Depending on the situation, these drugs can save lives, or threaten them.
by Randy Kidd, DVM, PhD
Corticosteroids are perhaps the most enigmatic of all the drugs in the western medicine man’s arsenal. It has been said by many practitioners that they are the most used and most abused of all our medicines. Corticosteroids are a necessary component of a healthy physiology and they can be life saving ... or they can cause multiple adverse side effects that can be devastating to a dog’s health and well-being. Since this class of biochemicals affects nearly all cells of the body, their beneficial effects can be widespread – and their adverse effects may be totally debilitating and long-lasting.
So who are these guys that can seemingly wear both white and black hats at the same time?
Corticosteroid drugs are less frequently overused than they once were, but the quick fix they provide in cases of allergy tempts many to abuse their use.
What they are
Naturally occurring corticosteroids are a class of steroid hormones that are produced in the cortex (thus the “cortico” prefix) of the adrenal gland. The adrenal medulla (inner part) manufactures epinephrine and norepinephrine, the hormones responsible for the “fight or flight” reaction, among other functions. Corticosteroids are made from the same steroidal chemical base that also produces the male and female sex hormones and the androgenic steroids made famous by athletes who want to enhance their muscle mass. However, the corticosteroids are slightly different from the androgenic and sex hormones in their chemical structure, and they are very different in the ways they affect the body.
Corticosteroids are further divided into two major classes of compounds: mineralocorticoids and glucocorticoids.
Mineralocorticoids are a vital component of the body’s hormonal balancing system, even though they make up only a small portion of the overall mix of the corticosteroids in the body. Mineralocorticoids function in the kidney (in the distal tubules) where they stimulate the exchange of sodium and potassium – increasing renal excretion of potassium and increasing resorption of sodium, which in turn helps maintain the body’s water balance by increasing resorption of water.
The principle steroid with mineralocorticoid activity is aldosterone. Cortisol, the major “natural” glucocorticoid in dogs (and other non-rodent species) has weak mineralocorticoid activity. But in the natural state, cortisol’s mineralocorticoid activity is of some importance because, in the healthy animal, there is so much more cortisol secreted than aldosterone.
The name glucocorticoid derives from early observations that these hormones were involved in glucose metabolism. The vast majority of glucocorticoid activity in most mammals is from cortisol, also known as hydrocortisone.
Since synthetic glucocorticoids are used extensively in veterinary therapy, this article will focus on them.
Activities of glucocorticoids
Glucocorticoids (especially cortisol, the predominant natural glucocorticoid) stimulate several processes that collectively serve to increase and maintain natural conversion of glucose. These effects include:
• Stimulation of gluconeogenesis, the synthesis of glucose from other sources such as amino acids (protein building blocks) and lipids (fats). Glucocorticoids stimulate the enzymes that enhance this process, especially in the liver.
• Mobilization of amino acids from tissues, generating a substrate for gluconeo-genesis.
• Inhibition of glucose uptake in muscle and fatty tissue, thus conserving glucose.
• Stimulation of fat breakdown, releasing fatty acids, which provides energy to various tissues and adds more substrate for gluconeogenesis.
Glucocorticoids have potent anti-inflammatory and immunosuppressive properties. These are the primary medicinal uses of the glucocorticoids and will be discussed more fully below.
Glucocorticoids also have multiple effects on fetal development, including their role in promoting maturation of the lung and production of the surfactant necessary for lung function immediately after birth.
Excessive glucocorticoid levels resulting from administration as a drug or hyperadrenocorticism (Cushing’s disease) have effects on many systems. Just a few of the examples include inhibition of bone formation, suppression of calcium absorption, and delayed wound healing. Note that these effects suggest that there probably are many physiologic roles for the glucocorticoids that we are not yet fully aware of. Also note that these effects can occur from drug administration, and most of them are ultimately detrimental to health and healing.