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(Hypertension. 1998;31:315.)
© 1998 American Heart Association, Inc.

Scientific Contributions

Systemic Hemodynamics and Regional Blood Flow During Chronic Nitric Oxide Synthesis Inhibition in Pregnant Rats

Salah Kassab; M. Todd Miller; Robert Hester; Jacqueline Novak; Joey P. Granger

From Department of Physiology and Biophysics and Center for Excellence in cared Cardiovascular and Renal Research, University of Mississippi Medical Center, Jackson, Miss.

Correspondence to Joey P. Granger, PhD, Department of Physiology and Biophysics, University of Mississippi Medical Center, 2500 North State Streeet, Jackson, MS 39216-4505. E-mail JPG{at}fiona.umsmed.edu

	Abstract

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Pregnancy-induced hypertension in women is associated with severe vasoconstriction and reductions in organ blood flow and cardiac output. Recent studies have indicated that nitric oxide (NO) synthesis inhibition during mid to late gestation in pregnant rats results in severe hypertension and proteinuria. The purpose of this study was to determine the systemic hemodynamic and regional blood flow alterations associated with chronic NO synthesis inhibition in the pregnant rat. The study was conducted in four groups of rats: virgin rats (n=6), pregnant rats (n=10), virgin rats treated with L-NAME (n=6), and pregnant rats treated with L-NAME (n=11). Rats were treated with L-NAME in drinking water at a dose of 1 mg/d for a week starting from day 13 of gestation in pregnant rats or an equivalent time for virgins. Mean arterial pressure (MAP), cardiac output, total peripheral resistance (TPR), and regional flows were measured by tracing radiolabeled microspheres in conscious rats. Pregnant rats that were given L-NAME showed significantly higher MAP (137±6 versus 96±2 mm Hg), higher TPR (5.08±0.58 versus 2.90±0.44 mm Hg/mL/min/100 g), and lower cardiac output (87.4±8.4 versus 113.3±11.1 mL/min) than pregnant controls. Chronic NO synthesis inhibition decreased the renal blood flow in pregnant rats at a significantly greater magnitude than in virgin rats. Significant reductions in regional blood flow to the heart, lungs, liver, diaphragm, and skeletal muscles were also observed in pregnant rats treated with L-NAME. The results of this study indicate that NO may play a role in mediating the alterations in systemic hemodynamics and regional blood flow in late pregnant rats.

Key Words: nitric oxide • blood flow • pregnancy • hypertension

Abbreviations: NO = nitric oxide • PIH = pregnancy-induced hypertension • MAP = mean arterial pressure • L-NAME = N-nitro-L-arginine methyl ester • L-NMMA = N^G-monomethyl-L-arginine • L-NNA = N^G-nitro-L-arginine • RBF = renal blood flow • RPF = renal plasma flow • RVR = renal vascular resistance • GFR = glomerular filtration rate • ANG II = angiotensin II • ET = endothelin • cAMP = cyclic adenosine monophosphate

	Introduction

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During normal pregnancy, maternal blood volume increases markedly, leading to approximately a 30% to 60% increase in cardiac output.¹ The blood pressure falls despite the increase in cardiac output, mostly because of decreased systemic vascular resistance.² Gestation in humans as well as in different animal models is also associated with significant changes in blood flow to different organs and tissues. Changes in renal hemodynamics include a 20% to 40% increase in GFR that has been correlated with increased RPF.³ Dramatic increases in uteroplacental blood flow also occur during pregnancy to accommodate the increasing needs of the growing fetus.^4–6 Furthermore, the pressor responses to exogenously administered vasoconstrictors such as norepinephrine and angiotensin-II are attenuated in pregnant rats^7,8 and humans.⁹ Recent studies have provided evidence that total body NO production as well as regional production in certain vascular beds is increased during pregnancy, indicating that NO could play a role in mediating the attenuated vascular reactivity and vasodilation during gestation.¹⁰ However, the role of NO in mediating the increased cardiac output, decreased vascular resistance, and regional blood flow alterations during pregnancy has not been elucidated.

