bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heart Valve Replacement Surgery: Past, Present And Future
Authors: Starr Albert , Fessler Cindy L , Grunkemeier Gary , He Guo‐Wei 
Published: March 2003

SUMMARY1. The present review covers the historical and present role of valvular surgery in treating heart disease and speculates what the future may be in this very important field of cardiac surgery.2. One of the important elements of tissue valve replacement is durability and how to analyse the valves mathematically, so that the projected durability could be described from the observed period to an extended period. We found that the Weibull distribution is a very good mathematical method of describing the deterioration of tissue valves.3. We also can see a very marked difference among different pericardial valves. The Carpentier–Edwards pericardial valve has tremendous durability compared with the previous generation of pericardial valves, namely the Ionescu–Shiley.4. The incidence of structural valve deterioration varies according to the age of the patient at the time of implant. A very important feature to analyse in making a clinical decision with regard to the type of valve to implant is the age of the patient at the time of implantation, because this determines their long‐term survival.5. Another very important feature of valve replacement is the problem of valve thrombosis. This was the problem that we encountered in experimental animals and why it is so difficult to obtain a long‐term survivor with mechanical valve replacement in dogs. Now, in humans, the incidence of thrombosis of these artificial valves is extremely low.6. Another important feature of valve replacement is the incidence of late thromboembolism (TE). Differences in reports using the same valve are greater than differences between different prostheses and the average is approximately 1.5–2%/year incidence of TE.7. We can conclude from this review that there has been significant progress in diminishing operative mortality and enhanced long‐term survival following valve replacement over the past four decades. Increased durability of tissue valves has now become apparent, from the earliest application to the current time with glutaraldehyde‐preserved pericardial valves. The late complication rates are approximately the same with all valve types, except that there is a dimunition in the possibility for valve thrombosis for tissue valves versus mechanical valves. Finally, anticoagulation continues to be required for mechanical valve replacement and we still require more durable tissue valves and freedom from anticoagulation for mechanical valves.
Cholinergic Modulation Of Respiratory Brain‐Stem Neurons And Its Function In Sleep–Wake State Determination
Authors: Bellingham Mark C , Funk Greg D 
Published: March 2003

SUMMARY1. Shifts in behavioural state are controlled by reciprocal changes in discharge of cholinergic and aminergic groups of brain‐stem/pontine neurons. During rapid eye movement (REM) sleep, cholinergic neurons are most active and aminergic neurons are least active.2. Significant changes occur in the central control of breathing during REM sleep; respiration rate increases in frequency and variability, brain‐stem respiratory neuron discharge is generally enhanced and the outputs of some respiratory motor neuron pools are depressed.3. Hypoglossal motor neurons (HM) control tongue movement and their depression during REM sleep has been implicated in obstructive sleep apnoea. The cellular basis of HM depression has been investigated in vitro and may be due to enhanced activation of cholinergic receptors or decreased activation of aminergic receptors.4. In vitro preparations that show respiratory rhythmogenesis possess advantages for the investigation of the neurochemical basis of state‐dependent changes in respiration. Cholinergic changes in respiratory modulation of HM recorded in rhythmic brain‐stem slices from mice depend on the site of activation of cholinergic receptors.
Effect Of Hypoxia On Respiratory Activity In The Foetus
Authors: Walker David W , Lee Brenda , Nitsos Ilias 
Published: March 2003

SUMMARY1. Breathing movements stop soon after the induction of hypoxia in foetal animals, a response attributed to the active inhibition of the respiratory centres. Separate studies using punctate lesions have identified lateral pontine and thalamic sites in foetal sheep from which respiratory inhibition may arise, but whether either of these loci are actually oxygen sensitive or whether they receive input from other regions responsive to hypoxia, has not been established.2. FOS immunocytochemistry was used to identify neuronal pools activated by hypoxia in the brain of late‐gestation foetal and newborn sheep. FOS‐positive cells were found in the pons in regions corresponding to the medial parabrachial and Kolliker–Fuse nuclei and were shown to be catecholaminergic. Neurons in this pontine region were also activated by the piperizine drug almitrine, which, like hypoxia, inhibits respiratory output in the foetus but is a respiratory stimulant in the newborn and adult. Because these pontine neurons do not express FOS protein after challenge with hypoxia or almitrine in the newborn lamb, we argue that they are crucial to the hypoxic inhibition of respiratory activity in foetal life.3. The role of the placenta in determining these foetal responses and how this may change at birth is discussed.
Effect Of Dopamine Agonists And Antagonists On The Lorazepam Withdrawal Syndrome In Rats
Authors: Nath C , Saxena Rc , Gupta Mb 
Published: March 2003

