bluuebunny/crossref_metadata_2025 huggingface dataset:
Population analyses of sustained‐release verapamil in patients: Effects of sex, race, and smoking
Authors: Kang Dongwoo , Verotta Davide , Krecic‐Shepard Mary Ellen , Modi Nishit B. , Gupta Suneel K. , Schwartz Janice B.
Published: February 2003

Objective

Our objective was to determine the effects of age, sex, and sustained‐release formulation on apparent oral clearance of sustained‐release racemic verapamil in patient populations.

Methods

Population pharmacokinetic analyses were performed on data from 186 patients with hypertension, coronary artery disease, or supraventricular arrhythmias who were receiving long‐term sustained‐release oral racemic verapamil (Covera SR in 105 patients, Calan SR in 67 patients, and other formulations in 14 patients; mean ± SD dose, 280 ± 139 mg) for clinical care or as a part of phase III efficacy studies. Of those 186 patients, 135 were men (age, 63 ± 12 years; ideal body weight, 70.7 ± 6.6 kg) and 51 were women (age, 60 ± 17 years; ideal body weight, 53.7 ± 7.2 kg) . Verapamil was measured by HPLC, and population analyses were performed by use of NONMEM software. Sex, age, and formulation were the covariates considered in the population model building. Subgroup analyses of race, smoking, and alcohol consumption were also performed. Significance of covariates was determined by likelihood ratio tests.

Results

Sex significantly affected steady‐state clearance of oral sustained‐release racemic verapamil. Apparent oral clearance of sustained‐release verapamil was 23.8 ± 2.3 mL/min per kilogram in women compared with 18.6 ± 3.4 mL/min per kilogram in men. Clearance estimates were faster in black subjects compared with white subjects, as well as in smokers compared with nonsmokers. Effects of age, formulation, and alcohol consumption were not detected.

Conclusions

In middle‐aged and older patients, apparent oral clearance of sustained‐release racemic verapamil was affected by sex (faster in women compared with men), race (faster in black subjects compared with white subjects), and smoking (faster in smokers compared with nonsmokers) but not by age, alcohol, or formulation.

Clinical Pharmacology & Therapeutics (2003) 73, 31–40; doi: 10.1067/mcp.2003.21
Kinetics of Thyroxine (T4) and Triiodothyronine (T3) Transport in the Isolated Rat Heart
Authors: Rosic Mirko A. , Pantovic Suzana B. , Lucic Aleksandra P. , Ribarac‐Stepic Nevena , Andjelkovic Ivan Z.
Published: February 2003

The dynamics and kinetics of thyroid hormone transport in the isolated rat heart were examined using the modified unidirectional paired tracer dilution method. The uptake of 125I‐thyroxine (125I‐T4) and 125I‐triiodothyronine (125I‐T3) from the extracellular space into heart cells was measured relative to the extracellular space marker 3H‐mannitol. The thyroid hormone maximal uptake was 54.4% for 125I‐T4 and 52.15% for 125I‐T3. The thyroid hormone net uptake was 25.69% for 125I‐T4 and 25.49% for 125I‐T3. Backflux from the intracellular space was 53.17% for 125I‐T4 and 61.59% for 125I‐T3. In the presence of unlabelled thyroid hormones, 125I‐T4 and 125I‐T3 maximal uptakes were reduced from 10.1 to 59.74% and from 34.6 to 65.3%, respectively, depending on the concentration of the unlabelled hormone, suggesting a saturable mechanism of the thyroid hormone uptake by the heart cells, with Km(T4)= 105.46 μM and the maximal rate of 125I‐thyroid hormone flux from the extracellular space to heart cells (Vmax(T4)) = 177.84 nM min−1 for 125I‐T4 uptake, and Km(T3)= 80.0 μM and Vmax(T3)= 118.5 nM min−1 for 125I‐T3 uptake.
Raised Extracellular Potassium Attenuates the Sympathetic Modulation of Sino‐Atrial Node Pacemaking in the Isolated Guinea‐Pig Atria
Authors: Choate J. K. , Nandhabalan M. , Paterson D. J.
Published: February 2003

Intense exercise or myocardial ischaemia can significantly increase both the concentration of extracellular potassium ([K+]o) and cardiac sympathetic nerve activity. Since changes in [K+]o modulate membrane currents involved in sino‐atrial node pacemaking, in particular the voltage‐sensitive hyperpolarization‐activated current (If), we investigated whether raised [K+]o (from 4 mM to 8 or 12 mM) could directly affect the heart rate response to cardiac sympathetic nerve stimulation (SNS). In the isolated guinea‐pig atrial‐right stellate ganglion preparation, raised [K+]o significantly decreased the maximum diastolic potential, amplitude and maximum rate of rise of the upstroke of sino‐atrial node pacemaker action potentials in 8 and 12 mM [K+]o (P < 0.05). At 12 mM [K+]o these effects were associated with significant decreases in baseline heart rate (4 mM [K+]o= 187 ± 5 beats min−1 (bpm); 12 mM = 144 ± 11 bpm; P < 0.05) and the heart rate response to SNS (1, 3 and 5 Hz; P < 0.05). A 10% increase in the baseline heart rate with sympathetic activation (3 Hz) was associated with a significant enhancement of the slope of the pacemaker diastolic depolarization at 4 mM [K+]o (increased by 16 ± 6%; n= 7; P < 0.05), but not with raised [K+]o. When the If current was blocked with 2 mM caesium (n= 8), 12 mM [K+]o had no effect on baseline heart rate and the heart rate response to 3 Hz SNS. The heart rate response to bath‐applied noradrenaline (0.01‐100 μM) was significantly attenuated by 12 mM [K+]o (at 4 mM [K+]o, EC50= ‐6.31 ± 0.18; at 12 mM [K+]o, EC50= ‐5.80 ± 0.10; n= 6, ANOVA, P < 0.05). In conclusion, extreme physiological levels of [K+]o attenuate the positive chronotropic response to cardiac sympathetic activation due to decreased activation of the If current. This is consistent with raised [K+]o protecting the myocardium from potentially adverse effects of excessive noradrenaline.
Altered Glycogen Synthase and Phosphorylase Activities in Skeletal Muscle of Tetraplegic Patients
Authors: Jiao Ying , Shashkin Pavel , Hjeltnes Nils , Wallberg‐Henriksson Harriet , Katz Abram
Published: February 2003

