Myogenic Autoregulation in Bone Marrow Arterioles and in Vivo Intramedullary Pressure in Femora of Conscious Female Long Evans Rats.

Objectives: The ability to regulate skeletal blood flow is critical for the maintenance of bone. The myogenic response is essential for regulating tissue blood flow. Myogenic responsiveness in bone marrow arterioles has not yet been determined. Furthermore, the literature is disparate regarding intramedullary pressures (IMP) within bone. The purposes of this study were to (1) determine whether bone marrow arterioles have myogenic activity and (2) assess if the autoregulatory zone corresponds with IMP. Also, this study provides detailed methodology on dissecting and isolating bone marrow arterioles for functional assessment. Methods: Experiment 1: Femoral shafts of female Long Evans rats were catheterized to assess in vivo IMP. Experiment 2: Bone marrow arterioles from female Long Evans rats were cannulated. Active and passive myogenic responses were determined. Results: In vivo intramedullary pressure averaged 32 +/- 3 mmHg, intramedullary pulse pressure averaged 5.28 +/- 0.03 mmHg, and the mean maximal diameter and wall thickness of the bone marrow arterioles were 96 +/- 7 mu m and 18 +/- 2 mu m, respectively. An active myogenic response was observed and differed (p <.001) from the passive curve. Conclusion: Bone marrow arterioles have myogenic responsiveness and the autoregulatory zone corresponded with the range of IMP (15-51 mmHg) within the femoral diaphysis of conscious animals.