Radioimmunoassay

Abstract

Radioimmunoassays for rat, ovine and bovine prolactins were recently described (Fig. 57). Kwa and Verhofstad (1967) developed a radioimmunoassay for rat prolactin, using rat prolactin prepared from transplants of pituitary tumors as a reference antigen. These authors were able to detect changes in prolactin levels in blood of individual female rats through the estrus cycle and through pseudopregnancy by taking a 1 ml blood sample daily from the tail vein. High concentration of prolactin was found during the onset of lactation and unexpectedly low values during pregnancy (Kwa, 1968). A similar method for rat prolactin has been described by Niswender, Chen, Midgley, Meites and Ellis (1969). Bovine and ovine prolactin do not appear to crossreact in this radioimmunoassay. Quantities of NIH-P-B2 and NIH-P-S8 as high as 1 μg/assay tube did not inhibit the reaction between the antirat prolactin and the rat prolactin-¹³¹I. It appears that a radioimmunoassay specific for rat prolactin has been developed which is capable of measuring the prolactin in as little as 100 μl of serum from an immature rat and in 10 μl obtained from most females on the afternoon of proestrus. This radioimmunoassay method is estimated to be about 1,000–2,000 times more sensitive than the local pigeon crop bioassay. It has been used to measure serum levels of prolactin in rats throughout their cycle, and when bearing prolactin secreting tumors. The purification of rat prolactin for these studies has been described by Ellis, Grindeland, Nuenk and Callahan (1969).