Comparison of the species specificity of gonadotropin binding to primate and nonprimate corpora lutea

Primate gonadotropins (human luteinizing hormone (hLH) and chorionic gonadotropin (hCG)) were 500-1000 times more effective than nonprimate gonadotropins (ovine, bovine, and porcine LH) in inhibiting ¹²⁵I-hLH binding to particulate preparations of the corpus luteum from the rhesus monkey. In contrast, all gonadotropins were equipotent in inhibiting ¹²⁵I-hLH binding to luteinized ovarian tissue from pregnant rats. Moreover, primate gonadotropins were only 10 times more effective than nonprimate gonadotropins in competing for LH binding sites in porcine corpora lutea. This comparative study indicates that the apparent species specificity of gonadotropin receptors in the monkey is not due to differences in purity or biological activity (as measured in the rat OAAD bioassay) between hormone preparations. Rather, primate gonadotropin receptors have an increased affinity for primate gonadotropins and a decreased affinity for non-primate hormones. This study emphasizes that the investigation of gonadotropin action in primate reproduction requires the use of primate gonadotropins.