The patient is a 56-year-old woman with a 10-year history of mild hypertension (stabilized with enalapril and hydrochlorothiazide/amiloride) and a 2-year history of bipolar disorder (stabilized with lithium). Three weeks ago, she was diagnosed with fibromyalgia and started working with a physical therapist to develop an exercise program to assist in pain relief. Weekly, she meets with the therapist to review and modify the exercise program and assess her fibromyalgia symptoms. Recent measurements of blood pressure and heart rate were 130/82 mm Hg and 80 beats per minute, respectively. Last week, the patient was diagnosed with functional hypothyroidism likely resulting from the lithium treatment. She was prescribed levothyroxine and started taking the drug that day. Today, she told the physical therapist that over the past week she has experienced increased muscle weakness and shortness of breath that has made her unable to comfortably exercise on the stationary bicycle. The therapist measured her blood pressure at 142/86 mm Hg and heart rate at 96 beats per minute and irregular.
The endocrine system integrates major organ systems with each other and with the nervous system. The endogenous ligands that the endocrine system uses to perform this integrative task are called hormones. Hormones released from specialized cells circulate in the blood and regulate physiologic processes in one or more target organs. In many endocrine systems, several hormones act in series to regulate organ function. The release of one hormone in the series regulates the release of the next hormone. This provides multiple levels of regulation and integration as well as the opportunity for negative feedback, in which the last hormone in the series can reduce the production of earlier hormones in the series and thereby regulate its own production. Feedback regulation is also critical to understand the pharmacologic treatments that affect endocrine systems.
While some endocrine drugs directly influence the practice of the physical therapist, other drugs influence the patients’ responses to the rehabilitation process. Many postmenopausal women use estrogens and progestins for hormone replacement therapy (HRT). A small percentage will experience cardiovascular events or develop breast or endometrial cancers, which are recognized adverse effects of HRT. Subsequently, these women may need rehabilitation. Androgen supplementation in older males with hypogonadism or decreased testosterone levels improves bone mineral density and exercise tolerance. However, abuse of androgens by athletes promotes abnormal distribution of cholesterol in serum lipoproteins and increases the risk of atherosclerosis and cardiovascular morbidities. Physical therapists should be aware of these adverse effects and counsel athletes appropriately. Drugs that affect endocrine function may also directly influence the response of the patient to rehabilitation. For example, excessive supplementation with levothyroxine can cause cardiovascular and respiratory dysfunction that may not appear at rest, but can be precipitated with exercise.
This chapter covers drugs that regulate three related endocrine systems. These are: ...