Hindsight: Bound Leptin and Sympathetic Activity
Saturday, June 23, 2012
As readers are probably well aware, leptin is one of the key hormones (secreted by fat cells), that regulate energy balance – not just by affecting food intake but also energy output. The latter happens in part through stimulation of the sympathetic nervous system.
In a paper we published in the Journal of Clinical Endocrinology and Metabolism in 2003, we examined the relationship between both free and protein-bound plasma leptin levels and sympathetic activity as assessed by microneurography.
Study participants included 25 healthy normal weight men, 8 individuals with central (multiple system atrophy) and 4 individuals with peripheral (pure) autonomic failure. Baroreflex sensitivity was measured using phenylephrine and nitroprusside infusions.
MSNA was consistently correlated with protein-bound leptin concentrations but not with free leptin levels. MSNA at baseline was about 15 bursts per minute in subjects with lower and about 24 bursts per minute in subjects with higher bound leptin concentrations.
We concluded that protein-bound rather than free leptin levels are correlated with basal sympathetic outflow, a relationship that was difficult to explain through a direct central nervous effect of protein-bound leptin. Rather, we suggested that protein-bound leptin may increase sympathetic vasomotor tone indirectly via a baroreflex mechanism.
According to Google Scholar, this paper has been cited 26 times.
AMS
Edmonton, Alberta
Sunday, June 24, 2012
It would be fascinating to hear hypothetical implications of this research connecting protein-bound Leptin and sympathetic vasomotor tone given the complex relationship between sympathetic nervous system and its role in activating the pituitary-adrenal-hypothalamic axis. Relying on polyvagal theory, for instance, a hypothesis could be tested to detect changes in vasovagal tone resulting from alterations in bioavailability of Leptin and the resulting physiological adaptations to various forms of stress. I am curious about the homeostatic role of intrinsic biochemical agents produced by fat (an essential organ), such as hormones, including Leptin, which may mediate stress responses differently in individuals who have never carried large amounts of fat and individuals who are formerly obese. Thanks, as always, for providing salient sources of research that underscores the complexity of various obesities.