Aging and estrogen status: a possible endothelium-dependent vascular coupling mechanism in bone remodeling.

Bone loss with aging and menopause may be linked to vascular endothelial dysfunction. The purpose of the study was to determine whether putative modifications in endothelium-dependent vasodilation of the principal nutrient artery (PNA) of the femur are associated with changes in trabecular bone volume (BV/TV) with altered estrogen status in young (6 mon) and old (24 mon) female Fischer-344 rats. Animals were divided into 6 groups: 1) young intact, 2) old intact, 3) young ovariectomized (OVX), 4) old OVX, 5) young OVX plus estrogen replacement (OVX+E2), and 6) old OVX+E2. PNA endothelium-dependent vasodilation was assessed in vitro using acetylcholine. Trabecular bone volume of the distal femoral metaphysis was determined by microCT. In young rats, vasodilation was diminished by OVX and restored with estrogen replacement (intact, 82±7; OVX, 61±9; OVX+E2, 90±4%), which corresponded with similar modifications in BV/TV (intact, 28.7±1.6; OVX, 16.3±0.9; OVX+E2, 25.7±1.4%). In old animals, vasodilation was unaffected by OVX but enhanced with estrogen replacement (intact, 55±8; OVX, 59±7; OVX+E2, 92±4%). Likewise, modifications in BV/TV followed the same pattern (intact, 33.1±1.6; OVX, 34.4±3.7; OVX+E2, 42.4±2.1%). Furthermore, in old animals with low endogenous estrogen (i.e., intact and old OVX), vasodilation was correlated with BV/TV (R(2) = 0.630; P<0.001). These data demonstrate parallel effects of estrogen on vascular endothelial function and BV/TV, and provide for a possible coupling mechanism linking endothelium-dependent vasodilation to bone remodeling.