LH-RH interactions with pituitary receptors: Properties and characterization

The plasma membrane initiator system for actions of LH-RH was characterized. Binding of 125-I-LH-RH to the anterior pituitary plasma membrane was studied at 4 degrees C and at 37 degrees C. Two binding sites were indentified which possessed apparent affinity constants of 2 times 10- minus 8M and 2 times 10- minus 7M, respectively. The high affinity binding site was competible and saturable by TRH. These data suggest that the low affinity binding site is the physiological receptor for mediation of LH-RH stimulated LHrelease. LH-RH-receptor interaction has been shown to be a temperature and pH-dependent process. Less binding was observed at 37 degrees C than at 4 degrees C. Below pH 6 and above pH 8 a sharp drop in LH-RH binding to the cell membrane was recorded. Ca++, Mg++ and Mn++ were shown to inhibit the binding. Mn++ (16 mM) showed 50 percent inhibition of binding of LH-RH to the anterior pituitary plasma membrane fractions. On the other hand, increasing ionic strength enhanced LH-RH binding. The results of our study on the LH-RH-receptor systems offer a new approach to the study of LH-RH actions and facilitate the interpretation of earlier observations.