Effects of aging on biologically active pituitary LH in rats

The effects of aging in the male rat on serum testosterone and LH and on the amounts of immunoreactive and biologically active pituitary LH were studied. Animals were killed at three, six, 12 and 24 months of age and serum and pituitary extracts prepared. Serum testosterone was significantly reduced by six months of age and remained at this low level throughout the study. The serum testosterone circadian rhythm was severely blunted in old animals. Serum LH was not effected by aging. Pituitary immunoreactive LH content was significantly decreased by 24 months of age, whereas the biological to immunological (B/I) ratio was not altered. However, the absolute amount of biologically active pituitary LH declined steadily with age from six months. These age-related effects were not caused by a gross redistribution of pituitary LH charge isohormones. These results suggest that the hypostimulated testis in the aging male rat may be related to a reduced amount of biologically active LH available for secretion.