单选题 Scientists have developed a slimming drug that successfully suppresses appetite and results in a dramatic loss of weight without any apparent ill effects. The drug interferes with appetite control and prevents the build-up of fatty tissue. More importantly, the drug appears to prevent a serious decline in metabolic rate—causing tiredness and lethargy—which is typically associated with living on a starvation diet. As a result, mice taking the drug lost 45 percent more weight than mice fed the same amount of food, which compensate for the lack of food by becoming more sluggish.
The scientists, from the Johns Hopkins University in Baltimore, said that C 75 is likely to produce a similar effect on humans because appetite control in the brain is thought to be based largely on the same chemical pathways as those in mice. "We are not claiming to have found the fabled weight-loss drug. What we have found, using C 75, is a major pathway in the brain that the body uses naturally in regulating appetite, at least in mice," said Francis Kuhajda, a pathologist and senior team member. "We badly need effective drugs for weight loss. Obesity is a huge problem. We"re hoping to explore the possibilities of this new pathway," he said.
Discovering a biochemical pathway in the brain that controls appetite raises new prospects for developing slimming aids. Research on leptin, a hormone produced in fatty tissue for controlling fat deposits, has so far failed to produce the expected slimming drug breakthrough. The latest study, published in the journal Science, showed that even moderate doses of C 75 produced a significant loss of appetite, which returned to normal after a few months.
The scientists believe that C 75, which they produced synthetically in the laboratory, binds to an enzyme called fatty acid sythase, which is involved in storing excess food intake as fat. Inhibiting the enzyme causes a build-up of a chemical in the liver which acts as a precursor to fat deposition. This precursor is thought to have an indirect effect on the brain, causing appetite suppression.
Normally, when animals fast, a hormone called neuropeptide Y increases sharply in the appetitecontrol centers of the brain, stimulating the desire for food. However, when animals are given C 75, levels of this hormone fall, leading to a loss of interest in food. Dr. Kuhajda said discovering that C 75 has no effect on metabolic rate is one of the most significant findings of the study. "If you try to lose weight by starving, your metabolism slows down after a few days," he said. "It"s a survival mechanism that sabotages many diets. We see this in fasting mice. Yet metabolic rate in the C 75-treated mice doesn"t slow at all." Further animals studies will be needed before C 75 could be tested on humans.

单选题 Living on a starvation diet may result in ______.

单选题 The scientists from the Johns Hopkins University said that C 75, the slimming drug proved effective in mice, is likely to work on humans because ______.

单选题 Leptin ______.

单选题 The newly-found slimming drug can successfully suppress appetite because ______.

单选题 What is the most remarkable about the new slimming drug C 75?