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The peptide relaxin has gained considerable attention as a new vasoactive drug, largely through its beneficial therapeutic effects in cardiovascular disease. In this study, we tested the hypothesis that relaxin treatment alleviates systemic vascular dysfunction characteristic of hypertensive diseases of pregnancy. We investigated vascular effects and mechanisms of relaxin action in (i) pregnant relaxin-deficient (Rln−/−) mice with enhanced responses to angiotensin II (AngII) and (ii) arteries pre-incubated ex vivo in trophoblast conditioned media (TCM) to induce endothelial dysfunction. Pregnant Rln−/−mice received 0.5 μg/h recombinant human H2 relaxin (rhRLX: n = 5) or placebo (20 nM sodium acetate; n = 7) subcutaneously via osmotic minipumps for 5 days prior to gestational day 17.5. This treatment protocol significantly reduced AngII-mediated contraction of mesenteric arteries and increased plasma 6-keto prostaglandin F1α. These vascular effects were endothelium independent and likely involve smooth muscle-derived vasodilator prostanoids. In the second study, mesenteric arteries were incubated ex vivo for 24 h at 37°C in TCM, which contained high levels of soluble Flt-1 (>20 ng/ml) and soluble Eng (>1 ng/ml). TCM incubation caused significant reduction in endothelium-dependent relaxation and increased sensitivity to AngII. Co-incubation of arteries with rhRLX for 24 h (n = 6–16/treatment) prevented endothelial dysfunction but had no effect on AngII-mediated contraction. In conclusion, relaxin treatment prevents and/or reverses vascular dysfunction in mesenteric arteries, but acts through different vascular pathways depending on duration of relaxin treatment and type of vascular dysfunction. Overall, our data suggest that relaxin is a potential therapeutic to alleviate maternal systemic vascular dysfunction associated with hypertensive diseases in pregnant women.Relaxin treatment reduces the vasoconstriction of the mesenteric artery to angiotensin II and protects the vasculature from developing endothelial dysfunction.

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Epidemiological studies reveal that children born with a solitary functioning kidney (SFK) have a greater predisposition to develop renal insufficiency and hypertension in early adulthood. A congenital SFK is present in patients with unilateral renal agenesis or unilateral multicystic kidney dysplasia, leading to both structural and functional adaptations in the remaining kidney, which act to mitigate the reductions in glomerular filtration rate and sodium excretion that would otherwise ensue. To understand the mechanisms underlying the early development of renal insufficiency in children born with a SFK, we established a model of fetal uninephrectomy (uni-x) in sheep, a species that similar to humans complete nephrogenesis before birth. This model results in a 30% reduction in nephron number rather than 50%, due to compensatory nephrogenesis in the remaining kidney. Similar to children with a congenital SFK, uni-x sheep demonstrate a progressive increase in arterial pressure and a loss of renal function with aging. This review summarizes the compensatory changes in renal hemodynamics and tubular sodium handling that drive impairments in renal function and highlights the existence of sex differences in the functional adaptations following the loss of a kidney during fetal life.

The role of endothelium‐derived hyperpolarizing factor (EDHF) in the regulation of blood flow in vivowas examined in the mesenteric and hindlimb circulations of anaesthetized rats. Basal mesenteric conductance decreased from 57 ± 5 to 20 ± 6 μl min−1mmHg−1when nitric oxide (NO) production was inhibited, and combined blockade of intermediate‐ and small‐conductance Ca2+‐activated K+(KCa) channels with charybdotoxin (ChTx) and apamin had no further effect. Basal hindlimb conductance was reduced from 39 ± 3 to 22 ± 2 μl min−1mmHg−1by NO synthesis inhibition, with no effect of the KCachannel blockers. Endothelial stimulation with acetylcholine (ACh) infusion directly into the mesenteric bed increased conductance by 20 ± 2 μl min−1mmHg−1. Blockade of NO synthesis decreased this conductance to 15 ± 1 μl min−1mmHg−1, leaving the response attributable to EDHF. This was reduced to 2 ± 1 μl min−1mmHg−1by ChTx plus apamin but not by iberiotoxin, which selectively blocks large‐conductance KCachannels. Similar results were obtained when bradykinin (BK) was used to stimulate the endothelium. Nitroprusside, which directly relaxes smooth muscle, evoked an increase in conductance that was resistant to all blockers tested. ACh‐induced increases in hindlimb conductance were reduced from 19 ± 1 to 12 ± 1 μl min−1mmHg−1by NO synthesis inhibition and further reduced to 2 ± 2 μl min−1mmHg−1by ChTx plus apamin. In contrast to NO, ChTx‐ and apamin‐sensitive EDHF appears to contribute little to basal conductance in rat mesenteric and hindlimb beds. However, EDHF accounts for a significant component of the conductance increase during endothelial stimulation by ACh and BK. In these beds, intermediate‐ and small‐conductance KCachannels underpin EDHF‐mediated vasodilatation.