SUMMARY1. The effects of dopaminergic agonists and antagonists were investigated on withdrawal signs in lorazepam‐dependent rats. Physical dependence was developed by giving lorazepam admixed with food in the following dose schedules: 10 × 4, 20 × 4, 40 × 4, 80 × 4 and 120 × 7 mg/kg, daily for x days.2. The parameters observed during the periods of administration of lorazepam and after its withdrawal were spontaneous locomotor activity (SLA), reaction time to pain, foot shock aggression (FSA) and audiogenic seizures.3. During the withdrawal period, rats were divided into groups of 10 rats each. One group did not receive any drug and served as the control withdrawal groups. Three other groups received, separately, one of the following dopamimetic drugs: (i) 200 mg/kg per day, i.m., L‐dihydroxyphenylalanine (DOPA; +50 mg/kg per day, i.m., carbidopa); (ii) 2 mg/kg per day, i.m., amphetamine; or (iii) 1 mg/kg per day, i.m., apomorphine. The remaining groups received one of the following dopamine antagonists: (i) 0.1 mg/kg per day, i.m., SCH 23390; (ii) 0.5 mg/kg per day, i.m., haloperidol; (iii) 0.5 mg/kg per day, i.m., centbutindol; and (iv) either 1 or 20 mg/kg per day, i.m., clozapine.4. The withdrawal signs observed in the control group were hyperkinesia, hyperaggression and audiogenic seizures.5. L‐Dihydroxyphenylalanine (+ carbidopa), amphetamine and apomorphine potentiated hyperaggression and audiogenic seizures. The dopamine D2 receptor antagonists haloperidol, centbutindol and clozapine (at 20 mg/kg, i.m.) blocked all withdrawal signs. The D1 receptor antagonist SCH 23390 inhibited hyperkinesia and hyperaggression. The D4 receptor antagonist clozapine (at 1 mg/kg, i.m.) had no effect on any of the withdrawal signs.6. It may be concluded that dopamine D2 receptors exert a dominant facilitatory influence, with partial contribution of D1 receptors, on the benzodiazepine withdrawal syndrome.
Regulation Of Sodium, Calcium And Vitamin D Metabolism In Dahl Rats On A High‐Salt/Low‐Potassium Diet: Genetic And Neural Influences
Authors: Wu Xiaoyan , Vieth Reinhold , Milojevic Susan , Sonnenberg Harald , Melo Luis G 
Published: March 2003

SUMMARY1. A dietary combination of high salt and low potassium (HSLK) exacerbates hypertension in Dahl salt‐sensitive (DS) rats and renders previously normotensive Dahl salt‐resistant (DR) rats hypertensive. In both strains, the severity of hypertension correlates with urinary calcium loss. However, the magnitude of excretory calcium losses is significantly greater in DS rats and is potentiated by chemical sympathectomy in both strains.2. We hypothesized that a defect in vitamin D metabolism may underlie the observed strain‐dependent differences in calcium balance.3. Arterial blood pressure (ABP), water and mineral bal‐ ance and serum concentrations of 1,25‐dihydroxyvitamin D3 (1,25(OH)2 D3) and 25‐hydroxyvitamin D3 (25(OH)D3) were measured in intact and chemically sympathectomized (6‐hydroxydopamine; 6‐OHDA) DS and DR rats after 8 weeks on a HSLK diet.4. Chronic ingestion of this diet resulted in marked and moderate levels of hypertension in DS and DR rats, respectively. The hypertension was abated and eliminated by 6‐OHDA in the DS and DR strains, respectively. Independent of treatment, DS rats had significantly higher urinary excretion of calcium and reduced intestinal absorption of the ion compared with DR rats. The DS rats had significantly higher serum levels of 1,25(OH)2 D3 and markedly lower serum levels of 25(OH)D3 than DR rats. Chemical sympathectomy tended to increase 1,25(OH)2 D3 and to decrease 25(OH)D3 levels in both strains.5. These data indicate a genetic difference in vitamin D metabolism between DS and DR rats. The abnormally elevated levels of 1,25(OH)2 D3 in DS rats may be an appropriate compensatory response to excessive excretory calcium loss and reduced target organ sensitivity to the hormone and may, maladaptively, directly contribute to hypertension, by stimulating vascular smooth muscle contractility.
Antihyperglycaemic And Anti‐Oxidant Properties Of Andrographis Paniculata In Normal And Diabetic Rats
Authors: Zhang Xiang‐Fan , Tan Benny Kwong‐Huat 
Published: March 2003

