Effects of slow and rapid cooling on catecholamine concentration in arterial plasma and the skin

Neuromotor deficits and altered physiological responses to repeated exertional heat stroke exposures in mice

Exertional heat stroke (EHS) is a life-threatening illness that can lead to negative health outcomes. Using a "severe" preclinical mouse model of EHS, we tested the hypotheses that one EHS exposure results in altered susceptibility to a subsequent EHS and reduced neuromotor performance. Female C57BL/6 mice underwent two protocols, 2 wk apart, either an EHS trial (EHS) or a sham exercise control trial (EXC). For EHS, mice ran in a forced running wheel at 37.5°C/40% relative humidity until loss of consciousness, followed by a slow cooling protocol (2 h recovery at 37.5°C). EXC mice exercised equally but in ∼22°C. Mice were randomized into three groups: 1) EXC-EXC (two consecutive EXC, n = 6, 2) EHS-EXC (EHS followed by EXC, n = 5), and 3) EHS-EHS (repeated EHS, n = 9). Mice underwent noninvasive neuromotor and behavioral tests during recovery and isolated soleus force measurements at the end of recovery. At the first EHS, mice reached average peak core temperatures (Tc,max) of 42.4°C, (46% mortality). On the second EHS, average Tc,max was reduced by ∼0.7°C (P < 0.05; mortality 18%). After the first EHS, both EHS-EX and EHS-EHS showed significant reductions in maximum strength (24 h and 1 wk post). After the second EHS, strength, horizontal rotation, hindlimb tone, suspended hindlimb splay, trunk curl, and provoked biting continued to decline in the EHS-EHS group. In conclusion, exposure to a second EHS after 2 wk leads to increased exercise times in the heat, symptom limitation at a lower Tc,max, and greater deficits in neuromotor and behavioral function during recovery.

Effect of the sympathetic nervous system co-transmitters ATP and norepinephrine on thermoregulatory response to cooling

The existence of co-transmitters of the sympathetic nervous system norepinephrine (NE) and ATP implies variations in the neuromodulator mechanisms of physiological processes. The role of ATP, as a transmitter of the peripheral part of sympathetic nervous system in the formation of thermoregulatory response is not clear. Whether ATP modulates any parameters of thermoregulatory response to cold; if yes, whether co-transmitters of sympathetic nervous system ATP and NE differently modulate thermoregulatory response and on which parameters of cold-defense response the influence of ATP is more pronounced. Experiments were carried out on rats. ATP (10(-6)), NE (10(-3)), and their mixture introduced iontophoretically into skin. Their effects on thermoregulatory parameters (temperature parameters, total oxygen consumption, carbon dioxide release, muscle activity, respiratory coefficient) were studied in thermoneutral conditions (without cold load) and under the cooling. In thermoneutral conditions both ATP and NE enhance total metabolism through increase in metabolic rate of lipids, NE effect being more expressed. It was shown that ATP and NE influence predominantly on the different components of the metabolic response to cold. ATP affects to the greatest extent on cold muscular thermogenesis by increasing shivering almost twofold and lowering its initiation temperature thresholds, whereas NE mainly promotes increase in non-shivering thermogenesis. When introducing the mixture of these biological substances the effect of NE is more expressed and the ATP effect is weakened. The obtained results allow to suggest that in vivo the NE effects can be more expressed when the sympathetic nervous system is stimulated by cold. Thus, NE and ATP being co-transmitters and predominantly acting on the different processes of cold thermogenesis (ATP on shivering and NE on non-shivering) may organize the certain sequence of cold defense responses.

Specificity study on concentration of monoamine transmitters at acupoint and effect of acupuncture on its distribution

To investigate the distribution of monoamine transmitters at acupoints and effect of acupuncture on it. Take this experiment by means of microdialysis. Twenty rabbits were randomly assigned to two groups (Group A: acupuncture Guanyuan (RN4), Group B: acupuncture nonacupoint which is besides Guanyuan (RN4) 1 cm). Before and after acupuncture was taken, tissue fluids both at Zhongwan (RN12) which is on the same meridian as Guanyuan and at a nonacupoint 1 cm away from Zhongwan were collected through microdialysis, respectively. The collected samples were analyzed to determine concentrations of monoamine transmitters. Epinephrine and 5-HT were detected. An unknown substance was found. Its concentration at acupoint was significantly higher than that at nonacupoint and decreased after acupuncture. Its significant specificity at acupoints suggests that it may play an important role in meridian's activity.

