It has been increasingly appreciated that steroids elicit acute vascular effects through rapid, so-called nongenomic signaling pathways. Though aldosterone, for example, has been demonstrated to mediate rapid vascular effects via both mineralocorticoid receptor–dependent and –independent pathways, the mechanism(s) of this mineralocorticoid receptor–independent effect of aldosterone is yet to be determined. For estrogen, its rapid effects have been reported to be, at least in part, mediated via the 7-transmembrane–spanning, G protein–coupled receptor GPR30. Previous studies have demonstrated common response outcomes in response to both aldosterone and estrogen on GPR30 expression, ie, activation of phosphatidylinositol 3-kinase–dependent contraction and extracellular signal-regulated kinase activation in vascular smooth muscle cells. The present studies were undertaken to test the hypothesis that the rapid response to aldosterone in smooth muscle is dependent on the availability of a GPR30-dependent signaling pathway. These findings not only reconcile differences in the literature for aldosterone response in freshly isolated versus cultured aortic smooth muscle cells but also suggest alternative therapeutic strategies for modulating aldosterone actions on the vasculature in vivo.

Decreased endothelial NO synthase (eNOS)-derived NO bioavailability and impaired vasomotor control are crucial factors in cardiovascular disease pathogenesis. Hereditary hemorrhagic telangiectasia type 1 (HHT1) is a vascular disorder associated with ENDOGLIN ( ENG ) haploinsufficiency and characterized by venous dilatations, focal loss of capillaries, and arteriovenous malformations (AVMs). We report that resistance arteries from Eng ^+/− mice display an eNOS-dependent enhancement in endothelium-dependent dilatation and impairment in the myogenic response, despite reduced eNOS levels. We have found that eNOS is significantly reduced in endoglin-deficient endothelial cells because of decreased eNOS protein half-life. We demonstrate that endoglin can reside in caveolae and associate with eNOS, suggesting a stabilizing function of endoglin for eNOS. After Ca ²⁺ -induced activation, endoglin-deficient endothelial cells have reduced eNOS/Hsp90 association, produce less NO, and generate more eNOS-derived superoxide (O ₂ ⁻ ), indicating that endoglin also facilitates eNOS/Hsp90 interactions and is an important regulator in the coupling of eNOS activity. Treatment with an O ₂ ⁻ scavenger reverses the vasomotor abnormalities in Eng ^+/− arteries, suggesting that uncoupled eNOS and resulting impaired myogenic response represent early events in HHT1 pathogenesis and that the use of antioxidants may provide a novel therapeutic modality.

Impaired vascular beta-adrenergic responsiveness may play an important role in the development and/or maintenance of hypertension. This defect has been associated with an alteration in receptor/guanine nucleotide regulatory protein (G-protein) interactions. However, the locus of this defect remains unclear. G-Protein-coupled receptor kinases (GRKs) phosphorylate serine/threonine residues on G-protein-linked receptors in an agonist-dependent manner. GRK activation mediates reduced receptor responsiveness and impaired receptor/G-protein coupling. To determine whether the impairment in beta-adrenergic response in human hypertension might be associated with altered GRK activity, we studied lymphocytes from younger hypertensive subjects as compared with older and younger normotensive subjects. We assessed GRK activity by rhodopsin phosphorylation and GRK expression by immunoblot. GRK activity was significantly increased in lymphocytes from younger hypertensive subjects and paralleled an increase in GRK-2 (beta ARK-1) protein expression. In contrast, no alterations in cAMP-dependent kinase (A-kinase) activity or GRK-5/6 expression were noted. GRK activity was not increased in lymphocytes from older normotensive subjects who demonstrated a similar impairment in beta-adrenergic-mediated adenylyl cyclase activation. These studies indicate that GRK activity is selectively increased in lymphocytes from hypertensive subjects. The increase in GRK activity may underlie the reduction in beta-adrenergic responsiveness characteristic of the hypertensive state.

