CAPTOPRIL REVERSES THE REDUCED VASODILATOR RESPONSE TO BRADYKININ IN HYPERTENSIVE PREGNANT RATS

Arterial endothelium-derived hyperpolarization: potential role in pregnancy adaptations and complications

Pregnancy encompasses substantial changes in vascular function to accommodate dramatic increases in blood volume and uteroplacental blood flow to the growing fetus. Despite increased hemodynamics, decreased peripheral resistance results in a reduction in mean arterial blood pressure. Vascular tone, and hence peripheral resistance, is determined by a delicate balance of constrictor and dilator capacities. In the normal physiological response to pregnancy, endothelial-derived hyperpolarization (EDH) has been shown to be a major contributor; both EDH and nitric oxide (NO) are predominantly involved in providing an increased vascular capacity for vasodilation. The ability of EDH and NO to adequately accommodate increased blood volume is tested in pathological states such as placental insufficiency or diabetes and both EDH and NO-dependent mechanisms seem to be impacted in these situations. Pregnancy complications also have an impact on the cardiovascular health of the offspring. In adult offspring born from complicated pregnancies, the data suggest that EDH mechanisms are largely maintained, whereas NO is commonly reduced. A diversity of EDH mechanisms may be useful in providing many targets for potential therapeutic avenues for compromised pregnancies; however, further research delineating the mechanisms of EDH and the interactions of NO and EDH, in normal and pathological pregnancies is required.

Adaptive changes of mesenteric arteries in pregnancy: a meta-analysis

The vascular response to pregnancy has been frequently studied in mesenteric artery models by investigating endothelial cell (EC)- and smooth muscle cell (SMC)-dependent responses to mechanical (flow-mediated vasodilation, myogenic reactivity, and vascular compliance) and pharmacological stimuli (G protein-coupled receptor responses: Gq(EC), Gs(SMC), Gq(SMC)). It is unclear to what extent these pathways contribute to normal pregnancy-induced vasodilation across species, strains, and/or gestational age and at which receptor level pregnancy affects the pathways. We performed a meta-analysis on responses to mechanical and pharmacological stimuli associated with pregnancy-induced vasodilation of mesenteric arteries and included 55 (188 responses) out of 398 studies. Most included studies (84%) were performed in Wistar and Sprague-Dawley rats (SDRs) and compared late gestation versus nonpregnant controls (80%). Pregnancy promotes flow-mediated vasodilation in all investigated species. Only in SDRs, pregnancy additionally stimulates both vasodilator Gq(EC) sensitivity (EC(50) reduced by -0.76 [-0.92, -0.60] log[M]) and Gs(SMC) sensitivity (EC(50) reduced by -0.51 [-0.82, -0.20] log[M]), depresses vasopressor Gq(SMC) sensitivity (EC(50) increase in SDRs by 0.23 [0.16, 0.31] log[M]), and enhances arterial compliance. We conclude that 1) pregnancy facilitates flow-mediated vasodilation at term among all investigated species, and the contribution of additional vascular responses is species and strain specific, and 2) late pregnancy mediates vasodilation through changes at the receptor level for the substances tested. The initial steps of vasodilation in early pregnancy remain to be elucidated.

Role of renin-angiotensin system and oxidative status on the maternal cardiovascular regulation in spontaneously hypertensive rats

BACKGROUND

The purpose of this study was to investigate the contribution of renin-angiotensin system (RAS) and oxidative status on the maternal cardiovascular regulation at the end of pregnancy in normotensive and spontaneously hypertensive rats (SHR).

METHODS

Blood pressure (BP), mesenteric arterial bed (MAB) reactivity, mesenteric oxidative damage, protein expression, and antioxidant activities were compared between four groups: SHR (SHR-P) and normotensive Wistar controls (W-P) in the 20th day of pregnancy or age-matched nonpregnant rats (SHR-NP and W-NP).

RESULTS

BP in W-P and SHR-P was reduced at the end of pregnancy. The vasodilator effects of angiotensin II (Ang II) and angiotensin 1-7 (Ang-(1-7)) were higher in SHR-P than in other groups. Endothelial nitric oxide synthase (eNOS) expression was increased in W-P and SHR-P compared to nonpregnant groups. Angiotensin-converting enzyme (ACE) and AT(1) receptor expressions were increased in SHR-NP compared to normotensive groups and pregnancy reduced their expressions in SHR. No difference was observed in AT(2) receptor expression among the groups. ACE2 expression was higher in hypertensive than normotensive groups. The levels of thiobarbituric acid-reactive substances (TBARS) were reduced in pregnant compared to nonpregnant groups. Superoxide dismutase (SOD) activity was reduced in SHR-P compared to SHR-NP. However, pregnancy increased catalase (CAT) and glutathione peroxidase (GPx) activities in normotensive rats and SHR, respectively.

CONCLUSIONS

The results suggest that the reduction of BP to normal values at the end of pregnancy in SHR may be related to an increased NO production and vasorelaxation to Ang II and Ang-(1-7) associated with decreased expression of vascular ACE and AT(1) receptors and oxidative status.

