Changes of beta-endorphin and Met-enkephalin content in the hypothalamus-pituitary axis induced by aging.

The amounts of beta-endorphin- and Met-enkephalin-immunoreactive material are higher in the pituitary of aged rats. However, the aging process decreases the content of beta-endorphin-, but does not affect that of Met-enkephalin-immunoreactive material, in hypothalamus. Thus, it seems that the regulatory mechanisms in the two areas are differentially affected by increasing age. On the other hand, the pituitary increase of these peptides is in line with the assumption that in the elderly the hormonal response to stress is impaired.