RELATIONSHIPS BETWEEN CALCIUM TRANSPORT AND THE LIPOLYTIC EFFECT OF SHEEP β-LIPOTROPIC HORMONE β-LPH) IN ADIPOSE TISSUE

Abstract

Intravenous injection of β-lipotropic hormone β-LPH) into rabbits caused a marked increase of Ca⁺⁺ concentration in perirenal or epididymal fat tissue. β-LPH also increased the amount of Ca⁺⁺ taken up during incubation of isolated fat cells. Incubation of fragments of rabbit fat tissue in presence of ⁴⁵Ca and ³H mannitol indicated that Ca⁺⁺ accumulated intra-cellularly after administration of β-LPH. In incubation media containing no Ca⁺⁺, or containing Ca⁺⁺ and the Ca⁺⁺ sequestering agent EGTA (ethylenebis [oxyethylene nitrilo]-tetraacetic acid), β-LPH did not induce lipolysis. Addition of excess Ca⁺⁺ to the EGTA containing medium restored lipolysis, whereas addition of EGTA to incubation mixtures containing Ca⁺⁺ in which lipolysis in the presence of β-LPH was already proceeding stopped the lipolytic reaction. These results indicated that Ca⁺⁺ is essential for lipolytic activity of β-LPH as it is for the lipolytic activity of ACTH and other structurally related peptides. Marked shift of Ca⁺⁺ towards the adipose cell was correlated with β-LPH induced lipolysis.