The study of hormones and their synthetic analogues remains fundamental in understanding human physiology, reproduction, and metabolic control. Alongside endocrine pharmacology, bioassay techniques form the backbone of experimental pharmacology, allowing precise measurement of biological responses to drugs. Unit 5 integrates both domains, offering students a complete understanding of hormonal therapy and the scientific principles behind drug potency testing.
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Androgens and Anabolic Steroids: Hormones That Shape Male Physiology
Role and Therapeutic Use of Androgens
Androgens—primarily testosterone—are responsible for male sexual development, spermatogenesis, and maintenance of muscle mass. Pharmacologically, testosterone and its analogues are used to treat androgen deficiency, delayed puberty, and certain catabolic states.
Anabolic Steroids
Anabolic steroids are synthetic derivatives designed to enhance protein synthesis and muscle growth. Therapeutically, they help manage wasting disorders, severe anemia, and recovery after extensive burns.
However, non-medical misuse—especially in sports—poses significant risks, including liver damage, cardiovascular complications, infertility, and psychological dependence. Proper medical supervision is essential when prescribing these agents.
Estrogens, Progesterone, and Oral Contraceptives: Regulating Female Reproductive Health
Estrogens
Estrogens influence female sexual development, menstrual regulation, and bone density. Synthetic forms such as ethinylestradiol and conjugated estrogens are used in hormone replacement therapy (HRT), treatment of menopausal symptoms, and prevention of osteoporosis.
Progesterone
Progesterone prepares the uterus for pregnancy and maintains gestation. Pharmacological progesterone and progestins help treat menstrual disorders, dysfunctional uterine bleeding, and endometriosis. They also play a central role in oral contraceptive formulations.
Oral Contraceptives
Combined oral contraceptives contain estrogen–progestin combinations that suppress ovulation, alter cervical mucus, and prevent implantation. They are widely used for family planning and management of acne, polycystic ovarian syndrome (PCOS), and dysmenorrhea.
Modern low-dose formulations emphasize safety while preserving contraceptive efficiency, though risks such as thromboembolism require careful assessment.
Drugs Acting on the Uterus: Managing Reproductive and Obstetric Conditions
Uterine Stimulants (Oxytocics)
Drugs such as oxytocin, ergometrine, and prostanglandin analogues stimulate uterine contraction. They are essential in inducing labor, controlling postpartum hemorrhage, and facilitating medical termination of pregnancy.
Uterine Relaxants (Tocolytics)
Tocolytic drugs—including beta-2 agonists, nifedipine, and magnesium sulfate—are used to suppress premature labor. Their goal is to delay delivery long enough to allow fetal lung maturation or safe patient transfer.
These agents must be administered with caution, as maternal cardiovascular side effects may occur.
Bioassay: Measuring Drug Potency Through Biological Responses
Principles and Applications of Bioassay
Foundational Concepts
Bioassay is a scientific method used to determine the potency and concentration of drugs by measuring their effects on living tissues or organisms. Unlike chemical assays, bioassays assess actual biological activity, making them crucial for substances whose effects cannot be measured chemically, such as hormones and toxins.
Clinical and Research Applications
Bioassays ensure consistency in drug manufacturing, evaluate new therapeutic agents, and support regulatory approvals. They play a key role in pharmacological research, especially when studying receptor interactions, dose–response relationships, and efficacy comparisons between drug batches.
Types of Bioassay: From Classical Methods to Modern Approaches
Qualitative Bioassays
These methods confirm the presence or absence of biological activity in a sample. They are often used in early screening stages of drug development.
Quantitative Bioassays
Quantitative methods measure the potency of a drug relative to a standard preparation. Key techniques include:
Graded response assays, which measure gradual changes in tissue response
Quantal assays, based on all-or-none responses in animal populations
LD50 and ED50 determinations, which help assess toxicity and therapeutic indices
These assays allow precise comparison of biological activity and ensure standardization of pharmaceutical preparations.
Bioassay of Insulin, Oxytocin, Vasopressin, ACTH, d-Tubocurarine, Digitalis, Histamine, and Serotonin (5-HT)
Insulin
Insulin bioassays traditionally use blood glucose reduction in rabbits or rodents to determine potency. Modern assays may measure insulin receptor activation or downstream signaling pathways.
Oxytocin
Oxytocin potency is assessed using isolated uterine preparations where contraction strength correlates with drug concentration. This assay ensures consistency in obstetric formulations.
Vasopressin
Bioassay of vasopressin utilizes isolated rat colon or kidney preparations, measuring its antidiuretic and vasoconstrictor responses.
ACTH
ACTH potency is evaluated by monitoring adrenal cortex stimulation, typically via cortisol secretion levels in test animals.
d-Tubocurarine
d-Tubocurarine, a neuromuscular blocker, is assessed by measuring muscle paralysis in experimental animals, helping determine accurate dosing for anesthesia.
Digitalis
Digitalis bioassay uses cardiac muscle tissue—often frog hearts—to observe changes in contractility. Its narrow therapeutic index makes precise potency measurement essential.
Histamine and Serotonin (5-HT)
Bioassays for these amines measure their effects on smooth muscle contraction, vascular permeability, or gastric acid secretion. Both substances remain central to research in inflammation, allergy, and neurotransmission.