Responses of the limpet, Cellana grata (Gould 1859), to hypo-osmotic stress during simulated tropical, monsoon rains

Although heat stress is often cited as the dominant physical stress on tropical shores, intertidal organisms in regions with monsoonal climates are also regularly exposed to prolonged periods of heavy rainfall. Such events are predicted to have adverse physiological effects on individuals and may result in mortality. In a series of laboratory experiments, the impact of simulated monsoonal rains was investigated on the patellid limpet, Cellana grata. Sub-lethal responses in terms of body water content, body fluid osmolality and heart rate were measured in two different size cohorts maintained on horizontal and vertical substrata. Limpets were unable to achieve any effective behavioural isolation, and exposure to either simulated rainfall or diluted seawater resulted in both large and small C. grata gaining water with subsequent dilution of mantle water and haemolymph osmolalities. With increased duration of rainfall, dilution of body fluids increased with little difference between individuals on horizontal and vertical surfaces. Body fluids generally showed proportional dilution during prolonged rain, but in some individuals there was evidence for regulation of the haemolymph relative to the mantle fluid. Overall, smaller limpets were more susceptible to prolonged rainfall than large animals in terms of swelling of soft tissues and detachment and also had higher heart rates than large limpets. Both cohorts reduced heart rates with prolonged rainfall, suggesting a degree of metabolic depression, especially on horizontal surfaces. In small limpets, no difference in heart rate was found with substratum orientation, whereas large limpets had elevated heart rates on vertical as compared to horizontal substrata, when exposed to either simulated rainfall or washed with dilute seawater. This may reflect the increased energetic costs required to maintain a relatively larger body on a vertical surface under stressful conditions. Monsoonal rainfall during emersion, and subsequent dilution of seawater, therefore, have sub-lethal physiological and possible lethal effects on intertidal limpets. This influence has been largely overlooked, but coupled with the possible synergistic effects of thermal stress, monsoon rains are likely to play an important role in community dynamics on tropical shores.     

Prolonged melatonin administration in 6-month-old Sprague-Dawley rats: metabolic alterations

The aim of this work was to evaluate the effect of prolonged melatonin administration on chosen metabolic and hormonal variables in male and female Sprague-Dawley rats. Melatonin was administered in tap water (4 microg/ml) daily from the 6th month of age. Rats were fed a standard type of diet ad libitum and were kept in a light regimen L:D--12:12h. The experiment was terminated after 12 weeks of melatonin administration. Melatonin decreased body mass during the whole experiment in females and from the 42nd day of the experiment in males. Relative heart muscle weight in females and absolute/relative thymus weight in males were increased after melatonin administration. Melatonin decreased glycaemia, heart muscle glycogen concentration in females and liver glycogen concentration in both sexes. Serum insulin concentration in males was decreased; serum corticosterone concentration was increased in both males and females. Serum triacylglycerol and heart muscle cholesterol concentration in females were decreased, however in males serum and heart muscle cholesterol concentration was increased. Liver phospholipid concentration in females was decreased and heart muscle phospholipid concentration in males was increased. Melatonin increased malondialdehyde concentration in heart muscle in males and in liver in both sexes. Melatonin induced prominent sex-dependent changes in both carbohydrate and lipid metabolism.     

The effect of prolonged physical training and high fat diet on heart size and body weight in rats

White male Woodlyn Wistar rats (aged 9-10 weeks) were subjected to prolonged physical training on a treadmill for 10 weeks. After 4 weeks half of the rats received a high fat test diet (45%) (Nutritional Biochemical Corporation) while the control group was fed standard lab chow (Purina lab chow). The body weights, heart weights, and heart weight per 100 g body weight were compared in a two by two factorial analysis, the independent variables being condition (exercise or sedentary) and diet (balanced or high fat). After 10 weeks the difference in body weight between the sedentary rats (body weight (BW) equals 514.4 plus or minus 76.4 g) and the exercise rats (BW equals 389 plus or minus 44 g) was significant (p less than 0.05). The difference in body weight between the high fat diet rats (BW equals 479 plus or minus 80 g, n equals 10) and the balanced diet group (BW equals 424 plus or minus 76 g, n equals 10) was also significant (p less than 0.05). No significant differences were observed in heart weight among any of the groups whereas a significant difference was noted between the sedentary group and the exercise group with respect to heart weight : body weight ratio. Thus the exercise rats had relatively larger hearts than the sedentary group (p less than 0.05) but no evidence for cardiac hypertrophy in the exercise group compared with the sedentary group ws observed. The difference with regard to heart ratios between the balanced diet and high fat diet groups was not significant and no interaction was present (p equals 0.065). It was concluded that cardiac hypertrophy is not necessarily a consequence of prolonged physical training but is a product of the type of training, the intensity and duration, and the emotional stress involved. Prolonged physical exercise was a powerful deterrent to weight gain even in rats on a high fat diet. In the absence of the development of cardiac hypertrophy in response to prolonged training, further work is needed to quantify the factors that result in cardiac hypertrophy and to identify other changes that may be occurring in the cardiovascular system in response to prolonged physical training.     

