Evaluation of serum apolipoprotein C-III concentration by enzyme-linked immunosorbent assay and its higher concentration in cows during midlactation than during the nonlactating stage

Abstract

Abstract Objective To determine serum apolipoprotein C-III (apoC-III) concentration in cows in various stages of lactation by use of an ELISA. Sample Population Sera obtained from 29 Holstein cows during early lactation, 65 cows during midlactation, 42 cows during late lactation, and 23 cows during the nonlactating stage. Procedure A 7.3-kd bovine apoC-III antiserum raised in rabbits was purified by affinity chromatography, and an ELISA was developed. Results In the immunoblot analysis, the antiserum reacted with the 7.3-kd apoC-III and moreover with another 8.2-kd apoC-III isoform. The 2 isoforms of apoC-III were also indistinguishable in the developed ELISA, the 2 proteins being measured as total apoC-III. In the ELISA for serum apoC-III concentration, addition of 2-mercaptoethanol to the coating buffer (50 mM sodium carbonate buffer, pH 9.6) was required. Mean ± SEM bovine serum apoC-III concentration (μg/ml of serum) was 71.6 ± 12.1 for the early lactating stage, 115 ± 14.0 for the midlactating stage, 104 ± 18.8 for the late lactating stage, and 55.3 ± 8.4 for the nonlactating stage. Concentration of apoC-III was significantly (P < 0.05) higher in cows during midlactation than in cows during the nonlactating stage and was correlated negatively with serum triglyceride concentration (r = −0.479; P< 0.01) and positively with total cholesterol (r = 0.421; P < 0.05) and phospholipids (r = 0.415; P < 0.05) concentrations. Conclusions Changes of apoC-III concentration in various stages of lactation suggest that this apolipoprotein is involved in a function related to lactation. (Am J Vet Res 1998;59:1358–1363)