Biological properties of chicken luteinizing hormone-releasing hormone: gonadotropin release from rat and chicken cultured anterior pituitary cells and radioligand analysis.

We have examined the biological properties of chicken LHRH, which has been isolated and characterized in our laboratory, using primary monolayer cultures of rat and chicken anterior pituitary cells. The radioligand receptor analysis using rat pituitary LHRH receptor was also performed. Biological activities of mammalian LHRH and a more potent analog, [D-Leu6]des-Gly10-LHRH N-ethylamide ([D-Leu6] LHRH analog), were compared with those of chicken LHRH. The ED50 values for [D-Leu6]LHRH analog, mammalian LHRH, and chicken LHRH were, respectively, 0.0166, 0.455, and 18.2 nM for LH secretion and 0.0089, 0.263, and 8.28 nM for FSH secretion from rat pituitary cells. Relative potencies of chicken LHRH were 2.5% that of mammalian LHRH for LH and 3.2% that for FSH. On the other hand, the ED50 for chicken LHRH for LH release from chicken anterior pituitary cells was 1.03 nM, indicating that the biological potency of chicken LHRH acting on chicken pituitary cells was higher than that of chicken LHRH acting on mammalian pituitary cells. The ID50 of chicken LHRH to inhibit the binding of 125I-labeled [D-Leu6]LHRH analog to rat anterior pituitary membrane was 708.5 nM, and was 200 times that of mammalian LHRH (3.39 nM). These results suggest that the substitution of arginine residue of mammalian LHRH for glutamine residue of chicken LHRH causes a decrease in the binding affinity of the hormone for the mammalian LHRH receptor and that the mammalian LHRH receptor has a binding site for the cationic center of the arginine residue of LHRH. On the other hand, chicken pituitary LHRH receptor seems to have more broad specificity than mammalian LHRH receptor.