Radioimmunoassay for PMSG and its application to in-vivo studies.

A double-antibody radioimmunoassay for PMSG, especially for meauring PMSG in cattle blood after exogenous application, has been developed. A rabbit antiserum against PMSG and pure PMSG for radioiodination were used. There was a strong cross-reaction against equine LH and FSH, but the slight cross-reaction against bovine LH and FSH could be eliminated by adding bovine LH to each tube during the assay. Unspecific, interfering influences of equine or cow serum could be eliminated by adding a constant amount of PMSG-free serum to each tube. PMSG added to 200 microliter of serum could be recovered by this method with a mean of 90 . 5 +/- 9 . 9%. Inhibition curves obtained with pregnant mare serum or cow serum after administration of PMSG were parallel to those obtained with the PMSG standard preparation. The intra-assay coefficient of variation (CV) was 6 . 9%. The inter-assay CV was 12 . 6%. Sensitivity of the assay was 1 mi.u. PMSG/tube. Values of PMSG measured in the serum of pregnant mares by this assay were comparable with those obtained by a bioassay on the same samples. PMSG was still measurable in blood serum about 10 days after injection of 1500-3000 i.u. PMSG. After infusion of 12,000 i.u. PMSG for 3 h (2 heifers), the half-life of PMSG was found to have two components, one of 51 or 40 h and a slower one of 123 or 118 h.

Determination of luteinizing hormone in bovine blood by radioligand receptor assay and comparison with radioimmunological evaluation.

A sensitive and specific radioligand receptor assay (RRA) using rat testis homogenate as the receptor source is described for measurement of luteinizing hormone (LH) in bovine blood. Interfering and non-specific substances in blood were removed by means of ion-exchange chromatography on CM-Sephadex C-50. Criteria of validation such as recovery of added LH to plasma or serum, reproducibility, and specificity gave good results. Inhibition curves obtained with bovine plasma and serum were parallel to those obtained with the bovine standard preparation. The range of the dose-response curve was between 0.5-20 ng of bovine LH. The pattern of LH concentrations in purified serum samples under different physiological conditions such as during the oestrus cycle and after administration of GnRH showed a very close correlation whether measured by means of radioimmunoassay (RIA) or receptor assay. Values of RRA-LH were consistently higher than those of RIA-LH. Thus the lower the RIA-LH levels, the more pronounced were the discrepancies between results of both assay systems. The mean ratio of RRA-LH/RIA-LH for basal levels (less than 1 ng RIA-LH/ml plasma) was 17.8 as compared to a mean ratio for higher peak values (more than 20 ng RIA-LH/ml plasma) of only 1.2.