Osmotic regulation of evaporative water loss and body temperature by intracranial receptors in the heat-stressed cat.

The effect on body temperature (Tb) regulation of alterations in the osmotic milieu of the intracranial compartment has been examined by intracerebroventricular (ICV) infusion of water (0.034 ml . min-1) in heat-stressed hydrated and dehydrated cats. At an ambient temperature (Ta) of 38 degrees C, before ICV water infusion, mean Tb (measured in the hypothalamus) of normally hydrated cats was 38.8 +/- 0.1 degree C and mean evaporative water loss (EWL) was 1.32 +/- 0.18 W . kg-1. ICV water infusion was without significant effect (P greater than 0.05, t-test) on either of these values in normally hydrated animals. In dehydrated animals at Ta 38 degrees C, Tb and EWL were both significantly altered (P less than 0.001) from the normally hydrated state and were measured at 39.9 +/- 0.2 degree C and 0.84 +/- 0.09 W . kg-1 respectively. Infusion of water into dehydrated animals significantly altered pre-infusion levels of Tb and EWL so that Tb fell to 39.4 +/- 0.2 degree C (P less than 0.001) and EWL rose to 1.46 +/- 0.09 W . kg-1 (P less than 0.001). No effect of ICV water infusion on mean plasma vasopressin levels (pAVP) was observed in normally hydrated animals (preinfusion pAVP = 1.3 +/- 0.2 microunit . ml-1, post-infusion pAVP equal 1.3 +/- 0.3 microunit . ml-1, P greater than 0.05). However, a significant reduction in pAVP occurred subsequent to infusion in dehydrated animals (pre-infusion pAVP equal 16.6 +/- 1.85 microunits . ml-1, post-infusion pAVP equal 10.7 +/- 2.3 microunits . ml-1, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)