| Research Abstract |
To examine heat loss effector function of prepubertal boys and older men, their heat and cold responses during a series of six experiments were compared with the responses of young men. (1) During both experiments of moderate exercise and heat exposure, prepubertal boys could thermoregulate as efficiently as young men by greater vasodilation on their trunk despite lower sweating. Furthermore, in the case of higher air temperature (than skin temperature), boys showed a rapid increment of vasodilation and sweating on the head, compared to young men. Based on the results that boys had higher maximal cutaneous vascular conductance (CVC_<max>) on the back and thigh compared to young men (by local heating test), the active vasodilation of boys may be affected partially by maturation-related modification in the structure of cutaneous vasculature. (2) In cold exposures boys showed lower skin temperatures on limbs, compared to young men. The mechanism of lower limb temperatures in boys differed
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by sites : 1) greater vasoconstriction and larger surface area-to-mass ratio (Ad/mass) on the finger, and 2) larger Ad/mass and greater body fatness (not due to vasoconstriction) on the thigh. Regional differences in maturation-related modification of vasoconstriction were not affected by the number of cold spots on skin, since boys had similar cold spots with young men. (3) Compared to young men, older men had lower vasodilation on the back and thigh during heat exposure, although vasodilation was similar between both groups on the forehead, chest, and finger. CVC_<max> on thigh and back (by local heating) was similar between young and older men, although forearm CVC_<max> was lower in older men. Therefore it was suggested that the lower vasodilation on the back and thigh to heat stress was due to age-related modification of vasoconstrictor and vasodilator system rather than to the change of cutaneous vasculature itself. (4) Furthermore, during cold exposure older men showed lower vasoconstriction on the back and thigh, but not on the forehead, chest and finger, suggesting that aging leads to blunt vasoconstriction, and regional differences exist in the age-related decrements of vasomotor function to not only heat but also cold stress. (5) Vasodilative and vasoconstrictive responses mentioned above were closely related to VO_<2max> in boys and both factors of pedometer readings and VO_<2max> in older men, respectively. It was concluded that exercise habits could be a means to improve vasomotor function in both boys and older men. Less
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