Characterization of the L-arginine-NO-cGMP pathway in spontaneously hypertensive rat platelets: the effects of pregnancy

Nitric oxide (NO) is a short-lived intercellular messenger that provides an efficient vascular regulatory mechanism to support homeostasis and prevent thrombosis. Endothelial dysfunction and reduced NO bioavailability have a central role in hypertension associated with pregnancy. The purpose of this study was to investigate the impact of pregnancy on the L-arginine-NO-cGMP pathway in platelets and its correlation to platelet function and blood pressure in normotensive rats and spontaneously hypertensive rats (SHRs). Platelets were obtained from blood on the 20th day of pregnancy from female SHRs (SHR-P) and normotensive controls (P) or age-matched nonpregnant rats (SHR-NP and NP). Intraplatelet NO synthase (NOS) activity was reduced in P compared to NP, despite unchanged L-arginine influx. The expression levels of endothelial NOS (eNOS) and inducible NOS (iNOS) were diminished during pregnancy in normotensive rats. Paradoxically, cyclic guanosine monophosphate (cGMP) levels were similar between NP and P, as were phosphodiesterase type 5 (PDE5) expression and platelet aggregation induced by adenosine diphosphate. In SHRs, L-arginine influx was reduced in SHR-P compared to SHR-NP. SHR-P exhibited impaired NOS activity and reduced iNOS expression compared with SHR-NP. Soluble guanylyl cyclase and PDE5 expression in platelets were lower in SHR-P than in SHR-NP, whereas no differences were noted between groups with respect to cGMP levels. However, increased levels of cGMP were observed in SHR-P compared to normotensive groups and platelet aggregability remained unaltered. In conclusion, these observations prompted the hypothesis that normal platelet aggregation in pregnant SHRs may be related to a reduction in PDE5 expression and consequently the maintenance of cGMP levels, independently of reduced platelet NO bioavailability.

Interaction of Endothelial Nitric Oxide and Angiotensin in the Circulation

Discovery of the unexpected intercellular messenger and transmitter nitric oxide (NO) was the highlight of highly competitive investigations to identify the nature of endothelium-derived relaxing factor. This labile, gaseous molecule plays obligatory roles as one of the most promising physiological regulators in cardiovascular function. Its biological effects include vasodilatation, increased regional blood perfusion, lowering of systemic blood pressure, and antithrombosis and anti-atherosclerosis effects, which counteract the vascular actions of endogenous angiotensin (ANG) II. Interactions of these vasodilator and vasoconstrictor substances in the circulation have been a topic that has drawn the special interest of both cardiovascular researchers and clinicians. Therapeutic agents that inhibit the synthesis and action of ANG II are widely accepted to be essential in treating circulatory and metabolic dysfunctions, including hypertension and diabetes mellitus, and increased availability of NO is one of the most important pharmacological mechanisms underlying their beneficial actions. ANG II provokes vascular actions through various receptor subtypes (AT1, AT2, and AT4), which are differently involved in NO synthesis and actions. ANG II and its derivatives, ANG III, ANG IV, and ANG-(1-7), alter vascular contractility with different mechanisms of action in relation to NO. This review article summarizes information concerning advances in research on interactions between NO and ANG in reference to ANG receptor subtypes, radical oxygen species, particularly superoxide anions, ANG-converting enzyme inhibitors, and ANG receptor blockers in patients with cardiovascular disease, healthy individuals, and experimental animals. Interactions of ANG and endothelium-derived relaxing factor other than NO, such as prostaglandin I2 and endothelium-derived hyperpolarizing factor, are also described.

Effects of oral beraprost sodium, a prostaglandin I2 analogue, on endothelium dependent vasodilatation in the forearm of patients with coronary artery disease

1. Previous clinical studies with prostaglandin I(2) (PGI(2)) analogue beraprost sodium suggested the potential effects on protection of cardiovascular events in patients with peripheral artery disease. Although the mechanism is not well known, experimental studies have shown protective effects of endothelial cells. This study was designed to examine the effects of beraprost sodium on vascular endothelial function in the forearm of patients with coronary artery disease. 2. Beraprost sodium (120 microg/day) was orally administered to 14 coronary artery disease patients for 4 weeks and then stopped for 4 weeks. Eleven control patients did not receive beraprost sodium treatment. Reactive hyperemia was induced in the forearm, endothelium-dependent vasodilatation was assessed by plethysmography, and urinary 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)) was measured at baseline, 4 weeks and 8 weeks. 3. Both groups had similar reactive hyperemic responses at baseline. In the control group, reactive hyperemic response and urinary 8-iso-PGF(2alpha) remained unchanged for 8 weeks. In the beraprost group, maximum forearm blood flow increased significantly (P = 0.01) after 4 weeks of treatment and returned to baseline at 8 weeks. Duration of hyperemia increased significantly (P = 0.003) after 4 weeks, and remained greater than baseline at 8 weeks (P = 0.02). Urinary 8-iso-PGF(2alpha) decreased significantly (P = 0.03) after 4 weeks, and tended to be lower at 8 weeks (P = 0.07). Changes in reactive hyperemia correlated weakly but significantly with changes in 8-iso-PGF(2alpha) (P < 0.001). 4. Beraprost sodium decreased oxidative stress and improved forearm endothelium-dependent vasodilatation in coronary artery disease patients. The favorable effects on vascular endothelium could potentially lead to a decrease in vascular events.