Blood gas concentrations and pH in rats treated with acute injections of heroin

The effects of different dosages of heroin on respiration were determined by evaluating arterial blood pO₂, pCO₂, and pH in naive animals. Female Sprague-Dawley rats were treated (s.c.) acutely with either 0.5, 1.0, 5.0, or 10.0 mg/kg heroin; appropriate saline controls were utilized. Blood was sampled from the tail artery before injection and 15, 30, 60, 120, 180, and 240 min postinjection. All animals exposed to heroin exhibited a respiratory depression that involved hypoxemia, hypercapnia and/or acidosis. In all heroin-treated groups, pO₂ values were significantly reduced by 15 min postinjection and maximal changes in pO₂, pCO₂, and pH were reached 30 min after heroin administration. Both the magnitude and length of time of heroin's effect on respiration were dose-dependent. This study demonstrated that acute heroin administration is associated with respiratory depression, with the extent of alterations in pO₂, pCO₂, and pH related to drug dosage.