What is the Difference Between hCG and GnRH

The main difference between hCG and GnRH is that hCG stimulates the corpus luteum to produce progesterone that maintains the pregnancy, whereas GnRH produces follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by stimulating the pituitary gland in the brain. 

hCG and GnRH are two hormones produced by the human body. They function in the reproductive system. 

Key Areas Covered

1. What is hCG
      – Facts, Features, Behaviour
2. What is GnRH
     – Facts, Features, Behaviour
3. Similarities Between hCG and GnRH
     – Outline of Common Features
4. Difference Between hCG and GnRH
     – Comparison of Key Differences

Key Terms 

GnRH, HCG, Gonadotropin-Releasing Hormone, Human Chorionic Gonadotropin

What is hCG

Human chorionic gonadotropin, or hCG, is a hormone produced by the syncytiotrophoblastic cells of the placenta. HCG stimulates the corpus luteum to produce and secrete progesterone that maintains pregnancy. The pituitary gland, colon, and the liver also produce hCG. HCG is a glycoprotein hormone composed of two subunits called alpha and beta. Both the intact form and the free subunits of hCG occur in the serum and urine during pregnancy. The liver catabolizes hCG, but 20% of it is excreted by urine. In the kidney, the beta subunit of hCG is degraded into a core fragment measured by urine hCG tests.

Figure 1: HCG Test

Furthermore, there are two types of tests for hCG. They are the serum test and urine test. Serum tests for hCG are immunometric assays that use two antibodies to bind to the hCG molecule. A fixed antibody and a radiolabeled antibody are used to sandwich the immobilized hCG in the serum. Then, this assay washes away the excess serum components to test hCG. The labeled antibodies allow the quantitative measure of hCG. In comparison, urine tests detect hCG with more than 20 mIU/mL concentration. Early pregnancy contains hyperglycosylated hCG that is not detectable by urine hCG tests. 

What is GnRH

Gonadotropin-releasing hormone (GnRH) is a component of the hypothalamic-pituitary-gonadal axis. Therefore, it is vital for human reproduction. It is also one of the hypothalamic-releasing hormones, having a pivotal role in reproduction in humans and all vertebrates. There are 20 different types of GnRH, and GnRH I and GnRH II are the most widely distributed. Additionally, GnRH serves as a neuromodulator of sexual behavior. Both GnRH I and GnRH II are present in humans. But the main isoform is GnRH I, with the most physiologic importance.

Figure 2: Hypothalamic–Pituitary–Gonadal Axis

Moreover, as GnRH production occurs in the hypothalamus’s neurons, it causes the production and secretion of sex hormones by the gonads. Therefore, GnRH is important in regulating puberty onset, sexual development, and ovulatory cycles in females. 

Similarities Between hCG and GnRH

• HCG and GnRH are two types of hormones produced by the human body.
• Both have a function in the reproductive system.

Difference Between hCG and GnRH

Definition

HCG, or human chorionic gonadotropin, refers to a hormone secreted by the placenta during pregnancy that stimulates the production of progesterone by the ovaries. In contrast, GnRH, or gonadotropin-releasing hormone, refers to a hormone secreted by the neurons of the hypothalamus that stimulates the pituitary gland to release gonadotropins.

Production

HCG is produced by syncytiotrophoblastic cells of the placenta, while the neurons of the hypothalamus produce GnRH.  

Occurrence

HCG is produced only in females during pregnancy, while GnRH is produced in both male and female bodies.

Function

Moreover, HCG stimulates the corpus luteum to produce progesterone to maintain pregnancy, while GnRH stimulates the pituitary gland to produce and secrete LH and FS.

Conclusion

In brief, hCG and GnRH are two types of hormones produced by the human body. They function in the reproductive system of the body. Syncytiotrophoblastic cells of the placenta produce hCG. Moreover, hCG is only produced in females during pregnancy. Additionally, hCG stimulates the corpus luteum to produce progesterone that maintains pregnancy. In comparison, GnRH is the hormone that stimulates the pituitary gland to produce and secrete FSH and LH. However, it occurs in both male and female bodies. Therefore, the main difference between hCG and GnRH is their function.   

References:

1. Betz D, Fane K. Human Chorionic Gonadotropin. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.
2. Casteel CO, Singh G. Physiology, Gonadotropin-Releasing Hormone. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.

Image Courtesy:

1. “Positive Pregnancy Test Result” By Melo20179 – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “Hypothalamic–pituitary–gonadal axis” By Artoria2e5 – Own Work (CC-BY 3.0) via Commons Wikimedia