Reassessing the role of growth hormone and sex steroids in thymic involution.
The concomitant decline in growth hormone (GH) and increase in sex steroid production with age is thought to be responsible for thymic involution. If changes in the production of these hormones trigger or sustain thymic involution, that process should be accelerated in little mice, which have a genetic deficiency resulting in reduced production of thymopoietic GH, and delayed in the hypogonadal strain, which fails to produce thymocytotoxic sex steroids. The results indicated that thymic involution in both strains progressed in a manner similar to their normal littermates. That blocking sex steroid production did not delay thymic involution was surprising since castration reportedly increases thymus cellularity. Re-examination of that phenomenon revealed that, while gonadectomy results in increased thymus size, its effects are transient, and the thymus ultimately undergoes involution. Taken together, these data suggest that age-related changes in the endocrine system do not underlie thymic involution.
Min
Hyeyoung
H
Department of Pathology and Laboratory Medicine 173216, David Geffen School of Medicine at UCLA, 10833 Le Conte Avenue, Los Angeles, CA 90095-1732, USA.
Montecino-Rodriguez
Encarnacion
E
Dorshkind
Kenneth
K
D000367:Age Factors; D000818:Animals; D016516:CD4-CD8 Ratio; D049109:Cell Proliferation; D002478:Cells, Cultured; D005260:Female; D012739:Gonadal Steroid Hormones / Q000502:physiology*; D013006:Growth Hormone / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D008297:Male; D051379:Mice; D009929:Organ Size; D013950:Thymus Gland / Q000166:cytology / Q000254:growth & development / Q000502:physiology*
D012739:Gonadal Steroid Hormones; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone