Seasonal peculiarities of thyroxine influence on the way of serotonin metabolism in the pineal gland of the rat

In intact Wistar pubertal male rats held on LD 8:16 (winter) and 16:8 (summer) pineal melatonin (M) production and other pineal indoles content serotonin (S), 5-methoxytriptamine (5-MT), N-acetylserotonin (N-aS), 5-hydroxyindoleacetic acid (5-HIAA) and 5-methoxyindoleacetic acid (5-MIAA) were investigated in basic conditions and after 10-days T4 administration. The results suggest, that intact control in winter comparing with summer demonstrates high M, N-aS, 5-HIAA and 5-MIAA level, but low 5-MT concentrations, S level was not changed. T4 administration in winter produced a pronounced augmentation of all parameters (excluding serotonin), in summer M production not only increased, but appears to be dependent on the active metabolism of his precursors (S, 5-MT, N-aS). The experimental data favour more profound comprehension to the mechanisms of pineal activity regulation.