Anabolic-Androgenic Steroids for Animals

Anabolic-androgenic steroids (AASs) are known primarily for their ability to promote muscle growth and development. They may be administered in rare instances in which severe muscle atrophy has developed secondary to another disease process. They are also used for their androgenic properties to treat hormone-responsive urinary incontinence in neutered male dogs (1).

AASs are synthetic derivatives of testosterone with variable anabolic activities (eg, building skeletal muscle) and androgenic activities (eg, promoting and maintaining male secondary sex characteristics).

Testosterone or its derivatives diffuse through cell membranes of target organs. Intracellularly, AASs might bind to their cognate receptor (the androgen receptor), or they might undergo biotransformation. Biotransformation might generate a more potent androgen, a less potent metabolite, or an estrogen.

Binding of an AAS to the androgen receptor enables migration of the hormone-receptor complex into the nucleus, where it binds androgen response elements in the genome and stimulates the production of specific messenger RNA. Messenger RNAs are primarily responsible for the physiological activities of AASs; however, nongenomic effects also appear to be important.

AASs stimulate and maintain a positive nitrogen balance by decreasing the renal elimination of nitrogen, sodium, potassium, chloride, and calcium. The production of myosin, sarcoplasm, and myofibrillar protein is enhanced, provided that the caloric and protein intake is adequate. In all cases, improved well-being depends on treatment of the underlying disease.

AASs tend to be well tolerated when used to treat urinary incontinence in neutered male dogs. However, although AASs can promote appetite and weight gain, their adverse effects often outweigh these benefits.

AASs have a variety of undesirable effects in animals:

• androgenic effects, such as increased libido in males and abnormal sexual behavior in females

• behavioral changes, including increased aggression

• adverse reproductive effects, including priapism, oligospermia, anestrus, testicular atrophy, and clitoral hypertrophy

• edema formation through sodium and water retention

In humans, AAS administration is associated with gynecomastia, nausea, headache, anxiety, myocardial infarction, icterus, and delayed growth due to early epiphyseal closure.

AASs may be used to treat debilitated animals; however, they are often misused to gain a competitive advantage in performance animals. Administration of AASs in performance horses is prohibited by most equine sports organizations, and these drugs can be detected for> 2 months after being administered.

Approved veterinary formulations of AASs are no longer marketed in North America. Currently, any anabolic product for veterinary use (aside from bovine ear implants) can be obtained only from a compounding pharmacy.