Despite marked differences in both the extent of physical activity and in muscle metabolism and structure between tetraplegic and control subjects, the glycogen content in the skeletal muscle of both groups is similar. We determined whether this similarity could be explained by the activities of key enzymes of glycogen metabolism. Muscle biopsies were analysed for glycogen synthase (GS) and glycogen phosphorylase (GP) activities, as well as for metabolites. Glycogen content did not differ significantly between the two groups. Total glycogen synthase activity was reduced by almost 60% in tetraplegics (P < 0.01), whereas total phosphorylase activity did not differ between groups. GS fractional activity did not differ between groups, whereas phosphorylase fractional activity (−/+ AMP) was significantly higher in the tetraplegics (0.08 ± 0.01, control; 0.25 ± 0.02, tetraplegics; P < 0.001). Neither uridine diphosphate (UDP)‐glucose nor glucose 6‐phosphate (G‐6‐P) content in muscle differed significantly between groups. These data demonstrate that, in tetraplegics, muscle glycogen content is preserved despite decreases in GS activity and increases in phosphorylase fractional activity. Muscle paralysis has differential effects on the activities of GS and GP.
Corticospinal Facilitation Studied During Voluntary Contraction of Human Abdominal Muscles
Authors: Tunstill Simon A. , Wynn‐Davies Anneli C. , Nowicky Alex V. , McGregor Alison H. , Davey Nick J.
Published: February 2003

Transcranial magnetic stimulation (TMS) of the human motor cortex was used to study facilitation of motor‐evoked potentials (MEPs) in the rectus abdominis (RA) muscle, a trunk flexor, during voluntary activation. MEPs could be produced in the relaxed RA muscles of all six normal subjects studied. The MEPs had short latencies (18‐22 ms) which are consistent with other studies suggesting a fast corticospinal input to the trunk muscles. Marked facilitation was observed in the MEPs when subjects were asked to produce graded levels of voluntary contractions. The two tasks used to produce voluntary contractions were a forced expiration during a breath‐holding task (FEBH) and bilateral trunk flexion (BTF). Maximal voluntary EMG activity during the BTF task produced around 4.2 times more integrated EMG than during the FEBH task. Similarly the MEP amplitude at MVC was 2.3 times greater during BTF than FEBH. The pattern of MEP facilitation with increasing voluntary EMG was not linear and a maximal MEP amplitude was observed at a level of voluntary contraction around 30% MVC in both tasks. There were some subtle differences in the pattern of facilitation in the two tasks. When TMS was applied to the right cortex only, MEPs were seen in both left and right RA muscles suggesting some ipsilateral corticospinal innervation. The latency of the right (ipsilateral) response was approximately 2 ms longer than the left. Comparison with studies in hand and leg muscles suggests that the facilitation pattern in RA may reflect a substantial degree of corticospinal innervation.
The Effect of Progesterone on Coronary Blood Flow in Anaesthetized Pigs
Authors: Molinari C. , Battaglia A. , Grossini E. , Mary D. A. S. G. , Stoker J. B. , Surico N. , Vacca G.
Published: February 2003

The present study was designed to investigate the effect of progesterone on the coronary circulation and to determine the mechanisms involved. In pigs anaesthetized with sodium pentobarbitone, changes in left circumflex or anterior descending coronary blood flow caused by intravenous infusion of progesterone at constant heart rate and arterial blood pressure were assessed using an electromagnetic flowmeter. In 14 pigs, infusion of 1 mg h−1 of progesterone caused an increase in coronary blood flow without affecting left ventricular dP/dtmax (rate of change of left ventricular systolic pressure) and filling pressures of the heart. In a further four pigs, this vasodilatory coronary effect was enhanced by graded increases in the dose of the hormone of between 1, 2 and 3 mg h−1. The mechanisms of the above response were studied in the 14 pigs by repeating the experiment after haemodynamic variables had returned to the control values observed before infusion. In six pigs, blockade of muscarinic cholinoceptors and adrenoceptors with atropine, propranolol and phentolamine did not affect the coronary vasodilatation caused by progesterone. In the remaining eight pigs, this response was abolished by intracoronary injection of Nω‐nitro‐L‐arginine methyl ester (L‐NAME) even when performed after reversing the increase in arterial blood pressure and coronary vascular resistance caused by L‐NAME with continuous intravenous infusion of papaverine. The present study showed that intravenous infusion of progesterone primarily caused coronary vasodilatation. The mechanism of this response was shown to involve the endothelial release of nitric oxide.
Inotropic Actions of Protein Kinase C Activation by Phorbol Dibutyrate in Guinea‐Pig Isolated Ventricular Myocytes
Authors: Mamas M. A. , Terrar D. A.
Published: February 2003

