MAGNESIUM POTENTIATION OF OXYTOCIC ACTIVITY OF PITUITARY EXTRACTS FROM AN ELASMOBRANCH (RAIA RHINA)

Different extracts from the neurointermediate lobe of the elasmobranch, Raia rhina, were assayed for their oxytocic activity by means of the isolated rat uterus, both with and without magnesium present in the supporting fluid, and with synthetic oxytocin used as standard. The magnesium potentiation was shown to vary from 1.8 to 17.5. This variation was not eliminated by partial purification by paper chromatography. Uniform results, obtained when different extracts were assayed jointly on the same uteri, suggested that the value of magnesium potentiation was partly dependent on the particular uteri used. Therefore it was not a suitable criterion for distinguishing different elasmobranch principles. © 1969.