Two strategies for response to 14 °C cold-water immersion: is there a difference in the response of motor, cognitive, immune and stress markers?

Here, we address the question of why some people have a greater chance of surviving and/or better resistance to cold-related-injuries in prolonged exposure to acute cold environments than do others, despite similar physical characteristics. The main aim of this study was to compare physiological and psychological reactions between people who exhibited fast cooling (FC; n = 20) or slow cooling (SC; n = 20) responses to cold water immersion. Individuals in whom the T(re) decreased to a set point of 35.5 °C before the end of the 170-min cooling time were indicated as the FC group; individuals in whom the T(re) did not decrease to the set point of 35.5 °C before the end of the 170-min cooling time were classified as the SC group. Cold stress was induced using intermittent immersion in bath water at 14 °C. Motor (spinal and supraspinal reflexes, voluntary and electrically induced skeletal muscle contraction force) and cognitive (executive function, short term memory, short term spatial recognition) performance, immune variables (neutrophils, leucocytes, lymphocytes, monocytes, IL-6, TNF-α), markers of hypothalamic-pituitary-adrenal axis activity (cortisol, corticosterone) and autonomic nervous system activity (epinephrine, norepinephrine) were monitored. The data obtained in this study suggest that the response of the FC group to cooling vs the SC group response was more likely an insulative-hypothermic response and that the SC vs the FC group displayed a metabolic-insulative response. The observations that an exposure time to 14 °C cold water--which was nearly twice as short (96-min vs 170-min) with a greater rectal temperature decrease (35.5 °C vs 36.2 °C) in the FC group compared with the SC group--induces similar responses of motor, cognitive, and blood stress markers were novel. The most important finding is that subjects with a lower cold-strain-index (SC group) showed stimulation of some markers of innate immunity and suppression of markers of specific immunity.

Modulating effects of calcium on immune response of homoiothermal animal under thermoneutral conditions and during deep cooling

Preliminary ionophoretic administration of Ca(2+) ions into the skin prevents the inhibitory effects of deep cooling on some processes characterizing the immune response. Differently directed changes in some immune response parameters induced by exogenous calcium and deep cooling suggest that competitive interactions between calcium-dependent processes can serve as mechanisms of functional changes in various physiological systems during the formation of the systemic reaction of a homoiothermal organism to cold.

Adrenaline is a critical mediator of acute exercise-induced AMP-activated protein kinase activation in adipocytes

Exercise increases AMPK (AMP-activated protein kinase) activity in human and rat adipocytes, but the underlying molecular mechanisms and functional consequences of this activation are not known. Since adrenaline (epinephrine) concentrations increase with exercise, in the present study we hypothesized that adrenaline activates AMPK in adipocytes. We show that a single bout of exercise increases AMPKalpha1 and alpha2 activities and ACC (acetyl-CoA carboxylase) Ser79 phosphorylation in rat adipocytes. Similarly to exercise, adrenaline treatment in vivo increased AMPK activities and ACC phosphorylation. Pre-treatment of rats with the beta-blocker propranolol fully blocked exercise-induced AMPK activation. Increased AMPK activity with exercise and adrenaline treatment in vivo was accompanied by an increased AMP/ATP ratio. Adrenaline incubation of isolated adipocytes also increased the AMP/ATP ratio and AMPK activities, an effect blocked by propranolol. Adrenaline incubation increased lipolysis in isolated adipocytes, and Compound C, an AMPK inhibitor, attenuated this effect. Finally, a potential role for AMPK in the decreased adiposity associated with chronic exercise was suggested by marked increases in AMPKalpha1 and alpha2 activities in adipocytes from rats trained for 6 weeks. In conclusion, both acute and chronic exercise are significant regulators of AMPK activity in rat adipocytes. Our findings suggest that adrenaline plays a critical role in exercise-stimulated AMPKalpha1 and alpha2 activities in adipocytes, and that AMPK can function in the regulation of lipolysis.

Effect of rapid slight cooling of the skin in various phases of immunogenesis on the immune response

Slight cooling had no effect on heat emission and heat production, but modulated the immune response to antigen in animals. Changes in the immune response upon rapid slight cooling of the skin (by 1.5 degrees C) depended on the phase of immunogenesis corresponding to cold exposure. When cooling was performed immediately after immunization, antibody production increased in the spleen and blood, while antigen binding in the spleen remained unchanged. Cold exposure on day 5 after antigen treatment as well as immunization at the peak of cooling did not modulate antibody production, but increased antigen binding in the spleen. Our findings attest to an important role of the temperature factor in the formation of the immune response, which should be taken into account during vaccination.

