Effects of aging and exercise training on bone and marrow blood flow and vascular function.

Aging leads to progressive bone loss, which is associated with impaired bone and marrow perfusion. The purpose of this study was to determine whether chronic exercise training enhances blood flow to the femur at rest and during exercise, and elucidate whether putative changes in training-induced bone perfusion are associated with alterations in the intrinsic vasomotor properties of the femoral principal nutrient artery (PNA) in old age. Young (4-6 mo old) and old (20-22 mo old) male Fischer-344 rats were either treadmill exercise trained (ET) or remained sedentary (SED). Regional blood flow to the femur was assessed at rest and during treadmill exercise. Endothelium-dependent (acetylcholine, ACh) and -independent (Dea-NONOate) vasodilator, and vasoconstrictor (phenylephrine (PE), KCl and myogenic) responses of femoral PNAs were determined. Exercise training led to higher blood flow to distal metaphysis and epiphysis in old rats at rest, and old ET rats showed greater regional blood flow during exercise compared to old SED rats. The increased blood flow to the proximal and distal metaphysis and epiphysis were also higher in old ET rats than that in young ET rats. Exercise training enhanced the vasodilator response to ACh, corresponding to increased eNOS expression in femoral PNAs from both young and old rats. Aging did not alter PE- or KCl-induced vasoconstriction, whereas myogenic responses were impaired. Exercise training enhanced vasoconstrictor responses to PE in old rats but had no effect on KCl or myogenic responses in either group. These data demonstrate that exercise training enhances both regional bone and marrow blood flow and vasodilator responses, which are impaired in the femora of old SED rats.