The Absorption of Glucose from the Alimentary Canal of the Locust Schistocerca Gregaria (Forsk.)

ABSTRACT The absorption of glucose from the alimentary canal of Schistocerca gregaria has been studied by filling the gut with a saline solution containing 14C-labelled glucose together with a dye, Amaranth, which was used as a marker. The net percentage absorption was calculated from the glucose/dye ratio in the various parts of the alimentary canal. The bulk of the glucose was absorbed from the mid-gut caeca, smaller amounts being absorbed by the ventriculus. Glucose absorption was studied at concentrations of 0·002, 0·02 and 0·20 M/1. in solutions in which the total osmolarity was maintained by altering the NaCl concentration. The percentage absorption was similar at concentrations of 0·002 and 0·02M/1., but was significantly less at 0·20M/1. The fate of the 14C-labelled glucose was followed using paper chromatography. The glucose was shown to be rapidly converted to trehalose in the haemolymph. At a concentration of 0·20M/1. this mechanism became saturated and excess glucose accumulated in the haemolymph. The absorption of glucose in vitro, from a gut suspended in a relatively large volume of poisoned saline, was found to be similar to that in the intact insect. From these observations it is suggested that glucose is absorbed by diffusion across the gut wall and that the process is facilitated by the rapid conversion of glucose to trehalose in the haemolymph, which tends to maintain a steep concentration gradient across the gut wall.