Enzyme-linked immunosorbent assay for apolipoprotein A-I in the serum of cattle

An ELISA was developed to evaluate the concentration of apolipoprotein A-I, a major apoprotein in high-density lipoprotein, in the serum of cattle. Serum apolipoprotein A-I was purified electrophoretically, and antibodies to this protein were raised in rabbits. The specificity of the antiserum was assessed by use of several immunologic techniques including western blotting. The ELISA was sensitive (detection limit was 70 ng of apolipoprotein A-I/ml) and reliable (coefficients of variance were in the range of 3.5 to 8.2%). By use of this method, the serum apolipoprotein A-I concentration was higher in 2- to 6-year-old Holstein cows (mean +/- SD, 0.580 +/- 0.304 mg/ml) than in 7- to 15-month-old heifers (0.339 +/- 0.237 mg/ml), 6-month-old heifers (0.238 +/- 0.188 mg/ml), and 6-month-old steers (0.173 +/- 0.146 mg/ml). The concentration, however, is not largely different in cows in early, middle, and late lactation and in non-lactating stages. Results also indicated that apolipoprotein A-I concentration was decreased in cows with hepatic lipidosis (fatty liver) induced by administration of ethionine, suggesting that this method is a useful tool for the pathophysiologic study of lipid metabolism and its impairment in cattle.