Failure of gonadotropin-releasing hormone or human chorionic gonadotropin to enhance the fertility of repeat-breeder cows when administered at the time of insemination

Repeat-breeder dairy cows failing to conceive to two previous inseminations were injected with saline (2 cc i.m.), gonadotropin-releasing hormone (GnRH, 2 cc i.m.) or human chorionic gonadotropin (hCG, 5000 IU i.v.) at the time of the third and succeeding inseminations. This field study involved 240 cows at three dairies. Mean conception rate was high (49.6%) for repeat-breeders, and did not differ among farms (P>0.10) or treatments (P>0.10), varying from 44.0 to 51.9% for farms and from 44.4 to 54.2% for treatments. The percentage of repeat-breeder cows bred during diestrus was very low on each of the three farms (mean = 7.9%). For this and other reasons discussed in the study, hormonal therapy was not successful in improving the conception rate of repeat-breeder cows under field conditions.

Association of Ig L chain-like protein lambda 5 with a 16-kilodalton protein in mouse pre-B cell lines is not dependent on the presence of Ig H chain protein

Using a polyclonal rabbit antiserum against recombinant mouse lambda 5 protein, we determined that the pre-B cell specific mouse lambda 5 gene encodes a 22-kDa protein. The lambda 5 protein, which is related to conventional Ig lambda L chain proteins forms a complex with Ig mu H chain protein and an as yet unidentified 16-kDa protein (p16) in mu+ pre-B cell lines carrying a functionally rearranged VH-DH-JH allele. In pre-B cell lines which carry DH-JH rearrangements and do not express mu H chain protein, lambda 5 protein is associated with p16. Thus the expression of lambda 5 protein precedes the expression of intact mu H chain protein. This suggests the existence of developmentally regulated protein complexes involving the Ig L chain-like protein lambda 5 and p16 in mu- pre-B cells; lambda 5, p16, and Ig H chain protein in mu+ pre-B cells and Ig H chain and conventional Ig L chain proteins in B cells and plasma cells.

Association of Ig L chain-like protein lambda 5 with a 16-kilodalton protein in mouse pre-B cell lines is not dependent on the presence of Ig H chain protein

Using a polyclonal rabbit antiserum against recombinant mouse lambda 5 protein, we determined that the pre-B cell specific mouse lambda 5 gene encodes a 22-kDa protein. The lambda 5 protein, which is related to conventional Ig lambda L chain proteins forms a complex with Ig mu H chain protein and an as yet unidentified 16-kDa protein (p16) in mu+ pre-B cell lines carrying a functionally rearranged VH-DH-JH allele. In pre-B cell lines which carry DH-JH rearrangements and do not express mu H chain protein, lambda 5 protein is associated with p16. Thus the expression of lambda 5 protein precedes the expression of intact mu H chain protein. This suggests the existence of developmentally regulated protein complexes involving the Ig L chain-like protein lambda 5 and p16 in mu- pre-B cells; lambda 5, p16, and Ig H chain protein in mu+ pre-B cells and Ig H chain and conventional Ig L chain proteins in B cells and plasma cells.

In vitro regulation of mammary glucose-6-phosphate dehydrogenase activity by palmitoyl coenzyme A, acetate, and polyamines

An in vitro study was conducted to determine whether bovine mammary glucose-6-phosphate dehydrogenase (G6PD) activity was regulated by palmitoyl coenzyme A (CoA), acetate, spermidine, and putrescine and whether these effects were dependent upon stage of lactation. Early lactation explants incubated in media containing palmitoyl CoA or acetate had reduced (P less than 0.01) G6PD activity compared with incubated control explants. G6PD activity in early lactation explants was reduced (P less than 0.05) when incubated with 5 microM palmitoyl CoA or 1 mM acetate compared with 25 microM palmitoyl CoA or 10 mM acetate. Spermidine (0.4 mM) reversed (P less than 0.05) palmitoyl CoA-induced inhibition of early lactation G6PD activity at 5 microM, but not at 25 microM palmitoyl CoA. G6PD activity in early lactation explants was decreased (P less than 0.05) when treated with putrescine (0.4 mM) compared with explants treated with spermidine. Addition of acetate in combination with 5 microM palmitoyl CoA reversed G6PD inhibition (P less than 0.05 for 1 mM and P less than 0.01 for 10 mM) while addition of either level of acetate in combination with 25 microM palmitoyl CoA failed to reverse G6PD inhibition. G6PD activity was higher (P less than 0.01) in early lactation than mid-lactation explants. No statistical differences (P greater than 0.1) were found among any treatments in explants from mid-lactation cows. We conclude that palmitoyl CoA and acetate will inhibit G6PD activity in early lactation, but not mid-lactation explants; addition of spermidine will reverse this inhibition.

