Changes in urinary and plasma oestrone sulphate concentrations after induction of foetal death in mares at 45 days of gestation

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Abstract
SUMMARY Foetal death was induced in 10 Standardbred mares at day 45 of gestation by injecting 20 to 45 ml of hypertonic (24% W/V) saline into the conceptus at surgery. Ten mares underwent sham treatment and acted as controls. Blood and urine samples were collected every other day between days 30 and 45 post ovulation and at 0, 3 and 6 h relative to the infusion of saline in the treated mares, or sham treatment in control mares. Blood and urine samples were then collected daily between days 46 and 55 post ovulation. Urine oestrone sulphate (E1S) concentrations, measured by radioimmunoassay, increased between day 34 and day 36 of gestation in treated and control groups. In mares in which foetal death was induced, urine EIS concentrations declined post-operatively and were significantly (p (.05) lower than controls by day 50. In plasma, EIS concentrations showed a major increase between days 36 and 40 in both groups. This was followed by a rapid decline after treatment in saline-injected mares, so that by day 48 plasma EIS concentrations in treated mares were significantly (P (.05) lower than the controls. The results show that urinary and plasma EIS concentrations rise rapidly during early pregnancy, and are associated with a viable foetus after day 45 of pregnancy.