The roles of acidosis and lactate in the behavioral hypothermia of exhausted lizards

We conducted this study to determine whether two of the physiological chang es associated with non-sustainable exercise, elevated blood lactate levels and decreased arterial pH, contribute to the behavioral hypothermia exhibit ed by exhausted lizards. Dipsosaurus dorsalis were placed in a thermal grad ient and their body temperatures were recorded from 08:00 to 14:00h. At 14: 00h, animals were subjected to different experimental regimens. In the exer cise (E) regimen, animals at 40 degrees C were forced to exercise maximally for 5 min on a treadmill. In the lactate (L) regimen, animals were infused with 11.5 ml kg(-1) of 250-500 mmol l(-1) sodium lactate. In the osmolarit y control (O) regimen, animals mere injected with 11.5 ml kg(-1) of 500 mmo l l(-1) NaCl, and in the injection control (I) regimen, animals were inject ed with 11.5 ml kg(-1) of 150 mmol l(-1) NaCl, In the hypercapnia (H) regim en, the thermal gradient was flushed n ith a gas mixture containing 10 % CO 2, 21 % O-2 and 69 % N-2, a treatment that lowers the arterial pH of D. dor salis to a value comparable with that imposed by exhaustive exercise. A gro up of control (C) animals was left undisturbed in the thermal gradient for 24 h, Animals in all experimental groups were returned to the thermal gradi ent, and their cloacal temperatures were monitored until 08:00 h the follow ing morning. The mean cloacal temperature of E animals underwent a signific ant decrease of 4-7 degrees C, relative to control animals, which persisted for 7 h, The mean cloacal temperatures of animals subjected to 2 h of regi men H also decreased by 3.5-9 degrees C and remained depressed for 12 h fol lowing the beginning of the treatment. L, O and I animals did not undergo a significant change in body temperature following treatment, and their mean body temperatures did not differ from those of C animals at any time durin g the experiment, The results of this study suggest that the metabolic acid osis, but not the elevated blood lactate level, that follows exhausting exe rcise might play a role in the behavioral hypothermia that follows exhausti ng exercise in D, dorsalis.