Lipid metabolism in the cockroach, Periplaneta americana, is activated by the hypertrehalosemic peptide, HTH-I

Abstract

Phosphatidylcholine and phosphatidylethanolamine are the major constituents of the phospholipid pool in cockroach ( Periplaneta americana) fat body and hemolymph. Both species of phospholipid are significantly decreased 6 h after injecting hypertrehalosemic hormone I (HTH-I) into the hemocoel. Loss of phospholipid is accompanied by an accumulation of the phospholipid degradation products glycerophosphorylcholine and glycerol. HTH-I also increases phospholipase activity in the hemolymph and this is thought to be responsible for the depletion of hemolymph phospholipid. Phospholipase activity peaks approximately 2 h after injection of HTH-I and returns to normal at 6 h. In vitro, total phospholipid in the fat body is decreased by HTH-I whereas the concentration of diacylglycerol displays a corresponding increase. HTH-I elevates free fatty acid levels but has no effect on triacylglycerol. These effects of HTH-I are blocked by the phospholipase inhibitor mepacrine.