Blood pressure response to daily stress provides clues for better hypertension...(er. When blood pressure goes up due to ...)

Dr. Harshfield's studies identified this impaired stress-induced sodium natriuresis. He believes it's also a primary reason blood pressure remains elevated at night in some blacks, rather than dipping as it should, which keeps stressing the cardiovascular system.

Using a rat bred to be salt-sensitive, the researchers are working to identify more about the genetics of impaired sodium-handling. "We have animal model data that says the endothelin system normally functions to help your kidneys get rid of salt," says Dr. Pollock. His studies have shown the kidney's endothelin B receptor plays a critical role in promoting excretion of acute and chronic salt loads by activating the precursor to nitric oxide, a powerful dilator of blood vessels. In the new studies, he'll control the rats' diet and see whether stress slows down sodium excretion. Preliminary evidence suggests it does. He'll also give the rats an endothelin antagonist, which blocks this hormone, and see if sodium excretion improves. He'll also see how a high-fat diet and obesity alter the equation.

Meanwhile, for about a week, young study participants with impaired sodium excretion will take a drug to block the powerful blood vessel constrictor, angiotensin. "From our point of view, angiotensin promotes sodium retention directly and it also increases aldosterone, another hormone which promotes sodium retention," Dr. Harshfield says. The researchers chose to study endothelin and angiotensin because they believe they work together. To explore the genetics, they'll also look at young adults with a different version of the angiotensin receptor gene that they believe exacerbates sodium-handling problems. MCG researchers identified this genetic variation in people who retain sodium; blocking the receptor gene will provide more evidence
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