Characterization of luteinizing hormone-releasing hormone receptor binding in rat pituitary cell monolayer cultures; influence of intercellular communication.

Receptors for the luteinizing hormone-releasing hormone (LHRH) were characterized in rat pituitary cells cultured for 3 days as monolayers on coverslips using 125I-[D-Ala6-Pro9-LHRH-NEt] as the labeled ligand. The monolayers were left intact during the binding assay. Specific binding displayed the various characteristics of binding to the physiological LHRH receptor. Various kinetic data corresponded to those reported previously. However, in these cultured cells, in which binding was tested in a physiological medium, the dose response of competition for binding by LHRH agonists ranged over a smaller concentration range (less than 2 orders of magnitude) than that by LHRH antagonists. In a cation-free buffer competition curves of agonists and antagonists were parallel but the apparent dissociation constant was lower than in the physiological medium. In cultures of pituitary cell populations separated by unit gravity sedimentation, the specific binding increased with the proportional number of gonadotrophs in the various populations. However, when the gonadotroph-richest population (approximately equal to 70% gonadotrophs) was cultured after recombination with gonadotroph-poor populations, binding capacity significantly increased. Microscopic examinations suggested that this phenomenon was the consequence of disrupting cellular contacts among gonadotrophs. It is concluded that certain characteristics of LHRH receptors tested on cells in a tissue-like organization and in a physiological environment are different from those reported previously in disrupted cells or monodispersed cell suspensions and that intercellular communication is an important factor controlling LHRH receptors.