The mechanisms which underlie the inotropic actions of phorbol dibutyrate (PDBu), a synthetic compound which can directly activate protein kinase C (PKC), were investigated in guinea‐pig isolated ventricular myocytes. Exposure of cells to PDBu (10−7 M) reduced myocyte contraction amplitude to 46 ± 3% of control (n = 8; P < 0.05) with an associated shortening in action potential duration (action potential duration at 90% repolarisation (APD90) was reduced to 83 ± 1% of control; P < 0.05). The negative inotropic actions of PDBu and the shortening in action potential duration were abolished in the presence of a selective PKC inhibitor, Ro31‐8220. Calcium transients (constructed from calcium‐activated tail currents following interruption of action potentials by voltage clamp to ‐70 mV) were reduced following exposure to 10−7 M PDBu by 38 ± 2% (n = 9, P < 0.05). L‐type calcium currents were not significantly altered following exposure to 10−7 M PDBu (98 ± 2% of control; P > 0.05). In contrast, delayed rectifier potassium currents (IK) were enhanced to 154 ± 8% of control (n = 7; P < 0.05) by 10−7 M PDBu. This enhancement of IK may contribute to the observed shortening in action potential duration observed following exposure to PDBu under the conditions of our experiments. When the action potential configuration was maintained throughout the experiment by applying a voltage‐clamp waveform, 10−7 M PDBu still reduced contraction amplitude to 57 ± 3% of control (P < 0.05). Exposure to 10−7 M PDBu also suppressed spontaneous activity (both spontaneous potential fluctuations induced by the β‐adrenergic agonist isoprenaline (40 nM), and transient inward currents induced by the cardiac glycoside ouabain (1 μM) under voltage clamp). It therefore appears that the reduction in myocyte contraction amplitude induced by exposure to PDBu may result in part through mechanisms independent of action potential shortening, which may include direct actions of protein kinase C on the function of the sarcoplasmic reticulum (SR) calcium store and/or on contractile proteins (though action potential shortening would be expected to cause a further decrease as a consequence of reduced calcium loading of the SR). The reduction of spontaneous activity caused by PDBu may also result from changes in the function of the SR store mediated by protein kinase C.
Effects of Direct Sympathetic and Vagus Nerve Stimulation on the Physiology of the Whole Heart – A Novel Model of Isolated Langendorff Perfused Rabbit Heart with Intact Dual Autonomic Innervation
Authors: Ng G. André , Brack Kieran E. , Coote John H.
Published: February 2003

A novel isolated Langendorff perfused rabbit heart preparation with intact dual autonomic innervation is described. This preparation allows the study of the effects of direct sympathetic and vagus nerve stimulation on the physiology of the whole heart. These hearts (n= 10) had baseline heart rates of 146 ± 2 beats min−1 which could be increased to 240 ±11 beats min−1 by sympathetic stimulation (15 Hz) and decreased to 74 ± 11 beats min−1 by stimulation of the vagus nerve (right vagus, 7 Hz). This model has the advantage of isolated preparations, with the absence of influence from circulating hormones and haemodynamic reflexes, and also that of in vivo preparations where direct nerve stimulation is possible without the need to use pharmacological agents. Data are presented characterising the preparation with respect to the effects of autonomic nerve stimulation on intrinsic heart rate and atrioventricular conduction at different stimulation frequencies. We show that stimulation of the right and left vagus nerve have differential effects on heart rate and atrioventricular conduction.
Contribution of Endothelial Nitric Oxide Synthase in the Blunted Renal Responses to Volume Expansion in Diabetic Rats
Authors: Wongmekiat Orawan , Johns Edward J.
Published: February 2003

The renal excretory responses to volume expansion (VE), by 10% body wt, were determined in groups of anaesthetised streptozotocin‐induced diabetic rats with one denervated and one innervated kidney in the presence and absence of nitric oxide synthase (NOS) inhibitors. VE in diabetic rats increased (P < 0.001) cumulative urine sodium excretion (CuUNaV) to 104 ± 9 and 69 ± 6 μmol min−1 (g kidney wt)−1 in the denervated and in the innervated kidneys, respectively, which were both less (P < 0.001) than in the non‐diabetic rats, at 225 ± 14 and 148 ± 14 μmol min−1 (g kidney wt)−1, respectively, in the denervated and the innervated kidney. The non‐selective NOS inhibitor, NG‐nitro‐L‐arginine‐methyl‐ester (L‐NAME) given to the diabetic rats with intact renal innervation enhanced CuUNaV after VE by 43% (P < 0.001), while the combination of L‐NAME and renal denervation restored CuUNaV to a value comparable to that of non‐diabetic rats. In diabetic rats treated with either a relatively selective inhibitor for the neuronal isoform of NOS, 7‐nitroindazole, or a relatively selective inhibitor for the inducible isoform of NOS, aminoguanidine, CuUNaV after VE was similar to the untreated diabetic rats irrespective of whether or not the renal nerves were present. This investigation demonstrated that NO production contributed, at least partly, to the depressed ability to excrete a saline load in diabetes mellitus. The endothelial isoform of NOS was most probably responsible for generating NO which caused the blunted excretory responses. The ability of NO to attenuate the excretory responses to volume expansion was an action independent of the renal innervation status.
Effects of 8 h of Isocapnic Hypoxia with and without Muscarinic Blockade on Ventilation and Heart Rate in Humans
Authors: Clar Christine , Dorrington Keith L. , Fatemian Marzieh , Robbins Peter A.
Published: February 2003

