Abstract
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 pD 2 values were approximately 7.4 for isoproterenol and norepinephrine, approximately 5.9 for isopropylnorsynephrine. Phentolamine (1 × 10 −5 M) elevated the maximal norepinephrine effects up to the isoproterenol maxima. Phenoxybenzamine (1 × 10 −5 M) had significantly lower potentiating effects. Phenylephrine depressed lipolytic actions of isoproterenol (1 × 10 −6 M) showing the same pI 2 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 α-blockers nor depressing effects of phenylephrine in human adipose tissue seem related to affecting adrenergic α-receptors. The existence of antilipolytic actions of adrenergic α-receptors is questioned.
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