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  • 1
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. In the present study, we assessed the protective effects of chronic hypoxia preconditioning against heatstroke-induced injury in urethane-anaesthetized rats. Heatstroke was induced by exposing the animals to an ambient temperature of 42°C. The time at which both the mean arterial pressure (MAP) and local cerebral blood flow (CBF) in the striatum began to decrease from peak levels was taken as the onset of heatstroke. Control rats were exposed to a temperature of 24°C.2. Mean arterial pressure, CBF, blood pH, PaO2, PaCO2 and survival time (the interval between onset of heatstroke and cardiac arrest) after heat stress were all lower than in control rats (in which ‘survival time’ was defined as 〉 360 min). However, blood lactate concentrations were greater in rats exposed to heat. Rats placed at high altitude (HA), when exposed to the same heat stress (42°C) survived much longer (113 ± 26 min; n = 8) than rats maintained at sea level (SL; 20 ± 2 min; n = 8).3. After the onset of heatstroke, blood pH and lactate concentrations were found to be significantly higher and lower, respectively, in HA rats than in SL rats.4. Western blot assay revealed that chronic hypoxia preconditioning induced heat shock protein (HSP) 72 expression in both the kidneys and lungs.5. Thus, it appears that the observed benefit of chronic hypoxia preconditioning is related to attenuation of tissue acidification and elevations of HSP72 expression in both kidneys and lungs during heatstroke.
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  • 2
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Chuang J-I, Lin M-T. Pharmacological effects of melatonin treatment on both locomotor activity and brain serotonin release in rats. J. Pineal Res. 1994: 17: 11–16.〈section xml:id="abs1-1"〉〈title type="main"〉AbstractThe effects of intraperitoneal administration of pharmacological doses of melatonin (60 mg/kg) on both locomotor activity and brain monoamine release were assessed in rats. The spontaneous levels of either horizontal motion, vertical motion, or total distance traveled were decreased following melatonin injection. On the other hand, the spontaneous levels of postural freezing increased after treatment. External heat exposure (36°C) produced increases in locomotion (including horizontal motion, vertical motion, and total distance traveled) as well as decreases of postural freezing in rats. The heat-induced increases of horizontal motion and total distance traveled as well as decreases of postural freezing were attenuated by melatonin treatment. In addition, cold exposure (4 C) produced increases of vertical motion as well as decreases of postural freezing. Again, the cold-induced behavioral responses were attenuated by melatonin treatment. Biochemical data revealed that the serum levels of melatonin were decreased by both heat and cold exposure in rats. Furthermore, voltammetric data revealed that intraperitoneal administration of melatonin (60 mg/kg) decreased serotonin, but not the dopamine, release in the hypothalamus, the corpus striatum or nucleus accumbens of rat brain. Neither the locomotor activity responses to thermal stress nor brain monoamine release was affected by a smaller dose of melatonin (30 mg/kg, i. p.). The results suggest that systemic administration of melatonin, at pharmacological doses, inhibits brain serotonin release and results in a reduction in both the spontaneous locomotion and the thermal stress-induced locomotor activity responses in rats.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford UK : Munksgaard International Publishers
    Journal of pineal research 33 (2002), S. 0 
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Effects of melatonin on both thermoregulatory responses and hypothalamic serotonin release were assessed in unanesthetized rats at three different ambient temperatures (Ta). Systemic administration of melatonin (30–120 mg/kg, i.p) caused a decrease in both colonic temperature and hypothalamic serotonin (5-HT) release in rats at both Ta 8 and 22°C. The hypothermia was brought about by a decrease in metabolic rate at Ta 8°C, whereas at Ta 22°C the hypothermia was produced by both a decrease in metabolic rate and an increase in cutaneous temperature. However, in the heat (Ta 31°C), neither thermoregulatory responses nor hypothalamic 5-HT release was affected by the same amount of administered melatonin. The melatonin-induced hypothermia and decreased 5-HT release in the hypothalamus were attenuated by selective depletion of brain 5-HT produced by intracerebroventricular injection of 5,7-dihydroxytryptamine. Furthermore, the melatonin-induced hypothermia was almost completely abolished by treatment with a 5-HT2A receptor agonist (DOI) or a 5-HT1A receptor antagonist [(−)-pindolol]. The data indicate that melatonin potentiates the 5-HT1A receptor activation in the hypothalamus and results in hypothermic effects which can be antagonized by the expected hyperthermic effect of DOI.
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  • 4
    ISSN: 1573-7373
    Keywords: blood-brain barrier ; brain tumor ; 5-fluorouracil ; leukotriene ; methotrexate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Leukotriene E4 (LTE4) infused into the carotid artery ipsilateral to an experimental glial tumor will selectively increase the blood-tumor permeability within the tumor. In this study the effects of intracarotid infusion of LTE4 on blood-tumor barrier (BTB) permeability for intravenously administered14C-aminoisobutyric acid,14C-5-fluorouracil (5-FU)14C-sucrose and3H-methotrexate (MTX) were examined in C6 gliomas of rats. The intracarotic administration of LTE4 selectively opened the BTB, without affecting permeability of normal brain tissue, to all of the above tracers. Intracarotid infusion of LTE4 had the tendency to increase the uptake of intravenously administered 5-FU within the tumor, but this effect was not statistically significant. The intracarotid infusion of LTE4, however, increased the uptake of intravenously injected MTX about twofolds within the tumor (Ki = 19.48 ±1.06 vs 10.12 ±1.19, p 〈 0.01) without increasing the uptake in the normal brain tissue.
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