A homologous radioimmunoassay for turkey prolactin: changes during the reproductive and ovulatory cycle.

A rabbit antiserum to turkey prolactin (tPRL) was used in a homologous radioimmunoassay with 125I-tPRL. This assay did not cross-react with turkey luteinizing hormone (tLH), chicken LH (cLH), turkey follicle stimulating hormone (tFSH), or turkey growth hormone (tGH). The within- and between-assay coefficients of variation were 6.2 and 14.0%, respectively, and the useful range of the standard curve extended from .5 to 10.0 ng/tube. In two separate experiments, the plasma concentrations of prolactin were estimated throughout the reproductive cycle of the turkey hen using a heterologous assay previously described and the current homologous assay. The correlation coefficients between the two estimates of prolactin in nonbroody hens were .84 and .83. In both experiments, the plasma concentrations of prolactin were low when egg production was initiated, rose to maximum concentrations 5 to 7 weeks later, and thereafter declined. In the first experiment, the hens were selected because their plasma contained large amounts of immunoreactive PRL during the first 2 weeks after photostimulation in the heterologous tPRL assay. This immunoactivity was not evident when using the homologous assay. Using the heterologous assay, no differences in the plasma prolactin concentrations were detected between broody and nonbroody hens during the reproductive cycle. However, using the homologous assay, a sustained increase in the concentration of prolactin was noted for several weeks after broody behavior was detected. The maximum levels observed in broody hens were equal to those observed when the rate of egg production was maximal. There were no statistically significant changes in the concentrations of prolactin during the ovulatory cycle.