Study could explain sex differences in nighttime blood pressure swings

A recently published mouse study may offer clues about why premenopausal women are less prone than men to “nondipping hypertension,” a condition in which blood pressure doesn’t drop its normal 10 to 20 percent at night.

“Loss of circadian rhythms in physiological function is associated with poor cardiovascular outcomes,” wrote Lauren Doma, PhD, a postdoctoral fellow at the University of Florida College of Medicine, and co-authors in the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology.

“Indeed, nondipping hypertension is a predictor of cardiovascular events and is associated with an increased risk of chronic kidney disease and adverse cardiovascular events.”

The group’s previous research demonstrated that knocking out PER1—one of the core circadian clock genes—resulted in nondipping hypertension in male mice exposed to a high-salt treatment. However, female mice without PER1 in this study appeared to be unaffected by this phenomenon and continued to exhibit the usual nighttime decline in blood pressure.

“The observation that the female Per1-(knockout mice) are protected from nondipping hypertension relative to male Per1-KO mice is consistent with human literature that premenopausal women are less likely to exhibit nondipping hypertension,” the authors wrote. “This study represents an important step in understanding sex differences in the regulation of cardiovascular function by the circadian clock.”

Doma et al. suspect ovarian hormones play a role in maintaining the circadian rhythms of female mice, a theory they plan to test in future studies. This could help explain why heart disease is less prevalent in premenopausal women versus men, they said, and why the sex-specific incidence of cardiovascular disease tends to narrow at older ages. Evidence from human studies suggests postmenopausal women have higher rates of nondipping.

“This specific study really represents the beginning of what could be a long-term line of investigation,” study co-author Michelle Gumz, PhD, with the UF College of Medicine’s division of nephrology, hypertension and renal transplantation, said in a press release. “I feel like we’ve barely begun to scratch the surface of what is happening.”