Human and mouse LSP1 genes code for highly conserved phosphoproteins

With use of the mouse LSP1 cDNA we isolated a human homologue of the mouse LSP1 gene from a human CTL cDNA library. The predicted protein sequence of human LSP1 is compared with the predicted mouse LSP1 protein sequence and regions of homology are identified in order to predict structural features of the LSP1 protein that might be important for its function. Both the human and mouse LSP1 proteins consist of two domains, an N-terminal acidic domain and a C-terminal basic domain. The C-terminal domains of the mouse and human LSP1 proteins are highly conserved and include several conserved, putative serine/threonine phosphorylation sites. Immunoprecipitation of LSP1 protein from 32P-orthophosphate-loaded cells show that both the mouse and human LSP1 proteins are phosphoproteins. The sequences of the putative Ca2(+)-binding sites present in the N-terminal domain of the mouse LSP1 protein are not conserved in the human LSP1 protein; however, a different Ca2(+)-binding site may exist in the human protein, indicating a functional conservation rather than a strict sequence conservation of the two proteins. The expression of the human LSP1 gene follows the same pattern as the expression of the mouse LSP1 gene. Southern analysis of human genomic DNA shows multiple LSP1-related fragments of varying intensity in contrast to the simple pattern found after similar analysis of mouse genomic DNA. By using different parts of the human LSP1 cDNA as a probe, we show that most of these multiple bands contain sequences homologous to the conserved C-terminal region of the LSP1 cDNA. This suggests that there are several LSP1-related genes present in the human genome.

Human and mouse LSP1 genes code for highly conserved phosphoproteins

With use of the mouse LSP1 cDNA we isolated a human homologue of the mouse LSP1 gene from a human CTL cDNA library. The predicted protein sequence of human LSP1 is compared with the predicted mouse LSP1 protein sequence and regions of homology are identified in order to predict structural features of the LSP1 protein that might be important for its function. Both the human and mouse LSP1 proteins consist of two domains, an N-terminal acidic domain and a C-terminal basic domain. The C-terminal domains of the mouse and human LSP1 proteins are highly conserved and include several conserved, putative serine/threonine phosphorylation sites. Immunoprecipitation of LSP1 protein from 32P-orthophosphate-loaded cells show that both the mouse and human LSP1 proteins are phosphoproteins. The sequences of the putative Ca2(+)-binding sites present in the N-terminal domain of the mouse LSP1 protein are not conserved in the human LSP1 protein; however, a different Ca2(+)-binding site may exist in the human protein, indicating a functional conservation rather than a strict sequence conservation of the two proteins. The expression of the human LSP1 gene follows the same pattern as the expression of the mouse LSP1 gene. Southern analysis of human genomic DNA shows multiple LSP1-related fragments of varying intensity in contrast to the simple pattern found after similar analysis of mouse genomic DNA. By using different parts of the human LSP1 cDNA as a probe, we show that most of these multiple bands contain sequences homologous to the conserved C-terminal region of the LSP1 cDNA. This suggests that there are several LSP1-related genes present in the human genome.

