bluuebunny/crossref_metadata_2025 huggingface dataset:
Porphyrinogenic effects in chick embryo liver cell culture of chloramphenicol analogues that are mechanism-based inactivators of cytochrome P-450
Authors: Green-Thompson R. P. , Riddick D. S. , Mackie J. E. , Marks G. S. , Halpert J. R.
Published: April 2011

Structural analogues of chloramphenicol (CAP) cause mechanism-based inactivation of rat liver cytochrome P-450 (P450) either via protein acylation or destruction of the heme prosthetic group. The goal of the present work was to determine whether CAP analogues that cause loss of the P450 heme moiety also cause porphyrin accumulation in chick embryo liver cell culture. The porphyrin profiles produced by exposure of cells to CAP analogues (160 μM) were determined by high-performance liquid chromatography with fluorescence detection. Of three CAP analogues that do not cause loss of the heme moiety of rat liver P450IIB1, two dichloroacetamides were not porphyrinogenic. The third compound, a chlorofluoroacetamide, caused porphyrin accumulation. This result may be due to the presence of P450 isozymes in chick embryo hepatocytes, distinct from rat liver P450IIB1, that are susceptible to destruction by this analogue. Of four CAP analogues that inactivate rat liver P450IIB1 with concomitant heme loss, a dichloroacetamide and two chlorofluoroacetamides caused porphyrin accumulation. The remaining compound, a monochloroacetamide, was not porphyrinogenic, perhaps because the P450 apoprotein cannot be reconstituted with fresh heme drawn from the regulatory "free heme pool" following inactivation by this analogue. Alternatively, there may be no P450 isozyme in chick embryo liver cell culture that is susceptible to inactivation by this compound.Key words: cytochrome P-450, chloramphenicol, chick embryo hepatocyte, mechanism-based inactivation, uroporphyrinogen decarboxylase.
Cocaine-enhanced arrhythmogenesis: neural and nonneural mechanisms
Authors: Gantenberg Nicholas S. , Hageman Gilbert R.
Published: April 2011

Cocaine abuse increases the susceptibility to cardiovascular complications and sudden cardiac death in man. We used programmed electrical stimulation of the heart to examine the arrhythmogenic influence of cocaine. Twenty-three pentobarbital-anesthetized adult dogs underwent programmed electrical stimulation using one to four extrastimuli before and during cocaine infusion. Autonomic decentralization was performed prior to the protocol in eight dogs. Induced ventricular arrhythmias included single premature ventricular depolarizations, doublets, triplets, ventricular tachycardia, and ventricular fibrillation. Intravenous cocaine, and subsequent adrenergic and muscarinic receptor blockade, or calcium channel blockade were evaluated for their influence on arrhythmogenesis. The incidence of induced ventricular arrhythmias was significantly elevated following cocaine and was reduced following propranolol and atropine. Verapamil, however, did not reduce the incidence of induced arrhythmias. In addition, cocaine significantly increased arrhythmia induction in decentralized animals, but propranolol, atropine, and phentolamine failed to reduce the proarrhythmic effects of cocaine in these animals. Thus, cocaine has a proarrhythmic effect on the heart with multiple mechanisms. The adrenergic mechanism appears to be a result of neurotransmitter uptake blockade, whereas the likely ionic mechanism is a neurally independent, direct effect on the heart.Key words: cocaine, programmed electrical stimulation, ventricular arrhythmias, sympathetic nervous system, sudden cardiac death.
Conopressin G, a molluscan vasopressin-like peptide, alters gill behaviors in Aplysia
Authors: Martínez-Padrón Manuel , Gray William R. , Lukowiak Ken
Published: April 2011

Superfusion of an invertebrate vasopressin structural analogue, conopressin G, over the abdominal ganglion of an in vitro preparation of Aplysia californica has significant neurophysiological and behavioral effects. Both the amplitude of the siphon-evoked gill withdrawal reflex and concomitant activity in gill motor neurons are reduced in the presence of conopressin G. Moreover, the frequency of spontaneous gill movements and their neural correlate, interneuron II activity, are increased. These behavioral modifications strongly resemble those that occur during the food-aroused behavioral state in intact Aplysia. In addition, conopressin G superfusion reduces both the excitability of gill motor neurons and the strength of gill contractions in response to gill motor neuron discharges elicited by direct depolarizing current. A role for conopressin G or a similar peptide in the modulation of gill behaviors associated with the food-aroused state is suggested.Key words: Aplysia californica, conopressin G, gill withdrawal reflex, spontaneous gill movements.
Rat atrial muscle responses with caffeine: dose–response, force frequency, and postrest contractions
Authors: MacIntosh Brian R. , Posner Philip , Lobo John , Harms Randy
Published: April 2011

Caffeine has been reported to have a positive and (or) a negative inotropic effect on cardiac muscle. In this study, the force-frequency and postrest characteristics of rat atrium were studied in the presence of caffeine (1.0–10 mM) to see if the interval between beats affected the response of cardiac muscle to caffeine. When stimulation frequency was 0.5 or 2.0 Hz, there was a positive followed by a negative inotropic response with 1, 5, or 10 mM caffeine. Incomplete relaxation occurred under these circumstances, giving rise to contracture. At low frequency of stimulation (0.1 Hz) caffeine had only a negative inotropic effect, and this effect was greater with 1 mM caffeine than with 5 mM caffeine. In the absence of caffeine, when stimulation at 0.5 or 3 Hz was interrupted, a pause of 2–20 s resulted in potentiation. When caffeine was present (2.0 mM), postrest potentiation was severely attenuated, but the steady-state contraction amplitude within the range 0.5–3.0 Hz was not different. These results are consistent with the hypothesis that caffeine induces a leak of Ca2+ from the sarcoplasmic reticulum, and this Ca2+ is extruded from the cell, possibly by Na+/Ca2+ exchange. Sarcoplasmic reticular uptake of Ca2+ and the translocation to release sites appear not to be affected by caffeine within 1–5 mM concentrations.Key words: contractility, excitation–contraction coupling, contraction, cardiac, rest potentiation.
Arcaine and magnesium inhibition of the NMDA receptor ionophore complex: Evidence for distinct voltage-dependent sites
Authors: Wang Jia , Johnson Kenneth M.
Published: April 2011

