A NEW NEUROHYPOPHYSEAL PEPTIDE, SERITOCIN ([SER(5),ILE(8)]-OXYTOCIN),IDENTIFIED IN A DRYNESS-RESISTANT AFRICAN TOAD, BUFO-REGULARIS

From the pituitary neurointermediate lobe of the African toad Bufo reg ularis, vasotocin, hydrin 2 (vasotocinyl-Gly) and a mesotocin-like pep tide have been isolated by HPLC and characterized by mass spectrometry , amino acid sequence and chromatographic coelution with synthetic pep tides. The mesotocin-like peptide has been identified as [Ser(5),Ile(8 )]-oxytocin in place of mesotocin ([Ile(8)]-oxytocin) found in all oth er amphibians investigated to date. The name seritocin is suggested. T he molecule is virtually devoid of oxytocic activity on rat uterus in contrast to mesotocin. On the other hand, the molar ratio of hydrin 2 to vasotocin in the pituitary reaches 2, whereas it is about 1 in toad s and frogs from temperate regions. B. regularis is an anuran species able to withstand a hot and dry season by burrowing. The possible rela tionship between occurrence of seritocin and adaptation to arid enviro nment remains to be demonstrated. (C) Munksgaard 1995.