However, at 18 months of age, the females have the same blood pressure as the males. Also, unlike humans, the older female rats used in the UMC research have a normal level of estrogen. The researchers are focusing on what happens after menopause. Dr. Reckelhoff says it's not the loss of estrogen that causes hypertension, because women don't become hypertensive immediately after menopause. Rather, the increase takes about 10 years.
Research is unclear on whether testosterone levels increase in women after menopause.
Dr. Reckelhoff says some studies show the levels remain the same, while others appear to prove an increase. Others, in fact, show a slight decrease. It's possible, though, that post-menopausal women develop a sensitivity to testosterone, at whatever level it is present. Such a sensitivity, suggests Dr. Reckelhoff, that even though testosterone levels are much higher in men, the hormone's effect on blood pressure is just as significant in older women. Dr. Reckelhoff says if her hypothesis is correct, physicians might need to look more closely at hormone replacement therapies that include testosterone.