en Tissue Engineering and Cell Biology Tissue Engineering and Cell Biology مقاله کامل Full Length/Original Article <strong>Background:</strong> Hypothyroidism is associated with dysfunction of the bone turnover with reduced osteoblastic bone formation and osteoclastic bone resorption. Mesenchymal stem cells (MSCs) secrete various factors and cytokines that may stimulate bone regeneration.&nbsp; The aim of this study was to determine the effects of MSCs-conditioned medium (CM) in hypothyroidism male rats after inducing bone defect. <strong>Methods:</strong> In this study, 24 male rats were randomly assigned to three groups: (I) hypothyroidism + bone defect (HYPO), (II) hypothyroidism + bone defect + CM (HYPO + CM), and (III) no hypothyroidism + bone defect (control). Four weeks after surgery, the right tibia was removed, and immediately, biomechanical and histological examinations were performed. <strong>Results:</strong> The results showed a significant reduction in bending stiffness (32.64 &plusmn; 3.99), maximum force (14.63 &plusmn; 1.89), high stress load (7.59 &plusmn; 2.31), and energy absorption (12.68 &plusmn; 2.12) at the osteotomy site in hypothyroidism rats in comparison to the control and hypothyroidism + condition medium groups (<em>p</em> < 0.05). There was also a significant decrease in the trabecular bone volume (3.86 &plusmn; 3.88) and the number of osteocytes (5800 &plusmn; 859.8) at the osteotomy site in hypothyroidism rats compared to the control and hypothyroidism + condition medium groups (<em>p</em> < 0.01 and&nbsp;<em>p</em> < 0.02, respectively).<strong> Conclusion: </strong>The present study suggests that the use of the CM can improve the<br> fracture regeneration and accelerates bone healing at the osteotomy site in hypothyroidism rats. Conditioned medium, Hypothyroidism, Mesenchymal stem cells, Osteotomy 90 98 http://ibj.pasteur.ac.ir/browse.php?a_code=A-10-1-683&slc_lang=en&sid=1 Niloofar Sefati No Department of Biology and Anatomical Sciences, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran Mohsen Norouzian No Department of Biology and Anatomical Sciences, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran Hojjat-Allah Abbaszadeh No Hearing Disorders Research Center and Department of Biology and Anatomical Sciences, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran Mohammad-Amin Abdollahifar No Department of Biology and Anatomical Sciences, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran Abdollah Amini No Department of Biology and Anatomical Sciences, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran Mohammad Bagheri No Medical School, Shahid Beheshti University of Medical Sciences, Tehran, Iran Arefeh Aryan No Department of Biology and Anatomical Sciences, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran Fatemeh Fadaei Fathabady Yes Laser Application in Medical Sciences Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran