Oxytocin concentration changes in different rat brain areas but not in plasma during aging

The concentration of oxytocin was measured by radioimmunoassay in different brain areas, hypophysis, and plasma of male Wistar Kyoto rats during aging. Although no difference in the concentration of oxytocin in any of the above tissues among 2- and 6-month-old rats was found, in 12-month-old rats a 21% decrease was observed in both septum and hippocampus, but not in the hypothalamus, hypophysis, and plasma, when compared to values of 2- and 6-month-old rats. In 18-month-old rats, the decrease of septal and hippocampal oxytocin content was higher than that found in 12-month-old rats, but no change was found in the hypothalamus, neurohypophysis, and plasma. In 24-month-old rats, oxytocin content was similar to that found in 18-month-old rats in all tissues analyzed. The results suggest that aging induces an impairment of oxytocinergic transmission in the central nervous system but not in the neurohypophyseal system.