What is the Difference Between GnRH Agonist and Antagonist

The main difference between GnRH agonist and antagonist is that GnRH agonist activates the pituitary gland whereas GnRH antagonist blocks the activation of the pituitary gland.

Generally, GnRH agonists and antagonists are two products for the prevention of stimulating ovaries by natural LH surge. GnRH agonist is better for women over 40 years with low ovarian reserve while GnRH antagonist is better for women under 30 years with high ovarian reserve.

Key Areas Covered

1. What is GnRH
    – Definition, Characteristics, Function
2. What is GnRH Agonist
    – Definition, Characteristics, Function
3. What is GnRH Antagonist
    – Definition, Characteristics, Function
4. Similarities Between GnRH Agonist and Antagonist
    – Outline of Common Features
5. Difference Between GnRH Agonist and Antagonist
    – Comparison of Key Differences

Key Terms

GnRH Agonist, GnRH Antagonist

What is GnRH

GnRH is a reproductive hormone that affects the pituitary gland in the brain. It stimulates the production of FSH (follicle-stimulating hormone) and LH (luteinizing hormone), hormones of the pituitary gland in females. The function of FSH and LH is to stimulate follicular growth and ovulation. Furthermore, neurons of the hypothalamus release GnRH. It is also important in the stimulation of the pituitary gland to produce and release FSH and LH. The release of GnRH occurs in rhythmic pulses. Faster pulses cause to release FSH while slow pulses cause to release LH from the pituitary gland. The surge of LH triggers ovulation.

What is GnRH Agonist

GnRH agonist is a substance that has the same characteristics as GnRH, which is the gonadotropin-releasing hormone. Therefore, it acts like GnRH. Generally, GnRH agonist stimulates the pituitary gland more when it is first given to the patient. 

Figure 1: Leuprorelin, GnRH Agonist

However, after a while, the pituitary gland stops reacting to GnRH agonist when its concentration is constant. Hence, this can prevent the natural LH surge in in vitro fertilization treatments.

What is GnRH Antagonist

GnRH antagonist is a substance that blocks the action of GnRH. This blocks the receptors and ultimately decreases the function of the GnRH hormone. Thus, it blocks the stimulation of the pituitary gland to the production of FSH and LH.  

Figure 2: Cetrorelix, a GnRH Antagonist

Due to the lack of response to the GnRH by the pituitary gland, the GnRH antagonist prevents the natural LH surge. The prevention of the natural LH surge is important in egg collection in in vitro fertilization treatments.

Similarities Between GnRH Agonist and Antagonist

• GnRH agonist and antagonist are two types of protocols of in vitro fertilization treatments.
• Both GnRH agonist and antagonist can prevent the natural LH surge in in vitro fertilization treatments.
• Moreover, they are important in treating prostate cancer in males.
• Both block the stimulation of the pituitary gland by GnRH.

Difference Between GnRH Agonist and Antagonist

Definition

GnRH agonist refers to the substance that keeps the testicles and ovaries from making sex hormones by blocking other hormones that are needed to make them, while GnRH antagonist refers to the substance that blocks the pituitary gland from making hormones called follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

Method of Prevention of the Natural LH surge

GnRH agonist prevents the response of the pituitary gland to GnRH while GnRH antagonist blocks the pituitary gland from responding GnRH.

Better for

Moreover, GnRH agonist is better for women over 40 years with low ovarian reserve while GnRH antagonist is better for women under 30 years with high ovarian reserve.

Conclusion

In brief, GnRH agonist and antagonist are two protocols for stimulating ovaries in females. They are important in in vitro fertilization treatments. Generally, GnRH agonist prevents the response of the pituitary gland to GnRH by stimulating the pituitary gland. GnRH antagonist, however, blocks the stimulation of the pituitary gland by GnRH. GnRH agonist is better for women over 40 years with low ovarian reserve while GnRH antagonist is better for women under 30 years with high ovarian reserve. Therefore, the main difference between GnRH agonist and antagonist is the method of preventing natural LH surge in each protocol.

References:

1. “GnRH Agonist.” National Cancer Institute, 
2. “GnRH Antagonist.” National Cancer Institute, 

Image Courtesy:

1. “Leuprorelin” By Fvasconcellos – Own work (Public Domain) via Commons Wikimedia
2. “Cetrorelix” By Fvasconcellos- Own Work (Public Domain) via Commons Wikimedia