Effects of rapid and slow cooling on thermoregulatory reactions in hypertensive rats after administration of calcium

Iontophoretic administration of calcium ions into the skin close to the application site of a cold stimulus decreased the threshold of thermoregulatory reactions in hypertensive rats to a greater extent than in normotensive control animals, which may be evidence that the tissues involved in thermoregulatory reactions to cold have a greater sensitivity to calcium in hypertensive rats. The initially earlier onset of vascular and metabolic reactions and the increase in the vascular reaction seen in hypertensive rats became more marked after administration of calcium. Treatment with calcium, increasing the vascular reaction to cooling, facilitates a more marked discrimination between hyper-and normotensive animals in terms of the appearance of the vasoconstrictor reactions of skin blood vessels in response to cold. The effects of the added calcium on cold-dependent reactions depended on the rate of cooling.

Central and peripheral thermoreceptors. Comparative analysis of the effects of prolonged adaptation to cold and noradrenaline

This report presents results obtained from many years of study of the effects of prolonged adaptation to cold and noradrenaline on the spike activity of central hypothalamic and peripheral skin thermoreceptors. The involvement of the sympathetic nervous system in forming adaptive changes in the regulatory characteristics of temperature homeostasis and the significance of the various components of thermoreceptor activity to the formation of effector responses are discussed. The roles of different groups of thermoreceptors in forming temperature sensations are analyzed.

Effect of substance P on thermoregulation parameters during different cooling modes

The modulatory effect of ionophoretic application of substance P to the skin on the formation of the cold-triggered thermal protection reactions depends on the rate of cooling. During rapid cooling substance P enhances heat production, while during slow cooling it promotes constriction of skin blood vessels aimed at reduction of heat emission.

Precooling leg muscle improves intermittent sprint exercise performance in hot, humid conditions

We used three techniques of precooling to test the hypothesis that heat strain would be alleviated, muscle temperature (Tmu) would be reduced, and as a result there would be delayed decrements in peak power output (PPO) during exercise in hot, humid conditions. Twelve male team-sport players completed four cycling intermittent sprint protocols (CISP). Each CISP consisted of twenty 2-min periods, each including 10 s of passive rest, 5 s of maximal sprint against a resistance of 7.5% body mass, and 105 s of active recovery. The CISP, preceded by 20 min of no cooling (Control), precooling via an ice vest (Vest), cold water immersion (Water), and ice packs covering the upper legs (Packs), was performed in hot, humid conditions (mean +/- SE; 33.7 +/- 0.3 degrees C, 51.6 +/- 2.2% relative humidity) in a randomized order. The rate of heat strain increase during the CISP was faster in Control than Water and Packs (P < 0.01), but it was similar to Vest. Packs and Water blunted the rise of Tmu until minute 16 and for the duration of the CISP (40 min), respectively (P < 0.01). Reductions in PPO occurred from minute 32 onward in Control, and an increase in PPO by approximately 4% due to Packs was observed (main effect; P < 0.05). The method of precooling determined the extent to which heat strain was reduced during intermittent sprint cycling, with leg precooling offering the greater ergogenic effect on PPO than either upper body or whole body cooling.

Melanin pigmentation in mammalian skin and its hormonal regulation

Cutaneous melanin pigment plays a critical role in camouflage, mimicry, social communication, and protection against harmful effects of solar radiation. Melanogenesis is under complex regulatory control by multiple agents interacting via pathways activated by receptor-dependent and -independent mechanisms, in hormonal, auto-, para-, or intracrine fashion. Because of the multidirectional nature and heterogeneous character of the melanogenesis modifying agents, its controlling factors are not organized into simple linear sequences, but they interphase instead in a multidimensional network, with extensive functional overlapping with connections arranged both in series and in parallel. The most important positive regulator of melanogenesis is the MC1 receptor with its ligands melanocortins and ACTH, whereas among the negative regulators agouti protein stands out, determining intensity of melanogenesis and also the type of melanin synthesized. Within the context of the skin as a stress organ, melanogenic activity serves as a unique molecular sensor and transducer of noxious signals and as regulator of local homeostasis. In keeping with these multiple roles, melanogenesis is controlled by a highly structured system, active since early embryogenesis and capable of superselective functional regulation that may reach down to the cellular level represented by single melanocytes. Indeed, the significance of melanogenesis extends beyond the mere assignment of a color trait.