The effect of sodium balance on sweat sodium secretion and plasma aldosterone concentration

The effect of manipulating sodium intake upon sweat sodium secretion was investigated during heat acclimation. Twenty-five male subjects were confined to an environmental chamber at a temperature of 25°C for 3 days, and then acclimated to heat by a further 5 days at 40°C. The subjects' daily sodium intake was controlled throughout as follows: high (HNa), 348.4 (0.8) mmol · day⁻¹, n = 7; moderate (MNa), 174.1 (0.6) mmol · day⁻¹, n = 9; or low (LNa), 66.3 mmol · day⁻¹, n = 9. Sodium losses were estimated from urinary, faecal and sweat collections using a whole-body washdown method. Plasma aldosterone concentration was also measured from venous blood sampled each morning. Measurements of body temperature and heart rate during the heat exposure phase indicated a degree of heat acclimation. During this heat phase there was a reduction (P < 0.01) in sweat sodium secretion for all three conditions which was greatest for the LNa condition, although this finding was not significant (P < 0.1). In the LNa condition, plasma aldosterone concentration increased (P < 0.05) prior to heat exposure, and the secretion of aldosterone was potentiated (P < 0.01) during the heat exposure in comparison with the MNa condition. In contrast, the HNa diet produced a fall (P < 0.05) in plasma aldosterone concentration prior to heat exposure and an attenuation of aldosterone secretion thereafter. These findings are inconsistent with the hypothesis that retention of sweat sodium is dependent upon a net body sodium deficit, but demonstrate that aldosterone secretion is potentiated under such conditions. Accepted: 22 May 1988     

Heat acclimation does not modify autonomic responses to core cooling and the skin thermal comfort zone

Exercise heat acclimation (HA) is known to magnify the sweating response by virtue of a lower threshold as well as increased gain and maximal capacity of sweating. However, HA has been shown to potentiate the shivering response in a cold-air environment. We investigated whether HA would alter heat loss and heat production responses during water immersion. Twelve healthy male participants underwent a 10-day HA protocol comprising daily 90-min controlled-hyperthermia (target rectal temperature, T_re 38.5 °C) exercise sessions. Preceding and following HA, the participants performed a maximal exercise test in thermoneutral conditions (ambient temperature 23 °C, relative humidity 50%) and were, following exercise, immersed in 28 °C water for 60 min. Thermal comfort zone (TCZ) was also assessed with participants regulating the temperature of a water-perfused suit during heating and cooling. Baseline pre-immersion T_re was similar pre- and post-HA (pre: 38.33 ± 0.33 °C vs post: 38.12 ± 0.36 °C, p = 0.092). The T_re cooling rate was identical pre-to post-HA (−0.03 ± 0.01 °C·min⁻¹, p = 0.31), as was the vasomotor response reflected in the forearm-fingertip temperature difference. Shivering thresholds (p = 0.43) and gains (p = 0.61) were not affected by HA. TCZ was established at similar temperatures, with the magnitude in regulated water temperature being 7.6 (16.3) °C pre-HA and 5.1 (24.7) °C post-HA (p = 0.65). The present findings suggest that heat production and heat loss responses during whole body cooling as well as the skin thermal comfort zone remained unaltered by a controlled-hyperthermia HA protocol.     

Thermal preference,tolerance and oxygen consumption of adult white shrimp Litopenaeus vannamei (Boone) exposed to different acclimation temperatures

Final temperature preferendum of white shrimp adults were determined with acute and gravitation methods. The final preferendum was similar, independent of method (26.2–25.6 °C). A direct relationship was determined between the critical thermal maxima values and the acclimation temperatures (P<0.05). The end point of Critical Thermal Maxima (CTMax) for adults was defined as the loss of righting response (LRR). The acclimation response ratio (ARR) for adults of white shrimp had an interval of 0.36–0.76, values that agreed with others obtained for crustaceans from tropical and subtropical climates. The oxygen consumption rates increased significantly (P<0.05) from 39.6 up to 90.0 mg O₂ kg⁻¹ h⁻¹ wet weight (w.w.) as the acclimation temperature increased from 20 to 32 °C. The range of temperature coefficient (Q₁₀) of the white shrimp between 23 and 26 °C was the lower 1.60. The results obtained in this work are discussed in relation to the species importance in the reproductive scope and maintenance of breeders.     

