Pilot study of once-a-day prophylaxis for youth and young adults with severe haemophilia A

INTRODUCTION

Standard prophylaxis has been shown to be an effective treatment for severe haemophilia A. According to pharmacokinetic principles, daily factor infusions of smaller doses can maintain similar trough factor VIII (FVIII) levels, and perhaps the same protection as standard prophylaxis.

AIM

This multicentre study examined the feasibility of daily prophylaxis for youth and young adults with severe haemophilia A in Montreal and Toronto.

METHODS

Bleeding rates, joint status, quality of life and physical activity were monitored for 14 patients during this study. At baseline, subjects continued their regular treatment regimen and switched to daily prophylaxis after 4 months; nine had begun daily prophylaxis before enrolment. Additional visits occurred at 8 and 12 months which included a physical examination, inhibitor testing, HJHS and FISH assessments, the CHO-KLAT/Haemo-QoL-A and PDPAR. Treatment satisfaction was assessed using the Treatment Satisfaction Questionnaire for Medication ver.II and perceived difficulty questions at the end of study.

RESULTS AND CONCLUSIONS

There were no significant changes in quality of life except for concerns with the demanding daily infusion schedule. The number of bleeds did not statistically differ from the initial 4 months of the study to the last 8 months. Monthly bleeding rates from the year prior to the study and during the intervention phase were not statistically different. It was also found that daily prophylaxis used 24% less FVIII compared to standard prophylaxis. Taking all of this into account, we have found that providing daily prophylaxis is feasible and that it is feasible to prospectively study daily prophylaxis in youth and young adults.

Generic and disease-specific quality of life among youth and young men with Hemophilia in Canada

Background

This study was undertaken to explore the longitudinal patterns of health-related quality of life (HRQoL) among youth and young adults with Hemophilia A (HA) over a 3-year period. This report presents the baseline characteristics of the study cohort.

Methods

Males, 14 to 29 years of age, with predominantly severe HA were recruited from six treatment centres in Canada. Subjects completed a comprehensive survey. HRQoL was measured using: the CHO-KLAT_2.0 (youth), Haemo-QoL-A (young adults) and the SF-36v2 (all).

Results

13 youth (mean age = 15.7, range = 12.9-17.9 years) and 33 young adults (mean age = 23.6; range = 18.4 -28.7 years) with moderate (7 %) and severe (93 %) HA were enrolled. All were on a prophylactic regimen with antihemophilic factor (Helixate FS®) during the study. The youth had minimal joint damage (mean HJHS = 5.2) compared to young adults (mean HJHS = 13.3). The mean HRQoL scores for youth were: 79.2 (SD = 11.9) for the CHO-KLAT, and 53.0 (5.5) and 52.3 (6.8) for the SF-36 Physical Component Summary (PCS) and Mental Component Summary (MCS) scores respectively. The mean HRQoL scores for young adults were: 85.8 (9.5) for the Haemo-Qol-A, and 50.8 (6.4) and 50.9 (8.8) for PCS and MCS respectively. PCS and MCS scores were comparable to published Canadian norms, however significant differences were found for the domains of Physical Functioning and Bodily Pain. The disease-specific HRQoL scores were weakly correlated with the PCS for youth (CHO-KLAT vs. PCS r = 0.28, p = 0.35); and moderately correlated for the MCS (r = 0.39, p = 0.19). Haemo-QoL-A scores for young adults were strongly correlated with the PCS (r = 0.53, p = 0.001); and weakly correlated with the MCS (r = 0.26, p = 0.13). Joint status as assessed by HJHS was correlated with PCS scores. A history of lifelong prophylaxis resulted in better PCS but worse MCS scores.

Conclusion

Despite having hemophilia, the youth in this cohort have minimal joint disease and good HRQoL. The young adults demonstrated more joint disease and slightly worse HRQoL in the domains of physical functioning and pain. The data presented here provide new information to inform the selection of Health Related Quality of Life (HRQoL) instruments for use in future clinical trials involving persons with hemophilia.

Trial registration

ClinicalTrials.gov : NCT01034904. Study funded by CSL Behring Canada.

Electronic supplementary material

The online version of this article (doi:10.1186/s12878-016-0052-x) contains supplementary material, which is available to authorized users.

Effects of moderate-intensity physical exercise on pharmacokinetics of factor VIII and von Willebrand factor in young adults with severe haemophilia A: a pilot study

INTRODUCTION

In persons with severe haemophilia A (pwshA), infused factor VIII (FVIII) half-life can vary according to such determinants as blood group, von Willebrand factor (VWF) level or age; however, FVIII pharmacokinetics (PK) has not been well studied in pwshA during exercise.

AIM

To investigate FVIII PK in pwshA performing moderate-intensity aerobic exercise.

METHODS

Twelve young-adult pwshA with the intron-22 inversion mutation, on relatively low-dose FVIII prophylaxis regimens, and relatively good musculoskeletal status were recruited. Abbreviated PK of FVIII activity and von Willebrand factor antigen (VWF:Ag) level were compared - during rest, and with 60-min exercise (2 × 15 min each of moderate-intensity stationary cycling and treadmill walking). During rest and exercise visits, a baseline blood specimen was drawn, routine prophylaxis FVIII infused; then six blood specimens were taken over the following 24 h.

RESULTS

For all subjects, mean half-life of infused FVIII did not change significantly with exercise vs. at rest (577 ± 190 vs. 614 ± 163 min; P = 0.4131). VWF:Ag rose transiently by 40-50% for 6-8 h with exercise (P < 0.01), particularly in non-O blood group subjects. No musculoskeletal bleeds occurred during the study.

CONCLUSION

Four × 15 min of moderate-intensity aerobic exercise increased VWF:Ag levels for 6-8 h, and showed no evidence of accelerated FVIII clearance or of musculoskeletal bleeding in these young-adult pwshA with relatively good musculoskeletal status, on relatively low-dose FVIII prophylaxis regimens. However, O blood group impact would merit larger studies, with longer durations of similar or more vigorous exercise intensities.

Patterns of tertiary prophylaxis in Canadian adults with severe and moderately severe haemophilia B

From a young age patients with severe and moderately severe FIX deficiency (haemophilia B) can experience spontaneous or traumatic bleeding and joint destruction may result. The use of coagulation factor IX concentrate to prevent anticipated bleeding, as primary or secondary prophylaxis, has become a common and recommended practice in children. The current practice of using tertiary prophylaxis, in the presence of established joint arthropathy, in adults with haemophilia B is not well characterized. This observational study was conducted to gain a better understanding of the recent Canadian experience with tertiary prophylaxis in adults with severe and moderately severe haemophilia B. Data were collected from all eligible adult (≥ 18 years of age) males with baseline FIX:C ≤ 2% from seven Canadian Hemophilia Treatment centres over a 2-year observation period from 2009 to 2011. Thirty-four per cent of the 67 subjects with moderately severe haemophilia B were exposed to prophylaxis with the majority as continuous prophylaxis (≥45 weeks year(-1) ). The severe subgroup (FIX:C < 1%) demonstrated a 52% exposure rate. None had primary prophylaxis exposure in childhood. Eighty-one per cent used once or twice weekly infusion regimens and reported a median annual bleeding rate of five bleeds per year versus four bleeds per year for those using on-demand treatment. Annual median factor utilization for all subjects using prophylaxis was 196,283 U year(-1) compared to 46,361 U year(-1) for on demand. Approximately 50% of adults with severe haemophilia B are using continuous tertiary prophylaxis in Canada, a practice likely to increase which warrants further study.

