Long-term action of prednisolone phosphate on a strain of short-lived mice

Food restriction enhances endogenous and corticotropin-induced plasma elevations of free but not total corticosterone throughout life in rats

Chronic food restriction (FR), which retards many aging processes, enhances the endogenous diurnal peak of plasma total corticosterone (B) in young rats. Although the FR-dependent enhancement of total B disappears in aged rats, increased levels of the bioavailable fraction, free B, appear to be maintained. In young rats, we previously found that the FR-induced increase in the diurnal peak of total B is associated with increased adrenal response to corticotropin, also known as adrenocorticotropic hormone (ACTH). Here we show that the FR-enhanced adrenal response of total B to ACTH disappears with age but that the enhanced response of free B is maintained. We measured the endogenous diurnal peak and the response to ACTH of total and free B in 10-, 16-, and 22-month-old ad-libitum fed and FR male Fischer 344 rats in the afternoon, when plasma B peaks. At 10 and 16 months, FR rats showed enhanced total plasma B responses to ACTH relative to ad-libitum fed rats, but not at 22 months. By contrast, the response of free B to ACTH was enhanced by FR at all ages. The effect of FR on patterns of endogenous total and free diurnal B in these three age groups paralleled the ACTH-response data. The enhanced adrenocortical response of FR rats to ACTH does not reflect an increased expression of ACTH-receptor (ACTH-R) mRNA, because ACTH-R mRNA/microg adrenal RNA and ACTH-R mRNA/mg adrenal weight did not differ between ad-libitum fed and FR rats at any age.

Life span extension and cancer risk: myths and reality

A significant increase in the number of old people in the populations of developed countries was followed by an increase in morbidity and mortality resulting from main age-related diseases -- cardiovascular, cancer, neurodegenerative, diabetes mellitus, decrease in resistance to infections. Obviously, the development of the means of prevention of the premature aging of humans is crucial for the realization of this program. However, data available on such kind of means are rather scarce, contradictory and are often not reliable from the points of view of the adequacy of the experiments to current scientific requirements as well as the interpretation of the results and safety. Data available on the increase in life span and the adverse effects of the following geroprotectors were critically analyzed: antioxidants, chelate agents and lathyrogens, succinate, adaptogens and herbs, neurotropic drugs, inhibitors of monoamine oxidase, glucocorticoids, dehydroepiandrosterone, sex and growth hormones, melatonin, pineal peptide preparations, protein inhibitors, antidiabetic biguanides, thymic hormones and peptides, immunomodulators, enteroadsorbents, lypofuscin inhibitors, as well as calorie intake restriction and special diets. Most of the available results were insufficient and could not provide convincing evidence for the life span extension and the safety of the suggested geroprotectors. Drugs and means prolonging the life span could be subdivided into three groups: (a) geroprotectors prolonging the life span equally in all the members of the population: these postponed the beginning of the population's aging; (b) geroprotectors decreasing the mortality rate in a long-lived subpopulation, which raised their maximal life span: these slowed down the population's aging rate; (c) geroprotectors increasing the survival rate in a short-lived subpopulation without changes in the maximal life span: in this case, the aging rate increased. There was a high positive correlation between the type of geroprotector-induced aging delay and the pattern of tumour development in the same population of animals. The first type of geroprotectors did not influence the incidence of tumour but increased tumour latency. The second type of geroprotectors was effective both in the inhibition of spontaneous carcinogenesis and the increase in tumour latency. Certain drugs of the third type raised tumour incidence in the exposed populations. According to the multistage model, geroprotectors either inhibit or accelerate the passage of carcinogen-exposed cells form one stage to another. Thus, the efficacy of geroprotectors as preventive means of cancer development will decrease with respect to the age of exposure onset. Recommendations of the available drugs and means of life span increase should be carefully reconsidered under the international scientific control.

Glucocorticoids and aging

Information on the role of glucocorticoids in the aging of vertebrate species is reviewed. There is strong evidence that elevated plasma glucocorticoid levels have a causal role in the rapid deterioration following reproduction in semelparous vertebrate species. If this deterioration is an example of rapid senescence, then it is clear that glucocorticoids can promote aging processes in vertebrate species. However, the evidence that glucocorticoids promote aging in the gradual senescence characteristic of most vertebrate species is not robust. Indeed, there is reason to believe that periods of moderately elevated plasma glucocorticoid levels may retard aging processes in rats, mice, and humans.

Stress-age syndrome

With aging a set of neurohormonal, tissue and cellular changes develop which can be defined as stress-age syndrome. They include irregular changes in the excitability of structures of the limbic system and hypothalamus, rise of the blood concentration of catecholamines, vasopressin, ACTH and cortisol, fall of the concentration of testosterone, thyroxin and other substances, change of the concentration of opioid peptides, immunodepression, dyslipoproteidemia hypercoagulation and free-radical damage of cells. One group of components of the above syndrome is of adaptive importance, while the other is damaging. Symptoms of stress-age syndrome have their individual peculiarities and cannot explain the whole complexity of symptoms of the organism's aging. Against the background of stress-age syndrome the course of developing stress reactions undergoes a change.