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Age-Specific Skin Blood Flow Responses to Acute Capsaicin

Noll Physiological Research Center, The Pennsylvania State University, University Park.

Local skin blood flow (SkBF) responses can be modified by vasoactive neurotransmitters released from sensory nerves, notably, capsaicin-sensitive primary afferents (CSPAs). Age-specific CSPA function was examined in this study by assessing the SkBF response to acute capsaicin (CPZ). Eight young (18–30 years), 8 middle-aged (40–55 years), and 9 older (65–80 years) healthy men participated in the study. Treatment patches of varying CPZ concentration (ethanol and 0.001%–10.0% CPZ) were applied to sites on the ventral forearm. SkBF was measured with a laser Doppler imager. There were significant (p <.001) age-specific differences in the SkBF response to CPZ. In the older group, SkBF was reduced at least 2-fold at all concentrations of CPZ compared with the younger group. The middle-aged group showed an intermediate response. SkBF was significantly elevated above that obtained with a vehicle solution when sites were treated with CPZ concentrations 0.1% in middle-aged and younger skin, whereas a significant elevation in SkBF was only achieved with 10% CPZ in older skin. The elevated SkBF in the young and middle-aged groups at higher concentrations of CPZ was the result of both an increased area of vasodilation and an increased magnitude of vasodilation within the vasodilated areas. In the older group, the increase in cutaneous vascular conductance at the highest concentration of CPZ was entirely the result of an increased area of vasodilation. These results suggest impaired CSPA function in aged skin and age-specific differences in the ability of sensory nerves to modify local inflammatory SkBF responses.