Bleeding disorders, menorrhagia and iron deficiency: impacts on health-related quality of life

von Willebrand disease (VWD) is a bleeding disorder that occurs in up to 1% of the general population. The great majority of females with VWD experience menorrhagia. The morbidity burden in females with VWD may relate to iron deficiency resulting from menorrhagia. To explore relationships between bleeding disorders, menorrhagia, iron deficiency and the outcomes of health-related quality of life (HRQL) and educational attainment. All subjects with VWD, and females with other bleeding disorders, in the Canadian national registry who were more than 12 years of age were eligible for survey. Survey measures included the HEALTH UTILITIES INDEX(®); abridged Clinical History Assessment Tool; socio-demographic questions and serum ferritin. Statistical analyses included testing differences among groups of means using analysis of variance and of proportions using chi-squared test. Significant size differences in mean HRQL scores were detected between VWD females and both females with other bleeding disorders [diff = (-0.08); P = 0.017] and VWD males [diff = (-0.07); P = 0.039]. Mean HRQL scores differed between females with and without menorrhagia (P < 0.001). Mean HRQL scores were not significantly different between females with and without iron deficiency. Educational attainment was not associated with disease group, menorrhagia status or iron status. Females with VWD have a greater morbidity burden than females in the general population, females with other bleeding disorders and males with VWD. Menorrhagia is associated with low HRQL scores in females with bleeding disorders, including VWD. Further investigation should assess how menorrhagia impacts HRQL in females with bleeding disorders.

Regulation of the sodium pump during cardiomyocyte adaptation to pregnancy

Regulation of the sodium pump during normal pregnancy and its effect on the function of cardiomyocytes is poorly understood. Our objective was to evaluate the possible implication of the Na(+)-K(+)-ATPase, the sodium pump which controls cellular ionic and metabolic homeostasis, in the adaptations of cardiomyocytes to normal pregnancy. We have used Western blots and patch-clamp measurements to identify changes in the sodium pump proteins. Confocal microscopy was applied to estimate intracellular sodium concentration. Time-resolved spectroscopy was employed to measure mitochondrial NAD(P)H fluorescence and estimate oxidative metabolic state. Optical microscopy was adopted to study the contractility responses of cardiomyocytes. Cells from non-pregnant and pregnant rats (1 day prior parturition) were studied. Our results showed lower protein expression of the α1 Na(+)-K(+)-ATPase isoform in cardiomyocytes in pregnant rats, decreased sodium pump membrane current and elevated steady-state sodium concentration. In addition, ouabain, the inhibitor of the sodium pump capable of increasing cardiomyocyte contractility in non-pregnant rats in a concentration-dependent manner, failed to affect cell contractions in pregnant rats. We also noted modified responsiveness of the mitochondrial metabolic state to ouabain in cardiac cells. The gathered data confirmed that in pregnant rats, the sodium pump protein content and transmembrane flux are decreased, while the sensitivity of cardiomyocyte contractility and the sensitivity of mitochondrial metabolic redox state to ouabain are modified, pointing to regulation of the Na(+)-K(+)-ATPase during cardiac cell adaptations to normal pregnancy.

Mineralocorticoids participate in the reduced vascular reactivity of pregnant rats

The renin-angiotensin-aldosterone (RAA) system is markedly activated in pregnancy. We evaluated if mineralocorticoid receptors (MR), a major component of the RAA system, are involved in the reduced vascular reactivity associated with pregnancy. Canrenoate (MR antagonist; 20 mg·kg(-1)·day(-1)) was administered to nonpregnant (NP) rats for 7 days and to pregnant rats from day 15 to 22 of gestation. These were killed on day 17, 19, or 22 of gestation and, for NP rats, after 7 days treatment. Constrictor responses to phenylephrine (PhE) and KCl were measured in endothelium-denuded thoracic aortic rings under the influence of modulators of potassium (activators) and calcium (blocker) channels. Responses to the constrictors were blunted from days 17 to 22 of gestation. Although canrenoate increased responses to PhE and KCl, it did not reverse their blunted responses in gestation. NS-1619 and cromakalim (respectively, high-conductance calcium-activated potassium channels and ATP-sensitive potassium channel activators) diminished responses to both PhE and KCl. Inhibition by NS-1619 on responses to both agonists was decreased under canrenoate treatment in NP, but the reduced influence of NS-1619 during gestation was reversed by the mineralocorticoid antagonist. Cromakalim reduced the response to PhE significantly in the pregnant groups; this effect was enhanced by canrenoate. Finally, nifedipine (calcium channel blocker) markedly reduced KCl responses but to a lesser extent at the end of pregnancy, an inhibiting effect that was increased with canrenoate treatment. These data demonstrate that treating rats with a MR antagonist increased vascular reactivity but that it differentially affected potassium and calcium channel activity in aortas of NP and pregnant animals. This suggests that aldosterone is one of the components involved in vascular adaptations to pregnancy.

Cross-cultural validation of the CHO-KLAT and HAEMO-QoL-A in Canadian French

Multi-site studies are necessary in the field of haemophilia to ensure adequate sample sizes. Quality of life (QoL) instruments need to be harmonized across languages and cultures to facilitate their inclusion. The purpose of this study was to adapt the Canadian Haemophilia Outcomes - Kids Life Assessment Tool (CHO-KLAT(©)) and HAEMO-QoL-A(©) to French for Canada. The CHO-KLAT and the HAEMO-QoL-A are haemophilia-specific measures of QoL for boys and men respectively. Both measures originated in English, were translated into Canadian French by clinicians with expertise in haemophilia care, back-translated by expert translators and harmonized by a multi-disciplinary team. The harmonized versions were evaluated through a cognitive debriefing process with 6 boys with haemophilia, their parents and 10 men with haemophilia. The final versions were validated in a sample of 19 boys with haemophilia, 19 parents, and 22 men with haemophilia along with a generic QoL scale: the PedsQL for children; and the SF-36 for adults. The translation and cognitive debriefing processes resulted in a preliminary version that maintained the intent of the original questions. The validation study estimated the mean score for the child-reported CHO-KLAT at 71.9 (SD 10.4), and the adult-reported HAEMO-QoL-A at 79.1 (SD 21.3). The CHO-KLAT correlated 0.64 with the PedsQL and the HAEMO-QoL-A correlated 0.78 with the SF-36 physical component summary score. The French-Canadian version of the CHO-KLAT and HAEMO-QoL-A are valid. These measures are available for use in multi-site haemophilia trials and clinical practices to capture QoL data from French Canadians.