SUMMARY1. Oxidative stress is believed to be a pathogenetic factor in the development of diabetic complications. In the present study, we investigated the ethanolic extract of the aerial parts of Andrographis paniculata for antihyperglycaemic and anti‐ oxidant effects in normal and streptozotocin‐induced type I diabetic rats.2. Normal and diabetic rats were randomly divided into groups and treated orally by gavage with vehicle (distilled water), metformin (500 mg/kg bodyweight) or the extract (400 mg/kg bodyweight), twice a day for 14 days.3. At the end of the 14 day period, the extract, like metformin, significantly increased bodyweight (P < 0.01) and reduced fasting serum glucose in diabetic rats (P < 0.001) when compared with vehicle, but had no effect on bodyweight and serum glucose in normal rats. Levels of liver and kidney thiobarbituric acid‐ reactive substances (TBARS) were significantly increased (P < 0.0001, P < 0.01, respectively), while liver glutathione (GSH) concentrations were significantly decreased (P < 0.005) in vehicle‐treated diabetic rats. Liver and kidney TBARS levels were significantly lower (P < 0.0001, P < 0.005, respectively), whereas liver GSH concentrations were significantly higher (P < 0.05) in extract‐ and metformin‐treated diabetic rats compared with vehicle‐treated diabetic rats. Andrographis paniculata significantly decreased kidney TBARS level (P < 0.005) in normal rats. Hepatic superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH‐Px) activities were significantly lower in vehicle‐treated diabetic rats compared with vehicle‐treated normal rats. The extract, as well as metformin, significantly increased the activity of SOD and CAT, but had no significant effect on GSH‐Px activity in diabetic rats. The extract and metformin did not produce significant changes in the activity of these anti‐oxidant enzymes in normal rats.4. Our results show that oxidative stress is evident in streptozotocin‐diabetic rats and indicate that the ethanolic extract of A. paniculata not only possesses an antihyperglycaemic property, but may also reduce oxidative stress in diabetic rats.
Eicosapentaenoic Acid Stimulates Nitric Oxide Production And Decreases Cardiac Noradrenaline In Diabetic Rats
Authors: Nishimura Masato , Nanbu Akira , Komori Toshiaki , Ohtsuka Ken , Takahashi Hakuo , Yoshimura Manabu 
Published: March 2003

SUMMARY1. The aim of the present study was to investigate whether long‐term oral administration of eicosapentaenoic acid increases nitric oxide (NO) production and affects cardiac sympathetic activity in rats with diabetes mellitus.2. We measured changes in urinary excretion of NO3–, a stable NO metabolite, and cardiac noradrenaline (NA) concentrations in non‐diabetic rats and streptozotocin‐induced diabetic rats treated with either ethyl icosapentate (EPA‐E; 100 mg/kg per day; n = 10), a purified ethyl esterification product of eicosapentaenoic acid, or vehicle (distilled water; n = 10) for 6 weeks. The effects of NG‐nitro‐
L‐arginine (
L‐NNA), a NO synthase inhibitor, on urinary NO3– excretion and cardiac NA concentrations were also investigated in diabetic rats treated with EPA‐E.3. Urinary NO3– excretion was higher at weeks 5 and 6 in diabetic rats treated with EPA‐E than in diabetic rats treated with vehicle (week 5: 120±8 vs 51±11 μmol/g per day, respectively (P < 0.01); week 6: 279±83 vs 73±9 μmol/g per day, respectively (P < 0.01)). Cardiac NA concentrations were higher in diabetic rats than in non‐diabetic rats and were decreased in the left atrium and both ventricles in diabetic rats treated with EPA‐E compared with control. Systemic administration of
L‐NNA abolished the increase in urinary excretion of NO3– and the decrease in cardiac NA concentrations in diabetic rats treated with EPA‐E.4. Long‐term oral administration of EPA‐E may stimulate NO production and increased NO is likely to play a role in inhibiting enhanced cardiac sympathetic activity in diabetic rats.
Ammonia Response To Constant Exercise: Differences To The Lactate Response
Authors: Ogino Kazuhide , Kinugawa Toru , Osaki Shuichi , Kato Masahiko , Endoh Akihiro , Furuse Yoshiyuki , Uchida Kazuhiko , Shimoyama Masaki , Igawa Osamu , Hisatome Ichiro , Shigemasa Chiaki 
Published: March 2003

