Inositol trisphosphate mediates the action of hypertrehalosemic hormone onfat body of the American cockroach, Periplaneta americana

The rate of synthesis of inositol trisphosphate (InSP3) in trophocytes deri ved from disaggregated cockroach (Peri-planeta americana) fat body increase s following treatment of the cells with hypertrehalosemic hormone I or II ( HTH-I, -II) in vitro. Trophocytes preloaded with [H-3]inositol display a si gnificant increase in InsP(3) synthesis as early as 15 s after addition of the hormone. When the trophocytes are pre-incubated with LiCl and subsequen tly incubated with HTH the [H-3] content of the InSP3 fraction is greater t han that found with HTH alone. This is taken as evidence that inositol. mon ophosphate phosphatase is part of the mechanism for clearing InSP3 from the cytosol. In contrast to HTH, octopamine, which is also capable of exerting a hypertrehalosemic effect in the cockroach, does not increase the synthes is of InSP3. 1-Octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) , a potent and selective inhibitor of phosphatidylinositol phospholipase C, blocks the activation of phosphorylase by HTH-I as well as the hypertrehal osemic effect induced by the hormone. (C) 2001 Elsevier Science Inc. All ri ghts reserved.