Examples of Autocrine Regulation

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Many autocrine regulatory molecules are also known as cy-tokines, particularly if they regulate different cells of the immune system, and as growth factors if they promote growth and cell division in any organ. This distinction is somewhat blurred, however, because some cytokines may also function as growth factors. Cytokines produced by lymphocytes (the type of white blood cell involved in specific immunity—see chapter 15) are also known as lymphokines, and the specific molecules involved are called inter-leukins. The terminology can be confusing because new regulatory molecules, and new functions for previously named regulatory molecules, are being discovered at a rapid pace. As described in chapter 15, cytokines secreted by macrophages (phago-cytic cells found in connective tissues) and lymphocytes stimulate proliferation of specific cells involved in the immune response.

Neurotrophins, including nerve growth factor, guide regenerating peripheral neurons that have been injured (chapter 7). Nitric oxide, which can function as a neurotransmitter in memory processes (chapters 7 and 8) and in other functions, is also produced by the endothelium of blood vessels. In this context, it is a paracrine regulator because it diffuses to the smooth muscle layer of the blood vessel and promotes relaxation, leading to dilation of the blood vessel. In this action, nitric oxide functions

Table 11.9 Examples of Autocrine and Paracrine Regulators

Autocrine or Paracrine Regulator

Major Sites of Production

Major Actions

Insulin-like growth factors (somatomedins)

Many organs, particularly the liver and cartilages

Growth and cell division

Nitric oxide

Endothelium of blood vessels; neurons; macrophages

Dilation of blood vessels; neural messenger; antibacterial agent

Endothelins

Endothelium of blood vessels; other organs

Constriction of blood vessels; other effects

Platelet-derived growth factor

Platelets; macrophages; vascular smooth muscle cells

Cell division within blood vessels

Epidermal growth factors

Epidermal tissues

Cell division in wound healing

Neurotrophins

Schwann cells; neurons

Regeneration of peripheral nerves

Bradykinin

Endothelium of blood vessels

Dilation of blood vessels

Interleukins (cytokines)

Macrophages; lymphocytes

Regulation of immune system

Prostaglandins

Many tissues

Wide variety (see text)

TNFa (tumor necrosis factor alpha)

Macrophages; adipocytes

Wide variety

Endocrine Glands as the paracrine regulator previously known as endothelium-derived relaxation factor. Neural and paracrine regulation interact in this case, since autonomic axons that release acetylcholine in blood vessels cause dilation by stimulating the synthesis of nitric oxide in those vessels (see chapter 20, fig. 20.23).

The endothelium of blood vessels also produces other paracrine regulators. These include the endothelins (specifically endothelin-1 in humans), which directly promote vasoconstriction, and bradykinin, which promotes vasodilation. These regulatory molecules are thus very important in the control of blood flow and blood pressure. They are also involved in the development of atherosclerosis, the leading cause of heart disease and stroke (see chapter 13). In addition, endothelin-1 is produced by the epithelium of the airways and may be important in the embryological development and function of the respiratory system.

All autocrine regulators control gene expression in their target cells to some degree. This is very clearly the case with the various growth factors. These include platelet-derived growth factor, epidermal growth factor, and the insulin-like growth factors that stimulate cell division and proliferation of their target cells. Regulators in the last group interact with the endocrine system in a number of ways, as will be described in chapter 19.

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Responses

  • Luisa Siciliano
    Are lymphokines autocrine or paracrine regulators?
    8 years ago
  • ELIAS
    What is autocrine regulation?
    8 years ago
  • awet
    What are examples of autocrine regulation?
    8 years ago
  • massawa massawa
    What are the steps involved in growth factor physiology?
    6 years ago
  • ASMARA
    What is the function of Endothelin as a paracrine/autocrine factor?
    3 months ago
  • Sam King
    Is insulin paracrine or autocrine?
    26 days ago

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