Decreased exercise muscle lactate release after high altitude acclimatization

Blood lactate concentration during exercise decreases after acclimatization to high altitude, but it is not clear whether there is decreased lactate release from the exercising muscle or if other mechanisms are involved. We measured iliac venous and femoral arterial lactate concentrations and iliac venous blood flow during cycle exercise before and after acclimatization to 4,300 m. During hypoxia, at a given O2 consumption the venous and arterial lactate concentrations, the venous and arterial concentration differences, and the net lactate release were lower after acclimatization than during acute altitude exposure. While breathing O2-enriched air after acclimatization at a given O2 consumption the venous and arterial lactate concentrations and the venous and arterial concentration differences were significantly lower, and the net lactate release tended to be lower than while breathing ambient air at sea level before acclimatization. We conclude that the lower lactate concentration in venous and arterial blood during exercise after altitude acclimatization reflected less net release of lactate by the exercising muscles, and that this likely resulted from the acclimatization process itself rather than the hypoxia per se.

Control of thermoregulatory sweating during exercise in the heat

The purposes of this study were the following: 1) to determine whether erythrocyte infusion alters the control of thermoregulatory sweating and 2) to demonstrate how increases and decreases of both plasma tonicity and blood volume influence the thermoregulatory control parameters of threshold temperature and sweating sensitivity. Six non-heat-acclimated and five heat-acclimated males attempted heat stress tests (HSTs) both before and shortly after (48-96 h) autologous erythrocyte infusion. The non-heat-acclimated subjects were euhydrated for both HSTs, whereas the heat-acclimated subjects were studied in a euhydrated and a hypohydrated (-5% body wt) condition both pre- and postinfusion (500 ml of solution containing approximately 60% hematocrit of autologous erythrocytes). The HSTs consisted of treadmill exercise (335 W.m-2) in a hot (35 degrees C, 45% relative humidity) environment, and esophageal temperature and local sweating rate were continuously measured during 25 min of exercise. These experiments resulted in a matrix of conditions where both plasma tonicity and blood volume were increased or decreased relative to control conditions (euhydration, preinfusion). The findings concerning thermoregulatory sweating during exercise in the heat were summarized as follows: 1) acute polycythemia decreases the threshold temperature and increases the sweating sensitivity, 2) both threshold temperature and sweating sensitivity are increased or decreased from control levels dependent on the combined influence of plasma tonicity and blood volume, and 3) equations are presented that describe how plasma tonicity and blood volume alter threshold temperature and sweating sensitivity values.

Human intravascular immunoglobulin responses to exercise-heat and hypohydration

Several investigators have suggested that prolonged exercise and hypohydration alter the intravascular mass of immunoglobulins. Those studies, however, have methodological concerns which make generalizations from their data very tenuous. This study examined the effects of prolonged moderate intensity exercise in the heat and hypohydration on changes in the intravascular mass of immunoglobulins. Five heat-acclimated males attempted two Heat Stress Tests (HSTs). One HST was completed when subjects were euhydrated and the other HST when subjects were hypohydrated (-5% from base line body weight). The HSTs consisted of 30 min of rest in a 20 degrees C antechamber, followed by a 120-min exposure (2 repeats of 15 min rest and 45 min walking) in a hot (35 degrees C, 45% rh) environment. The following observations were made concerning immunoglobulin responses to hypohydration and exercise-heat stress: a) the changes in concentrations (mg.dl-1) of the measured immunoglobulins were often a reflection of changes in the plasma volume; b) hypohydration increased the intravascular mass (g) of the complement enzyme C3 during resting conditions, but did not alter the intravascular mass of IgG, IgA, and IgM, and c) prolonged treadmill exercise in the heat, when either euhydrated or hypohydrated, did not alter the intravascular mass of IgG, IgA, IgM, and C3. These data indicate that the intravascular mass of immunoglobulins does not change during prolonged moderate intensity exercise in the heat, and that hypohydration results in a translocation of C3 to the intravascular space. In addition, these data indicate that immunoglobulins do not provide a stress index for hypohydration.