This study examined the role of muscarinic parasympathetic mechanisms in generating the progressive increases in ventilation (V̇E) and heart rate previously reported with 8 h exposures to hypoxia. The sensitivities of V̇E (Gp) and heart rate (GHR) to acute variations in hypoxia, and V̇E and heart rate during acute hyperoxia were assessed in 10 subjects before and after two 8 h exposures to isocapnic hypoxia (end‐tidal PO2= 50 mmHg). The responses were measured during muscarinic blockade with glycopyrrolate (0.015 mg kg−1) and without glycopyrrolate, as a control. There were significant increases in Gp (P < 0.01) and V̇E during hyperoxia (P < 0.01) following hypoxic exposure, but these were unaffected by glycopyrrolate. GHR increased significantly by 0.29 ± 0.08 beats min−1%−1 (mean ± S.E.M.) following exposure to hypoxia under control conditions, but only non‐significantly by 0.10 ± 0.08 beats min−1%−1 with glycopyrrolate. This difference was significant. Changes in heart rate during hyperoxia were slight and inconclusive. We conclude that muscarinic mechanisms play little role in the progressive ventilatory changes that occur over 8 h of hypoxia, but that they do mediate much of the progressive increase in heart rate.
Uterine Quiescence: The Role of Cyclic AMP
Authors: Price Sarah A. , Bernal Andrés López
Published: February 2003

It is accepted that whilst hormones such as oxytocin, vasopressin and prostaglandin F2α induce myometrial contractions, essentially via an elevation of intracellular calcium, other ligands, such as β‐adrenoceptor agonists, calcitonin gene‐related peptide, and prostaglandin E2, promote uterine quiescence via their ability to increase intracellular cyclic AMP levels. At present, the exact factors initiating human parturition remain unknown, and labour may occur due to a loss of uterine quiescence, an increase in uterine contractility, or a combination of both. Whilst many studies have aimed to understand the mechanisms underlying uterine contractility there is a relative paucity of data regarding myometrial relaxation. We have verified the presence of mRNA encoding adenylyl cyclase (AC) isoforms I, II, III, V, VI, VII, VIII and IX in both non‐pregnant and pregnant human myometrium, and in isolated myometrial cells maintained in cell culture. Furthermore, by means of immunoblotting and immunocytochemistry, we have demonstrated the expression of these isoforms as membrane‐associated AC proteins, and identified changes in individual AC isoform expression during gestation. These findings illustrate the diversity of potential cAMP generating pathways in human myometrium, and the complexity of the signal transduction systems underlying uterine quiescence.
Oxytocin Antagonists: Clinical and Scientific Considerations
Authors: Thornton Steven , Vatish Manu , Slater Donna
Published: February 2003

Preterm delivery is the largest cause of perinatal mortality and morbidity, yet the treatment of preterm labour has not been demonstrated to improve outcome. The reasons are numerous and complex, but they include a failure to understand the mechanism(s) of preterm labour, the multitude of different causes, the difficulty in diagnosis and the problems of outcome measurement in clinical trials. Recently, an oxytocin antagonist (atosiban) has been introduced into clinical practice in Europe. Although it may be an effective tocolytic, a beneficial effect on perinatal outcome has not been demonstrated. Atosiban has an effect at both oxytocin and vasopressin (V1a) receptors, which (assuming efficacy) raises the question as to whether oxytocin or vasopressin V1a antagonism is required for tocolysis. This review examines the rationale for tocolysis in preterm labour, the evidence for administration of atosiban and the role for oxytocin, vasopressin and their receptors in the onset of labour.
Responses to Stimulation of Coronary and Carotid Baroreceptors and the Coronary Chemoreflex at Different Ventricular Distending Pressures in Anaesthetised Dogs
Authors: Wright C. I. , Drinkhill M. J. , Hainsworth R.
Published: February 2003

Stimulation of left ventricular mechanoreceptors was believed not only to exert important effects on the circulation, but also to influence the responses to baroreceptor reflexes. However, most previous work is flawed due to inadequate localisation of stimuli to specific reflexogenic areas. In this study, we applied a discrete stimulus to left ventricular mechanoreceptors to examine other reflexes known to effect the circulation. Dogs were anaesthetised, artificially ventilated and a cardiopulmonary bypass established. The pressure distending the left ventricle was controlled through an apical cannula with the aortic valve obstructed by a balloon. Changes in ventricular systolic and end‐diastolic pressure had only a small effect on vascular resistance, assessed as perfusion pressure in the systemic circulation (flow constant). Responses to changes in carotid or coronary pressure or to stimulation of chemosensitive afferents by injecting veratridine into the coronary circulation were always much larger. Responses to stimulation of these reflexes were little affected by the level of stimulus to the ventricular receptors. These experiments confirm that responses to stimulation of ventricular mechanoreceptors are very small and show that they remain small at different levels of input to other baroreceptive regions. There was no evidence of interaction between ventricular mechanoreceptor reflexes and carotid or coronary baroreceptors or ventricular chemosensitive reflexes.
Effects of Carbonic Anhydrase Inhibition on the Responsiveness of Laryngeal Receptors in Cats to CO2
Authors: Wang Z.‐H. , Bradford A. , O'Regan R. G.
Published: February 2003