SUMMARY1. We evaluated the plasma ammonia response to constant exercise at different intensities. Ten healthy male volunteers were asked to perform constant exercise for 15 min at five different intensities: 80, 90, 100, 110 and 120% of their ventilatory threshold (VT). Blood concentrations of lactate, ammonia and hypoxanthine were measured during and after exercise.2. The concentration of lactate increased continuously during exercise intensities equivalent to 100, 110 and 120% VT. Plasma ammonia began to increase at 6 min exercise and continued increasing during exercise at all five exercise intensities. Plasma hypoxanthine levels also increased continuously during exercise at all exercise intensities; however, they peaked at 5–10 min after exercise. The response of plasma ammonia and hypoxanthine increased with increasing intensities of exercise.3. While the extent of the increase in lactate levels during exercise at 100, 110 and 120% VT was significantly higher than that at 80% VT, only the increase in ammonia and hypoxanthine levels at 120% VT were significantly higher than those at 80% VT.4. In conclusion, the plasma ammonia response to constant exercise differed to the lactate and ammonia responses to short‐term exhaustive exercise.
Genetically Targeted Calcium Sensors Enhance The Study Of Organelle Function In Living Cells
Authors: Petrou Steven , Bowser David N , Nicholls Robert A , Panchal Rekha G , Smart Megan L , Reilly Angela M , Williams David A 
Published: March 2003

SUMMARY1. Understanding the regulation of calcium (Ca2+), the most common of the mineral ions within the human body, has always been of extreme interest to physiologists. While the importance of Ca2+ in contributing to physiological events through regulation of levels has been significantly established, seldom is consideration given to the intricacies of this ion and its mechanics in producing such diverse physiological responses in different regions of the cell.2. The present review will summarize new methodologies used in our laboratories for the study of two major intracellular organelles, mitochondria and the nucleus. These techniques are based predominantly on the use of molecular biological approaches to both create and then target protein‐based sensor molecules to specific intracellular locations.3. The regulation of Ca2+ in the mitochondria and nucleus is of particular interest to us because of the central involvement of these organelles in: (i) cardiac cell responses during ischaemia/reperfusion; and (ii) the control of gene expression, respectively.
Effect Of Fentanyl On Baroreflex Control Of Circumflex Coronary Conductance
Authors: Moore Peter G , Quail Anthony W , Cottee David BF , McIlveen Stephen A , White Saxon W 
Published: March 2003

SUMMARY1. Fentanyl, a synthetic μ‐opioid receptor agonist, is the preferred induction and maintenance anaesthetic agent in cardiac surgery.2. Its actions on myocardial blood flow are poorly understood. There are reports of intra‐operative myocardial ischaemia. Its reported actions on cardiorespiratory control vary widely, but do involve hypertension, bradycardia and peripheral vasoconstriction.3. Accordingly, the postulate that fentanyl would cause coronary vasoconstriction and myocardial disadvantage was examined in awake dogs with a continuous wave Doppler flow probe mounted on the circumflex coronary artery.4. Continuous intravenous infusion of fentanyl citrate (550 ng/kg per min) raised plasma concentrations of fentanyl to 3.37 ng/mL in a linear fashion at 20 min. There was a fall in core temperature of 0.7°C and, although no apparent depression of ventilation or fall in arterial or coronary sinus PO2, there was a rise in PCO2 and H+ concentration. Some dogs salivated and panted transiently. Thus, fentanyl may reset temperature regulation in low doses but, at higher doses, is associated with metabolic acidosis.5. In sinus rhythm, the arterial pressure of the dogs fell slightly, then rose to 115% of resting control. Circumflex flow and conductance rose early, then conductance steadily declined to 83%. Heart rate fell, then rose before returning to pre‐infusion levels. The early circumflex coronary vasodilator effects, but not the later vasoconstrictor effects, were reduced in dogs with paced hearts.6. In dogs with paced hearts, a dose–effect study using 138, 275, 550 and 1100 ng/kg per min fentanyl suggested that, at low plasma concentrations of 1–2 ng/mL, vasodilatation does occur in both coronary and systemic circulations; however, at higher doses, intense coronary and systemic vasoconstriction supervenes.7. The dose–response effect of fentanyl on arterial baroreflex control of circumflex conductance was examined during the immediate 8 s circumflex vasodilator response to a step rise in aortic pressure caused by inflation of an intra‐aortic balloon. At low plasma concentrations of fentanyl, baroreflex control of circumflex conductance appears to be enhanced but, with increasing plasma concentrations of fentanyl, appears to be depressed.8. Therefore, the effects of fentanyl are dose dependent. At low plasma concentrations, left ventricular blood flow and its baroreflex control is enhanced but, at higher concentrations, it is depressed.
Effect Of Plasma Cholesterol On Red Blood Cell Oxygen Transport
Authors: Buchwald Henry , O'Dea Thomas J , Menchaca Hector J , Michalek Van N , Rohde Thomas D 
Published: March 2003

