Sexually dimorphic effects of aging on rat somatotroph cells. An immunohistochemical and ultrastructural study

Aging produces alterations in certain functions of the hypothalamo-pituitary axis that result in sexually dimorphic changes in the somatotrophs. Since quantitative morphological data on these age-associated alterations are scarce, we prompted to make a morphometric immunohistochemical assessment as well as undertake an ultrastructural study of the somatotrophic (GH) cell population in male and female rats of different ages. Young (3-month-old), old (20-month-old), and senescent (29-month-old) Sprague-Dawley rats of both sexes were sacrificed by rapid decapitation, their pituitaries immediately dissected out, and processed for both immunohistochemistry and electron microscopy. Analysis of different morphometric parameters revealed that surface density, volume density, and cell density significantly decreased in old and senescent rats as compared to young animals, with this reduction being clearly more marked in females. Both the GH-cell area and perimeter decreased in senescent male rats, while these parameters increased in senescent females. The ultrastructure of the GH cells from old and senescent animals of both sexes evinced changes suggestive of an immature state, with some somatotrophs having the appearance of cells undergoing an involutive process. We conclude that aging has a differential impact on the GH cells of male and female rats with respect to the immunohistochemical and ultrastructural features of that cell population.