1Membrane currents attributed to endothelium‐derived hyperpolarizing factor (EDHF) were recorded in short segments of submucosal arterioles of guinea‐pigs using single microelectrode voltage clamp. The functional responses of arterioles and human subcutaneous, rat hepatic and guinea‐pig coronary arteries were also assessed as changes in membrane potential recorded simultaneously with contractile activity.2The current‐voltage (I‐V) relationship for the conductance due to EDHF displayed outward rectification with little voltage dependence. Components of the current were blocked by charybdotoxin (30‐60 nM) and apamin (0.25‐0.50 μM), which also blocked hyperpolarization and prevented EDHF‐induced relaxation.3The EDHF‐induced current was insensitive to Ba2+(20‐100 μM) and/or ouabain (1 μM to 1 mM).4In human subcutaneous arteries and guinea‐pig coronary arteries and submucosal arterioles, the EDHF‐induced responses were insensitive to Ba2+and/or ouabain. Increasing [K+]oto 11‐21 mM evoked depolarization under conditions in which EDHF evoked hyperpolarization.5Responses to ACh, sympathetic nerve stimulation and action potentials were indistinguishable between dye‐labelled smooth muscle and endothelial cells in arterioles. Action potentials in identified endothelial cells were always associated with constriction of the arterioles.618β‐Glycyrrhetinic acid (30 μM) and carbenoxolone (100 μM) depolarized endothelial cells by 31 ± 6 mV (n= 7animals) and 33 ± 4 mV (n= 5), respectively, inhibited action potentials in smooth muscle and endothelial cells and reduced the ACh‐induced hyperpolarization of endothelial cells by 56 and 58 %, respectively.7Thus, activation of outwardly rectifying K+channels underlies the hyperpolarization and relaxation due to EDHF. These channels have properties similar to those of intermediate conductance (IKCa) and small conductance (SKCa) Ca2+‐activated K+channels. Strong electrical coupling between endothelial and smooth muscle cells implies that these two layers function as a single electrical syncytium. The non‐specific effects of glycyrrhetinic acid precludes its use as an indicator of the involvement of gap junctions in EDHF‐attributed responses. These conclusions are likely to apply to a variety of blood vessels including those of humans.

The contribution of endothelium‐derived hyperpolarizing factor (EDHF), nitric oxide (NO) and a prostanoid (PG) to endothelium‐dependent hyperpolarization and relaxation were assessed in coronary and mammary arteries of guinea‐pigs by integration of the responses evoked during discrete applications of acetylcholine (ACh). The results of this integration approach were compared with those using traditional peak analysis methods.Nω‐nitro‐L‐arginine methyl ester (L‐NAME, 100 μM) and indomethacin (1 μM), alone or in combination, were without effect on peak hyperpolarizations or relaxations while they markedly reduced the integrated responses in both arteries.Integrated responses attributed to NO and PG were larger than those attributed to EDHF in the coronary artery (at 2 μMACh, hyperpolarization (mV s): NO, 4200±91; PG, 5046±157; EDHF, 1532±94; relaxation (mN s mm−1): NO, 2488±122; PG, 2234±96; EDHF, 802±54). Integrated responses attributed to NO, PG and EDHF were similar in the mammary artery (at 2 μMACh, hyperpolarization: NO, 347±69; PG, 217±49; EDHF, 310±63; relaxation: NO, 462±94; PG, 456±144; EDHF, 458±40).Gilbenclamide (1 μM) all but abolished the hyperpolarization attributable to NO and PG but not EDHF in both arteries allowing assessment of the role of the hyperpolarization in relaxation. Gilbenclamide was without effect on the integrated relaxation due to NO but significantly reduced the relaxation associated with PG in the two arteries.In conclusion, integration of the responses enabled a more complete assessment of the contribution of EDHF, NO and PG to endothelium‐dependent responses, which were strikingly different in the two arteries. There is commonality in the role of hyperpolarization in relaxation in both arteries: EDHF‐dependent relaxation is strongly dependent on hyperpolarization; hyperpolarization plays an important role in PG relaxation, whereas it has a small facilitatory role in NO‐dependent relaxation.

