Functional and dispositional tolerance develops during continuous cocaine exposure

Abstract

Despite the fact that high doses of cocaine are abused chronically, relatively little is known regarding the development of tolerance and/or sensitization under these circumstances. Therefore, male Sprague-Dawley rats were infused continuously i.v. for 10 days, at a rate of 150 mg/kg/day (0.1 mg/kg/min) with cocaine hydrochloride. Body weight, food and water consumption, urine and fecal excretion, as well as blood pressure, heart rate and stereotypic behavior were monitored daily. Blood samples were also drawn daily so that plasma could be analyzed for cocaine and BEG by gas chromatography/mass spectrometry. Severe body weight loss on days 1 through 4 was followed by a gradual return to pre-drug levels. In addition, cocaine's effects on food and water consumption and urine and fecal excretion, which were maximal by day 2, were imperceptible by day 5. Complete tolerance developed rapidly to the remarkable rise in blood pressure noted on the first day. However, tolerance did not develop to the cocaine-induced increase in heart rate. A profound decrease in heart rate was noted in some animals which was interpreted to be cardiotoxicity since these animals subsequently died. On the other hand, sensitization or intensification of behavioral stereotypy occurred during the first 2 days followed by complete tolerance to this effect by day 5. No withdrawal phenomena were noted 24 h after cocaine was abruptly withdrawn. Plasma concentrations of cocaine rose rapidly during the first day and remained elevated at a constant level until day 5. Then, a sharp decline in plasma levels occurred at day 6 which remained depressed for the duration of the infusion.(ABSTRACT TRUNCATED AT 250 WORDS)