BOMBYXIN, AN INSULIN-RELATED PEPTIDE OF INSECTS, REDUCES THE MAJOR STORAGE CARBOHYDRATES IN THE SILKWORM BOMBYX-MORI

The effects of an insect insulin-related peptide, bombyxin, on carbohy drate metabolism were investigated in the silkworm Bombyx mori. Bombyx in lowered the concentration of the major hemolymph sugar, trehalose, in a dose dependent manner when injected into neck ligated larvae. Bom byxin also caused elevated trehalase activity in the midgut and muscle , suggesting that bombyxin induces hypotrehalosemia by promoting the h ydrolysis of hemolymph trehalose to glucose and thereby facilitating i ts transport into tissues. In addition, bombyxin reduced the glycogen content in the fat body and concurrently raised the percentage of acti ve glycogen phosphorylase in this tissue. Because hemolymph trehalose is also a major storage form of carbohydrate in insects, our results i ndicate that bombyxin reduces the amount of both principal storage car bohydrates in B. mori larvae. It is therefore suggested that although bombyxin is involved in the control of carbohydrate metabolism like in sulin, the physiological role of bombyxin in insects is different from that of insulin in mammals. (C) 1997 Elsevier Science Inc.