Stimulation by angiotensin II of the release of vasopressin from incubated rat neurohypophyses---possible involvement of cyclic AMP.

1. Calcium did not influence the spontaneous release of vasopressin from rat neurohypophyses in vitro when used in concentrations of 0.05, 0.5 and 2.8 mM in the bathing medium. 2. Stimulation of the basal output of vasopressin by angiotensin II (1 X 10(-9) M) required at least 0.5 mM calcium in the medium. 3. Angiotensin II stimulated the release of vasopressin within 2.5 min of incubation, maximal release was observed after 10 min. 4. Angiotensin II rapidly promoted the accumulation of tissue cyclic AMP; maximal accumulation was observed after 5 min of incubation. 5. Theophylline and dibutyryl cyclic AMP produced varying degree of stimulation of the release of vasopressin. 6. Increases in vasopressin secretion and in the accumulation of cyclic AMP were always present when neurohypophyses were exposed to optiman concentrations of angiotensin II. The results presented suggested that cyclic AMP may be an intermediate step for the release of vasopressin by endogenous angiotensin II.