DYNAMICS OF HEMOLYMPH SORBITOL-6-PHOSPHATE AND ITS CONTROL BY ECDYSTEROID IN THE LARVAE OF THE SILKWORM, BOMBYX-MORI

Developmental changes in the concentration of sorbitol-6-phosphate (S- 6-P) and trehalose in the Bombyx haemolymph were determined from fourt h larval stadium to adult eclosion by gas-liquid chromatography, In th e fourth stadium, haemolymph trehalose concentration transiently decre ased after ecdysis and then gradually increased from day 1 to day 3, f ollowed by an abrupt increase immediately before the last larval ecdys is, The trehalose concentration decreased again after the last larval ecdysis, recovered to a level similar to that which was found on days 1-3 of the fourth stadium, and remained relatively constant during the feeding period of the fifth stadium, Concomitant with the onset of th e wandering stage, the trehalose concentration decreased to a low leve l, but gradually increased again during the pupal period, Haemolymph S -6-P concentrations were always higher than trehalose concentrations d uring the feeding period of the fourth and fifth stadia and 2.5-fold h igher immediately before spinneret pigmentation, S-6-P concentration b egan to decrease to a low level (less than 1 mM) concomitantly with th e occurrence of spinneret pigmentation, one day earlier than the onset of the wandering stage, In contrast to the slow increase in the treha lose concentration after the wandering stage, the S-6-P concentration remained low throughout the pupal period, After the dilution of larval haemolymph by the replacement of larval haemolymph with insect Ringer 's solution, or an artificial increase in haemolymph S-6-P and trehalo se concentration by an injection of each of S-6-P and trehalose, S-6-P concentration did not recover to the level before manipulation, where as trehalose concentration became similar to the initial level in a fe w hours, indicating that S-6-P concentration is not under homeostatic control, in contrast to trehalose, Injections of ecdysone or 20-hydrox yecdysone induced a decrease in the haemolymph S-6-P concentration in a dose-dependent manner, These findings suggest that S-6-P accumulates in the haemolymph during the feeding period, as a storage form of sug ar and ecdysteroid is involved in the sharp decrease in haemolymph S-6 -P concentration at the end of the feeding period in Bombyx larvae. (C ) 1997 Elsevier Science Ltd.