Drugs and reagents Atropine sulfate, verapamil hydrochloride, hexadecyltrimethylammonium bromide, activated charcoal, serotonin, hydrogen peroxide, o-dianisidine, sodium nitrite, Cremophor®, carboxymethylcellulose, and phenol red were obtained from Sigma-Aldrich (USA). Bethanechol chloride was purchased from Henrifarma (Brazil). Calcium chloride was obtained from Dinâmica Química (Brazil). Ondansetron and naloxone hydrochloride were acquired from União Química (Brazil).
