Abstract
The present study was undertaken to develop a novel, practical and simple procedure for enzyme immunoassay of plasma estrone sulfate (E1S) in cows. Diluted plasma was applied directly to wells without extraction and incubated with anti-estrone antibody and horseradish peroxidase-labeled estrone. The sensitivity of the assay was estimated as 40 pg/ml. The intra-assay and inter-assay coefficients of variation were 7.8-9.6% and 7.2-14.4%, respectively. When 2, 5, 10 and 20 ng of E1S were added to 1 ml of plasma, the recovery rates ranged between 84.6 and 98.5%. Only 3 hr were needed to complete an assay to measure E1S concentration. Plasma concentrations of E1S were measured in six crossbred cows after the first trimester of pregnancy. A dramatic increase in the plasma concentrations of E1S was observed from days 240 to 284 of gestation (7.40-13.00 ng/ml to 18.00-36.00 ng/ml). These results suggest that the present direct enzyme immunoassay is a practical and suitable method for measuring the plasma concentration of E1S.
