Skin microvascular adaptations during maturation and aging of hairless mice.

Using intravital fluorescence microscopy in the ears of hairless mice, we determined skin microvascular adaptations during the process of aging from juvenile to adult and senescent life (6-78 wk). Despite an increase of ear area within the first 36 wk, the number and branching pattern of both arteriolar and venular microvessels remained constant during the whole life period. Both arterioles and venules exhibited an increase in length, diameter, and intervascular distance up to the age of 36 wk. With the increase of the size of the ears, the observation that cutaneous capillary density remained unchanged implied new capillary formation. During aging to 78 wk, capillary density in the ears was reduced to approximately 40%. Functional analysis revealed an appropriate hyperemic response to a 2-min period of ischemia during late juvenile and adult life, which, however, was markedly reduced during senescence. Thus, except for capillaries, there is no indication for age-related new vessel formation. The process of aging from adult to senescent life does not cause any significant remodeling but is associated with a decrease of nutritive perfusion and a functional impairment to respond to stimuli such as ischemia.