Elution and rebinding of gonadotropins to receptors in corpora lutea: comparisons among treatments and species.

Several treatment regimens have been used to dissociate bound gonadotropins from their target tissues to quantify numbers of occupied receptors. To compare the efficacy of these methods, we evaluated the ability of a number of treatments to elute bound gonadotropins from corpora lutea of various species. In addition, we examined the capacity of luteal tissue to rebind gonadotropins after efficacious elution (greater than 90% dissociation of bound gonadotropin). Particulate (20,000 g) preparations of luteal tissue from pseudopregnant rats and from nonpregnant pigs and rhesus monkeys were incubated with 125I-labeled human luteinizing hormone (hLH, NIH-LH-11) or 125I-labelled chorionic gonadotropin (hCG, CR119) for 20 h at 25 degrees C to occupy gonadotropin receptors. Heat treatment (60 degrees C) eluted greater than 80% of bound 125I-hLH from rat tissue within 30 min, but similar treatment dissociated only 35% of 125I-hLH bound to porcine tissue (p less than 0.01). Likewise, heat treatment eluted only 57% of 125I-hLH bound to macaque tissue. At 4 degrees C, the following treatments dissociated greater than 90% of specifically bound 125I-hLH from porcine and rat luteal particulates within 5 min: acetic acid (pH 2.3), formic acid (pH 2.3), propionic acid (pH 2.3), acetic acid: HCl (pH 2.3 and 3.3), and MgCl2 (4 M). After 1-2 h at 4 degrees C, exposure to urea (4 M) or acetic acid:HCl (pH 4.3) also eluted greater than 90% of bound 125I-hLH.(ABSTRACT TRUNCATED AT 250 WORDS)