Adrenergic neuronal-blocking drugs

Reserpine (Serpasil) depletes the store of catecholamine peripherally and centrally and attenuates, but does not abolish, sympathetic reflexes. Reserpine is useful in the management of mild to moderate hypertension. Its onset of action is very slow (2 to 3 weeks) when given orally. The side effects of reserpine are manifested by cholinergic hyperactivity such as diarrhea, bradycardia, and nasal stuffiness. Reserpine can activate a peptic ulcer (cholinergic dominance) and cause depression (depletes norepinephrine stores). Reserpine and propranolol have potential cardiac depressant activity and should not be used together. 

Although the Rauwolfia compounds were pioneers among tranquilizing agents (neuroleptics), they are hardly used for that purpose anymore for two main reasons first, they tend to cause serious depressions second, the phenothiazine derivatives and newer neuroleptics such as clozapine are 

Although the Rauwolfia alkaloids show a low degree of acute toxicity, their continued use may be accompanied by serious side effects. One of the most troublesome symptoms observed in the therapeutic use of Rauwolfia alkaloids is nasal congestion and stuffiness, which may be so severe as to necessitate discontinuing of therapy. Increased motility of the bowel, diarrhea, and increased gastric secretion resulting from its action on the autonomic nervous system are frequently observed. Skin eruptions, epistaxis, and peptic ulceration are rare complications. 

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The adrenergic neuron-blocking drugs are antihypertensive because they prevent the release of transmitters from peripheral postganglionic sympathetic nerves. The contraction of vascular smooth muscle due to sympathetic nerve stimulation is thereby reduced, and blood pressure decreases. Guanethidine is the prototypical member of this class. 

Amphetamines and other stimulatory anorectic agents, apart from fenfluramine, would be expected to impair the hypotensive effects of adrenergic neuron blocking drugs such as guanethidine. Not only do they release noradrenaline from stores in adrenergic neurons and block the reuptake of released noradrenaline into the neuron, but they also impair re-entry of the antihypertensive drugs (109). 

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