ORIGINAL ARTICLE P J M H S Vol. 9, NO. 4, OCT – DEC 2015 1217 Melatonin can restore the density of bone decreased by hyperthyroidism-induced osteoporosis MARIYAH HIDAYAT 1 , INAYATULLAH 2 , YASMEEN MAHAR ABSTRACT Background: Hyperthyroidism is accompanied by increased rates of bone formation and resorption. Melatonin through its free radical scavenging and antioxidant properties, impairs osteoclast activity and bone resorption in hyperthyroid state. Aim: To study the effect of melatonin on bone density decreased during hyperthyroidism. Duration of study: 01 November to 30 th of January, 2014-15. Study design: Randomized Controlled Trial. Place of study: Anatomy department at BMSI, JPMC, Karachi. Methods: Ninety healthy adult albino rats were included in the study and divided equally into 3 groups for 12 weeks. Group-A was taken as control. Group-B received levothyroxine orally, daily in a dose of 8 μgm /100 g BW for 12 weeks to induce experimental hyperthyroidism. Group C was given levothyroxine orally in the above mentioned dose as well as melatonin in drinking water daily in a dose of 10 mg/100 g BW. Results: Melatonin significantly restored the thickness of bone cortex in the shaft of femur in group B without affecting the levels of TSH in hyperthyroid state. Conclusion: Melatonin canpromote bone formation and prevent bone resorption during hyperthyroidism. Keywords: Melatonin, Hyperthyroidism, levothyroxine, BMD,Albino rats. INTRODUCTION Thyroid hormones are essential for the normal growth and maturation of skeleton 1 . Hyperthyroidism is accompanied by increased rates of bone formation and resorption 2 .Thyrotoxicosis speeds up bone remodelling which is the reason why it leads to osteoporosis 3 . It is very rare to see osteoclasts in bone under physiological conditions, but their number increase in many pathological states, which results in decrease in the density of bone 4 . TSH inhibits osteoclast formation and in the hyperthyroid state, where TSH is severely suppressed, osteoclast formation is enhanced 5 . The basal metabolic rate of the body increases during hyperthyroidism which leads to an increase in the production of reactive oxygen species causing obvious changes in antioxidants. This is the reason why hyperthyroidism causes oxidative stress 6 . Melatonin is a hormone secreted endogenously by the pineal gland. The suprachiasmatic nucleus regulates the its secretion and so does the light-dark cycle 7 . Apart from its powerful antioxidant properties, -------------------------------------------------------------------- 1 Asst Prof.Anatomy, Rahbar Medical & Dental College, Lahore. 2 Asst. Prof. Anatomy, Gajju Khan Medical College,Swabi 3 Assistant Professor, Anatomyt, Bahria University of Medical and Dental College, Karachi. Correspondence to Dr MariyahHidayat, D- 256,Street5,Phase5,DHA,Lahore.E-mail drmariyah.hidayat@gmail.com Cell: 0300-2588375. melatonin has recently attracted the interest of various investigators as a multifunctional molecule 8 .Melatonin plays an important role in many aspects of physiology of living things by acting on various cells of the body through its two types of G protein coupled receptors MT1 and MT2 9 . Infact, it is because of the activation of these receptors that many physiological effects of melatonin occur. Other effects of melatonin are due to its anti-oxidant effects. Its role in the protection of nuclear and mitochondrial DNA cannot be underestimated and has led researchers to explore this hormone in depth in order to heal many diseases which are due to DNA damage 10 . Currently, the role of melatonin in the proliferation and development of hard tissues, including bone and tooth, is the main topic of interest. It is still under investigations how melatonin effects the composition of bone in conditions which leads to bone loss. The role of melatonin has been investigated in bone remodelling, osteoporosis and dentine formation.Osteoporosis is a prolonged structural deterioration of the skeletal system, usually associated with age, and with a major prevalence in women 11 . The World Health Organization (WHO) defines osteoporosis as bone mineral density (BMD) 2.5 or more standard deviations below that of a young adult at any site.