Jean St-Louis

Antibody to marinobufagenin lowers blood pressure in pregnant rats on a high NaCl intake

Objective The pathogenesis of pre-eclampsia (PE), a major cause of maternal and fetal mortality, is not fully understood. Digitalis-like sodium pump ligands (SPLs) are believed to be implicated in PE, as illustrated by clinical observations that DIGIBIND, a digoxin antibody that binds SPLs, lowers blood pressure (BP) in PE. We recently reported that plasma levels of marinobufagenin (MBG), a vasoconstrictor SPL, are increased four-fold in patients with PE. In the present study, we tested whether a polyclonal antibody to MBG can lower BP in rats with pregnancy-associated hypertension. Methods Systolic BP (SBP), 24-h renal excretion of MBG and endogenous ouabain (EO), and sodium pump activity in the thoracic aortae were measured in virgin and pregnant Sprague–Dawley rats without and with NaCl supplementation (drinking 1.8% NaCl solution). Results NaCl supplementation of virgin rats stimulated renal excretion of MBG by 60%, but not that of EO, and did not change the BP. Compared with virgin rats, the last week of pregnancy in non-NaCl-loaded rats was associated with a decrease in SBP (106 ± 2 versus 117 ± 2 mmHg); a moderate increase in renal excretion of MBG (97.6 ± 4.9 versus 57.4 ± 7.0 pmoles/24 h) and EO (36.2 ± 4.3 versus 24.1 ± 3.2 pmoles/24 h). NaCl-loaded pregnant rats exhibited elevation in SBP (139 ± 3 mmHg; P < 0.01 versus non-NaCl-loaded pregnant rats), in renal excretion of MBG (160.0 ± 17.5 pmoles/24 h; P < 0.01 versus non-NaCl-loaded pregnant rats), but not in EO, and showed fetal growth retardation. Administration of the anti-MBG antibody to NaCl-loaded pregnant rats lowered SBP (111 ± 2 mmHg; P < 0.01) and increased aortic sodium pump activity (144 ± 3 versus 113 ± 5 nmol 86Rb/g per min; P < 0.01 versus non-NaCl-loaded pregnant rats). Conclusions These observations provide evidence that MBG contributes to BP elevation in pregnant rats rendered hypertensive by NaCl supplementation.

Prostaglandin- or endothelium-mediated vasodilation is notinvolved in the blunted responses of blood vessels to vasoconstrictors in pregnant rats

Pregnancy is associated with decreases of blood pressure and vascular sensitivity to vasopressor agents. We have hypothesized that the increased liberation of endogenous vasodilator(s) by the vascular endothelium or other structures could mediate these blunted responses. Thoracic aorta rings of nonpregnant, 21 days pregnant, and first day post partum rats respond similarly to acetylcholine, an endothelium-dependent vasorelaxant. In contrast, the potency of the response to sodium nitroprusside, an endothelium-independent vasorelaxant, is unchanged in tissues of pregnant rats and increased (p less than 0.05) in those of post partum animals. In the presence of indomethacin (10 mumol/L) the three groups of tissues show a decreased potency. The effects of phenylephrine on aortic rings of both nonpregnant and pregnant rats are markedly increased in the presence of Ng-monomethyl-L-arginine. Indeed, the concentration producing 50% of the maximum response of phenylephrine decreases (p less than 0.001) from 50.7 to 8.02, from 93.8 to 37.6, and from 60.4 to 5.97 nmol/L with the use of Ng-monomethyl-L-arginine (0.1 mmol/L) in rings from nonpregnant, pregnant, and postpartum rats, respectively. Simultaneously, the maximum response to phenylephrine increases markedly in the three groups of tissues. In the presence of Ng-monomethyl-L-arginine, indomethacin does not influence the response to phenylephrine. Our results do not support the possible involvement of an endogenous vasodilator (prostaglandin-like or endothelium-derived) in the blunted responses to vasoconstrictors during pregnancy.

Blunted Responses to Vasoconstrictors in Mesenteric Vasculature but not in Portal Vein of Spontaneously Hypertensive Rats Treated with Relaxin

Abstract Relaxin (RLX), an ovarian polypeptide hormone that is particularly associated with gestation in viviparous species, has recently been shown to decrease blood pressure in virgin spontaneously hypertensive rats (SHR) upon chronic infusion. In this investigation, vascular reactivity to angiotensin II, arginine-vasopressin, and norepinephrine was studied in the perfused mesenteric artery and isolated portal vein of control and RLX-treated virgin spontaneously hypertensive rats. The latter received an intravenous infusion of 75 ng/hr purified rat RLX for 2 days, whereas the controls were given an equal infusion of saline. All of the animals were then killed and their tissues processed for in vitro study. In the perfused mesenteric artery, the concentration-response curves for arginine-vasopressin and norepinephrine were shifted to the right by a factor of about 2 (P < 0.05 and P < 0.005, respectively) after RLX treatment. In the isolated portal vein, the response to angiotensin II was not affected; the effect of norepinephrine was slightly displaced to the right (increase in EC50) and the maximum response remained unchanged. These results demonstrate that RLX treatment for 42 hr blunted the vascular response to vasoconstrictor agents in the mesenteric vasculature and are consistent with similar observations reported previously in the same tissue of 20-day-old pregnant rats. It is concluded that RLX may be involved in the blunted response to vasoconstrictor agents during gestation in the rat.

