New insights into the control of small artery function in human pregnancy and estrogen receptor beta knockout mice

Background: Available data clearly indicates functional and morphological differences between small and large arteries, and observations from studies on large arteries may not be applicable to understand the physiology of small arteries (~200-300 m) that actively participate in the regulation of peripheral vascular resistance, blood pressure and flow to target organs. These events confer cardiovascular adaptation to normal pregnancy (NP), however they are disturbed in preeclampsia (PE) and in estrogen receptor knockout (ER KO) mice at a certain age. Aims: (1) To assess endothelial function and morphology with focus on the role and mechanisms of endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation in small subcutaneous arteries isolated from pregnant women with and without PE; (2) To estimate the predisposition for sex difference in blood pressure of ER KO mice at the level of small arteries’ function with a focus on endothelium-dependent dilatation (EDHF) and adrenergic vasoconstriction. Methodology: Small subcutaneous arteries obtained from pregnant women and femoral arteries obtained from age-matched (14-22 weeks old) female and male wild type (WT, ER +/+) and ER KO mice were used in a wire-myography set-up for functional studies. Immunohistochemistry for connexins (Cx) and/or ER subtypes (as appropriate), as well as scanning and transmission electron microscopy techniques were also utilized for evaluation of small arteries’ morphology with particular focus on prerequisite for gap junction communications. Results and conclusions: (1) The overall endothelium-dependent response in arteries from pregnant women with and without PE was similar. However, EDHF-mediated relaxation was reduced in PE. The results demonstrated heterogeneity in the relative contribution of endothelium-derived factors and in the mechanisms responsible for the EDHF-mediated relaxation in PE. Gap junctions and/or H2O2 and/or cytochrome P450 epoxygenase metabolites of arachidonic acid appeared to be involved in the EDHF-mediated response in PE. In NP women, communication via gap junctions via Cx 43 represented a common pathway responsible for EDHF action. The link between morphological alterations within the vascular wall, and changes in the contribution of gap junctions to EDHF-mediated relaxation of small arteries isolated from women with PE was suggested. (2) Endothelium-dependent relaxation in arteries (<200 m of internal diameter) was greater in WT females vs. males, and this was attributed to a greater EDHF component in the relaxation. This difference was absent in ER KO mice. The data suggests that in WT male mice ER reduces EDHF-mediated relaxation. The pharmacological evidence and morphological prerequisite for involvement of gap junctions in EDHF-mediated responses was indicated in male arteries. However, the absence of ER had no influence on expression of the main Cx subtypes within the vascular wall or on the ultrastructure and morphology of the endothelium. The increased EDHF contribution to endothelium-dependent dilatation in ER KO male mice vs. WT could not explain the hypertension observed in ER KO animals. (3) Femoral arteries from ER KO male mice demonstrated an enhancement of the contractile response to 1-adrenoceptor agonist (phenylephrine) that was accompanied by elevated basal tension attributable to endothelial factors. Contractile responses to the mixed adrenoceptor agonist, norepinephrine, were similar in ER KO and WT mice; however the addition of adrenoceptor inhibitor unmasked the enhancement of the underlying 1-adrenoceptor responsiveness pertinent to males. -Adrenoceptor-mediated dilatation was also enhanced in ER KO vs. WT males. We suggest that ER modifies the adrenergic control of small artery tone in males, but not in females. The alterations in the adrenergic modulation of small artery tone might commence the hypertension in ER KO males. Significance: Heterogeneity in manifestation of functional and morphological signs of endothelial dysfunction at the level of small arteries in PE indicates a complexity and multifactor genesis of this pregnancy-related disorder. The relative importance of ER for the control of small artery function found in males in the rodent model substantiates a genderrelated approach for prevention and treatment of cardiovascular disease.