hCG

Overview

Human chorionic gonadotropin (hCG) is a placental glycoprotein hormone best known for its role in early pregnancy, where it supports the corpus luteum and progesterone production. hCG is structurally and functionally similar to luteinizing hormone (LH) and activates the same receptor. This LH-like activity makes hCG a valuable tool in reproductive endocrinology research, fertility treatment, and hypogonadism studies.

Clinically, hCG is used to trigger ovulation in assisted reproduction protocols, to stimulate testicular testosterone production in men with secondary hypogonadism, and in certain pediatric endocrine conditions such as undescended testes. Recombinant forms (choriogonadotropin alfa) are available alongside urinary-derived preparations from pooled pregnancy urine.

hCG is frequently discussed in peptide research contexts alongside GnRH analogs including Gonadorelin, Buserelin, Triptorelin, and Leuprolide, because all these compounds operate within the hypothalamic-pituitary-gonadal axis that hCG influences downstream.

Structure / Chemistry

hCG is a heterodimeric glycoprotein with α and β subunits. Its α subunit is shared with LH, FSH, and TSH. The β subunit is largely unique to hCG and is the basis of specific immunoassays. Extensive glycosylation — including N- and O-linked glycans — contributes to its long half-life relative to LH.

Mechanism of Action

hCG binds LH/CG receptors on ovarian theca cells, granulosa cells, and testicular Leydig cells. Activation stimulates cAMP production and steroidogenesis, leading to testosterone production in men and progesterone/estradiol production in women. The LH-like action enables hCG to "mimic" an LH surge for ovulation induction and to sustain testicular steroidogenesis when endogenous LH is suppressed.

Research Summary

Pharmacokinetics

hCG has a long half-life for a glycoprotein hormone — approximately 24-36 hours for the initial phase after intramuscular or subcutaneous injection. Clinical protocols use dosing schedules ranging from a single ovulation-trigger injection to intermittent smaller injections for chronic testicular support. Specific doses are clinical parameters, not guidance.

Common Discussion Topics

• Distinction from testosterone replacement in male hypogonadism research.
• Preservation of testicular volume and spermatogenesis.
• Use in IVF and ART protocols.
• Relationship to LH and cross-reactivity with its receptor.
• Unapproved off-label weight-loss claims and associated regulatory concerns.

Related Compounds

• Gonadorelin
• GnRH
• Buserelin
• Triptorelin
• Leuprolide