Pharmacodynamic studies on Polypodium vulgare (Linn.)

Aqueous extract of the root of P. vulgare (PV) produced CNS depressant effect. It decreased the spontaneous motor activity, prolonged the pentobarbitone induced hypnosis, reduced body temperature and increased the reaction time to pain stimuli. PV also caused prevention against supramaximal electroshock and pentylenetetrazol induced seizures. PV showed a positive inotropic and chronotropic effect on perfused frog heart and caused hypotension and tachycardia in anaesthetised dogs. The effects were blocked by propranolol. PV produced dose dependent inhibition of contractions of rabbit small intestine and the effect was blocked by propranolol. PV appears to possess CNS depressant and beta-adrenoceptor agonistic activities.     

Metabolic, body temperature and hormonal responses to repeated periods of prolonged cycle-ergometer exercise in men.

This study was designed to find out whether rest intervals and prevention of dehydration during prolonged exercise inhibit a drift in metabolic rate, body temperature and hormonal response typically occurring during continuous work. For this purpose in ten healthy men the heart rate (fc), rectal temperature (Tre), oxygen uptake (VO2), as well as blood metabolite and some hormone concentrations were measured during 2-h exercise at approximately 50% maximal oxygen uptake split into four equal parts by 30-min rest intervals during which body water losses were replaced. During each 30-min exercise period there was a rapid change in Tre and fc superimposed on which, these values increased progressively in consecutive exercise periods (slow drift). The VO2 showed similar changes but there were no significant differences in the respiratory exchange ratio, pulmonary ventilation, mechanical efficiency and plasma osmolality between successive periods of exercise. Blood glucose, insulin and C-peptide concentrations decreased in consecutive exercise periods, whereas plasma free fatty acid, glycerol, catecholamine, growth hormone and glucagon concentrations increased. Blood lactate concentrations did not show any regular drift and the plasma cortisol concentration decreased during the first two exercise periods and then increased. In conclusion, in spite of the relatively long rest intervals between the periods of prolonged exercise and the prevention of dehydration several physiological and hormonal variables showed a distinct drift with time. It is suggested that the slow drift in metabolic rate could have been attributable in the main to the increased concentrations of heat liberating hormones.     

Effect of a Single Fat Load on Major Hemostasis Parameters in Subjects with Different Types of Obesity

The relationship between disturbances of hemostasis, blood insulin, and type of obesity was studied in nonobese subjects and in obese subjects with different body fat distribution under the conditions of postprandial lipemia (after a single standard fat load). In total, 44 subjects (16 men and 28 women aged 18–58) were divided into three groups according to the presence and type of obesity: a group with normal body weight, a group with abdominal obesity, and a group with gluteofemoral obesity. In abdominal obesity, triglyceride clearance was low and insulin secretion after a fat load was abnormally prolonged over 6 h; consequently, fibrinolysis decreased. Hemostasis disturbances in the obese subjects were aggravated by increased fibrinogen. Thus, a combination of metabolically associated disturbances (hypertriglyceridemia, hyperinsulinemia, and hypofibrinolysis) increases considerably the risk of coronary heart disease (CHD) in obese subjects, especially, in those with abdominal obesity.     

Comparison of ketmine with the combination of ketamine and xylazine for effective anesthesia in the rhesus monkey (Macaca mulatta).

