今天前程百利小编为大家分享的是托福听力的背景学习。备考托福听力就要把听力文本吃透分析彻底。这样不仅能积累背景材料，还能把听力的专业词汇积累起来一块背诵，为托福听力打下坚实的基础。下面跟小编一起看一下血压疫苗是如何延长老鼠的寿命的?
A DNA-based vaccine gave rats six months of protection against high blood pressure as well as healthier hearts.
Some 70 million American adults have high blood pressure. Three quarters of them rely on medication to keep the condition in check. But you've got to remember to actually take the daily dose. Now researchers have devised a longer-lasting alternative: a vaccine to lower blood pressure…for rats, at least.
Scientists jabbed hypertensive rats with three doses of the formulation. It's a DNA vaccine—containing DNA fragments from angiotensin II—a hormone that boosts blood pressure, as well as fragments from hepatitis B, to guarantee the immune system’s attention. Cells suck up the vaccine's DNA, and start pumping out the proteins the DNA codes for. When the host’s defenses gets a whiff of the proteins, it reacts. It really revs up against the hepatitis B fragments. And while it’s at it, it starts taking out some angiotensin II as well.
The result is a reduction in angiotensin II's usual blood pressure raising effects—similar to what blood pressure meds like Benicar do. Less angiotensin II means more relaxed blood vessels, and a drop in pressure. That effect lasted six months in the vaccinated rats, and lengthened their lifespan by eight weeks. Necropsies on the vaccinated rats revealed healthier heart tissue than normally found with high blood pressure, and no damage to their kidneys or livers. The results are in the journal Hypertension.
Other blood pressure vaccines have been tried, unsuccessfully. But this novel DNA-based vaccine could induce a longer-lasting effect. And the hope of twice-yearly shots instead of daily pills.
疑难词汇：
Vaccine n. 疫苗;牛痘苗adj. 疫苗的;牛痘的
Medication n. 药物;药物治疗;药物处理
Jab vt. 戳;猛击;用拨火棒等捅vi. 戳;刺;用拳猛击n. 戳;猛击;注射
Hypertensive n. 高血压患者adj. 高血压的
Angiotensin n. 血管紧张肽;血管紧缩素
Hormone n. [生理] 激素，荷尔蒙
Angiotensin n. 血管紧张肽;血管紧缩素
blood vessels 血管
kidney n. [解剖] 肾脏;腰子;个性
hepatitis B n. [内科] 乙型肝炎
长难句解析：
1. The result is a reduction in angiotensin II's usual blood pressure raising effects—similar to what blood pressure meds like Benicar do..
难句类型：
what引导的宾语从句
句子主干：
The result is a reduction
难句拆分：
what blood pressure meds like Benicar do，what引导的宾语从句，作similar to的宾语;in angiotensin II's usual blood pressure状语。
2. It's a DNA vaccine—containing DNA fragments from angiotensin II—a hormone that boosts blood pressure, as well as fragments from hepatitis B, to guarantee the immune system’s attention.”
难句类型：
That引导的定语从句
句子主干：
It's a DNA vaccine
难句拆分：
containing DNA fragments from angiotensin II，插入语，解释DNA vaccine; that boosts blood pressure，That引导的定语从句修饰a hormone。
文本结构特点：
本篇文章主要讲的是经科学研究一种血压疫苗可以延长老鼠的寿命。接受疫苗的老鼠并没有损害心脏相反，没有注射疫苗并且患有血压病的老鼠心脏反而不健康。
好了，以上就是前程百利小编为大家整理的备考托福听力背景材料以及专业词汇的学习。大家学会了吗?希望能在备考托福的路上助大家一臂之力。预祝大家在托福考试中取得好成绩。
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