The effects of two inositol (1,4,5)-trisphosphate 5-phosphatase inhibitors on thyrotropin releasing hormone stimulated inositol (1,4,5)-trisphosphate production in GH3 cells.

The effects of FLA99 and EWP840, two disulfiram analogs which potently inhibit Ins(1,4,5)P3 5-phosphatase, upon basal and thyrotropin-releasing hormone (TRH)-stimulated inositol (1,4,5)-trisphosphate (Ins(1,4,5)P3) levels were investigated. Neither test compound affected the characteristics of the [3H]Ins(1,4,5)P3 binding site used in the competitive protein binding assay of Ins(1,4,5)P3 levels. In rat GH3 pituitary cell suspensions, TRH (100 nM) produced a large and time-dependent increase in Ins(1,4,5)P3 concentration, the maximum response being obtained within 5 seconds of stimulation in these cells. Neither FLA99 (100, 300 and 1000 microM) nor EWP840 (100 microM) produced obvious effects on the Ins(1,4,5)P3 response to TRH stimulation. Higher concentrations of EWP840 (300 and 1000 microM) abolished the Ins(1,4,5)P3 response to TRH stimulation. The lack of effect of the 5-phosphatase inhibition in the cells may indicate that 5-phosphatase is not the major metabolic pathway of this second messenger in this cell line under the assay conditions used.