From New Orleans, La., at Experimental Biology 2002
In early pregnancy, several days of intense, unremitting mental stress in a mother–such as might occur with the death of a loved one or loss of a job–may reprogram a baby's development in ways that foster high blood pressure in adulthood. That conclusion, from Australian studies with sheep, supplies a physiologic basis for the link between fetal stress and adult hypertension that has been suggested by several studies of human populations.
E. Marelyn Wintour-Coghlan and her colleagues at the University of Melbourne continuously administered cortisol–a natural stress hormone–to pregnant sheep for 2 days during their 5-month pregnancies. The researchers induced blood concentrations of cortisol that are typical in highly stressed animals. In an upcoming FASEB Journal, Wintour-Coghlan's team reports that cortisol can cross the placenta from mother to fetus.
In the current study, some ewes received cortisol early–during a period corresponding to between the fifth and seventh week of human gestation, some toward the middle of pregnancy, and others not at all. The ewes' lambs were then studied for up to 7 years–into late middle age.
The Australian team showed that at birth, the animals exposed to cortisol early in their fetal development had unusual gene expression in organs controlling blood pressure. By 5 months of age, these offspring began showing blood pressure higher than that of animals whose mothers were stressed later or not stressed. The pressure was elevated by up to 15 millimeters of mercury (mmHg) in males and 10 to 12 mmHg in females. In human populations, even a 2-mmHg increase in blood pressure can heighten risk of cardiovascular disease.
By age 7, animals born into the early-stress group had enlarged hearts and 40 percent fewer blood-filtering units in their kidneys. Wintour-Coghlan, a fetal physiologist, suspects that with fewer such units, called nephrons, the animals may retain somewhat more dietary salt.
"The little extra retained salt will tend to increase the blood volume and the work of the heart–leading to hypertension," she told Science News. The "astonishing fact," she adds, is that the tissue that would develop into kidneys didn't yet exist during the early fetal exposure to cortisol in the study.
Wintour-Coghlan advises that pregnant women should regularly take time to relax. She suggests a swim, a distracting book, or perhaps a cup of chamomile tea.
E. Marelyn Wintour-Coghlan
Howard Florey Institute
University of Melbourne