PIH, on the other hand, is characterized by increased systemic vascular resistance, contracted blood volume, enhanced sensitivity to vasopressor agents, altered renal hemodynamics, and vascular endothelial cell damage.¹¹ Although the exact mechanism responsible for PIH is unclear, there is substantial evidence that maternal vascular endothelial cell dysfunction could be involved.^12,13 Because NO is thought to play an important role in the control of arterial pressure and regional blood flow in nonpregnant animals, and since its levels have been reported to be elevated during pregnancy, decreased NO production has been proposed to contribute to the pathogenesis of PIH.^10,14,15 Recent studies have indicated that chronic administration of NO synthesis inhibitors during mid to late gestation in rats leads to the development of hypertension and proteinuria that returned to prepregnant levels after delivery, a result suggesting a potential model that may mimic human preeclampsia.^16–18 However, the hemodynamic and regional blood flow alterations in this rat model of PIH have not been fully characterized.

The aim of this study was to determine the systemic hemodynamic and regional flow changes during normal pregnancy and in a rat model of PIH caused by chronic NO synthesis inhibition. To achieve these goals, we examined the systemic hemodynamics and regional blood flows using radiolabeled microspheres in conscious pregnant rats and in rats chronically treated with L-NAME for 1 week starting from mid-gestation.

	Methods

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Virgin female Sprague Dawley rats were purchased from Harlan Sprague Dawley, Inc. Animals were placed two in a cage in a temperature-controlled room (23°C) with a 12:12 hour light/dark cycle and fed a standard rat chow (Teklad) and water ad libitum. All experimental procedures in this study were executed in accordance with the National Institutes of Health guidelines for use and care of animals, and the protocols were approved by the Animal Care and Use Committee at the University of Mississippi Medical Center.

The study was conducted on four groups of rats: virgin rats (n=6), pregnant rats (n=11), pregnant rats (n=10) that received the NO synthesis inhibitor L-NAME in drinking water for 7 prenatal days (days 13 to 19 gestation), and virgin rats that received L-NAME (n=6) in drinking water for one week before the experiment. L-NAME (Sigma Chemical Co.) was dissolved in distilled water at a dose of 50 mg/L ad libitum. On the basis of a preliminary study in our laboratory using this concentration of L-NAME in distilled water, each rat received approximately 1 mg of L-NAME per day. We also found that no difference in water intake was observed between virgin and pregnant rats until day 20 of pregnancy.¹⁶ A sperm-positive vaginal smear from females was considered day 1 of pregnancy. Pregnant rats were then housed individually in cages from the first day of pregnancy until the time of experimentation.

	Surgical Procedures

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On the morning of the experiment, rats were anaesthetized with isoflurane that was delivered to the rat by using a portable anesthesia machine for rodents modified from a model described by Henry and Casto.¹⁹ A catheter of heat-stretched PE 50 tubing was inserted into the right carotid artery and advanced 3.5 to 4.5 cm into the left ventricle of the heart. The location of the catheter was determined operatively by the left ventricular pulse pressure tracing and was confirmed by postmortem examination. Another length of PE-50 tubing was inserted into the left femoral artery for measurement of arterial pressure and for blood withdrawal of the reference sample. The catheters were filled with heparin, and animals were allowed to recover for approximately 4 hours. Each rat was placed in a Plexiglas restrainer, the size of which was chosen so that it did not allow the rat to move around without external pressure. Furthermore, rats were pretrained before the experiment to minimize the stress of the restraining procedure. The femoral catheter was connected to a Statham pressure transducer, and MAP was continuously recorded on a Grass Model 7B polygraph (Grass Instruments Co.) for a period of 30 minutes before the experiment.

	Microsphere Injection

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Microspheres radiolabeled with ⁴⁶Sc (New England Nuclear) with a mean diameter of 15±3 µm were purchased dry and suspended in a 1.3 specific gravity dextrose solution with one drop of 0.05% tween 80 to prevent clumping of microspheres as previously described.²⁰ The microsphere solution was then dispersed by using an ultrasonic bath (Radiograph) for 5 minutes and then mixed with a vortex shaker for 3 minutes. Precoiled PE-50 tubing (72 cm long, 0.2 mL filling volume) was filled with the microsphere solution, which was adjusted to a dilution to contain 300,000 microspheres per coil. The coils were sealed with metal plugs at both ends, and radioactivity was determined by using a gamma counter (Series 1185). Each rat was prepared for microsphere injection in the conscious state by interposing the preloaded coil between the left ventricular catheter and a Gilford infusion pump and connecting the femoral catheter to a withdrawal pump of the same type. Microspheres were injected into the left ventricle and flushed with 0.6 mL of saline over a period of 20 seconds. The withdrawal pump was adjusted to collect a 1-mL blood sample from the femoral artery over a period of 90 seconds starting at the same time as the microsphere injection.

