She who laughs gas conceives last.

She who laughs gas conceives last

Infertility among women who work in dental offices might result from exposure to nitrous oxide used to anesthetize and sedate patients, if new findings in labatory animals hold true for humans. In a study presented last week at the American Association of Dental Research meeting, nitrous oxide or "laughing gas" disrupted hormonal cycles and prevented conception in female rats.

For more than 20 years, anecdotal reports and epidemiologic studies have hinted at a link between nitrous oxide and miscarriage or infertility. One study, for example, showed higher-than-usual rates of fetal deformity, miscarriage and infertility among female anesthesiologists - but it didn't prove nitrous oxide responsible. Animal studies have implicated laughing gas in both male and female infertility, deformed offspring and miscarriage, but only at very high doses.

The new study is the first to implicate nitrous oxide in amounts commonly received by dental workers and to suggest how the gas sabotages the hormonal cycle. Gerard Kugel, a dentist and neurobiologist at Tufts University in Boston, along with colleague Carlos Letelier, described the results at the San Francisco meeting.

Eight hours a day for 35 days, Kugel and Letelier exposed 12 female rats to 500 parts per million nitrous oxide -- a dose comparable, they say, to what a dentist might breathe over the same time period. In examining the exposed rats, they found the normal four-day ovulation cycle stuck in the proestrus phase, which occurs right before ovulation. Only six of the 12 conceived when mated, whereas all 12 control rats conceived.

To determine the cause, Kugel dissected the brains from some of the rats. In exposed rats, he discovered that an excess of a crucial reproductive hormone, called luteinizing-hormone-releasing hormone (LHRH), was apparently trapped in the hypothalmus. Normally, in rats and humans, the hypothalamus produces LHRH, which is then channeled to the pituitary gland to trigger the next step leading to ovulation. Kugel suggests the LHRH in the exposed rats became backed up like water in a clogged sink.

He says his results are not terribly surprising in light of the profound effect nitrous oxide has on the brain's pain response. It increases the production of brain chemicals called opioids, known to suppress pain and to interfere with the release of reproductive hormones, he notes.

Kugel stresses his study examined only the effects of chronic exposure -- not the one-time dose a patient receives. An earlier study, he notes, revealed that dentists get a higher dose than other medical workers because they often work in closed offices, hovering close to the mouth of a patient who is exhaling the gas. To reduce exposure, Kugel says, some dentists use a "scavenger" machine that sucks excess laughing gas out of the office. In studying the effectiveness of these machines, he found many left potentially harmful levels behind.

Kugel also points out that some people increase their exposure by nipping at nitrous oxide after work. Some medical and dental workers, he says, use laughing gas as a recreational drug. One dental assistant who suffered eight years of infertility told Krugel she had been slipping into the dentist's chair and administering the gas to herself every day after work during that period. Research has shown abusers can become addicted to nitrous oxide, he adds.

Kugel says he doesn't want to scare doctors and dentists out of administering laughing gas to their patients. He still uses it occassionally to calm very anxious patients. His aim, he says, is to make medical professionals aware of any possible risks. "If you are careful with it, use it only when needed and get a scavenger," he says, "you cut down on these risks."