The effects of carbonic anhydrase inhibition on the responsiveness to CO2 of pressure‐sensitive laryngeal receptors were examined in anaesthetised, paralysed cats. Laryngeal CO2‐sensitive receptors from the superior laryngeal nerve were selected by their responsiveness to intralaryngeal pressure and to perfusion of solution equilibrated with 9% CO2. The carbonic anhydrase inhibitor, methazolamide, when given intralaryngeally at 10−4 M, diminished or abolished the responses to the CO2‐equilibrated solution in four of six pressure‐sensitive receptors. Histochemical staining for carbonic anhydrase activity showed that the larynges perfused with methazolamide had diminished carbonic anhydrase activity, especially on the superficial layers of surface epithelium. Compared to untreated controls, when given intravenously (50 mg kg−1) methazolamide diminished or abolished the responses to CO2 of five of the six fibres studied. Histochemical staining of these larynges showed no carbonic anhydrase reactivity at the sites of laryngeal receptors. These results suggest that the responses to CO2 of laryngeal pressure‐sensitive receptors are dependent on the presence of carbonic anhydrase. Inhibition of laryngeal receptor carbonic anhydrase activity by methazolamide is more reliably achieved by systemic rather than by luminal administration.
Right Ventricular Distension Alters Monophasic Action Potential Duration During Pulmonary Arterial Occlusion in Anaesthetised Lambs: Evidence for Arrhythmogenic Right Ventricular Mechanoelectrical Feedback
Authors: Greve Gottfried , Lab Max J. , Chen Ruoli , Barron David , White Paul A. , Redington Andrew N. , Penny Daniel J.
Published: February 2003

Abnormal loading and distension of the right ventricle may induce arrhythmia through the process of mechanoelectrical feedback. Nonetheless, the electrophysiological effects of right ventricular distension are ill‐defined and the mechanisms which underpin mechanoelectrical feedback in the right ventricle are unknown. We examined the effects of changes in right ventricular load (complete occlusion of both caval veins or the main pulmonary artery) in 14 anaesthetised lambs, instrumented with right ventricular surface electrodes and strain gauges for recording monophasic action potential and segment length, and an integrated conductance and micromanometer‐tipped catheter for measurement of right ventricular pressure and volume. Caval occlusion did not alter right ventricular segment length and monophasic action potential duration. By contrast, pulmonary arterial occlusion increased the segment length and decreased the monophasic action potential duration at 25, 50 and 70% repolarisation by 29 ± 6, 22 ± 4 and 17 ± 3 ms, respectively (all P < 0.01). Of the 42 pulmonary arterial occlusions, 38 were associated with early afterdepolarisations (EADs) which increased progressively in magnitude as the occlusion was maintained until, in 32, overt arrhythmia was observed. By contrast, none of the four occlusions in which EADs were not observed resulted in arrhythmia. As a result, the proportion of occlusions which resulted in arrhythmia were greater in those associated with EADs than in those which were not (P = 0.002). Right ventricular distension alters the pattern of repolarisation, precipitates early afterdepolarisations and results in a variety of ventricular arrhythmia, including ventricular tachycardia.
Interstitial Adenosine Concentration in Rat Red or White Skeletal Muscle During Systemic Hypoxia or Contractions
Authors: Lo S. M. , Mo F. M. , Ballard H. J.
Published: February 2003

Interstitial adenosine concentrations in red soleus (SL) or white extensor digitorum longus (EDL) muscles of anaesthetised rats were determined using microdialysis and HPLC. Systemic hypoxia was induced by ventilating the animals with 10% oxygen in nitrogen for 15 min: arterial PO2 decreased from 111.8 ± 10.9 to 42.2 ± 4.3 mmHg (n = 4; P < 0.01) and mean systemic arterial blood pressure from 97.6 ± 4.9 to 59.0 ± 3.6 mmHg (n = 22; P < 0.001). The interstitial adenosine concentration was not significantly changed from its control values of 294 ± 44 nM (n = 20) in EDL and 302 ± 36 nM (n = 20) in SL during hypoxia or the recovery period. The interstitial lactate concentration did not change in the early part of the hypoxia but increased from 1.0 ± 0.2 to 1.4 ± 0.3 mM (n = 6; P < 0.05) in SL and from 2.0 ± 0.4 to 2.4 ± 0.4 mM (n = 6; P < 0.05) in EDL during the later part of the hypoxia, and remained elevated in the recovery period. Muscle contractions (2 Hz for 15 min) produced a transient increase in the interstitial adenosine concentration of SL from 150 ± 35 to 244 ± 75 nM (n = 10; P < 0.05) during the first 5 min of stimulation. In EDL the interstitial adenosine concentration increased from 145 ± 50 to 435 ± 144 nM (n = 10; P < 0.05) in the later part of the contraction and remained elevated in the early part of the recovery period. These data suggest that: (i) in systemic hypoxia adenosine does not appear in the interstitial space, which rules out its release from skeletal muscle, although it may be formed by the vascular tissues in this condition; (ii) adenosine is formed in the interstitial space of skeletal muscle during muscle contractions; (iii) there is slow clearance of adenosine from the interstitial space of white muscle, perhaps due to the low vascularity of the tissue.
Corticospinal Inhibition Appears Normal in Patients with Chronic Fatigue Syndrome
Authors: Zaman Rashid , Puri Basant K. , Main Janice , Nowicky Alex V. , Davey Nick J.
Published: February 2003

