Ovine fetal hormonal and hypothalamic neuroendocrine responses to maternal water deprivation at late gestation

New conception for the development of hypertension in preeclampsia

Placental vascular dysfunction was suggested to be critical for placental ischemia-initiated hypertension in preeclampsia, although the contributions of endothelium involved are unclear. The present study found, unlike non-placental vessels, acetylcholine showed no vasodilatation effect on placental vessels, indicating that endothelial-derived nitric oxide (NO) was extremely weak in placental vessels. Placental vascular responses to exogenous NO from sodium nitroprusside (SNP) were significantly different from non-placental vessels. These results were further confirmed in sheep, and rat vessels. In preeclamptic placental vessels, acetylcholine also showed no vasodilatation effects, while vascular responses to SNP were suppressed, associated with impaired cGMP/sGC pathway in vascular smooth muscle cells (VSMCs). The current theory on placental ischemia-initiated hypertension in preeclampsia focused on changes in placental vascular functions, including endothelial dysfunction. This study found the placental endothelium contributed very poorly to vasodilatation, and altered vascular functions in preeclampsia mainly occurred in VSMCs instead of endothelial cells. The findings contribute importantly to understanding the special feature of placental vascular functions and its pathophysiological changes in the development of hypertension in preeclampsia.

Ovine uterine space restriction causes dysregulation of the renin-angiotensin system in fetal kidneys

In ovine pregnancy, uterine space restriction (USR) resulting from decreased space for placental attachment caused intrauterine growth restriction and impaired nephrogenesis. The fetal kidney renin-angiotensin system (RAS) is involved in nephrogenesis, fluid balance, and iron deposition. Angiotensin II exerts its effects via multiple receptors: angiotensin II 1-8 receptor type 1 (AT 1 R) and type 2 (AT 2 R), and angiotensin II 1-7 Mas receptor (MASR).

Objective

: To test the hypothesis that ovine USR is associated with dysregulation of the fetal renal RAS.

Methods

: Multiparous pregnant ewes (n = 32), 16 with surgical bifurcated disconnection of one uterine horn to further reduce placental attachment sites, were studied. USR (n = 31) ovine fetuses were compared to nonspace restricted (NSR) singleton controls (n = 22) on gestational day (GD) 120 or GD130, term GD147. Fetal plasma was collected to evaluate plasma renin activity and iron indices. Fetal kidney AT 1 R, AT 2 R, and MASR proteins were assessed by Western immunoblotting and immunohistochemistry.

Results

: AT 1 R, AT 2 R, and MASR protein expression was higher in USR at GD130 than aged-matched NSR and USR at GD120, ( P < 0.05 all). AT 1 R and AT 2 R localization was homogenous throughout proximal and distal tubules in both USR and NSR at both gestational dates. MASR localization was punctate throughout renal cortical structures including tubules and glomeruli in both USR and NSR, shifted to intranuclear at GD130. Plasma renin activity was inversely related to plasma osmolarity ( P < 0.02) and was downregulated in USR at GD130 ( P < 0.05).

Conclusions

: By late gestation, USR upregulated renal angiotensin receptor expression, an effect with potential functional implications.