Journal of Applied Physiology, Vol 51, Issue 6 1601-1606, Copyright © 1981 by American Physiological Society
Enhanced heat production in physically restrained rats in hypoxia
M. Hayashi and T. Nagasaka
Combined effects of restraint and hypoxia (9.5% O2 in N2) on heat
production (M), heat loss (HL), colonic temperature (Tcol), and
cardiovascular activity were studied in unanesthetized rats. In freely
moving (F) rats, hypoxia decreased M, HL, Tcol, and heart rate (HR). In
restrained (R) rats, however, hypoxia increased M, HL, Tcol, and HR. The
increase in these parameters was greatest within 30 min of hypoxia, and the
peak value of M was 10.4 W X m-2 higher than in normoxia. After chemical
sympathectomy with 6-hydroxydopamine hydrobromide, no such increase was
observed in R rats. l-Norepinephrine bitartrate (0.4 mg X kg-1) increased M
and HR in F rats in hypoxia. The increase in M was, however, 9.5 W X m-2
and significantly less than that observed in normoxia. Hypoxia
significantly reduced blood flow to the brown adipose tissues (BAT) in R
rats. The BAT may not be responsible for the increased metabolism in
restrained hypoxia-exposed rats. Hypoxia significantly increased blood flow
to the heart and the diaphragm, and to a lesser extent to the limb muscles.
The increased metabolism in the cardiac and respiratory muscles may be a
cause of hyper-metabolism in restrained rats. The limb muscles may also
play some role in increasing metabolism in these rats.
