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

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.

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.

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.

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.