	Cardiac Output and Regional Flow Measurement

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At the end of the experiment, rats were euthanized by intraventricular injection of pentobarbital. Individual placentas, uterus, heart, lungs, liver, stomach, intestines, kidneys, brain, and a tissue sample from the skeletal muscle of the forelimbs and hindlimbs were carefully separated and weighed. The arterial reference sample, along with tissues and organs, were counted in a gamma counter that was set at the photopeak of the isotope that was used. The residual activity in the microsphere injection coil and plugs was determined and subtracted from the radioactivity of the coil before injection for calculation of the net amount of radioactivity that was infused in each rat. The uniformity of distribution of microspheres was considered adequate on the basis of a <5% difference in the number of microspheres entrapped in the right and left kidneys.

Cardiac output was calculated as follows:

Tissue and organ flows were determined by the ratio of the number of microspheres in the tissue to the total number of injected microspheres times total cardiac output divided by the organ weight and expressed as mL/min/100 g of tissues.

	Statistical Analysis

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All data in the experiment are expressed as mean±SEM. Differences between groups were determined by using factorial ANOVA followed by Scheffé’s test. Differences in placental flow and resistance between pregnant rats and rats treated with L-NAME were analyzed by using unpaired t-test. A value of P<0.05 was considered statistically significant.

	Results

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Changes in Systemic Hemodynamics in Virgin and Pregnant Rats in Response to Chronic NO Synthesis Inhibition
Fig 1 illustrates the systemic hemodynamics in virgin and pregnant rats and in rats chronically-treated with L-NAME. In pregnant rats, MAP was 25% lower (96±2 versus 120±1 mm Hg, P<.05) and cardiac output was 30% higher (113.3±11.1 versus 86.7±10.2 mL/min, P<.05) than in virgin rats. Although TPR was 14% lower in pregnant rats than in virgin rats, this difference was not statistically significant. Pregnant rats that were given L-NAME showed significantly higher MAP (137±6 versus 96±2 mm Hg. P<.01), higher TPR (5.08±0.58 versus 2.90±0.44 mm Hg/mL/min/100 g, P<.05), and lower cardiac output (87.4±8.4 versus 113.3±11.1 mL/min, P<.05). On the other hand, the changes in MAP and cardiac output in L-NAME-treated virgin rats were not statistically significant in comparison with control virgin rats. However, TPR was higher (3.30±0.44 versus 4.7±0.60 mm Hg/mL/min/100 g, P<.05) in virgin rats that were treated with L-NAME compared with virgin controls.

View larger version (19K): [in this window] [in a new window]   Figure 1. Mean arterial pressure, cardiac output, and total peripheral resistance in virgin and pregnant rats and in those chronically treated with L-NAME (1 mg/d) for 1 week. Data are mean±SEM. *P<.05 in control rats compared with rats treated with L-NAME. P<.05 in virgin versus pregnant rats.

Changes in Regional Hemodynamics in Virgin and Pregnant Rats in Response to Chronic NO Synthesis Inhibition
Fig 2 illustrates the renal hemodynamic changes in virgin and pregnant rats and in virgin and pregnant rats treated with L-NAME for 1 week. RBF in pregnant rats was 44% higher (14.59±3.92 versus 10.1±1.29 mL/min) and RVR was 12% lower (10.33±1.62 versus 11.73±1.70 mm Hg/mL/min) than in virgin rats. However, the renal hemodynamics in virgin and pregnant rats were not statistically different. In L-NAME-treated pregnant rats, RBF was significantly lower (6.06±0.83 versus 14.59±3.92 mL/min, P<.01) and RVR was significantly higher (28.25±3.61 versus 10.33±1.62 mm Hg/mL/min, P<.01) compared with pregnant controls. On the other hand, RBF in L-NAME-treated virgin rats was not statistically different from that in virgin controls despite the increase in RVR.

