The hormone, a small protein, or peptide, called gonadotropin-inhibitory hormone (GnIH), puts the brakes on reproduction by directly inhibiting the action of the central hormone of the reproductive system - gonadotropin releasing hormone (GnRH). GnRH stimulates the pituitary gland to activate the reproductive system, whereas GnIH appears to reduce the effects of GnRH stimulation.

Researchers have long sought inhibitors of pituitary gonadotropins, but many had come to believe that such a direct inhibitor was unlikely in the complex cast of hormones and factors in the reproductive system. The inhibiting or braking hormone may complement the "gas pedal" role played by another recently discovered hormone, kisspeptin, that stimulates GnRH.

The discovery in rats, mice and hamsters of this new system for regulating reproduction strongly suggests that the hormone plays a similar role in the reproductive systems of humans and other mammals. The human genome, in fact, contains a gene for GnIH.

If the new finding is mirrored in humans and other mammals, it would offer physicians another means of tweaking the reproductive system to fix problems ranging from infertility to precocious puberty, and also provide animal breeders with a new way to manipulate the productivity of livestock.

The findings by Kriegsfeld and colleagues are reported this week in the online early edition of Proceedings of the National Academy of Sciences.

The human reproductive system is regulated like a thermostat, with a number of hormones and factors produced along the "reproductive axis" acting via feedback loops to keep the body's hormones within the optimal range for fertility and successful mating. The head of the axis is the brain's GnRH-producing hypothalamus,
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Contact: Robert Sanders
rsanders@berkeley.edu
510-643-6998
University of California - Berkeley
6-Feb-2006