METHOD FOR ASSESSMENT OF VASCULAR REACTIVITY IN BONE - IN-VITRO STUDIES ON RESISTANCE ARTERIES ISOLATED FROM PORCINE CANCELLOUS BONE

Knowledge about vascular regulation in bone is central to the understa nding of both normal and pathological bone physiology. This article de scribes a new method for direct assessment of the reactivity of bone-b lood vessels. Resistance arteries (diameter approximately 250 mu m) we re isolated from epiphyseal cancellous bone (porcine femoral condyle). Arterial segments (2 mm long) were mounted as ring preparations on a myograph, and isometric force development was measured continuously. F ifty-nine vessels from 31 pigs were investigated. The active force dev elopment was maximal at 0.9 x L(100) in nine of 12 investigated arteri es (L(100) corresponds to the circumference the vessel would have if r elaxed and exposed to a luminal pressure of 100 mm Hg [13.3 kPa]). In all subsequent experiments, the vessels were stretched to 0.9 x L(100) . Noradrenaline (2 x 10(-8) to 10(-5) M) induced a concentration-depen dent vasoconstriction; mean maximal tension development was 3.69 Nim. This force development would enable the arteries to contract against a pressure of more than 22 kPa (165 mm Hg), indicating preserved functi on of the media smooth muscle. Response to acetylcholine (10(-7) to 10 (-5) M) was observed in only two of 12 arteries. Bradykinin (10(-11) t o 10(-6) M) induced a concentration-dependent and reproducible relaxat ion in all vessels; the relaxation was endothelium-dependent, since no effect of bradykinin was detected after mechanical removal of the end othelium. Sodium nitroprusside (10(-4) M) induced a reproducible and e ndothelium-independent vasorelaxation. The results demonstrate preserv ed function of both smooth muscle and endothelium in this preparation. The model allows pharmacological investigations of bone arteries unde r well defined conditions and enables studies on focal bone lesions an d human bone tissue.