Aging and caloric restriction: human effects and mode of action.
Explore the source record for details and available documents.
Adrenal Cortex Hormones↗
Biomedical subjects
S N Austad
Publications and source records attributed to S N Austad.
Menopause: an evolutionary perspective.
Evolutionary biologists classify theories of menopause as either: 1) adaptive, suggesting that female reproductive cessation results from its selective advantage, in that the increased risk of personal reproduction late in life makes it biologically more advantageous to rechannel reproductive energy into helping existing descendents, or 2) nonadaptive, indicating menopause is an artifact of the relatively recent dramatic increase in human longevity. With the possible exception of pilot whales, no mammals studied to date are known to commonly exhibit reproductive cessation in nature. To demonstrate adaptive menopause, one would need to establish both that the longevity of preagricultural humans commonly allowed them to exhibit menopause, and that postreproductive females could assist their descendents sufficiently to compensate for the loss of personal reproduction. The data on longevity of preagricultural humans with respect to the adaptive menopause hypothesis are mixed. Evolutionary models evaluated with data from modern hunting-gathering or agricultural humans fail to find that humans can assist their descendents sufficiently to offset the evolutionary cost of ceasing reproduction. However, assuming the human body has been physiologically adapted to the conditions extant during the vast majority of human history, it may be well worth pursuing how the signs and symptoms of menopause are affected by dietary, exercise, and reproductive hormone regimes mimicking those of the late Paleolithic era.
Animals↗
The uses of intraspecific variation in aging research.
The artificial creation of genetically long-lived populations of several invertebrate species has illustrated how researchers may take advantage of genetic variation within a species to investigate the nature and mechanisms of aging. The advantage of studying intraspecific variation is that populations will be generally similar except for the relevant demographic differences. Also, there are reasons to suspect that genetic mechanisms of aging may differ from mechanisms associated with life extension via environmental manipulations such as caloric restriction. However creating a long-lived mammalian aging model will be expensive and time consuming. An alternative approach is to seek to identify naturally occurring slowly aging populations to contrast mechanistically with a reference population. Ecologists have already noted that demographic alterations of the appropriate type are frequently associated with populations from differing latitudes, differing altitudes, or from islands. Therefore, it is likely that genetically longer- (and shorter)-lived mammal populations of the same species already exist in nature, and could potentially be exploited to inquire into the genetics and mechanisms of aging and longevity. Of particular interest is the indication that some island populations of house mice may exhibit extended longevity compared with laboratory strains.
Aging↗
Issues in the choice of genetic configuration for animal aging models.
Animals used in aging research are generally of three genetic types-outbred, inbred, and hybrid. These three types have differing uses and characteristics. Outbred animals are heterozygous at many genetic loci and all individuals are genetically unique. Inbred animals are homozygous at all loci and genetically identical to one another. F1 hybrids are heterozygous at many loci, but genetically identical. Both theoretical and empirical findings suggest that each of these models behaves somewhat differently with respect to aging. This presentation will detail these theoretical and empirical findings, and suggest what uses each genetic type might best be put to with respect to aging research.
Aging↗
Comparative aging and life histories in mammals.
A comparative assessment of aging and longevity in mammals has four uses in aging research. These are: (1) hypothesis formulation and evaluation, (2) investigating the generality of putative aging mechanisms, (3) isolating key physiological factors influencing aging rate, and (4) allowing the most appropriate choice of animal models for particular research questions. The first use requires detailed information on a wide variety of species, and I will examine general patterns of aging in a sample of over 600 species of mammals. The second use requires the selection of several models as distantly related to one another as feasible. The third use is best served by evaluating species or populations as closely related to one another as possible, assuming that they differ substantially in aging rate. The fourth use requires a logic of animal model selection, as well detailed information about a wide range of species. Specific examples of each use will be given.
Aging↗
Fecal glucocorticoids: a noninvasive method of measuring adrenal activity in wild and captive rodents.
To determine the utility of fecal corticosteroid concentration as a measure of chronic stress under laboratory and field conditions, we biochemically and physiologically validated a radioimmunoassay for corticosteroids in three rodent species, house mice (Mus musculus), deer mice (Peromyscus maniculatus), and red-back voles (Clethrionomys gapperi). The biochemical validations demonstrated that the assay accurately and precisely measured corticosteroid concentration in the feces. The physiological validation indicated that the assay was sensitive enough to detect the stress associated with (a) brief handling and bleeding of animals, (b) chronic caloric restriction, (c) exposure to a novel environment, and (d) exposure to a novel cold environment. Our results suggest that fecal measurements reflect stress levels experienced by these animals approximately 6-12 h before defecation. Therefore, given a judicious trapping and trap-monitoring protocol, this assay has considerable utility for measuring the stress levels at which animals actually exist in the field.
Adrenal Cortex Hormones↗
Natural selection, dietary restriction, and extended longevity.
Explore the source record for details and available documents.
Animals↗