Thermoregulation during cold water immersion is unimpaired by low muscle glycogen levels

This investigation studied the importance of muscle glycogen levels for body temperature regulation during cold stress. Physiological responses of eight euglycemic males were measured while they rested in cold (18 degrees C, stirred) water on two separate occasions. The trials followed a 3-day program of diet and exercise manipulation designed to produce either high (HMG) or low (LMG) preimmersion glycogen levels in the muscles of the legs, arms, and upper torso. Preimmersion vastus lateralis muscle glycogen concentrations were lower during the LMG trial (144 +/- 14 mmol glucose/kg dry tissue) than the HMG trial (543 +/- 53 mmol glucose/kg dry tissue). There were no significant differences between the two trials in shivering as reflected by aerobic metabolic rate or in the amount of body cooling as reflected by changes in rectal temperature during the immersions. Postimmersion muscle glycogen levels remained unchanged from preimmersion levels in both trials. Small but significant increases in plasma glucose and lactate concentration occurred during both immersions. Plasma glycerol increased during immersion in the LMG trial but not in the HMG trial. Plasma free fatty acid concentration increased during both immersion trials, but the change was apparent sooner in the LMG immersion. It was concluded that thermoregulatory responses of moderately lean and fatter individuals exposed to cold stress were not impaired by a substantial reduction in the muscle glycogen levels of several major skeletal muscle groups. Furthermore, the data suggest that, depending on the intensity of shivering, other metabolic substrates are available to enable muscle glycogen to be spared.

Gastric emptying during walking and running: effects of varied exercise intensity

Gastric emptying is increased during running (50%-70% maximal aerobic uptake, VO2max) as compared to rest. Whether this increase varies as a function of mode (i.e. walking vs running) and intensity of treadmill exercise is unknown. To examine the gastric emptying characteristics of water during treadmill exercise performed over a wide range of intensities relative to resting conditions, 10 men ingested 400 ml of water prior to each of six 15 min exercise bouts or 15 min of seated rest. Three bouts of walking exercise (1.57 m.s-1) were performed at increasing grades eliciting approximately 28%, 41% or 56% of VO2max. On a separate day, three bouts of running (2.68 ms-1) exercise were performed at grades eliciting approximately 57%, 65% or 75% of VO2max. Gastric emptying was increased during treadmill exercise at all intensities excluding 75% VO2max as compared to rest. Gastric emptying was similar for all intensities during walking and at 57% and 65% VO2max during running. However, running at 74% VO2max decreased the volume of original drink emptied as compared to all lower exercise intensities. Stomach secretions were markedly less during running as compared to walking and rest. These data demonstrate that gastric emptying is similarly increased during both moderate intensity (approximately 28%-65% VO2max) walking or running exercise as compared to resting conditions. However, gastric emptying decreases during high intensity exercise. Increases in gastric emptying during moderate intensity treadmill exercise may be related to increases in intragastric pressure brought about by contractile activity of the abdominal muscles.

Gastric emptying during exercise: effects of heat stress and hypohydration

To determine the effects of acute heat stress, heat acclimation and hypohydration on the gastric emptying rate of water (W) during treadmill exercise, ten physically fit men ingested 400 ml of W before each of three 15 min bouts of exercise (treadmill, approximately 50% VO2max) on five separate occasions. Stomach contents were aspirated after each exercise bout. Before heat acclimation (ACC), experiments were performed in a neutral (18 degrees C), hot (49 degrees C) and warm (35 degrees C) environment. Subjects were euhydrated for all experiments before ACC. After ACC, the subjects completed two more experiments in the warm (35 degrees C) environment; one while euhydrated and a final one while hypohydrated (-5% of body weight). The volume of ingested water emptied into the intestines at the completion of each exercise bout was inversely correlated (P less than 0.01) with the rectal temperature (r = -0.76). The following new observations were made: 1) exercise in a hot (49 degrees C) environment impairs gastric emptying rate as compared with a neutral (18 degrees C) environment, 2) exercise in a warm (35 degrees C) environment does not significantly reduce gastric emptying before or after heat acclimation, but 3) exercise in a warm environment (35 degrees C) when hypohydrated reduces gastric emptying rate and stomach secretions. Reductions in gastric emptying appear to be related to the severity of the thermal strain induced by an exercise/heat stress.

