Immunohistochemical and radioimmunological study of pituitary gonadotrophs during aging in male rats

The impact of aging on pituitary gonadotrophs in rats is little known. We therefore undertook a quantitative immunohistochemical assessment of the follicle-stimulating hormone (FSH) and luteinizing hormone (LH) immunoreactive cell population in the pituitaries of young (4 months), old (20 months) and senescent (29 months) male rats. In addition, an attempt was made to correlate morphometric parameters with serum levels of FSH and LH. Gonadotrophs were immunostained by the peroxidase-antiperoxidase method using anti-rat LH and anti-rat FSH rabbit sera as primary antibodies. Hormones were measured in serum by specific radioimmunoassays. Analysis of morphological parameters revealed, for both types of gonadotrophs, a marked age-related reduction in cell density, volume density and surface density. Gonadotroph cell perimeter and area showed a trend towards an increase from 5 to 20 months of age but appeared drastically reduced in the 29-month-old rats. Basal serum levels of LH and FSH showed a significant increase from 4 to 20 months of age but remained at the same level in the senescent rats. The correlation between serum levels of gonadotropins and gonadotroph morphometric parameters was low in all cases. We conclude that in male rats aging brings about a significant reduction in both the number and size of pituitary gonadotrophs which, nevertheless, seem to be still capable of keeping appropriate basal levels of circulating LH and FSH.