Induction of intrauterine growth restriction with a low-sodium diet fed to pregnant rats

OBJECTIVE A low-sodium diet fed to female rats before mating through parturition leads to pups of lower weight. We characterized the effect of low dietary sodium during the last week of gestation (after fetal organogenesis) on fetal and maternal homeostasis. STUDY DESIGN Pregnant Sprague-Dawley rats were randomly assigned to a control group or to a group fed a low-sodium diet from gestational days 15 through 22. Systolic blood pressures were measured throughout pregnancy. On day 22 plasma volume was measured and blood samples were taken for electrolyte and hormonal measurements. Fetal and placental weights were also determined. RESULTS Plasma renin activity and aldosterone level were significantly higher in the experimental group than in the control group. Plasma volume was significantly lower in pregnant rats receiving a low-sodium than in those receiving a control diet. Rats receiving a low-sodium diet had pups of lower weight and length (4.45 +/- 0.22 g, 3.90 +/- 0.06 cm) than pups of the control group (5.21 +/- 0.12 g, 4.10 +/- 0.02 cm). Pups born to mothers with low-sodium diets recuperated from intrauterine growth restriction by 14 days after birth. CONCLUSION These data indicate that a low-sodium diet given to pregnant rats for the last 7 days of gestation leads to reduced plasma volume expansion and fetal growth restriction. This could prove to be a simple animal model for studying the relationship between maternal plasma volume and fetal growth.

Umbilical and placental vessels: Modifications of their mechanical properties in preeclampsia

OBJECTIVES Our objective in this study was to assess the basic mechanical properties of umbilical and chorionic vessels of placentas delivered after both normal and preeclamptic pregnancies. STUDY DESIGN Placentas were selected when the parturient women were admitted to the delivery room. Normal pregnancy (n = 17) was characterized by delivery at term (38 to 40 weeks) after uncomplicated pregnancy without any medication. Preeclamptic pregnancy (n = 7) was characterized by delivery after 28 weeks of pregnancy (28 to 39 weeks) after sustained hypertension and proteinuria. Arteries and veins from the umbilical cord and chorionic plate were prepared in rings for in vitro study in tissue baths. Passive and active (on stimulation by potassium chloride or serotonin) mechanical properties of these vessels were studied. RESULTS In vessels from normal pregnancy, responsiveness, but not sensitivity, was increased with increasing passive tension on vessels until optimal tension was reached. The passive stretch-tension curve was shifted downward in umbilical veins and upward in umbilical arteries and chorionic veins obtained from preeclamptic mothers in comparison with normal parturient women. In the absence of passive tension, contractions in response to potassium chloride were produced in all umbilical veins and some chorionic veins from preeclampsia but not from normal pregnancy. Developed wall tension curves in chorionic vessels from preeclampsia were shifted upward. In umbilical veins and arteries and in chorionic veins, the optimal passive tension was lower in tissues from preeclampsia than in tissues from normal pregnancy. CONCLUSION Our results indicate that both passive and active mechanical properties of umbilical vessels are modified after pregnancy complicated by preeclampsia.

Smooth muscle contractility and protein tyrosine phosphorylation

During the last 5 years several studies have documented an involvement of protein tyrosine kinases (PTKs) in smooth muscle contraction and Ca2+mobilization. Most of these studies have utilized highly selective inhibitors of PTKs, genistein and tyrphostin and have shown that these inhibitors attenuated smooth muscle contraction induced by growth factors - epidermal growth factor (EGF) and platelet derived growth factor (PDGF) and several vasoactive peptides. It has also been demonstrated that inhibitors of protein tyrosine phosphatases (PTPases) such as vanadate and pervanadate mimic growth factors and vasoactive peptides in causing the contraction of smooth muscle. In this brief review, we have summarized some of the recent observations suggesting a possible link between protein tyrosine phosphorylation pathway and smooth muscle contraction.

Can activated recombinant factor VII be used to postpone the exposure of infants to factor VIII until after 2 years of age

Summary.  Two retrospective studies have suggested that exposure to factor VIII (FVIII) in early infancy is associated with an increased risk of FVIII inhibitor development. We prospectively studied 11 infants who needed replacement therapy for bleeding episodes before the age of 2 years. They received activated recombinant factor VII (rFVIIa) concentrate on demand, with the intention of postponing their first exposure to FVIII after 2 years of age. Thirty‐three bleeding episodes were treated with 154 doses of rFVIIa with no evidence of adverse effect. Bleeding was controlled in 27 of 33 episodes. Mouth bleeds were most difficult to treat. The use of rFVIIa allowed postponement of the use of FVIII for a mean of 5.5 months (median 4, range 0–12) but in only three of 11 children could be the first exposure to factor postponed after the age of 2 years. With this modest effect of rFVIIa in postponing the first exposure to FVIII, more convincing evidence for the benefit of such a postponement will have to be demonstrated before rFVIIa could be recommended for this indication.