Thermal tolerance and standard metabolic rate of juvenile gilthead seabream (Sparus aurata) acclimated to four temperatures

Temperature variation affects the growth, maturation and distribution of fish species due to increasing constraints on physiological functions therefore, the aim of the present study is to evaluate effect of temperature on thermal tolerance and standard metabolic rate (SMR) of gilthead seabream (Sparus aurata). For this purpose, tolerable temperature ranges of juvenile gilthead seabream acclimated at 15, 20, 25, and 30 °C for 30 days were estimated using dynamic and static thermal methodologies. The SMRs of the fish were also determined based on oxygen consumption rate (OCR). The dynamic and static thermal tolerance zones of gilthead seabream were calculated as 737 °C² and 500 °C², respectively, with a resistance zone area of 155.5 °C². The SMR of the fish at the above acclimation temperatures (AT) was determined as 138, 257, 510, and 797 mg O₂ h⁻¹ kg⁻¹, respectively and were significantly different (P < 0.01, n = 10). The temperature quotient (Q₁₀) in relation to the SMR of the fish was calculated as 3.45, 3.91, and 2.44 for acclimation temperature ranges of 15–20, 20–25, and 25–30 °C, respectively. The fact that the SMR increased with rising temperatures and then decreased gradually after 25 °C indicates that the temperature preference of juvenile gilthead seabream lies between 25 and 30 °C. This study shows that gilthead seabream tolerates a relatively narrow temperature range, and consequently, a low capacity for acclimatisation to survive in aquatic systems characterised by temperature variations.     

The effect of heat acclimation on maximal urine osmolality in humans

The purpose of the current study was to determine the effect of 9 days of active heat acclimation on maximal urine osmolality (MUO) in humans. Eight subjects completed 9 days of heat acclimation, which consisted of a daily 90 min exercise session in a heated environmental chamber. Before and following heat acclimation the subjects abstained from drinking fluids for 15 h, and urine samples were collected to measure MUO. The subjects successfully heat acclimated as evidenced by a significant (P<0.05) decrease in the mean±SD exercise core temperature (37.7±0.3 °C on day 1 to 37.4±0.3 °C on day 9) and heart rate (143±17 bpm on day 1 to 128±14 bpm on day 9). The mean pre- and post-heat acclimation MUOs were 868±117 and 846±89 mmol kg⁻¹, respectively, which were not significantly different (P>0.05). Previous studies have shown that prolonged dehydration can increase the MUO in various mammalian species, including humans. In contrast, the results of the current study suggest that 9 days of active heat acclimation, without significant dehydration, does not affect the MUO in humans.     

Sweat rate and sweat composition during heat acclimation

The purpose of this study was to determine local sweat rate (LSR) and sweat composition during heat acclimation (HA). For ten consecutive days of HA, eight participants cycled in 33 °C and 65% relative humidity at an intensity such that a rectal temperature of 38.5 °C was reached within ~40 min, followed by a 60-min clamp of this rectal temperature (i.e., controlled hyperthermia). Four participants extended HA by a 28-day decay period and five consecutive days of heat re-acclimation (HRA) using controlled hyperthermia. Sweat from the upper arm and upper back was collected three times during each heat exposure session. LSR and sweat sodium, chloride, lactate, and potassium concentrations were determined. Relative to HA day 1, LSR was increased at the final day of HA (day 10) (arm: +58%, P < 0.001; back: +36%, P < 0.05). Concentrations of sodium, chloride, and lactate significantly (P < 0.05) decreased to ~60% at HA day 10 compared to day 1 on the arm and back. Potassium concentration did not significantly differ on HA day 10 compared to day 1 (arm: +11%, P > 0.05; back: +8%, P > 0.05). The induction patterns of the sudomotor adaptations were different. Whilst LSR increased from HA day 8 on the arm and from HA day 7 on the back, sodium and chloride conservation already occurred from HA day 3 on both skin sites. Lastly, the sweat lactate reduction occurred from HA day 6 on the arm and back. Initial evidence is provided that adaptations were partly conserved after decay (28 days) and that a 5-day HRA may be sufficient to restore HA adaptations. In conclusion, ten days of exercise-induced HA using controlled hyperthermia led to increases in LSR and concomitant reductions of sweat sodium, chloride, and lactate concentrations, whilst potassium concentrations remained relatively constant.     

