Melatonin does not affect p21 expression in rat thyroid follicular cells

OBJECTIVES: The cell-cycle (cc) is, in part, controlled by cyclin-dependent kinases (CDKs), which are activated after binding cyclins (positive regulators of cc). CDK inhibitors (CDKIs), such as p15, p16, p21, and p27, inhibit cyclin-CDK complex activity, and function as negative cell cycle regulators, blocking cell-cycle progression. The aim of our study was to examine the influence of late-afternoon (16(00)-18(00)) subcutaneous (s.c.) melatonin (Mel) injections, administered for 2 weeks, on the p21 expression in male Wistar rat thyroid follicular cells (TFC). METHODS: In order to detect the anti-p21 antibodies, the DAKO LSAB(R)2 Rat Kit/HRP (DAKO, USA) and DAKO(R) Liquid DAB Substrate-Chromogen System (DAKO, USA) were employed. RESULTS: No statistically significant changes of p21(LI) (p21 labelling index) values were observed in particular groups of the rats receiving Mel injections, in comparison to the controls. The statistical difference of p21(LI) values (p < 0.03) was only observed between groups of rats, receiving Mel injections in the dose of 25 mug/daily and 100 mug/daily. CONCLUSION: Melatonin - in the applied doses and in the experimental conditions without any factors revealing anti-DNA activity - did not change, in any statistical way, p21 expression in rat thyroid follicular cells, as compared to the control group.