Adrenaline and noradrenaline receptors

S-adenosyl-L-methionine -I- noradrenaline- S-adenosyl-L-homocysteine -I- adrenaline (7.1) 

The four corticosteroids, corticosterone, cortisol, cortisone and aldosterone, are structurally and biosynthetically related (see Fig. 10.1, p. 161). The principal ones are corticosterone and aldosterone. The former is present in the highest concentrations in plasma. The ratio corticosteronealdosterone in plasma is approximately 14 1 in domestic fowl, and 63 1 in the duck (Harvey, Scanes Brown, 1986). The enzymes together with P-450 cytochrome, which catalyse the biosynthesis of corticosteroids, are present on the endoplasmic reticulum. 

Adrenaline and noradrenaline interact with receptors present on the plasmalemma of target tissues and cdk. The receptors are referred to as a- and /5-receptors, and they are classified according to the potency of various agonists (stimulating) and antagonists (inhibiting) that elicit responses. More recently, the two main classes have been subdivided, largely on the basis of mammalian studies, into at least four classes (Table 7.4). Both / i- and / 2-receptors are linked to the effector adenylyl cyclase, via the transducer Gg-protein and their stimulation thus increases intracellular levels of cAMP. 

The i-receptors activate phospholipase C (1-phosphatidylinositol-4,5-bisphosphate, EC.3.1.4.11), through an as yet unknown transducer. Phospholipase C acts on phosphoinositides to catalyse the formation of diacylglycerol and inositol triphosphate. 

Diacylglycerol, in turn, activates protein kinase C, which catalyses the phosphorylation of a number of intracellular proteins  

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