Distribution and Retention of Nicotine and Its Metabolite, Cotinine, in the Rat as a Function of Time

Nicotine is oxidized to its major metabolite, cotinine, which has a long biological half-life (19-24 h). The plasma concentration of cotinine has been used as an index of tobacco smoke exposure. Cotinine possibly increases the turnover rate of platelet-activating factor (PAF) because it is a potent activator of PAF hydrolase, and it may play a significant role in tobacco-induced arterial thrombosis. Therefore, we studied the distribution and retention of nicotine as it was metabolized to cotinine in the rat. Nicotine (1 mg/kg, 5 microCi/kg) was administered into the femoral vein of male Sprague-Dawley rats under nembutal anesthesia. At different times (5-60 min) after nicotine administration, nicotine and its metabolite, cotinine, were determined by HPLC in plasma, liver, kidney, heart and brain. Within 5-10 min after administration, nicotine concentrations reached peak values in plasma (2,160 pmol/ml) and the organs analyzed. The plasma level of nicotine decreased by 50% within 20 min (half-time) after its intravenous administration. The half-time of nicotine in the brain was about 50 min. The half-times of nicotine for the other organs were about 20-25 min. The major metabolite, cotinine, accumulated in plasma, and by about 30 min the concentrations of nicotine and cotinine in plasma were about equal (890-1,000 pmol/ml). While cotinine accumulated in plasma, nicotine was eliminated by the kidney. While the nicotine concentrations decreased with time in all organs, cotinine concentrations remained constant. These observations indicate that nicotine is renally eliminated or metabolized to cotinine while cotinine exhibits a long retention time and accumulates in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)