New rat work examines the role of perivascular adipose tissue (PVAT)— the fat that forms around the arteries— in preserving vascular santé. The findings could have implications for conditions such as hypertension and atherosclerosis.
The study’s first and corresponding author is Stephanie Watts, a professor of pharmacology and toxicology at the College of Osteopathic Medicine at Michigan State University in East Lansing.
In their paper, Prof. Watts and the team explain that PVAT secretes substances which help to relax the arteries, noting that this is a known fact in the medical community.
They hypothesized that there was another way in which PVAT could be good for the arteries in addition to producing those vasoactive substances.
More precisely, the scientists wondered if it might be something systemic about PVAT in itself rather than the vasoactive substances that lead to blood vessel health.
We did a series of tests with rats to find out. They then published their findings in Scientific Reports, the journal Nature.
PVAT improves stress relaxation
The scientists studied Sprague Dawley rats ‘ thoracic aorta rings with and without PVAT, observing how tissue tension relaxed in over 30 minutes.
The term “stress relax” refers to the ability of the artery, after stretching or straining, to release muscle tension.
Prof. Watts and team have observed in the new experiments that the thoracic aortas of rats with PVAT have more stress relief than those without PVAT.
“The presence of PVAT increased the amount of relaxing stress,” the authors write. In fact”[ a] PVAT ring separated from the aorta showed a deeper relaxation of stress than the aortic ring itself did.”
“In our study, PVAT reduced the tension that blood vessels experience when stretched. And that’s a good thing because the vessel then expends less energy. It’s not under as much stress.”
– Prof. Stephanie Watts
When looking at the thoracic aorta— which envelops brown fat — the researchers also tested the superior mesenteric artery, which is surrounded by white fat.
Studies in both arteries showed the same result: In the existence of PVAT, there was more tension relief than in its absence.
“So, that shows us, it’s not just a one-off,” Prof. Watts says. “It’s not something that you see only in this particular vessel, or in this particular species or strain. But that maybe it is a general phenomenon.”
Importantly, the tests also showed that it was PVAT’s unique structure, not just its presence, that was crucial to its ability to boost relaxation in stress.
“When PVAT mass remained in the tissue bath while attached to the tissue but no longer included the aorta ring, it lost its ability to aid relaxation of arterial stress,” the authors note.
Redefining ‘functional blood vessels’
The researchers believe the findings will help redefine the function of PVAT, as well as the blood vessel structure.
Experts have believed until now, they explain, that PVAT only served to store fat, and that the standard blood vessel structure consisted of three parts: an innermost layer, a middle layer, and an outermost layer.
The researchers believe PVAT should be considered by the medical community as the fourth structural layer of a blood vessel.
“We ignored this layer for years-it was thrown out in the laboratory; it wasn’t pictured in the clinic. Yet now we think this could be important to our blood vessels,” says Prof. Watts.
“Our finding redefines what the functional blood vessels are and is part of what can be dysfunctional in diseases that afflict us, including hypertension. We need to pay attention to this layer of a blood vessel because it does far more than we originally thought.”
– Prof. Stephanie Watts
The authors note in the paper that”[ t]he loss of PVAT’s’ anti-contractile’ structure, including the development of endothelial dysfunction, was observed in[ several] cardiovascular disease models,” including diabetes, and in various species.