Reactivities to serotonin and histamine in umbilical and placental vessels during the third trimester after normotensive pregnancies and pregnancies complicated by preeclampsia.

OBJECTIVE The aim of the study was to evaluate responses of umbilical and placental arteries and veins to serotonin and histamine after normotensive pregnancies and pregnancies complicated by preeclampsia. STUDY DESIGN Each pair of placentas from a normotensive woman and a woman with preeclampsia was matched for gestational age. Rings of these vessels were prepared and mounted in tissue baths under their respective optimal passive tension. Cumulative concentration-response curves to serotonin and histamine were measured. RESULTS Responses to serotonin were decreased in umbilical vessels from the preeclampsia group with respect to the normotensive group. This is reflected by reduced maximum responses and sensitivity (negative logarithm of the 50% effective concentration) to serotonin. Maximum response to serotonin was significantly decreased in placental vein rings from the preeclampsia group. We recorded a decreased maximal response to histamine in placental vein rings from pregnancies complicated by preeclampsia with respect to those from normal pregnancies. Among normotensive women there was a significant positive linear relationship between neonatal weight and sensitivity to serotonin in umbilical and placental veins. This relationship was totally absent in preeclampsia. Sensitivity to histamine was linearly related to neonatal weight in umbilical vessels of the pooled results of both experimental groups. CONCLUSION The vasoconstrictive effects of serotonin, but not those of histamine, are decreased in umbilical and placental vessels after preeclampsia. Sensitivities to serotonin and histamine change in umbilicoplacental vessels during the third trimester. Altered reactivity to serotonin may play a significant role in the reduction of umbilicoplacental blood flow in preeclampsia.

Vascular binding sites and biological activity of vasopressin in DOCA-salt hypertensive rats

In order to understand the regulation of vascular vasopressin receptors in hypertension, vasopressin (AVP) binding sites and the pressor response to AVP in the perfused mesenteric vasculature of DOCA-salt hypertensive rats, sodium-loaded and DOCA-treated rats were investigated. The binding capacity for AVP (Bmax) was significantly reduced (P less than 0.05) in uninephrectomized, DOCA-treated rats (70 +/- 17 fmol/mg protein) and in DOCA-salt hypertensive rats (90 +/- 9 fmol/mg protein) with respect to uninephrectomized rats (130 +/- 32 fmol/mg protein) or uninephrectomized salt-loaded rats (155 +/- 47 fmol/mg protein), with no change in affinity. In these rats with lower receptor density, however, the maximal pressor response to AVP in the perfused mesenteric vascular bed was increased (P less than 0.05). In DOCA-salt hypertensive rats plasma AVP was higher than in the other groups. In similarly treated rats with intact kidneys, which therefore did not become hypertensive, receptor density was significantly decreased after combined DOCA-salt treatment, together with an exaggerated pressor response to AVP and increased plasma AVP concentrations. These results suggest that AVP receptors are down-regulated when there is an increment in the plasma concentration of AVP, although other factors may also play a role. Biological responses to AVP are, however, increased in spite of decreased receptor density and this phenomenon is independent of the elevation in blood pressure and results from an exaggerated response mediated by post-receptor mechanisms.

Effects of nifedipine and Bay K 8644 on myotropic responses in aortic rings of pregnant rats

The hypothesis that Ca2+ channel function is altered during pregnancy was tested by comparing responses to potassium chloride (KCl) and phenylephrine in aortic rings of virgin and term-pregnant rats under the influence of nifedipine and Bay K 8644. Maximum response to KCl was progressively reduced by increasing nifedipine concentrations (1.0-100 nM) in both groups of tissues. Nifedipine produced a smaller inhibition of KCl-induced contraction in aortic rings of pregnant than of virgin rats. It exerted little inhibition on the concentration-response curve to phenylephrine. The Ca2+ channel antagonist (100 nM) reduced the maximum response to the alpha-adrenoceptor agonist in rings from virgin rats, but had no effect in pregnant rats. Bay K 8644, a Ca2+ channel activator, potentiated the responses to low concentrations of both phenylephrine and KCl in the tissues of both virgin and pregnant rats, but did not affect maximum responses. It also induced concentration-dependent contractions in rings of virgin but not of pregnant rats. The effects of Bay K 8644 were markedly potentiated by precontracting the aorta with 10mM KCl. Nevertheless tissues from pregnant rats were still less responsive to Bay K 8644. However, when the strips were precontracted to the same level by different concentrations of KCl, the concentration-response curves to Bay K 8644 were identical in both groups. [3H]Nitrendipine binding to membrane preparations of the thoracic aorta was similar in virgin and pregnant rats.(ABSTRACT TRUNCATED AT 250 WORDS)