Production and utilisation of antibodies directed against oestrone sulphate using specific hapten synthesis

Oestrone-3-sulphate (E13S) is an important metabolite of oestrone. Studies in cattle had previously shown that it is synthesised in the gravid uterus by the foetus, but not by the corpus luteum. Progesterone measurement in milk by radioimmunoassay (RIA) is routinely carried out in some laboratories as a pregnancy test for cattle. The major drawback of progesterone measurement in milk, by RIA, as a pregnancy test was the failure to detect the lack of conceptus in those cows where early embryonic death had occurred but the corpus luteum still persisted thereby giving false positive results. We have developed a direct RIA for E13S by raising antibodies to an immunogen prepared from a specific hapten synthesised by an unambiguous chemical synthesis. The sensitivity of the RIA in milk was found to be 0.368 nmol/l. The levels of E13S in non-pregnant cows are undetectable but during a viable pregnancy, the levels are elevated to greater than 0.40 nmol/l by day 100. There was no cross-reactions in the assay with any free oestrogens. The measurement of this metabolite of oestrone promises to provide an accurate marker for the detection of a viable conceptus in cattle.