SUMMARYA 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\g=m\lplasma 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.

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The molecular mechanisms underlying photoperiodic time measurement are not well understood in any organism. Relatively recently, however, it has become clear that thyroid hormones play an important role in photoperiodism, and in a previous study we reported that long daylengths in Japanese quail increase hypothalamic levels of T(3) and of the thyroid hormone-activating enzyme, type 2 iodothyronine deiodinase. The present study extends these observations to measure gene levels of the thyroid hormone-inactivating enzyme, type 3 deiodinase. Levels decreased after exposure to long days, but increased under short days. Changes in the two genes were then analyzed during the precisely timed photoinduction that occurs in quail exposed to a single long day. The two gene switches are the earliest events yet recorded in the photoinduction process, and overall, these reciprocal changes offer the potential to regulate active brain thyroid hormone concentrations rather precisely at the site in the brain where photoinduction is triggered.