Low prevalence of inhibitor antibodies in the Canadian haemophilia population

Annual reporting of inhibitors to factors (FVIII) and IX (FIX) to the Canadian Haemophilia Registry has suggested a lower prevalence than that published in the literature. We performed a prospective study to determine the prevalence of patients with inhibitors directed against either FVIII or FIX. Patients with inhibitors were classified as: (i) inhibitor test positive; (ii) inhibitor test negative but on immune tolerance induction (ITI); (iii) inhibitor test negative but bypass treatment recommended; or (iv) inhibitor resolved. One year later, the cohort was re-classified. The prevalence of inhibitors on 1 May, 2007 was 3.3% for haemophilia A, 0.6% for haemophilia B and 8.9% and 2.1% for severe haemophilia A and B. One year later 17 individuals gained and 11 individuals lost inhibitor status (10 of these with ITI). This study suggests that the prevalence of inhibitors in our population is lower than that was previously published. We hypothesize that this is primarily due to the increased use of ITI, but other factors may be the unselected nature of the cohort and the restriction of the study to one date thereby conforming as close as practical to the definition of prevalence rather than incidence. The classification system used in this study was easy for clinics to apply and was important in defining the population with inhibitors.

Placental oxidative stress in a rat model of preeclampsia

The onset of preeclampsia is associated with increased maternal insult that could affect placental function. By increasing sodium intake (0.9% or 1.8% NaCl in drinking water) during the last week of gestation in the rat, we developed an animal model that shows many characteristics of preeclampsia such as increased blood pressure, decreased circulatory volume and diminished activity of the renin-angiotensin-aldosterone system. The aim of the present study was to determine in this model whether maternal perturbations in pregnancy lead to placental oxidative stress. Sprague-Dawley pregnant rats receiving salted-water were compared to not-supplemented pregnant rats. Markers of oxidative stress, ensuing cell death, and changes in the production of vasoactive substances (prostanoids: thromboxane, TxB(2); and prostacyclin, PGF(1alpha)) and the pro-inflammatory cytokine tumour necrosis factor-alpha (TNF-alpha) were measured in the placenta. In tissue from pregnant rats on 1.8% NaCl supplement, 8-iso-PGF(2alpha) levels, TxB(2)/6-keto-PGF(1alpha) ratios, total TNF-alpha RNA expression, as well as the apoptotic index (Bax/Bcl-2 ratio) and endothelial nitric oxide synthase protein expression increase while total glutathione content decreases. These findings demonstrate that maternal insult during gestation induced an imbalance in the oxidative environment in the placenta favouring oxidation. This was accompanied by an increased synthesis of vasoconstrictive substances and TNF-alpha by the placenta as well as the increased rate of placental cell apoptosis.

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

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.

Vascular responses to alpha-adrenergic stimulation and depolarization are enhanced in insulin-resistant and diabetic Psammomys obesus

Since vascular complications often accompany diabetes, we examined the influence of the endothelial lining on vascular reactivity in Psammomys obesus, a desert gerbil that acquires insulin resistance and diabetes when exposed to a laboratory diet. Vasoconstriction to phenylephrine and depolarizing KCl, as well as carbachol endothelium-dependent relaxation, were assessed in rings of thoracic aortae obtained from three groups: (i) group A, normoglycemic-normoinsulinemic; (ii) group B, normoglycemic-hyperinsulinemic, and (iii) group C, hyperglycemic-hyperinsulinemic animals. As expected, marked hypertriglyceridemia and hypercholesterolemia characterized groups B and C, which developed enhanced contractile responsiveness to phenylephrine and KCl compared with controls (group A). Furthermore, both experimental groups displayed a significant decrease in endothelium-dependent relaxation to carbachol. Altered lipid profiles are considered to play some role in the observed modification of aortic reactivity. Overall, our data indicate that vascular contractile responsiveness is enhanced early in the development of insulin resistance and diabetes in the female P. obesus.

Optimization of storage conditions for diluted working solutions of porcine factor VIII and performance of the Bethesda assay for the determination of antiporcine FVIII inhibitor titres

The use of porcine factor VIII (FVIII) (Hyate:C, Ipsen) has proven to be very successful in treating patients with FVIII inhibitors. The best way to predict the usefulness of porcine FVIII therapy, and/or to estimate the appropriate treatment dose in a given patient, is to measure the patient inhibitor titre against porcine FVIII with the Bethesda assay, using porcine FVIII as the source of FVIII in the assay. The goals of the present study were to (1) find the optimal storage temperature, diluent and concentration for a working solution of porcine FVIII to be used as the source of FVIII for the porcine Bethesda assay, (2) assess the reliability of the labelled FVIII units in the preparation of such working solutions of porcine FVIII and (3) compare the inhibitor titres determined by the Bethesda assay using both porcine and human standard reference curves for measuring residual FVIII. The results of the present study demonstrate that a ready-to-use working solution of 1 U mL(-1) of Hyate:C diluted in human FVIII deficient plasma, either containing or deficient in von Willebrand factor antigen, is stable for up to 12 months, at -20 degrees C. The preparation of the 1 U mL(-1) working solution could be reliably calculated based on the units indicated on the vial label. Finally, using the human standard curve yields similar results to using the porcine standard curve for measuring any titre of allo- or auto-antibody against FVIII in the Bethesda assay, using Hyate:C as the source of FVIII. These findings are of practical value when performing a porcine FVIII-based Bethesda assay.

Blockade of angiotensin receptor subtypes in arcuate uterine artery of pregnant and postpartum rats

During pregnancy, uterine circulation undergoes hypertrophy and hyperplasia. We investigated the effects of angiotensin (Ang) II receptor subtype (AT(1)/AT(2)) blockade on increased responses to the peptide during reversible remodeling of the uterine vasculature in pregnant and postpartum rats. Uterine arcuate arteries were set up in wire myographs for microvessel and submitted to a tension equivalent to 50 mm Hg transmural pressure. Cumulative concentration-response curves to Ang II were measured in the absence and presence of losartan on the same vascular segment. A similar protocol was repeated in the presence of PD 123,319, an AT(2) receptor blocker, again in the absence and presence of losartan. Responses to Ang II on the arcuate artery increased markedly during pregnancy and returned to the prepregnant level within 12 days postpartum. Losartan (10(-7) mol/L) produced a parallel right shift of the concentration-response curve to Ang II in all groups of tissues, but potency of the AT(1) receptor blocker was reduced at the end of pregnancy and in the early postpartum period. PD 123,319 (10(-7) mol/L) significantly increased maximum response to Ang II in arterial segments of the nonpregnant, term-pregnant, and 5 days postpartum rats. AT(1) receptor expression was decreased in arcuate arteries of term-pregnant rats. These results show that contractile responses to Ang II on the uterine arcuate artery of the rat are mediated by the AT(1) receptor and that blockade of AT(2) receptors potentiated responses to the peptide. They also indicate that, in uterine vessels, AT(2) receptor stimulation interferes with Ang II responses, but this effect is decreased in uterine arcuate arteries in the peripartum period.

