Adrenergic Blocking Agents or Antagonists:
Adrenergic blocking agents are drugs that selectively inhibit
specific receptor sites from sympathetic stimulation. There
are several modes of action which over all result in a depression
of adrenergic nerves. Blocking agents may interact with specific
alpha and beta receptors. The release of norepinephrine from
storage sites may be blocked. The storage of norepinephrine
may be inhibited. Drugs in this category are mostly antihypertensive
agents. Depression of adrenergic nerves results in a vasodilation
effect and relieves high blood pressure caused by a constriction
of the capillaries.
Antagonists which block alpha receptors sites include:
Prazosin and analogs - terazosin, doxazosin, trimazosin
These are used to treat hypertension by relaxing arterial
and venous smooth muscle, decreasing vascular resistance and
venous return, and decreasing blood pressure without a significant
increase in heart rate.
Antagonists which block beta receptors sites include:
Hypertension. Inderol or Propranolol and Nadolol is effective
in treating mild to moderate hypertension. In severe hypertension,
it is useful in preventing the reflex tachycardia that often
results from treatment with direct vasodilators.
Xylocholine bromide is an example of an agent which blocks
the release of norepinephrine from storage.