[Disruption of the circadian rhythm of the body temperature in monkeys during head-down tilt hypokinesia].

A rhesus monkey was restrained in the prone position with the head kept at -6 degrees. The day: night cycle was 16:8 and ambient temperature 20-22 degrees C. Skin temperature (ST) in the ankle area and body temperature (BT) in the armpit were measured by thermistors every 16 min during 14 days. Mean daily values of both temperatures decreased continuously beginning with day 5 and reached a minimum on day 11. Between days 5 and 11 the BT rhythm was split into two components, i. e. morning and evening (with the 12-hour periodicity being predominant in the spectrum). The amplitude of the ST rhythm declined and reached a minimum on day 4. On that day the rhythm phase was sharply shifted (6-7 hour delay) and thereafter the amplitude and phase of the ST rhythm gradually restored. The above effects (dissociation of the BT rhythm, drop of the amplitude and delay of the phase of the BT rhythm) can be explained by a transient attenuation of the relationship (release) of circadian oscillators due to a greater load on the mechanisms of adaptation to simulated microgravity.