Specifically, relaxin affects kidney arteries by revving up production of nitric oxide in a layer of cells lining the inside of blood vessels called the endothelium. Finding the key to this physiologic response could have significant implications for the treatment of hypertension and other cardiovascular diseases.
"This study, which mainly targeted small renal arteries isolated from rats, is consistent with our earlier work showing that relaxin increases renal blood flow and kidney filtration by as much as 40 percent in non-pregnant rats," said Kirk P. Conrad, M.D., senior study author and an investigator at the Magee-Womens Research Institute. The hormone causes similar increases in kidney function during pregnancy.
"Linking relaxin with nitric oxide is another peptide hormone called endothelin which has a receptor on endothelial cells that increases nitric oxide," he added. It is the action of endothelin and nitric oxide that increases dilation in the blood vessels, improving blood flow.
"What happens to the cardiovascular and renal systems during pregnancy is in many respects the antithesis of changes associated with aging," continued Dr. Conrad, who is also professor of obstetrics, gynecology and reproductive sciences and of cell biology and physiology at the University of Pittsburgh School of Medicine. "If we can discover the hormones responsible for these pregnancy changes and how they work, they might be useful for fighting high blood pressure and other cardiovascular diseases such as heart attack and stroke."
Cardiovascular disease remains the No. 1 killer of Americans.
"Relaxin is an ovarian hormone that was discovered in 1926," said Jacqueline Novak, Ph.D., primary study author and assistant professor of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh School of Medicine. "When a woman becomes pregnant, relaxin rapidly increases in the blood. Changes in the renal circulation are nearly at their highest by the end of the first trimester of pregnancy."
Experiments have shown relaxin to be "a potent renal vasodilator even in male rats," said Dr. Novak.
"I don't know where this will go," added Dr. Conrad. "But our studies on relaxin suggest that it may be time to evaluate other female hormones besides estrogen for affects on cardiovascular health - particularly in light of the newest findings on hormone-replacement therapy."
In addition to Drs. Conrad and Novak, study authors include Rolando J.J. Ramirez, Ph.D., and Robin Gandley, Ph.D., both of the Magee Research Institute, and O. David Sherwood, Ph.D., University of Illinois at Urbana-Champaign.
Funding for the study was provided by the National Institutes of Health.
Magee-Womens Research Institute is the country's first research institute devoted to women and infants. It was formed in 1992 by Magee-Womens Hospital of the UPMC Health System. The University of Pittsburgh School of Medicine's department of obstetrics, gynecology and reproductive sciences is one of the top three departments in the country in National Institutes of Health funding.