Regional differences in peripheral vasoconstriction of prepubertal boys

To elucidate the mechanisms that underlie the greater decline of skin temperature on the limbs in prepubertal boys as compared to young men, we compared cutaneous vascular conductance (CVC) of the boys and men in response to a reduced ambient temperature (T a). The boys had a greater surface area-to-mass ratio (A D/mass) and a lower mean skinfold thickness on the trunk but not on the limbs compared to the men. As T a decreased from 30 to 17°C over 60 min, the skin temperature (T sl) on the limbs (as represented by forearm, finger and thigh) decreased significantly more in the boys than in the men; while T sl on the trunk (chest, back and abdomen) and forehead decreased to the same extent. The CVC decreased at all body sites in all subjects, but regional difference existed in age-related alterations in CVC responses despite the similar rectal and mean body temperatures of the groups. The decline in the finger CVC was greater for the boys than for the men, suggesting that greater vasoconstriction and greater A D/mass on the fingers may have contributed to the lower finger T sl of the boys. However, thigh CVC in the boys was similar to that in the men over the 60-minute exposure, indicating that the lower thigh T sl of the boys may be the result of greater heat loss owing to the greater A D/mass on the limbs of the boys (but not to greater vasoconstriction or subcutaneous fat). The CVC on the chest and back was greater in the boys over the cold exposure, suggesting that similar T sl on the chest and back of the boys and men may result from greater cooling owing to the larger A D/mass being offset by combination of less vasoconstriction and more conductive heat transfer in the presence of less subcutaneous fat. These results suggest that the age-related difference in T sl in response to mild cold stress may not directly reflect that in cutaneous vasoconstriction alone owing to the differences in anthropometric characteristics (such as greater A D/mass and lower subcutaneous fat on trunk) between boys and men.