Elevation of metabolic rate by pyrogen administration does not affect the gain of respiratory peripheral chemoreflexes in unanesthetized kittens.

We previously reported that reducing environmental temperature from 30 to 25 degrees C increases the gain of respiratory chemoreflexes. To investigate the role of increased metabolism in mediating the effect on the gain of the respiratory chemoreflex, we compared the respiratory responses, at ca. 26 degrees C to breath-by-breath alternations of inspired gas between air and 14% oxygen (hypoxia run) or air and 5% CO2 (CO2 run) with that to alteration of air between two inspired lines (control run) before and after the injection of a pyrogen (IL-1beta 400 ng/kg i.p.) in eight kittens at 27-35 d of postnatal age. The respiratory chemoreflex was quantified from the alternations in inspiratory and expiratory variables produced during test runs in terms of the direction and the amplitude of the alternation for each variable and compared with the results of control runs at the same temperature. Pyrogen administration produced a rise in rectal temperature and in oxygen consumption. However, there was no difference in the chemoreflex response to hypoxia or CO2 runs, in terms of either the pattern or of the amplitude of alternation, before and after the injection of the pyrogen. We conclude that the increase in the gain of chemoreflex observed during cooling in a previous study is not due to an increase in metabolism. Some change in input from thermoreceptors may bias the gain of chemoreflexes.