Functional evidence that alpha 2A-adrenoceptors are responsible for antilipolysis in human abdominal fat cells

The effects of alpha 2-adrenoceptor agonists (dexmedetomidine, oxymetazoline), alone or in combination with various alpha-adrenoceptor subtype-selective antagonists (CH-38083, idazoxan, WB4101, BRL44408, ARC-239, prazosin), on noradrenaline- and isoprenaline-induced lipolysis were investigated in human isolated abdominal subcutaneous fat cells. The rank order of potency of antagonists in preventing dexmedetomidine- and oxymetazoline-evoked suppression of isoprenaline-induced lipolysis was (pA2-values): CH-38083 (7.69 and 7.48) congruent to idazoxan (7.5 and 7.41) > BRL44408 (7.23 and 7.19) congruent to WB4101 (7.13 and 7.12) > prazosin (5.18 and 5.17) > ARC-239 (4.72, 4.9). While CH-38083 and idazoxan, non-subtype selective alpha 2-adrenoceptor antagonists and BRL44408, a selective alpha 2A-adrenoceptor antagonist as well as WB4101 potentiated the lipolytic effect of noradrenaline, ARC-239, the selective alpha 2B-adrenoceptor antagonist failed to affect it. In addition since the alpha 2A-adrenoceptor selective agonist, oxymetazoline concentration dependently inhibited the lipolytic effect of isoprenaline, and WB4101 and BRL44408 (alpha 2A-adrenoceptor antagonists) antagonised the effect of oxymetazoline in a competitive manner, it is concluded that the alpha 2A-adrenoceptor subtype is involved in antilipolysis. In addition, functional evidence was obtained that there is an interaction between alpha 2A- and beta-adrenoceptors located on the cell surface of adipocytes, through which locally released noradrenaline and/or circulating circulating adrenaline influence lipolysis.