Control of protease secretion in the intestine of fifth instar larvae of Rhodnius prolixus.

Groups of four Rhodnius prolixus larvae in the 5th-instar received no food or were given once only through a special feeder, similar weights of food solutions. These were either protein solutions (whole human blood, its plasma or erythrocytes, egg albumin, bovine serum albumin, haemoglobin) or non-protein solutions (saline, casein hydrolysate, dextran, maltose). Following feeding, the protein content and caseinolytic activity of the larval midgut homogenates, determined between the 3rd and 14th days, were practically the same in starved larvae and in larvae receiving non-protein solutions. In the protein-fed larvae the protein content and the specific protease activity increased. These findings exclude neurosecretory control and indicate that ingested protein stimulate the proteolytic activity of R. prolixus midgut.