Validity of a wearable sweat rate monitor and routine sweat analysis techniques using heat acclimation

Introductionthe aim of this study was to assess the validity of a novel wearable sweat rate monitor against an array of sweat analysis techniques which determine sudomotor function when exercising moderately under heat stress. Construct validity was determined utilising a 5-day short-term heat acclimation (STHA) intervention.MethodsNineteen healthy individuals (age: 41 ± 23 years, body mass: 74.0 ± 12.2 kg, height: 174.9 ± 6.9 cm) [male; n = 15, female; n = 4] completed nine trials over a three-week period, in a controlled chamber set to 35 °C, 50% relative humidity for all sessions. The pre and post-trials were separated by five consecutive controlled hyperthermia HA sessions. Sweat analysis was compared from pre and post-trial, whereby whole body sweat rate (WBSR) was assessed via pre and post nude body mass. Local sweat rate (LSR) was determined via technical absorbent patches (TA) (weighed pre and post) and a novel wearable KuduSmart® (SMART) monitor which was placed on the left arm during the 30-min of exercise. Tegaderm patches, used to measure sweat sodium chloride conductivity (SC), and TA patches were placed on the back, chest and forearm for the 30-min cycling.ResultsSudomotor function significantly adapted via STHA (p < 0.05); demonstrated by a WBSR increase of 24%, LSR increase via the TA method (back: 26%, chest: 45% and arm: 48%) and LSR increase by the SMART monitor (35%). Finally, SC decreased (back: -21%, chest: -25% and arm: -24%, p < 0.05).ConclusionAll sweat techniques were sensitive to sudomotor function adaptation following STHA, reinforcing their validity. The real time data given by the wearable KuduSmart® monitor provides coaches and athletes instant comparable sudomotor function feedback to traditional routinely used sweat analysis techniques.     

Thermoregulatory reflexes and cutaneous active vasodilation during heat stress in hypertensive humans

During dynamic exercise in the heat, increasesin skin blood flow are attenuated in hypertensive subjects whencompared with normotensive subjects. We studied responses to passiveheat stress (water-perfused suits) in eight hypertensive and eightnormotensive subjects. Forearm blood flow was measured byvenous-occlusion plethysmography, mean arterial pressure (MAP) wasmeasured by Finapres, and forearm vascular conductance (FVC) wascalculated. Bretylium tosylate (BT) iontophoresis was used to blockactive vasoconstriction in a small area of skin. Skin blood flow was indexed by laser-Doppler flowmetry at BT-treated and untreated sites,and cutaneous vascular conductance was calculated. In normothermia, FVCwas lower in hypertensive than in normotensive subjects(P < 0.01). During heat stress, FVCrose to similar levels in both groups(P > 0.80); concurrent cutaneousvascular conductance increases were unaffected by BT treatment(P > 0.60). MAP was greater in hypertensive than in normotensive subjects during normothermia (P < 0.05, hypertensive vs.normotensive subjects). During hyperthermia, MAP fell in hypertensivesubjects but showed no statistically significant change in normotensivesubjects (P < 0.05, hypertensive vs.normotensive subjects). The internal temperature at which vasodilationbegan did not differ between groups (P > 0.80). FVC is reduced during normothermia in unmedicatedhypertensive subjects; however, they respond to passive heat stress ina fashion no different from normotensive subjects.

