Objectives:Homeostatic regulation of various physiological and behavioral systems may be altered as a function of the ambient gravitational environment of the organism. Changes in homeostasis have been observed in these and other systems as a result of chronic exposure to a hyperdynamic environment induced by centrifugation. Life science research capabilities are now being extended into the realm of the hypodynamic environment by research capabilities aboard spacecraft. This study examined the regulation of body temperature and heart rate in rats with biotelemetry implants.
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Approach:
Four rats were implanted preflight with a biotelemetry transmitter capable of sensing and transmitting information on heart rate and deep body temperature. The telemetry data from the animals was monitored during the period which Spacelab was activated (approximately from eight hours after launch to six hours prior to re-entry). The average 24-hour waveforms of body temperature in preflight and flight conditions were examined. Four ground control animals were similarly implanted and monitored.
Results:
Microgravity altered the steady state regulation of heart rate and body temperature. During the preflight conditions, the animals demonstrated no net change in phase relationship with the mean period 23.9 ± 0.2 over the course of the pre- flight study; while inflight, the phase of all the animals consistently delayed such that the average period of the temperature rhythm inflight was 24.4 ± 0.3 hours. A longer flight will be necessary to identify whether or not the animals are freerunning with a period independent 24-hours or rather simply showing an internal phase angle shift which had not reached a steady state during the seven-day flight. Heart rate phase rhythm was stable in both conditions with a mean period of 23.9 ± 0.2 in either. The heart rate itself was, however, depressed inflight, the possible result of a reduced load on the cardiovascular system in space or a resetting of some other component within this regulatory system. Data suggest that normal expression of the circadian timing system is extensively modified in microgravity.
Fuller CA, Edger DM. Homeostasis and Biological Rhythms in the Rat During Spaceflight. Abstract 83.10. 36th Annual Fall Meeting of the American Physiological Society; 1985 Oct 13-18; Buffalo(NY): 377.
Fuller CA. Homeostasis and Biological Rhythms in the Rat During Spaceflight. Abstract S-199. Proceedings of the Seventh Annual Meeting on the IUPS Commission on Gravitational Physiology; 1985 Oct 13-18; Niagara Falls(NY).
Fuller CA. Homeostasis and Biological Rhythms in the Rat During Spaceflight. Physiologist 1985; 28(6 Suppl): S199-200.
Ishihama LM, et al. Temperature regulation in rats exposed to a 2 G field. Physiologist 1989; 32 Suppl: S61-2.
Murakami D, et al. Effects of Gravity on the Circadian Period in Rats. Physiologist 1991; 34 Suppl: S147-8.
Activity, Heart rate, rat, Implanted transmitter, continuous EKG, rate algorithm
Temperature, Body, rat, Biotelemetry implant, computer
Temperature, Body, rat, Implant, biotelemetry system
Temperature, RAHF data, SL-3, (quads 1-4, TEU air in/out, TEU coolant in/out), Recorder, downlink (1/sec)