus muscle and the effect of protease inhibitors on these enzymes. Three days after nerve transplant, the muscle showed a significant increase in all three enzymes assayed. The protease inhibitors leupeptin and pepstatin totally prevented the nerve-induced increase in hydrolase activity. Our data suggest that muscle degeneration is secondary to an inflammatory response induced by the nerve.
Response of adrenal 3β-hydroxy-Δ5-steroid dehydrogenase to adrenocorticotropin treatment in thiouracil-fed male mice
Authors: Meserve Lee A. , Ting Shu-Mei
Published: April 2011

A number of parallels can be drawn between the reported endocrine status of thiouracil-fed young rodents and that of aged animals, particularly with regard to the hypothalamus–pituitary–adrenal axis. Since the activity of the adrenal steroidogenic enzyme 3β-hydroxy-Δ5-steroid dehydrogenase (3β-HSD) has been shown to be depressed in aged rats and mice, the present study was done to determine whether exposure of young mice to thiouracil had a similar effect on adrenal 3β-HSD activity. Feeding the goitrogen thiouracil at 0.25% (w/w) of the maternal diet from conception, and keeping it 0.25% of the offsprings diet after weaning, significantly elevated activity of 3β-HSD per gram of adrenal gland above control levels in 4-month-old mice, perhaps to compensate for depressed adrenal mass. Daily subcutaneous injections of physiological saline (0.9%) for 4 days was sufficient to increase 3β-HSD activity per gram of adrenal tissue in euthyroid (P < 0.05) but not in thiouracil-fed mice. Subcutaneous administration of ACTH (2 IU daily for 4 days) significantly increased adrenal 3β-HSD activity to comparable levels in thiouracil-fed and euthyroid animals. Thus, thiouracil enhances the activity of 3β-HSD per gram of adrenal tissue and does not prevent response of enzyme activity to exogenous ACTH.
Effect of β-adrenergic blockers on the sickling phenomenon
Authors: Ohnishi S. Tsuyoshi , Hashimoto Koji , Sato Takashi , Devlin Mark T. , Singer Mark
Published: April 2011

Dichloroisoproterenol (DCI) and propranolol were found to inhibit sickling in vitro when they were added to red-cell suspensions prior to deoxygenation. The effectiveness was maximal between [Formula: see text]'s of 30 and 40 mmHg (1 mmHg = 133.322 Pa). When cells were sickled at a low oxygen tension [Formula: see text], and then DCI was added later, the drug decreased the degree of sickling while the suspension was maintained at the same oxygen tension. The antisickling effect of these drugs was not antagonized by isoproterenol, a β-adrenergic stimulator, by the addition of cAMP or increase of the intracellular calcium concentration. Other β-blockers, such as MJ1999 (sotalol) and timolol, did not show antisickling activity. It was also found that DCI, propranolol, and timolol had some effect on the delay time of gelation of sickle-cell hemoglobin (Hb S), as well as on the oxygen affinity of sickle cells.
Roles of extracellular and "trigger" calcium ions in excitation–contraction coupling in skeletal muscle
Authors: Frank George B.
Published: April 2011

The experimental observations leading to the development of the "trigger" calcium hypothesis of excitation–contraction (E–C) coupling in skeletal muscle are discussed. Also considered in some detail are the experimental technique problems which interfere with the demonstration of this role for calcium. New findings reported are observations showing that in a zero Ca2+ solution after a delay of about 6–10 min, there is a stimulation of Ca2+ efflux. This is of sufficient size, even in very small toe muscles, to restore the twitch which previously had been reduced in size in the zero Ca2+. In studies with isolated fibre preparations it was demonstrated that depolarization contractures required extracellular Ca2+ ions for E–C coupling whereas twitches could use membrane-bound "trigger" calcium ions. Thus in zero Ca2+ the contractures were eliminated in a few seconds but twitch elimination took a few minutes. Finally, the roles in E–C coupling played by "trigger" and extracellular Ca2+ ions are summarized and discussed.
External calcium and contractile activation during potassium contractures in twitch muscle fibres of the frog
Authors: Cota G. , Stefani E.
Published: April 2011

