e. Central Nervous System (CNS) Excitatory Actions. Adrenergic stimulation
results in respiratory stimulation, an increase in wakefulness, and in a reduction of
7-5. ADRENERGIC (SYMPATHOHIMETIC) DRUGS
Sympathomimetic drugs are agents which when administered will mimic (produce
the same effects) normal adrenergic (sympathetic) stimulation. This normal adrenergic
stimulation refers to the effects produced by epinephrine on the body. Two agents
produce the adrenergic effects: epinephrine and norepinephrine. Epinephrine is the
original model of the sympathomimetic agent. It has both Alpha and Beta activity.
Figure 7-2 shows the chemical structure of epinephrine.
Figure 7-2. Chemical structure of epinephrine.
7-6. SPECIFIC ADRENERGIC (SYMPATHOMIMETIC) AGENTS
(a) Blood pressure. The blood pressure in the skin and mucosa is
increased via vasopressor action of peripheral vessels.
(b) Vascular effects. Epinephrine constricts the blood vessels of
mucosa and the skin (alpha1 effect). Physiological doses (0.5-1.0 milligram)
administered subcutaneously) causes dilatation of vessels in skeletal muscle tissue.
This effect decreases peripheral resistance and overcomes the vasoconstriction of
peripheral vessels so that blood pressure is not greatly affected (predominantly beta
effect). Large doses of epinephrine increase blood pressure: Alpha-receptor
stimulation in the skeletal muscles overcome beta stimulation and the blood pressure is
(c) Cardiac effects. Epinephrine acts upon Beta1 receptors to greatly
increase heart rate and output.
(d) Smooth muscle. The effect upon smooth muscle by epinephrine
varies according to the organ stimulated and the type of adrenergic receptor effected in