Opposite changes in the content of oxytocin- and vasopressin-like immunoreactive peptides in the rat thymus during aging.

The content of oxytocin- and vasopressin-like immunoreactive (IR) peptides was measured in the thymic extract of 2, 5, 10, 15 and 20 month-old rats by radioimmunoassay before or after fractionation by high-pressure liquid chromatography. In both cases the content of the oxytocin-like IR peptide, which behaved like authentic oxytocin in the chromatography column, increased during aging. Compared to 2 month-old rats a significant 30% increase was observed in 5 month-old rats, whereas the maximal increase (200%) was found in 20 month-old rats. In contrast, the content of the vasopressin-like IR peptide, which behaved like authentic arg8-vasopressin in the chromatography column, decreased during aging. The decrease (30%) was evident in 5 month-old rats, and was maximal (80%) in 15 month-old rats. The present results suggest that the mechanisms regulating the content of oxytocin- and vasopressin-like IR peptides in the rat thymus undergo differential changes during aging. These processes might be linked to thymic involution.