Orciprenaline is a moderately selective beta(2)-adrenergic agonist that stimulates receptors of the smooth muscle in the lungs, uterus, and vasculature supplying skeletal muscle, with minimal or no effect on alpha-adrenergic receptors. Intracellularly, the actions of orciprenaline are mediated by cAMP, the production of which is augmented by beta stimulation. The drug is believed to work by activating adenylate cyclase, the enzyme responsible for producing the cellular mediator cAMP.
Orciprenaline (also known as metaproterenol), a synthetic amine, is structurally and pharmacologically similar to isoproterenol. Orciprenaline is used exclusively as a bronchodilator. The pharmacologic effects of beta adrenergic agonist drugs, such as orciprenaline, are at least in part attributable to stimulation through beta adrenergic receptors of intracellular adenyl cyclase, the enzyme which catalyzes the conversion of adenosine triphosphate (ATP) to cyclic- 3', 5'- adenosine monophosphate (c-AMP). Increased c-AMP levels are associated with relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells.
Hepatic and gastric. The major metabolite, orciprenaline-3-0-sulfate, is produced in the gastrointestinal tract. Orciprenaline is not metabolized by catechol-0-methyltransferase nor have glucuronide conjugates been isolated to date.
Symptoms of overdose include angina, hypertension or hypotension, arrhythmias, nervousness, headache, tremor, dry mouth, palpitation, nausea, dizziness, fatigue, malaise and insomnia. LD50=42 mg/kg (orally in rat).