The membrane potential responses in guinea‐pig coronary and mammary arteries attributable to endothelium‐derived nitric oxide (NO), prostaglandin (PG) and hyperpolarizing factor (EDHF), and to exogenous NO and the prostacyclin analogue, iloprost, were compared at rest and when depolarized with the thromboxane analogue, U46619.In the coronary artery, stimulation of the endothelium with acetylcholine (ACh) evoked hyperpolarization attributable to NO and a PG with similar pD2s at rest and in the presence of U46619. However, in depolarized tissues, the pD2of the response attributed to EDHF required a 10 fold lower concentration of ACh compared with at rest.In the mammary artery, lower concentrations of ACh were required to evoke NO‐ and EDHF‐dependent hyperpolarizations in depolarized mammary artery compared with at rest, while PG‐dependent hyperpolarization did not occur until the concentration of ACh was increased some 10 fold both at rest and in U46619.The smooth muscle of the coronary artery of guinea‐pigs was some 4 fold more sensitive to exogenous NO and iloprost than was the mammary artery.In conclusion, the membrane potential response in arteries at rest, that is, in the absence of constrictor, may be extrapolated to events in the presence of constrictor when NO and PG are under study. However, the sensitivity to ACh and the magnitude of the hyperpolarization attributed to EDHF obtained in tissues at rest may underestimate these parameters in depolarized tissues.

Reduction of vascular RGS5 causes hypertension and preeclampsia, which can be reversed by PPAR agonist treatment in mouse models.

Pregnancy is associated with a progressive remodeling of the uterine artery. This adaptation is influenced by local and systemic pregnancy-dependent factors. We recently demonstrated that the peptide hormone relaxin mediates uterine artery remodeling in late pregnant rats. The objective of this study in relaxin gene knockout (Rln−/−) mice was to test the hypothesis that relaxin deficiency throughout pregnancy disrupts uterine artery remodeling, an effect that is exacerbated by aging and reversed with relaxin treatment. Passive mechanical wall properties and extracellular matrix components were measured using pressure myography, quantitative PCR, and zymography in uterine arteries from pregnant wild-type (Rln+/+) and Rln−/−mice aged 5 and 8 mo on Days 12.5 and 17.5 pregnancy. In a second study, 8-mo-old Rln−/−mice received either placebo or human recombinant relaxin subcutaneously for 5 days from Day 12.5 pregnancy. Relaxin deficiency in pregnancy did not alter uterine artery remodeling in young mice. However, remodeling was impaired in older pregnant Rln−/−mice, resulting in significantly stiffer uterine arteries. Uterine arteries of aged Rln−/−pregnant mice had increased expression of elastin, whereas several matrix metalloproteinases and cell adhesion molecules were decreased relative to Rln+/+mice. Fetal weight was also significantly reduced in Rln−/−mice in late pregnancy in both young and old dams, whereas placental weight was unchanged. Arterial stiffness and reduced fetal weight were reversed after relaxin treatment. In conclusion, relaxin deficiency compromises uterine artery remodeling in older pregnant females, increasing the risk of pregnancy complications such as hypertension and intrauterine growth restriction.

Renal denervation (RDNX) attenuates the development of hypertension in animal models. Recent ongoing clinical trials using a catheter-based RDNX procedure in humans show promising long-term blood pressure-attenuating results. However, the mechanisms underpinning this attenuation are unclear. The aim of this study was to examine the functional reinnervation of the renal vasculature by the sympathetic nerves following RDNX.

Fetal uni-nephrectomy (uni-x) at 100 days of gestation in sheep is associated with a 30 nephron deficit, hypertension and renal dysfunction in adulthood. We hypothesized that the control of renal vascular function would be altered in uni-x animals, with a reduced contribution of nitric oxide (NO).

Many women of reproductive age are vitamin D (VitD) deficient and the implications for the cardiovascular health of their offspring are unknown. The aim of this study was to examine the effects of in uteroand early life VitD insufficiency in rats on cardiovascular and renal function in the offspring.

In recent years there has been a resurgence of vitamin D deficiency in the community, largely due to the lack of exposure of individuals to sunlight. Importantly, there is substantial evidence linking vitamin D deficiency with increased risk of cardiovascular disease, including hypertension, coronary artery disease (including myocardial infarction) and heart failure.