THERMOREGULATORY CHANGES BY HYPOXIA - LESSONS FROM THE PARAMECIUM

1. In organisms ranging from paramecia to mammals, hypoxia elicits a r egulated decrease in body temperature (Tb), A decrease in Tb is an imp ortant adaptation to hypoxia primarily because it lowers metabolic rat e when oxygen supply is limited, thus facilitating survival, 2. Althou gh this beneficial response is extremely widespread among taxa, little is known of the cellular mechanisms that mediate hypoxia-induced decr eases in Tb, This is due, in large part, to the extreme complexity of vertebrate thermoregulatory systems, 3. The thermoregulatory system of the unicellular paramecium is much simpler than that of vertebrates, yet it responds similarly to hypoxia, Research has explored the functi onal importance of hypoxia-induced decreases in Tb. In addition, a num ber of possible mediators and signalling pathways in hypoxia-induced r eductions in Tb have been assessed, 4. In Paramecium caudatum, hypoxia appears to exert its thermoregulatory effects by inhibiting oxidative phosphorylation, Decreases in intracellular [ATP] and pH may be impor tant intermediate signals, In addition, an endogenous opioid system ap pears to help mediate hypoxia-induced changes in thermoregulatory beha viour.