title: An inhibitor of the sodium pump obtained from human placenta.
abstract: BACKGROUND
  Much effort has been expended in the search for an endogenous inhibitor of the cellular sodium/potassium pump, a compound of major physiological importance, which has been implicated in the mechanism of essential hypertension. Others have suggested that ouabain or an isomer of ouabain may be the endogenous pump inhibitor. Neonatal cord serum contains an inhibitor of the sodium pump; we attempted to isolate and characterise this substance from human placentas.
  
  
  METHODS
  Homogenised placentas were dialysed and the resulting solutes were trapped on octadecylsilyl silica and then separated by high-performance liquid chromatography. Measurement of the activity of the sodium pump of human leucocytes was used to test each fraction for the presence of the inhibitor.
  
  
  RESULTS
  An inhibitor of the sodium pump was obtained by this technique in a mass spectrometrically pure form with a mass of 370 Da, an empirical formula of C24H34O3 and only one hydroxyl group. The characteristic fragmentation pattern observed in negative-ion mass spectrometry was compared with those of various model compounds; this comparison suggested that the active material was a dihydropyrone-substituted steroid.
  
  
  CONCLUSIONS
  These results suggest that a dihydropyrone-substituted steroid is an endogenous regulator of the sodium pump in humans and, presumably, other mammals. Proof of the endogenous origin will require the demonstration of a previously unrecognised biosynthetic pathway.
authors.affiliation: St Thomas' Hospital, London, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Hilton
authors.forename: R W
authors.initials: RW
authors.lastname: White
authors.forename: G A
authors.initials: GA
authors.lastname: Lord
authors.forename: G V
authors.initials: GV
authors.lastname: Garner
authors.forename: D B
authors.initials: DB
authors.lastname: Gordon
authors.forename: M J
authors.initials: MJ
authors.lastname: Hilton
authors.forename: L G
authors.initials: LG
authors.lastname: Forni
authors.forename: W
authors.initials: W
authors.lastname: McKinnon
authors.forename: F M
authors.initials: FM
authors.lastname: Ismail
authors.forename: M
authors.initials: M
authors.lastname: Keenan
authors.forename: K
authors.initials: K
authors.lastname: Jones
authors.forename: W E
authors.initials: WE
authors.lastname: Morden
mesh_terms: D002018:Bufanolides / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006801:Humans; D007962:Leukocytes / Q000187:drug effects* / Q000378:metabolism; D015394:Molecular Structure; D010920:Placenta / Q000737:chemistry*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D016339:Spectrometry, Mass, Fast Atom Bombardment
chemical_list: D002018:Bufanolides; D000254:Sodium-Potassium-Exchanging ATPase