NEUROHYPOPHYSEAL HORMONES IN AMPHIBIA - A COMPARISON OF THEIR ACTIONS AND STORAGE

Vasotocin was 40 to 50 times more active (on a mole basis) than oxytocin in promoting water retention in Bufo marinus. The latter peptide was five times as active as 8-Ile-oxytocin (mesotocin). Vasotocin was 200 times as active as either oxytocin or 8-Ile-oxytocin in increasing water transfer (hydro-osmotic response) across the toad bladder in vitro and 100 times as active as the other two peptides in stimulating sodium transport (natriferic response) across this tissue. Storage of active peptides in the neurohypophyses of terrestrial Amphibia was about 10-9-10-8M/kg body weight but in two aquatic amphibians it was 10 times less than this. The isolated skin of aquatic amphibians had a lower osmotic permeability than that of more terrestrial species. Vasotocin failed to increase water transfer across the skin of the three urodeles or the aquatic toad Xenopus. Sodium transport was stimulated by vasotocin in Xenopus as well as Bufo and Rana but not in the urodeles. The results are discussed in relation to the evolutionary adaption of Amphibia to terrestrial life. © 1969.