Postglandular Endocrinopathies

Transport Link Disorders

The first barrier on the path of a hormone to tissues is the plasma protein system. The essence of the disorder lies in an excessive increase or decrease in the binding of the hormone to blood transport proteins.

The pathogenetic outcome is always a change in the level of the free (active) hormone, since the bound form serves merely as a reserve. The clinical picture depends directly on this fraction:

• Decrease in the free fraction leads to symptoms of hypofunction.
• Increase in the free fraction causes signs of hyperfunction.

Insulin, cortisol, and iodine-containing thyroid hormones (T3 and T4) are the most dependent on plasma carriers.

Counter-Hormonal Link of Pathogenesis

This stage is characterized by the inactivation of the hormone even before it manages to bind to the target cell receptor. Suppression mechanisms include:

1. Formation of antibodies to hormones. Immunoglobulins bind to any protein hormones (e.g., ACTH, growth hormone, insulin), sharply reducing their free fraction in body fluids.
2. Hyperactivity of degrading enzymes. For adrenaline, this is the excessive action of monoamine oxidase (MAO) and catechol-O-methyltransferase. For insulin, it is the excessive activity of insulinase, glutathione reductase, or glutathione transferase.
3. Change in molecular conformation. The structure of the hormone can be deformed under the influence of severe tissue acidosis, free radicals, toxins, or heavy metal salts.
4. Action of antagonist hormones. High concentrations of counter-regulatory hormones (cortisol, glucagon, catecholamines, GH, and thyroid hormones) physiologically prevent the realization of insulin effects.

Receptor (Reactive) Link

If the hormone has successfully reached the target cell, a failure may occur at the level of membrane receptors. This block includes several fundamentally different types of breakdowns:

• Quantitative changes: an inadequate decrease or increase in the number of receptors on the membrane.
• Impaired affinity: an imbalance between high-affinity and low-affinity receptors, which distorts the strength of the response.
• Anti-receptor antibodies: autoantibodies physically block receptors (commonly found in TSH and insulin receptors), preventing the hormone from binding.
• Blockade by non-hormonal ligands: foreign substances structurally similar to a hormone fragment occupy the receptor. This is characteristic of thyroid hormones, insulin, and insulin-like growth factors (IGF).
• Cross-effects: the hormone erroneously binds to "foreign" receptors. A classic example is the activation of prolactin receptors by an excess of growth hormone (GH), which clinically manifests as galactorrhea.

Metabolic (Post-Receptor) Link

The final stage of postglandular pathologies is associated with disorders of intracellular metabolism after successful contact of the hormone with the receptor, as well as with disorders of systemic hormone utilization.

• Decreased rate of hormone destruction. In severe hepatocyte pathology, the liver loses the ability to effectively inactivate insulin and steroids. As a result, active substances accumulate in the blood, forming the clinical picture of hyperinsulinism or hypercortisolism.
• Disorders of peripheral metabolism. Excessive peripheral deiodination of thyroxine (T4) leads to the excessive formation of a more active form, which manifests as a hyperthyroid state.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of Alteration in Cellular Receptor Affinity
• The Role of Tissue Acidosis in Protein Hormone Denaturation
• Autoimmune antibodies to receptors: blocking and stimulating effects
• Interaction of insulin with antagonistic hormones at the tissue level

Other topics in "Chapter 27. Typical Forms of Endocrine System Pathology"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.