Effects of hypoxia and hypercapnia on circadian rhythms in the golden hamster (Mesocricetus auratus)

This study was designed to determine whether respiratory stimuli can influe nce the mammalian circadian timing system. Three-hour pulses of hypoxia (in spired O-2 concentration = 8%) or hypercapnia (inspired CO2 concentration = 11%) were presented for 7 days at mid-subjective day (circadian time 6-9) under constant darkness. Hypoxic and hypercapnic pulses caused cumulative p hase delays of 46.4 +/- 6.9 and 25.9 +/- 12.3 min, respectively. Distance r un per day was significantly reduced on hypoxic and hypercapnic pulse days, compared with nonpulsed days. Phase shifts were correlated with the reduct ion in daily running activity (multiple r(2) = 0.521, P = 0.036), metabolic depression (multiple r(2) = 0.772, P < 0.001), and reduction in body tempe rature (multiple r(2) = 0.539, P = 0.027), but not lung ventilation (multip le r(2) = 0.306, P = 0.414) during pulses. We conclude that hypoxia and hyp ercapnia can influence the phase and quantity of activity in free-running h amsters.