Polycythemia and hydration: effects on thermoregulation and blood volume during exercise-heat stress

We studied the effects of autologous erythrocyte infusion on thermoregulation and blood volume during exercise in the heat. Specifically, we wanted to determine whether heat-acclimated subjects, as well as hypohydrated subjects, would have a thermoregulatory advantage from acute polycythemia during exercise in the heat. Five heat-acclimated males attempted four heat stress tests (HSTs): two pre- and two postinfusion. Autologous erythrocyte infusion was accomplished with 500 ml of a NaCl-glucose-phosphate solution containing approximately 60% hematocrit. One HST, both pre- and postinfusion, was done while subjects were euhydrated, and one HST was done while subjects were hypohydrated (-5% of body wt). After 30 min of rest in a 20 degrees C antechamber, the HST consisted of a 120-min exposure (2 repeats of 15 min rest and 45 min walking) in a hot (35 degrees C, 45% relative humidity) environment. The findings concerning acute polycythemia in heat-acclimated subjects are summarized: 1) polycythemia increased (P less than 0.05) sweating rate and reduced (P less than 0.01) core temperature during exercise-heat stress for both euhydrated and hypohydrated subjects; 2) the erythrocyte infusion caused an increased (P less than 0.05) plasma volume and increased (P less than 0.01) blood volume; 3) the increased plasma volume was associated with an increased (P less than 0.05) total circulating protein mass; 4) the increased total circulating protein mass tended to better maintain plasma volume when hypohydrated; and 5) heat acclimation may increase extravascular protein mass. Therefore, it is concluded that erythrocyte infusion provides a thermoregulatory advantage during exercise in the heat for heat acclimated subjects when both euhydrated and hypohydrated.

Influence of skeletal muscle glycogen on passive rewarming after hypothermia

To examine the influence of muscle glycogen on the thermal responses to passive rewarming subsequent to mild hypothermia, eight subjects completed two cold-water immersions (18 degrees C), followed by 75 min of passive rewarming (24 degrees C air, resting in blanket). The experiments followed several days of different exercise-diet regimens eliciting either low (LMG; 141.0 +/- 10.5 mmol.kg.dry wt-1) or normal (NMG; 526.2 +/- 44.2 mmol.kg.dry wt-1) prewarming muscle glycogen levels. Cold-water immersion was performed for 180 min or to a rectal temperature (Tre) of 35.5 degrees C. In four subjects (group A, body fat = 20 +/- 1%), postimmersion Tre was similar to preimmersion Tre for both trials (36.73 +/- 0.18 vs. 37.26 +/- 0.18 degrees C, respectively). Passive rewarming in group A resulted in an increase in Tre of only 0.13 +/- 0.08 degrees C. Conversely, initial rewarming Tre for the other four subjects (group B, body fat = 12 +/- 1%) averaged 35.50 +/- 0.05 degrees C for both trials. Rewarming increased Tre similarly in group B during both LMG (0.76 +/- 0.25 degrees C) and NMG (0.89 +/- 0.13 degrees C). Afterdrop responses, evident only in those individuals whose body core cooled during immersion (group B), were not different between LMG and NMG. These data support the contention that Tre responses during passive rewarming are related to body insulation. Furthermore these results indicate that low muscle glycogen levels do not impair rewarming time nor alter after-drop responses during passive rewarming after mild-to-moderate hypothermia.

Thermoregulatory responses of middle-aged and young men during dry-heat acclimation

Thermoregulatory responses during heat acclimation were compared between nine young (mean age 21.2 yr) and nine middle-aged men (mean age 46.4 yr) who were matched (P greater than 0.05) for body weight, surface area, surface area-to-weight ratio, percent body fat, and maximal aerobic power. After evaluation in a comfortable environment (22 degrees C, 50% relative humidity), the men were heat acclimated by treadmill walking (1.56 m/s, 5% grade) for two 50-min exercise bouts separated by 10 min of rest for 10 consecutive days in a hot dry (49 degrees C ambient temperature, 20% relative humidity) environment. During the first day of heat exposure performance time was 27 min longer (P less than 0.05) for the middle-aged men, whereas final rectal and skin temperatures and heart rate were lower, and final total body sweat loss was higher (P less than 0.05) compared with the young men. These thermoregulatory advantages for the middle-aged men persisted for the first few days of exercise-heat acclimation (P less than 0.05). After acclimation no thermoregulatory or performance time differences were observed between groups (P greater than 0.05). Sweating sensitivity, esophageal temperature at sweating onset, and the sweating onset time did not differ (P greater than 0.05) between groups either pre- or postacclimatization. Plasma osmolality and sodium concentration were slightly lower for the young men both pre- and postacclimatization; however, both groups had a similar percent change in plasma volume from rest to exercise during these tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory and cardiovascular responses to cold stress following repeated cold water immersion