The inhibitory effects of the polyamine antagonist, arcaine, and magnesium on N-methyl-D-aspartate (NMDA) induced hippocampal [3H]norepinephrine release and [piperidyl-3,4-3H(N)]-[N-1-(2-thienyl)cyclohexyl]-3,4-piperidine (TCP) binding were studied. We report that the inhibitory effect of arcaine and magnesium on NMDA-induced [3H]norepinephrine release is diminished by increasing the extracellular K+ concentration, presumably reflecting a voltage-dependent block for both. However, unlike MK-801, the block by arcaine shows no evidence of use dependence. Further, the IC50 value for magnesium inhibition of [piperidyl-3,4-3H(N)]TCP binding varies with the state of activation of the channel, being the lowest when the channel is maximally activated and the highest when the channel is least activated. On the other hand, the apparent affinity of arcaine is not significantly affected by the activation of the channel by glutamate and glycine, but is decreased by the polyamine agonist, spermidine. These data suggest that the polyamine antagonist binding site is distinct from either the phencyclidine/MK-801 site or the voltage-dependent channel site for magnesium. Nonetheless, these data suggest that the site must be located in a region of the NMDA receptor ionophore complex capable of sensing transmembrane potential.Key words: N-methyl-D-aspartate (NMDA) receptor, polyamines, arcaine, phencyclidine, spermidine.
Excitability of canine colon circular muscle disconnected from the network of interstitial cells of Cajal
Authors: Liu Louis W. C. , Daniel Edwin E. , Huizinga Jan D.
Published: April 2011

The 6 cpm omnipresent slow waves recorded in the circular muscle (CM) layer of canine colon are generated at the submucosal surface of the CM layer. After removal of the submucosal network of interstitial cells of Cajal (ICC), 66% of the CM preparations (25 of 38) were quiescent in Krebs solution. In the presence of carbachol, seven of nine of these spontaneously quiescent CM preparations demonstrated slow wave-like activity with mean frequency, duration and amplitude of 5.9 ± 0.4 cpm, 2.8 ± 0.5 s, and 0.8 ± 0.2 mV, respectively. Similar slow wave-like activities were induced by TEA (seven out of eight quiescent CM preparations) with frequency, duration and amplitude of 6.1 ± 0.2 cpm, 2.7 ± 0.5 s, and 1.0 ± 0.2 mV, respectively, and by BaCl2 (eight of eight quiescent CM preparations) with frequency, duration, and amplitude of 6.3 ± 0.3 cpm, 1.8 ± 0.2 s, and 0.5 ± 0.1 mV, respectively. All the induced activities were abolished in the presence of 1 μM D600. CM preparations with the submucosal ICC network intact (ICC–CM) showed slow wave activity in Krebs solution at a frequency of 6.2 ± 0.2 cpm, a duration of 3.6 ± 0.2 s, and an amplitude of 1.0 ± 0.1 mV (n = 22). When ICC–CM preparations were stimulated by BaCl2, carbachol, or TEA, the slow wave frequency did not change significantly, but the duration increased as well as the amplitude. In the presence of D600, the upstroke of slow waves remained and the frequency was not affected. The ability to generate slow wave-like activity after potassium conductance blockade in spontaneously quiescent CM disconnected from the ICC network suggested that circular muscle cells have ionic mechanisms for intrinsic oscillatory activity and are capable of actively participating in the conduction and generation of slow waves.Key words: colon, smooth muscle, interstitial cells of Cajal, canine, slow waves, excitability.
Effects of cAMP, its analogues, and forskolin on lung fluid production by in vitro lung preparations from fetal guinea pigs
Authors: Kindler Pawel M. , Ziabakhsh Sepideh , Perks Anthony M.
Published: April 2011

Lungs from fetal guinea pigs (62 ± 1 days of gestation) were supported in vitro for 3 h and fluid production was determined by a dye dilution method, based on Blue Dextran 2000. Twenty untreated lungs produced fluid at 1.41 ± 0.22 mL∙kg−1 body weight∙h−1, with no significant changes during later hours. Treatments with analogues of cAMP, cAMP, or forskolin during the middle hour reduced production significantly. Dibutyryl cAMP at 10−3 M produced reabsorption (117.8 ± 13.6% reduction, p < 0.001, n = 10); at 10−4 M it reduced production (77.3 ± 11.0% fall, p < 0.001, n = 10). 8-Bromo-cAMP appeared more effective; at 10−4 M it caused slight reabsorption (109.0 ± 8.9% reduction, p < 0.001, n = 6) and at lower concentrations it decreased production (at 10−6 M, 67.6 ± 9.6% fall, p < 0.001, n = 6; at 10−7 M, 40.0 ± 14.3% fall, p < 0.001, n = 6). At high doses, cAMP itself produced similar effects (at 5 × 10−3 M, 141.6 ± 22.8% reduction, p < 0.001, n = 6); at 10−4 it was ineffective (n = 3). Forskolin at 10−6 M induced the strongest reabsorptions seen (159.1 ± 10.9% reduction, p < 0.001, n = 6); at lower concentrations it reduced production (at 10−8 M, 73.8 ± 5.5% fall, p < 0.001, n = 6; at 10−9 M, 29.2 ± 9.2% fall, p < 0.05, n = 6). These results suggest a possible role for the adenylate cyclase system in the arrest of lung liquid production in the guinea pig around birth.Key words: cAMP, forskolin, fetal lung, lung fluid.
The effect of methacholine and histamine on cyclic AMP-dependent protein kinase activity in the guinea-pig isolated trachea
Authors: Langlands J. M. , Rodger I. W.
Published: April 2011

