Bone blood flow and vascular reactivity.
Blood flow is essential for normal bone growth and bone repair. Like other organs, the regulation of blood flow to bone is complex and involves numerous physiologic mechanisms including the sympathetic nervous system, circulating hormones, and local metabolic factors. Our studies addressed the following questions: (1) Which endogenous vasoconstrictor agents regulate in vivo blood flow to bone? (2) Does a decrease in bone vascular reactivity to vasoconstrictor hormones account for the increase in blood flow during bone healing? (3) Does the endothelium influence bone arteriolar function? An intact bone model was developed in the rat to assess hormonal regulation of in vivo bone blood flow and in vivo bone vascular reactivity. An isolated, perfused bone arteriole preparation was employed to characterize the responsiveness of small resistance-size arterioles (diameter < 100 microm) to vasoconstrictor hormones and to evaluate the role of the vascular endothelium to modulate vascular smooth muscle reactivity. Our results indicate that: (1) though exogenous endothelin is a potent constrictor of the in vivo bone vasculature, endogenous endothelin does not actively regulate in vivo blood flow; (2) the increase in blood flow to a bone injury site is not due to a decrease in bone vascular sensitivity to norepinephrine, and (3) isolated bone arterioles of young rats are very sensitive to vasoconstrictor hormones but exhibit only modest endothelium-mediated vasodilation.
Fleming
J T
JT
Osteohemodynamics Lab, Department of Physiology and Biophysics, University of Louisville, Louisville, Ky. 40292, USA. John.Fleming@Louisville.edu
Barati
M T
MT
Beck
D J
DJ
Dodds
J C
JC
Malkani
A L
AL
Parameswaran
D
D
Soukhova
G K
GK
Voor
M J
MJ
Feitelson
J B
JB
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000502:physiology; D001842:Bone and Bones / Q000098:blood supply*; D019332:Endothelin-1 / Q000037:antagonists & inhibitors; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology; D017102:Fracture Healing / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
D019332:Endothelin-1; D010456:Peptides, Cyclic; D000109:Acetylcholine; C072247:cyclo(Trp-Asp-Pro-Val-Leu); D009638:Norepinephrine