HETEROLOGOUS RADIOIMMUNOASSAY FOR BOVINE FOLLICLE-STIMULATING HORMONE AND ITS APPLICATION DURING THE OESTROUS CYCLE IN CATTLE

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Abstract
A specific heterologous radioimmunoassay for bovine follicle-stimulating hormone (bFSH) was developed using guinea pig antiserum to ovine FSH with radio-iodinated ovine FSH. Slight cross-reactions with bovine TSH [thyrotropin] and LH [luteinizing hormone] could be eliminated by adding bovine TSH and LH to each tube during the assay. The labeling method with lactoperoxidase turned out to be more useful than the chloramine-T method. Inhibition curves obtained with male and female bovine plasma were parallel to those obtained with the bovine standard preparation. Exogenous bFSH could be quantitatively recovered from 200 .mu.l of plasma or serum with a mean of 101.7 .+-. 7.7%. The intra-assay coefficient of variation (CV) was .ltoreq. 6%. The inter-assay CV was 13.5%. Sensitivity was 70 ng/ml NIH-FSH-B1. Mean plasma concentrations of FSH (National Institute of Health-FSH-B1) during the estrous cycle were 303 .+-. 101 ng/ml. When plasma samples were collected in 6 h intervals from 17 estrous cycles from 13 regularly cycling heifers and cows, a significant FSH peak occurred just before and during estrus and coincided with the preovulatory LH peak. Further FSH elevations could be measured on day 4, 8 and 12 after ovulation, and 5 and 3 days before ovulation and showed a rhythmic pattern of approximately 4-day intervals.