By Neus Ferrando Gilabert BSc, MSc (embryologist).
Last Update: 05/03/2014

GnRH analogues are molecules created in the laboratory. They were synthesised to look like natural peptide GnRH and to cause its effect consisting in the pituitary gland releases FSH and LH gonadotropins.

However, this medicine is not made in the same way as the natural molecule, but some components were modified in order that their affinity for GnRH receptors increase.

When GnRH analogue combines with its receptor, a massive release of FSH hormones (follicle stimulating hormone) and LH (luteum stimulating hormone) occurs, it is called flare-up effect. In addition, it also extends the response time of the cell.

Flare-up effect

The release of gonadotropins (FSH and LH) occurs endogenously, that is to say, the hypophysis or the pituitary gland, located in the brain, synthesises and releases these hormones into the bloodstream.

The flare-up effect happens, approximately, during the two first days after the administration of GnRH analogues.

After this time the pituitary gland desensitises to the initial effect of the GnRH analogue and blocks the synthesis of gonadotropins.

Authors and contributors

 Neus Ferrando Gilabert
BSc, MSc
Bachelor's Degree in Biology from the University of Valencia (UV). Postgraduate Course in Biotechnology of Human Assisted Reproduction from the Miguel Hernández University of Elche (UMH). Experience managing Embryology and Andrology Labs at Centro Médico Manzanera (Logroño, Spain). More information