View larger version (16K): [in this window] [in a new window]   Figure 2. Renal blood flow and renal vascular resistance in virgin and pregnant rats and in those chronically treated with L-NAME (1 mg/d) for 1 week. Data are mean±SEM. *P<.05 in control rats compared with rats treated with L-NAME.

Table 1 shows the regional blood flow (mL/min/g) (Table 1A) and regional vascular resistance (mm Hg/mL/min/g tissue weight) (Table 1B) in different vascular beds (other than reproductive organs) in virgin and pregnant rats and in those chronically treated with L-NAME. Chronic inhibition of NO synthesis in virgin rats led to a significant (P<.01) decrease in pulmonary blood flow with no significant effects on blood flow to other vascular beds. However, in pregnant rats chronically treated with L-NAME, significant reductions in blood flow occurred in a wide variety of vascular beds, including heart, lungs, liver, and skeletal muscles (P<.05).

View this table: [in this window] [in a new window]   TABLE 1A. Regional Blood Flow (mL/min/g tissue) in Different Organs and Tissues in Virgin and Pregnant Rats and in Those Chronically Treated With L-NAME (1 mg/d) for 1 Week. Data Are Mean±SM

View this table: [in this window] [in a new window]   TABLE 1B. Regional Resistance (mm Hg/mL/min/g tissue ) in Different Organs and Tissues in Virgin and Pregnant Rats and in Those Chronically Treated With L-NAME (1 mg/d) for 1 Week. Data Are Mean±SEM

Table 2 shows the regional blood flow (mL/min) and vascular resistance (mm Hg/mL/min) in the uterus, ovary, and placenta in each group of rats. Pregnancy was associated with a 17-fold increase in uterine flow and a 22-fold decrease in uterine vascular resistance. Ovarian blood flow was also significantly higher and resistance was significantly lower in pregnant rats than in virgin rats and was not significantly altered in response to chronic NO synthesis inhibition in both groups. Uterine and placental flows in pregnant rats that were chronically treated with L-NAME were not statistically different from its values in the control pregnant group whether the data are expressed in total flow or flow per fetus.

View this table: [in this window] [in a new window]   TABLE 2. Regional Blood Flow (mL/min) and Vascular Resistance (mm Hg/mL/min) in Reproductive Organs in Virgin and Pregnant Rats and in Those Chronically Treated With L-NAME (1 mg/d) for 1 Week. Data Are Mean±SEM

	Discussion

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The main finding in this study is that chronic NO synthesis inhibition during mid to late gestation in rats caused a significant increase in arterial pressure associated with a significant reduction in cardiac output, increased TPR, and reduction in blood flow to different vascular beds such as the kidneys, heart, lungs, liver, and skeletal muscles. Moreover, the hemodynamic alterations in virgin rats treated with the same dose of L-NAME for the same period of time either were not observed or were significantly less than those observed in pregnant rats.

The data presented herein indicate that NO may play an important role in mediating the high-output, low-resistance, low-pressure state that is a hallmark of rat gestation. Nathan et al⁷ recently reported that in ganglion-blocked pregnant rats, inhibition of NO synthesis led to an increase in arterial pressure that was significantly greater in late pregnant rats than in nonpregnant rats. Molnar et al¹⁸ similarly observed a greater increase in blood pressure in pregnant rats given L-NAME chronically during late gestation than in virgin rats. In humans, a greater reduction in forearm flow was observed in late pregnant than in nonpregnant or early pregnant women during infusion of L-NMA into the brachial artery.²¹ Therefore, it appears that NO plays an important role in gestational dilation and decreased blood pressure during late stages of pregnancy but not during early or mid pregnancy. Other investigators, however, reported that the pressor responses to NO synthesis inhibition in late pregnant and nonpregnant rats were not statistically different.^8,22 A major cause of the discrepancy between the results of these studies could be the doses used in the previous studies, which were high enough to cause marked hemodynamic changes in both virgin and pregnant rats.

