Receptor postreceptor actions

Cellsurface and intracellular receptors have different postreceptor actions. 

Divish MM, Sheftel G, Boyle A, et al Differential effect of lithium on fos protooncogene expression mediated by receptor and postreceptor activators of protein kinase C and cyclic adenosine monophosphate model for its antimanic action. J Neurosci Res 28 40-48, 1991... 

Sulphonylureas block the ATP-sensitive potassium channels on the P-islet cell plasma membrane. This results in the release of stored insulin in response to glucose. They do not increase insulin formation. Sulphonylureas appear to enhance insulin action on liver, muscle and adipose tissue by increasing insulin receptor number and by enhancing the postreceptor complex enzyme reactions mediated by insulin. The principal result is decreased hepatic... 

Although several chapters of this textbook detail a variety of endocrine disorders, a brief introduction is appropriate here. In general, endocrine diseases result from either a deficiency or an excess of a single hormone or several hormones, or from resistance to the action of hormones. Hormone deficiency can be congenital or acquired and hormone excess can be from endogenous overproduction (from within the body) or exogenous overmedication. Hormone resistance can occur at several levels, but can most simply be characterized as receptor mediated, postreceptor mediated, or at the level of the target tissue. The clinical manifestations will depend on the hormone system affected and the type of abnormality. 

The mechanism of action of insulin is complex and can be divided into three parts. The first part is the binding of insulin to its receptor on the cell membrane the second consists of postreceptor events and the third consists of biological responses. 

Cell surface receptors, which detect water-soluble hormones that do not enter the cell (peptides, proteins, glycoproteins, catecholamines). The mechanism of action of each of these receptor types is different because each is associated with different postreceptor events in the cell. 

Many hormones, such as the hormonal amines and all pep-tidic hormones, are unable to penetrate the lipid matrix of the cell membrane, and thus depend on the presence of receptor sites at the surface of target cells. As listed in Table 30-4, there are several types of cell membrane receptors for these hormones, each of which is coupled to a distinct set of intracellular postreceptor pathways. The surface receptors all initiate postreceptor events that involve the phosphorylation of one or more intracellular proteins, some of which are enzymes whose activities depend on the state of phosphorylation. In two of these cases, an intracellular second messenger is utilized to implement the hormonal action and involves G-protein-coupled receptors. One is coupled to the adenylate cyclase-cAMP system and the other is associated with the phosphatidylinositol-Ca + pathway (IP3 pathway). 

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