Morphometric analysis of somatotrophs: effects of age and dietary restriction

We investigated changes in the cell number of somatotrophs in the anterior pituitary of male F344 rats caused by age and lifelong dietary restriction (DR). Morphometric and immunohistochemical techniques were performed on the pituitary gland at 6, 18, and 24 months of age. In ad lib fed (AL) rats, cell density of somatotrophs progressively decreased with age. However, when normalized according to the increased volume of the anterior lobe, which occurs during aging, the total number of somatotrophs remained constant until 18 months, then decreased. In contrast, the cell density of DR rats was not affected to the same extent as that of AL rats, and the total number of cells seemed to remain constant through 24 months, thus, retarding the age-related numerical changes. However, the cell number in DR rats, when normalized by body weight, was larger than that found in AL rats. We also found that average cell volume of somatotrophs shows little age or dietary restriction effects, but the nucleus volume significantly increases at 24 months in both groups. The numerical changes which occur in somatotrophs during the aging process may be associated with the aging phenomena found in GH secretion.