Plasma progestagen concentrations in the normal and dysmature newborn foal

Radioimmunoassay (RIA) and gas chromatography-mass spectrometry (GC-MS) were used to determine plasma progestagen concentrations in the normal and premature foal. Radioimmunoassay provides a profile of plasma progestagens with respect to time but, due to the non-specific nature of the technique and without prior chromatographic purification, quantitative data based on RIA analysis must be interpreted with caution. In contrast, the greater specificity of GC-MS allows identification of specific plasma progestagens and measuring of multiple analytes in a single analysis. Both techniques demonstrated a marked difference in plasma progestagen concentrations between the normal and abnormal foal. GC-MS studies demonstrated that the plasma steroid profile was dominated by pregnenolone and 5-pregnene-3 beta, 20 beta-diol. Measuring the amounts of these 2 steroids in a single analysis demonstrated persistent high concentrations in premature foals, whereas concentrations decreased rapidly in the first few hours following birth in the normal foal. Preliminary analyses of urinary concentrations in the 2 steroids demonstrated again differences between normal and abnormal foals.