(CNN) -- Two American scientists won the Nobel Prize in chemistry Wednesday for their work revealing protein receptors that tell cells what is going on in and around the human body. Their achievements have allowed drug makers to develop medication with fewer side effects.

Research spanning four decades by Robert J. Lefkowitz and Brian K. Kobilka on "G-protein-coupled receptors" has increased understanding of how cells sense chemicals in the bloodstream and external stimuli like light, according to the Royal Swedish Academy of Sciences, which awarded the prize.

G-protein-coupled receptors：G蛋白偶联受体

Lefkowitz began the research by tracking adrenalin receptors. The Nobel Prize announcement apparently set off some of the excitement hormone in his own body.

set off：引起

"I'm feeling very, very excited," he said in a predawn phone call from the United States to the committee in Stockholm, Sweden, which announced the winners at 5:45 a.m. ET.

ET.：East Time 缩写，美国东部时间

"Did I even have any inkling that it was coming?" Lefkowitz said. "I'd have to say no."

He contacted Kobilka via a Skype video call to celebrate the news after receiving the call from the Nobel committee.

Lefkowitz, with the Howard Hughes Medical Institute and Duke University Medical Center in Durham, North Carolina, began tracking cell receptors with radioactive substances in 1968.

radioactive substance：放射性物质

In the 1980s, Kobilka, from Stanford University School of Medicine in California, joined the research to isolate the human gene that produces the adrenalin receptor, the academy said.

"Kobilka achieved another break-through" in 2011, the academy said in a news release: a photographic image of a hormone triggering a receptor to send an impulse into its cell.

"This image is a molecular masterpiece -- the result of decades of research," the academy said.

Humans experience G-protein-coupled receptors most consciously when they smell, see and taste, the academy explained in a background document. But within the body, they sense "signaling substances, such as adrenalin, serotonin, histamine and dopamine."

"They serve as the gateway to the cells," Lefkowitz said.

"Around half of all medications act through these receptors, among them beta blockers, antihistamines and various kinds of psychiatric medications," the academy explained.

beta blocker：β-受体阻滞药（治高血压和心脏病的药物）

In the case of adrenalin -- known in science as epinephrine -- receptors in cells of the heart make it beat faster and receptors in muscle cells signal them to activate to mobilize a person's strength.

Newly anointed Nobel Laureate Lefkowitz can use the energy boost.

"I'm thinking that this is going to be a very hectic day," he said. "I was going to get a haircut," he revealed, triggering laughter at the academy, as he explained that he really felt he needed one. "But I'm afraid it will probably have to be postponed."

Nobel Prizes in chemistry have gone to predominantly to organic (or carbon-based) chemistry, particularly to discoveries in the area of life sciences, such as genetics.

organic chemistry：有机化学

This year's monetary award will be 8 million Swedish kronor (about $1.2 million). This represents a drop of 20%, compared with last year, from 10 million Swedish kronor, and is due to the turbulence that has hit financial markets.

Last year, Israeli scientist Daniel Shechtman from Technion - Israel Institute of Technology won the award for the discovery of quasicrystals, which was made in 1982 and "fundamentally altered how chemists conceive of solid matter," according to the Royal Swedish Academy of Sciences.

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