What are somatomedins and where are they synthesized?
Somatomedins (insulin-like growth factors, IGF) are bioactive substances. Their primary site of production is the liver.
Two main types are distinguished:
- Somatomedin C (IGF-1).
- Somatomedin A (IGF-2).
Growth hormone (GH), secreted by the anterior pituitary gland, stimulates the production of somatomedin in the liver.
Mechanism of action and physiological effects
Somatomedins are the main mediators of the anabolic action of growth hormone.
- Tissue growth: The complex of GH and IGF-1 stimulates bone tissue growth, which is especially important during adolescence. During the embryonic period, this function is mediated by IGF-2.
- Anabolism and proliferation: Somatomedins exert a direct stimulating effect on cell proliferation and amino acid anabolism.
- Effect on mesenchyme: Insulin-like growth factors stimulate the proliferation of cells of mesenchymal origin, participating in tissue growth and stroma formation.
How is production regulated (regulatory axis)?
The synthesis of somatomedins is regulated by the hypothalamic-pituitary system:
- The hypothalamus releases the releasing hormone somatoliberin (GHRH).
- Via the hypophyseal portal system, GHRH reaches the adenohypophysis and stimulates the production of growth hormone (GH).
- GH stimulates the production of IGF-1 in the liver.
Role in pathology and clinical significance
- Tumor growth: Stromal fibroblasts in lung cancer are capable of producing IGF-2. Via a paracrine mechanism, it acts on cancer cell receptors and stimulates their proliferation.
- Benign breast dysplasia: Elevated levels of IGF-1 are positively associated with the risk of developing breast cancer.
- Liver fibrosis: IGF-1 is among the growth factors involved in stimulating hepatic fibrogenesis. Fibrosis is associated with the replacement of dead hepatocytes with connective tissue and an imbalance between the synthesis and degradation of extracellular matrix components.
- Liver cirrhosis and sarcopenia: In patients with decompensated liver cirrhosis, hyperammonemia, and sarcopenia, combination therapy with ornithine leads to a decrease in IGF-1 levels. This is considered a potential mechanism for correcting sarcopenia; ornithine has a positive effect on muscle function, mass, and strength.
Class and exam questions
What is the difference between somatomedin C and A?
Somatomedin C is insulin-like growth factor 1 (IGF-1), which, together with GH, stimulates bone growth during adolescence. Somatomedin A is IGF-2, whose action predominantly mediates growth during the embryonic period.
What is the role of somatomedins in tumor growth?
Stromal cells, such as fibroblasts, can secrete somatomedins. In lung cancer, stromal fibroblasts produce IGF-2, which acts via a paracrine pathway on cancer cell receptors and stimulates their proliferation.
How are somatomedins related to the hypothalamus?
The hypothalamus releases a releasing hormone (GHRH), which stimulates the pituitary gland to secrete growth hormone (GH). GH, in turn, stimulates the liver to produce somatomedin (IGF-1).
What else to study on this topic
- Growth Hormone (GH)
- Hypothalamo-pituitary system
- Paracrine and autocrine regulation
- Diffuse endocrine system
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