Biologic Markers in Reproductive Toxicology (1989) / Chapter Skim
Currently Skimming:
13. Biologic Markers of Reproductive Development and Aging
13. Biologic Markers of Reproductive Development and Aging
Pages 169-178
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 169... ...
Chronic exposure of mice to endogenous ovarian steroids secreted during young adult life is a cause of age-related estrous cycle lengthening (Felicio et al., 1986) or premature loss of estrous cycles after the 169 estrogen treatment ends (Mobbs et al.
|
From page 170... ...
Among the best-characterized markers used in epidemiologic surveys and individual case studies are infertility and length of menstrual cycles, which appear to be sensitive to many of the same environmental influences in humans and rodent models. However, human neuroendocrine reproductive functions appear to differ in important ways from those of rodents; the hypothalamus might be less crucial in regulating the preovulatory surge in humans than of rodents (Knobil, 1980~.
|
From page 171... ...
Breast and pubic hair stages often are asynchronous and by themselves do not precisely indicate the rate of development. MENSTRUATION Menstrual cycles constitute the most accessible and noninvasive biologic marker of female reproductive function in humans.
|
From page 172... ...
Rodents are susceptible to premature infertility syndromes in association with neuroendocrine damage, as when steroids are administered to neonates in submasculinizing doses (Mobbs et al., 1984~. Natural variation of rodent infertility occurs due to in utero factors; female fetuses flanked by males eventually become infertile several months before fetuses flanked by females; such effects probably are limited to a critical period during development (Vom Saal and Moyer, 1985~.
|
From page 173... ...
However, extensive diurnal fluctuations and response to activity and ambient temperature contraindicate cortisol as a useful general biologic marker of reproductive function. NERVOUS SYSTEM A major issue in interpreting the impact of chronic exposure to toxicants on brain functions is the extent of underlying age changes.
|
From page 174... ...
normal age trend for loss of nigro-striatal dopaminergic activity to exceed putative threshold (Finch, 1976~. Greater induction of reversible parkinsonian symptoms in older patients by antipsychotic dopaminergic antagonists (Ayd, 1961)
|
From page 175... ...
In rodents, at least three markers of age-related neuron damage are available. Glial hyperactivity in the arcuate nucleus increases during female reproductive senescence (Schipper et al., 1981 ~ and can be induced in young rats by estrogen exposure (Brewer et al., 1983~.
|
From page 176... ...
Differential Susceptibility of Individuals and Populations Biologic markers are needed to identify individuals or populations whose reproductive functions are particularly susceptible to toxic effects. Human individuality might arise from genotypic differences or from a broad spectrum of environmental influences throughout life.
|
From page 177... ...
that causes intolerance to the lactose in milk and unfermented milk products also supports the presence of genetic polymorphisms that could influence responses to environmental toxicants. Analysis of Menstrual Cycle Lengths The frequency of menstrual cycles generally has been characterized in statistical terms.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.