Effect of central and peripheral body fat distribution on sympathetic and baroreflex function in obese normotensives.
BACKGROUND
Previous studies have shown that obesity is characterized by a sympathetic overactivity coupled with an insulin resistance state and a baroreflex impairment. The present study was set out to compare the effects of peripheral versus central obesity on sympathetic, metabolic and reflex function.


METHODS
In 36 lean subjects (age 35.8 +/- 1.4 years, mean +/- SEM), 20 subjects with peripheral obesity (PO) and 26 subjects with central obesity (CO), all age-matched and with normal blood pressure values, we measured beat-to-beat arterial blood pressure (Finapres), heart rate (HR, ECG), homeostasis model assessment (HOMA) index, plasma norepinephrine (NE, high-performance liquid chromatography) and postganglionic muscle sympathetic nerve traffic (MSNA, microneurography) at rest and during baroreceptor stimulation and deactivation induced by stepwise intravenous infusions of phenylephrine and nitroprusside, respectively.


RESULTS
Both HOMA index, NE and MSNA values were significantly increased (P < 0.01) in obese as compared with lean individuals. Subjects with CO displayed MSNA and HOMA values significantly greater than those found in individuals with PO (65.4 +/- 2.0 versus 47.9 +/- 1.9 bs/100hb and 2.85 +/- 0.10 versus 2.43 +/- 0.11 a.u., respectively, P < 0.05 for both). Both in male and female subjects with CO or PO, MSNA, HOMA index and waist-to-hip ratio were significantly related to each other. Baroreceptor-HR and -MSNA control was significantly (P < 0.01) impaired in obese as compared with lean subjects, the degree of impairment being similar in CO and PO.


CONCLUSIONS
These data suggest that CO is characterized by a sympathetic activation greater for magnitude than that detectable in PO. This appears not to be related to gender or to baroreflex mechanisms but rather to metabolic factors, i.e. to the greater insulin resistance characterizing CO.
Grassi
Guido
G
Clinica Medica, Dipartimento di Medicina Clinica, Prevenzione e Biotecnologie Sanitarie, Università di Milano-Bicocca, Milano, Italy.
Dell'Oro
Raffaella
R
Facchini
Annalisa
A
Quarti Trevano
Fosca
F
Bolla
Giovanni Battista
GB
Mancia
Giuseppe
G
D000328:Adult; D000959:Antihypertensive Agents / Q000494:pharmacology; D017704:Baroreflex; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D006706:Homeostasis; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation; D009599:Nitroprusside / Q000494:pharmacology; D009638:Norepinephrine / Q000097:blood; D009765:Obesity / Q000097:blood / Q000473:pathology* / Q000503:physiopathology*; D010656:Phenylephrine / Q000494:pharmacology; D011311:Pressoreceptors / Q000187:drug effects / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D013566:Sympathomimetics / Q000494:pharmacology; D049629:Waist-Hip Ratio
D000959:Antihypertensive Agents; D013566:Sympathomimetics; D009599:Nitroprusside; D010656:Phenylephrine; D009638:Norepinephrine