Paracrine effects

P and Pg, exist in foUicular fluid. Control of inhibin secretion involves a feedback relationship in which circulating FSH stimulates inhibin secretion, which in turn reduces the secretion of FSH (8). Both the homo- and the heterodimers of the P-subunits of inhibin promote the secretion of FSH and thus have been termed activins. Activin is secreted by the ovary and the testes into the circulation. In addition, both inhibin and activin have intragonadal autocrine and paracrine effects that influence gonadal steroidogenesis (9). 

Knapp PE, Itkis OS, Zhang L, Spruce BA, BakaUdn G, Hauser KF (2001) Endogenous opioids and oligodendroglial function possible autocrine/paracrine effects on cell survival and development. Glia 35 156-165... 

Additionally, we could neither find any evidence that MSCs are able to differentiate into vascular endothelial cells nor did we find more vessels within the transplantation areas as compared to the control group. But, in contrast to normal myocardium the amount of vessels was twice as high in the injection areas. This might indicate that the injury (puncture) of the myocardium caused by the syringe needle alone can be an adequate stimulus for the induction of angiogenesis. Therefore, rather the paracrine effects of implanted MSCs than the incorporation of these cells into the vessel walls may be required for vascular growth in the adult (Kinnaird et al., 2004). 

They act as local messengers in tissues and they provide communication between one cell type and another within a single tissue or an organ (i.e. they have a paracrine effect). They are synthesised from the polyunsaturated fatty acids that contain 20 carbons (e.g. arachidonate, eicosapentaenoic acids). These fatty acids are generated from the hydrolysis of membrane phospholipids by the activity of a phospholipase which releases the fatty acids from position 2 of the phospholipids. Their roles are described in detail below. 

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. 

Insulin, which is formed in the B cells of the pancreas, has both endocrine and paracrine effects. As a hormone with endocrine effects, it regulates glucose and fat metabolism. Via a paracrine mechanism, it inhibits the synthesis and release of glucagon from the neighboring A cells. 

The hydrophilic hormones are derived from amino acids, or are peptides and proteins composed of amino acids. Hormones with endocrine effects are synthesized in glandular cells and stored there in vesicles until they are released. As they are easily soluble, they do not need carrier proteins for transport in the blood. They bind on the plasma membrane of the target cells to receptors that pass the hormonal signal on (signal transduction see p.384). Several hormones in this group have paracrine effects—i.e., they only act in the immediate vicinity of their site of synthesis (see p. 372). 

The eicosanoids are a group of signaling substances that arise from the C-20 fatty acid arachidonic add and therefore usually contain 20 C atoms (Greek eicosa = 20). As mediators, they influence a large number of physiological processes (see below). Eicosanoid metabolism is therefore an important drug target. As short-lived substances, eicosanoids only act in the vicinity of their site of synthesis (paracrine effect see p.372). 

Endocrine and paracrine effects of cytokines and secondary mediators lead to vasodilation and hypotension, hyperactivation of coagulation systems, endothelium damage, increase of leukocyte adhesion as a resnlt of reduced perfusion and hypoxia. 

Several other nonsteroidal substances such as corticotropin-releasing hormone, follistatin, and prostaglandins are produced by the ovary. These probably have paracrine effects within the ovary. 

Figure 4. Schematic representation of the Ca2+/CaM/CaMKK/CaMKIV/CREB/immediate early genes/IL pathway in T cells. Activation only takes place after the triple stimulation of the TCR, IL-1R and CD4/8 receptors. The end point effect of CaMKIV, which is die synthesis of interleukins and other growth factors, is common to T cells and thymocytes. Interleukins and other growth factors may have an autocrine or a paracrine effect. The different pathways included here have been addressed using Camk4-/- mouse models. Since die role of die CaMK cascade in hematopoietic stem cells and neutrophils is a little different, they are not included here...

In acute or chronic ischemia patients, angiogenic potential of transplanted cells is of the greatest importance. The patients with chronic nonviable scar and myocardial dysfunction are more likely to benefit from the cells that, either directly or indirectly (via paracrine effect) (47), improve the contractility of the treated myocardium (9). Autologous skeletal myoblasts have been successfully expanded in vitro and implanted in the myocardia of animals. Although they do not contract synchronously with the rest of the myocardium and do not integrate into it, they have been shown to improve contractility... 

IL-1/3 has a potentiating effect on insulin secretion, suggesting a priming effect on B-cell function and also a paracrine effect on A -I- B-cell function. IL-1/3 should be considered to be a physiological modulator of insulin and... 

Other secretory products of the nephron are not weU understood. For example, a significant proportion of normal urinary protein is formed by Tamm Horsfall glycoprotein (THG). This protein is secreted by the distal tubule and is thought to play a role in inhibiting kidney stone formation, but this has not been confirmed conclusively. The tubular epithelial cells also synthesize a vast range of growth factors and cytokines in response to a variety of stimuli that can have both autocrine and paracrine effects. All cells also secrete a range of cell adhesion molecules that are essential to cellular attachment to the tubular basement membrane. 

Natriuretic peptides (ANP, BNP, CNP) were first described by Genest and are now recognized to have several autocrine and paracrine effects within the myocardium and coronary circulation. Natriuretic peptide receptor A (NPR-A) and B (NPR- B) are widely expressed in the cardiovascular system. The natriuretic peptides produce cellular responses through the elevation of intracellular c-GMP concentration that in turn regulates... 

In the gut, SST influences the functions of adjacent cells—a paracrine effect—and also acts in an autocrine manner to inhibit its own pancreatic release. The 5 cell is the last islet cell to receive blood flow thus, SST likely regulates insulin and glucagons secretion by /3 and a cells only via the systemic circulation. 

Finally, glucagon stimulates insulin release from the (3 cells of the pancreas. Whether this is a paracrine effect or an endocrine effect has not been established. The pattern of blood flow in the pancreatic islet cells is believed to bathe the (3 cells... 

HT has been found to stimulate corticosteroid secretion in various models. In addition, 5-HT is present in adrenochromaffin cells, but also in mast cells localized at the adrenocortical level [98, 99]. Therefore, 5-HT released within the adrenal gland may have a paracrine effect on corticoid secretion. In- frog and human, the receptor involved in 5-HT induced cortisol secretion displays the pharmacological profile of a typical 5-HT4-R [98, 99]. In human volunteers the aldosterone-stimulating effects were observed after administration of 5-HT4-agonists [137]. 

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