Sustained hypoxic hypoxia is physiologically encountered at high altitude and pathologically in many lung pathologies. The carotid body (CB) arterial chemoreceptors are activated by hypoxic hypoxia, generating a reflex hyperventilation aimed to minimize the intensity of hypoxia and its deleterious effects. The intensity of the CB response to hypoxia changes with prior exposure to sustained hypoxia: a sensitization of the CB function (i.e., higher CB responses; acclimatization) occurs if the exposure is short, and a desensitization (adaptation) appears if the hypoxic exposure is too prolonged. However the precise time-course of acclimatization and desensitization have not been adequately studied. The aim of our work has been to define this time-course. We have exposed groups of males and females rats to a hypoxic atmosphere (11-12% O₂) for 1 to 30 days, and study their ventilatory response to hypoxias (12, 10 and 7% O₂) and to hypercapnia (5% CO₂).

Sustained hypoxia in males produced minor modifications in ventilatory frequency to any stimulus. Contrary to that, tidal volume and minute ventilation increased with the duration of hypoxic exposure. The weight of the CB increased at hypoxic exposures >8 days. CB dopamine levels and rate of synthesis (per unit weight) increased in a time- dependent manner and therefore its turnover time was nearly constant. CB norepinephrine followed a slightly different time-course. Data from male and female rats will be presented comparatively. It is concluded that acclimatization in rat last longer than 30 days.

Support: BFU2004-06394, CIBER CB06/06/0050, FISS PI042462, JCyL VA045/04 and VA011C05.