Regulation of water transport in the cockroach rectum by the corpora cardiaca-corpora allata system: The requirement for Na+

Abstract

1. The antidiuretic activity of the corpora cardiaca-corpora allata extract is destroyed by heat. 2. Hormone stimulated water transport across the rectal wall will occur only if Na+ is present in the medium bathing the basal (haemocoel) surface. 3. Osmotic flow of water into the rectal lumen can be reversed by the gland extract. 4. Removal of Na+ from the basal surface has no effect on inward or outward osmotic flow of water across the unstimulated rectal wall. 5. The antidiuretic effect of the gland extract is blocked by 2 mM ouabain. 6. Dibutyryl cyclic AMP (1 mM) increases water transport across the rectal wall but is only 50–75% as effective as the gland extract. 7. Recta taken from dehydrated cockroaches transport water more rapidly than those taken from hydrated individuals. The difference disappears if Na+ is omitted from the bathing medium.