Phylogenetic distribution of the effects of neurohypophysial hormones on water and sodium metabolism

Abstract

The injection of homologous neurohypophysial hormones into cyclostomes, elasmobranchs, teleosts, and dipnoans did not alter their body weight significantly. Injections of vasotocin into species belonging to the following anuran families resulted in an increase in body water which seamed to vary characteristically from species to species: Discoglossidae, Pelobatidae, Hylidae, Bufonidae, and Ranidae. No effect was obtained in Pipidae. Dose-response regression lines for naturally occurring neurohypophysial peptides were established for the increase in body water in Bufo bufo and Rona esculenta. The order of potency was arginine vasotocin > arginine vasopressin > oxytocin > lysine vasopressin. Bufo bufo was about ten times as sensitive to all the hormones tested as was R. esculenta. The injection of vasotocin and oxytocin into the African lungfish ( Protopterus) resulted in a net sodium loss. This effect could not be demonstrated in the anurans Xenopus or R. esculenta. The responses are diseussed in relation to the evolution of the vertebrates and the variations in the chemical composition of the neurohypophysial hormones.