University of California: Berkeley researchers have found what they think is a critical and, until now, missing piece of the puzzle about how stress causes sexual dysfunction and infertility. Scientists know that stress boosts levels of stress hormones - glucocorticoids such as cortisol - that inhibit the body's main sex hormone, gonadotropin-releasing hormone (GnRH), and subsequently suppresses sperm count, ovulation and sexual activity.
The new research shows that stress also increases brain levels of a reproductive hormone named gonadotropin-inhibitory hormone, or GnIH, discovered nine years ago in birds and known to be present in humans and other mammals. This small protein hormone, a so-called RFamide-related peptide (RFRP), puts the brakes on reproduction by directly inhibiting GnRH.
The common thread appears to be the glucocorticoid stress hormones, which not only suppress GnRH but boost the suppressor GnIH - a double whammy for the reproductive system.
"We know stress affects the top-tier reproductive hormone, GnRH, but we show, in fact, that stress also affects another high-level hormone, GnIH, to cause reproductive dysfunction," said lead author Elizabeth Kirby, a graduate student at UC Berkeley's Helen Wills Neuroscience Institute. "This work provides a new target for researchers, a new way to think about infertility and dysfunction. The more we know, the more we can look for ways to treat it."
The results will be published the week of June 15 in the Online Early Edition of the journal Proceedings of the National Academy of Sciences (PNAS).
The conclusions are based on experiments in rats and inferences from the effects of the hormone in birds. But if this new reproductive hormone acts the same way in all mammals, researchers say the finding could not only change the way physicians look at human reproductive problems, but also affect how breeders approach animal husbandry and captive breeding programs for endangered species.
"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.