COPPER DEFICIENCY INCREASES TOTAL PROTEIN AND APOLIPOPROTEIN-A-I SYNTHESIS IN THE RAT SMALL-INTESTINE

This study was designed to determine whether an enhanced intestinal sy nthesis of apolipoprotein (ape) A-l is associated with the hyperapolip oproteinemia observed in copper-deficient rats. Male weanling Sprague- Dawley rats were assigned to two dietary treatments, Cu deficient (0.6 ppm Cu) and Cu adequate (6.0 ppm Cu) for 6 weeks. In vive studies wer e then performed after rats were injected with a flooding dose of 150 mu M [H-3]phenylalanine (PHE, 50 mu Ci/ml/100 g body wt). Three rats f rom each treatment were sacrificed at 5, 10, 15, 30, and 60 min postin jection. The small intestine was rapidly rinsed and frozen in liquid N -2. In vitro studies were performed by labeling freshly isolated 6-cm segments from duodenum, jejunum, and ileum with [H-3]PHE (33 mu Ci/ml, 49.7 Ci/mmol) in PHE-free minimum essential medium for 7 and 14 min. In vive and in vitro intestinal samples were sonicated, solubilized in 1% Triton X-100, and centrifuged to provide the detergent soluble fra ction for the isolation of nascent apo A-l and total protein. Radioact ivities associated with nascent apo A-l isolated by immunoprecipitatio n and SDS-PAGE, and with total protein precipitated by trichloroacetic acid, were measured to determine the influence of cu deficiency on na scent apo A-l and total protein synthesis. In the Cu-deficient small i ntestine, the synthesis of total protein was measured only in the duod enum and was enhanced after 1 hr for the in vive studies. Moreover, to tal protein synthesis was enhanced at both 7 and 14 min of the in vitr o studies for all three small intestinal segments of the cu-deficient rats. 400 A-l synthesis was measured only at the jejunum and was also enhanced by cu deficiency in the in vitro studies. Thus, an increase i n intestinal apo A-l synthesis may contribute to the elevated plasma a po A-l level in Cu-deficient rats.