The Japanese journal of physiology
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Dehydration due to hyperthermia induces both hyperosmolality and hypovolemia. Hyperosmolality reduces evaporative cooling, and alters the thermal responsiveness of the hypothalamic center to changes in both the central and peripheral milieu. Hypovolemia also reduces the thermoregulatory response, but its effect is more variable. ⋯ Regulation of fluid replacement after thermal dehydration can be considered both from the point of view of osmoregulation and volume regulation. In the rehydration process, control of plasma osmolality precedes blood volume regulation, which also suggests that changes in blood volume sensed as changes in the CVP are regulated within a narrow range by various mechanisms. These findings suggest a hierarchic structure for the homeostatic mechanisms related to thermoregulation, with higher priority being given to the maintenance of cardiac output and the cellular volume of the brain at the expense of peripheral circulation and cell volume.
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The effects of electrical stimulation of cervical sympathetic trunks for 1-min duration at supramaximal intensity with various stimulus frequencies on local cortical cerebral blood flow were investigated in urethane-anesthetized rats. Electrical stimulation with low frequency (1-2 Hz) produced a significant increase in local cortical cerebral blood flow during the stimulation. ⋯ High-frequency stimulation (20-30 Hz) produced the short-term increase during the stimulation, which was followed by the dominant and long-lasting decrease, and the local cortical CBF reached 87% (at 30 Hz) of the resting value after the end of stimulation. The response of increase in flow was abolished by intravenous administration of beta adrenergic blocking agent (propranolol, 1.3 mg/kg i.v.), while the response of decrease in flow was abolished by alpha adrenergic blocking agent (phenoxybenzamine, 0.5 mg/kg i.v.).