[Influence of pinealectomy and long-term melatonin administration on bone metabolism in orchidectomized rats].

Introduction: The aim of the study was to demonstrate whether pinealectomy and long-term MEL administration can affect bone metabolism (as evaluated on the basis of serum concentrations of PICP and ICTP) in orchidectomized rats.

Material And Methods: The study included 248 adult male Wistar rats; 6 remained intact, 120 were orchidectomized (Orch), and the remaining ones underwent a sham operation (SOrch). Two weeks after surgery, the rats were divided into 8 groups: 1) SOrch + SPx; 2) SOrch + SPx + MEL; 3) Orch + SPx; 4) Orch + SPx + MEL; 5) SOrch + Px; 6) SOrch + Px + MEL; 7) Orch + Px; 8) Orch + Px + MEL. Animals from 5(th), 6(th), 7(th) and 8(th) groups were pinealectomized (Px) while the remaining ones underwent a sham operation (SPx). Two weeks after surgery rats in the 2(nd), 4(th), 6(th) and 8(th) groups were administered MEL (50 microg/100 g of bm) intraperitoneally while the remaining animals were administered solvent only (daily between 5 and 6 pm during a month). The animals were decapitated before the experiment (intact rats), after 2 weeks from Orch and SOrch, Px and SPx, after 4 weeks from MEL or solvent administration and after 4 and 8 weeks from discontinuing administration of MEL, and blood was collected for PICP and ICTP concentrations assays with the use of RIA method.

Discussion: In Orch rats, a distinct tendency to increase the studied bone markers, especially ICTP was shown. Pinealectomy had inducing, while MEL suppressing effect upon the level of PICP and ICTP; these changes were more pronounced in Orch + Px and SOrch + Px + MEL groups, respectively. After discontinuing administration of MEL distinct tendency to increase of PICP and ICTP level was shown.

Conclusions: Our findings indicate that MEL is an important modulator of bone tissue metabolism in male rats and that deficiency of MEL concentration may be a co-factor in osteoporosis development.