Vol. 89, Issue 1, 259-264, July 2000
Age-dependent core temperature responses of conscious rabbits
to acute hypoxemia
James E.
Fewell,
Sarah H. M.
Wong, and
Kim C.
Crisanti
Department of Physiology and Biophysics, The University of Calgary
Health Sciences Centre, Calgary, Alberta, Canada T2N 4N1
Experiments were carried out on chronically
instrumented newborn and older rabbits to characterize their core
temperature (Tc) responses to acute hypoxemia and to
differentiate "forced" vs. "regulated" thermoregulatory
responses. Three age ranges of kits were studied: 4-6, 9-11,
and 28-30 days of age. During an experiment, Tc,
selected ambient temperature (Ta), and oxygen consumption
were measured from kits studied in a thermocline during a control
period of normoxemia, an experimental period of normoxemia or hypoxemia
(fraction of inspired oxygen 0.10), and a recovery period of
normoxemia. We reasoned that no change or a decrease in Ta
while Tc decreased during hypoxemia would indicate a
regulated thermoregulatory response, whereas an increase in
Ta while Tc decreased during hypoxemia would
indicate a forced thermoregulatory response. Tc decreased
during acute hypoxemia in the older kits but not in the 4- to 6-day-old
kits; the decrease in Tc was accentuated on postnatal
days 28-30 compared with postnatal days
9-11. Ta decreased or stayed the same during
exposure to acute hypoxemia. Our data provide evidence that postnatal
maturation influences the Tc response of rabbits to acute
hypoxemia and that the decrease in Tc during hypoxemia in
the older kits results from a regulated thermoregulatory response.
autonomic thermoregulation; behavioral thermoregulation; forced
thermoregulatory response; postnatal maturation; regulated
thermoregulatory response
