METABOLIC EVENTS DURING PROGRAMMED CELL-DEATH IN INSECT LABIAL GLANDS

The labial gland of Manduca sexta is a valuable system to study the me chanisms of programmed cell death since the death of the gland is near ly synchronous and, except for the anterior duct, involves all of the tissue. The gland degenerates in 5 days during pupation. Our previous work documents a drop in total protein synthesis as the gland degenera tes. To evaluate potential causes of this altered protein synthesis, w e monitored several parameters of metabolism in dying cells: levels of adenosine triphosphate to estimate the energy resources of the gland; reduction of (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromi de to assess mitochondrial respiration; levels of acid phosphatase to assay lysosomal enzyme activity; and concentrations of cyclic nucleoti des and inositol triphosphate to monitor signaling. While protein synt hesis fell precipitously on day 0, total adenosine triphosphate and mi tochondrial respiration were unchanged until the cells underwent massi ve collapse on day 3. Lysosomal acid phosphatase increased during earl y metamorphosis, and ultimately the bulk of the cytoplasm was destroye d in autophagic vacuoles. Changes in the concentrations of second mess engers were modest and late. The relationships between the metabolism and the collapse of the labial gland are under investigation