Leptin-Induced Hypertension Linked to Adrenergic Activation
--------------------------------------------------------------------------------
CHICAGO (Reuters Health) Sept 24 - Researchers at the University of Mississippi, Jackson, report that leptin's effect on blood pressure appears to be mediated through the hormone's activation of the adrenergic system, and counteracted by beta blockade.
Dr. John E. Hall noted to attendees of the American Heart Association's 55th Annual Conference and Scientific Sessions of the Council for High Blood Pressure Research, held here in Chicago on Sunday, that excess weight accounts for about 70% of all hypertension in humans.
"What we've been searching for," said Dr. Hall, "is the link between weight gain and how the sympathetic nervous system...is triggered to raise blood pressure and heart rate."
The investigators implanted catheters into the abdominal aortas and vena cavae of Sprague-Dawley rats. They then infused the animals with leptin, followed by a placebo, the alpha-blocker terazosin, or the beta-blocker propranolol.
Leptin infusion reduced food intake and fasting plasma insulin levels in all animals, the investigators observed. Adrenergic blockade effectively inhibited increases in mean arterial pressure and heart rate.
"This mouse experiment was designed to determine whether it was through the sympathetic nervous system that leptin does raise blood pressure," Dr. Hall told meeting attendees. "And what we showed here was that the effect of leptin to raise the blood pressure and heart rate is caused entirely by the sympathetic nervous system, because after blocking this system, we find that leptin no longer raises the blood pressure."
Dr. Hall said this study shows that not only might leptin be a major link in the chain of events leading to obesity, but also that "the increased nervous system activity is the key mechanism by which leptin does raise blood pressure."
Assuming these findings apply to humans, said Dr. Hall, it is much too early to talk about therapies to block this leptin-induced sequence of events. For now, overweight people with hypertension can reduce leptin levels only by losing weight. |
