Adrenergic lipolysis in human adipose tissue in vitro.

In human adipose tissue in vitro, dose-response curves of lipolytic agents in releasing free fatty acids and glycerol into an albumine-containing medium were followed. Norepinephrine and adrenaline produced about 20% of the maximal effect of isoproterenol, isopropylnorsynephrine about 40%, theophylline more than 100%. Found pD2 values were approximately 7.4 for isoproterenol and norepinephrine, approximately 5.9 for isopropylnorsynephrine. Phentolamine (1 times 10-5 M) elevated the maximal norepinephrine effects up to the isoproterenol maxima. Phenoxybenzamine (1 times 10-5 M) had significantly lower potentiating effects. Phenylephrine depressed lipolytic actions of isoproterenol (1 times 10-6 M) showing the same pI2 value 3.0 as well in human as in rat adipose tissue and exerted per se weak lipolytic effects also. It is concluded neither potentiating actions of alpha-blockers nor depressing effects of phenylephrine in human adipose tissue seem related to affecting adrenergic alpha-receptors. The existence of antilipolytic actions of adrenergic alpha-receptors is questioned.