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.

Effects of glucose and fructose loading on glycogenesis in chicks infected with avian tuberculosis

The chick was used as a rapid metabolic model to determine the fate of ingested fructose vs. glucose in noninfected chicks and in those subjected to the stress of avian tuberculosis. The chicks were crop-loaded with either a 72% fructose or glucose solution 21 and 28 days post TB inoculation and killed 2 and 4 hr after loading. In noninfected chicks, both sugars were rapidly converted to glycogen, and there was an interaction with time and the amount of glycogen formed from each sugar. Infection depressed glycogen formation from both fructose and glucose. While the total amount of glycogen formed from glucose could be directly correlated to increased liver size in the TB chicks loaded with glucose, in the chicks loaded with fructose less glycogen was formed even though liver size was increased as a result of the TB infection. The depression in glycogen formation was not related to the severity of the infection since the TB involvement was not the same in the two experiments conducted; but in both cases chicks loaded with fructose showed a greater reduction in the capacity of the liver to synthesize glycogen.

Studies on hyperlymphoid mice

Injection of syngeneic, but chromosomally distinguishable, lymph node or spleen cells into adult mice resulted in both T- and B-lymphocyte chimaerism. In spleen-injected mice haematopoietic chimaerism was also established. It appeared that the donor T lymphocytes were added to the host recirculating T-cell pool so that a hyperlymphoid state was produced. The percentage of donor T lymphocytes declined very slowly in normal mice, but remained stable in adult-thymectomized animals. There was no evidence of a homeostatic mechanism involving destruction of excess peripheral T lymphocytes or grossly affecting the flow of T lymphocytes from the thymus into the recirculating T-cell pool. A preliminary model of the T-lymphocyte system is proposed.