Effect of essential fatty acid deficiency on activity of liver plasma membrane enzymes in the rat

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Abstract
Liver plasma membranes (LPM) were isolated from rats fed an essential fatty acid‐supplemented diet (+EFA) or from rats fed an essential fatty acid‐deficient diet (‐EFA). The proportions of linoleate and arachidonate in membrane total fatty acids in the −EFA preparations were one‐half or less than the values for the +EFA preparations. Basal, F−, or glucagon‐stimulated adenylate cyclase activities were significantly lower in EFA‐deficient livers than in nondeficient ones. Addition of GTP significantly enhanced glucagon‐stimulated adenylate cyclase in both groups, but extent of stimulation above basal was greater in EFA‐deficient livers. Portal vein injection of glucagon in vivo resulted in significantly higher cAMP formation in +EFA livers than in −EFA livers. When glucagon was used in vitro at 1–1,000 nM, stimulation of adenylate cyclase remained lower in EFA‐deficient membranes, but extent of stimulation above basal activity was larger in −EFA membranes than in +EFA. Total Na+, K+ (Mg2+)‐ATPase from EFA‐depleted LPM exhibited significantly higher values of apparent Km and Vmax. 5′‐Nucleotidase activity, in contrast, was considerably decreased in EFA‐deficient rats. These findings show that, in animals, changes in unsaturated fatty acid composition can affect the properties of membrane‐bound enzymes. These alterations could be due to changes in membrane physical properties and/or prostaglandin formation.
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