Effects of external Ca2+ concentration reduction on the amplitude and time course of K+ contractures were studied in single muscle fibres. The resting potential, effective resistance, threshold for the Na current, action potential and K+-induced depolarizations did not change when 1.8 mM Ca2+ was replaced by 3 mM Mg2+ (3–6 μM Ca2+). Identical results were obtained after the addition of 5 mM EGTA (≤ 10−9 M Ca2+; Ca-free saline). The rate of tension development during the initial phase of K+ contractures was independent of external Ca2+ while the amplitude, the duration, and the time constant of spontaneous relaxation decreased progressively as Ca2+ concentration was diminished. The activation curve shifted by 3–5 mV towards more positive potentials while the inactivation curve shifted by 16–18 mV in the opposite direction and both curves became steeper in Ca-free saline. External Ca2+ may play a role in excitation–contraction coupling during K contractures either via the inward Ca current or via specific interactions between external Ca2+ ions and the coupling mechanism or both.
Fluorescence and differential light absorption recordings with calcium probes and potential-sensitive dyes in skinned cardiac cells
Authors: Fabiato Alexandre
Published: April 2011

This report describes an optical system for microspectrophotometry in a single cardiac cell from which the sarcolemma has been removed by microdissection (skinned cardiac cell). This system is attached to the high power inverted microscope used for the microdissection and includes (a) a single variable wavelength microspectrophotometer used to define the spectrum of a given dye or Ca2+ probe; and (b) a dual wavelength, differential microspectrophotometer used to record differentially between the optimum wavelength and a wavelength separated by 25–30 nm. Results are presented using the following optical methods: (a) fluorescence measurements with chlorotetracycline to monitor the amount of Ca2+ bound to the inner face of the sarcoplasmic reticulum (SR) membrane; (b) differential absorption measurements with arsenazo III to measure changes of myoplasmic [Ca2+]free resulting from Ca2+ release from the SR; (c) fluorescence and (or) differential absorption measurements with the potential-sensitive dyes merocyanine 540, NK 2367, and di-S-C3(5) to monitor changes of charge distribution on the SR membrane during Ca2+ accumulation in the SR, as well as before and during Ca2+-induced release of Ca2+ from the SR. A small and rapid signal is observed which precedes the Ca2+-induced release of Ca2+ from the SR. It is detected as an increase of Ca2+ binding inside the SR with chlorotetracycline and as a "hyperpolarization" with potential-sensitive dyes, while no transient change of myoplasmic [Ca2+]free is detected with arsenazo III. This small and rapid signal preceding the Ca2+ release may be a first hint to an understanding of the mechanism whereby a small increase of [Ca2+]free outside the SR triggers Ca2+ release from the SR.
Effect of adenosine on the cardiac actions of prostaglandins E2, I2, and F2α
Authors: Karmazyn Morris , Dhalla Naranjan S.
Published: April 2011

Previous reports have demonstrated an antagonistic influence of adenosine on the biological effects of prostaglandins (PGs). We examined such a possible relationship on the isolated rat heart perfused at constant pressure and maintained at a constant heart rate. PGE2 and PGF2α (2.8 × 10−11 to 2.8 × 10−7 M) exerted a positive inotropic influence on the heart with PGF2α demonstrating the greater maximum effect. PGI2 had a negative inotropic effect only at high concentrations (2.8 × 10−9 to 2.8 × 10−7 M). The coronary flow was decreased by both PGE2 and PGF2α. The concentrations of PGI2 employed had minimal vasoactive properties (20% increase in flow at 2.9 × 10−7 M). Adenosine at concentrations which increased coronary flow by 24 to 63% (0.1 to 10 μM) had no influence on either the alteration in contractile force produced by PGE2, PGF2α, or PGI2 or on the coronary effects of PGE2, or PGI2. Adenosine did however, attenuate the degree of coronary flow reduction produced by PGF2α administration. These results are suggestive of a selective inhibiting influence of adenosine on the coronary constricting effects of PGF2α in the isolated rat heart.
The effects of substance P and met-enkephalin in dog ileum
Authors: Daniel E. E. , Gonda T. , Domoto T. , Oki M. , Yanaihara N.
Published: April 2011

