Theresa Parrish is certain there are differences between men and women that go far deeper than sex organs and who's in charge of the remote.

If Parrish didn't firmly believe that, the disabled, HIV-positive liver transplant recipient wouldn't journey all the way from Springfield, Mo., every year to participate in a Georgetown University study that's attempting to spotlight those differences and how they affect health and disease.

Parrish, 51, makes the trip to get poked and prodded and questioned by a team of researchers focusing on the rate at which women absorb HIV drugs into their bloodstreams. The results are regularly compared with those from a similar study on men that's taking place at Johns Hopkins University.

"I hope we'll be able to find out if we're underdosing or overdosing women and make the adjustments they need," said Parrish, referring to the fact that up until the early 1990s, most clinical drug trials were done on men only, which left doctors unsure whether they should be offering different doses to women.

The HIV drug research on women is just one of the studies going on under the aegis of Georgetown's new Center for the Study of Sex Differences, which will officially launch next month.

The hope, said Kathryn Sandberg, director of the new center and a professor of nephrology and hypertension at Georgetown, is that the center will encourage collaboration among researchers across myriad areas of study, leading to a better understanding of the way sex influences health, disease and aging. From there, improving detection and treatment for both men and women should follow.

"There aren't enough evidence-based studies out there on why men and women have such different experiences with diseases like AIDS, cancer, diabetes and renal failure," said Sandberg. "We want to help facilitate researchers who think they may be onto some new insights about these diseases but just don't have the resources to study both males and females."

Known health-related sex differences include the following:

* Men don't live as long as women in almost all societies studied;

* Women are more likely to develop lung cancer when exposed to the same amount of smoke as men;

* Men are more likely to develop renal failure and to have a faster progression of kidney disease;

* Women are more susceptible to autoimmune diseases such as multiple sclerosis, scleroderma and lupus;

* Men die at an earlier age from heart disease than women, but after menopause, this difference disappears and as a result more women actually die from heart disease each year than men.

Too many of the underlying causes for these differences are unknown, Sandberg said. The new center -- which has 60 researchers working under its umbrella, bringing together new studies as well as some that have been going on for years -- is charged with changing that.

Already, the study in which Parrish is participating has unearthed important differences between women and men. In 2000, it became clear to the researchers that women, unlike men, are often attacked by multiple variants of the HIV virus. This is important to know if a vaccine is to be developed to help both sexes, said Mary Young, principal investigator for the HIV study's Washington site and assistant professor of Georgetown's division of infectious diseases.

The multi-site Women's Interagency HIV Study, funded by the National Institutes of Health (NIH), also found that women would benefit from starting antiretroviral therapy to prevent the onset of AIDS sooner than men. .

Other investigations into drug metabolism differences are being conducted, with the hope that drug dosing can be modified more appropriately according to sex.

Other studies being undertaken under the banner of the new center include examinations of sex-based differences in multiple sclerosis, post-traumatic stress disorder and high blood pressure.

Thus far, all the studies that fall under Georgetown's new center have their own funding from other sources, including NIH, the American Heart Association, the National Science Foundation, the National Kidney Foundation, the American Diabetes Association and the American College of Rheumatology. The center itself funds only small pilot experiments that, if successful, could compete for larger grants to study more patients.

"Researchers already at work on a particular experiment often say, 'I know there are sex differences in what I'm studying, but it's just too expensive to double the number of subjects we can study,' " said Sandberg. "We supplement and enhance existing research by allowing researchers to . . . include both sexes in their studies."

To catch up with the medical research that focused on men for so many years, Sandberg says the new center will have to turn much of its attention to women for a while. That's all right with Robert Tan, associate professor of medicine at Baylor College of Medicine in Houston and a board member of the D.C.-based group lobbying Congress to fund an Office of Men's Health -- as long, he says, as research efforts eventually level out. Tan cites the Office of Women's Health as evidence that much funding and attention has gone to women's health issues since 1991.

"We feel that lately there isn't enough men-based research," said Tan. "But the pendulum is swinging back that way." Tan called Georgetown's new Center for Sex Differences "a step in the right direction."

Insufficient data

Until the early 1990s, most clinical research studies excluded women as a matter of policy. It was thought that menstrual cycles would complicate findings. And, of course, including an equal cohort of women in each study adds significantly to costs. Additionally the Food and Drug Administration (FDA), concluding that clinical trails might harm women's reproductive health, recommended in 1977 that women be excluded from them.

Those restrictions weren't lifted until 1993. A later Congressional mandate required that drug researchers analyze data specifically by sex, explained Joseph Verbalis, chief of the division of endocrinology and metabolism at Georgetown and director of clinical research of the new center.

Now that the gate is open, researchers say the task before them is vast.

"There are probably differences in all our physiological functions," said Susan Mulroney, associate professor of physiology and biophysics at Georgetown, who's working with Sandberg on identifying sex differences in renal failure. "The point is that we just haven't really looked for them yet."

Other institutions are focusing on sex differences. In 1999, the Partnership for Gender-Specific Medicine at Columbia University was launched. Two years ago, the Center for Gender Physiology and Environmental Adaptation at the University of Missouri School of Medicine got started.

Meredith Hay founded the Missouri center two years ago after she noticed that several researchers on campus were looking at sex differences, but none were collaborating.

Now the center has a $4.3 million grant from the National Aeronautics and Space Administration (NASA) to study the effects of space travel on women (25 percent of the astronaut corps is female). The center has received another $4 million from the NIH and others for other gender-related physiology studies.

Hay's center is also collaborating with the Georgetown center on a few projects, including one looking at the effects of estrogen and testosterone on fluid balance in the bodies of men and women.

The level of cooperation -- both among professors at Georgetown and between Georgetown and other universities -- has surprised some researchers.

"In order to get very complicated, very sweeping things done, collaboration among people in various, specific areas of expertise is what's needed. That's been the real value of the center; it's almost an incubator for this sort of thing," said Jason Umans, associate professor of medicine in Georgetown's division of nephrology and hypertension, who recently won an NIH grant to start a center at Washington Hospital Center that will focus on on the effects of drugs and drug metabolism in pregnant women. It will be one of only four of its kind.

Sandberg predicts that centers for sex differences will soon begin springing up at academic medical institutions just like cardiovascular and cancer institutes have. It's the sort of work that Parrish, the Springfield, Mo., woman who comes to Georgetown once a year to participate in a study on sex differences, seems to understand intuitively.

"Women's and men's bodies are just different," she said. "Somebody needs to figure out exactly how, soon, so we all can have healthier, more productive lives."

Suz Redfearn last wrote for the Health section about her experiences with traditional Chinese medicine and other alternative methods to battle infertility.

Kathryn Sandberg, director of Georgetown University's new Center for the Study of Sex Differences, and Joseph Verbalis, director of clinical research, want to better understand how sex influences health, disease and aging. Theresa Parrish, an HIV-positive liver transplant recipient from Missouri, travels to Georgetown University each year for a study measuring the rate at which women absorb HIV drugs in their bloodstreams. The new Center for the Study of Sex Differences is encouraging such studies.