Effects of exogenous melatonin administration on bone mineral density in ovariectomized and pinealectomized rats

SUMMARYEFFECTS OF EXOGENOUS MELATONIN ADMINISTRATION ON BONEMINERAL DENSITY IN OVARIECTOMIZED AND PINEALECTOMIZED RATSObjective: Postmenopausal osteoporosis is the most common metabolic bonedisease. There is currently considerable interest in pathogenesis ofpostmenopausal osteoporosis. Altough there is evidence that estrogen deficiency isan important contributory factor, the pathogenesis of osteoporosis multifactorial andnot well understood. There is evidence that pineal melatonin is an anti-aginghormon and that the menopause is associated with a substantial decline inmelatonin secretion and increased rate of pineal calcification. Hence, the pinealgland may function as a ?fine tuner? of calcium homeostasis. In our study weproposed the pinealectomy induced melatonin deprivation in menopause may becontributary factor in the development of postmenopausel osteoporosis.Material and Method: A total of 49 young Wistar-albino rats were submited to thestudy. Chosen groups submitted to bilateral ovariectomy by the dorsal route, andpinealectomized with Kuszack ve Rodin method. All surgical procedures wereperformed while the rats were under intraperitoneal ketamine and xylazine HClanesthesia. After pinealectomy and ovariectomy, choosen groups, dose of 5 mg/kg/gün was administered intraperitonealy (daily between 17.00 and 18.00 h for a3-week period). We measured bone mineral density of the femur by using dualenergyX-ray absorptiometry (DXA; 4500W, Hologic, USA) and results wereevaluated. The BMD of femur named as proximal 1/3 (R2); middle 1/3 (R1);distal1/3 (R3); total (R4).Results: Compared with the sham group, PX + MLT group had significantlyhigher BMD values at R3 subregion. There is no statiscally significantrelationship between PX + OVX group and sham group at subregions. Alsothere is no statiscally significant relationship between OVX group and shamgroup at subregions. Compared with the sham group, PX group had significantly38higher BMD value at R3 subregion. There is no statiscally significant relationshipbetween PX group and PX+MLT group at subregions. There is no statiscallysignificant relationship between PX + OVX group and PX + OVX+MLT groupat subregions. Compared with the OVX + MLT group, PX+OVX+MLT group hadsignificantly higher BMD values at R1, R3, R4 subregions. Compared with theOVX group, OVX + MLT group had significantly lower BMD values at R3, R4subregions.Conclusion: Pinealectomy significantly increases BMD at R3 subregion, but itsnot reversed by exogen melatonin administration. Ovariectomy canceled theeffects of pinealectomy with respect to increases in the levels of reached bonemass. Exogen melatonin administration to ovariectomized and pinealectomizedgroup did not increase BMD values.Key Words: Ovariectomy, Pinealectomy, Melatonin, DEXA, Bone Mineral Density,Rats