     

Passive heat exposure induced by hot water leg immersion increased oxyhemoglobin in pre-frontal cortex to preserve oxygenation and did not contribute to impaired cognitive functioning

This study investigated the effects of passive heat exposure on pre-frontal cortex oxygenation and cognitive functioning, specifically to examine whether the change in pre-frontal cortex oxygenation coincided with cognitive functioning during heat exposure. Eleven male students who participated in this study immersed their lower legs to the knees in three different water temperatures, 38 °C, 40 °C, and 42 °C water in an air temperature of 28?º C and 50 % relative humidity for 60 min. After 45 min of leg immersion they performed cognitive functioning tasks assessing their short-term memory while immersing their lower legs. There were higher rectal temperature (P?<?0.05) and higher increase of oxyhemoglobin in both left (P?<?0.05) and right (P?<?0.05) pre-frontal cortex at the final stage of 45-min leg immersion in the 42 °C condition with unaltered tissue oxygenation index among the three conditions (P?>?0.05). No statistical difference in cognitive functioning among the three conditions was observed with a higher increase of oxyhemoglobin during the cognitive functioning in the 42 °C condition for the left (P?=?0.05) and right (P?<?0.05) pre-frontal cortex. The findings of this study suggest, first, passive heat exposure increases oxygen delivery in the pre-frontal cortex to maintain pre-frontal cortex oxygenation; second, there is no evidence of passive heat exposure in cognitive functioning in this study; and third, the greater increases of oxyhemoglobin in the pre-frontal cortex during cognitive functioning at the hottest condition suggests a recruitment of available neural resources or greater effort to maintain the same performance at the same level as when they felt thermally comfortable.     

Effects of heat acclimation on sweating during graded exercise until exhaustion

The aim of the present study was to test the hypothesis that the sweating during graded exercise until exhaustion in a temperate environment would be greater after heat acclimation. Six healthy young males performed an exercise–heat stress acclimation protocol during 9 days. Before (PRE) and after (POS) the acclimation protocol they performed a graded exercise until exhaustion and the sweat loss during exercise increased after acclimation (3.94±1.10, PRE, and 4.86±1.70 g m⁻² min⁻¹, POS; p<0.05). The results showed that daily prolonged exposures to exercise-heat stress increased sweating during a graded and short duration exercise in a temperate environment.     

Indirect hand and forearm vasomotion: Regional variations in cutaneous thermosensitivity during normothermia and mild hyperthermia

In this experiment, hand and forearm vasomotor activity was investigated during localised, but stable heating and cooling of the face, hand and thigh, under open-loop (clamped) conditions. It was hypothesised that facial stimulation would provoke the most potent vascular changes. Nine individuals participated in two normothermic trials (mean body temperature clamp: 36.6 °C; water-perfused suit and climate chamber) and two mildly hyperthermic trials (37.9 °C). Localised heating (+5 °C) and cooling (−5 °C) stimuli were applied to equal surface areas of the face, hand and thigh (perfusion patches: 15 min), while contralateral forearm or hand blood flows (venous-occlusion plethysmography) were measured (separate trials). Thermal sensation and discomfort votes were recorded before and during each thermal stimulation. When hyperthermic, local heating induced more sensitive vascular responses, with the combined thermosensitivity of both limb segments averaging 0.011 mL·100 mL⁻¹·min⁻¹·mmHg⁻¹·°C⁻¹, and 0.005 mL·100 mL⁻¹·min⁻¹·mmHg⁻¹·°C⁻¹ during localised cooling (P<0.05). Inter-site comparisons among the stimulated sites yielded minimal evidence of variations in local thermal sensation, and no differences were observed for vascular conductance (P>0.05). Therefore, regional differences in vasomotor and sensory sensitivity appeared not to exist. When combined with previous observations of sudomotor sensitivity, it seems that, during mild heating and cooling, regional representations within the somatosensory cortex may not translate into meaningful differences in thermal sensation or the central integration of thermoafferent signals. It was concluded that inter-site variations in the cutaneous thermosensitivity of these thermolytic effectors have minimal physiological significance over the ranges investigated thus far.     

