A radioimmunoassay for the measurement of turkey LH (TLH) is described. The antiserum used was developed against purified TLH (No. 70355). Another TLH (CG-C) preparation was used for iodination and as a reference standard. Linear logit vs log dose plots were obtained with standard between 0.10 and 16.0 ng TLH/assay tube. Sera from laying famales, nonlaying females, intact males, castrate males, thyroidectomized males and broody females inhibit bindings of 125 I-TLH, yielding dose-response curves parallel to the standard curve. Sera from a hypophysectomized turkey, at levels up to 200 μl/assay tube did not inhibit binding of 125 I-TLH. Assay of TLH, added to hypophysectomized sera, resulted in essentially 100% recovery. Luteinzing hormone releasing hormone elicited an increase in immuroreactive LH within 10 min after injection. Castration of male turkeys resulted in elevated immunoreactive LH. Manipulation of the pituitary-thyroid axis yielded conflicting results. Thyroidectomy, triiodothyronine (T 3 ) and thyroxine (T 4 ) treatment, and thiouracil feeding had no effect on serum LH, but TRH injection elevated the immunoreactive material. Evidence is presented that suggests TRH releases LH in Aves .
