SYMPATHETIC VASOCONSTRICTOR RESPONSIVE DURING SMALL MUSCLE EXERCISE AGE &SEX

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to determine whether there are differences in sympathetic responsiveness in exercising muscles in younger and older subjects. It is hypothesized that older subjects will have greater sympathetic vasoconstrictor responsiveness than younger subjects, as evaluated by changes in leg vascular conductance in response to ischemic handgrip (sympathetic stimulus) during leg exercise. For this study a total of 78 healthy subjects will be studied. A total of 100 subjects are requested for recruitment to account for dropouts. Subjects will be stratified into 6 groups of 13 individuals consisting of male and female untrained subjects age 20 to 30 years, and trained and untrained men and women 60 to 75 years of age. The study entails three visits to the GCRC for each subject. An initial screening visit will be used to administer tests used for inclusion and exclusion criteria and to determine level of exercise fitness. The first experimental visit will obtain reproducibility data on leg blood flow, and maximal handgrip and leg extension force production used to establish exercise target points for the subsequent study. During the second experimental visit subjects will perform non-dominant leg extension exercise at 10 watts. After 6-minutes there will a 4-minute period during which the subject will perform static ischemic handgrip exercise at 60% maximal force. The subjects will then cease the handgrip exercise while continuing leg exercise. Blood flow in both legs will be measured throughout the exercise protocol. The protocol will then be repeated with a higher level of leg exercise (30 watts).