Chorionic Gonadotropin (HCG)
Chorionic Gonadotropin (HCG) is a gonad-stimulating polypeptide hormone obtained from the urine of pregnant women. It is widely used in veterinary theriogenology across multiple species. **Key Clinical Uses:** * **Cattle:** Treatment of nymphomania due to cystic ovaries. * **Dogs & Cats:** HCG challenge testing to diagnose retained testicular tissue (cryptorchidism) or functional ovarian tissue (ovarian remnant syndrome). * **Horses:** Induction of ovulation and management of persistent follicles. * **Exotics:** Management of estrus in ferrets, cystic ovaries in guinea pigs, and empirical treatment for feather plucking in birds. > **Clinical Pearl:** Because HCG is a large, foreign human protein, repeated administration in veterinary patients can lead to the formation of neutralizing antibodies, which may progressively diminish its clinical efficacy over time.
Mecanismo: HCG is a glycoprotein that primarily mimics the action of **luteinizing hormone (LH)**, with minor **follicle-stimulating hormone (FSH)**-like activity. * **In Males:** Binds to LH receptors on testicular interstitial (**Leydig**) cells → stimulates differentiation and **androgen (testosterone)** production → promotes testicular descent and spermatogenesis. * **In Females:** Binds to LH receptors on the ovary → stimulates the **corpus luteum** to produce **progesterone** → triggers ovulation of mature follicles. In bitches, it also induces estrogen secretion.
Dosificación por especie
- HCG Challenge test (Male cats or females with suspected sexual differentiation disorder) · 250 micrograms · IM · once · Take sample for resting testosterone level. Administer HCG and take a 4 hour post sample.
- HCG Challenge test (Queens to diagnose functional ovarian tissue) · 50-100 Units · IM · once · Give during apparent estrous episode. Measure progesterone level in 5-7 days. >1 ng/mL indicates functional tissue.
- Infertility, reduced libido, testis descent in male cats · 50-100 Units · IM/SC · repeated if necessary
- Infertility in queens due to confirmed ovulation failure · 100-500 Units · IM · once
- To induce ovulation in anestrus queens · 250 micrograms · IM · once daily for 2 days · 2 days · Give FSH-P 2 mg IM daily until estrus is observed. Give HCG on first and second day of estrus.
- After artificial insemination · 50-75 Units · IM · immediately after insemination; repeat in 24 hours · 24 hours
- Estrus management · 100 Units · IM · repeat in 1 week as necessary · Most effective 14 days after onset of estrus.
- Treatment of ovarian cysts · 10,000 Units deep IM or 2500-5000 Units IV. Alternatively, 500-2500 Units injected directly into the follicle. · IM/IV/Intrafollicular · once · May repeat in 14 days if animal's behavior or physical exam indicates a need for retreatment.
Vías de administración
Contraindicaciones
- Androgen-dependent neoplasias (e.g., prostatic carcinoma)
- Precocious puberty
- Known hypersensitivity to HCG
- Pregnancy (FDA Category X in humans, unless specifically indicated for reproductive management)
Efectos adversos
- Hypersensitivity reactions / Anaphylaxis
- Pain at the injection site
- Antibody production leading to diminished efficacy (with repeated use)
- Abortion in mares if given prior to the 35th day of pregnancy
- Gynecomastia, headache, depression, irritability, and edema (reported in humans)
Monitoreo
- Testosterone levels (for HCG challenge test in males)
- Progesterone levels (for HCG challenge test in females)
- Resolution of clinical signs (e.g., cessation of estrus behavior, resolution of cystic ovaries)
- Signs of hypersensitivity or anaphylaxis post-injection
Sobredosis
No overdosage cases have been reported with HCG in veterinary medicine.
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