FORT WORTH, Texas – What’s a glamorous superstar like Cybill Shepherd doing here in Fort Worth, early in the morning, talking about constipation before she jets off to Toronto to film a new two-hour CBS television movie about Martha Stewart?

“It’s important to get women talking about IBS (irritable bowel syndrome) with constipation,” says Shepherd, yawning as she leans back in one chair, her feet, clad in raspberry pink metallic sneakers, up in another. “Six million women suffer from it.”

While Martha herself might be the last person to bring up the subject of constipation in polite company, Shepherd, who also played Martha in a 2003 NBC Movie of the Week, “Martha, Inc.,” says she has always been outspoken, some would say irreverent, when it comes to health issues affecting women.

“I’ve been talking about unmentionables for 30 years,” Shepherd says. “My first real cause was reproductive freedom, and it still is, but I also helped bring menopause out of the closet. Long before the big controversy over HRT (hormone replacement therapy), I talked about menopause and periods and ways to deal with them on `Oprah.’ In fact, I once walked up to a group of women I hardly knew at a party and said, ‘So, about menopause, how’s it going with you?’ Everybody quit talking and started backing away.”

Now, Shepherd is traveling the country talking about IBS with constipation (as opposed to IBS with diarrhea) and Zelnorm, a prescription drug to treat the abdominal pain, bloating and chronic constipation that IBS can cause. She is a spokeswoman for the “Amazing Women” campaign, designed to empower women to seek proper diagnosis and treatment for recurring constipation. Shepherd’s tour is sponsored by Novartis Pharmaceuticals, the company that developed Zelnorm.

“I tell women to talk to everyone, your family and friends and mothers and sisters and especially your doctor, even if it is embarrassing,” Shepherd says. “I was misdiagnosed for 20 years. My doctor told me it was nothing. It was psychological, all in my head. There’s nothing to make you go crazy like being told that pain is all in your head . . . The bloating was so bad that sometimes a costume wouldn’t fit from day to day and I would just have to leave it unzipped in back.”

She finally went to a new doctor who correctly diagnosed IBS about two years ago.

Traditionally, diagnosis of IBS with constipation has been a problem simply because patients are reluctant to talk about it.

“It’s not that it is difficult to diagnose, but people don’t talk about their bowels much with their primary care physicians,” says Dr. Stephen Furs, a gastroenterologist who participated in a double-blind clinical study on Zelnorm at the University of North Carolina at Chapel Hill. “Doctors weren’t asking, and patients weren’t volunteering the information needed for proper diagnosis.

“It’s not that IBS with constipation is underappreciated, it’s just that it can’t be readily explained,” says Furs. “For years, we attributed it to unresolved stress. That’s how it got the reputation for being ‘in your head.’ We treated it with high-fiber diets and fiber supplements and laxatives, but in most studies those treatments were no better than placebo. I would say about three out of four of my patients who are properly diagnosed get significant relief with Zelnorm.” He notes that he has been prescribing the drug since it came out in fall 2002.

“Nothing helped all the symptoms until I got on the right medication,” Shepherd says, trying to suppress another yawn as she twirls the office chair she is sitting in around and asks her assistant for a bottle of water and a hard-boiled egg white to help her through the early-morning interview.

“You know it’s 5:20 my time (in Los Angeles), and I’ve been up and at this for a couple of hours already,” she points out.

Still, she appears none the worse for the hectic schedule and says that at 55, “it’s too late to start lying about my age now” she’s feeling better than ever before.

“I’ve been singing and dancing (on stage) for the first time ever at the Soho Theater in London,” says Shepherd, a stage, movie and television actress who recalls dancing, on the toes of her father’s wingtip shoes, by the time she could walk and singing in her church choir from age 8.

The one-woman show is based on her book, “Cybill Disobedience: How I Survived Beauty Pageants, Elvis, Sex, Bruce Willis, Lies, Marriage, Motherhood, Hollywood, and the Irrepressible Urge to Say What I Think.” Published five years ago, the book was on The New York Times bestseller list for seven weeks and will be republished in May. Shepherd hopes to bring the show to New York next fall.

“It doesn’t really matter if it’s on Broadway. I just need a dance floor,” she says. “I once wanted my epitaph to read, ‘Dancevery chance you get,’ but now I want it to say, ‘We’ll make this a comedy yet.’ ”