Autocrine effects hormones

However, hormones may act on the neighboring nonhormone-producing cells. This type of interaction between the hormone-producing cells and the target tissues is termed the paracrine effect. Some hormones are released into the intercellular compartment where they act on receptors found on the same cells secreting them this action is called the autocrine effect. Hormones can also act within the cell without being released, an effect known as intracrine effect (Figure 7.2). 

Hormones transfer signals by migrating from their site of synthesis to their site of action. They are usually transported in the blood. In this case, they are said to have an endocrine effect (1 example insulin). By contrast, tissue hormones, the target cells for which are in the immediate vicinity of the glandular cells that produce them, are said to have a paracrine effect (2 example gastrointestinal tract hormones). When signal substances also pass effects back to the cells that synthesize them, they are said to have an autocrine effect (3 example prostaglandins). Autocrine effects are often found in tumor cells (see p. 400), which stimulate their own proliferation in this way. 

Despite the diversity of hormones - endocrine, paracrine, autocrine or pheromones - they all influence intracellular events by intracellular signalling mechanisms, and the number of such mechanisms is remarkably small, hi this chapter, the signalling mechanisms, the effects and the functions of hormones are described, discussed and illustrated by reference to selected hormones. In addition, the principles underlying the mechanisms by which hormones affect the biochemistry in cells are discussed. 

The primary purpose of the endocrine system is to maintain homeostasis — that is, to maintain a relatively constant internal environment in the face of a constantly changing external environment. The endocrine system consists of hormones and the glands and tissues that produce the hormones. A hormone is a chemical substance released by certain cells to effect the function of other distant cells (endocrine function). Many compounds act as endocrine hormones as well as having paracrine and autocrine functions. Paracrine and autocrine describe actions on nearby cells and on other cells that produce the substance, respectively. There is considerable overlap between substances classified as hormones and other chemical messengers such as neurotransmitters and cytokines. Many substances function in more than one of these categories. For example, epinephrine and norepinephrine function as both neurotransmitters and adrenal medullary hormones. 

Disturbances of the metabolism of bone tissue that usually exhibit not very specific clinical signs and symptoms are induced by the effects of both systemic and local agents. The role of hormones has already been described and defined many times, but news and new views keep appearing all the time. Without doubt, practically all systemic agents, hormones, but also drugs act on the bone tissue only through mediators. Their effect is provided by local, paracrine, and autocrine substances effective on the level of the cell, and by cellular components and on molecular level. Some of the hormones and local agents will be mentioned below. 

Since the discovery of cAMP by Rail and Sutherland in 1958 (6) and cGMP by Ashman in 1963 (23), considerable work has been done to show that these nucleotides mediate the intracellular effects of many first messengers such as hormones, neurotransmitters, paracrine and autocrine factors. An important early discovery... 

IGF levels. IGF-I mediates the effects of growth hormone, which is mainly secreted by liver but is also produced in several other tissues. IGF-I can act in an autocrine and paracrine maimer to promote normal growth and malignant cellular proliferation. In vitro, low micromolar concentrations of lycopene have slowed cancer cell proliferation by suppressing response to IGF-I. " There has been considerable progress recently in the understanding of the hormonal causes of prostate cancer. Particularly, a number of studies have shown a positive association between IGF-I and the incidence of prostate cancer, whereas the association was reversed after radical prostatectomy and/or treatment with lycopene. ... 

The hormonal actions include Endocime denotes the action at a distance of hormones that may pCTvade the whole organism, searching out specific target tissues. Paracrine denotes the action of an extracellular messenger that takes effect only locally. When a substance affects the same cell from which it has been released, the activity is termed autocrine. 

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