Influence of Bovine LH Tracer Quality on Levels of LH In GnRH-Treated Cows

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Abstract
Chromatography of 125I-bovine LH (LER-1716-2 and USDA-I-1) by means of anion exchange high performance liquid chromatography (HPLC) revealed two main peaks of radioactivity regardless as to whether or not the tracer was initially purified on cellulose CF11. The content of radioactivity in the first peak tended to increase as the storage time of the bLH preparation, either before or after iodination, increased. The first peak of radioactivity after HPLC fractionation either with or without cellulose adsorption consisted of rraterial with low binding ability to bLH antisem (6.9%∗0.5 and 13.0%k1.0, respectively) and high binding ablity to ovine LHa antiserum (51.0%k2.7 and 35.2%f3.6, respectively). The average ratio of a-subunit hno- reactivity to 1251-bLH inmunoreactivity in this material was 7.4k0.1 and 2.7k0 2 respectively (P<0.001). Peaks in 1251-bLH radioactivity and i2hI-bLH irrnrmnoreactivity had different elution times. Radioinmunoassays with tracers obtained from fractions derived from the first radioactive peak after HPLC chromatography (i.e. 1251-bLH-LEEt-1716-2) both with and without cellulose adsorption, yielded significantly lower mean plasm LH levels in GnRH-treated cows conpared with the control tracer routinly purified only on cellulose CFll (e.g. 5.7 vs. 8.2 pg/; 4.6 vs. 8.2 pg/l). Plasm LH levels in GnRH-treated cows were (significant1 P<O.OO1) lower as measured by radiohncassay utilizing T25 I-USDA-blH-I-1 tracers than by radioinmunoassays utilizing 1251-blH-LER-17L6-2 tracers (i.e. ej-ther Y = 0.17 + 0.75X or Y = 1.18 + 0.60X).

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