Osmotic Regulation of Body Fluids

¹ From the Aero Medical Laboratory, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio

Intracarotid injections of hypertonic solutions were made in animals, using light chloralose anesthesia to rule out the possibility of conditioning an antidiuretic response. These experiments, raising carotid osmolarity by approximately 50% for a 10-second period, confirmed previous observations that an antidiuresis follows an increase in carotid osmolarity. When carotid osmolarity is increased by less than 2% over a 40-minute period an antidiuresis also results. Little difference was observed in the relative effectiveness of hypertonic urea, sodium chloride or sodium sulfate, all of which were calculated to raise osmolarity by approximately equal amounts. Bioassay techniques showed greatly increased amounts of antidiuretic substance in urine after intracarotid injections of hypertonic solutions. Controls given isotonic saline injections showed only minimal antidiuretic activity.