Key result
Obese men exhibited a significantly blunted beta-adrenergically mediated lipolytic response per unit of abdominal subcutaneous adipose tissue compared to lean men (Δ total glycerol release: 140 vs 394 nmol/100g/min).
Why the study?
Does beta-adrenergic stimulation with isoprenaline reveal an impaired lipolytic response in abdominal subcutaneous adipose tissue of obese compared to lean men?
Observational (n=23)
No
Does beta-adrenergic stimulation with isoprenaline reveal an impaired lipolytic response in abdominal subcutaneous adipose tissue of obese compared to lean men?
Absolute Event Rate: 140% vs 394%
p-value: p=<0.05
Obese men exhibit a systematically blunted beta-adrenergically mediated lipolytic response in abdominal subcutaneous adipose tissue compared to lean men, which may contribute to the maintenance of increased fat stores.
May sustain fat accumulation in obesity; hypothesis-generating for beta-adrenergic adipose pathways without practice implications.
AIMS/HYPOTHESIS: Obesity is characterised by increased triacylglycerol storage in adipose tissue. There is in vitro evidence for a blunted beta-adrenergically mediated lipolytic response in abdominal subcutaneous adipose tissue (SAT) of obese individuals and evidence for this at the whole-body level in vivo. We hypothesised that the beta-adrenergically mediated effect on lipolysis in abdominal SAT is also impaired in vivo in obese humans. METHODS: We investigated whole-body and abdominal SAT glycerol metabolism in vivo during 3 h and 6 h [2H5]glycerol infusions. Arterio-venous concentration differences were measured in 13 lean and ten obese men after an overnight fast and during intravenous infusion of the non-selective beta-adrenergic agonist isoprenaline [20 ng (kg fat free mass)(-1) min(-1)]. RESULTS: Lean and obese participants showed comparable fasting glycerol uptake by SAT (9.7+/-3.4 vs 9.3+/-2.5% of total release, p=0.92). Furthermore, obese participants showed an increased whole-body beta-adrenergically mediated lipolytic response versus lean participants. However, their fasting lipolysis was blunted [glycerol rate of appearance: 7.3+/-0.6 vs 13.1+/-0.9 micromol (kg fat mass)(-1) min(-1), p<0.01], as was the beta-adrenergically mediated lipolytic response per unit SAT [Delta total glycerol release: 140+/-71 vs 394+/-112 nmol (100 g tissue)(-1) min(-1), p<0.05] compared with lean participants. Net triacylglycerol flux tended to increase in obese compared with lean participants during beta-adrenergic stimulation [Delta net triacylglycerol flux: 75+/-32 vs 16+/-11 nmol (100 g tissue)(-1) min(-1), p=0.06]. CONCLUSIONS/INTERPRETATION: We demonstrated in vivo that beta-adrenergically mediated lipolytic response is impaired systematically and in abdominal SAT of obese versus lean men. This may be important in the development or maintenance of increased triacylglycerol stores and obesity.
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Jocken et al. (2007) conducted an observational in Obesity (n=23). Isoprenaline vs. Lean men was evaluated on Δ total glycerol release per unit abdominal subcutaneous adipose tissue (nmol/100g/min) (p=<0.05). Obese men exhibited a significantly blunted beta-adrenergically mediated lipolytic response per unit of abdominal subcutaneous adipose tissue compared to lean men (Δ total glycerol release: 140 vs 394 nmol/100g/min).
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