Evidence for antidiuretic control of rectal water absorption in the cockroach Periplaneta americana L.

Abstract

An in vitro method has been devised for the study of water absorption by the cockroach rectum. The method permits measurement of the amount of water absorbed over a period of time. Passive water movement occurs across the rectal wall. Water absorption appears to occur from isosmotic and hyperosmotic trehalose solutions, and is DNP sensitive. Water absorption by recta from dehydrated animals was compared with that of recta from hydrated animals. Recta from dehydrated animals absorbed water at a higher rate than recta from hydrated animals. This is interpreted as an antidiuretic response, and indicates that the cockroach possesses a regulatory system to control rate of rectal water absorption. Dehydration of cockroaches produced by lowering the r.h. of the atmosphere, by supplying with hyperosmotic saline, or by withholding water gave similar results. Extracts of various insect tissues were applied to in vitro recta to determine if factors were present which affect rate of water absorption. Extracts of corpora allata, metathoracic ganglia, and last abdominal ganglia from hydrated animals produced an increase in rate of water absorption. When the same tissues were taken from dehydrated animals, their extracts had less activity. However, brain extracts from dehydrated animals produced an increase in water absorption. These results indicate that rate of rectal water absorption may be regulated by a factor or factors of neuroendocrine origin.