Effects of aging on circadian and ultradian respiratory rhythms of rats synchronized by an LD12:12 lighting (L = 100 lx).

Continuous monitoring of emitted carbon dioxide (VCO2) was taken as an index of respiratory exchanges in male Sprague-Dawley rats of different ages (31-814 days) submitted to a light (100 lx)-dark (LD) 06.00-18.00 h alternation at a temperature of 20 degrees C and with food and water ad libitum. In grouped 82- and 426-day-old rats harmonic and spectral analyses show that aging decreases the amplitudes of the circadian (tau = 24 h) respiratory rhythms, decreases the amplitudes and modifies the phases of the ultradian respiratory rhythms of mean and great (10 min less than tau less than 24 h) periods. Under the environmental conditions of the experiments, the techniques utilized show no statistically significant changes with aging for the circadian rhythms and only small changes in the ultradian respiratory frequencies.