Salt gland and kidney responses to intracerebral osmotic stimulation in salt- and water-loaded ducks.

Saltwater-adapted ducks with functioning supraorbital salt glands were chronically implanted with a device for perfusion of the third cerebral ventricle (icv perfusion) with artificial cerebrospinal fluid (CSF) of different tonicities. The osmoregulatory responses to icv stimulation were studied at conditions of salt and water loading in which only the salt glands, both salt glands and urinary fluid excretion, or only urinary fluid excretion were stimulated; in the latter experiments plasma antidiuretic hormone (ADH) was measured with a radioimmunoassay. Hypertonic icv stimulation enhanced salt gland secretion and caused antidiuresis, due to the increase of plasma ADH. Hypotonic icv stimulation inhibited salt gland activity and caused diuresis, due to the decrease of plasma ADH. Salt gland activity, urine formation, and plasma ADH reacted more sensitively to changes of icv tonicity in the hypertonic than in the hypotonic range. The effect of icv hypotonic stimulation could be obtained also with icv perfusion of isosmotic artificial CSF deficient in NaCl content. Perfusion with artificial CSF exceeding plasma tonicity by 50 mosmol X kg-1 or more caused inhibition of salt gland secretion associated with enhanced urinary output in several experiments.