RESUMO
1. Nicotine and its main derivative. cotinine, are reported to have distinct central activities in mammals. In this study, the cotinine receptor was separated by biochemical procedures including radio receptor, affinity-chromatography, SDS-PAGE, and N-terminal sequencing assays. 2. Consistently, the results showed that distinctive cotinine receptors exist in different tissues of mammals. In rat brain, the affinity chromatography and [125I]cotinine receptor essays were used to isolate a 40-kDa protein (p40) with higher affinity for cotinine than alpha-bungarotoxin and nicotine. The N-terminus amino acid sequences of the p40 and its internal tryptic peptides showed no identity to recently described protein sequences, with the exception of homology to the human p205 synovial fluid protein. 3. These results, in agreement with other behavioral studies, are the first molecular evidence for distinctive nicotine and cotinine receptors in mammals.
Assuntos
Encéfalo/metabolismo , Cotinina/farmacocinética , Receptores Nicotínicos/química , Receptores Nicotínicos/metabolismo , Sequência de Aminoácidos , Animais , Sítios de Ligação , Membrana Celular/metabolismo , Cromatografia de Afinidade , Humanos , Radioisótopos do Iodo , Cinética , Masculino , Dados de Sequência Molecular , Peso Molecular , Fragmentos de Peptídeos/química , Ensaio Radioligante , Ratos , Ratos Sprague-Dawley , Receptores Nicotínicos/isolamento & purificação , Homologia de Sequência de Aminoácidos , Líquido Sinovial/químicaRESUMO
The toxicity of nicotine, cotinine and their mixtures was studied in Mus musculus mice as well their effects on growth after repetitive administration to young mice. The affinity constants of the two alkaloids for the nicotinic acetylcholine receptors (nAChRs) of Torpedo and rat brain membranes were determined. The administration of these alkaloids produced distinct symptoms of intoxication. Nicotine was 100-fold more toxic than cotinine and 10-fold more rapid than cotinine at producing respiratory arrest. The affinity of nicotine for both subtypes of nAChRs was > 100-fold higher than that of cotinine. Repetitive administrations of nicotine caused weight loss, whereas that of cotinine caused weight gain (P < 0.01). The administration of the two alkaloids as mixtures to mice caused significantly (P < 0.01) higher mortality than theoretically expected. Furthermore, hexamethonium pretreatment reduced by 2-fold (P < 0.01) the toxicity of nicotine but enhanced by 1.6-fold (P < 0.01) that of cotinine and was without effects on toxicity of mixtures. We suggest that nAChRs are not the main targets of cotinine toxicity.
Assuntos
Cotinina/toxicidade , Receptores Nicotínicos/efeitos dos fármacos , Animais , Peso Corporal/efeitos dos fármacos , Interações Medicamentosas , Feminino , Compostos de Hexametônio/farmacologia , Dose Letal Mediana , Masculino , Camundongos , Nicotina/toxicidade , Agonistas Nicotínicos/toxicidade , Tamanho do Órgão/efeitos dos fármacos , Ratos , Doenças Respiratórias/induzido quimicamente , Fatores de TempoRESUMO
1. Nicotine and its main metabolite, cotinine, were reported to have distinct behavioral activities in mammals. 2. In this study, cotinine was synthesized without detectable nicotine contamination to compare the ability of nicotine and cotinine to pass the blood-brain barrier (BBB) in rats. 3. The alkaloids were extracted from plasma and brain tissues by methanol, identified by thin-layer chromatography, and quantified by high-pressure liquid chromatography and radioimmunoassays. 4. Consistently, the three methods showed that the passage of cotinine was time, route of administration, and dose dependent and that nicotine was more efficient than cotinine to pass the BBB. 5. The results suggest that these alkaloids may have central activities that probably result from their actions at distinct molecular levels.