Multiple mechanisms have been proposed to explain enhanced systemic vasoconstriction and accentuated arterial pressure response to NO synthesis blockade in pregnant rats. Edwards et al²³ recently reported that long-term NO synthesis inhibition during mid to late gestation causes sustained hypertension and elevated levels of plasma ET-1. However, whether elevated ET-1 levels are a cause of increased blood pressure or a consequence of the endothelial injury caused by hypertension due to NO synthesis blockade is still unclear. Another possible mechanism is that NO synthesis blockade in pregnant rats unmasks of the vasoconstrictor effects of circulating ANG II, which is known to be elevated during pregnancy.⁷ Whether increased vascular smooth muscle tone during chronic NO synthesis inhibition in pregnant rats is due to a direct effect of reduced NO availability or indirectly due to enhanced activity of endogenous vasoconstrictors is still unclear and requires further investigation.

In addition to the peripheral vasoconstrictor effects of NO synthesis inhibition in pregnant rats, we observed a significant decrease in RBF and increase in RVR that were greater in pregnant than in virgin rats. NO has been previously shown to play an important role in the control of renal hemodynamics in the rat.^24,25 A possible role for NO in mediating the gestational increases in renal blood flow is supported by studies by Danielson and Conrad,²⁶ who reported that acute blockade of NO synthesis abrogates the renal vasodilation and hyperfiltration in pregnant rats. The same group of investigators,²⁷ however, demonstrated that chronic blockade of NO (for 48 hours) failed to prevent the renal vasodilation during midgestation in rats mainly because of the compensatory increase in renal prostaglandins, since the vasodilation was prevented by meclofenamate. The difference between these results and the present study may be due to the gestational age when rats were examined or the dose, route, and duration of administration of L-NAME. Although the mechanism through which chronic NO inhibition increases renal vascular smooth muscle tone is unknown, it is unlikely that this effect is mediated through overexpression or increased sensitivity of endogenous vasoconstrictors, since we recently reported that L-NAME-treated pregnant rats exhibited the same degree of renal vascular response to exogenously administered ANG II as control pregnant rats.²⁸ Therefore, it appears that NO may play an important role in mediating the gestational increases in RBF; further investigation is required to elucidate the mechanisms through which NO mediates renal vasodilation in pregnant rats.

We also observed a reduction in blood flow to other organs, including the heart, lungs, liver, and skeletal muscles, confirming the importance of NO in regulating regional blood flow during pregnancy. NO has been previously reported to play an important role in long-term regulation of regional blood flow in virgin rats.²⁵ However, the state of NO production and its role in regulating regional blood flow during pregnancy have been studied mostly by using in vitro preparations. Using in situ blood-perfused mesenteric vessels, Chu and Beilin²⁹ reported a comparable potentiation of basal perfusion pressure and vascular reactivity to L-NNA in late pregnant and non-pregnant rats. In isolated mesenteric vessels, the vasoconstrictor response to phenylephrine was attenuated in late pregnant rats compared with nonpregnant rats, and L-NAME³⁰ or L-NNA³¹ caused a twofold potentiation of the vasoconstrictor response in both groups. In isolated hindlimb preparations, vascular reactivity to ANG II, but not to NE, was attenuated in late pregnant rats and was enhanced by LNMA to nonpregnant levels.³² Although these data support our observation that NO does not play a role in regulating mesenteric blood flow in pregnant rats, the pathological significance of NO in mediating the flow alterations to other vascular beds still needs to be investigated.

