Adrenergic agonists direct-acting

The direct-acting adrenomimetics described next are a-adrenergic agonists that are structurally very different from the drugs described above. 

FIGURE 7—42. Adrenergic combo 3 The actions of bupropion at dopamine neurons can be double-boosted by a direct-acting dopamine D2 and D3 agonist such as pramipexole. Norepinephrine is also single-boosted by bupropion. 

FIGURE 12-6. Postsynaptic alpha 2 adrenergic receptors are postulated to mediate cognitive effects of norepinephrine in the frontal cortex. Direct-acting alpha 2 agonists such as clonidine and guanfacine can be helpful in attention deficit disorder, perhaps because of actions at this site. 

Sites of action of direct-, indirect-and mixed-acting adrenergic agonists. 

Indirect-acting adrenergic agonists cause norepinephrine release from presynaptic terminals (see Figure 6.8). They potentiate the effects of norepinephrine produced endogenously, but these agents do not directly affect postsynaptic receptors. 

Neurotransmission across adrenergic junctions is mediated by norepinephrine (NE). Adrenergic effectors may act indirectly by influencing NE synthesis, monoamine oxidase (MAO) enzymes, the mobile NE pool, the NE transporter, prejunctional a-adrenoceptors, granule uptake, or release of NE, or they may ad directly on the postjunctional receptor as agonists or antagonists. 

Property Alpha2 Agonists Alphat Blockers Beta Blockers Diuretics ACE inhibitors and AT-1 Antagonists Calcium Channel Antagonists (CCAs) Adrenergic Neuron Blockers Direct-acting Vasodilators... 

The drug exhibits a direct-acting sympathomimetic agent having predominantly P-adrenergic activity plus a selective action on the P2-receptors (i.e., (P2-agonist). This is, therefore, recommended for the treatment of severe and acute forms of bronchospasm via IM, IV, sub-cutaneous routes. 

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