The term steroid relates to the main structural frame of this series of compounds (Figure 36–1).
The main steroid structure is shown, along with two examples of adrenocortical hormones.
The steroid compounds produced by the adrenal cortex are called adrenocorticosteroids, and they can be divided into two main groups depending on their relative metabolic (glucocorticoid) versus electrolyte-regulating (mineralocorticoid) activity. Of course, each compound has effects on both metabolism and electrolyte balance, but one effect is usually more potent than the other. Almost every cell in the body will respond to these compounds.
|Glucocorticoid ||Equal Potency ||Mineralocorticoid |
Compare this list of drugs with the list in your textbook or class handouts and make any necessary changes. I have found lists of more than 20 glucocorticoids, so the table above is quite abbreviated.
HYDROCORTISONE (CORTISOL) is the main glucocorticoid produced by the adrenal glands.
Notice that hydrocortisone and its close relative, cortisol, are the only two drugs that have equal metabolic (glucocorticoid) and electrolyte balance (mineralocorticoid) actions. Remember this. Next, notice that there are many more drugs listed on the left (glucocorticoid) than on the right (mineralocorticoid). Therefore, if you have to guess about the activity of a drug, guess glucocorticoid. Better yet, just learn the mineralocorticoid drug on the right (it starts with “f,” but it’s not the only one that does).
Aldosterone is the main mineralocorticoid produced by the adrenal glands.
It is useful at this point to review some of the anatomy and physiology of the adrenal gland, with a particular emphasis on the adrenal cortex (Figure 36–2). Remember that the adrenal medulla produces epinephrine and norepinephrine. Within the adrenal cortex, there are three layers. The zona glomerulosa (outer layer) produces the compounds that control electrolyte balance, such as aldosterone. The zona fasciculata (middle layer) produces the compounds that regulate metabolism, such as hydrocortisone. The zona reticularis (inner layer) produces the sex hormones (see Chapter 37). The pituitary hormone adrenocorticotropic hormone (ACTH) controls the secretion of, primarily, the inner two layers. The production of mineralocorticoids is mainly controlled by the renin-angiotensin system.
This figure reminds you of the layers of the adrenal cortex and the hormones that each layer produces.
The pharmacological actions of steroids are an extension of their physiological effects.
This should seem self-evident, but sometimes it is forgotten.
All of the steroids (including the sex steroids) bind to intracellular receptors ...