Substance P initiated tonic contraction of dog ileum when administered in doses from 1 pg to 20 μg intraarterially (ED50 = 67 ng). Low doses acted to excite cholinergic postganglionic neurones since atropine or tetrodotoxin (TTX) increased the ED50 of substance P about 25-fold, while hexamethonium and local field stimulation had only a small effect to increase the ED50. Also atropine and tetrodotoxin effects were not additive. Higher doses apparently acted to stimulate smooth muscle directly, but no evidence was obtained that local field stimulation could release substance P to act on smooth muscle. Substance P tachyphylaxis prevented substance P actions on cholinergic nerves, but it did not affect responses to intraarterial acetylcholine or block distal inhibition from proximal distention or field stimulation. Met-enkephalin given intraarterially, was also excitatory in doses from 1 ng to 20 μg; the amplitude of tonic and phasic contractions produced was significantly decreased by TTX and atropine but was not diminished by hexamethonium or substance P tachyphylaxis. Partial tachyphylaxis to met-enkephalin was produced without affecting the ED50 for substance P. We conclude that substance P acts in small amounts on receptors in myenteric nerves to release acetylcholine by a mechanism, presumably involving postganglionic cholinergic nerves, while met-enkephalin also apparently may act at least in part through a similar TTX- and atropine-sensitive mechanism. These peptides also caused activation of other receptors, probably on smooth muscle by noncholinergic, TTX-insensitive mechanisms. Also the receptors for each peptide which are located on nerves were distinct and independent since tachyphylaxis could be produced to each without affecting the response to the other.not available
Excitability of primary afferents in feline spinal cord: taurine, homotaurine, and γ-aminobutyric acid compared
Authors: Čapek Radan , Esplin Barbara
Published: April 2011

Effects of taurine and homotaurine (3-aminopropancsuIfonic acid), on excitability of primary afferents were compared with effects of γ-aminobutyric acid (GABA) in spinal unanaesthesized cats. Homotaurine and GABA, administered intravenously or topically, produced a marked increase in afferent excitability. Homotaurine was about 10 times more potent than GABA. Taurine (up to 2 mmol/kg i.v., or 10 mM topically) did not produce a consistent change in afferent excitability. The effect of homotaurine was antagonized by bicuculline or picrotoxin in doses which suppressed the primary afferent depolarization, as indicated by an increase of afferent excitability, evoked by conditioning stimulation of an antagonistic muscle nerve. Semicarbazidc, an inhibitor of GABA synthesis, did not attenuate the homotaurine-induced excitability changes of afferents while suppressing entirely the primary afferent depolarization. These findings suggest that homotaurine exerts a direct GABA-like action on feline primary afferents.
The determination of the specific activity of plasma glycerol
Authors: Gauthier Clément , Layberry Ross
Published: April 2011

A method for the determination of the specific activity of plasma glycerol is described. Anionic contaminants are first removed from deproteinized plasma by anionic exchange resins (treated plasma). Glycerol in treated plasma is then quantitatively converted to glycerol-3-phosphate (G3P), which is isolated by column chromatography and counted for 14C radioactivity. The specific activity thus calculated was 100.1 ± 2.9% of a standard of known specific activity. When the specific-activity of glycerol is determined from plasma without prior removal of anionic contaminants (untreated plasma), the calculated specific activity is 1.99 ± 0.15 times higher than the one calculated after their removal. Omission of the removal of contaminants leads to a near 100% error in the calculation of the turnover rate of glycerol.not available
Monodansylcadaverine inhibition of testicular 17-ketosteroid reductase
Authors: Moger William H.
Published: April 2011

Dispersed mouse testicular interstitial cells were treated with the transglutaminase inhibitor monodansylcadaverine (500 μM) for 30 min. Subsequent incubation of the cells with [3H]pregnenolone revealed increased formation of steroidogenic intermediates, tentatively identified as progesterone, 17α-hydroxyprogesterone, and androstenedione, but decreased testosterone formation by monodansylcadaverine-treated cells. Measurement of 17-ketosteroid reductase activity (the enzyme that converts androstenedione to testosterone) demonstrated that monodansylcadaverine treatment caused a reversible, noncompetitive inhibition of this enzyme. These results suggest that transglutaminase catalyzed protein cross-links may influence the activity of 17-ketosteroid reductase.
Atrial natriuretic factor has a direct, prostaglandin-independent action on kidneys
Authors: Keeler R.
Published: April 2011