Functional alteration of dihydropyridine-sensitive Ca(2+) channels in the adrenal glomerulosa of pregnant rats

Our previous work on aldosterone secretion suggested that dihydropyridine-sensitive calcium channels, one type of voltage-dependent calcium channels (VDCC), are functionally impaired in adrenal capsule preparations from the pregnant rat. The aim of this study was to determine whether, during pregnancy, the density and/or activity of these channels is altered in the adrenal zona glomerulosa. These VDCC measured with [(3)H]nitrendipine binding were not different between membrane preparations of nonpregnant and pregnant rats. Western blots were performed using two different antibodies, a polyclonal (PcAb) directed against the alpha(1)-subunit of VDCC and a monoclonal (McAb) that recognizes an intracellular domain of that protein. McAb immunoreactivity showed a significant decrease in preparations from pregnant rats, whereas no difference was observed with PcAb. VDCC activity was estimated by (45)Ca(2+) uptake in isolated adrenal cortex and by intracellular calcium concentration ([Ca(2+)](i)) in adrenal glomerulosa cells with the Ca(2+) probe fura PE3. These measurements revealed that KCl stimulation produced greater Ca(2+) influx in nonpregnant than in pregnant rats. Nifedipine (a blocker of VDCC) inhibited this stimulation only in nonpregnant rats, whereas BAY K 8644 (an activator of VDCC) increased Ca(2+) influx in pregnant rats only. These data suggest that, during pregnancy, the altered regulation of calcium homeostasis in adrenal glomerulosa is linked to a conformational alteration of VDCC.

Effects of potassium channel modulators on myotropic responses of aortic rings of pregnant rats

The contribution of potassium channels [ATP-sensitive potassium (K(ATP)) and high-conductance calcium-activated potassium (BK(Ca)) channels] in the resistance of aortic rings of term pregnant rats to phenylephrine (Phe), arginine vasopressin (AVP), and KCl was investigated. Concentration-response curves to tetraethylammonium (TEA), a nonselective K(+) channel inhibitor, were obtained in the absence or presence of KCl. TEA induced by itself concentration-dependent responses only in aortic rings of nonpregnant rats. These responses to TEA could be modulated in both groups of rings by preincubation with different concentrations of KCl. Concentration-response curves to Phe, AVP, and KCl were obtained in the absence or presence of cromakalim or NS-1619 (K(ATP) and BK(Ca) openers, respectively) and glibenclamide or iberiotoxin (K(ATP) and BK(Ca) inhibitors, respectively). Cromakalim significantly inhibited the responses to the three agonists in a concentration-dependent manner in both groups of rats. Alternatively, in the pregnant group of rats, glibenclamide increased the sensitivity to all three agonists. NS-1619 also inhibited the response to all agonists. With AVP and KCl, its effect was greater in aortic rings of pregnant than nonpregnant rats. Finally, iberiotoxin increased the sensitivity to all three agents. This effect was more important in aortic rings of nonpregnant rats and was accompanied by an increase of the maximal response to Phe and AVP. These results suggest that potassium channels are implicated in the control of basal membrane potential and in the blunted responses to these agents during pregnancy.

Modulation of calcium mobilization in aortic rings of pregnant rats: Contribution of extracellular calcium and of voltage-operated calcium channels

Pregnancy is associated with decreased vascular responsiveness to vasopressor stimuli. We have tested the involvement of Ca2+ mobilization in myotropic responses of aortic rings obtained from pregnant and virgin rats. Contractions of the rings to phenylephrine, in the absence of calcium in the bathing medium, were lower in tissues from virgin than from pregnant rats. Concentration-response curves to CaCl2 that were measured after stimulation by phenylephrine in the absence of Ca2+ were shifted to higher levels of contraction. This was not observed when KCl was used to prestimulate the aorta. D-600, a phenylalkylamine calcium channel blocker, similarly inhibited these responses to CaCl2 in tissues from both pregnant and virgin animals. D-600 exerted a concentration-dependent inhibition of responses to phenylephrine and KCl. However, the calcium antagonist was less effective in aortic rings of pregnant than of virgin rats. Basal 45Ca2+ uptake was lower in aortic rings from pregnant than from virgin rats, and Bay K 8644 was unable to reverse this difference. The time course of basal and stimulated (KCl) 45Ca2+ influx was lower in aorta of pregnant rats at all times studied. Moreover, when the intracellular calcium pools were emptied with phenylephrine, the refilling of these pools was delayed in aortic rings of pregnant rats. These results indicate an altered extracellular calcium mobilization of aortic rings from pregnant rats. These changes may be due to a functional alteration of the voltage-operated calcium channels during pregnancy.

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.

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.

In vivo regulation of enzymes controlling aldosterone synthesis in pregnant rats

There are two main regulatory sites of aldosterone biosynthesis, the early rate-limiting step by the P450scc and the final steps by the P450aldo. We have already demonstrated that, during gestation, activity and mRNA levels of P450aldo are increased. It has been shown that changes in sodium and potassium in the diet modulate the expression of P450aldo in adrenal zona glomerulosa (ZG). In the present study, we compared the effects of low-sodium (Na+) and high-potassium (K+) diet on the expression of enzymes controlling aldosterone synthesis during gestation. Pregnant and nonpregnant rats were randomly assigned to control group or to group receiving low Na+ or high K+ diet during the last week of pregnancy. By the end of the treatment, the two diets induced increases of plasma aldosterone and P450aldo mRNA levels in nonpregnant and pregnant rats. However, plasma renin activity and P450scc mRNA levels were only in the pregnant group fed the low Na+ diet. High K+ diet had no effect on these parameters. We, thus, suggest that the renin-angiotensin system and the enzymes implicated in aldosterone synthesis are differently regulated during gestation.

Tyrosine kinase and MAPK inhibition of TNF-alpha- and EGF-stimulated IEC-6 cell growth

The role of TNF-alpha in modulating intestinal crypt cell growth was examined, in comparison with EGF. Both significantly increased IEC-6 cell proliferation. Neither EGF nor TNF-alpha overcame the inhibitory effect on growth exerted by the tyrosine kinase inhibitor genistein. Immunoblots with phosphotyrosine antibodies showed increased tyrosine phosphorylation of IEC-6 cell proteins in response to EGF and TNF-alpha stimulation. TNF-alpha increased ERK1 and ERK2 MAPK phosphorylation. A MAPK assay confirmed the increased activity upon TNF-alpha stimulation. Selective inhibition of MAPK activation by PD98059 resulted in a dose dependent inhibition of TNF-alpha or EGF-induced IEC-6 cell growth. These findings suggest a role for TNF-alpha in the regulation of intestinal epithelial cell growth and that the mitogenic effect of TNF-alpha requires protein tyrosine phosphorylation and MAPK activation.