The pathogenesis of chronic fatigue syndrome (CFS) remains unknown. Thresholds and latencies of motor evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) are normal but intracortical inhibition has not been investigated. Eleven patients with CFS were compared with 11 control subjects. Each patient completed a questionnaire using visual analogue indices of pain, fatigue, anxiety and depression. Subjects released a button to initiate simple (SRTs) and choice reaction time (CRTs) tasks; for each task, movement times were measured between release of the initiation button and depression of a second button 15 cm away. Subjects held a 10% maximum voluntary contraction in the thenar muscles of their dominant hand while TMS was applied to the motor cortex; the duration and extent of inhibition of surface electromyographic (EMG) activity were assessed at stimulus strengths above and below the threshold for MEPs. Patients had significantly (P < 0.05) higher mean indices of fatigue than of pain, anxiety or depression. Mean (± S.E.M.) SRTs (but not CRTs) were longer in patients (309 ± 45 ms) than in controls (218 ± 9 ms). Movement times were longer in patients for both SRTs and CRTs. TMS thresholds, expressed as a percentage of the maximum stimulator output, were not significantly (P > 0.05) different in both groups for both MEPs (patients, 34 ± 3%; controls, 36 ± 3%) and inhibition of voluntary contraction (patients, 29 ± 2%; controls, 34 ± 4%). The duration and extent of inhibition did not differ significantly between groups at any stimulus strength. The pattern of change in duration and extent of inhibition with increasing stimulus intensity was no different in the two groups. The duration and extent of corticospinal inhibition in patients with CFS did not differ from controls, adding further evidence to the notion that the feeling of fatigue and the slowness of movement seen in CFS is not manifest in corticospinal output pathways.
Actions of Arachidonic Acid on Contractions and Associated Electrical Activity in Guinea‐Pig Isolated Ventricular Myocytes
Authors: Mamas M. A. , Terrar D. A.
Published: February 2003

The actions of arachidonic acid (AA) were investigated in guinea‐pig isolated ventricular myocytes. Exposure of myocytes to 10 μM AA reduced the amplitude of contractions and calcium transients accompanying action potentials at a frequency of 1 Hz. AA (10 μM) also reduced the amplitude of calcium currents recorded under voltage‐clamp conditions. The suppression of contraction by AA was not prevented by either 10 μM trihydroindomethicin (to inhibit cyclo‐oxygenase) or 10 μM ETYA (5,8,11,14‐eicosatetraynoic acid, to inhibit AA metabolising enzymes), showing that the actions of AA appeared not to be mediated by these metabolites. The reduction of contraction by 10 μM AA was also not prevented by the protein kinase C inhibitor, Ro31‐8220 (1 μM), showing that this pathway appeared not to be required for the observed effect. Direct effects of AA may be involved. A further action of 10 μM AA was to suppress spontaneous electrical activity induced by either the β‐adrenergic agonist isoprenaline or the Na+ pump inhibitor, ouabain. This effect of AA on spontaneous activity might be associated with the observed reduction of calcium entry through L‐type calcium channels, although additional effects of AA on calcium release from the sarcoplasmic reticulum might also be involved.
Reflex‐Elicited Increases in Female Rat Parotid Protein Synthesis Involving Parasympathetic Non‐Adrenergic, Non‐Cholinergic Mechanisms
Authors: Ekström J. , Reinhold A.‐C.
Published: February 2003

Normal rats or rats parasympathetically denervated on one side by cutting the auriculo‐temporal nerve were maintained on a liquid diet for 1 week. After fasting overnight, experimental rats were then offered hard, pelleted food over a period of 2 h, while unfed animals served as controls. The reflex‐induced increase in the [3H]leucine incorporation into trichloroacetic acid‐insoluble material of the parotid glands following intake of the food in the presence of the muscarinic blocker atropine and α‐ and β‐adrenoceptor antagonists was greater (104%) than in the absence of the blockers (75%) in normal rats. The picture was the same when the innervated glands of rats subjected to unilateral parasympathetic denervation were examined. In this case, the protein synthesis increased by 108% in the presence of the blockers and by 63% in their absence. Analysis of the parasympathetically denervated and contralateral innervated glands revealed no support for a cholinergic or adrenergic contribution to this response. The increase in protein synthesis in the innervated glands was 86% in the rats treated with atropine, whilst it was 76% in those treated with α‐ and β‐adrenoceptor antagonists. The protein synthesis in the denervated glands increased by 57% in the absence of receptor blockade. Neither atropine (51%), nor a‐ and b‐adrenoceptor antagonists (52%), nor a combination of the three blockers (55%) affected the response of the denervated glands. A large part of the response in the presence of the traditional autonomic receptor blockers was thus dependent on the parasympathetic auriculo‐temporal nerve. Under natural feeding conditions, the parasympathetic non‐adrenergic, non‐cholinergic (NANC) mechanisms are likely to contribute to the synthesis of secretory proteins.
The Presence of NHE1 and NHE3 Na+‐H+ Exchangers and an Apical cAMP‐Independent Cl− Channel Indicate that Both Absorptive and Secretory Functions are Present in Calf Gall Bladder Epithelium
Authors: Bazzini Claudia , Bottà Guido , Meyer Giuliano , Baroni Maurizio David , Paulmichl Markus
Published: February 2003

We investigated the transport systems that can sustain Na+ and Cl− movements across bovine gall bladder epithelium, focusing on the Na+‐H+ exchanger (NHE) family and chloride conductive pathways. Experiments conducted using the fluorescent probe acridine orange (AO) with brush‐border membrane vesicles (BBMV) or vesicles obtained from the total epithelium (EMV) demonstrated the presence of a Na+‐H+ exchange in both preparations. The use of specific inhibitors indicated the presence of an apical NHE3 exchanger and a NHE1 isoform which should reside in the basolateral membrane. Using reverse transcriptase (RT) PCR, we identified cDNA fragments corresponding to the NHE1, NHE3, Cl−‐HCO3− (AE2a) transporters and to the CFTR channel. Using the patch‐clamp technique, we investigated Cl− conductances on cultured epithelial cells. We found a 5 pS Cl− channel with a voltage‐independent open probability, insensitive to stilbenes (SITS), Zn2+ and cAMP. The results suggest that absorption and secretion coexist in calf gall bladder epithelium. A Na+‐H+‐Cl−‐HCO3− double exchange may, at least partially, sustain the absorptive function, and a Cl− apical conductive pathway may be involved in secretion. The conductance we observed does not seem to be cAMP‐regulated, unlike other mammalian gall bladders.
Combined Oral Contraceptives do not Influence Post‐Exercise Hypotension in Women
Authors: Birch Karen , Cable Nigel , George Keith
Published: February 2003

