Relation of sex and ageing to serotonin metabolism in rats.

The present study deals with serotonin (5-HT) metabolism at the central and peripheral levels in young, middle-aged and old male and female rats. From middle age, the level of endogenous 5-HT and the uptake of [14C] 5-HT were higher in the platelets of female rats than in those of male rats. By contrast, the retention of [14C] 5-HT by the platelets of male rats decreased after middle age. The 5-hydroxyindoleacetic acid (5-HIAA) level in plasma was lower in males than in females, and this level increased significantly with age in males. In brain, the tryptophan level decreased significantly with age in male rats, while the 5-HT level increased in males as well as females. The brain 5-HIAA level increased significantly with age in male rats. These results confirm that 5-HT metabolism is modified during the ageing process in rats, and that several factors may be involved in this modification.