Radioimmunoassay of blood plasma progesterone during estrous cycle in the cow

Abstract

Radioimmunoassay method (RIA) was compared to competitive protein binding assay (CPBA) and fluorometric assay method for the determination of plasma progesterone of the cow. Peri-pheral blood progesterone of the cow during estrous cycle wasdetermined by RIA.
High potent antiserum against progesterone-3-oxime-BSA (optimal dilution, 1 : 40, 000) was prepared for RIA. Calibration curve made by the antiserum showed clear lineality between 0 and 400 pg of progesterone, and percent binding of ³H-progesterone was 70% or higher at 0 pg. The antiserum also showed highly specificity against progesterone, and no significant cross reac-tion was found against other various steroids except 5α-pregnanedione.
In RIA method, values of progesterone determined on the crude samples which was extracted from blood samples with ether (direct method), were compared to those determined on the purified samples obtained by earring out column chromatography (chromatographic method). There was a good correspondence in the values of progesterone between direct and chro-matographic methods.
No significant differences were foundbetween the direct method of RIA, CPBA and flu-orometric assay method, in valuesof progesterone, determined on the same plasma samples collected from the cow atvarious stages of the estrous cycle.
Concentrations of plasma progesterone, determined by the direct method of RIA in 9 cows during estrous cycle, showed minimum level (0.2-0.3 ng/ml) at estrus and maximum level (3.2-5.8 ng/ml) during luteal stage of 11 to 16 days after ovulation. The concentration was rapidly decreased about 4 to 6 days before the next ovulation.