The addition of xylazine to ketamine hydrochloride was found to enhance analgesia, anesthesia, and muscle relaxation in rhesus monkeys. At 0.10 ml/kg body weight, this combination provided adequate anesthesia for such procedures as cisternal puncture, lumbar spinal puncture, insertion of urinary catheters, finger amputations, and tattooing. The combination of ketamine and xylazine did depress the heart rate, respiration rate, and body temperature more than the administration of ketamine alone. The period of anesthesia also was prolonged, but the monkeys regained consciousness more rapidly at the end of the anesthetic period.     

Oxytocin levels in the posterior pituitary and in the heart are modified by voluntary wheel running

We hypothesized that voluntary wheel running results in increased secretion of oxytocin, a peptide involved in the stress response. An additional hypothesis was that prolonged exercise affects oxytocin levels in the heart, which is in line with the potential role of oxytocin in cardiovascular functions. Voluntary wheel running lasted 3 weeks and daily running distances increased progressively reaching maximum levels about 8 km (Sprague-Dawley rats) and 4 km (Lewis strain). The exercise resulted in significant reduction of epididymal fat, slight increase in glucose transporter GLUT4 mRNA levels and significant enhancement of plasma density. Voluntary exercise failed to influence plasma oxytocin levels either in Lewis or Sprague-Dawley rats, but it resulted in a significant decrease of oxytocin concentrations in the posterior pituitary. Plasma oxytocin concentrations were not modified even if the measurements were made in the dark phase of the day. In voluntary wheel running Sprague-Dawley rats, the content of oxytocin in the right heart atrium was lower than in controls. Thus, the present findings demonstrate that prolonged voluntary wheel running results in a decrease in pituitary oxytocin content without evident changes in hormone concentrations in peripheral blood. However, prolonged exercise used has a significant impact on oxytocin levels in the heart.     

Pre-exercise hyperhydration delays dehydration and improves endurance capacity during 2 h of cycling in a temperate climate

Whether the use of pre-exercise hyperhydration could improve the performance of athletes who do not hydrate sufficiently during prolonged exercise is still unknown. We therefore compared the effects of pre-exercise hyperhydration and pre-exercise euhydration on endurance capacity, peak power output and selected components of the cardiovascular and thermoregulatory systems during prolonged cycling. Using a randomized, crossover experimental design, 6 endurance-trained subjects underwent a pre-exercise hyperhydration (26 ml of water x kg body mass(-1) with 1.2 g glycerol x kg body mass(-1)) or pre-exercise euhydration period of 80 min, followed by 2 h of cycling at 65% maximal oxygen consumption (VO(.)2max) (26-27 degrees C) that were interspersed by 5, 2-min intervals performed at 80% V(.)O2max. Following the 2 h cycling exercise, subjects underwent an incremental cycling test to exhaustion. Pre-exercise hyperhydration increased body water by 16.1+/-2.2 ml.kg body mass(-1). During exercise, subjects received 12.5 ml of sports drink x kg body mass(-1). With pre-exercise hyperhydration and pre-exercise euhydration, respectively, fluid ingestion during exercise replaced 31.0+/-2.9% and 37.1+/-6.8% of sweat losses (p>0.05). Body mass loss at the end of exercise reached 1.7+/-0.3% with pre-exercise hyperhydration and 3.3+/-0.4% with pre-exercise euhydration (p<0.05). During the 2 h of cycling, pre-exercise hyperhydration significantly decreased heart rate and perceived thirst, but rectal temperature, sweat rate, perceived exertion and perceived heat-stress did not differ between conditions. Pre-exercise hyperhydration significantly increased time to exhaustion and peak power output, compared with pre-exercise euhydration. We conclude that pre-exercise hyperhydration improves endurance capacity and peak power output and decreases heart rate and thirst sensation, but does not reduce rectal temperature during 2 h of moderate to intense cycling in a moderate environment when fluid consumption is 33% of sweat losses.     

