DEAR DR. DONOHUE: I have high blood pressure. What’s unusual about it is that I’m a 30-year-old woman with no family history of high blood pressure. My doctor has had a hard time lowering my pressure, and he now says I might have renovascular high blood pressure. I would be indebted to you if you can explain this for me. – M.C.

ANSWER: Most people, 90 percent, with high blood pressure – hypertension – have primary hypertension, also called essential hypertension or idiopathic hypertension. This is the kind of high blood pressure whose cause isn’t known. Less than 10 percent of hypertensives have secondary hypertension – elevated blood pressure secondary to some other distinct process going on. In your case, that secondary process is suspected to be a narrowing of one or more arteries that serve the kidneys.

Secondary hypertension is odd in a number of ways. It often begins at young ages, and it can be quite difficult to control with the usual blood pressure medicines.

The narrowed kidney artery of renovascular hypertension makes the kidney think body blood pressure is too low. It starts to produce, in great abundance, renin, a substance that elevates blood pressure. Correcting the kink in the kidney artery restores normal blood flow to it, and the kidney stops pouring out renin. Blood pressure falls.

You have to prepare yourself for special tests. Scans of the kidneys, X-rays of their arteries and sampling kidney veins for renin levels are examples of some of those tests.

If the suspicion proves correct, the artery narrowing can often be expanded in the same way that plugged heart arteries are expanded, with a balloon-tipped catheter inched into the narrowed blood vessel. In a way, you would be lucky to have this kind of high blood pressure; it’s curable.

The high blood pressure pamphlet discusses this common and complicated subject in detail. Readers can obtain a copy by writing: Dr. Donohue – No. 104, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6.75 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: Two weeks ago, I happened to stick my tongue out while I was looking in the mirror. It had a wide, black stripe on it. I saw my doctor, who said it was nothing and told me to brush it with toothpaste. I have. It’s still there. What is this, and how do I get rid of it? – K.D.

ANSWER: It’s black tongue, one of those things whose looks are far worse than their significance. Something has gone haywire with the way your tongue’s cells are shed from its surface. They pile up to create the black streak. It doesn’t indicate ill health.

If you’re a smoker, stop smoking. If your mouth is dry most of the time, carry with you a plastic squeeze bottle filled with water and make liberal use of it. Sugarless gum can also keep the mouth moist and hasten the departure of black tongue. Make a dilute solution of hydrogen peroxide by mixing one part hydrogen peroxide with two parts of water. Gently brush your tongue with a soft toothbrush dunked in the peroxide solution.

If the tongue is still black after a week or two of brushing, see your dentist. The dentist might have you use a solution with urea in it.

DEAR DR. DONOHUE: The doctor has told my daughter that my grandson’s “sutures” have closed too early. I have no idea what this means. What are sutures? Can this be corrected? – L.G.

ANSWER: Infants’ skulls have to expand to make room for their growing brains. To achieve this, their skulls have a number of “sutures” – lines in the skull, like fault lines – that are bridged by soft, fibrous tissue. That permits the skull to accommodate the expanding brain. Once brain growth is complete, the sutures fill in with bone. If the sutures fill in with bone too early, the brain cannot enlarge. Artificial sutures can be surgically created when the need arises.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com