The aim of the present study was to examine the pattern of cardiovascular recovery from exercise in 15 women (age, 20.3 ± 1.4 years; body mass, 61.5 ± 4.3 kg) across two phases of oral contraceptive (OC) use: 21 days of consumption and 7 days of withdrawal. Cardiovascular recovery was measured in the supine position for 60 min following 30 min of exercise at 60% maximal rate of oxygen consumption (V̇O2,max). Central and peripheral haemodynamics were assessed during consumption and withdrawal of the OC pill using occlusion plethysmography, Doppler flowmetry and echocardiography. Significant hypotension occurred following exercise (P < 0.05), returning to baseline values after 60 min. The peak hypotension occurred 5 min into recovery. Cardiac output and heart rate were elevated for 60 min following exercise (P < 0.05), whilst stroke volume remained at baseline values. Heart rate was greater throughout recovery during consumption compared to withdrawal (P < 0.05); however, although there was a trend for greater responses during consumption, phase of OC use did not affect the other central cardiovascular variables (P > 0.05). Post‐exercise blood flow parameters were not significantly affected by exercise or OC phase; however, calf blood flow was greater, and resistance to flow lower during consumption (P > 0.05). The pattern of post‐exercise fluctuations in cardiovascular parameters may differ from those seen in men, whilst oestrogen variation may influence research findings.
Electroreception inG. carapo: detection of changes in waveform of the electrosensory signals
Authors: Aguilera Pedro A. , Caputi Angel A.
Published: February 2003

Electric fish evaluate the near environment by detecting changes in their self-generated electric organ discharge. To investigate impedance modulation of the self-generated electric field, this field was measured at the electrosensory fovea of Gymnotus carapo in the presence and absence of objects. Changes in local fields provoked by resistive objects were predicted by the change in total energy. Objects with capacitive impedance generated large variations in the relative importance of the different waveform components of the electric organ discharge. We tested the hypothesis that fish discriminate changes in waveform as well as increases in total energy using the novelty response, which is a behavioural response consisting of a transient acceleration of EOD frequency that can follow a change in object impedance. For resistive loads, the amplitude of novelty responses was well predicted by the increase in total energy. For complex loads, the amplitude of novelty responses was correlated not only with increases in total energy but also with waveform changes, consisting of reductions in the early slow negative wave and increases in the late sharp negative wave. The total energy and waveform effects appeared to be additive. These results indicate that G. carapo discriminates complex impedance based on an evaluation of different waveform parameters.
Melatonin effect on renal oxidative stress under constant light exposure
Authors: Túnez Isaac , del Carmen Muñoz María , Feijoo Montserrat , Valdelvira Manuel E. , Rafael Muñoz‐Castañeda Juan , Montilla Pedro
Published: February 2003

Recently, numerous studies have shown antioxidant actions of melatonin. Melatonin at both physiological and pharmacological levels stimulates glutathione peroxidase, glutathione reductase and superoxide dismutase activities in the brains of rats and chickens. This study was designed to evaluate the effect of melatonin on nephropathy and oxidative stress under constant light exposure. Nephropathy was induced by adriamycin administered in a single dose (25 mg kg−1 b.w., i.p.). Melatonin was injected i.p. (1000 μg kg−1 b.w./day). Malondialdehyde, reduced glutathione, glutathione peroxidase, glutathione reductase, glutathione transferase, catalase and superoxide dismutase were determined in kidney. Urea, creatinine and total proteins in plasma and proteinuria were evaluated and melatonin was determined. Results show a decrease in melatonin levels. Similar effects occurred with the antioxidant enzyme activities and reduced glutathione. Likewise, adriamycin and constant light induced significant enhancement of malondialdehyde. All changes induced both by adriamycin and constant light were reverted to normal by melatonin administration. Constant light exposure was associated with an increase in oxidative stress and nephropathy induced by adriamycin. Treatment with melatonin decreased lipid peroxides, and permitted a recovery of reduced glutathione, scavenger enzyme activity and parameters of renal function. Copyright © 2002 John Wiley & Sons, Ltd.
Bone formation in CaP‐coated and noncoated titanium fiber mesh
Authors: Vehof J. W. M. , van den Dolder J. , de Ruijter J. E. , Spauwen P. H. M. , Jansen J. A.
Published: February 2003

The osteogenic activity of calcium phosphate (CaP)‐coated and noncoated porous titanium (Ti) fiber mesh loaded with cultured syngeneic osteogenic cells after prolonged in situ culturing was compared in a syngeneic rat ectopic assay model. Rat bone marrow (RBM) cells were loaded onto the CaP‐coated and noncoated Ti scaffolds using either a droplet or a suspension loading method. After loading, the RBM cells were cultured for 8 days in vitro. Thereafter, implants were subcutaneously placed in 39 syngeneic rats. The rats were euthanized and the implants retrieved at 2, 4, and 8 weeks postoperatively. Further, in the 8 week group fluorochrome bone markers were injected at 2, 4, and 6 weeks. Histological analysis demonstrated that only the CaP‐coated meshes supported bone formation. The amount of newly formed bone varied between single and multiple spheres to filling a significant part of the mesh porosity. In the newly formed bone, osteocytes embedded in a mineralized matrix could be observed clearly. On the other hand, in the noncoated titanium implants, abundant deposition of calcium‐containing material was seen. This deposit lacked a bonelike tissue organization. Further analysis revealed that the cell‐loading method did not influence the final amount of bone formation. In CaP‐coated implants the accumulation sequence of the fluorochrome markers showed that bone formation started on the mesh fibers. In conclusion, our results prove that the combination of a thin CaP coating, Ti‐mesh, and RBM cells can indeed generate ectopic bone formation after prolonged in vitro culturing. No effect of the loading method was observed on the final amount of bone. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 64A: 417–426, 2003
Proinflammatory phenotype of endothelial cells after coculture with biomaterial‐treated blood cells
Authors: Lester Elizabeth A. , Babensee Julia E.
Published: February 2003