Heart rate, body temperature and physical activity are variously affected during insulin treatment in alloxan-induced type 1 diabetic rat

Diabetes mellitus is associated with a variety of cardiovascular complications including impaired cardiac muscle function. The effects of insulin treatment on heart rate, body temperature and physical activity in the alloxan (ALX)-induced diabetic rat were investigated using in vivo biotelemetry techniques. The electrocardiogram, physical activity and body temperature were recorded in vivo with a biotelemetry system for 10 days before ALX treatment, for 20 days following administration of ALX (120 mg/kg) and thereafter, for 15 days whilst rats received daily insulin. Heart rate declined rapidly after administration of ALX. Pre-ALX heart rate was 321+/-9 beats per minute, falling to 285+/-12 beats per minute 15-20 days after ALX and recovering to 331+/-10 beats per minute 5-10 days after commencement of insulin. Heart rate variability declined and PQ, QRS and QT intervals were prolonged after administration of ALX. Physical activity and body temperature declined after administration of ALX. Pre-ALX body temperature was 37.6+/-0.1 °C, falling to 37.3+/-0.1 °C 15-20 days after ALX and recovering to 37.8+/-0.1 °C 5-10 days after commencement insulin. ALX-induced diabetes is associated with disturbances in heart rhythm, physical activity and body temperature that are variously affected during insulin treatment.     

POLYNOMIAL REGRESSION IN THE RESEARCHOF HEROIN′S TOXICITY

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Hemodynamic and hormonal effects of prolonged anti-G suit inflation in humans.

This study examined the hemodynamic consequences of prolonged lower body positive-pressure application and their relationship to changes in the plasma concentration of the major vasoactive hormones. Six men [36 +/- 2 (SE) yr] underwent 30 min of sitting and then 3 h of 70 degrees head-up tilt. An antigravity suit was applied (60 Torr legs, 30 Torr abdomen) during the last 2 h of tilt. In a similar noninflation experiment, the endocrine responses were measured in the suited subjects tilted for 3 h. Two-dimensional echocardiography was used to calculate ventricular volume and cardiac output. Measurements were made 30 min before and 30 and 90 min after inflation. Immediately after inflation, mean arterial pressure increased by 7 +/- 2 Torr and heart rate decreased by 16 +/- 4 beats/min. Left ventricular end-diastolic volume and systolic volume increased significantly (P less than 0.05) at 30 and 90 min of inflation. Cardiac output increased after 30 min of inflation and returned to the preinflation level at 90 min. Plasma norepinephrine and plasma renin activity were maximally suppressed after 15 and 90 min of inflation, respectively (P less than 0.05). No such hormonal changes occurred during control. Plasma sodium, potassium, and osmolality remained unchanged during both experiments. Thus, prolonged application of lower body positive pressure induces 1) a transient increase in cardiac output and 2) a marked and sustained decrease in plasma norepinephrine and plasma renin activity, which reflect an inflation-induced decrease in sympathetic activity.     

In vitro incorporation of labelled amino acids into heart muscle ribosomes at early and late stages of compensatory heart hyperfunction]

The activity of a protein-synthesizing cell-free system from heart muscle was studied at early and late stages of compensatory heart hyperfunction. It was found that the incorporation of amino acids into heart ribosomes during 48 hours after the hyperfunction had been produced, increased by 30% as compared to the control. The incorporation of amino acids into heart ribosomes at the late stage of hyperfunction (after 6 months) was decreased by 46% as compared to the early stages. The addition of homologous tRNA to the cell-free system of protein synthesis under prolonged heart hyperfunction stimulated the incorporation of amino acids into the ribosomes by 40--50%.     

Oxygen consumption, ventilatory frequency and heart rate of lampreys (Lampetra fluviatilis) during their spawning run.

1. The standard rate of oxygen consumption, ventilatory frequency and heart rate of adult Lampetra fluviatilis were measured during the light phase of the photoperiod and at times corresponding to various stages in the upstream migration. 2. All three parameters increased during the spawning run but only in mature individuals were significant differences found between the sexes. 3. The regression coefficients for the logarithmic relationship between oxygen consumption and body weight of immature animals were 0.912 and 0.925 at 9.5 and 16 degrees C respectively. 4. Both the standard rate of oxygen consumption and the amount of oxygen taken up during activity increased greatly during the hours of darkness. 5. Oxygen consumption, ventilatory frequency and, to a lesser extent, heart rate increased significantly at 9.5 degrees C over the 100-20% range of saturation with air. 6. Below 20% saturation with air, lampreys no longer remained attached by their oral disc for prolonged periods and the ventilatory frequency rose even more rapidly to reach a maximum of 175 beats/min at 12.5%. Exposure to 7.5% resulted in death within 5-8 h.     

