Radioimmunoassay for bovine luteinizing hormone (BLH)

Recent progress in immunological techniques has revealed the possibility for more sensitive methods for assaying protein hormones. A radioimmunoassay technique has been developed for the detection and direct measurement of physiological levels of human pituitary luteinizing hormone in blood plasma. The radioimmunoassay is based on the competition between ¹³¹labeled hormone and unlabeled hormone for antibodies to the hormone. The separation of free hormone from antibody-bound hormone is achieved by precipitation using antibody to Y-globulin of an animal in which the antihormonal serum was produced. This study was initiated to develop the radioimmunoassay technique which could be used to measure physiological levels of bovine LH directly from blood without concentration or purification. The assay was used to measure the variation of luteinizing hormone in the blood of four cows during the estrual cycle. The average levels of the hormone was less than 1.5 mug. equivalents of the standard (NIH-LH-B5) per ml. of serum during diestrus but increased 10 to 20 fold during estrus. The concentration of the hormone in the blood increased sharply in the early stages of estrus and decreased rapidly in the late stage of estrus. The results indicated that the procedures can be used to measure the luteinizing hormone activity in 1 ml. of blood.