The endocrine system governs essential physiological processes through a network of hormones that regulate growth, metabolism, reproduction, and stress responses. Disorders of endocrine function are common and often require lifelong pharmacological management. Unit 4 explores the mechanisms, therapeutic applications, and clinical significance of drugs acting on key hormonal pathways. This article presents a concise, news-style overview designed for pharmacy and healthcare students.
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Basic Concepts in Endocrine Pharmacology
Hormonal Signaling and Regulation
Endocrine pharmacology focuses on hormones—chemical messengers secreted into the bloodstream—and the drugs that mimic, enhance, or inhibit their actions. Hormones act on specific receptors and maintain homeostasis through negative feedback mechanisms. Disorders arise when hormone levels become deficient, excessive, or when tissues become resistant.
Pharmacological Approaches
Endocrine therapy may involve hormone replacement (as in hypothyroidism), suppression of overactive glands (as in hyperthyroidism), or use of antagonists to block excessive hormonal signaling. Synthetic analogues offer improved potency and longer duration of action, while inhibitors help manage tumors or glandular hyperactivity.
Anterior Pituitary Hormones: Analogues and Their Inhibitors
Physiological Role of Anterior Pituitary Hormones
The anterior pituitary secretes several tropic hormones, including growth hormone (GH), prolactin, thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and gonadotropins (FSH, LH). These hormones regulate downstream endocrine glands and are essential for growth, metabolism, and reproduction.
Therapeutic Analogues
Synthetic GH (somatropin) treats growth hormone deficiency and wasting disorders, while gonadotropin analogues support fertility management. TSH analogues assist in diagnosing thyroid disorders.
Prolactin antagonists such as bromocriptine and cabergoline inhibit excessive prolactin secretion seen in prolactinomas, restoring normal reproductive function.
Pituitary Hormone Inhibitors
Agents like octreotide, a somatostatin analogue, inhibit GH release and are used to treat acromegaly. These drugs offer targeted suppression of hormonal excess and help alleviate complications associated with pituitary tumors.
Thyroid Hormones: Analogues and Their Inhibitors
Thyroid Function and Its Pharmacological Control
Thyroid hormones—T3 and T4—regulate metabolic rate, growth, and energy balance. Hypothyroidism leads to fatigue, weight gain, and cognitive impairment, while hyperthyroidism causes excessive metabolism, tachycardia, and irritability.
Analogues for Thyroid Hormone Deficiency
Levothyroxine, a synthetic T4 analogue, remains the drug of choice for hypothyroidism due to its stable pharmacokinetics and predictable conversion to T3. Proper dosing restores metabolic balance and prevents complications such as myxedema.
Drugs Inhibiting Thyroid Activity
Antithyroid medications, including propylthiouracil (PTU) and methimazole, block hormone synthesis and treat hyperthyroidism. Beta blockers are often added to control symptoms like tremors and palpitations. In severe cases, radioactive iodine or surgery may be required for long-term control.
Hormones Regulating Plasma Calcium: Parathormone, Calcitonin, and Vitamin D
Parathormone (PTH)
PTH increases calcium levels by stimulating bone resorption, enhancing renal calcium reabsorption, and activating vitamin D. Synthetic PTH analogues such as teriparatide are used to treat osteoporosis by promoting bone formation, paradoxically taking advantage of intermittent PTH signaling.
Calcitonin
Calcitonin, produced by the thyroid gland, lowers blood calcium by inhibiting osteoclast activity. It is used clinically for conditions like Paget’s disease, hypercalcemia, and certain osteoporosis cases. Its role in therapy is more limited compared to vitamin D analogues.
Vitamin D and Its Analogues
Vitamin D enhances intestinal calcium absorption and supports bone mineralization. Deficiency leads to rickets or osteomalacia. Therapeutic forms such as calcitriol treat chronic kidney disease–associated hypocalcemia, while nutritional vitamin D (cholecalciferol) supports long-term bone health.
Insulin, Oral Hypoglycemic Agents, and Glucagon
Insulin: Cornerstone of Diabetes Management
Insulin is essential for glucose uptake and metabolism. In type 1 diabetes—and advanced type 2 diabetes—insulin therapy restores glycemic control. Various formulations exist, including rapid-acting, intermediate-acting, and long-acting analogues designed to mimic physiological secretion patterns.
Oral Hypoglycemic Agents
Oral drugs for type 2 diabetes include sulfonylureas, which stimulate insulin release; biguanides like metformin, which improve insulin sensitivity; and SGLT2 inhibitors, which enhance glucose excretion through urine.
Newer agents such as GLP-1 agonists help reduce appetite and improve metabolic control, highlighting the expanding range of therapeutic innovations.
Glucagon
Glucagon raises blood glucose by promoting glycogen breakdown and gluconeogenesis. It is used in emergency treatment of severe hypoglycemia and during certain diagnostic procedures. Its ability to counterbalance insulin highlights the delicate balance maintained within endocrine homeostasis.
ACTH and Corticosteroids: Managing Stress and Inflammation
Role of ACTH
Adrenocorticotropic hormone stimulates the adrenal cortex to release cortisol. Synthetic ACTH analogues assist in diagnosing adrenal insufficiency and may support treatment in specific endocrine deficiencies.
Corticosteroids
Corticosteroids—including prednisolone, dexamethasone, and hydrocortisone—possess powerful anti-inflammatory and immunosuppressive properties. They treat conditions such as asthma, rheumatoid arthritis, autoimmune diseases, and adrenal insufficiency.
Long-term use requires caution due to side effects like osteoporosis, hyperglycemia, hypertension, and increased infection risk.