Release of vasopressin from isolated guinea pig posterior pituitaries

Abstract

Isolated guinea pig posterior pituitaries, incubated in a modified Krebs-Ringer solution at 37 C, released vasopressin at a relatively constant basal rate. Electrical stimulation at a voltage gradient of 3–9 v/cm (200-msec pulses of 60 cycles/sec ac every 2 sec) resulted in an elevation of vasopressin output. Stimulation at lower field strengths was not effective and maximal vasopressin release was produced by stimulation at any voltage gradient between 3 and 9 v/cm. Vasopressin secretion was augmented at rest and during electrical stimulation by the presence of 2 mm Ba⁺⁺ in the incubation medium (increase of Ca⁺⁺ by 2 mm had no effect). Tetracaine (0.5 mm) blocked the response to electrical stimulation. Chemical, biological, and enzymic tests indicated that the pressor material secreted by the tissue was identical with arginine vasopressin. The experimental findings support the hypothesis that conduction of action potentials along the hypothalamo-neurohypophysial tract releases vasopressin from the posterior pituitary.