The role of hormones in changing adaptive mechanisms during aging.

A generalized characteristic of all aging populations is the progressively impaired ability to adapt to an altered environment. The increased latent period for the response of hepatic glucokinase activity to glucose in aging rats is one specific example of this phenomenon. The disturbed regulation of hepatic glucokinase activity probably is the consequence of altered control of the secretion of key hormones rather than effects of aging on hepatic function. Such changes in the regulation of hormone secretion already are documented or suspected at least for insulin, glucagon, adrenal glucocorticoids, and thyroid hormones. The regulation of insulin secretion by glucose is altered during aging within the predominant population of islets of Langerhans, perhaps by differences in cell-to-cell communication within these islets. Once the nature of limiting biochemical modifications is established within a specific cell population, it may be possible to identify the origin of at least a distinct set of gerontological phenomena.