Indirect antagonism

Functional antagonism is a term used to represent the interaction of two agonists that act independently of each other but happen to cause opposite effects. Thus, indirectly, each tends to cancel out or reduce the effect of the other. A classic example is acetylcholine and epinephrine. These agonists have opposite effects on several body functions. Acetylcholine slows the heart, and epinephrine accelerates it. Acetylcholine stimulates intestinal movement, and epinephrine inhibits it. Acetylcholine constricts the pupil, and epinephrine dilates it and so on. 

There is good evidence that the facilitation of peripheral sympathetic nervous system transmission prcxluced by the amphetamines also occurs in the CNS.The possibihty that amphetamines act indirectly (i.e., by releasing monoamines) at monoaminergic synapses in the brain and spinal cord seems likely. However, amphetamine has effects beyond displacement of catecholamines these include inhibition of neuronal amine uptake, direct stimulation of dopamine and serotonin receptors, antagonism of catecholamine action at certain subtypes of adrenoceptors, and inhibition of monoamine oxidase. Interestingly, none of these actions explains the therapeutic benefit of the amphetamines in hyperkinetic children. 

Other available antidepressants have unique mechanisms of action that may have an impact on norepinephrine, serotonin, or dopamine indirectly through other mechanisms. For example, mirtazapine s direct antagonism of presynaptic a2-adrenergic receptors results in an indirect increase in central noradrenergic and serotonergic activity. 

Nicotinic Receptor Interactions. After producing an initial brief augmentation of the twitch response and fasciculatlons 2-PAM and TMB-4 at 1-20 mg/kg abolished the indirectly stimulated twitch response of skeletal muscle, but did not alter the response to direct stimulation. Neostigmine and edrophonium antagonized, whereas... 

Warifteine Inhibited indirectly stimulated twitch response of tibialis anterior and gastrocnemius muscles in anesthetized cats and isolated rat diaphragm effect antagonized by neostigmine methosulfate anesthetic 536... 

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