Age-specific modification of local cutaneous vasodilation by capsaicin-sensitive primary afferents

Noll Physiological Research Center, The Pennsylvania State University, University Park, Pennsylvania 16802-6900 Submitted 9 October 2002 ; accepted in final form 28 April 2003 Age-related changes in neurogenic vasodilation mediated by sensory nerves may alter local skin blood flow (SkBF) responses in older individuals. The purpose of this study was to determine the age-specific modification of cutaneous vasodilation by capsaicin-sensitive primary afferent (CSPA) nerves during local heating. Nine young (18-30 yr), eight middle-aged (40-55 yr), and eight older (65-80 yr) healthy men participated in the experiments. Two local-heating protocols (rapid and slow) were performed before and after 1 wk of capsaicin pretreatment (CP), used to desensitize CSPAs. All temperatures were below those that elicit pain. SkBF was measured with a laser-Doppler imager and indexed to percentage of maximal cutaneous vascular conductance (%CVC max ). CP caused a significant reduction in %CVC max in the middle-aged and older groups during slow heating ( P < 0.05), without affecting %CVC max in the young group. During rapid heating, CP significantly reduced (53.9 ± 4.4 vs. 74.4 ± 7.4% CVC max , P < 0.05), but did not abolish, the initial sensory nerve-mediated rise in SkBF in the young group. No significant effects of CP on SkBF were observed during rapid heating in the middle-aged or older groups. These results indicate that, with advanced age, CSPA activity is more important to the maximal SkBF response during prolonged local heating, whereas it has a reduced role in the initial SkBF peak elicited by rapid local heating. In summary, CSPA activity contributes modestly to the overall SkBF response to local heating in an age-specific manner. skin blood flow; aging; laser-Doppler imaging Address for reprint requests and other correspondence: T. A. Munce, 229 Noll Laboratory, University Park, PA 16802-6900 (E-mail: tam275{at}psu.edu ).