Pharmacodynamics is the science dealing with interactions between the chemical components of living systems and the foreign chemicals, including drugs, that enter those systems. All living organisms function by a series of complicated, continual chemical reactions.
药效学是说明生命系统化学成分与进入这些系统的外来化学制品--包括药物--之间相互作用的科学，所有有生命的有机体通过一系列复杂、连续的化学反应发挥作用。
Drugs usually work in one of four ways:
药物的作功方式通常有下列4种：
1. To replace or act as substitutes for missing chemicals. 补充或作为所丢失的化学制品的替代物
2. To increase or stimulate certain cellular activities. 增加或刺激特定细胞活性
3. To depress or slow cellular activities. 抑制或降低细胞活性
4. To interfere with the functioning of foreign cells, such as invading microorganisms or neoplasms.
干扰外来细胞的作用，如入侵的微生物或肿瘤。
Receptor Sites 受体位点
Areas or sites on cell membranes at which many drugs are thought to act are called receptor sites. They react with certain chemicals to cause an effect within the cell.
药物在细胞膜上的作用部位就称为受体位点。他们通过与一定化学制品的反应而使细胞产生效应。
Some drugs interact directly with receptor sites to cause the same activity that natural chemicals would cause at that site. These drugs are called agonists. For example, insulin reacts with specific insulin-receptor sites to change cell membrane permeability, thus promoting the movement of glucose into the cell. Other drugs act to prevent the breakdown of natural chemicals that are stimulating the receptor site. Monoamine oxidase (MAO) inhibitors, for example, block the breakdown of norepinephrine by the enzyme MAO. The blocking action of MAO inhibitors allows norepinephrine to stay on the receptor site, stimulating the cell longer and leading to prolonged norepinephrine effects. Those effects can be therapeutic (e.g., relieving depression) or adverse (e.g., increasing heart rate and blood pressure).
有些药物直接与受体位点发生作用，在这些位点造成自然化学制品可能产生的作用。这些药物就称为激动药。如，胰岛素与特定的胰岛素受体位点发生作用，改变细胞膜渗透性，从而促进葡萄糖向细胞内移动。其他药物则会阻止可刺激受体位点的自然化学物质的分解。如，单胺氧化酶（MAO）抑制剂通过MAO酶阻断去甲肾上腺素的分解。MAO抑制剂的阻断作用促使去甲肾上腺素停留在受体位点，延长刺激细胞的时间，最终延长去甲肾上腺素效应。这些效应可以是治疗性的（如，减轻抑郁），也可以是不良效应（如加快心率，提高血压）。
Some drugs react with receptor sites to block normal stimulation, producing no effect. For example, curare occupies receptor sites for acetylcholine, which is necessary for muscle contraction and movement. Curare prevents muscle stimulation, causing paralysis. Curare is said to be a competitive antagonist of acetylcholine.
Still other drugs react with specific receptor sites on a cell and, by reacting there, prevent the reaction of another chemical with a different receptor site on that cell. Such drugs are called noncompetitive antagonists.
有些药物与受体位点发作反应，阻断正常的兴奋作用，产生不了效应。如，箭毒占据乙酰胆碱受体位点后（后者是起肌肉收缩和运动所必需的），它就会阻止肌肉刺激，造成麻痹。同时，箭毒也是乙酰胆碱的竞争性拮抗剂。
还有一些药物与细胞的特定受体位点发生反应，并通过这种反应，阻止其他化学物质与细胞不同受体位点的反应。这些药物称为非竞争性拮抗剂。
Drug–Enzyme Interactions药酶相互作用
Drugs also can cause their effects by interfering with the enzyme systems that act as catalysts for various chemical reactions. Enzyme systems work in a cascade fashion, with one enzyme activating another, and then that enzyme activating another, until a cellular reaction eventually occurs. If a single step in one of the many enzyme systems is blocked, normal cell function is disrupted.
药物还可以通过影响酶系统产生效应，由酶系统充当各种化学反应的催化剂。酶系统以级联方式发挥作用，由一种酶激活另一种然后再激活又一个，起到最终细胞反应出现。如果其中一个酶系统中的某个步骤被阻断，正常细胞功能就会中断。
Selective Toxicity 选择性毒性
Ideally, all chemotherapeutic agents would act only on enzyme systems that are essential for the life of a pathogen or neoplastic cell and would not affect healthy cells. The ability of a drug to attack only those systems found in foreign cells is known as selective toxicity. Penicillin has selective toxicity. It affects an enzyme system unique to bacteria, causing bacterial cell death without disrupting normal human cell functioning.
最理想的情况是，所有的化疗剂都只对病原体或肿瘤细胞生命至关重要的酶系统产生作用，不会影响健康细胞。药物只攻击外来细胞酶系统，这种能力被称为选择性毒性。青霉素就具有选择性毒性，只影响细菌独有的酶系统，促使细菌细胞死亡，但不会中断正常的人细胞功能。
Unfortunately, most other chemotherapeutic agents also destroy normal human cells, causing many of the adverse effects associated with antipathogen and antineoplastic chemotherapy. Cells that reproduce or are replaced rapidly are more easily affected by these agents. Consequently, the goal of many chemotherapeutic regimens is to deliver a dose that will be toxic to the invading cells yet cause the least amount of toxicity to the host.
不幸的是，大多数的其他化疗药物也会摧毁正常的人体细胞，引起很多与抗病原、抗肿瘤化疗相关的不良效应。繁殖或替换较快的细胞更容易受这些药物的影响。结果，很多化疗法的目标只停留在把毒性药物投送到入侵细胞，同时尽可能降低对宿主的毒性。
Vocabulary for Today
pharmacodynamics – n. 药效学，药物效应动力学
receptor sites – 受体位点
agonist -- n. 激动剂
breakdown – n. 分解
MAO -- monoamine oxidase单胺氧化酶
norepinephrine – n. 去甲肾上腺素
curare – n. 箭毒
acetylcholine – n. 乙酰胆碱
competitive antagonist – 竞争性拮抗剂
noncompetitive antagonist – 非竞争性拮抗剂
catalyst – n. 催化剂
cascade fashion – 级联方式
selective toxicity – 选择性毒性
antipathogen – n. 抗病原药
antineoplastic – a. 抗肿瘤的
1. When a drug binds to a receptor to produce a pharmacologic effect, the drug may be called a(n):
A. Agonist
B. Antagonist
C. Blocker
D. Accelerator 2. Which of the following is an example of competitive antagonism?
A. Adrenaline vs histamine
B. Benzodiazepine vs histamine
C. Naloxone vs morphine
D. A proton pump inhibitor vs an H2 blocker
1. A. Agonist. An agonist is the action described in the stem. B and C are synonymous. ELiminate choice D because there is no such action described in drug nomenclature. 2. C. Naloxone vs morphine. Naloxone (an opioid receptor antagonist that is structurally similar to morphine), when given shortly before or after morphine, blocks morphine’s effects. However, competitive antagonism by naloxone can be overcome by giving more morphine.
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