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Plastics chemical retards growth, function of adult reproductive cells
July 09, 2009CHAMPAIGN, Ill. - Bisphenol A, a chemical widely used in plastics and known to cause reproductive problems in the offspring of pregnant mice exposed to it, also has been found to retard the growth of follicles of adult mice and hinder their production of steroid hormones, researchers report.
Their study is the first to show that chronic exposure to low doses of BPA can impair the growth and function of adult reproductive cells. The researchers will describe their findings this month at the annual meeting of the Society for the Study of Reproduction.
A healthy, mature follicle, called an antral follicle, includes a single egg cell surrounded by layers of cells and fluid which support the egg and produce steroid hormones, said University of Illinois veterinary biosciences professor Jodi Flaws, who led the study with graduate student Jackye Peretz.
"These are the only follicles that are capable of ovulating and so if they don't grow properly they're not going to ovulate and there could be fertility issues," Flaws said. "These follicles also make sex steroid hormones, and so if they don't grow properly you're not going to get proper amounts of these hormones." Such hormones are essential for reproduction, she said, "but they're also required for healthy bones, a healthy heart and a healthy mood."
BPA is widely used in plastics and is a common component of food containers and baby bottles.
The chemical structure of BPA is similar to that of estradiol, a key steroid hormone, and it can bind to estrogen receptors on the surface of some cells. It is not known whether BPA blocks, or mimics or enhances estrogen's activity on these cells, Flaws said.
Human studies have found BPA in many tissues and fluids, including urine, blood, breast milk, the amniotic fluid of pregnant women and the antral fluid of mature follicles. A national survey conducted by the federal Centers for Disease Control and Prevention in 2003-2004 found BPA in 93 percent of the 2,517 people (age 6 and up) who were tested.
BPA has a short half-life, Peretz said, and the chemical is quickly eliminated from the body. The fact that so many people tested positive "probably means that we're being constantly exposed to BPA," she said. The new study found that follicle growth was impaired after 48 hours of exposure to BPA, Peretz said. Reductions in three key steroid hormones - progesterone, testosterone and estradiol - were also seen after 120 hours of exposure to BPA.
The drop in steroid hormone production was quite dramatic. After 120 hours in a medium that included 10 micrograms per milliliter of BPA, mouse follicle cells produced about 85 percent less estradiol, 97 percent less progesterone and 95 percent less testosterone. Lower doses of BPA had a less dramatic - but still considerable - dampening effect on steroid hormone levels. And at 120 hours, follicle cells grown in the BPA medium were 25 percent smaller than normal, the researchers report.
A review of the health risks of BPA by the National Toxicology Program of the U.S. Department of Health and Human Services concluded in 2008 that while BPA has been shown to harm the reproductive health of laboratory animals in some studies, such adverse effects "are observed at levels of exposure that far exceed those encountered by humans."
However, the NTP reported that laboratory studies that showed effects in animals exposed to low doses of BPA led it to have "some concern for effects on the brain, behavior and prostate gland in fetuses, infants and children at current human exposures to bisphenol A."
The new study points to possible concerns in adults as well, Flaws said.
"I think there's a need for more studies where people look in adult humans to see if BPA is affecting follicle growth and steroid hormone levels," she said. If it is, that might help explain some infertility or menopausal symptoms, she said.
University of Illinois at Urbana-Champaign
"These are the only follicles that are capable of ovulating and so if they don't grow properly they're not going to ovulate and there could be fertility issues," Flaws said. "These follicles also make sex steroid hormones, and so if they don't grow properly you're not going to get proper amounts of these hormones." Such hormones are essential for reproduction, she said, "but they're also required for healthy bones, a healthy heart and a healthy mood."
BPA is widely used in plastics and is a common component of food containers and baby bottles.
The chemical structure of BPA is similar to that of estradiol, a key steroid hormone, and it can bind to estrogen receptors on the surface of some cells. It is not known whether BPA blocks, or mimics or enhances estrogen's activity on these cells, Flaws said.
Human studies have found BPA in many tissues and fluids, including urine, blood, breast milk, the amniotic fluid of pregnant women and the antral fluid of mature follicles. A national survey conducted by the federal Centers for Disease Control and Prevention in 2003-2004 found BPA in 93 percent of the 2,517 people (age 6 and up) who were tested.