The effects of methacholine and histamine were examined on cyclic AMP-dependent protein kinase (A-kinase) activity in guinea-pig isolated trachea, using kemptide as a substrate for phosphorylation during the determination of the enzyme activity. Methacholine (EC90, 10 μM) induced a rapid reduction in the basal A-kinase activity ratio, which was maximal after 30 s. This initial reduction coincided with the early phase of isometric tension development, and returned to control levels 4 min after the addition of methacholine. Pretreatment with atropine inhibited the methacholine response. In contrast, histamine (EQ90, 30 μM) was without effect upon A-kinase activity ratio. The results establish the sensitivity of the A-kinase assay using kemptide and demonstrate that not all contractile agonists have the capacity to inhibit basal activity of A-kinase in airway smooth muscle.Key words: A-kinase, cholinomimetics, guinea-pig trachealis, smooth muscle contraction.
Influence of varions mixtures of inhaled toluene and xylene on the biological monitoring of exposure to these solvents in rats
Authors: Tardif R. , Plaa G. L. , Brodeur J.
Published: April 2011

The present study was undertaken to describe the influence of simultaneous exposure by inhalation to toluene and xylene on some aspects of their respective metabolic disposition. Adult male rats were exposed acutely (5 h) to 75, 150, and 225 ppm of toluene or xylene and to various mixtures of these solvents: toluene (75 ppm) and xylene (225 ppm), toluene (150 ppm) and xylene (150 ppm), toluene (225 ppm) and xylene (75 ppm). Compared with single exposure, simultaneous exposure resulted in lower amounts of excreted hippuric acid (20–30%) and methylhippuric acids (4–40%) in urine over a period of 24 h, even though significant differences were seen only with the toluene (150 ppm) and xylene (150 ppm) combination. In addition, increased concentrations of solvents in blood (toluene, 230%; xylene, 500%) and in brain (toluene, 230%; xylene, 320%) were found during the immediate post-exposure period. Simultaneous exposure also enhanced the pulmonary elimination of both solvents (toluene, 190–240%; xylene, 340–650%). Influence of repeated simultaneous exposure (9 days) was investigated for the toluene (150 ppm) and xylene (150 ppm) combination and the results compared with those of repeated exposure to each solvent administered singly. Under these conditions, repeated simultaneous exposure decreased the excretion of urinary metabolites, but only after the first exposure. On the other hand, simultaneous exposure resulted in significantly higher concentrations of toluene (210%) and xylene (240%) in blood throughout the entire 9-day exposure period. These results strongly suggest mutual metabolic interactions (inhibition) between toluene and xylene that affect the metabolic disposition of both solvents and ultimately the biological monitoring of data of exposure to a combination of solvents in rats.Key words: toluene, xylene, simultaneous exposure, biological monitoring, metabolic interaction, inhalation.
Metabolism during normoxia, hyperoxia, and recovery in newborn rats
Authors: Frappell Peter B. , Dotta Andrea , Mortola Jacopo P.
Published: April 2011

Aerobic metabolism (oxygen consumption, [Formula: see text], and carbon dioxide production, [Formula: see text]) has been measured in newborn rats at 2 days of age during normoxia, 30 min of hyperoxia (100% O2) and an additional 30 min of recovery in normoxia at ambient temperatures of 35 °C (thermoneutrality) or 30 °C. In normoxia, at 30 °C [Formula: see text] was higher than at 35 °C. With hyperoxia, [Formula: see text] increased in all cases, but more so at 30 °C (+20%) than at 35 °C (+9%). Upon return to normoxia, metabolism readily returned to the prehyperoxic value. The results support the concept that the normoxic metabolic rate of the newborn can be limited by the availability of oxygen. At temperatures below thermoneutrality the higher metabolic needs aggravate the limitation in oxygen availability, and the positive effects of hyperoxia on [Formula: see text] are therefore more apparent.Key words: neonatal respiration, oxygen consumption, thermoregulation.
Effects of clentiazem (TA-3090) and nifedipine on basal circulating catecholamine levels and on stimulation-evoked adrenal catecholamine secretion in anesthetized dogs
Authors: Gaspo Rania , Lamarche Louis , Yamaguchi Nobuharu , Champlain Jacques de , Garceau Denis
Published: April 2011

The effects of TA-3090 (clentiazem) and nifedipine on basal sympathoadrenal activity and on the adrenal medullary response during splanchnic nerve stimulation were studied in dogs anesthetized with sodium pentobarbital. Plasma concentrations of epinephrine and norepinephrine were measured in aortic and adrenal venous blood before and after acute administration of the drugs, as well as during left splanchnic nerve stimulation before and after administration of drugs. Following intravenous injections, TA-3090 (30, 100, and 300 μg/kg) did not affect basal circulating catecholamine levels, whereas nifedipine (10, 30, and 100 μg/kg) markedly increased aortic epinephrine and norepinephrine concentrations in a dose-dependent manner in correlation with progressive decreases in mean arterial pressure. The changes in aortic epinephrine and norepinephrine concentrations were inversely related to those in mean arterial pressure (r = 0.603, p < 0.01; r = 0.536, p < 0.01; respectively). In response to direct splanchnic nerve stimulation (2 Hz, 2 ms, 1 min, 12 V), adrenal venous epinephrine and norepinephrine concentrations significantly increased, with a high degree of reproducibility. The catecholamine responses to splanchnic nerve stimulation were not affected by either TA-3090 or nifedipine at any dose tested. The present results suggest that the increases in circulating catecholamine levels following nifedipine administration are due to baroreflex activation secondary to the drug-induced hypotension. The study indicates that both TA-3090 and nifedipine did not significantly affect L-type Ca2+ channels related to catecholamine release in the adrenal medulla under the present experimental conditions.Key words: calcium antagonists, nifedipine, clentiazem, adrenal gland, catecholamines, splanchnic nerve, baroreflex.
Prostaglandin production by porcine allantochorion in vitro: effect of cortisol infusion in vivo
Authors: Gibb W. , Randall G. C. B.
Published: April 2011

