Nicotine addiction studied

April 14, 1994|By Jonathan Bor | Jonathan Bor,Sun Staff Writer

Humans crave it. So do mice and monkeys. Give these animals repeat doses of nicotine and they will practically beg for more.

More than a decade of laboratory experiments has established a scientific basis for what smokers and research scientists have long suspected: that nicotine is a powerfully addictive chemical that makes cigarettes as difficult to kick as heroin, cocaine or alcohol.

Once hooked, human subjects given nicotine-free cigarettes will quickly recognize the fraud. Rats will run like mad through an obstacle course to reach a nicotine source. Monkeys will press levers a hundred times to get a single intravenous dose.

"They were pressing the levers as if their lives depended on it, as if it were a biologically important substance like food or water," said Dr. Jack Henningfield, pharmacology chief of the National Institute on Drug Abuse in Baltimore.

Charges that the tobacco industry manipulates the nicotine content of cigarettes to keep smokers hooked have caused policy-makers to wonder whether the chemical should be recognized as an addictive "drug" and either banned or more tightly regulated.

Recently, Food and Drug Administration Commissioner David Kessler surprised anti-smoking forces when he said that his agency has the power to regulate nicotine under the same law that gives it jurisdiction over drugs.

Today, Rep. Henry A. Waxman, D-Calif., is to resume a hearing on the content of cigarettes and whether the FDA should regulate them.

Although the issue has recently whipped up controversy on Capitol Hill, scientists have quietly been studying nicotine for many years.

Around the turn of the century, European scientists conducting animal experiments discovered that nicotine affected the central nervous system. When they applied the chemical to nerve endings, muscles twitched.

Tobacco use wasn't a major public health problem until the 1920s when automated rolling machines became widely used in cigarette production.

World War II

World War II brought a surge in tobacco's popularity when the military shipped cigarettes to troops overseas. By war's end, about 40 percent of adult males smoked.

It wasn't until the late 1960s that research scientists began serious experiments to see whether nicotine was the substance that kept smokers hooked, as they had long suspected.

Nicotine is actually a poison in much larger concentrations than people typically get from cigarettes or other tobacco products. It has been used extensively as a pesticide, and tobacco growers who handle the leaf without wearing gloves can absorb large enough concentrations to make them nauseous.

In some early experiments, scientists adjusted the nicotine content in cigarettes to see if that affected the number of cigarettes people smoked. When smokers were given low-nicotine cigarettes, they smoked more. When they were given high-nicotine cigarettes, they smoked less.

Similarly, committed smokers tended to light up less frequently when they were given nicotine injections.

And in another experiment, people who were given a drug that blocked nicotine's effect on the brain smoked more.

All this suggested that nicotine was satisfying a craving that dogged committed smokers. The chemical doesn't cause cancer many other carcinogens have been identified in tobacco smoke -- but it appears to be the agent that keeps smokers reaching for cigarette after cigarette.

Animal experiments

In the 1980s, animal experiments strengthened the case against nicotine. Many of them were conducted at the research facilities of the National Institute on Drug Abuse.

In an experiment done by Dr. Stephen R. Goldberg, first at Harvard University and later at NIDA, monkeys hooked intravenously to bottles of nicotine and salt water would quickly learn to press the lever that delivered nicotine.

Initially, pressing the lever once would deliver the drug. Later, the machinery was rigged so that the animals would have to press it several times. Still later, they would have to hit the lever 100 times to get a single dose. The monkeys were undeterred.

Similar experiments were done in the early 1980s by scientists working for the Phillip Morris Co. Rats would choose a nicotine lever over one that delivered salt water.

Tobacco firm pulls report

The study was accepted for publication by a scientific journal, Psychopharmacology, but was ultimately withdrawn by the tobacco company.

"This kind of work [with animals] was so important because it completely gets away from the taste, the advertising, from smoking to look good or feel cool," Dr. Henningfield said. "It gets right to the basic biology."

Dr. Henningfield's own experiments showed that smokers who were also addicted to a wide range of drugs could easily distinguish a nicotine injection from a placebo, or a nicotine-free cigarette from a standard smoke.

In a laboratory setting, smokers who were denied cigarettes satisfied their craving by dosing themselves intravenously with a nicotine solution.

Despite extensive research to the contrary, the tobacco industry maintains that nicotine is not addictive.

"We don't see it falling into any part of the profile of what is called classic addiction," said Thomas Lauria, a spokesman for the Tobacco Institute.

"It doesn't distort users' perception. It doesn't require professional intervention or hospitalization to quit."

Many scientists disagree.

Dr. Maxine L. Stitzer, an addictions researcher at Francis Scott Key Medical Center, said fewer than 10 percent of the 17 million people who try to quit smoking each year will succeed.

Success rates, she said, are lowest among people who try to quit on their own and highest among people who receive professional help while using such aids as a nicotine patch or gum.

The federal government exempts airline pilots from rules banning smoking in planes, noted Dr. Henningfield. Regulators fear that the impaired judgment of pilots suffering nicotine withdrawal could endanger passenger safety.

Baltimore Sun Articles
|
|
|
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.