A model system for the biochemical study of luteinizing hormone/chorionic gonadotropin receptor synthesis

A model system for the biochemical study of LH/CG receptor synthesis has been developed. Culture conditions for porcine granulosa cells were adapted that maximized the selective induction of LH/CG receptors by cAMP-inducing stimuli with an elimination of background LH/CG receptor appearance. It was found that the addition of FSH (1.5 micrograms/ml) or cholera toxin (10 ng/ml) 1 day after plating resulted in optimal induction of the LH/CG receptor (20-60 pg [125I]CG bound/micrograms DNA 72 h after addition) with virtually no LH/CG receptor appearance in the absence of added stimuli. Later additions of FSH or cholera toxin required insulin (1.0 microgram/ml) which alone caused background LH/CG receptor appearance in the absence of any additional stimuli. Furthermore, insulin increased the general rate of cellular protein synthesis, whereas FSH or cholera toxin each decreased it. Thus, the use of FSH or cholera toxin, without insulin, may enable one to detect the synthesis of the LH/CG receptor by metabolic labeling techniques where background protein synthesis has been lowered.