Abstract
Biopsy samples of subcutaneous adipose tissue of lactating cows were used to study the noradrenalin-stimulated lipolysis and its inhibition by free (unesterified) fatty acids. A reciprocal relationship was found between the rate of lipolysis and the molar ratio of free fatty acid to albumin in the medium, both when the concentration of free fatty acids and that of albumin was varied. The release of glycerol and free fatty acids from the tissue into the medium is gradually inhibited when the fatty acid to albumin ratio increases from 0.1 to 6.5. When this ratio exceeds 4, fatty acid release is inhibited to a greater extent than glycerol release. With increasing fatty acid to albumin ratios, the amount of free fatty acids which is associated with the adipose tissue also rises. This accumulation of free fatty acid in the tissue is probably responsible for the inhibition of lipolysis. It was found that after parturition the plasma free fatty acid level of dairy cows rises to 0.7–1.0 mM, corresponding to a free fatty acid to albumin ratio in the blood of 1.5–2.0. At the same time the level of tissue-associated free fatty acids in the subcutaneous adipose tissue increases from about 1 to 2–4 μmoles/g wet weight. All these values are in the range where inhibition of lipolysis is observed in vitro. It is suggested, therefore, that also in vivo the degree of saturation of plasma albumin with fatty acids is one of the regulatory factors of fat mobilization in adipose tissue.
Published Version
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