Search

Turnover rates of cerebral proteins were examined in control adult rats and in those subjected to prolonged in vivo treatment with "low" (0.02 mg/ml) or "high" (0.04 mg/ml) doses of nicotine (added to drinking water), using [14C]bicarbonate as the label. It was found that the turnover of proteins in various subcellular fractions consisted of two distinct components turning over at a "fast" or a "slow" rate and having relatively short or long half-lives, respectively. Thus in control animals the half-lives of the protein components turning over at a fast rate ranged from 1.31 to 3.61 days whereas for those turning over at a slow rate the half-lives ranged from 8.56 to 24.28 days. Treatment with low doses of nicotine resulted in a more rapid turnover of nuclear fast turning over component with a concomitant decreased turnover of homogenate, cytosol, mitochondrial, and microsomal proteins; in the synaptosomal membranes this component disappeared altogether. The half-lives of the slow turning over components decreased in general from 14.3 to 33.3% with the exception of the nuclear proteins, where the half-live increased by 71.1%. Turnover of microsomal proteins was not affected. When the animals were given a high dose of nicotine, the turnover of fast components became even more rapid for nuclear, myelin, and microsomal proteins with a decrease in half-life from 26.6 to 32.3%. By contrast, half-lives of synaptosomal and mitochondrial proteins increased by 16.1-89.3%. These changes were not reflected in the turnover rate of whole homogenate proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prolonged in vivo treatment with nicotine on synaptosomal ATPase activity in rat brain were examined by employing doses of nicotine (0.02 and 0.04 mg/ml in the drinking water) which simulated intake by moderate and heavy smokers. Under these conditions the "low" dose of nicotine resulted in increased body weight whereas "high" dose of nicotine inhibited weight gain. Examination of synaptosomal ATPase activities revealed a dose and time dependent stimulatory/inhibitory effect. With "low" dose of nicotine, maximum stimulatory effect on ATPase activity was seen at the end of the 3rd week, while "high" dose stimulated the enzyme activities maximally by the 2nd week itself; further treatment up to the 4th week caused inhibition of the ATPase activities (10% to 43% decrease).