The effects of cold acclimation (CA) on the cardiorespiratory responses to cold air and water stress tests (CST) were studied in 7 males before and after a CA program of daily 90-min cold water (18 degrees C) immersions repeated 5 times a wk for 5 consecutive wk. The CST consisted of a 90-min resting exposure to cold air (5 degrees C, 30% relative humidity) or water (18 degrees C) during which rectal temperature, oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), heart rate, cardiac output (Q), and blood pressure (BP) were periodically measured. In cold air following CA, the VO2 at 10 min was lower (P less than 0.02) post- than pre-CA, however, no differences were found in cold water. The VE increased (P less than 0.01) during CST as a function of VCO2. The CA did not affect the VE-VCO2 relationship or the pattern of breathing during CST in cold air or water. The CA had no effect on Q or (a-v) O2 difference, which both increased (P less than 0.01) during the first 45 min of CST, then remained stable. BP increased significantly during the first cold water exposure, but not during the last cold water immersion. These data indicate that CA attenuated the onset of metabolic heat production during CST in air but did not alter its ultimate magnitude or the relationships between the cardiorespiratory variables and metabolic requirements. Also, the thermoregulatory adjustments associated with CA altered the control of blood pressure during acute cold stress.

Autologous red blood cell reinfusion: effects on stress and fluid regulatory hormones during exercise in the heat

This study assessed the effects of induced erythrocythemia on stress and fluid regulatory hormones during walking exercise in the heat. Six unacclimated male subjects received approximately 600 ml of a sterile saline solution containing 50% volume-to-volume of autologous erythrocytes. Three heat stress tests (HSTs) were attempted: one approximately 2 weeks prior to the reinfusion procedure, a second 48 h after the reinfusion procedure, and a third 1 week later, corresponding to 9 d subsequent to reinfusion. Each HST comprised three consecutive 45-min exercise and 15-min rest intervals (VO2 approximately 2.0 L.min-1, 1.56 m.s-1, 6% incline, 35 degrees C, 45% rh). Blood was withdrawn before the HST and 30 min into each exercise (EX) bout. In all three HST's plasma cortisol (PC) levels were significantly (p less than 0.01) reduced during the first EX bout compared to preexercise levels, and then progressively increased during the second and third EX intervals during HST 1. During HST 2 (48 h postinfusion), however, PC levels were significantly (p less than 0.05) reduced in two blood samples (EX 2, 3) compared to the same blood samples from HST-1 (preinfusion). Plasma renin activity (PRA) and aldosterone (ALD) were significantly (p less than 0.01) increased by the exercise/heat stress, but were unaffected by erythrocythemia either 48 h or 9 d subsequent to reinfusion. PRA and ALD were correlated (r = 0.84, p less than 0.001) under all conditions. We concluded from this study that acutely induced erythrocythemia reduced the stress response to consecutive exercise/heat intervals as manifested in PC responses during HST 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Elite special forces: physiological description and ergogenic influence of blood reinfusion