The effect of cortisol infusion into the porcine fetus on subsequent prostaglandin (PG) production in vitro by the fetal placenta (the allantochorion) was studied. Also, the possible in vitro effects of glucocorticoids and other steroids on PG production by dispersed cells were examined. Two fetuses in each of 6 sows were catheterized on day 100 or 101 of gestation (normal gestation is 114–116 days); one was infused with cortisol (6 mg/day) and one with saline for 5 days beginning on day 103. On day 108, fetal allantochorionic tissue was aseptically collected from the infused fetuses and 2 uninfused litter mates (controls). Pieces of tissues were cut from the allantochorion (4 sows) and dispersed cell preparations were made from each fetus (4 sows). Each preparation was cultured for 24 h, and the production of PGE2, PGF2α, and 6-keto-PFG1α (prostacyclin metabolite) measured. In vivo cortisol infusion had no significant effect on the in vitro production of PGE2 or PGF2α by tissues or dispersed cell preparations. However, tissue from the fetuses infused with cortisol produced significantly less 6-keto-PGF1α than uninfused controls (54% of control, p < 0.05). The dispersed cells from uninfused fetuses and 2 cortisol-infused animals were also incubated for 24 h with 10−7 and 10−9 M concentrations of estrone, estradiol, progesterone, cortisol, and dexamethasone, and the production of PGE2, PGF2α, and 6-keto-PFG1α was measured. No significant effect of any of these steroids in vitro on prostanoid production was observed. These studies indicate that prolonged in vivo cortisol exposure inhibits prostacyclin production by the allantochorion but that this effect cannot be reproduced by short-term (24 h) in vitro incubations with cortisol. Cortisol may be one of the factors responsible for the decreased prostacyclin production by allantochorion previously reported to occur during labor in this species.Key words: labor, prostaglandins, glucocorticoids, pig, allantochorion.
Pharmacological characterization of lower esophageal sphincter relaxation induced by swallowing, vagal efferent nerve stimulation, and esophageal distention
Authors: Paterson W. G. , Anderson M. A. B. , Anand N.
Published: April 2011

To characterize the neural pathways involved in lower esophageal sphincter relaxation, intraluminal pressures from the lower esophageal sphincter of the opossum were monitored during swallowing, vagal efferent nerve stimulation, and intraluminal balloon distention in the presence and absence of pharmacologic antagonism of putative neurotransmitters. The combination of atropine, hexamethonium, and 5-methoxydimethyltryptamine, which is known to block ganglionic transmission in the vagal inhibitory pathway to the lower esophageal sphincter, significantly antagonized LES relaxation induced by both swallowing and vagal stimulation, but did not affect the LES relaxation induced by balloon distention. Administration of the nitric oxide synthase inhibitor Nωnitro-L-arginine methyl ester, on the other hand, markedly inhibited LES relaxation induced by vagal stimulation, swallowing, and balloon distention, and this effect was reversed by administration of the nitric oxide synthase substrate L-arginine. These studies indicate that the distension-induced intramural pathway mediating LES relaxation does not involve ganglionic transmission similar to that of the vagal inhibitory pathway to the LES. However, the LES relaxation induced by all forms of stimuli appears to depend on nitric oxide as a final mediator.Key words: ganglionic transmission, muscarinic, nicotinic, serotonergic, nitric oxide.
Inhibition of cardiac sarcolemmal Na+/H+ antiporter by opioids
Authors: Periyasamy S. M.
Published: April 2011

In our routine screening of chemicals that would inhibit cardiac sarcolemmal Na+/H+ antiporter, we discovered that some of the opioids produced inhibition of cardiac sarcolemmal Na+/H+ antiporter in micromolar concentrations. Using U-50,488H, a selective κ-opioid agonist, we characterized the nature of interaction between opioids and the Na+/H+ antiporter. The inhibitory effect of U-50,488H on Na+/H+ antiporter was immediate and reversible, and was not mediated through the interaction with the opioid receptors but due to the direct interaction of U-50.488H with the Na+/H+ antiporter. The kinetic data show that in the presence of U-50,488H the Km for Na+ was increased from 2.5 ± 0.2 to 5.0 ± 0.3 mM, while the Vmax (52.0 ± 5.0 nmol∙mg−1∙min−1) remained the same. These results suggest that U-50,488H and Na+ compete for the same site on the antiporter. When testing the effect of U-50,488H on other transport systems of cardiac sarcolemma, we found that U-50,488H also inhibited Na+/Ca2+ antiporter and Na+/K+ pump but at much higher concentrations suggesting that U-50,488H shows some degree of selectivity for cardiac sarcolemmal Na+/H+ antiporter. When we compared the inhibitory potency of U-50,488H with amiloride and its analog, namely 5-(N,N-hexamethylene)amiloride, we found that U-50,488H (IC50 = 100 ± 15 μM) was threefold more potent than amiloride (IC50 = 300 ± 20 μM) but it was threefold less potent than the amiloride analog (IC50 = 30 ± 10 μM) in inhibiting cardiac sarcolemmal Na+/H+ antiporter. These results show that although U-50,488H is more potent than amiloride, the inhibitory characteristics of U-50,488H on cardiac sarcolemmal Na+/H+ antiporter are similar to amiloride.Key words: Na+/H+ antiporter, Na+ uptake, cardiac sarcolemmal vesicles, opioid agonists, U-50,488H.
The influence of calcium on ANF release in the isolated rat atrium
Authors: Deng Yiming , Lang Rudolf
Published: April 2011