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.

Increased reactivity of rat uterine arcuate artery throughout gestation and postpartum

Significant modifications of the uterine circulation are observed during pregnancy, with uterine circulation accounting for up to 11% of cardiac output at the end of pregnancy. We studied the reactivity of the uterine microcirculation to determine the time course of uterine mechanical and pharmacological alterations during pregnancy and postpartum. Arcuate artery segments, obtained from virgin, pregnant (7, 14, and 22-23 days), and postpartum (5 days) rats, were set up in wire myographs for microvessels under a passive tension equivalent to a transmural pressure of 50 mmHg (L50). Cumulative concentration-response curves to angiotensin II (ANG II), phenylephrine (PE), and potassium chloride (KCl) were measured. Diameter of the arcuate artery at L50 increased progressively until term from 108 +/- 4 microns in virgins to 188 +/- 9 microns at day 22 of pregnancy. This increase in diameter was partially reversed at day 5 postpartum (151 +/- 9 microns). Surprisingly, the passive length-tension relationship on arcuate arteries showed greater stiffness from day 14 of pregnancy through day 5 postpartum. The maximum response of the arteries to ANG II was markedly increased during pregnancy (from 0.78 +/- 0.02 to 1.43 +/- 0.09 mN/mm at day 22) and was already evident at day 14 (1.20 +/- 0.07 mN/mm) but was reversed in postpartum rats (0.81 +/- 0.04 mN/mm, nonsignificant). Similar results were obtained for maximum responses to PE and KCl, but the reversal at day 5 postpartum was only partial. Sensitivity (measured as the negative log of the concentration of stimulant required to produce 50% of the maximum response) of the uterine arcuate artery to the three vasopressors increased during the postpartum period and also at day 21 of pregnancy with PE and day 14 with KCl. The present results show that the uterine arcuate artery doubles in diameter during pregnancy. This increase in diameter is accompanied by increased stiffness of the vessel and heightened responsiveness to ANG II, PE, and KCl. These data demonstrate that pregnancy induces changes in reactivity of the rat uterine arcuate artery that appear to be linked to modifications in the mechanical properties of the vessel, at least for ANG II and PE.

Effects of dihydropyridines on aldosterone secretion in adrenal capsule preparations from pregnant rats

The primary aim of this study was to determine when sensitivity in the aldosterone response to extracellular potassium (K+) decreases during pregnancy. Second, it tested the hypothesis that calcium channel alterations occur in the adrenal cortex during pregnancy. The decreased sensitivity to K+, observed at 22 days of gestation, was not evident at 15 days and between 18 and 36 h postpartum. Increases in extracellular calcium concentration heightened sensitivity to K+ in adrenal capsule preparations derived from nonpregnant rats but had no effect in pregnant animals. The influence of nifedipine and BAY K 8644 (blocker and activator, respectively, of voltage-operated calcium channels) on the aldosterone response to K+ and to adrenocorticotropic hormone (ACTH) was studied. Sensitivity to K+ in nonpregnant rats decreased in the presence of nifedipine and became similar to that in pregnant rats. Responses to ACTH were not affected by nifedipine. BAY K 8644 produced a larger increase in sensitivity in adrenal capsule preparations from pregnant than from nonpregnant rats, leading to superposition of the two dose-response curves to K+. These results indicate that voltage-operated calcium channels involved in aldosterone secretion are functionally impaired during pregnancy.

Increase of aldosterone secretion in adrenal cortex suspensions derived from pregnant rats

Plasma aldosterone levels increase markedly during pregnancy, but not in proportion to the rise in plasma renin activity (PRA). We have developed a reliable in vitro method to investigate aldosterone secretion during pregnancy. With this method, we have assessed the potency and effectiveness of ACTH and potassium to stimulate this secretion during pregnancy. Adrenal capsules from pregnant and nonpregnant rats were incubated in 1 ml of culture medium within wells of tissues culture plates. The cortex was transferred every 20 min to another well containing fresh medium with or without ACTH or potassium. Basal and stimulated aldosterone secretions were not significantly affected by time under our experimental conditions. The glands remained responsive to stimulants throughout the study period (360 min). Plasma aldosterone levels and PRA were increased during pregnancy. Basal aldosterone secretion in adrenal cortex suspensions from pregnant rats showed a 1.6-fold increment (P < 0.001) in comparison with nonpregnant controls. The dose-response curves of ACTH were not significantly different between pregnant and nonpregnant animals. However, sensitivity to potassium was significantly reduced during pregnancy, as demonstrated by an elevated ED50 (4.01 +/- 0.08 vs 4.71 +/- 0.07 mM for nonpregnant versus pregnant rats respectively, P < 0.001). These data indicate that adrenal cortex suspensions are a reliable and reproducible way to study aldosterone secretion during pregnancy. They reveal that, during pregnancy, sensitivity of potassium to stimulate aldosterone secretion is decreased while the response to ACTH is not affected.

Characteristics of ANP-binding sites in the adrenal capsules of term-pregnant rats

Significant increases of circulatory volume and plasma aldosterone levels are observed in pregnancy. We investigated whether a decrease of atrial natriuretic peptide (ANP) receptors in the adrenal zona glomerulosa (ZG) could explain the marked elevation of plasma aldosterone occurring during pregnancy. 125I-ANP binding was measured in competition experiments using rANP(1-28), ANP(4-23), a truncated analog which has high specificity for the ANP-C receptor, or a combination of both. Western blot experiments were also performed with an investigation into the effect of ANP on aldosterone secretion in adrenal capsule suspensions. 125I-ANP binding on adrenal ZG membranes was displaced by ANP(1-28) with an affinity (Kd) of 313 +/- 39 and 323 +/- 60 pM (NS) for pregnant and non-pregnant rats, respectively. The density of sites (Bmax) decreased slightly but not significantly during pregnancy. Displacement experiments with ANP(4-23) demonstrated a Bmax of 137 and 134 fmol/mg of proteins (NS) for pregnant and non pregnant rats, respectively. Studies were performed to block the ANP-C site. Displacing the remaining 125I-ANP binding with ANP(1-28) led to an affinity constant and receptor density which were not significantly different between the two groups of rats. The results obtained with Western blots showed a single band of 123 kDa with no significant variations in ANP-R1 receptors in the ZG during gestation. The sensitivity of potassium-, ACTH- or angiotensin II-stimulated aldosterone secretion to ANP was not altered by gestation. These data show that the apparent hyperaldosteronism found in normal term-pregnant rats is not the consequence of modifications in the affinity, number and properties of ANP receptor types or in the sensitivity of the aldosterone response to ANP.

