Developmental hyperoxia diminishes the carotid body response to hypercapnia

Abstract

Rats reared in hyperoxia have smaller carotid bodies with reduced hypoxic responses. Since the carotid body (CB) also responds to changes in arterial CO2/pH, we hypothesized that developmental hyperoxia would alter CB and ventilatory responses to hypercapnia. Rats were reared in normoxia (21% O2) or hyperoxia (60% O2) until studied at 4, 6–7, or 13–14 days of age. Single‐unit chemoafferent activities were recorded in vitro from the soma of petrosal neurons with projections to the CB. Hyperoxia‐treated rats had significantly reduced carotid chemoafferent responses to hypercapnia (10% and 15% CO2) at all ages; CB CO2 sensitivity recovered within 7 days after return to room air. Ventilation was measured by plethysmography. Although steady‐state ventilatory responses to 4% and 8% CO2 were unaffected by developmental hyperoxia, ventilation increased more slowly during the normocapnia‐hypercapnia transition in hyperoxia‐treated rats. We conclude that developmental hyperoxia impairs CB chemosensitivity to both hypoxic and hypercapnic stimuli. Decreased CB CO2 sensitivity may compromise protective ventilatory reflexes during dynamic respiratory challenges. Supported by NIH grant P20 GM‐103423 (Maine INBRE).