Effects of oophorectomy on functional properties of resistance arteries isolated from the cancellous bone of the rabbit femur

Abstract

Information is sparse concerning the effect of oophorectomy (OOX) on bone vascularization and blood flow of possible significance for altered remodeling. Whether OOX affects functional characteristics of isolated bone resistance arteries was investigated. Ring preparations (diameter -250 pm) of small femoral bone arteries from oophorectomized and sham-operated rabbits were mounted on a myograph six weeks postoperatively. Cumulative concentration-response curves were obtained for various agonists at a normalized lumen diameter. Oophorectomy did not significantly influence lumen diameter, maximal response to high potassium, or maximal response to high potassium and M noradrenaline. However, OOX significantly increased the maximal response to noradrenaline (OOX 2.14 * 0.36 N/m, Sham 1.25 * 0.14 Nlm) and endothelin-1 (OOX 1.76 0.32, Sham 0.95 3~ 0.15) in metaphyseal arteries. Moreover, the corresponding maximal active pressure for the agonists was significantly increased. OOX did not influence endothelial function assessed by the effects of acetylcholine or substance P. The functional responses of diaphyseal arteries were unaffected by OOX. The study demonstrates regional differences in the effects of OOX on small arteries of importance for control of vascular resistance in bone which suggests a relation between altered vascular function after ovarian hormonal withdrawal and the changes in bone turnover associated with osteoporosis.

Mechanical, hormonal and metabolic influences on blood vessels, blood flow and bone

“…Six weeks after bilateral OVX in rabbits, force development in femoral metaphyseal arteries was significantly enhanced following stimulation with norepinephrine and endothlin-1, suggesting increased vasoconstrictor responsiveness of these vessels. However, no changes in force development were observed in diaphyseal arteries of the femur (Hansen et al 2001). Additionally, OVX did not alter vasodilator responsiveness to ACh or substance P in metaphyseal and diaphyseal arteries (Hansen et al 2001), indicating that vasodilator mechanisms are unaltered.…”

“…However, no changes in force development were observed in diaphyseal arteries of the femur (Hansen et al 2001). Additionally, OVX did not alter vasodilator responsiveness to ACh or substance P in metaphyseal and diaphyseal arteries (Hansen et al 2001), indicating that vasodilator mechanisms are unaltered. Unfortunately, no bone parameters were reported.…”

Bone medullary arterioles from ovariectomized rats have smaller baseline diameters but normal eNOS expression and NO-mediated dilation

“…Hansen et al (2001) arrived at a similar conclusion. Vascular rings of the nutrient artery from the diaphysis of the rabbit femur maintained normal dilator responses to ACh even as long as 6 weeks after OVX.…”

“…However, estrogens may regulate bone blood flow by altering flow though other bone vascular networks, such as the periosteal network, the metaphyseal and epiphyseal arteries and their arcades (Brookes and Revell, 1998). This notion is also supported by the Hansen study (Hansen et al, 2001). Following ovariectomy in rabbits, the constriction of metaphyseal arteries in response to norepinephrine and endothelin was enhanced.…”

“…Following ovariectomy in rabbits, the constriction of metaphyseal arteries in response to norepinephrine and endothelin was enhanced. However, the constriction of diaphyseal arteries to these same two constrictor agonists was not (Hansen et al, 2001). Therefore, estrogens may exert disparate effects on the various vascular networks of bone.…”