Nitric oxide in retinal and choroidal blood flow autoregulation in newborn pigs: interactions with prostaglandins

The role of nitric oxide (NO) as well as its interaction with prostaglandins (PG) in setting the limits of autoregulation of retinal blood flow (RBF) and choroidal blood flow (ChBF) were studied in newborn pigs (1-5 d old). Blood flows were measured by the microsphere technique. Low and high ocular perfusion pressures (OPP) were induced by inflating balloon-tipped catheters placed at the aortic root and isthmus, respectively. Animals were treated with the NO synthase inhibitors, NG-nitro-L-arginine methyl ester (L-NAME, 1 mg/kg followed by 50 mu g/kg/min; n = 12) or NG-monomethyl-L-arginine (L-NMMA, same dose as L-NAME; n = 3), or with saline (n = 12). In separate animals (n = 42), guanosine 3',5'-cyclic monophosphate (cGMP), the second messenger for NO, and PG were measured at an average OPP of 90 mm Hg and 125 +/- 6 mm Hg; cGMP levels served as an index of NO release. The effect of the NO donor sodium nitroprusside on choroidal vessel diameter was determined using video imaging of isolated eyecup preparations. In control animals RBF was constant only within a range of 30 to 80 mm Hg OPP (r = 0.03, p > 0.9). There was no autoregulation of ChBF which increased as a function of OPP (tau = 0.58-0.72, p < 0.01). L-NAME and L-NMMA prevented a change in RBF and ChBF from 30 to 146 mm Hg [the highest OPP studied (r < 0.3, p > 0.15)] and caused an increase in retinal as well as choroidal vascular resistance as OPP was raised; these agents did not affect ocular blood flow at OPP < 30 mm Hg. Elevated OPP caused increases in cGMP, 6-keto-PGF1alpha, and PGE2 in the choroid (a vascular tissue), which were prevented by L-NAME and L-NMMA. Sodium nitroprusside caused a dilatation of choroidal vessels in isolated eyecup preparations, which was significantly attenuated by indomethacin. Data suggest a role for NO in the autoregulation of RBF and ChBF in the newborn such that a release of NO during a rise in OPP prevents adequate constriction necessary for maintaining RBF and ChBF constant; data also suggest that the vasodilator effect of NO might in part be mediated through a release of PG.

Contractile effects of vanadate on aorta rings from virgin and pregnant rats

The present study was undertaken to characterize the contractile effects of vanadate on thoracic aorta rings from virgin and term-pregnant rats. Vanadate caused concentration-dependent contraction in rat aortic rings with an EC50 (concentration producing 50% maximum response) of 0.10 mM. Contractions in response to vanadate were equivalent to the ones measured with 1 microM phenylephrine. The effects of vanadate were not affected by indomethacin (up to 10 microM), an inhibitor of prostanoid cyclooxygenase, but were blocked in a concentration-dependent manner by staurosporine (0.1-1.0 microM), an inhibitor of protein kinase C. Vanadate exhibited a significant decrease of contractile responses in aorta of pregnant as compared to virgin rats. When aortic rings were bathed in presence of different concentrations of vanadate, the concentration-response curve to phenylephrine was shifted to the left, but maximum response was not affected. The potentiation of the contractions to phenylephrine by vanadate was significantly more prominent in aorta of virgin than of pregnant rats. These results suggest that the contractile effect of vanadate on rat aorta is independent of endogenous prostanoids and may be mediated by protein kinase C-dependent pathway. These results also show that the contractile response to vanadate on the rat aorta is impaired during pregnancy.

Angiotensin II receptor subtypes in the adrenals of pregnant rats

During human and rat pregnancy, several hemodynamic and endocrine processes are markedly modified. These include activation of the renin-angiotensin system (RAS) and increase of plasma aldosterone. However, the rise of plasma aldosterone is greater than expected from the elevation of RAS activity. Gestational alterations in angiotensin II receptors (AT receptor) in the adrenal could explain this apparent hyperaldosteronism. This study was conducted to determine differences between AT receptor subtypes in the adrenal glands of non-pregnant and pregnant (22 days) rats. Using plasma membrane preparations from adrenal glomerulosa and medulla, we determined receptor density and affinity with 125I-angiotensin II (ANG II); the AT receptor subtypes were assessed by displacement of 125I-ANG II binding with subtype-specific antagonists (DuP753 and PD123319). In zona glomerulosa of non-pregnant and pregnant rats, AT1 receptors predominated (approximately 80%) with no statistical difference in receptor density (Bmax) and affinity (Kd) and the ratio of receptor subtypes between the two groups of rats. In adrenal medulla of both groups of rats, the major portion of 125I-ANG II binding (60-70%) was displaced by the AT2 receptor antagonist, PD123319. Neither Bmax nor Kd differed in this tissue during gestation. The results for AT1 receptor density were confirmed by Western blot. Northern blot analysis showed that AT1 mRNA level in the adrenal is not modified by gestation. These results indicate that the number, the affinity and the transcription of the AT1 receptor in the adrenal are not altered during pregnancy, indicating that the rise in aldosterone secretion during pregnancy could not be explained by increase of AT1 receptors in the zona glomerulosa, or modification of AT1/AT2 ratio.

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)

Decreased response to vasopressin in the mesenteric resistance arteries of pregnant rats: effects of nifedipine and Bay K 8644

OBJECTIVE

The purpose of this study was to investigate the contribution of potential-operated calcium (POC) channels in the mechanisms of the blunted effects of vasoconstrictors on mesenteric resistance arteries during normal pregnancy.

METHODS

Mesenteric resistance arteries of virgin and term pregnant rats were set up under optimum passive tension in wire myograph systems. Cumulative concentration-response curves of arginine8-vasopressin (AVP) were measured in the absence and presence of nifedipine or Bay K 8644, a blocker and an activator, respectively, of POC channels. Binding studies were performed on membrane preparations of the mesenteric vascular bed of both groups of rats using saturation with [3H]nitrendipine.

RESULTS

The maximal response to AVP was statistically similar in the two groups of arteries. Pregnancy shifted the AVP concentration-response curves to the right. Nifedipine (1 mumol/L) similarly reduced the maximum response to AVP in arteries of both groups, but produced a larger increase in EC50, the concentration inducing 50% maximum response, in resistance arteries of virgin versus pregnant rats. Bay K 8644 did not affect the maximum tension reached with AVP. However, it increased the effects of small concentrations of AVP in arteries of both groups. This was more important in tissues of virgin than pregnant rats. Binding of [3H]nitrendipine to membrane preparations of mesenteric vessels was not modified by pregnancy.

CONCLUSION

Our results suggest a reduced functional influence of POC channels in the myotropic effects of AVP on mesenteric resistance arteries in pregnancy. This decreased influence of POC channels may contribute to resistance of the vasculature to vasopressor agents during pregnancy.

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.

Prostaglandin- or endothelium-mediated vasodilation is not involved 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.