We measured the physical exercise capabilities of U.S. Army Special Forces soldiers (male) and determined the subsequent ergogenic influence of autologous blood reinfusion. Twelve subjects (Ss) completed maximal exercise treadmill testing in a comfortable (Ta = 20 degrees C, Tdp = 9 degrees C) environment. Six Ss were later transfused with a 600 ml autologous red blood cell (50% Hct) NaCl glucose-phosphate solution and completed identical maximal exercise tests 3 and 10 d posttransfusion. Pretransfusion, the 12 Ss had a maximal oxygen uptake (VO2max) of 4.36 +/- 0.56 L . min-1 and 55 +/- 4 ml . kg-1 . min-1 with a heart rate of 188 +/- 10 b . min-1 and ventilatory equivalent for oxygen of 37 +/- 3. For the 6 reinfused Ss, hemoglobin and red cell volume (RCV) increased by 10% (p less than 0.05) and 11% (p less than 0.05), respectively, posttransfusion. Reinfusion increased (p less than 0.05) VO2max from 4.28 +/- 0.22 L . min-1 (54 +/- 5 ml . kg-1 . min-1) to 4.75 +/- 0.42 L . min-1 (60 +/- 6 ml . kg-1 . min-1) and 4.63 +/- 0.21 L . min-1 (59 +/- 6 ml . kg-1 . min-1) at 3 and 10 d posttransfusion, respectively. No significant relationship was found between the individual change in RCV and VO2max values pre- to posttransfusion. We conclude that Special Forces soldiers have high levels of aerobic fitness that can be further increased by blood reinfusion for at least 10 d.

Cooling different body surfaces during upper and lower body exercise

The effect of varying the body surface area being cooled by a liquid microclimate system was evaluated during exercise heat-stress conditions. Six male subjects performed a total of six exercise (O2 uptake = 1.2 l/min) tests in a hot environment (ambient temperature = 38 degrees C, relative humidity = 30%) while dressed in clothing having low moisture permeability and high insulation. Each subject completed two upper body exercise (U; arm crank) tests: 1) with only the torso surface (T) cooled; and 2) with the surfaces of both the torso and upper arms (TA) cooled [coolant temperature at the inlet (Ti) was 20 degrees C for all upper body tests]. Each subject also completed four lower body exercise (L; walking) tests: 1) with only the T cooled (Ti = 20 degrees C); 2) with only the T cooled (Ti = 26 degrees C); 3) with torso, upper arm, and thigh surface (TAT) cooled (Ti = 20 degrees C); and 4) with TAT cooled (Ti = 26 degrees C). During U exercise, TA cooling had no effects compared with cooling only T. During L exercise, sweat rates, heart rates, and rectal temperature (Tre) changes were less with TAT cooling compared with cooling only the T. Altering Ti had no effect on Tre changes, but higher heart rates were observed with 26 than with 20 degrees C. These data indicate that cooling arms during upper body exercise provides no thermoregulatory advantage, although cooling the thigh surfaces during lower body exercise does provide an advantage.

Erythrocyte reinfusion and maximal aerobic power. An examination of modifying factors

Induced erythrocythemia is associated with a variable increase in maximal oxygen uptake. To examine the roles of the magnitude of change in hemoglobin concentration and the individual's initial aerobic fitness in this effect, we combined individual data from our own research and three other studies. In each study freeze-preserved erythrocytes from the product of 2 units of blood were reinfused, and maximal oxygen uptake was measured within 24 to 72 hours after reinfusion. The 30 subjects had an initial aerobic power of 36 to 88 mL of oxygen per kilogram per minute. The combined results from these studies indicate that after erythrocyte reinfusion the increase in hemoglobin concentration is fairly homogeneous (mean +/- SD, 1.36 +/- 0.6 g/dL [13.6 +/- 6 g/L]), nearly all individuals demonstrate an increase in maximal oxygen uptake (0.357 +/- 0.216 L/min), the magnitude of increase in hemoglobin concentration is not related to the magnitude of increase in maximal oxygen uptake, and the magnitude of increase in maximal oxygen uptake is related to the individual's initial aerobic fitness. Individuals with an initial aerobic fitness between 50 and 65 mL X kg-1 X min-1 experience approximately twice the increase in maximal oxygen uptake after erythrocyte reinfusion of individuals with greater fitness and also of lesser fitness.