We developed an in vitro model of the isolated, perfused rat atrium with which to examine the mechanisms linking muscular stretch to atrial natriuretic factor (ANF) secretion. It was shown that an increase in atrial pressure causing distension of the atria is associated with a rise in ANF secretion correlating with the degree of pressure load. Pressure-induced ANF secretion is enhanced by the calcium blocker nifedipine or omission of calcium from the perfusion buffer. The changes in atrial volume in response to a given pressure load are also more pronounced in the absence of calcium or following the addition of the calcium blocker. These data suggest that in nonbeating atria, stretch-induced ANF secretion does not rely on calcium influx.Key words: atria, stretch, ANF release, calcium.
Effects of K+ on the twitch and tetanic contraction in the sartorius muscle of the frog, Rana pipiens. Implication for fatigue in vivo
Authors: Renaud Jean Marc , Light Peter
Published: April 2011

The effects of increasing the extracellular K+ concentration on the capacity to generate action potentials and to contract were tested on unfatigued muscle fibers isolated from frog sartorius muscle. The goal of this study was to investigate further the role of K+ in muscle fatigue by testing whether an increased extracellular K+ concentration in unfatigued muscle fibers causes a decrease in force similar to the decrease observed during fatigue. Resting and action potentials were measured with conventional microelectrodes. Twitch and tetanic force was elicited by field stimulation. At pHo (extracellular pH) 7.8 and 3 mmol K+∙L−1 (control), the mean resting potential was −86.6 ± 1.7 mV (mean ± SEM) and the mean overshoot of the action potential was 5.6 ± 2.5 mV. An increased K+ concentration from 3 to 8.0 mmol∙L−1 depolarized the sarcolemma to −72.2 ± 1.4 mV, abolished the overshoot as the peak potential during an action potential was −12.0 ± 3.9 mV, potentiated the twitch force by 48.0 ± 5.7%, but did not affect the tetanic force (maximum force) and the ability to maintain a constant force during the plateau phase of a tetanus. An increase to 10 mmol K+∙L−1 depolarized the sarcolemma to −70.1 ± 1.7 mV and caused large decreases in twitch (31.6 ± 26.1%) and tetanic (74.6 ± 12.1%) force. Between 3 and 9 mmol K+∙L−1, the effects of K+ at pHo 7.2 (a pHo mimicking the change in interstitial pH during fatigue) and 6.4 (a pHo known to inhibit force recovery following fatigue) on resting and action potentials as well as on the twitch and tetanic force were similar to those at pHo 7.8. Above 9 mmol K+∙L−1 significant differences were found in the effect of K+ between pHo 7.8 and 7.2 or 6.4. In general, the decrease in peak action potential and twitch and tetanic force occurred at higher K+ concentrations as the pHo was more acidic. The results obtained in this study do not support the hypothesis that an accumulation of K+ at the surface of the sarcolemma is sufficiently large to suppress force development during fatigue. The possibility that the K+ concentration in the T tubules reaches the critical K+ concentration necessary to cause a failure of the excitation–contraction coupling mechanism is discussed.Key words: excitation–contraction coupling, fatigue, potassium, tetanus, twitch.
Influence of chronic nadolol treatment on blood pressure and vascular changes in spontaneously hypertensive rats
Authors: Lee Robert M. K. W. , Tsoporis Jim , Wang Roger R. J.
Published: April 2011

Chronic treatment of spontaneously hypertensive rats (SHR) and Kyoto–Wistar normotensive rats (WKY) with nadolol was carried out from gestation until 28 weeks of age. Nadolol treatment caused some lowering of blood pressure but did not prevent the development of hypertension or cardiac hypertrophy in the SHR, in spite of significant β-blockade. The lumen of large mesenteric arteries from control SHR was smaller than from WKY, and nadolol treatment increased the lumen size in the SHR. An increased number of smooth muscle cell layers present in the control SHR as compared with WKY was reduced slightly by nadolol treatment. However, the changes produced by nadolol did not reach the levels of control and treated WKY. In the aorta, the incidence of polyploid smooth muscle cells was higher in the SHR than the WKY in the control group. Nadolol treatment reduced the percentage of polyploid cells in both SHR and WKY, so that the difference between these two groups of animals was eliminated in the treated groups. The tissue level of norepinephrine in the plasma, heart, mesenteric arteries, and adrenal glands in the SHR and WKY was not affected by the treatment. We suggest that the ineffectiveness of nadolol in preventing hypertension development may be due to its lack of effect in preventing primary changes in the resistance arteries, and that the development of polyploidy of smooth muscle cells may be mediated by β-receptors.Key words: nadolol, vascular changes, hypertension, spontaneously hypertensive rats, β-receptor, catecholamines.
Reabsorption of lung liquid produced by 2,4-dinitrophenol in in vitro lungs from fetal guinea pigs
Authors: Perks A. M. , Ruiz T. , Chua B. , Muhll I. Vonder , Kindler P. M. , Blair W.
Published: April 2011

