Journal of Applied Physiology, Vol 48, Issue 3 495-499, Copyright © 1980 by American Physiological Society
Variable open-loop gain in the control of thermogenesis in cold-exposed rabbits
J. T. Stitt
We have previously demonstrated a multiplicative interaction between mean
skin temperature (Tsk) and hypothalamic temperature (Thy) in the control of
thermogenesis in cold exposed rabbits. Such a model predicts that open-loop
gain will not be constant, but will vary according to the direction and
degree of Thy displacements and to the prevailing level of Tsk when Thy is
altered. Open-loop gain was calculated from steady-state displacements in
body temperature induced by sustained step displacements in Thy.
Hypothalamic temperature of rabbits was clamped at various levels ranging
from 2 degrees C above to 3 degrees C below normal Thy and the resulting
changes in rectal temperature attained at steady state were recorded.
Experiments were conducted at ambient temperatures (Ta) of 2 degrees and 15
degrees C. Open-loop gain in response to hypothalamic heating was always
greater than that obtained in response to equivalent levels of hypothalamic
cooling. Furthermore, at lower levels of Tsk (Ta = 2 degrees C) open-loop
gain was greater for all levels of Thy displacement when compared to that
measured at higher levels of Tsk (Ta = 15 degrees C).