The effect of 15 consecutive days of heat–exercise acclimation on heat shock protein 70

The purpose of this study was to investigate the alterations in serum heat shock protein (Hsp) 70 levels during a 15-consecutive-day intermittent heat–exercise protocol in a 29-year-old male ultra marathon runner. Heat acclimation, for the purpose of physical activities in elevated ambient temperatures, has numerous physiological benefits including mechanisms such as improved cardiac output, increased plasma volume and a decreased core temperature (T _c). In addition to the central adaptations, the role of Hsp during heat acclimation has received an increasing amount of attention. The acclimation protocol applied was designed to correspond with the athlete’s tapering period for the 2007 Marathon Des Sables. The subject (VO₂max = 50.7 ml·kg⁻¹·min⁻¹, peak power output [PPO] = 376 W) cycled daily for 90 min at a workload corresponding to 50% of VO₂max in a temperature-controlled room (average WBGT = 31.9 ± 0.9°C). Venous blood was sampled before and after each session for measurement of serum osmolality and serum Hsp70. In addition, T _c, heart rate (HR) and power output (PO) was measured throughout the 90 min to ensure that heat acclimation was achieved during the 15-day period. The results show that the subject was successfully heat acclimated as seen by the lowered HR at rest and during exercise, decreased resting and exercising T _c and an increased PO. The heat exercise resulted in an initial increase in Hsp70 concentrations, known as thermotolerance, and the increase in Hsp70 after exercise was inversely correlated to the resting values of Hsp70 (Spearman’s rank correlation = −0.81, p < 0.01). Furthermore, the 15-day heat–exercise protocol also increased the basal levels of Hsp70, a response different from that of thermotolerance. This is, as far as we are aware, the first report showing Hsp70 levels during consecutive days of intermittent heat exposure giving rise to heat acclimation. In conclusion, a relatively longer heat acclimation protocol is suggested to obtain maximum benefit of heat acclimation inclusive of both cellular and systemic adaptations.     

Eleven days of moderate exercise and heat exposure induces acclimation without significant HSP70 and apoptosis responses of lymphocytes in college-aged males

The purpose of this study was to assess whether a lymphocyte heat shock response and altered heat tolerance to ex vivo heat shock is evident during acclimation. We aimed to use flow cytometry to assess the CD3⁺CD4⁺ T lymphocyte cell subset. We further aimed to induce acclimation using moderately stressful daily exercise-heat exposures to achieve acclimation. Eleven healthy males underwent 11 days of heat acclimation. Subjects walked for 90 min (50 ± 8% VO_2max) on a treadmill (3.5 mph, 5% grade), in an environmental chamber (33°C, 30–50% relative humidity). Rectal temperature (°C), heart rate (in beats per minute), rating of perceived exertion , thermal ratings, hydration state, and sweat rate were measured during exercise and recovery. On days 1, 4, 7, 10, and 11, peripheral blood mononuclear cells were isolated from pre- and post-exercise blood samples. Intracellular and surface HSP70 (SPA-820PE, Stressgen, Assay Designs), and annexin V (ab14085, Abcam Inc.), as a marker of early apoptosis, were measured on CD3⁺ and CD4⁺ (sc-70624, sc-70670, Santa Cruz Biotechnology) gated lymphocytes. On day 10, subjects experienced 28 h of sleep loss. Heat acclimation was verified with decreased post-exercise rectal temperature, heart rate, and increased sweat rate on day 11, versus day 1. Heat acclimation was achieved in the absence of significant changes in intracellular HSP70 mean fluorescence intensity and percent of HSP70⁺ lymphocytes during acclimation. Furthermore, there was no increased cellular heat tolerance during secondary ex vivo heat shock of the lymphocytes acquired from subjects during acclimation. There was no effect of a mild sleep loss on any variable. We conclude that our protocol successfully induced physiological acclimation without induction of cellular heat shock responses in lymphocytes and that added mild sleep loss is not sufficient to induce a heat shock response.     

