Species Differences in Luteinizing Hormone as Inferred from Slope Variations in a Radioligand Receptor Assay 1

Abstract

Luteinizing hormone preparations from a variety of sources were compared with respect to the slopes of their radioligand uptake inhibition curves. The system utilized human luteinizing hormone as the radioligand and homogenates of testis from mature rats as the receptor source. Based on the weighted mean values from replicate slope measurements, four major groups could be detected. In order of decreasing slope steepness, these were: Group I = human urinary LH, monkey pituitary LH, human pituitary LH and human chorionic gonadotropin; Group II = bovine pituitary LH, ovine pituitary LH, rat pituitary LH and equine pituitary LH; Group III = rabbit pituitary LH and chicken pituitary LH; Group IV = porcine pituitary LH and canine pituitary LH. There was no overlap of 95% fiducial limits for calculated slope values between groups. These groupings are at variance in some instances with those of a previous report (Endocrinology73: 509, 1963), based on slopes of dose response curves obtained using the ventral prostate assay for LH. These differences probably reflect the independence of the in vitro radioligand assay from influence by factors related to plasma half-life.(Endocrinology92: 646, 1973)