Intravenous injection of a saline extract of lyophilized rat atrial myocardium into anesthetized rats caused a massive diuresis and natriuresis of short duration. There was also a significant increase in potassium excretion and a fall in urine osmolality. There were no significant changes in solute-free water reabsorption, glomerular filtration rate, renal plasma flow, or filtration fraction as measured by conventional clearance methods. Mean arterial pressure was significantly reduced during the natriuretic response. The natriuretic and diuretic response was not blocked by inhibition of prostaglandin synthesis with aspirin and indomethacin. Infusion of a small amount of atrial extract directly into the left kidney resulted in a natriuretic and diuretic response which was predominantly localized to the left kidney. It is concluded that saline extracts of rat atrial myocardium contain a potent natriuretic substance which acts directly on kidneys by a mechanism which does not depend upon increased synthesis of prostaglandins.
Effect of calcium concentration on isolated hamster brain Na-K-, Mg-dependent ATPase
Authors: Rohani F. , Welty J. D. , Hastings D. F.
Published: April 2011

In these experiments the effect of different concentrations of calcium on the specific activity of isolated Na-K-ATPase was studied. The result of these investigations showed that calcium at 10−6 and 10−7 M stimulated the Na-K-ATPase activity. These studies also show that at higher calcium concentrations (10−5–10−3 M), the activity of the enzyme is inhibited. The results from calcium binding to isolated membranes, rich in Na-K-ATPasc, strongly suggest the existence of a low-affinity binding site which exhibits a large positive cooperativity, Kd = 2.8 × 10−5 ± 0.4 × 10−5 M and Hill coefficient of 2.9 ± 0.2. The calcium concentration (1.9 × 10−5 M sufficient to produce significant (24%) inhibition of the Na-K-ATPase is approximately equal to the Kd observed for calcium binding.
Intrarenal localization of the natriuretic effect of cardiac atrial extract
Authors: Sonnenberg H. , Cupples W. A. , Bold A. J. de , Veress A. T.
Published: April 2011

In anesthetized rats micropuncture and microcatheterization were used to collect tubular fluid from end proximal and distal tubules and from the outer medullary collecting duct. Urine was collected at the papilla tip. Samples were taken from the same sites before and after intravenous injection of atrial tissue extract; rats injected with ventricular extract served as controls. Sodium excretion increased 17-fold after atrial extract, a significantly greater rise than the 3-fold increase after ventricular extract. Clearances of inulin and single nephron filtration rates did not change significantly in either group. Tubular fluid collection results showed a similar reduction (16 to 20%) of proximal fluid and sodium reabsorption in both groups. In the experimental group only, NaCl reabsorption failed to rise in response to increased load in the medullary collecting duct. The resulting fall in fractional reabsorption in the medullary collecting duct accounted for 80% of the natriuresis. We conclude that atrial tissue from rat hearts contains a factor which causes increased renal NaCl excretion by inhibiting transport in the medullary collecting duct.
Effect of chlorothiazide on renal calcium and magnesium handling in the hamster
Authors: Wong Norman L. M. , Quamme Gary A. , Dirks John H.
Published: April 2011

Recollection micropuncture and clearance studies were performed on 21 thyroparathyroidcetomized hamsters to characterize the effect of chlorothiazide on tubular sodium, calcium, and magnesium transport. Acute administration of chlorothiazide resulted in a marked natriuresis while urinary calcium excretion fell and magnesium remained unchanged. The fraction of sodium, calcium, and magnesium remaining at the late proximal tubule increased modestly from 65 ± 4 to 75 ± 3, 68 ± 3 to 75 ± 4, and 78 ± 4 to 85 ± 2%, respectively. Distal tubular fluid to ultrafilterable plasma (TF/UF) sodium concentration rose from 0.24 ± 0.03 to 0.44 ± 0.04 whereas distal TF/UFCa concentration fell from 0.58 ± 0.05 to 0.38 ± 0.06. The fraction of sodium remaining at the distal tubule rose from 4.0 ± 1.4 to 10.0 ± 1.4% while that of calcium decreased from 10.2 ± 1.1 to 7.6 ± 1.2% following administration of chlorothiazide. No change was observed in distal delivery of magnesium. Thus chlorothiazide acted in the distal tubule to decrease sodium reabsorption, enhance calcium transport, and had little effect on distal magnesium reabsorption. These data are consistent with the distal tubular action of chlorothiazide which is independent of parathyroid hormone.