During the third trimester, a dramatic increase in blood flow to the uterus and placenta occurs to fulfill the nutritional needs of the rapidly growing fetus.⁶ Recent studies have presented evidence that NO production increases not only systemically during pregnancy but also in the uterine arteries in different animal species.¹⁰ Total nitrite production and cGMP levels are markedly elevated in rat uterine tissue during late gestation.³³ Furthermore, calcium-dependent NO synthase activity has been shown to be elevated during pregnancy in guinea pig uterine arteries.³⁴ A recent in vitro study has also demonstrated that the basal or activated endothelial-derived vasodilation is augmented in uterine arteries of late pregnant compared with nonpregnant rats, mainly because of enhanced release of NO.³⁵ On the basis of these and other studies, it has been proposed that diminished NO synthesis in the uteroplacental circulation will cause a reduction in placental perfusion. Surprisingly, we did not observe a decrease in uterine or placental blood flow after chronic NO synthesis blockade in pregnant rats. In fact, uteroplacental flow tended to be higher in L-NAME-treated pregnant rats than in controls. This observation could be explained by different mechanisms. First, chronic L-NAME administration could induce the expression of inducible NO synthase, an enzyme that is known to produce a large amounts of NO and is less susceptible to inhibition by L-NAME.^36,37 Second, since placental vessels lack the autoregulation, it is possible that the increased systemic arterial pressure in L-NAME-treated pregnant rats is transmitted to the placental circulation, overcoming the lack of vasodilation due to NO deficiency. Third, it is possible that a compensatory mechanism is present in the placenta to maintain placental perfusion by increasing synthesis (or enhancing the tissue sensitivity) of other vasodilators such as prostaglandins. This explanation is supported by recent studies demonstrating that pregnancy is associated with a twofold to threefold increase in uterine artery PG12 from both the endothelium and vascular smooth muscle. Furthermore, alterations in basal uterine cAMP production are related directly to alterations in PG₁₂ production, and NO synthesis blockade does not alter either cAMP or PG₁₂ production.^38,39 Further regional flow studies using combined NO and prostaglandin blockade or servocontrolled uterine perfusion pressure may be needed to clarify this point.

In summary, we confirm our previous observations that chronic NO synthesis inhibition during mid to late gestation in rats is associated with a significantly greater increase in arterial pressure than in virgin rats. Chronic NO synthesis inhibition in pregnant rats was also associated with significant reduction in cardiac output and an increase in total peripheral resistance. L-NAME also caused significant reductions in blood flow to the kidneys, heart, lungs, liver, and skeletal muscles in pregnant rats. The changes in systemic and regional hemodynamics in response to NO synthesis inhibition in virgin rats either were not observed or were significantly less than in pregnant rats. The results of this study indicate that NO plays a role in mediating the alterations in systemic hemodynamics and regional flow in late pregnant rats.

	Acknowledgments

 
The authors thank also Dr Raouf Khalil, Dr Jane Reckelhoff, and Dr Barbara Alexander for critical review of the manuscript. We also thank Gerry McAlpin for excellent secretarial assistance. This work was supported by NIH grants HL38499 and HL51971.

Received September 17, 1997; first decision October 10, 1997; accepted October 22, 1997.

	References

Top Abstract Introduction Methods Surgical Procedures Microsphere Injection Cardiac Output and Regional... Statistical Analysis Results Discussion References

 
1. Clark SL, Cotton DB, Lee W, Bishop C, Hill T, Southwick J, Pivarnik J, Spillman T, DeVore GR, Phelan J. Central hemodynamic assessment of normal term pregnancy. Am J Obstet Gynecol. 1989; 161 : 1439 –1442.[Medline] [Order article via Infotrieve]

2. Christianson RE. Studies on blood pressure during pregnancy: influence of parity and age. Am J Obstet Gynecol. 1976; 125 : 509 –513.[Medline] [Order article via Infotrieve]

3. Davison JM, Dunlop W. Renal hemodynamics and tubular function in normal human pregnancy. Kidney Int. 1980; 18 : 152 –161.[Medline] [Order article via Infotrieve]

4. Magness RR, Zheng J. Maternal cardiovascular alterations during pregnancy. In P. D. Gluckman and MA Heymann, ed.: Pediatric and Perinatal Perspectives: The Scientific Basis. London: Arnold: 1996: 762 –772.

5. Dowell RT, Kauer CD. Uteroplacental blood flow at rest and during exercise in late gestation conscious rats. J Appl Physiol. 1993; 74 : 2079 –2085.[Abstract/Free Full Text]

6. Bruce NW. The distribution of blood flow to the reproductive organs of rats near term. J Reprod Fertil. 1976; 46 : 359 –362.[Abstract/Free Full Text]

7. Nathan L, Cuevas J, Chaudhuri G. The role of nitric oxide in the altered vascular reactivity of pregnancy in the rat. Br J Pharmacol. 1995; 114 : 955 –960.[Medline] [Order article via Infotrieve]

8. Molnar M, Hertelendy F. N o-nitro-L-arginine, an inhibitor of nitric oxide synthesis, increases blood pressure in rats and reverses the pregnancy-induced refractoriness to vasopressor agents. Am J Obstet Gynecol. 1992; 166 : 1560 –1567.[Medline] [Order article via Infotrieve]

