ARE BETA-ENDORPHINS AND THERMOREGULATION DURING COLD-WATER IMMERSION RELATED

The purpose of this investigation was to determine the relationship be tween core temperature (T(re)), tissue insulation (I), and beta-endorp hins (beta-END) during immersion in cold water. To test this, 21 males were immersed to the first thoracic vertebra for 120 min in stirred w ater at either 18-degrees, 22-degrees, or 26-degrees-C. Subjects were divided with respect to body fat [high fat (HF) = 18-22%, n = 11; low fat (LF) = 8-12%, n = 10] and randomly assigned to one of the three te mperatures. Blood was drawn at 25 and 5 min (T - 25 and T - 5, respect ively) before immersion, after 1 h of immersion, and 5 min before the completion of the second hour (T + 60 and T + 120, respectively). No s ignificant relationship was found between DELTAbeta-END and DELTAI or DELTAT(re). The relationship between the change in thermoregulatory va riables and DELTAbeta-END did not differ between the HF and LF groups. Also, beta-END (adjusted for plasma volume) was lower (P < 0.05) in t he HF vs. the LF group. beta-END (pg . ml-1) increased (P < 0.05) as t ime increased from T - 25 to T + 60 and were not progressive with dura tion of immersion. Thus, beta-END did not increase in proportion to le vel of heat loss.