The importance of the rapid vascular effects of aldosterone is increasingly appreciated. Through these rapid pathways, aldosterone has been shown to regulate vascular contractility, cell growth, and apoptosis. In our most recent studies, we demonstrated the effects of aldosterone on cell growth and contractility in vascular smooth muscle cells. We showed that these effects could occur via activation of the classic mineralocorticoid receptor, as well the recently characterized G protein-coupled estrogen receptor (GPER), initially characterized as an estrogen-specific receptor. However, the mechanisms underlying aldosterone's endothelium-dependent actions are unknown. Furthermore, the ERK regulatory and proapoptotic effects of aldosterone mediated by GPER activation in cultured vascular smooth muscle cells were only apparent when GPER was reintroduced into these cells by gene transfer. Whether GPER activation via aldosterone might be an important regulator in native vascular cells has been questioned. Therefore, to determine the role of GPER in mediating aldosterone's effects on cell growth and vascular reactivity in native cells, we examined rat aortic vascular endothelial cells, a model characterized by persistent robust expression of GPER, but without detectable mineralocorticoid receptor expression. In these endothelial cells, the GPER agonist G1 mediates a rapid increase in ERK phosphorylation that is wholly GPER-dependent, paralleling the actions of aldosterone. The effects of G1 and aldosterone to stimulate ERK phosphorylation paralleled their proapoptotic and antiproliferative effects. In previous studies, we reported that aldosterone mediates a rapid endothelium-dependent vasodilatory effect, antagonistic to its direct vasoconstrictor effect in endothelium-denuded preparations. Using a rat aortic ring/organ bath preparation to determine the GPER dependence of aldosterone's endothelium-dependent vasodilator effects, we demonstrate that aldosterone inhibits phenylephrine-mediated contraction. This vasodilator effect parallels the actions of the GPER agonist G1. Furthermore, the effects of aldosterone were completely ablated by the GPER antagonist G15. These data support an important role of GPER activation in aldosterone-mediated regulation of endothelial cell growth, as well as in aldosterone's endothelium-mediated regulation of vasoreactivity.

Glucagon-like peptide-1 (GLP-1) acts via its G protein-coupled receptor (GLP-1R) to regulate blood glucose. Although the GLP-1R is widely expressed in peripheral tissues, including the heart, and exogenous GLP-1 administration increases heart rate and blood pressure in rodents, the physiological importance of GLP-1R action in the cardiovascular system remains unclear. We now show that 2-month-old mice with genetic deletion of the GLP-1R (GLP-1R^−/−) exhibit reduced resting heart rate and elevated left ventricular (LV) end diastolic pressure compared with CD-1 wild-type controls. At the age of 5 months, echocardiography and histology demonstrate increased LV thickness in GLP-1R^−/− mice. Although baseline hemodynamic parameters of GLP-1R^−/− did not differ significantly from those of wild type, GLP-1R^−/− mice displayed impaired LV contractility and diastolic function after insulin administration. The defective cardiovascular response to insulin was not attributable to a generalized defect in the stress response, because GLP-1R^−/− mice responded appropriately to insulin with increased c-fos expression in the hypothalamus and increased circulating levels of glucagon and epinephrine. Furthermore, LV contractility after exogenous epinephrine infusion was also reduced in GLP-1R^−/− mice. These findings provide new evidence implicating an essential role for GLP-1R in the control of murine cardiac structure and function in vivo.

Background— Myocardial expression of endothelin-1 (ET-1) and its receptors ET _A and ET _B is increased in heart failure. However, the role of ET-1 and its signaling pathways in the pathogenesis of myocardial diseases is unclear. Methods and Results— Human ET-1 cDNA was placed downstream of a promoter responsive to a doxycycline (DOX)-regulated transcriptional activator (tTA). This line (ET ⁺ ) was bred with one harboring cardiac myocyte-restricted expression of tTA (αMHC-tTA). Myocardial ET-1 peptide levels were significantly increased in binary transgenic (BT, ET ⁺ /tTA ⁺ ) compared with nonbinary transgenic (NBT, ET ⁺ /tTA ⁻ ; ET ⁻ /tTA ⁺ ; ET ⁻ /tTA ⁻ ) or DOX-treated BT littermates (40.1±4.7 versus 2.6±1.2 fmol/mL, P <0.003). BT mice demonstrated progressive mortality between 5 and 11 weeks after DOX withdrawal, associated with left ventricular dilatation and contractile dysfunction (peak +dP/dT, 4673±468 versus 5585±658 mm Hg/s, P <0.05). An interstitial inflammatory infiltrate, including macrophages and T lymphocytes, was evident in the myocardium of BT mice, associated with sequential increases in nuclear factor-κB translocation and expression of tumor necrosis factor-α, interferon-γ, interleukin-1 and interleukin-6. Significant prolongation of survival was observed with the combined ET _A /ET _B antagonist LU420627 (n=8, P <0.05) in BT mice but not the ET _A -selective antagonist LU135252 (n=5, P =0.9), consistent with an important role for ET _B in this model. Conclusions— These are the first data to demonstrate that cardiac overexpression of ET-1 is sufficient to cause increased expression of inflammatory cytokines and an inflammatory cardiomyopathy leading to heart failure and death.