BPA has a short half-life, Peretz said, and the chemical is quickly eliminated from the body. The fact that so many people tested positive "probably means that we're being constantly exposed to BPA," she said. The new study found that follicle growth was impaired after 48 hours of exposure to BPA, Peretz said. Reductions in three key steroid hormones - progesterone, testosterone and estradiol - were also seen after 120 hours of exposure to BPA.
The drop in steroid hormone production was quite dramatic. After 120 hours in a medium that included 10 micrograms per milliliter of BPA, mouse follicle cells produced about 85 percent less estradiol, 97 percent less progesterone and 95 percent less testosterone. Lower doses of BPA had a less dramatic - but still considerable - dampening effect on steroid hormone levels. And at 120 hours, follicle cells grown in the BPA medium were 25 percent smaller than normal, the researchers report.
A review of the health risks of BPA by the National Toxicology Program of the U.S. Department of Health and Human Services concluded in 2008 that while BPA has been shown to harm the reproductive health of laboratory animals in some studies, such adverse effects "are observed at levels of exposure that far exceed those encountered by humans."
However, the NTP reported that laboratory studies that showed effects in animals exposed to low doses of BPA led it to have "some concern for effects on the brain, behavior and prostate gland in fetuses, infants and children at current human exposures to bisphenol A."
The new study points to possible concerns in adults as well, Flaws said.
"I think there's a need for more studies where people look in adult humans to see if BPA is affecting follicle growth and steroid hormone levels," she said. If it is, that might help explain some infertility or menopausal symptoms, she said.
University of Illinois at Urbana-Champaign
Steroid Hormone Current Events and Steroid Hormone News RSSBUSM researchers propose a relationship between androgen deficiency and cardiovascular disease
Researchers from Boston University School of Medicine (BUSM) in collaboration with researchers from Lahey Clinic Northshore, Peabody, Mass., believe that androgen deficiency might be the underlying cause for a variety of common clinical conditions, including diabetes, erectile dysfunction, metabolic syndrome and cardiovascular disease (CVD).
Life and death in the living brain
Like clockwork, brain regions in many songbird species expand and shrink seasonally in response to hormones. Now, for the first time, University of Washington neurobiologists have interrupted this natural "annual remodeling" of the brain and have shown that there is a direct link between the death of old neurons and their replacement by newly born ones in a living vertebrate.
2 reproductive factors are important predictors of death from ovarian cancer
Researchers from the Centers for Disease Control and Prevention (CDC) found that survival among women with ovarian cancer is influenced by age of menarche and total number of lifetime ovulatory cycles.
Toxic chemicals affect steroid hormones differently in humans and invertebrates
In a study with important consequences for studies on the effects of chemicals on steroid responses in humans, a team of French and American scientists, including Michael E. Baker, PhD, professor in UC San Diego's Department of Medicine, Division of Nephrology-Hypertension, have found that - contrary to earlier assumptions - enzymes used for the synthesis of steroids in insects, snails, octopuses and corals are unrelated to those used in humans.
VBI researchers develop new method for breast cancer biomarker discovery
Three researchers from the Virginia Bioinformatics Institute (VBI) at Virginia Tech have developed and evaluated a new one-step bioanalytical approach that allows them to profile in detail complex cellular extracts of proteins.
A stronger backbone: DHEA hormone replacement increases bone density in older women
Taking a DHEA supplement combined with vitamin D and calcium can significantly improve spinal bone density in older women, according to a new study from a Saint Louis University scientist and his colleagues at Washington University.
Worms control lifespan at high temperatures, UCSF study finds
The common research worm, C. elegans, is able to use heat-sensing nerve cells to not only regulate its response to hotter environments, but also to control the pace of its aging as a result of that heat, according to new research at the University of California, San Francisco.
Balancing hormones may help prevent preterm births
The relationship between two different types of estrogen and a hormone produced in the placenta may serve as the mechanism for signaling labor, according to a new study accepted for publication in The Endocrine Society's Journal of Clinical Endocrinology & Metabolism (JCEM).
Pregnancy-related hormonal changes linked to increased risk of restless legs syndrome
A study in the Feb. 1 issue of the journal Sleep shows that the elevation in estradiol levels that occurs during pregnancy is more pronounced in pregnant women with restless legs syndrome (RLS) than in controls.
Insomnia in women with breast cancer linked to heart rate dysregulation
A study in the October 15 issue of the Journal of Clinical Sleep Medicine shows that respiratory sinus arrhythmia (RSA) is a significant predictor of insomnia in women with breast cancer and confirmed that longer nocturnal wake episodes were associated with a flatter diurnal cortisol slope.
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