Effect of clentiazem on lipid profile, lipoprotein composition and aortic fatty streaks in cholesterol-fed rabbits

Numerous experimental studies have reported that common antihypertensive drugs such as diuretics, beta-blockers, and methyldopa have adverse effects on plasma lipids and lipoproteins. The present study was designed to define the effect of clentiazem (10 mg/kg/day) an antihypertensive drug, on hyperlipidemia in rabbits on a cholesterol-rich diet (1%) for 12 weeks. Compared with controls, clentiazem treated rabbits had lower plasma concentrations of triglycerides (55%), total cholesterol (24%), free cholesterol (27%), esterified cholesterol (23%) and phospholipids (24%). The decrease in cholesterol was accounted for by a reduction of VLDL-cholesterol (13%), IDL-cholesterol (24%) and primarily LDL-cholesterol (45%). Neither HDL-cholesterol nor chemical composition of VLDL, IDL, LDL and HDL was altered. When the aortic atherosclerotic involvement was evaluated by computerized planimetry, a 24% reduction of lesions was noted in clentiazem treated animals (P less than 0.05). Similarly, cholesterol content extracted from aortic wall was decreased. Our data therefore demonstrated that clentiazem is a potential antiatherosclerotic agent capable of decreasing plasma lipids and atherogenic lipoproteins as well as aortic fatty streaks.

Receptors for Arg8-vasopressin, angiotensin II, and atrial natriuretic peptide in the mesenteric vasculature of pregnant rats

Blood pressure and sensitivity of blood vessels to vasoconstrictors are decreased in term-pregnant rats (20-21 days). To determine if changes in receptors for vasoactive peptides could account for these observations, receptor kinetics were measured for Arg8-vasopressin (AVP), angiotensin II (Ang II), and atrial natriuretic peptide (ANP) in the mesenteric vascular bed of the rat throughout pregnancy. Receptors for AVP were statistically similar in the five groups of animals (nonpregnant; pregnant 9, 15, and 21 days; and postpartum). The dissociation constant (KD) for [3H]AVP varied from 0.41 to 0.52 nmol/L (NS), while receptor density (Bmax) varied from 310 +/- 110 to 455 +/- 135 fmol/mg protein for six experimental measurements. Similar observations were made for Ang II receptors where KD of 125I-labelled Sar1, Ile8-Ang II was between 0.60 and 0.97 nmol/L and Bmax between 215 +/- 30 and 250 +/- 40 fmol/mg protein in the different groups. 125I-labelled ANP (101-126) receptors were markedly modified in terms of number of sites. Bmax was significantly increased during pregnancy (9 days, 429 +/- 86; 15 days, 541 +/- 54; 20 days, 438 +/- 72) and decreased in the postpartum period (133 +/- 21) by comparison with the nonpregnant group (245 +/- 35 fmol/mg protein), while KD was similar in the different experimental groups (57 to 82 pmol/L). Despite these increases in receptor density, the vasorelaxant effects of ANP was only increased at 9 days of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the endothelium in adrenergic responses of mesenteric artery rings of pregnant rats

Responses to adrenergic agents were measured on rings of mesenteric, artery of nonpregnant and pregnant rats at 21 days' gestation. In tissues from pregnant rats, norepinephrine, and phenylephrine were less sensitive than in rings from nonpregnant animals; maximum responses were not affected. The effect of isoproterenol was not modified in tissues from pregnant rats. The presence of endothelium in tissue rings was evaluated as fractional relaxation to acetylcholine. Sensitivity to phenylephrine and norepinephrine was inversely related to the effect of acetylcholine. This relationship was similar in slope in both groups but different in intercept. The sensitivity to isoproterenol was directly related to the presence of endothelium (curves similar in both slope and intercept). This demonstrates that the responses of mesenteric artery rings depends on the presence of endothelium. Furthermore, vascular endothelium is not involved in the blunted responses to adrenergic vasoconstrictor during pregnancy.

Regulation of ANG II and AVP receptors in isolated hepatocytes of pregnant rats

Recent evidence suggests that angiotensin II (ANG II) and vasopressin (AVP) act on the liver via specific receptors. We have examined the binding properties of these receptors in isolated rat hepatocytes and studied the regulation of the biological responses to ANG II and AVP during pregnancy in the rat. In contrast to [3H]ANG II, 125I-labeled-[Sar1-Ile8]ANG II was markedly resistant to degradation by isolated liver cells. Displacement and saturation experiments with this iodinated antagonist revealed the presence of a single class of binding sites [2 x 10(5) sites/cell, dissociation constant (KD) = 1.0 nM]. The potency of ANG II analogues to displace 125I-[Sar1-Ile8]-ANG II agrees closely with data reported for vascular smooth muscle cells. Isolated hepatocytes have approximately 8 x 10(4) [3H]AVP binding sites/cell (KD = 1.0 nM) based on saturation experiments. AVP analogues selectively displaced [3H]AVP, suggesting the presence of V1-AVP receptor subtype. The maximum response of [Sar1]ANG II-induced glycogenolysis in the cells was decreased during gestation, whereas the effective concentration producing 50% of maximum response (EC50) was significantly increased (0.15-0.28 nM) when compared with cells from nonpregnant animals. In pregnancy, receptors for 125I-[Sar1-Ile8]ANG II were not changed in affinity (KD) or in density (Bmax). The maximum response and EC50 of AVP on liver glycogenolysis were not significantly decreased during pregnancy, whereas an increased number of AVP binding sites (from 5.0 +/- 0.5 x 10(4) to 11.0 +/- 1.7 x 10(4)) with similar KD was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive properties of linoleic acid and fish oil omega-3 fatty acids independent of the prostaglandin system

Polyunsaturated fatty acids of the omega-6 and the omega-3 series have been shown to lower arterial pressure in humans and in various models of experimental hypertension by uncharacterized mechanisms. The objectives of our study were to compare the antihypertensive properties of linoleic acid (omega-6 series) and of fish oil fatty acids (omega-3 series) in a model of hypertension induced by the continuous subcutaneous infusion of angiotensin II in the rat and to determine whether or not their antihypertensive effects were mediated by the biosynthesis of vasodilator prostaglandins of classes 2 or 3. Linoleic acid and fish oil fatty acids (administered by subcutaneous injections) were equally potent in reducing, by half, the rise in systolic arterial pressure induced by the chronic infusion of angiotensin II. These antihypertensive effects were observed in the absence of any significant influence of either linoleic acid or fish oil fatty acids on the systemic and the renal synthesis of PGI2 or on the renal formation of PGE2 in vivo. Indomethacin caused a profound inhibition of the biosynthesis of PGI2 but not of PGE2 and could only partially neutralize the antihypertensive effects of linoleic acid and of fish oil fatty acids. These results suggest that, in this model of angiotensin II-induced hypertension, linoleic acid and fish oil fatty acids exert equipotent antihypertensive effects which are mainly independent of the prostaglandin system.

