Osmotic regulation and rectal absorption in the blowfly, Calliphora erythrocephala

Abstract

The osmoregulatory ability of blowflies was investigated by measuring osmotic pressures and chloride concentrations of haemolymph, urine, and, under some conditions, crop and hindgut fluids from water-fed and water-deprived animals. Blood levels were kept within narrow limits by production of either very hyposmotic or strongly hyperosmotic urine. Water and chloride reabsorption from isolated recta were measured directly in vivo. While no positive evidence was obtained that ion reabsorption in the rectum plays an important role in production of hyposmotic urine, it was clearly established that hyperosmotic urine resulted from absorption of water against an increasing osmotic gradient in the latter organ. The rate of water absorption was dependent on the osmotic gradient across the rectal wall and occurred from an initially pure sugar solution as well as from saline. Current ideas on the possible mechanism of water transport in the insect rectum are discussed and assessed.