VASOPRESSIN RELEASE FROM THE RAT SUPRAOPTICO-NEUROHYPOPHYSIAL SYSTEM IN VITRO IN RESPONSE TO HYPERTONICITY AND ACETYLCHOLINE

Abstract

Vasopressin release from isolated supraoptico-neurohypophysial systems of rats was studied by means of an antidiuretic bioassay procedure using iv hydration. Preparations which included adjacent areas released less hormone during the post-isolation recovery period. Following the recovery period less than 20 pg/min of arginine-vasopressin was released from a single preparation; but on challenge with acetylcholine (1 mg/l) or with strongly hypertonic salt solutions (950 mosm/kg) the hormone release was increased to over 100 pg/min/preparation. Cross-tachyphylaxis between these two forms of stimulation occurred after less than 1% of the total vasopressin content of the supraoptico-neurohypophysial system had been released. A concentration of potassium of 56 mmol/l caused release of much larger amounts of vasopressin than stimulation with acetylcholine or hypertonicity.