Time-dependent ventilatory response to poikilocapnic hypoxia during light and dark periods and the role of histamine H1 receptors in mice.

We tested the hypothesis that the biphasic ventilatory response to poikilocapnic hypoxia shows circadian variation and contribution of histamine H1 receptors in mice. Initial increases in ventilation were augmented during dark periods. H1 receptors had no major relationship with circadian variation, but affected the declined phase.