An understanding of the endothelial cell/blood/biomaterial interactions is central to advancing the success of cardiovascular devices that continue to fail because of the lack of nonthrombogenic biomaterials. A simplified endothelial cell/blood cell/biomaterial static model was used to assess these interactions. Human whole blood or isolated blood cells (mononuclear cells, neutrophils, platelets) were pretreated with biomaterial beads with different surface chemistries: polystyrene (PS), PS beads grafted with 3‐kDa polyethylene glycol (PEG) with either hydroxyl (PS‐PEG‐OH) or amine (PS‐PEG‐NH2) terminal groups at bead concentrations of 5.4 or 54 × 104 beads/mL. Leukocyte and platelet activation and microparticle formation was assessed using flow cytometry. Biomaterial‐activated whole blood or isolated cells or mononuclear cell fractions were applied to human umbilical cord endothelial cells (HUVEC) for static coculture, and the resultant proinflammatory HUVEC phenotype was characterized. ICAM‐1 and E‐selectin expression on HUVEC was increased after 4‐h static coculture with biomaterial‐treated human whole blood or mononuclear cells but not neutrophils or platelets. VCAM‐1 expression on HUVEC was similarly increased after 24‐h static coculture but not after 4 h of coculture. Increased concentrations of cytokines, IL‐6, IL‐8, and MCP‐1, were detected in the supernatant of cocultures of HUVEC with biomaterial‐treated whole blood or mononuclear cells but not neutrophils or platelets, compared with the media control. After 24 h, cytokine release was significantly increased for both IL‐8 and MCP‐1 but not IL‐6 above concentrations after 4 h of coculture. Neither the cell adhesion molecule (CAM) expression nor cytokine release induced by coculture with biomaterial‐treated whole blood or isolated cells was dependent on either material surface chemistry or material surface area. The changes in HUVEC CAM expression and cytokine release induced by biomaterial‐treated mononuclear cells can be attributed predominantly to adherent cells on beads and nonadherent bulk cells with moderate regulation by the soluble supernatant; however, mononuclear cell‐derived microparticles induced no significant changes in CAM expression or cytokine release after static coculture with HUVEC. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 64A: 397–410, 2003
RGTA modulates the healing pattern of a defect in a monolayer of osteoblastic cells by acting on both proliferation and migration
Authors: Blanquaert Frédéric , Carpentier Gilles , Morvan Frédéric , Caruelle Jean‐Pierre , Barritault Denis , Tardieu Michèle
Published: February 2003

A family of heparan‐like polymers, RGTAs, was shown to promote repair of various tissues. Like heparin and heparan‐sulfates, RGTAs potentiate in vitro the biological activities of heparin‐binding growth factors (HBGFs) and protect them against proteolytic degradation. It was postulated that RGTAs stimulate bone healing by interacting with HBGFs released in the wound site and, subsequently, by promoting the proliferation of cells implicated in this process. In a previous report, we examined how RGTA can modulate the proliferation of MC3T3‐E1 osteoblastic cells. To further complete this study and to support this hypothesis, we developed an in vitro model of bone repair and examined the effects of RGTA alone or in association with FGF2, BMP‐2, and TGF‐β1 which are representative of HBGFs known to stimulate bone repair. The model consisted of a 6‐mm reproducible defect created on a MC3T3‐E1 cell monolayer. In the presence of the different products added to the medium, the process of wound repair was measured through the filling of the acellular defect. We show that in 8 days, RGTA slightly inhibits repair alone compared to the control (2% FBS), that it inhibits the mitogenic effect of FGF2, and that it amplifies the inhibitory effect of BMP‐2 and TGF‐β1. Repair was realized by an association of cell migration and cell proliferation mechanisms. To determine the part played by each process, DNA synthesis was evaluated for cell proliferation using an immunodetection technique [to measure incorporation of 5‐bromo‐2‐deoxyuridine (BrdU)], coupled with a computer‐assisted image analysis. The results show that the presence of RGTA (1) amplified the number of labeled nuclei compared to the control, (2) added to FGF2 or TGF‐β1, it reduced the number of labeled nuclei compared to FGF2 or TGF‐β1 alone, and (3) in the presence of BMP‐2, it amplified the number of labeled nuclei compared to BMP‐2 alone. Proper interpretation of these data requires a better understanding of the mechanism of action of RGTA on bone healing. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 64A: 525–532, 2003
Who plays the client? Collaborating with theater departments to enhance clinical psychology role‐play training exercises
Authors: Pomerantz Andrew M.
Published: February 2003

This article offers a description of a student‐active method of teaching clinical psychology applications, such as interviewing and psychotherapy, that involves collaboration between psychology and theater departments. Clinical psychology instructors recruit theater students to play the client roles in live dyads with the instructors or other students. These dyads may take place during or outside of class and may be videotaped for use in other educational settings. Practical and logistical issues are discussed, and empirical data are presented to demonstrate the effectiveness of this method. © 2003 Wiley Periodicals, Inc. J Clin Psychol 59: 363–368, 2003.