Blood pressure (BP) is measured across two parameters - systolic and diastolic. The systolic measure is the top number in a BP measurement. For instance, in a BP of 116/82 millimeters of mercury (mm Hg), the "116" represents the BP measurement when the heart beats, and the "82" (the diastolic pressure) is the pressure when the heart rests between beats.
Hypertension is clinically defined as a consistent systolic BP of 140 mm Hg or higher, and a consistent diastolic BP of 90 mm Hg or higher.
It is estimated that approximately 85 million people in the United States (or 1 in 3 adults) aged 20 and older have hypertension. Of these, almost 20 percent are unaware that they have it.
Because high BP does not usually cause any symptoms, the condition has been dubbed "the silent killer." If high BP is left untreated, it can cause kidney failure, heart attack, angina, stroke, and even heart failure.
Although there are therapies available for treating high BP, the cause remains unknown.
New research, published in the journal Experimental Physiology, set out to investigate the early development of stress-induced hypertension.
The researchers - from the Institute of Cytology and Genetics in Russia - examined physiological changes in rodents using an ISIAH rat model, which is short for inherited stress-induced arterial hypertension.
Changes in arterial blood flow and brain activity may cause hypertension
The scientists induced stress-sensitive hypertension in ISIAH rats, which then developed high BP at 4-6 weeks of age. In an ISIAH model, the hypertension acquired then is sustained throughout their lives.
The team compared the high BP in 10 male ISIAH rats with a normal BP control group of eight male rats. They used MRI techniques to assess the hemodynamic and the changes in brain metabolites in the two groups at 1 month and 3 months of age, respectively.
With aging, the scientists noticed changes in the blood flow rates to certain arteries. Specifically, they noted an increased blood flow in the renal arteries, and a decreased blood flow in the abdominal aorta.
In ISIAH rats, the scientists also noticed a decrease in renal vascular resistance that occurred with age. However, renal vascular resistance remained higher than that of control rats at both 1 month and 3 months of age.
The study also revealed differences in brain activity. The ISIAH rat group revealed a decrease in the prefrontal cortex and an increase in the hypothalamus - neither of which were noticed in the control group.
Additionally, the hypothalamus of 3-month-old rats showed more excitatory neurotransmitters than inhibitory ones.
"Thus," the authors conclude, "the early development of the stress-sensitive hypertension in the ISIAH rats is accompanied by considerable changes both in brain metabolite ratios and in the parameters of blood flow through the main arteries."
This goes some way toward proving that there is a link between the development of hypertension and changes in brain activity and arterial blood flow. The authors speculate that these changes - especially if they take place in early life - could trigger hypertension.
"The study of early physiological changes in ISIAH rats may help clarify the cause of high blood pressure. Understanding this could help us prevent the disease early on."
Alisa Seryapina, first author