Both cocaine and amphetamine increase systolic and diastolic blood pressure. In humans, a dose of 10 mg of D-amphetamine administered intravenously produces an increase in blood pressure that is equal to that produced with a dose of 32 mg of intravenous cocaine (Figure 4.3). In addition to increasing blood pressure, cocaine and amphetamines also stimulate the heart rate, but amphetamines may cause less of an effect than one would expect based on other physiological measures because of a reflexive slowing of heart rate. These drugs also produce bronchial dilation, pupillary dilation, and decreases in glandular secretions, all of which are effects observed after activation of the sympathetic nervous system.
The mechanism of action for the autonomic effects of indirect sympathomimetics such as amphetamines and cocaine has long been known. Both drugs indirectly release norepinephrine and epinephrine by either blocking reuptake (cocaine) or stimulating release (amphetamines). Conversely, chemical or physical destruction of noradrenergic (norepinephrine) fibers or pharmacological treatment with drugs that decrease the levels of catecholamines (e.g., norepinephrine and dopamine) abolishes the autonomic effects of cocaine and amphetamine. The exact mechanism by which psychostimulants directly affect various neurochemical and neurocircuitry systems to produce their psychostimulant effects is discussed in greater detail below.