Ovariectomy enhances mechanical load-induced solute transport around osteocytes in rat cancellous bone

Abstract To test if osteoporosis alters mechanical load-induced interstitial fluid flow in bone, this study examined the combined effect of estrogen deficiency and external loading on solute transport around osteocytes. An in vivo tracer, FITC-labeled bovine serum albumin, was injected into anesthet...

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Published in:	Bone (New York, N.Y.) N.Y.), 2014-02, Vol.59, p.229-234
Main Authors:	Ciani, Cesare, Sharma, Divya, Doty, Stephen B, Fritton, Susannah P
Format:	Article
Language:	eng
Subjects:	Animals Biological and medical sciences Biological Transport Canaliculi Cattle Diseases of the osteoarticular system Female Fundamental and applied biological sciences. Psychology Interstitial fluid Mechanotransduction Medical sciences Orthopedics Osteocyte Osteocytes - metabolism Osteoporosis Osteoporosis. Osteomalacia. Paget disease Ovariectomy Perilacunar remodeling Rats Rats, Sprague-Dawley Stress, Mechanical Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases Surgery of the genital tract and mammary gland Tibia - physiology Tibia - ultrastructure Vertebrates: anatomy and physiology, studies on body, several organs or systems Weight-Bearing
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Summary:	Abstract To test if osteoporosis alters mechanical load-induced interstitial fluid flow in bone, this study examined the combined effect of estrogen deficiency and external loading on solute transport around osteocytes. An in vivo tracer, FITC-labeled bovine serum albumin, was injected into anesthetized ovariectomized and control female Sprague–Dawley rats before the right tibia was subjected to a controlled, physiological, non-invasive sinusoidal load to mimic walking. Tracer movement through the lacunar–canalicular system surrounding osteocytes was quantified in cortical and cancellous bone from the proximal tibia using confocal microscopy, with the non-loaded tibia serving as internal control. Overall, the application of mechanical loading increased the percentage of osteocyte lacunae labeled with injected tracer, and ovariectomy further enhanced movement of tracer. An analysis of separate regions demonstrated that ovariectomy enhanced in vivo transport of the injected tracer in the cancellous bone of the tibial epiphysis and metaphysis but not in the cortical bone of the metaphysis. These findings show that bone changes due to reduced estrogen levels alter convectional transport around osteocytes in cancellous bone and demonstrate a functional difference of interstitial fluid flow around osteocytes in estrogen-deficient rats undergoing the same physical activity as controls. The altered interstitial fluid flow around osteocytes is likely related to nanostructural matrix–mineral level differences recently demonstrated at the lacunar–canalicular surface of estrogen-deficient rats, which could affect the transmission of mechanical loads to the osteocyte.
ISSN:	8756-3282 1873-2763