ROLE OF CALCIUM IN THE RELEASE OF VASOPRESSIN AND OXYTOCIN FROM POSTERIOR PITUITARY PROTEIN

Abstract

Using film dialysis experiments of crude posterior pituitary protein in 0.1 M acetic acid/ sodium acetate buffer (PH 5.6) it was demonstrated that addition of Ca in concentrations of 0.2 or 0.5 mM increased the rate of dialysis of vasopressin activity from the film of protein solution. Sodium chloride, magnesium chloride or acetylcholine had no such effect. Ca in a concentration of 0.2 mM also increased the rate of dialysis of oxytocin activity from the protein solution. The results seem to support the hypothesis that Ca ions function in the excitation-secretion coupling for vasopressin and oxytocin by releasing hormone peptide from its binding to neurophysin within the neurosecretory nerve endings. Thus, the hormone becomes free to diffuse into the blood stream.