Effects of Hypo- and Hyperthyroidism on Noradrenergic Activity and Glycerol Concentrations in Human Subcutaneous Abdominal Adipose Tissue Assessed with Microdialysis

Thyroid hormones play a major role in lipid metabolism. However, whether they directly affect lipolysis locally in the adipose tissue remains unknown. Therefore, we measured abdominal sc adipose tissue norepinephrine (NE), basal, and isoprenaline-stimulated lipolysis in 12 hypothyroid patients (HYPO), six hyperthyroid patients (HYPER), and 12 healthy controls by in vivo microdialysis. Adipose tissue NE was decreased in HYPO and increased in HYPER compared with controls (90.4 ± 2.9 and 458.0 ± 69.1 vs. 294.9 ± 19.5 pmol/liter, P < 0.01). Similarly, basal lipolysis, assessed by glycerol assay, was lower in HYPO and higher in HYPER than in controls (88.2 ± 9.9 and 566.0 ± 42.0 vs. 214.3 ± 5.1 μmol/liter P < 0.01). The relative magnitude of isoprenaline-induced glycerol increase was smaller in HYPO (39 ± 19.4%, P < 0.05 vs. basal) and higher in HYPER (277 ± 30.4%, P < 0.01) than in controls (117 ± 5.6%, P < 0.01). The corresponding changes in NE after isoprenaline stimulation were as follows: 120 ± 9.2% (P < 0.05), 503 ± 113% (P < 0.01), and 267 ± 17.2 (P < 0.01). In summary, by affecting local NE levels and adrenergic postreceptor signaling, thyroid hormones may influence the lipolysis rate in the abdominal sc adipose tissue.