<p>Aminophylline is a combination of theophylline and ethylenediamine. Ethylenediamine is inactive; it increases the solubility of theophylline in water. Theophylline relaxes bronchial smooth muscle. Suggested mechanisms are an increase in intracellular cAMP through inhibition of phosphodiesterase; adenosine receptor antagonism, prostaglandin antagonism and effects on intracellular calcium.</p>