Zeranol

Zeranol is a synthetic, non-steroidal compound classified as an anabolic agent and a potent estrogen mimic (a synthetic estrogen or phytoestrogen-derived compound).

Other Name: Its most well-known brand name is Ralgro (used in veterinary medicine). Chemically, it is also known as α-zearalanol or P-1496. It is a metabolite of the naturally occurring mycoestrogen zearalenone.

Primary Use: Zeranol is primarily used in the U.S. beef industry as an implantable growth promoter for cattle (weaned beef calves, growing beef cattle, feedlot steers, and heifers) to increase the rate of weight gain and improve feed efficiency. Its use for this purpose is banned in the European Union and some other regions due to human health concerns related to its estrogenic activity.

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Side Effects and Benefits (Primarily in the Context of Animal Use and Potential Human Exposure)

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Dosage and Frequency

In Commercial Cattle (Ralgro):

• Dosage: A typical single dose is 36 mg (three 12 mg pellets).

• Frequency: Administered as an implant, usually once per animal for a period (implants are estimated to be effective for around 90 days).

For Human Use:

• Zeranol is not approved or recommended for human use as a drug or supplement.

• The World Health Organization (WHO) has set an Acceptable Daily Intake (ADI) for humans from food residues at 0 to 0.5μg/kg body weight per day.

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Half-Life and Detection Time

• Half-life (in Humans/Monkeys): The blood elimination half-life of total radioactivity (zeranol and its metabolites) in humans is approximately 22 hours, and in monkeys, it is about 18 hours.

• Detection Time (in Cattle Urine): Zeranol concentrations in cattle urine following a 36 mg implant reached a mean maximum around 22 days after implantation and declined to near the limit of detection around 69 days after implantation. Note: Detection time in humans would depend heavily on the dose, route of administration, and analytical method.

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Hormonal Effects and Anabolic Androgenic Ratio

Zeranol's primary and most significant hormonal activity is estrogenic.

• Steroidogenic Effect: Zeranol is a non-steroidal estrogen-mimic. It does not produce steroid hormones itself, but its strong estrogenic activity interferes with the endocrine system.

• Progestogenic Effect: Zeranol is not primarily a progestogen. However, some sources note that the related compound, zearalenone (from which zeranol is derived), and other hormones like melengestrol acetate (MGA) which are used as growth promoters, can interact with progesterone hormone receptors. Zeranol itself is primarily estrogenic.

• Prolactin Effect: Studies on the related compound zearalenone (ZEA) in animals (e.g., gilts) have shown that ZEA contamination in feed can lead to increased serum prolactin levels. Given that zeranol is an estrogenic metabolite of ZEA, it may share this effect, as estrogenic compounds can influence prolactin secretion.

• Anabolic Androgenic Ratio: Zeranol is classified as an anabolic agent in the context of increasing weight gain in livestock. However, this anabolic effect is primarily achieved through its estrogenic activity (which can promote pituitary growth hormone release and protein synthesis), not through androgenic activity.

  • It mimics estradiol (an estrogen) and has little to no significant affinity for the androgen receptor.

  • Therefore, the Anabolic:Androgenic ratio is not typically calculated or is considered high/infinite (because it is highly anabolic through an estrogenic mechanism but essentially non-androgenic) for this substance, unlike traditional anabolic-androgenic steroids (AAS).

  • 0:100 (Androgenic:Estrogenic) or X:0 (Anabolic:Androgenic, where X is high due to estrogenic activity) is a conceptual way to view its profile, highlighting its lack of androgenic activity. It is an estrogen, not an androgen.