稻纵卷叶螟幼虫驯化产生的热适应能力的继代效应

摘要: 【目的】在全球不断变暖背景下,昆虫受到热胁迫的频率不断增加。短期内反复受到热胁迫会使昆虫产生热适应性,但是昆虫热驯化所产生的耐热能力的传代效应还不完全清楚。稻纵卷叶螟Cnaphalocrocis medinalis是水稻上的重要害虫,对其幼虫在特定温度下进行几代热锻炼可提高其对高温的适应能力。本研究旨在摸清稻纵卷叶螟热适应的传代能力,为在全球变暖形势下以温度因子预测其种群发展趋势提供指导。【方法】将实验室内分别经39℃和41℃连续锻炼30代建立的稻纵卷叶螟热锻炼品系HA39和HA41以及非锻炼品系HA27的1-5龄期幼虫在不同温度(36℃和41℃)下进行不同时长(1~144 h)的暴露处理,调查幼虫的存活率,确定热锻炼品系幼虫的耐热能力;采用两品系间杂交实验测定HA39和HA27各交配组合的繁殖力及后代3龄幼虫的耐热能力;对HA39停止高温锻炼,并测定停止锻炼2代后3龄幼虫的耐热能力。【结果】稻纵卷叶螟3龄幼虫经历多代次短期热锻炼不仅可提高该龄幼虫的高温适应力,而且可提高其他龄期幼虫对特定高温的耐受能力,表现为HA39和HA41在36或41℃下处理特定时长的存活率显著高于HA27。锻炼高温的不同,幼虫获得的热耐受能力也有差异。39℃下锻炼可提高4龄幼虫在36℃下暴露2和4 d以及5龄幼虫在41℃下暴露5和6 h时的存活率,但41℃下锻炼则不可。HA39和HA27的自交及杂交后代的繁殖力之间均无显著差异,杂交后代3龄幼虫在41℃下处理5和6 h时的存活率与HA39自交后代的相当,并且显著高于HA27自交后代的,幼虫通过热锻炼获得的耐热能力可从亲本遗传给后代。停止热锻炼2代后,在39℃下处理4 h时HA39 3龄幼虫的存活率显著高于HA27的,但39℃下其余处理时间以及36和41℃下处理1~7 h HA39 3龄幼虫的存活率均与HA27的无显著差异,表明幼虫热锻炼产生的耐热能力在停止锻炼后2代仍可部分保持。【结论】稻纵卷叶螟幼虫的热适应能力具有继代效应。经过长期的气候变暖适应后,稻纵卷叶螟种群的热适应能力很可能在不断增强,从而夏季高温对其种群的抑制作用减弱,其种群暴发频率增加。     

Thermal tolerance and preferred temperature range of juvenile meagre acclimated to four temperatures

The present study reports the temperature tolerance, estimated using dynamic and static methodologies, and preferred temperature range, based on oxygen consumption rate (OCR), of juvenile meagre (Argyrosomus regius) (Asso, 1801) (3.4±0.9 g) after 30 days of acclimation at 18, 22, 26 and 30 °C. Meagre has dynamic and static thermal tolerance zones of 551 °C² and 460 °C², respectively and is a low resistance fish species, with a resistance zone area of 87 °C². The OCR of juvenile meagre at the above acclimation temperatures was 370, 410, 618 and 642 mg h⁻¹ kg⁻¹, respectively, and is significantly different (P<0.0001, n=20). The fact that OCR increases by rising temperatures and gradually decreases after 26 °C indicates that the preferred temperature range of juvenile meagre is between 26 and 30 °C. Our study suggests that meagre is unable to respond to low and high temperature variation in aquaculture facilities or its natural habitats.     

