Effect of phenylephrine on lipolysis in rat adipocytes: No evidence for an α-adrenergic mechanism

Abstract

1. 1. Phenylephrine. a strong α 1-adrenergic agonist, exerted a concentration dependent antilipolytic effect against isoproterenol-activated lipolysis in rat adipocytes with the effect decreasing as the isoproterenol concentration increased. 2. 2. The α-adrenergic antagonists phentolamine and phenoxybenzamine did not reverse phenylephrinc's antilipolytic effect. 3. 3. Phenylephrine alone activated lipolysis at concentrations above 10 −5M and at 5 × 10 −4 M the rate of lipolysis was increased 3.4-fold. Propranolol abolished this effect. 4. 4. In the presence of sub-maximum concentrations of dibutyryl cyclic-AMP (< 10 −4M), 10 −4M phenylephrine increased the rate of lipolysis above that activated by dibutyryl cyclic-AMP alone. At maximum dibutyryl cyclic-AMP concentrations, or in the presence of propranolol, phenylephrine had no effect on dibutyryl cyclic-AMP-dependent lipolysis. 5. 5. There is no evidence to support an α 1-adrenergic mechanism for regulation of lipolysis in the rat adipocyte. All effects of the α-adrenergic agonist phenylephrine appear to be due to its weak β -adrenergic activity.