Stress puts double whammy on reproductive system,...(y and captive breeding programs for enda...)

"There is a growing body of work that points to GnIH as being a big player in the inhibition of reproduction in mammals," said co-author George Bentley, UC Berkeley assistant professor of integrative biology. "We didn't have any hint of this stress effect nine years ago, when GnIH was first discovered."

In humans, chronic stress can lead to a drop in sex drive as well as a drop in fertility. Even the stress of infertility treatments can block their effectiveness, as evidenced by many anecdotes about couples conceiving children after the failure of assisted reproduction.

Animal breeding also is affected by stress. Zoos, in particular, have difficulty getting some animals to reproduce in captivity, Bentley said.

Based on animal experiments, researchers attribute much of this stress effect on sexual function to an increase in glucocorticoids - stress hormones - produced by the adrenal gland. In the brain, these glucocorticoids suppress the main reproductive hormone, GnRH, which in turn causes a shut-down of the release of the gonadotropins luteinizing hormone and follicle-stimulating hormone by the pituitary, and then a suppression of testosterone, estradiol and sexual behavior.

In 2000, however, a new reproductive hormone was discovered in birds and dubbed gonadotropin-inhibitory hormone (GnIH) because it had the opposite effect of GnRH - it inhibited release of gonadotropins, thereby suppressing reproduction.

"It's very adaptive to not be wasting resources on reproduction during times of acute stress, to just shut down reproduction for 24 hours or so until the stress is gone," said co-author Daniela Kaufer, a UC Berkeley assistant professor of integrative biology who looks at how stress affects molecular processes in the brain. "These functions go back in evolution a long way."

Because of the negative effects of GnIH on reproduction, Bentley, who hel
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