Effects of dexamethasone on lipid metabolism in rat organs

Injecting of dexamethasone (10 mg/kg body weight) for 8 days to rats decreased the body weight and feed intake by 29 and 50%, respectively. The increase in weights of liver, heart, kidneys and testes per 100 g body weight was 55, 37, 33 and 13%, respectively. Though, in general, the triglyceride content increased in all the organs, maximum increase (9-fold) was observed in the liver. The plasma showed elevated levels of triglycerides, cholesterol and phospholipids. In hepatic mitochondrial membranes, the content of protein, phospholipids and cholesterol decreased/g tissue. The percent 14C distribution, as a part of total incorporation in nonpolar lipids, of [14C]acetate into triglycerides of liver, kidneys and testes increased significantly. The increased turnover of phospholipids in liver and heart was mainly due to increased turnover of phosphatidyl choline (PC) and phosphatidyl ethanolamine in liver and PC in heart. Turnover of phospholipids of testes was not affected.     

Physiological effects of an ultra-marathon run

Autonomic functions of the body and gas exchange have been studied in one athlete (master of sports in skiing, aged 27 years, with a maximal oxygen consumption of 67 mL/(min kg)); during a 6-h indoor ultra-marathon race; at an average speed of 2.7 m/s. Continuous monitoring of the heart rate was carried out using a Polar RS 800 heart rate monitor. Gas analysis of the exhaled air and recording of the parameters of external respiration were carried out during the first hour with subsequent repetitions during 20?C30 minutes each hour, using a Metamax mobile device (Germany) mounted on the subject throughout the race. Before and after the subject passed the intervals of a distance when these parameters were measured, the blood lactate content was measured. Our data demonstrate a number of features that accompany fatigue at the final stage of the race, such as a decrease in efficiency of body functions, which is expressed by an increased heart rate and oxygen usage, an activation of anaerobic glycolysis path of energy production, and intensification of the external respiration. In addition, the methods of correlation and regression analysis revealed the changes (increase and decrease) of the relationship between the functions depending on whether muscular performance is at the stage of warming up, sustainably high performance, or in at a stage of extreme fatigue. These findings suggest interference of the effects of the central and tissue mechanisms of fatigue on the organization of oxygen transportation in the body. Apparently, in the instance of an ultra-marathon run, i.e., a prolonged performance of moderate power, autonomic functions, rather than the energy resources of the body, play the role of the main limiting factor.     

Acute plasma volume expansion alters cardiovascular but not thermal function during moderate intensity prolonged exercise

To investigate the hypothesis that the increase in plasma volume (PV) that typically occurs with training results in improved cardiovascular and thermal regulation during prolonged exercise, eight untrained males (V(O2)peak = 3.52 +/- 0.12 L x min(-1)) performed 90 min of cycle ergometry at 62% V(O2)peak before and after acute PV expansion. Subjects were infused with a PV-expanding solution (dextran (6%) or Pentaspan (10%)) equivalent to 6.7 mL x kg(-1) body mass (PVX) or acted as their own control (CON) in a randomized order. PVX resulted in a calculated 15.8% increase in resting PV, which relative to CON, was maintained throughout the exercise (P < 0.05). During PVX, heart rate was lower (P < 0.05) and stroke volume and cardiac output were higher (P < 0.05) during the exercise. Mean arterial pressure and total peripheral resistance, although altered by exercise (P < 0.05), were not different between the two conditions. Core temperature, which was progressively increased by the exercise (P < 0.01), was not affected by PVX. A similar decrease in body weight was observed between the conditions as a result of the exercise (P < 0.01). These results indicate that acute PVX alters cardiovascular performance without affecting the thermoregulatory response to prolonged cycle exercise.     

