Abstract

SUMMARY A radioimmunoassay for avian luteinizing hormone (LH) is described, using antisera raised against chicken pituitary gonadotrophins of varying degrees of purity, and purified chicken LH for radio-iodination. A postprecipitation double antibody method was developed with a sensitivity to 30–60 pg of purified chicken LH. The specificity of the method was investigated. Fractions of follicle-stimulating hormone with high biological activity showed little immunological activity, whilst all the fractions of LH tested showed strong immunological potency. Human, ovine and bovine LH showed virtually no cross-reaction. The method measures immunoreactive LH in 25–200 μl plasma from chickens and quail. The plasma levels correlate well with known physiological processes, being absent in hypophysectomized birds and low in sexually immature quail. When testicular growth begins in quail the level rises eightfold; castration increases it still further while the level is lowered by testosterone. Manipulation of the pituitary-thyroid system in quail did not significantly affect the level of plasma activity. Estimates of activity are independent of either the antiserum or the iodinated preparation of LH used in the assay. The antisera used all blocked gonadotrophic activity in vivo .