Methylxanthines such as caffeine and theophylline exert all of the following Pharmacologic effects EXCEPT:
- A- Cardiac stimulation
- B- Peripheral vasoconstriction
- C- Relaxation of smooth muscle
- D- Diuresis
- E- CNS stimulation.
The exception to the pharmacologic effects of methylxanthines like caffeine and theophylline is: C. Relaxation of smooth muscle.
Here's why:
- Cardiac stimulation:
Methylxanthines increase heart rate and contractility by blocking adenosine receptors, leading to increased intracellular cyclic AMP (cAMP).
- Peripheral vasoconstriction:
They cause narrowing of blood vessels in the periphery, initially increasing blood pressure.
- Diuresis:
They increase urine output by inhibiting tubular reabsorption of sodium and water in the kidneys.
- CNS stimulation:
They block adenosine receptors in the brain, leading to increased alertness, wakefulness, and cognitive function.
- Relaxation of smooth muscle:
While methylxanthines can have some bronchodilatory effects by relaxing smooth muscle in the airways, they generally have the opposite effect on most other smooth muscle tissues, causing contraction.
Therefore, methylxanthines typically cause smooth muscle contraction, not relaxation. This is an important distinction to remember when considering their overall pharmacological effects.