Effects of chronic and acute exercise on cardiovascular beta-adrenergic responses.

beta-Adrenergic receptor density and responsiveness may be increased in experimental animals by physical conditioning, and the opposite effects have been observed after a single bout of exercise. To determine whether the chronic and acute effects of exercise include similar alterations in cardiovascular function in humans, we characterized heart rate, blood pressure, and distal lower extremity blood flow responses to graded-dose isoproterenol infusion in 15 young healthy subjects before and after exercise training and with and without a single preceding bout of prolonged exercise of either low or high intensity (61 +/- 1 or 82 +/- 1% maximal heart rate). VO2max was increased 18% after exercise training (43.2 +/- 2.7 to 51.1 +/- 3.3 ml.kg-1.min-1; P less than 0.001). Despite a concomitant fall in resting heart rate (59 +/- 3 to 50 +/- 2 beats/min; P less than 0.001), chronotropic and lower extremity blood flow responses to isoproterenol remained unchanged. Similarly, 1 h of acute high-intensity treadmill exercise altered baseline heart rate (58 +/- 4 to 74 +/- 5 beats/min; P less than 0.02), but neither low- nor high-intensity acute exercise influenced heart rate or lower extremity blood flow responses to isoproterenol. In contrast, the systolic pressure response to isoproterenol was blunted after high- but not low-intensity prolonged exercise (P less than 0.02). These data indicate that cardiac chronotropic (primarily beta 1) and vascular (beta 2) adrenergic agonist responses are not altered in humans by training or acute exercise. The systolic blood pressure response to beta-adrenergic stimulation is decreased by a single bout of high-intensity prolonged exercise by mechanisms that remain to be defined.     

Role of impaired myocardial relaxation in the production of elevated left ventricular filling pressure

Although present in many patients with heart failure and a normal ejection fraction, the role of isolated impairments in active myocardial relaxation in the genesis of elevated filling pressures is not well characterized. Because of difficulties in determining the effect of prolonged myocardial relaxation in vivo, we used a cardiovascular simulated computer model. The effect of myocardial relaxation, as assessed by tau (exponential time constant of relaxation), on pulmonary vein pressure (PVP) and left ventricular end-diastolic pressure (LVEDP) was investigated over a wide range of tau values (20-100 ms) and heart rate (60-140 beats/min) while keeping end-diastolic volume constant. Cardiac output was recorded over a wide range of tau and heart rate while keeping PVP constant. The effect of systolic intervals was investigated by changing time to end systole at the same heart rate. At a heart rate of 60 beats/min, increases in tau from a baseline to extreme value of 100 ms cause only a minor increase in PVP of 3 mmHg. In contrast, at 120 beats/min, the same increase in tau increases PVP by 23 mmHg. An increase in filling pressures at high heart rates was attributable to incomplete relaxation. The PVP-LVEDP gradient was not constant and increased with increasing tau and heart rate. Prolonged systolic intervals augmented the effects of tau on PVP. Impaired myocardial relaxation is an important determinant of PVP and cardiac output only during rapid heart rate and especially when combined with prolonged systolic intervals. These findings clarify the role of myocardial relaxation in the pathogenesis of elevated filling pressures characteristic of heart failure.     

Antioxidant defense in hibernation: cloning and expression of peroxiredoxins from hibernating ground squirrels, Spermophilus tridecemlineatus

Mammalian hibernation is characterized by prolonged torpor bouts interspersed by brief arousal periods. Adequate antioxidant defenses are needed both to sustain cell viability over weeks of deep torpor and to defend against high rates of oxyradical formation associated with massive oxygen-based thermogenesis during arousal. The present study shows that up-regulation of peroxiredoxins contributes to antioxidant defense during torpor in thirteen-lined ground squirrels, Spermophilus tridecemlineatus. Expression levels of three isozymes of the 2-Cys peroxiredoxin (Prdx) family were quantified by Western blotting, the results showing 4.0- and 12.9-fold increases in Prdx1 protein in brown adipose tissue (BAT) and heart, respectively, during hibernation compared with euthermia. Comparable increases in Prdx2 were 2.4- and 3.7-fold whereas Prdx3 rose by 3.1-fold in heart of torpid animals. Total 2-Cys peroxiredoxin enzymatic activity also rose during hibernation by 1.5-fold in heart and 3.5-fold in BAT. Furthermore, RT-PCR showed that prdx2 mRNA levels increased by 1.7- and 3.7-fold in BAT and heart, respectively, during hibernation. A partial nucleotide sequence of prdx2 from ground squirrels was obtained by PCR amplification, the deduced amino acid sequence showing 96-97% identity with Prdx2 from other mammals. Some unique amino acid substitutions were identified that might contribute to stabilizing Prdx2 conformation at the near 0 degrees C body temperatures during torpor.