COLUMBUS, Ohio - New research shows that high blood pressure plays an important role during acute rejection of transplanted kidneys.
More than 12,000 people a year in the United States undergo kidney transplantation, and one in every four of them experience acute rejection of the organ.
Acute rejection is an inflammation of the transplanted kidney. Early in the history of kidney transplantation, acute rejection was common and usually resulted in almost immediate loss of the organ.
"These new results give us an important way to identify patients who are at high risk of rejecting a transplanted kidney," said Fernando Cosio, professor of internal medicine at Ohio State University and leader of the study. "If we know a patient has a high risk of acute rejection, we can intensify treatments to prevent it."
Medications available today can control acute rejection in 95 percent of cases, although it may cause some loss of functionin the transplanted kidney, Cosio said.
The study also yielded a second important finding. "The research suggests that if we control blood pressure with the right drugs, we may be able to prevent rejection in these cases. This paper doesn't prove that, but we are finding it to be true," he said.
The group of blood-pressure medications that were most effective in preventing rejection are known as calcium channel blockers.
The retrospective study, published in a recent issue of the journal Kidney International, reviewed the records of 1,641 adult recipients of kidney transplants at Ohio State University from 1982 to 1996.
Cosio and his team of researchers then identified factors associated with acute rejection. Most were risks that had long been known, factors such as being young in age, being African American, and a delay in the functioning of the new organ.
"To our surprise, having high blood pressure following transplantation also emerged as a very strong marker for rejection," said Cosio.
In fact, the researchers found that the highest incidence of acute rejection - 81 percent of patients - occurred in people whose blood pressure became high following transplantation, while the lowest incidence of acute rejection - 22 percent of patients - was among people who had lower blood pressure after transplantation than before it.
Why or how high blood pressure leads to rejection isn't understood, he said.
The blood vessels of the kidneys play a major role in regulating blood pressure generally in the body, however. The cells making up the blood-vessel walls release an enzyme, renin, when blood pressure should be higher, and then stop releasing the hormone when the blood pressure needs to drop. The kidneys also help control blood pressure by reducing the amount of water lost as urine.
Cosio suspects that the condition of the blood vessels in a transplanted kidney affect's the organ's ability to regulate blood pressure.
Whenever a kidney is removed from a donor, the organ's blood supply is momentarily lost, reducing the supply of oxygen to the blood-vessel cells and damaging them to some degree. This is particularly true when the kidney comes from a person who has died and whose circulation is maintained artificially.
This subtle damage may then inhibit that kidney's ability to efficiently maintain blood pressure following transplantation.
Looked at another way, high blood pressure after transplantation may sometimes reflect the degree of damage to the blood vessels of the kidney after it is removed from the donor, he said.
Cosio's research was funded by grants from the National Institutes of Health.
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