Studies of Prolactin and Growth Hormone Secretion in Dairy Cattle by Radioimmunoassay

For the studies of endocrine control of lactation and growth of dairy farm animals, it is essential to examine the hormone secretion as well as hormonal action. Until the appearance of radioimmunoassay procedure around 1960, there had been no reliable and sensible assay method to determine hormone concentration in blood 1'. Bioassay techniques for hormone determination provided valuable information but were often lacking specificity, sensitivity and precision. Attempts of direct chemical assay have always failed because of the low concentration of hormones in the presence of plasma proteins at concentration of millions of times greater. The introduction of radioimmunoassay into the field of endocrinology has revolutionized the techniques of assay of hormones in blood 1.2 .cn . Since the later years of 1960', radioassay techniques, mainly radioimmunoassay, for protein and steroid hormones in blood of farm animals, have been developed successfullyo,10>. With these techniques it has become possible to assay a series of pg to ng levels of immunoreactive hormones in a large number of samples at a time. In recent years, development of radioimmunoassay techniques for bovine prolactin (PRL) and growth hormone (GH) have been studied successfully in our laboratory bringing in new information on PRL and GH secretion in cattle24,s>.