title: Hormones and hemodynamics in pregnancy.
abstract: BACKGROUND
  Normal pregnancy is associated with sodium and water retention, which results in plasma volume expansion prior to placental implantation. The explanation offered for these events is that pregnancy 'resets' both volume and osmoreceptors.
  
  
  METHODS
  The mechanisms for such an enigmatic 'resetting' in pregnancy have not previously been explained. However, recent human pregnancy studies have demonstrated that the earliest hemodynamic change in pregnancy is primary systemic arterial vasodilation. This arterial underfilling is associated with a secondary increase in cardiac output and activation of the neurohumoral axis, including stimulation of the renin-angiotensin-aldosterone, sympathetic, and non-osmotic vasopressin systems. Resistance to the pressor effects of angiotensin and sympathetic stimulation in pregnancy is compatible with an increase in endothelial nitric oxide synthase activity.
  
  
  RESULTS
  In contrast to the sodium and water retention which occur secondary to the primary arterial vasodilation in cirrhosis, glomerular filtration and renal blood flow are significantly increased in normal pregnancy. A possible explanation for this difference in arterial vasodilation states is that relaxin, an arterial vasodilator which increases during pregnancy, has a potent effect on both systemic and renal circulation. Endothelial damage in pregnancy is pivotal in the pathogenesis of preeclampsia in pregnancy.
  
  
  CONCLUSIONS
  Against a background of the primary arterial vasodilation hypothesis, it is obvious that reversal of the systemic vasodilatation in pregnancy, without subsequent activation of the renin-angiotensin-aldosterone system (78), will evoke a reversal of all the links in the chain of events in normal pregnancy adaptation, thus, it may cause preeclampsia. Namely, a decrease of renal vasodilation will decrease glomerular filtration rate.
authors.affiliation: Division of Renal Diseases and Hypertension, University of Colorado Denver, Denver, Colorado, USA.
authors.forename: Oleksandra
authors.initials: O
authors.lastname: Tkachenko
authors.affiliation: Division of Renal Diseases and Hypertension, University of Colorado Denver, Denver, Colorado, USA.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Shchekochikhin
authors.affiliation: Division of Renal Diseases and Hypertension, University of Colorado Denver, Denver, Colorado, USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Schrier
keywords: Arterial; Nitric Oxide; Osmolar Concentration; Pre-Eclampsia, Endothelium; Pregnancy; Relaxin