Lungs from near-term fetal guinea pigs (62 ± 2 days of gestation) were supported in vitro for 3 h, and lung liquid production was measured by a dye dilution technique. Twelve untreated preparations produced fluid at 1.54 ± 0.29 mL∙kg−1 body weight∙h−1 during the 1st h, with no significant changes in later hours. Twelve preparations treated with 2 × 10−4 M 2,4-dinitrophenol (DNP) showed strong reabsorptions (significant, ANOVA and regression analysis); total loss of lactate from the preparations doubled (significant, same tests). In 12 additional preparations, increasing DNP fivefold did not abolish reabsorption; results resembled those at the lower concentration. Amiloride at 10−6 M abolished reabsorptions after 2 × 10−4 M DNP, although fluid production still halted (n = 6; reductions significant, same tests). Amiloride alone had no effect (n = 6); untreated controls showed no change (n = 6). Similarly, 10−4 M sodium iodoacetate virtually abolished reabsorptions after 2 × 10−4 M DNP, although fluid production still stopped (n = 6; reductions significant, same tests). Iodoacetate alone only reduced fluid production (n = 6; significant, same tests); untreated controls showed no change (n = 6). The results suggest that reabsorptions seen after inhibition of oxidative processes depend on amiloride-sensitive Na+ channels and glycolytic metabolism.Key words: fetus, lung liquid, 2,4-dinitrophenol, amiloride, iodoacetate.
Effect of K channel blockers on basal and β-agonist stimulated ion transport by fetal distal lung epithelium
Authors: O'Brodovich Hugh , Rafii Bijan
Published: April 2011

To determine whether basolateral K channels play an important role in the basal and β-agonist stimulated ion transport by fetal distal lung epithelium we harvested these cells from fetal rats (20 days gestation, term = 22 days) and studied them in Ussing chambers. Short-circuit current (Isc) fell with basal 3 mM BaCl2 (3.0 ± 0.2 (±SEM) to 2.0 ± 0.2 μA∙cm−2, n = 18, p < 0.01) without affecting monolayer resistance (R = 693 ± 57 Ω∙cm2). Basal quinine sulfate (1 mM) also decreased Isc (3.7 ± 0.15 to 3.0 ± 0.10 μA∙cm−2; n = 4, p < 0.01). None of apical BaCl2 (3 mM), apical quinine (1 mM), nor bilaterally applied tetraethylammonium (10 mM), lidocaine (1 mM), or 4-aminopyridine (2 mM) decreased Isc. Cell monolayers treated with basal BaCl2 (3 mM) demonstrated an impaired ability to increase their Isc in response to the β2-agonist terbutaline (1 mM). Basal 3 mM BaCl2 also decreased Isc in amiloride (0.1 mM) and furosemide (1 mM) treated monolayers, indicating that barium also affected the previously described amiloride-insensitive Na transport by these cells (n = 8, p < 0.01). Together these experiments suggest that normal basolateral K channel function is required for normal and β2-stimulated Na transport in fetal distal lung epithelium.Key words: type II alveolar epithelium, potassium channels, β-agonist, sodium transport, Na channels.
Antifibrillatory effects of α1-adrenoceptor blocking drugs in experimental coronary artery occlusion and reperfusion
Authors: Benfey B. G.
Published: April 2011

The myocardium of animals and man possesses α1-adrenoceptors in addition to β-adrenoceptors. Ischemia increases sympathetic tone, and ventricular arrhythmias can occur by β- and α1-adrenoceptor stimulation. I believe that α1-adrenoceptor blocking drugs have antifibrillatory effects and will review the data that support this condition. The effect of α1,-adrenoceptor blocking drugs on the incidence of ventricular fibrillation in acute coronary artery occlusion and (or) reperfusion has been determined in 24 studies in conscious and anesthetized dogs and rats, anesthetized cats and pigs, and rat and guinea-pig isolated hearts. The drugs reduced the incidence of fibrillation from 35 to 24% in coronary occlusion and from 61 to 29% in reperfusion.Key words: heart, coronary occlusion, coronary reperfusion, ventricular fibrillation, α1-adrenoceptor blocking drugs.
Characterization of leukotriene-induced contraction of the guinea-pig gallbladder in vitro
Authors: Freedman Stephen M. , Wallace John L. , Shaffer Eldon A.
Published: April 2011

Metabolites of arachidonic acid like prostaglandins have an established role in the pathogenesis of gallstone formation and cholecystitis, but any contribution by leukotrienes is less clear. Leukotrienes might contribute to the disease process by contracting the inflamed and (or) obstructed gallbladder, resulting in further inflammatory damage and biliary pain. To better define the role of leukotrienes, we assessed their effects on gallbladder contracility in vitro. Both leukotriene C4 (LTC4) and D4 (LTD4) had a concentration-dependent excitatory effect on guinea-pig gallbladder smooth muscle. The LTD4-receptor antagonist MK-571 (1 μM) competitively depressed the contractile response, to both LTD4 and LTC4. The source of calcium was defined using ryanodine to deplete intracellular calcium stores and nifedipine to block extracellular entry. Ryanodine (10 μM) antagonized gallbladder contraction at low concentrations of LTD4 (10−10 and 10−9 M). Nifedipine (1 μM) had a greater inhibitory effect on the contractile response at high concentrations of LTD4 (10−8–10−6 M). LTD4-induced contractions were unaffected in tissues pretreated with the neural blocker tetrodotoxin or the muscarinic antagonist atropine. Thus, leukotrienes act directly on the gallbladder smooth muscle, causing contraction at concentrations found in models of cholecystitis, suggesting that these inflammatory mediators contribute to the symptoms and morbidity associated with gallbladder disease.Key words: gallstones, cholecystitis, guinea-pig, gallbladder, leukotriene.
Selective growth inhibition of the male progeny of mice treated with trimethylamine during pregnancy
Authors: Guest Ian , Varma D. R.
Published: April 2011

