Adrenergic receptor effector mechanisms

Very commonly, a target tissue will be stimulated by the S3mipathetic system and inhibited by the paras5mipathet-ic system, or vice versa. Examples are found in table 7.1. Among the paras mipathetic responses listed there, we find stimulation of smooth muscle in the bronchi, and relaxation of smooth muscle in the arterioles both are mediated by muscarinic acetylcholine receptors (cf. Figure 7.6). Here, we have an example of diverse effector mechanisms triggered from similar receptors. Similarly, the adrenergic receptors can operate different intracellular switches as needed. These different effector mechanisms are covered in some more detail in the chapter on G protein-coupled receptors. 

In Figure 8.1a, the effector was shown to be activated by the G-protein. An example of this is the stimulation of adenylate cyclase, which occurs upon stimulation e.g. of (3-adrenergic receptors and is mediated by the stimulatory G protein (G Figure 8.2a). Other major effector mechanisms include ... 

Table 8.1 lists several transmitters, and their cognate receptor and signalling mechanisms. All three of the effector mechanisms listed in table 8.1 for the adrenergic receptors also occur among the metabotropic glutamate receptors. 

Figure 1. General mechanism of action of polypeptide hormones and -adrenergic agonists. The hormone receptor is in the external portion of the plasma membrane and the effector [usually adenylate cyclase (A.C.)] is in the inner portion in contact with the cell cytoplasm.

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