title: Prolactin, a natriuretic hormone, interacting with the renal dopamine system.
abstract: BACKGROUND
  Although prolactin affects sodium and water transport across the plasma membrane and interacts with dopamine in the brain, its role in the kidney is unclear. Here we examined the effect of prolactin and its possible interaction with the intrarenal natriuretic hormone dopamine, on proximal tubular Na(+), K(+)-ATPase activity in vitro and renal function in anesthetized rats.
  
  
  METHODS
  Na(+), K(+)-ATPase activity was measured as ouabain-sensitive adenosine triphosphate (ATP) hydrolysis in microdissected proximal tubular segments. Renal function was studied during euvolemic conditions by conventional clearance techniques.
  
  
  RESULTS
  Prolactin induced a dose-dependent inhibition of proximal tubular Na(+), K(+)-ATPase activity. A maximal inhibitory effect of 48% of control was observed at an in vitro prolactin concentration of 1 microg/mL. This effect was completely abolished by a dopamine D1 receptor antagonist. In tubules preincubated with inhibitors of aromatic amino acid decarboxylase (AADC), the rate-limiting enzyme in renal dopamine formation, prolactin had no effect on Na(+), K(+)-ATPase activity. In rats, prolactin infusion resulted in an increase in urinary sodium, potassium, and water excretion. These effects were also completely abolished by the D1 receptor antagonist. Prolactin had no significant effects on glomerular filtration rate (GFR) or mean arterial blood pressure.
  
  
  CONCLUSIONS
  We conclude that prolactin is a natriuretic hormone which interacts with the renal dopamine system for its effects. The natriuretic response is associated with inhibition of proximal tubular Na(+), K(+)-ATPase activity.
authors.affiliation: Department of Woman and Child Health, Pediatric Unit, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Fernando
authors.initials: F
authors.lastname: Ibarra
authors.forename: Susanne
authors.initials: S
authors.lastname: Crambert
authors.forename: Ann-Christine
authors.initials: AC
authors.lastname: Eklöf
authors.forename: Annika
authors.initials: A
authors.lastname: Lundquist
authors.forename: Peter
authors.initials: P
authors.lastname: Hansell
authors.forename: Ulla
authors.initials: U
authors.lastname: Holtbäck
mesh_terms: D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D004298:Dopamine / Q000502:physiology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009318:Natriuresis / Q000187:drug effects / Q000502:physiology*; D011388:Prolactin / Q000494:pharmacology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000037:antagonists & inhibitors / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology*
chemical_list: D001552:Benzazepines; D018492:Dopamine Antagonists; D017447:Receptors, Dopamine D1; D011388:Prolactin; D000254:Sodium-Potassium-Exchanging ATPase; D004298:Dopamine