Injections of 1–7.5 mmol trimethylamine (TMA) per kilogram into mice daily from day 6 to day 15 (period of organogenesis) of gestation caused a dose-dependent decrease in fetal weights and in postnatal growth. The decrease in postnatal body weight gain, in brain and kidney weights, and in brain protein and DNA was more marked in the male than in the female offspring of TMA-treated animals; seminal vesicle weight and serum testosterone levels were also reduced. It is suggested that the selective growth inhibition of male progeny might be due to a decrease in testosterone synthesis. Since endogenous TMA levels are influenced by renal and liver disease and food habits, it might be one of the environmental factors influencing pregnancy outcome.Key words: testosterone, sexual dimorphism, postnatal growth retardation, trimethylamine.
Cholinergic effects on spatial exploration and its memory
Authors: Kelly Peter H. , Malanowski Jan
Published: April 2011

In their first swim in an unfamiliar circular swimming pool, control rats showed declines in average swimming speed and in the time spent in the perimeter of the pool. Both declines were antagonized by the muscarinic antagonist scopolamine, but not by methylscopolamine, a muscarinic antagonist that crosses the blood–brain barrier only poorly, indicating that these declines depend upon central cholinergic activity. In the first minute of a second swim 3 days later, control rats spent a much longer time in the central region of the pool than in the first minute of the first swim. This modification of behaviour by previous experience suggests that a long-term memory of the first swim was formed. Scopolamine, but not methylscopolamine, administered before the first swim attenuated this modification of behaviour. Pilocarpine, administered shortly after scopolamine before the first swim, significantly normalized all the scopolamine-induced changes, whereas oxotremorine and arecoline normalized only habituation of perimeter preference; agonists administered alone decreased swimming speed and perimeter preference without affecting their rates of decline. The results suggest that in this test, different cholinergic mechanisms are involved in habituation of swimming speed and habituation of perimeter preference.Key words: scopolamine, muscarinic cholinergic agonists, swimming exploration pattern, habituation, memory.
Anatomical distribution of brainstem sites where PGE1 induces hyperthermia in macaque species
Authors: Simpson C.W. , Ruwe W. D. , Myers R. D.
Published: April 2011

The neuroanatomical distribution of sites in the diencephalon and mesencephalon within which a prostaglandin (PG) of the E series elicits hyperthermia was characterized in Macaca mulatta and Macaca nemestrina. In 420 experiments undertaken in 13 animals, 225 loci were examined for their reactivity to PGE1 microinjected in a dose of 30 or 100 ng given in a volume of 1.0–1.5 μL. The regions of the brainstem for injection extended rostrally from the thermosensitive cells of the anterior hypothalamic, preoptic area (AH/POA) to the caudal border of the mesencephalon. Colonic and skin temperatures of the monkeys were measured continuously by thermistor probes. A hyperthermic response of ≥0.5 °C and a latency of ≤45 min was evoked by PGE1 within sites located primarily in the AH/POA. When PGE1 was microinjected at loci located caudal to the AH/POA, the elevation in body temperature (Tb) not only was less intense but rose at a slower rate. A higher concentration of PGE1 in these caudal regions was required to induce hyperthermia comparable with that elicited at loci within the AH/POA. In a second series of experiments either 1.0–5.0 μg 5-hydroxytryptamine (serotonin) or a concentration of 108 organisms/mL of Escherichia coli was microinjected at PGE1-reactive sites. A close anatomical concordance within the AH/POA of the animal was found in terms of the temporal characteristics and magnitude of the hyperthermia evoked by the indoleamine or lipopolysaccharide. The present results coincide with the reported neuroanatomical distribution of sites in the diencephalon and mesencephalon of other species in which PGE1 causes hyperthermia. Furthermore, these findings support the concept that the local neuronal mechanism of action of a pyrogen in the brainstem of the primate may involve phasic changes in the endogenous activity of both the serotonergic pathway and cyclo-oxygenase system in the AH/POA. In turn, their commonality of action suggests a functional similarity in their effect of shifting the set point for Tb.Key words: prostaglandin E1, hyperthermia, serotonin, Escherichia coli, anterior hypothalamus, thermoregulation, bacterial pyrogen, preoptic area, neuroanatomical localization, Macaca nemestrina, Macaca mulatta.
Effects of dietary fish oil on cardiovascular responsiveness to adrenergic agonists in spontaneously hypertensive rat
Authors: Smith Jacquelyn M. , Kopp Stephen J. , Paulson Dennis J. , Daar June T.
Published: April 2011

To test the hypothesis that dietary fish oil supplementation decreases systolic blood pressure in hypertensive rats by modifying cardiovascular responsiveness to adrenergic agonists, spontaneously hypertensive rats (SHR) and Wistar–Kyoto rats (WKY) received either a corn or fish oil diet, 5% (g/kg) for 10 weeks. Mean aortic pressure was lower in fish oil treated (161 ± 7 mm Hg (1 mmHg = 133.3 Pa)) than corn oil treated (191 ± 6 mmHg) SHR. Although dietary fish oil supplementation decreased responsiveness to norepinephrine in isolated thoracic aorta from SHR, there was no change in cardiovascular responsiveness to the β1 agonist dobutamine or the α1, agonist phenylephrine when these adrenergic agonists were administered in vivo. However, dietary fish oil did decrease the spontaneous basal tone in aorta from both SHR and WKY. This study provides further evidence that dietary fish oil lowers blood pressure in an animal model genetically predisposed to hypertension. However, the mechanism for this decrease in mean aortic pressure in vivo does not appear to be related to modification of cardiovascular responsiveness to α1- or β1-adrenergic agonists and may be related to a decrease in basal vasomotor tone.Key words: fish oil, antihypertensive, spontaneously hypertensive rats, dobutamine, vascular smooth muscle.
Carnitine musculaire chez les souris hyperammoniémiques: effet du traitement au benzoate de sodium
Authors: Michalak Adrianna , Qureshi Ijaz A.
Published: April 2011

