Alpha 2A-adrenergic regulation of cyclic AMP accumulation and lipolysis in human omental and subcutaneous adipocytes.

OBJECTIVE: To characterize differences in alpha 2-adrenergic regulation between subcutaneous and omental adipocytes which could offer a possibility of pharmacological intervention in the metabolic syndrome. DESIGN: Both subcutaneous and omental adipocytes were isolated from 32 patients. Adipocytes were incubated in the presence of adrenoceptor agonists, and cyclic AMP and glycerol levels were measured. alpha 2-Adrenoceptors of isolated plasma membranes were characterized. RESULTS: Adrenaline increased cyclic AMP levels about two-fold in omental adipocytes but had almost no effect in subcutaneous fat cells. The inhibition of cyclic AMP accumulation and glycerol release by UK-14304 and dexmedetomidine was less pronounced in omental adipocytes. The maximal effect of isoprenaline on cyclic AMP levels and glycerol release was similar at the two sites. The subcutaneous and omental alpha-adrenoceptors had similar affinities to 3H-RX821002 and showed characteristics of the alpha 2A subtype. The receptor densities were 220 +/- 21 and 460 +/- 84 fmol/mg of protein (means +/- s.e.m.) in omental and subcutaneous membranes, respectively. CONCLUSION: Inhibition of cyclic AMP accumulation and lipolysis by alpha 2A-adrenoceptors is less pronounced in omental than subcutaneous adipocytes which could be due to differences in receptor number. These differences in alpha 2A-adrenergic regulation could be of value in the treatment of the metabolic syndrome.