Peripheral heat loss: A predictor of the hypothermic response to melatoninadministration in young and older women

Core hypothermia following daytime melatonin administration typically displ ays significant interindividual variability. As this hypothermia has been a ssociated with significant increases in skin temperature, the mechanism by which melatonin decreases core temperature may involve increasing periphera l heat loss. If so, the interindividual variability in this effect may refl ect concomitant interindividual variability in heat loss capacity at the di stal periphery. For six younger (mean +/- SEM: 23.4 +/- 0.3 years) and 10 o lder women (mean +/- SEM: 65.6 +/- 0.7 years), the maximum decrease in core body temperature following a 5-mg (p.o.) dose of melatonin was correlated with the capacity to lose heat. This was determined by the maximum increase in contralateral hand temperature following a mild positive thermal challe nge (PTC). The regression analysis yielded a significant (p < 0.01)correlat ion of 0.80, suggesting that the individual magnitude of hypothermia follow ing melatonin administration may reflect the capacity of an individual to d issipate heat at the distal periphery. (C) 1999 Elsevier Science Inc.