Central thermoregulatory effects of lactate in the toad Bufo paracnemis

Hypoxia induces a regulated decrease in body temperature (Tb; anapyrexia) i n organisms ranging from protozoans to mammals, but very little is known ab out the mechanisms involved. Several candidates have been suggested to medi ate hypoxia-induced anapyrexia, among them lactate, which is a classical co mpanion of hypoxic stress in vertebrates. The present study was designed to assess the central thermoregulatory effects of lactate in Bujo paracnemis. Toads equipped with a temperature probe were tested over a thermal gradien t (10-40 degrees C). Lactate injected systemically (4.0 mmol kg(-1)) caused a significant reduction of Tb from 24.6 +/- 2.1 to 17.4 +/- 3.9 degrees C. To assess the role of central thermoregulatory mechanisms, a lower dose (0 .4 mmol kg(-1)) of lactate was injected into the fourth cerebral ventricle or systemically. Intracerebroventricular injection of lactate caused a simi lar decrease in Tb, whereas systemic injection caused no change. The data i ndicate that lactate may play a role in hypoxia-induced anapyrexia in centr al rather than peripheral sites. (C) 1999 Elsevier Science Inc. All rights reserved.