The effect of temperature on the ventilatory response to carbon dioxide in the neonatal rat.

The rectal temperature of newborn rats in the nest varies between 32 and 39 degrees C, depending on environmental temperature and the presence of the dam. Because rebreathing of CO2 occurs in the nest, experiments were carried out to examine the effects of body temperature on the ventilatory response (VR) to CO2 at different postnatal ages. The VR to 2 and 4% carbon dioxide was examined in rat pups by the body plethysmograph method whereas rectal temperature was manipulated to 32-33 degrees C, 36-37 degrees C, and 38-39 degrees C. At three different ages, 2-3 d, 5-6 d, and 8-9 d, rat pups had a VR to both concentrations of CO2 due, principally, to an increase in tidal volume (Vt). Ventilation (Vi) in air was highest at the lowest rectal temperature, and there was a significant, inverse correlation with temperature in the 2-3-d-old and 5-6-d-old rats. The VRs to 2 and 4% CO2 were significantly, inversely, related to body temperature in the youngest group. The direction of temperature modification also had a significant effect, because VRs to both 2 and 4% CO2 were significantly lower in rat pups which were being warmed compared with those being cooled.