POSTNATAL MATURATION OF PERIPHERAL CHEMORECEPTOR VENTILATORY RESPONSETO O-2 AND CO2 IN NEWBORN LAMBS

Although studies on lambs have shown that carotid body sensitivity to O-2 is reset postnatally, it is still unknown whether O-2 and CO2 peri pheral chemoreflexes undergo parallel postnatal maturation. The presen t study was designed to analyze maturation of O-2 and CO2 peripheral c hemoreflexes in 10 lambs at <24 h and at 12 days of age. We measured t he ventilatory (V over dot E) response to three tidal breaths of pure N-2 or 13% CO2 in air. Overall, the N-2 peripheral chemoreflex increas ed significantly with maturation [V over dot E/end-tidal O-2 (ml . min (-1) . kg(-1) . Torr(-1)) = 2.94 +/- 0.91 at <24 h vs. 5.13 +/- 0.59 a t 12 days, P < 0.05], whereas the CO2 peripheral chemoreflex did not c hange (V over dot E/end-tidal CO2 = 7.04 +/- 0.98 at <24 h vs. 7.75 +/ - 1.07 at 12 days, not significant), We conclude that the CO2 peripher al chemoreflex does not change in awake lambs within the time frame st udied, in contrast to a marked postnatal maturation of the O-2 periphe ral chemoreflex. The different time courses of O-2 and CO2 peripheral chemoreflex maturation support the concept that carotid body sensitivi ties to O-2 and CO2 do not depend on the same basic mechanisms.