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Polyethylene Glycol in Conjunction with a Second Antibody for 24-Hour Radioimmunoassays of Bovine Prolactin and Growth Hormone^{1, 2, 3,}

Department of Animal Sciences, Washington State University, Pullman 99164-6320

ABSTRACT

Separate 24-h radioimmunoassays were validated for bovine prolactin and growth hormone using polyethylene glycol in conjunction with a second anti-body for separating bound from free labeled hormone. Buffer, standards, sera, antisera, and radioiodinated hormone were added to assay tubes and incubated 24 h. The second antibody was added and incubated for 15 min. Then 1 ml of 6% polyethylene glycol (3% final concentration) was added, and tubes immediately were centrifuged. Polyethylene glycol effectively decreased incubation time. There was no significant difference of percent binding, percent nonspecific binding, or sensitivity of these assays as compared to assays requiring a 72-h incubation with the second antibody when polyethylene glycol was not used. Specificities of the assays were demonstrated by parallelism between varying volumes of bovine serum and standard hormones. Sensitivities of the assays were .4 and .8 ng for prolactin and growth hormone. Intra- and interassay coefficients of variations were 8 and 12% for prolactin and 5 and 18% for growth hormone. Recoveries of known amounts of added hormones were 81 and 75% for prolactin and growth hormone.

¹ Scientific Paper No. 6317. College of Agriculture Research Center, Washington State University, Pullman. Project 0524.

² Partly supported by Washington State Dairy Products Commission.

³ The authors wish to thank the National Institute of Arthritis, Metabolism, and Digestive Diseases for providing antisera and purified hormones. The technical assistance of Teri Tanaka is acknowledged gratefully.