Hypothalamus/pituitary pharmacology

Hypothalamus and Pituitary Pharmacology Notes

Introduction

  • Instructor: Dr. Julia Macedo Rosa

  • Focus: Endocrine Pharmacology; includes mechanisms of action, clinical uses, side effects, and drug interactions.

Learning Outcomes

  • Understand the mechanisms of action of drugs.

  • Recognize key clinical indications for these drugs.

  • Identify common side effects.

  • Understand important drug interactions and off-label uses.

  • Differentiate between similar agents (e.g., vasopressin vs. desmopressin).

Topics Covered

  • Posterior and Anterior Pituitary Revision

  • Growth Hormone Related Compounds

  • Growth Hormone Antagonists

  • Prolactin and Dopamine Receptor Agonists

  • Oxytocin, Ergometrine, Carboprost

  • Vasopressin, Desmopressin

Anatomy of the Hypothalamus and Pituitary Gland

  • The control of metabolism, growth, and reproduction is mediated by the neural and endocrine systems located in the hypothalamus and pituitary gland.

The Hypothalamic-Pituitary Endocrine System

  • Hormones released from the anterior pituitary stimulate the production of hormones by peripheral endocrine glands (e.g., liver) or other tissues.

  • Prolactin and hormones from the posterior pituitary (vasopressin and oxytocin) act directly on target tissues.

Anterior Pituitary Hormones

  • List of Hormones:

    • Growth Hormone (GH)

    • Prolactin (PRL)

    • Melanocyte Stimulating Hormone (MSH)

    • Adrenocorticotropic Hormone (ACTH)

    • Thyroid-Stimulating Hormone (TSH)

    • Luteinizing Hormone (LH)

    • Follicle-Stimulating Hormone (FSH)

Posterior Pituitary Hormones

  • Hormones:

    • Antidiuretic Hormone (ADH)

    • Oxytocin

Pharmacologic Applications of Hypothalamic and Pituitary Hormones

  1. Replacement Therapy for Hormone Deficiency States

  2. Antagonists for Excess Production of Pituitary Hormones

  3. Diagnostic Tools for Identifying Endocrine Abnormalities

Growth Hormone Related Compounds

Somatropin (GH)

  • Mechanism of Action:

    • Agonist at growth hormone receptors, promoting protein deposition, enhancing fat utilization, and decreasing carbohydrate utilization.

    • Stimulates growth of cartilage and bone via Insulin-like Growth Factor 1 (IGF-I).

    • Associated with overall growth and metabolism in childhood, adolescence, and postnatal life.

Side Effects of Somatropin

  • Injection site reactions (redness, swelling, itching, pain).

  • Edema (swelling in hands, feet, ankles, and face).

  • Musculoskeletal pain (arthralgia, myalgia, stiffness).

Drug Interactions

  • Corticosteroids: Can block growth-promoting effects of somatropin.

  • Thyroid Hormone Replacement: Somatropin may reduce the activation of thyroid hormones.

Contraindications

  • Active malignancy (risk of stimulating tumor recurrence).

  • Potential off-label uses in bodybuilding and performance enhancement, which may lead to severe health risks (e.g., organ enlargement, increased cancer risk).

Growth Hormone Antagonists

Somatostatin Analogues

  • Somatostatin (Growth Hormone-Inhibiting Hormone or GHIH):

    • Produced primarily in the hypothalamus, pancreas, and gastrointestinal tract.

    • Opposes the effects of somatropin.

Octreotide

  • Mechanism of Action:

    • Binds to somatostatin receptors (SSTR2, SSTR5), inhibiting hormone secretion and enzyme production.

Clinical Uses of Octreotide

  • Primarily used for the treatment of tumors and to manage symptoms of endocrine disorders.

Side Effects of Octreotide

  • Abdominal pain, cramping, constipation, bradycardia, hypothyroidism, and low blood pressure.

Drug Interactions with Octreotide

  • Drugs affecting heart rhythm, insulin, and oral hypoglycemics may interact with octreotide's effects.

Contraindications

  • Thyroid disorders, bradycardia, heart disease, diabetes.

Prolactin and Dopamine Receptor Agonists

  • Dopamine inhibits prolactin production in a negative feedback loop.

Cabergoline

  • Mechanism of Action: Inhibits prolactin production, used for hyperprolactinemia and off-label for conditions like Parkinson’s disease.

Side Effects of Cabergoline

  • Nausea, vomiting, dizziness, lightheadedness, fatigue, and weakness.

Drug Interactions with Cabergoline

  • Interacts with other dopamine agonists, blood pressure medications, and alcohol.

Posterior Pituitary Hormones

Oxytocin and Its Application

  • Acts as a neurotransmitter and hormone affecting uterine contractions during childbirth and lactation.

Syntocinon (Synthetic Oxytocin)

  • Mechanism of Action: Increases calcium levels in uterine muscles, leading to contractions. Used for labor induction and management of postpartum hemorrhage.

  • Side Effects: Hypotension, excessive uterine contractions, drowsiness, fetal bradycardia, and low Apgar scores.

Ergometrine

  • Produces prolonged contractions, used to stop postpartum hemorrhages.

  • Mechanism of Action: Acts as an agonist at serotonin and alpha-adrenergic receptors, having some activity on dopamine receptors.

Carboprost (15-methyl-PGF₂α)

  • Primary Use: Manages postpartum hemorrhage refractory to other treatments.

Vasopressin Related Compounds

  • Vasopressin: Released in response to plasma tonicity and blood pressure fluctuations. Exhibits antidiuretic and vasopressor properties.

  • Desmopressin: A synthetic analog with a primarily antidiuretic effect and longer duration of action than vasopressin.

Clinical Uses of Vasopressin and Desmopressin

  • Vasodilatory shock, cardiac arrest, diabetes insipidus (less common now for vasopressin), nocturnal enuresis, hemophilia A.

Side Effects of Vasopressin and Desmopressin

  • Hypertension, abdominal cramps, water intoxication, headaches, flushing.

References

  • Rang, H., Dale, M., Ritter, J., Flower, R., and Henderson, G. (10th Edition). Rang and Dale’s Pharmacology. Elsevier Churchill Livingstone Publisher.

  • Katzung, B.G. (16th Edition). Basic & Clinical Pharmacology.