Abstract
Neurohypophysial extracts of an amphibian, Rana pipiens, and a reptile, Crotalus atrox, were subjected to ion exchange column chromatography. Fractions obtained by gradient elution were carefully assayed and activity ratios were determined. Tentative identifications of the neurohypophysial principles were based on these pharmacologic ratios. R. pipiens appears to secrete 2 active neurohypophysial principles, arginine vasotocin and oxytocin. C. atrox also secretes 2 active principles; one is arginine vasotocin, but the other appears to be 8-isoleucine oxytocin. Vasopressin was found in neither species. These results differ in some respects from those of other investigators. Current evolutionary concepts regarding neurohypophysial principles are discussed in view of these findings.