Abstract
The properties of adenylyl cyclase and cyclic nucleotide phosphodiesterases from GH-strains of rat pituitary tumor cells have been investigated. Adenylyl cyclase was inhibited by calcium ion and stimulated by fluoride ion, 5'-guanylylimidodiphosphate and by prior treatment of intact releasing hormone (TRH), which stimulates prolactin releasing hormone (TRH), which stimulates prolactin release and synthesis in GH-cells, did not cause a significant stimulation of adenylyl cyclase activity under a wide variety of assay conditions; under the same conditions, [3H]TRH bound to a previously characterized membrane receptor. GH-cells contain phosphodiesterase activity catalyzing the hydrolysis of cAMP which gives nonliner Lineweaver-Burk plots with apparent Km's for cAMP of 1.5 muM and 4mM. TRH did not affect the activity of cyclic nucleotide phosphodiesterase at high or low cAMP concentrations when added to broken cell preparations. Treatment of intact cells with TRH caused no changes in the total adenylyl cyclase and cyclic nucleotide phosphodiesterase activites within the first 2 h of incubation, when stimulation of prolactin release occurs, but did lead to slight decrease in adenylyl cyclase and the apparent low Km phosphodiesterase after 72 h of treatment.
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