NAASO Meeting 2005, Vancouver #2
Impaired Lipolysis in Perifused Retroperitoneal and Subcutaneous Adipocytes from Obese Hypertensive SHROB Rats Relative to Lean SHR Littermates
Janean Johnson & Paul Ernsberger
Recent studies in human and rat adipocytes have shown that cells isolated from obese subjects are deficient in fatty acid mobilization. We tested lipolytic response not in a static incubation but in a perifusion system to mimic contact with the circulation, to reduce autocrine effects, and to allow continuous monitoring of glycerol output. We compared freshly isolated retroperitoneal adipocytes from SHROB (Koletsky) rats which have a naturally occurring knockout of the leptin receptor relative to lean SHR littermates. We also tested subscapular adipocytes from SHROB. A perifusion system was used to reduce autocrine effects and allow continuous monitoring of glycerol output in 4min fractions. Krebs' medium was perifused at 0.25mL/min and contained 1 mg/mL albumin as a lipid carrier and 2 μg/mL adenosine deaminase. The first 4 fractions defined baseline glycerol concentration, which was higher in SHROB than in SHR retroperitoneal adipocytes (27±2 vs. 21±2μM), and higher still in SHROB subscapular adipocyte perifusates (42±4μM). As shown in the figure, the response of retroperitoneal adipocytes to 4min exposure 1μM isoproterenol was robust in SHR, with a maximum increase of nearly 75% in the rate of glycerol efflux, peaking at 12 min and recovering only gradually over the next 16 min. The isoproterenol response in SHROB was attenuated by two-thirds in peak magnitude and also reduced in duration. Subscapular adipocytes showed no detectable lipolytic response to 1μM isoproterenol. Insulin (10 and 100 nM) suppressed glycerol release in both basal and isoproterenol-stimulated conditions, and 1 nM insulin almost completely suppressed responses even in insulin resistant SHROB cells. Impaired mobilization of adipocyte triglyceride in SHROB may contribute to resistance to weight loss and susceptibility to weight regain.
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