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DRUGS AFFECTING THE ENDOCRINE SYSTEM
The Endocrine System
The endocrine system secretes physiologically active substances into the bloodstream. (In contrast, exocrine glands deliver their product through tubes/ducts.)
For example, the pancreas is both an endocrine gland (insulin) and an exocrine gland (pancreatic enzymes via the pancreatic duct).
The endocrine system controls most of the long-term processes like fluid balance, metabolism, sexual development, mood, growth, and the secretion of hormones.
Included in the endocrine system are the following glandular organs:
- Gonads (Ovaries & Testes)
- (Pineal gland--not discussed)
THYROID GLAND: produces T4 (thyroxine) and T3 (triiodothyronine), which control metabolism.
Thyroid T4 converts the majority of the metabolically active T3 outside of the thyroid gland.
- weight loss,
- heat intolerance,
- increased frequency of bowel movements, and
- shortness of breath.
Hypothyroidism causes a slowing of metabolic processes:
- slow movement and slow speech,
- cold intolerance,
- weight gain,
- delayed relaxation of deep tendon reflexes, and
- Thyroid hormone: T4 as thyroxine (levothyroxine) and other preparations to supplement thyroid function in hypothyroidism.
- PTU (propylthiouracil): lowers T3 by blocking its conversion from T4--for hyperthyroidism.
The PARATHYROID GLAND: produces parathyroid hormone and calcitriol.
- Parathyroid hormone controls calcium concentration in partnership with the kidneys;
- Calcitriol inhibits parathyroid hormone secretion.
Hyperparathyroidism causes hypercalcemia:
- bone disease,
- mental changes.
Hypoparathyroidism causes hypocalcemia (→ tetany, fatigue, depression, or hyperirritability.
- Calcium,Vitamin D: for hypoparathyroidism, since it leads to hypocalcemia.
(Surgery to remove parathyroid tissue is the only treatment for hyperparathyroidism.)
Hypothalamus & Pituitary
The hypothalamic-pituitary axis is a complex negative and positive feedback system that orchestrates the actions of the reproductive organs, growth factor, the thyroid/parathyroid system. The hypothalamic-pituitary axis directly to affect the functions of the thyroid gland, the adrenal gland, and the gonads, as well as influencing growth, milk production, and water balance.
The hypothalamus is the coordinating center of the endocrine system.
- It consolidates signals from the brain and provokes autonomic function by reacting to environmental cues such as light and temperature, as well as from peripheral endocrine feedback.
- In turn, the hypothalamus delivers precise signals to the pituitary gland via GNRH, ACTH, etc., which causes the pituitary to release hormones that influence most endocrine systems in the body.
The pituitary gland partners with the hypothalamus in the hypothalamic-pituitary axis.
DRUGS ASSOCIATED WITH THE PITUITARY
- Bromocryptine: dopamine agonist for hyperfunction of the anterior pituitary leading to hyperprolactinemia and galactorrhea (lactation).
- Growth hormone: indicated with known deficiencies affecting stature.
PANCREAS: produces insulin and glucagon (endocrine); digestive enzymes (exocrine).
Most EXOCRINE problems of the pancreas involve pancreatic tissue responsible for its exocrine function for digestion (pancreatitis, etc.), whereas ENDOCRINE problems impact glucose utilization and metabolism via endocrine islet cells and the resulting insulin-glucose dysfunction.
The combination of insulin and glucagon maintains the proper level of sugar in the blood. Failure of insulin production causes diabetes.
DRUGS USED IN PANCREATIC DYSFUNCTION
- Antidiabetic drugs (Insulin used in the treatment of Type 1 Diabetes Mellitus) help in glucose efficient import into your heart, muscle, and fat. Insulin must be administered subcutaneously because it needs to be absorbed into the bloodstream and because it is destroyed by the GI tract.
- Insulin: comes in short-acting and long-acting versions and must be given parenterally since the GI tract destroys it.
- Hypoglycemic drugs (not for hypoglycemia, but for hyperglycemia): they lower or maintain blood sugar levels when diet fails.
Oral hypoglycemic drugs either stimulate insulin release from the pancreas or increases the amount and effectiveness of already-circulating insulin. Oral hypoglycemic drugs are used to manage type 2 diabetes.