The object of this study was to measure carnitine levels in skeletal muscles of experimental mice with acute, subacute, and chronic hyperammonemia, with or without sodium benzoate treatment. Normal Swiss–ICR mice in which acute hyperammonemia was created through intraperitoneal injection of ammonium acetate showed a significant decrease in free carnitine in the skeletal muscles. The same phenomenon was observed in spf mice with chronic congenital hyperammonemia caused by an X-linked deficiency of liver ornithine transcarbamylase. In spf mice with subacute hyperammonemia created through treatment with an arginine-deficient diet, free carnitine of muscles increased compared with basal levels seen in chronic hyperammonemia. The changes in carnitine metabolism during chronic and subacute hyperammonemia were accompanied by a significant increase of creatine kinase levels in the plasma, which are an index of damage to the sarcolemma. A decrease in free and esterified levels of carnitine in the muscles was observed among normal mice treated with sodium benzoate. A decrease in esterified carnitine was also noticed among spf mice given an acute treatment with sodium benzoate as well as among normal and spf mice given a prolonged treatment with sodium benzoate. Plasma creatine kinase levels were high in normal mice, after both acute and prolonged treatments. However, the levels in spf mice treated with sodium benzoate were not significantly different from those in untreated spf controls in which a significant increase in plasma creatine kinase was already caused by chronic hyperammonemia. This study indicates that the metabolism and (or) distribution of carnitine go through significant changes during various levels of hyperammonemia, and that a treatment with sodium benzoate causes a secondary deficiency in carnitine of muscles. The increase in plasma levels of creatine kinase could signify a secondary effect of these factors on the function or the integrity of the sarcolemma.Key words: hyperammonemia, carnitine, sodium benzoate, mice, muscle.
Skeletal muscle ammonia production and repeated, intense exercise in humans
Authors: Graham T. , Bangsbo J. , Saltin B.
Published: April 2011

We investigated the impact of repeated, high-intensity exercise on NH3 metabolism using the single-leg knee extensor model. The muscle glycogen level would be lowered by the initial exercise and low glycogen may stimulate NH3 production independent of any other effects of previous exercise. Therefore a high muscle glycogen condition was included in the protocol so that the pre-exercise glycogen concentration would be at least at a normal resting level for the second exercise. The subjects (n = 6) used previous exercise and (or) diet to begin the exercise with either normal (87.0 ± 14.4 mmol/kg wet weight) or high (176.8 ± 22.9 mmol/kg wet weight) glycogen (C and HG, respectively) in the quadriceps. They exercised (Ex1) one leg to exhaustion (140% leg [Formula: see text]), rested 1 h, repeated the exercise (Ex2), and then repeated the protocol with the opposite leg. The exercise durations of Ex1 and Ex2, respectively, for C were 2.82 ± 0.51 and 2.47 ± 0.47 min (p < 0.05) and for HG were 2.92 ± 0.57 and 2.77 ± 0.50 min. The NH3 efflux was reduced (p < 0.05) from Ex1 to Ex2 in both C (516 ± 159 and 250 ± 69 μmol, respectively) and HG (618 ± 233 and 275 ± 124 μmol, respectively). While NH3 efflux was virtually identical between C and HG in both Ex1 and Ex 2, HG consistently had a greater arterial NH3 concentration (p < 0.05). The decreased efflux in Ex2 compared with Ex1 was not due to greater accumulation of muscle NH3. The changes in creatine phosphate and ATP were very similar in all four exercises; however, the reduced NH3 response in Ex2 was associated with less net lactate production and presumably less muscle acidosis.Key words: AMP deaminase, lactate, purine nucleotide cycle, high energy phosphates, intermittent exercise, fatigue, glycogen.
Post-translational processing of atrial natriuretic factor by adult rat atrial cardiocytes in culture
Authors: Dubé Gilles R. , Kuroski - de Bold Mercedes L. , Bold Adolfo J. de
Published: April 2011

Post-translational processing of the cardiac polypeptide hormone atrial natriuretic factor (ANF) was studied using primary cultures of cardiocytes derived from adult rat atria. Atrial cardiocytes attached to microcarrier beads were maintained for up to 15 days under continuous superfusion in minichromatographic columns. The cultures were characterized for their ability to store, process, and release ANF and by immunofluorescence microscopy for ANF, desmin, and myosin. Nuclear staining using the fluorescent DNA stain Hoechst 33258 was carried out to determine the total number of cells in culture. Column eluates were assayed for ANF by radioimmunoassay and analyzed by reverse phase high-performance liquid chromatography. For comparison purposes, superfusion experiments using freshly isolated cardiocytes supported in Bio-Gel P2 were carried out. Freshly isolated atrial cardiocytes stored high molecular weight ANF (5.2 ± 1.9 pmol/μg DNA) and released mostly (83.3 ± 6.7%) low molecular weight ANF, at an average rate of 97 ± 18 fmol∙min−1∙μg−1 DNA. The cell content and the rate of release of ANF after 15 days in culture were 1.3 ± 0.4 pmoi/μg DNA and 1.7 ± 0.4 fmol∙min−1∙μg−1 DNA, respectively, and 62.7 ± 6.3% of the released peptide was of a low molecular weight. There was no correlation between changes in cell population and the extent of processing. Cultures of noncardiocytes, superfused with exogenous proANF, did not significantly process proANF to a lower molecular weight peptide. The present investigation shows that adult rat atrial cardiocytes, maintained superfused in microcarrier culture and in a serum-supplemented medium for up to 15 days, retain phenotypic and biochemical characteristics normally associated with the dual contractile–endocrine nature of mammalian atrial cardiocytes in vivo. The results obtained in the present work strongly support the view that ANF post-translational processing is an intrinsic property of the atrial cardiocytes and is independent of any other cell type.Key words: atrial natriuretic factor, post-translation processing, cardyocytes, adult rats, cell cultures.