SUMMARY1. Oxygen (O2) transfer from the blood to tissues is a function of the red blood cell (RBC) O2 saturation (SO2), the plasma O2 content being negligible. Under conditions of increased tissue O2 demand, the SO2 of arterial blood does not change appreciably (97%); however, the SO2 of mixed venous blood, equal to that of the perfused tissues, can go as low as 20%.2. Tissue O2 availability is limited by the exposure time to a RBC, which decreases under conditions of maximum stress (< 1 s). If the O2 unloading time was to increase significantly, because of a decrease in the RBC diffusion constant or an increase in the RBC membrane thickness, the RBC O2 unloading time would exceed tissue (e.g. cardiac) transit time and O2 transfer would be impaired.3. Cholesterol constitutes the non‐polar, hydrophobic lipid of the enveloping layer of the RBC membrane. As the cholesterol content of the RBC increases, the fluidity of the membrane decreases and the lipid shell stiffens.4. Early studies demonstrated that high blood cholesterol concentrations were associated with reduced blood O2 transport; in essence, the haemoglobin dissociation curve was shifted to the left.5. Current investigations have shown that the cholesterol RBC membrane barrier to O2 diffusion delayed O2 entry into the RBC during saturation and delayed O2 release from the RBC during desaturation. In an analysis of 93 patients divided by their cholesterol concentration into five groups, the percentage change in blood O2 diffusion was inversely proportional to the cholesterol concentration.6. The RBC membrane cholesterol is in equilibrium with the plasma cholesterol concentration. It stands to reason that as the plasma cholesterol increases, the RBC membrane becomes impaired and O2 transport is reduced.7. The implications of this new perspective on O2 transport include the ability to increase tissue oxygenation by lowering plasma cholesterol.
Experimental Biology 2000 Symposium on Differential Control of Sympathetic Outflow NEUROANATOMICAL SPECIFICITY OF THE CIRCUITS CONTROLLING SYMPATHETIC OUTFLOW TO DIFFERENT TARGETS
Authors: Sved Alan F , Cano Georgina , Card J Patrick 
Published: March 2003

SUMMARY1. Despite the emerging framework that central neural pathways controlling the activity of the sympathetic nervous system are capable of producing highly selective responses, the specific neural pathways governing different sympathetic outflows are poorly understood.2. Anatomical studies suggest that five brain areas, namely the rostral ventrolateral medulla, the rostral ventromedial medulla, the caudal raphe nuclei, the region containing the A5 noradrenergic neurons and the paraventricular hypothalamic nucleus, provide dominant supraspinal innervation of sympathetic preganglionic neurons.3. The anatomical parcellation of different functions within and among these cell groups is uncertain. However, recent studies using transynaptic retrograde labelling of neural pathways connected to various sympathetic targets suggest that the circuits controlling these different targets may be partially distinct. Similarly, anatomical studies relying on stimulus‐evoked expression of immediate early genes, such as c‐fos, suggest that different sympathetic responses may be controlled by distinct neural circuits.4. Thus, although many similarities exist in the anatomical circuits innervating different sympathetic targets, possibly supporting the orchestration of global sympathetic responses, differences are also discernible.
Proceedings of the Australian Physiological and Pharmacological Society Symposium: The Hypothalamus LEPTIN AND THE REGULATION OF FOOD INTAKE AND THE NEUROENDOCRINE AXIS IN SHEEP
Authors: Clarke Iain J , Henry Belinda , Iqbal Javed , Goding James W 
Published: March 2003

SUMMARY1. Leptin is secreted by fat and acts on the brain.2. Central infusion of leptin reduces food intake but does not alter endocrine secretions in normally fed sheep.3. Leptin treatment can correct for altered hormonal secretion in fasted animals.4. Alterations in bodyweight (leptin status) affect the expression of a number of genes in the hypothalamus that are involved in the regulation of food intake and neuroendocrine function.5. Leptin receptors are found in both the hypothalamus and pituitary and direct action of leptin can be demonstrated on the somatotrophs in the pituitary.