Blood collection approx. 30 minutes after rest (lying down); discontinue medication, if possible, approx. 1 week before; avoid the following foods from 3 days before collection: cocoa, coffee, tea, chocolate, nuts, citrus fruits, products containing vanilla. No nicotine consumption. Avoid psychological and physical stress. If possible, no use of: Nitroglycerin, alpha-methyldopa, MAO inhibitors, tricyclic antidepressants, L-dopa, no acute administration of calcium antagonists, theophylline, nasal drops, bronchodilators, appetite suppressants, cough drops.