Effects of hair coat characteristics on radiant surface temperature in horses

Horse owners may lack knowledge about natural thermoregulation mechanisms in horses. Horses are managed intensively; usually stabled at night and turned out during the day. Some are clipped and many wear a blanket, practices which reduce the horse's ability to regulate heat dissipation. The aim of this study was to investigate the relationship between hair coat characteristics, body condition and infrared surface temperatures from different body parts of horses. Under standard conditions, the body surface temperature of 21 adult horses were investigated using infrared thermography. From several readings on the same body part, a mean temperature was calculated for each body part per horse. Detailed information on horse breed, age, management and body condition was collected. Hair coat samples were also taken for analyses. A mixed statistical model was applied. Warmblood horse types (WB) had lower hair coat sample weights and shorter hair length than coldblood horse types (CB). The highest radiant surface temperatures were found at the chest 22.5 ± 0.9 °C and shoulders 20.4 ± 1.1 °C and WB horses had significantly higher surface temperatures than CB horses on the rump (P < 0.05). Horses with a higher hair coat sample weight had a lower surface temperature (P < 0.001) and hind hooves with iron shoes had a significant lower surface temperature than unshod hind hooves (P = 0.03). In conclusion, individual assessment of radiant surface temperature using infrared thermography might be a promising tool to gather data on heat loss from the horses' body. Such data may be important for management advice, as the results showed individual differences in hair coat characteristics and body condition in horses of similar breeds.     

Osmo- and ionoregulatory responses of green sturgeon (<Emphasis Type="Italic">Acipenser medirostris</Emphasis>) to salinity acclimation

The green sturgeon is a long-lived, highly migratory species with populations that are currently listed as threatened. Their anadromous life history requires that they make osmo- and ionoregulatory adjustments in order to maintain a consistent internal milieu as they move between fresh-, brackish-, and seawater. We acclimated juvenile green sturgeon (121 ± 10.0 g) to 0 (freshwater; FW), 15 (estuarine; EST), and 24 g/l (SF Bay water; BAY) at 18°C for 2 weeks and measured the physiological and biochemical responses with respect to osmo- and ionoregulatory mechanisms. Plasma osmolality in EST- and BAY-acclimated sturgeon was elevated relative to FW-acclimated sturgeon (P < 0.01), but there was no difference in muscle water content or abundance of stress proteins. Branchial Na⁺, K⁺-ATPase (NKA) activity was also unchanged, but abundance within mitochondrion-rich cells (MRC) was greater in BAY-acclimated sturgeon (P < 0.01). FW-acclimated sturgeon had the greatest NKA abundance when assessed at the level of the entire tissue (P < 0.01), but there were no differences in v-type H⁺ATPase (VHA) activity or abundance between salinities. The Na⁺, K⁺, 2Cl⁻ co-transporter (NKCC) was present in FW-acclimated sturgeon gills, but the overall abundance was lower relative to sturgeon in EST or BAY water (P < 0.01) where this enzyme is crucial to hypoosmoregulation. Branchial caspase 3/7 activity was significantly affected by acclimation salinity (P < 0.05) where the overall trend was for activity to increase with salinity as has been commonly observed in teleosts. Sturgeon of this age/size class were able to survive and acclimate following a salinity transfer with minimal signs of osmotic stress. The presence of the NKCC in FW-acclimated sturgeon may indicate the development of SW-readiness at this age/size.     

Effects of cold exposure discontinuation on finger cold-induced vasodilation of older retired Korean female divers ‘Haenyeos’

The purpose of the present study was to investigate the effects of cold exposure discontinuation on local cold tolerance of older retired female haenyeos in Korea. A total of 30 older women participated in this study: older retired haenyeos (89 ± 4 y in age, N = 10), active haenyeos (current divers) (75 ± 4 y, N = 10), and age-matched non-divers (75 ± 6 y, N = 10). Our criterion for local cold tolerance was cold-induced vasodilation (CIVD) of the finger. Active haenyeos showed greater local cold tolerance in terms of higher minimum temperature of the left finger during immersion and recovery than the other two groups (P < 0.05). Furthermore, active haenyeos showed higher skin temperatures of the right finger and left foot as well (P < 0.05). Older retired haenyeos displayed the second best minimum finger temperature both during immersion and during recovery (15 min and 20 min), whereas their local cold tolerance was evaluated as inferior to active haenyeos and the age-matched non-divers in CIVD frequency, finger pain sensation, thermal comfort, and finger temperature during the earlier period of recovery (5 min and 10 min). These results suggested that older retired haenyeos’ cold tolerance in their extremities disappeared in terms of finger temperature in their initial recovery periods, but that they might still retain cold adaptation in terms of minimum finger temperature or later recovery responses, even though the attributes were not marked as much as those of active haenyeos.