Norepinephrine turnover in brown and white adipose tissue after partial lipectomy

Total body fat is restored after the surgical removal (i.e., partial lipectomy) of white adipose tissue (WAT), and this is accomplished via increases in the mass of nonexcised WAT pads. The underlying mechanism for this apparent regulation of total body fat is unknown. One possibility is via the sympathetic nervous system (SNS) innervation of WAT and brown adipose tissue (BAT) through the regulation of lipolysis and thermogenesis, respectively. Specifically, decreases in SNS activity might fuel lipectomy-induced body fat compensation through energy saved from decreased BAT thermogenesis and would promote lipid accretion through decreased WAT basal lipolysis. Therefore, we tested whether lipectomy triggered decreases in the SNS drive [as indicated by the norepinephrine turnover (NETO)] to nonexcised WAT or to BAT, at times before the lipectomy-induced fat pad mass compensation was complete. Siberian hamsters received either sham or bilateral epididymal WAT lipectomy, and NETO was measured in the remaining WAT and interscapular BAT (IBAT) before, and 3 and 6 weeks after surgery. Total dissected WAT, and inguinal and retroperitoneal WAT masses were significantly increased following lipectomy, whereas dorsal subcutaneous WAT and IBAT masses, as well as food intake, were unchanged. The only significant change in NETO was a marked decrease (approximately 90%) in IBAT NETO at Week 3 postlipectomy compared with the sham-lipectomized controls. These findings suggest that the lipid accretion of nonexcised WAT pads triggered by lipectomy may be partially fueled by decreased BAT thermogenesis, inasmuch as decreased IBAT NETO reflects decreased BAT heat production.