science on mechanisms affecting sperm quantity and quality
Kuriyama, SN, CE Talsness, K Grote and I Chahoud. 2004. Developmental exposure to low dose PBDE 99: 1- effects on male fertility and neurobehavior in rat offspring. Environmental Health Perspectives, in press.
Kuriyama et al. report that rats exposed in the womb to a single low dose of a widespread brominated flame retardant become hyperactive and have decreased sperm counts. The effects are observed at an exposure level within the range that has been found in samples of breast milk from US mothers.
LE, J Ostby, E Monosson and WR Kelce. 1999. Environmental antiandrogens:
low doses of the fungicide vinclozolin alter sexual differentiation
of the male rat. Toxicology and Industrial Health 15: 48-64.
et al. found that ejaculated sperm counts in adult mice were reduced
by about 90% for males that had been in the womb when their mothers
were exposed, via feeding, to 50 mg/kg/day of vinclozilin, a powerful
anti-androgen used as a fungicide. More...
RM, JS Fisher, MM Millar, S Jobling and JP Sumpter. 1995.Gestational
and lactational exposure of rats to xenoestrogens results in reduced
testicular size and sperm production Environmental Health Perspectives
experiment, Sharpe et al. tested a key hypothesis on the mechanism
by which exposures to endocrine disruptors in utero might affect adult
sperm count. This hypothesis, advanced by Sharpe
and Skakkebaek in 1993, proposes that the reported decline in
sperm count is part of a syndrome of disorders of the male reproductive
tract that may have arisen because of increased exposure of the developing
fetus to estrogens, including xenoestrogens. By this hypothesis, altering
the fetal hormone experience reduces the capacity of the adult male
to produce sperm because it results in inadequate growth of specialized
cells (Sertoli cells) necessary to support sperm production.
et al. gave pregnant rats water containing the synthetic estrogen
DES and two common estrogenic chemicals found in the environment
(octylphenol, a detergent breakdown product, and butyl benzyl phthalate,
a plasticizer that is among the most ubiquitous of all environmental
contaminants). Exploring possible relevance to humans, the researchers
administered low doses--doses they said were roughly comparable
to estimated human intake--to the rats throughout their pregnancy
and for the 21 days they were nursing their pups. Octylphenol and
butyl benzyl phthalate produced effects similar to DES: males exposed
to these estrogenic chemicals in early life had smaller testicles
and sperm production reduced by as much as 21 percent when they
RA and PS Cooke. 1996.Neonatal thyroid status as one determinant
of adult testis size. pp 11-14 in Chapin, RE, JT Stevens, CL Hughes,
WR Kelce, RA Hess and GP Daston. Symposium Overview. Endocrine modulation
of reproduction. Fundamental and Applied Toxicology 29: 1-17.
and Cooke summarize work showing that neonatal thyroid status in rats
is an important determinant of adult testis size and thus of adult
sperm count. "Hypothyroidism" in utero produces overgrowth
of testes while "hyperthyroidism" can lead to dramatically smaller
testes. According to Hess and Cooke, in the normal animal, thyroid
(T3) concentrations increase during the neonatal period
and inhibit Sertoli cell differentiation. In other words, thyroid
is an important signal shutting off testicular growth. Hypothyroidism
causes a reduction in T3 and therefore Sertoli cell growth
is not inhibited appropriately, leading to enlarged testes (hypergonadism).
is relevant to the toxicology of endocrine disruption because some
PCBs (e.g., Aroclor 1242 and 1254) are known to induce hyperthyroidism
and thus cause enlarged testes and greater numbers of Sertoli cells.
Individuals thus affected can have higher sperm counts than normal.
Also see Cooke
et al. 1994.