A novel function of cockroach (Periplaneta americana) hypertrehalosemic hormone: translocation of lipid from hemolymph to fat body.

The hypertrehalosemic hormones Pea HTH-I and Pea HTH-II have a lipogenic effect in the cockroach, Periplaneta americana. This has been determined by measuring the change in tri-, di-, monoacylglycerol, phospholipid and free fatty acids in the hemolymph and fat body in response to the hormones. The effect of both hormones 6h after injection is comparable and is expressed as an increase in fat body triacylglycerol and a decrease in hemolymph triacylglycerol. Coincident with this effect the concentration of diacylglycerol in the hemolymph decreases while that in the fat body increases. Hemolymph and fat body phospholipid are both lowered by HTH. The concentration of free fatty acids in the hemolymph, as well as fat body, are increased by both hormones. Confirmation of the lipogenic effect of HTH has been obtained by feeding cockroaches [3H]oleic acid and measuring the incorporation of label into hemolymph and fat body lipid. The data show that the specific activity of the hemolymph phospholipid fraction increases more than 50%. In fat body, the specific activity of the label in the triacylglycerol fraction increased more than 2-fold while that in the free fatty acid fraction increased more than 20-fold. The data support the view that the fatty acids incorporated into fat body triacylglycerol under the influence of HTH are not formed de novo but are derived from the sn-1 and sn-2 positions of phospholipid which is initially formed in the midgut wall.