- Metformin: can be given orally; it
- decreases glucose production in the liver;
- decreases intestinal absorption of glucose, and
- increases insulin sensitivity (increases glucose uptake and utilization).
- Glucagon: promotes hepatic glycogenolysis (breakdown of glycogen into glucose) and gluconeogenesis (synthesis of glucose from non-sugar sources like fats and proteins), causing a rise in blood glucose levels. The American Diabetes Association (ADA) recommends that glucagon is prescribed for all diabetic patients at increased risk of clinically significant hypoglycemia.
ADRENAL GLAND: synthesizes epinephrine and norepinephrine, cortisol, androgens and estrogens, aldosterone.
ADRENAL HYPERPLASIA (congenital) causes
- impaired synthesis of cortisol and aldosterone and
- increased synthesis of androgenic precursors (virilization).
ADRENAL INSUFFICIENCY ("Addison's disease") causes
- malabsorption and other
- GI disorders.
There is a "triad" of symptoms seen:
- hypoparathyroidism and
- adrenal failure.
ADRENAL INSUFFICIENCY DRUGS
- Dexamethasone: for new cases;
- IV Hydrocortisone: for previously diagnosed adrenal insufficiency, which requires cortisol level testing (ACTH);
- dexamethasone or prednisone can be added for chronic disease.
ADRENAL CRISIS: a life-threatening emergency that requires immediate treatment. In the less dramatic adrenal insufficiency, the goal of therapy is the treatment of hypotension and reversal of electrolyte abnormalities and of cortisol deficiency.
OVARIES, TESTES: Reproductive glands (testes, ovaries).
- Produce hormones and function as part of a broader axis extending from the hypothalamic-pituitary axis in feedback loops. Hormonal supplementation (estrogen or testosterone) is used when needed for documented deficiencies in a risk vs. benefit approach.
DRUGS AFFECTING THE GONADS
- Hormone replacement: estrogens, progestins.
- Contraceptives: combination formulations of daily estrogen/progestin; progestin-only "mini-pill," or progestin subdermal implants.
- Gonadotropin-releasing hormone (GnRH) agonists: for treatment of endometriosis, which induces a menopausal state after spiking ovarian stimulation into exhaustion (leuprolide as Lupron)
- Selective Estrogen Receptor Modulators (SERMs): competitive for estrogen binding at receptors sites--useful in treating estrogen-sensitive breast tumors.
- Ovulation inducers: (clomiphene "Clomid") can cause a hyper-reaction that results in large ovarian cysts at risk for torsion with an acute abdomen.
In The Field Endocrine Emergencies
In the field your most frequent ENDOCRINE life-threatening emergencies will be almost always diabetic in nature, followed--distantly--in frequency by thyroid storm, adrenal crisis, and embolism.
- Diabetic emergencies--hyperglycemia and ketoacidosis, or insulin shock.
Depending on the diagnosis, administration of insulin or glucose can be life-saving. Of any of the emergencies related to the endocrine system, diabetic emergencies will be almost all of them.
CAVEAT: Be aware that many diabetics are using a combination of long-acting and short-acting insulin preparations, so that treating a short-acting repercussion may not end the need for intervention, with more hypoglycemia surprises to come!
- Thyroid "storm." Thyroid storm is a rare, life-threatening condition with severe or exaggerated clinical manifestations of thyrotoxicosis. It can develop from untreated hyperthyroidism but can also be precipitated by thyroid or nonthyroidal surgery, trauma, infection, an acute iodine load, or delivery.
S&S of Thyroid Storm:
- stupor, or coma, and
- gastrointestinal symptoms (nausea, vomiting, abdominal pain).
Thyroid storm is an ICU-severity event, requiring rapid transport so that steroids and iodine solutions can be added to the standard hyperthyroid drugs.
- Adrenal crisis, causing hyponatremia and vasoconstriction, leading to
- nausea and vomiting,
- abdominal pain,
- confusion, and
Treatment includes reversing hypotension and electrolyte abnormalities and cortisol and ADH deficiencies.
- Pulmonary Embolus from oral contraceptives or hormone replacement, requiring oxygen and rapid transport for anticoagulant therapy.
All of the above require support, maintenance of ABC (airway, breathing, circulation), IV access, and rapid transport.