In recent years, a class of drugs known as COX-2 inhibitors has gotten much publicity for the drugs' power to relieve inflammation and pain. These drugs are relatively new to the pharmaceutical industry, their mechanisms of action having been discovered only in 1971. That year, John Vane discovered the relationship between nonsteroidal anti-inflammatory drugs, such as aspirin, and a group of molecules, called prostaglandins, responsible for producing the sensation of pain in the human body, among other functions.
Prostaglandins were first discovered in the 1930s and are now known to be generated by most mammalian tissues in response to external stimuli. Unlike classical hormones that are synthesized in one tissue but act on a distant one, prostaglandins act on the cells that produce them or on cells located close to the prostaglandins’ cells of origin. Aspirin alleviates pain by inhibiting the function of an enzyme called cyclooxygenase or COX; this inhibition prevents the production of prostaglandins. The three forms of this enzyme, COX-1, COX-2, and COX-3, all stimulate the production of prostaglandins, but each serves a different purpose. COX-1 functions to protect the stomach from irritating gastric acids. COX-2 functions to induce inflammation in injured tissue and COX-3 functions to control the sensation of pain. Aspirin and other similar drugs, such as naproxen, inhibit both COX-1 and COX-2, sometimes producing or aggravating stomach ulcers in patients who take them.
In order to eliminate the side effects of aspirin and related drugs, several pharmaceutical companies in the 1990s developed drugs that inhibited only COX-2. However, side effects almost always cropped up, even after clinical trials that seemed to indicate none. This often occurs because trials are conducted within very limited parameters; once the drug has been approved for mass distribution, however, the number of people taking it and the length of time that it is taken increase dramatically. Several COX-2 drugs that have been popular in recent years fit this pattern: initially successful in clinical trials, subsequent studies showed them to have serious, potentially lethal side effects.
Though prostaglandin chemistry and enzymology have been studied for half a century, pinpointing the exact role of the molecules in physiological processes still remains a challenge for researchers. Hence it is not surprising that recent therapeutic attempts to interfere with the formation of certain prostaglandins have produced unexpected side effects. It now seems that the hype surrounding COX-2 drugs may have been premature.
1 . The passage suggest which the following about COX- 2 inhibitors?
A. They fail to protect the stomach from gastric acids that can cause irritation, but protect the body from tissue inflammation.
B. They produce similar side effects as those caused by Naproxen.
C. They were introduced approximately 20 years after the relationship between aspirin and prostaglandins was discovered.
D. They stimulate production of prostaglandins that cause tissue inflammation.
E. They are generated by external stimuli and act on the cells that produce them.
2. According to the passage, all of the following are true of prostaglandins EXCEPT:
A. They were discovered in the 1930s.
B. They are generated by most mammalian tissues.
C. They produce the sensation of pain in the body, but are also responsible for other bodily functions.
D. They cause side effects that clinical trials failed to detect.
E. Their production is affected by enzymes COX-1, COX- 2, and COX-3.
3. The author mentions that prostaglandins are generated in response to external stimuli primarily in order to support the contention that
A. Prostaglandins can produce or aggravate stomach ulcers.
B. Prostaglandins act in the same tissue that produces them.
C. Prostaglandins prevent the enzyme cyclooxygenase from functioning.
D. Prostaglandins are significantly different from most mammalian hormones.
E. Prostaglandins are responsible for the human sensation of pain.
4. The primary purpose of this passage is to
A. explain the therapeutic benefits of a new type of pain reliever
B. initiate a debate concerning the benefits of COX-2 inhibitors
C. warn the public that clinical trials cannot ensure drug safety
D. describe the impetus for and result of COX-2 inhibitors’ introduction
E. introduce research findings to support COX-2 inhibitors over COX-1 inhibitors
参考答案：
CDED
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2021-7-12 07:23:21
收藏
收藏