Influence of polycythemia on blood volume and thermoregulation during exercise-heat stress

We studied the effects of autologous erythrocyte infusion on blood volume and thermoregulation during exercise in the heat. By use of a double-blind design, nine unacclimated male subjects were infused with either 600 ml of a NaCl-glucose-phosphate solution containing a approximately 50% hematocrit (n = 6, reinfusion) or 600 ml of this solution only (n = 3, saline). A heat stress test (HST) was attempted approximately 2-wk pre- and 48-h postinfusion during the late spring months. After 30 min of rest in a 20 degrees C antechamber, the HST consisted of a 120-min exposure (2 repeats of 15 min rest and 45 min treadmill walking) in a hot (35 degrees C, 45% rh) environment while euhydrated. Erythrocyte volume (RCV, 51Cr) and plasma volume (PV, 125I) were measured 24 h before each HST, and maximal O2 uptake (VO2max) was measured 24 h after each HST. Generally, no significant effects were found for the saline group. For the reinfusion group, RCV (11%, P less than 0.01) and VO2max (11%, P less than 0.05) increased after infusion, and the following observations were made: 1) the increased RCV was associated with a reduction in PV to maintain the same blood volume as during the preinfusion measurements; 2) polycythemia reduced total circulating protein but did not alter F-cell ratio, plasma osmolality, plasma protein content, or plasma lactate at rest or during exercise-heat stress; 3) polycythemia did not change the volume of fluid entering the intravascular space from rest to exercise-heat stress; and 4) polycythemia tended to reduce the rate of heat storage during exercise-heat stress.

Thirst and fluid intake following graded hypohydration levels in humans

The relationship among changes in thirst sensations, blood variables, and differential fluid intake in hypohydrated humans was examined. Seven subjects were hypohydrated by 0%, 3%, 5%, and 7% of their body weight on four separate trials which were systematically randomized between subjects. Hypohydration levels were achieved with a regimen of restricted food and fluid intake and moderate heat-exercise stress. Statistically significant linear and quadratic trends were found for the intensity of several sensations with progressive hypohydration levels. In general, plasma osmolality and renin activity increased and plasma volume decreased with increasing hypohydration levels. During a one hour period of ad lib drinking, all subjects consumed insufficient fluid to rehydrate back to baseline body weights. Using regression analyses, fluid intake was predicted by the magnitude of subjective and physiological indices of hypohydration. Results demonstrate that both hypovolemia and plasma osmolality contribute significantly to fluid intake in hypohydrated humans. The results also indicate that thirst sensations make a substantial contribution to differential fluid intake in humans.

Power spectral analysis of the surface electromyogram during shivering

The purpose of this study was to describe the frequency content of the electromyogram (EMG) recorded during shivering and determine if the EMG power spectrum changed as a function of the shivering duration. Six semi-nude males were exposed to cold air (5 degrees C, 20% rh) for 80 min while quietly sitting. Rectal (Tre) and mean skin (Tsk) temperatures were recorded. Shivering of the masseter muscle was determined using bipolar surface electrodes. The EMG was amplified, recorded, and subsequently digitized at 2048 Hz. The power spectrum was calculated from eight serial 0.25s EMG samples by Fourier analysis from a frequency of 4 through 480 Hz. The eight power spectra were averaged and centroid frequency (fc) calculated. During the first 10 min of exposure, Tsk rapidly dropped from 32.6 +/- 1.6 to 26.2 +/- 1.3 degrees C, then slowly declined reaching 22.5 +/- 0.7 degrees C after 80 min. Tre rose from 37.1 +/- 0.1 to 37.4 +/- 0.1 degrees C, declining after 40 min to 37.2 +/- 0.1 degrees C. Shivering was observed within 5 min after entering the cold chamber. EMG activity after 10 min exhibited an fc of 177.2 +/- 6.2 Hz. When power was integrated over 60 Hz bandwidths, the predominant frequency band of the EMG power spectrum was 60-120 Hz. Although shivering intensity increased with time, the EMG power spectrum exhibited no significant changes. These results suggest that the EMG power spectrum during shivering did not exhibit changes characteristic of muscle fatigue or muscle cooling during the 80-min cold air exposure.