Two avian luteinizing hormone radioimmunoassay procedures compared by measurement of changes during the ovulatory cycle of turkey and broiler hens.

Two radioimmunoassay (RIA) procedures for measuring avian luteinizing hormone (LH) were compared using divided aliquots of plasma samples collected during the ovulatory cycles of turkey and broiler breeder hens in three separate experiments. The RIA systems compared were the homologous turkey LH assay Wentworth et al. (1976) and the homologous chicken LH assay of Follett et al. (1972). Both assays provided the same assessment of circulating LH changes. The preovulatory surge of LH was observed 6 hr before ovulation in turkeys and 4 hr before ovulation in chickens. In addition, both assays detected an increase in chicken LH after ovulation, followed by a gradual decline prior to the next preovulatory surge. The correlation between RIA were highly significant (P less than .001) in each experiment. The crossreaction of purified ostrich LH, FSH, and TSH and of the alpha and beta subunits of turkey LH was assessed in each assay system. Ostrich LH, FSH, and TSH crossreacted in the chicken LH assay in a dose-related manner: ostrich LH showed the highest activity. Only ostrich TSH produced a response in the turkey assay that was dose related. The alpha subunit, but not the beta subunit, of turkey LH was quite potent in the chicken LH RIA, but neither subunit competed as well as the native hormone in the turkey RIA. Thus, the two LH antisera recognize different portions of the LH molecule. The chicken antiserum apparently recognizes a site on the alpha subunit that may be at least partially masked in the FSH and TSH molecules. The turkey antiserum recognizes a site on the native LH molecule that is altered when the subunits are separated.