The authors tested the hypothesis in a rat model that hypervolemic
hemodilution during
heatstroke affected the mean arterial pressure (MAP), striatal
dopamine (DA) release, and local cerebral blood flow and neuronal damage score in different brain structures. The
heatstroke was induced by exposing the
urethane-anesthetized rats to an ambient temperature of 42 degrees C. Hypervolemic
hemodilution was produced by
intravenous administration of 10%
human albumin. Relative and absolute blood flow in the corpus striatum were determined using the
laser Doppler flowmetry and the autoradiography diffusible tracer technique, respectively. The DA release in the striatum was estimated using the in vivo microdialysis technique. After onset of
heatstroke, animals with hypervolemic state alone, produced by saline or heparinized blood injection, displayed higher values of DA release, as well as neuronal damage score in the striatum, hypothalamus, or cortex, but lower values of MAP and blood flow in the striatum, hypothalamus, or cortex compared to normothermic controls. However, the
heatstroke-induced arterial
hypotension,
cerebral ischemia, increased striatal DA overload, and increased neuronal damage score were attenuated by induction of both hypervolemic and
hemodilution state with 10%
albumin either before or after the onset of
heatstroke. In addition, constant infusions of a
vasopressor agent phenylephrine (2 microg kg(-1) min(-1)) after the onset of
heatstroke failed to maintain appropriate levels of MAP and resulted in no protection against
heatstroke. Thus, it appears that the observed benefit of the 10%
albumin is secondary to
hemodilution and/or maintenance of MAP.