The influence of pinealectomy and melatonin administration on the dynamic pattern of biochemical markers of bone metabolism in experimental osteoporosis in the rat.

BACKGROUND AND OBJECTIVES: There have been suggestions in literature that characteristic changes of bone mass in osteoporosis may be related to the melatonin (Mel): The aim of this study was to demonstrate whether pinealectomy and Mel administration can affect postmenopausal osteoporosis processes induced in female rats by way of ovariectomy.

METHODS: The study included 198 animals; 6 remained intact (0), 96 were ovariectomized (Ox), and the remaining ones underwent a sham operation (SOx). Two weeks after surgery, the rats were divided into eight groups: 1) SOx + SPx, 2) SOx + SPx + Mel, 3) Ox + SPx, 4) Ox + SPx + Mel, 5) SOx + Px, 6) SOx + Px + Mel, 7) Ox + Px, 8) Ox + Px + Mel. Animals from the 5th, 6th, 7th and 8th groups were pinealectomized (Px) while the remaining ones underwent a sham operation (SPx). Two weeks after surgery Mel (50microg/100g of bm) were administered intraperitoneally in rats in the 2nd, 4th, 6th and 8th groups while the remaining animals were administered with solvent only (5% solution of ethyl alcohol in physiological saline). Rats were administered the Mel solution or the solvent daily between 5 and 6 pm during a 4-week period. At the appropriate time, i.e. prior to surgery (group 0) and after 6, 12, 18 and 24 weeks from Px or SPx (time subgroups a, b, c and d) the animals were placed separately in metabolic cages (from 6.30 until 9.30 am) in order to collect urine aliquots for HYP and Ca determinations. The blood for the assay of ALP, PICP and ICTP was collected within the next 24 hours at 8 am (rats killed by decapitation).

RESULTS: The study has shown that pinealectomy had inducing, while exogenous Mel suppressing effect upon the level of investigated markers of bone metabolism; these changes were more pronounced in ovariectomized rats. Administration of Mel only partially levelled changes of bone metabolism caused by pinealectomy. In rats with preserved pineal gland effect of Mel on bone turnover markers was less pronounced. After discontinuing administration of Mel distinct tendency to increase studied biochemical markers of bone metabolism was shown.

CONCLUSION: Our findings suggest that Mel is an important modulator of experimental osteoporosis processes induced in female rats by way of ovariectomy.