Vasopressin receptors and inositol trisphosphate production in blood vessels of spontaneously hypertensive rats

To understand the regulation of vasopressin (AVP) receptors in spontaneous hypertension, we investigated the pressor response of AVP in the perfused mesenteric vasculature, AVP binding sites in the membrane preparation of the same vascular bed, and the production of inositol trisphosphate (InsP3) stimulated by AVP in the aorta of spontaneously hypertensive rats (SHR), Wistar-Kyoto rats (WKY), and Wistar rats (WR) at different ages (4-16 weeks). Plasma AVP concentrations were similar in SHR, WKY, and WR at all ages. The density of AVP vascular binding sites was significantly higher in WKY than in SHR and WR at 12 weeks. Receptor affinity was similar in all strains. The pressor response of the mesenteric vasculature to AVP was similar in the three strains of rats at 4 weeks (prehypertensive stage) and increased progressively in SHR compared with WKY and WR at 8 and 12 weeks of age by 43 and 35%, respectively, and by more than 80% at 16 weeks of age (established hypertensive stage). There was no difference in vascular sensitivity to AVP. A significantly increased pressor response to a supramaximal dose of norepinephrine was also found at 16 weeks in SHR, but not in younger rats. InsP3 production in the aorta in response to AVP was increased in SHR at 8, 12, and 16 weeks, compared with WKY and WR. These results suggest that the vascular response to AVP is increased in SHR, in spite of decreased or normal density of binding sites compared with WKY or WR.(ABSTRACT TRUNCATED AT 250 WORDS)

Blunted responses to vasoconstrictors in mesenteric vasculature but not in portal vein of spontaneously hypertensive rats treated with relaxin

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 less than 0.05 and P less than 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.

Vascular vasopressin receptors in renal hypertensive rats

We investigated the plasma concentration of [Arg8]-vasopressin (AVP), the density of AVP-binding sites on membranes from the mesenteric vascular bed, and the pressor response to AVP of the perfused mesenteric vasculature in vitro from one-kidney, one-clip (1K, 1C) and two-kidney, one-clip (2K, 1C) Goldblatt hypertensive rats. The plasma concentration of AVP was increased in 1K, 1C hypertensive rats. The density of AVP-binding sites was similar in sham-operated normotensive, in 2K, 1C hypertensive, and in uninephrectomized rats but was significantly decreased in 1K, 1C hypertensive rats (P less than 0.05). The binding affinity of AVP was similar in all experimental groups. Vasoconstrictor response to AVP was increased in 2K, 1C hypertensive rats (27% higher than sham-operated normotensive rats, P less than 0.05). Responses in 1K, 1C hypertensive rats were similar to those of uninephrectomized rats. Our results indicate that together with an increased concentration of AVP in plasma the number of vascular AVP-binding sites is decreased in 1K, 1C hypertensive rats, whereas both are unaltered in 2K, 1C hypertensive rats. Vascular AVP receptors appear to be regulated inversely to plasma AVP concentrations. Pressor responsiveness to AVP is normal in 1K, 1C hypertensive rats and exaggerated in 2K, 1C hypertensive rats. Increased vascular responsiveness to AVP may occur independently of the regulation of AVP receptors and may contribute to elevation of blood pressure in renal hypertension in the rat.

Atrial natriuretic peptide interferes with calcium requirements in vascular tissues of the rat

The inhibitory effect of atrial natriuretic peptide on the myotropic action of phenylephrine on superior mesenteric artery and thoracic aorta rings was studied to test the hypothesis that this peptide interferes with the mobilization of intra- or extra-cellular calcium produced by vasoconstrictor agents. In the absence of calcium in the bathing solution, phenylephrine (10(-6) M) produced a residual effect, which was antagonized in a concentration-dependent manner by the atrial peptide in both mesenteric artery and aorta rings. When calcium (2.5 mM) was added to the bathing solution after the response to phenylephrine in the absence of calcium, a further increase in the tonus of the tissue was observed. This effect was also antagonized by atrial natriuretic peptide in a dose-dependent manner in the two tissues. These results suggest that atrial natriuretic peptide inhibits the effect of vasoconstrictor agents by functionally interfering with the mobilization of intra- and extra-cellular calcium produced by these vasoconstrictors.

Vasorelaxant effects of and receptors for atrial natriuretic peptides in the mesenteric artery and aorta of the rat

Vasorelaxant effects of different atrial natriuretic peptides (ANP) were measured on rat aortic strips and mesenteric artery rings. These results were compared with the potency of the same peptides to displace 125I-labelled ANP (101-126) on membrane preparations of aorta and of mesenteric vascular bed. In aortic strips and mesenteric artery rings precontracted with phenylephrine (3 X 10(-8) and 10(-6) M, respectively), the order of potency of ANP was as follows: ANP (99-126) greater than ANP (101-126) greater than ANP (103-126) = ANP (103-125) much greater than ANP (103-123). In the displacement binding assays, the order of potency of ANP peptides was similar to that of the relaxation experiments: ANP (99-126) = ANP (101-126) greater than ANP (103-126) = ANP (103-125) much greater than ANP (103-123). When the vessels were precontracted by a smaller concentration of phenylephrine (10(-7) M in mesenteric artery and 10(-8) M in aorta), the IC50 of ANP (101-126) was significantly lower than when the higher concentration of phenylephrine was used. These results show that ANP receptors in the mesenteric artery and in the aorta have similar structural requirements, according to the order of potency of different length ANP, both for binding and myotropic responses.

Platelet binding sites and plasma concentration of atrial natriuretic peptide in patients with essential hypertension

The plasma concentration of atrial natriuretic peptide (ANP) and the density and affinity of binding sites for ANP in platelets was investigated in patients with essential hypertension. Severe hypertensives were studied whilst still on medication. All subjects were ambulatory and were investigated after 3 days on a 135 mmol/day sodium intake. Plasma ANP levels were significantly increased from 13 +/- 1 fmol/ml in healthy normotensive controls to 39 +/- 5 fmol/ml (P less than 0.01) in moderate or severe hypertensives uncontrolled by treatment. Platelet binding sites varied in a non-linear inverse relationship to plasma concentration of ANP (r = -0.76), from 14 +/- 1 fmol per 10(9) platelets in healthy subjects to 8 +/- 1 fmol per 10(9) platelets in severe hypertensives, uncontrolled by treatment, (P less than 0.05). The latter group with elevated plasma ANP and reduced density of ANP platelet sites, had a high incidence of left ventricular hypertrophy and increased left ventricular mass index by echocardiography. When a diuretic was added or stopped, plasma ANP and ANP sites in platelets varied inversely, with lower ANP concentration in plasma and higher density of ANP receptors in platelets when receiving the diuretic. Plasma concentrations of ANP are increased and the density of ANP receptors is decreased in moderate to severe uncontrolled essential hypertensives with left ventricular hypertrophy, but neither parameter differs from those of healthy age-matched volunteers in mild essential hypertension.