A glycoprotein hormone that mimics LH to stimulate testosterone production and preserve testicular volume.
A 237-amino-acid glycoprotein with alpha and beta subunits. The beta subunit binds the LH/hCG receptor on testicular Leydig cells with high affinity, stimulating cAMP production and the steroidogenic cascade (cholesterol → pregnenolone → testosterone). Also maintains Sertoli cell function and intratesticular testosterone levels.
HCG is widely used in testosterone replacement therapy (TRT) protocols to maintain testicular volume and intratesticular testosterone, which is essential for spermatogenesis. Exogenous testosterone alone suppresses LH and causes testicular atrophy.
In women, hCG triggers ovulation in fertility protocols (IUI, IVF) and is used as a trigger shot when follicles are mature. The pregnancy test detects hCG as the earliest hormonal signal of implantation.