9. Williams DJ, Vallance PJT, Neild GH, Spencer JAD, Imms FJ. Nitric oxide-mediated vasodilation in human pregnancy. Am J Physiol. 1997; 272 : H748 –H752.[Medline] [Order article via Infotrieve]

10. Sladek SM, Magness RR, Conrad KP. Nitric oxide and pregnancy. Am J Physiol. 1997; 272 : R441 –R463.[Medline] [Order article via Infotrieve]

11. National High Blood Pressure Education Program Working Group Report on High Blood Pressure in Pregnancy. Consensus report. Am J Obstet Gynecol. 1990; 163 : 1689 –1712.

12. De Groot CJM, Taylor RN. New insight into the etiology of preeclampsia. Ann Med. 1993; 25 : 243 –249.[Medline] [Order article via Infotrieve]

13. Brown MA. The physiology of pre-eclampsia. Clin Exper Pharmacol Physiol. 1995; 22 : 781 –791.[Medline] [Order article via Infotrieve]

14. Morris NH, Eaton BM, Dekker G. Nitric Oxide, the endothelium, pregnancy and pre-eclampsia. Br J Obstet Gynecol. 1996; 103 : 4 –15.[Medline] [Order article via Infotrieve]

15. Friedman SA, Lubarsky SL, Ahokas RA, Nova A, Sibai BM. Pre-eclampsia and related disorders: clinical aspects and relevance of endothelin and nitric oxide. Clin Perinatol. 1995; 2 : 343 –355.

16. Novak J, Cockrell K, Kassab S, Reckelhoff JF, Granger JP. Chronic nitric oxide synthesis inhibition during pregnancy increases thromboxane excretion in rats. FASEB J. 1997; 11 : A78 .

17. Baylis C, Engels K. Adverse interactions between pregnancy and a new model of systemic hypertension produced by chronic blockade of endothelial derived relaxing factor (EDRF) in the rat. Clin Exp Hypertens. 1992; B11 : 117 –129.

18. Molnar M, Suto T, Toth T, Hertelendy F. Prolonged blockade of nitric oxide synthesis in gravid rats produces sustained hypertension, proteinuria, thrombocytopenia, and intrauterine growth retardation. Am J Obstet Gynecol. 1994; 170 : 1458 –1466.[Medline] [Order article via Infotrieve]

19. Henry RT, Casto R. Simple and inexpensive delivery of halogenated inhalation anesthetics to rodents. Am J Physiol. 1989; 257 : R668 –R671.[Medline] [Order article via Infotrieve]

20. Stanek KA, Smith TL, Murphy WR, Coleman TG. Hemodynamic disturbances in the rat as a function of the number of microspheres injected. Am J Physiol. 1983; 245 : H920 –H923.[Medline] [Order article via Infotrieve]

21. Williams DJ, Vallance PJT, Neild GH, Spencer JAD, Imms FJ. Nitric oxide-mediated vasodilation in human pregnancy. Am J Physiol. 1997; 272 : H748 –H752.[Medline] [Order article via Infotrieve]

22. Umans JG, Linheimer MD, Barron WM. Pressor effect of endothelium-derived relaxing factor inhibition in conscious virgin and gravid rats. Am J Physiol. 1990; 259 : F293 –F296.[Medline] [Order article via Infotrieve]

23. Edwards DL, Arora CP, Bui DT, Castro LC. Long-term nitric oxide blockade in the pregnant rat: effects on blood pressure and plasma levels of endothelin-1. Am J Obstet Gynecol. 1996; 175 : 484 –488.[Medline] [Order article via Infotrieve]

24. Baylis C, Harton P, Engels K. Endothelium-derived relaxing factor controls renal hemodynamics in the normal rat kidney. J Am Soc Nephrol. 1990; 1 : 875 –881.[Abstract]

25. Huang M, Manning D, LeBlanc MH, Hester RL. Overall hemodynamic studies after the chronic inhibition of endothelial-derived nitric oxide in rats. Am J Hypertens. 1995; 8 : 358 –364.[Medline] [Order article via Infotrieve]

26. Danielson LA, Conrad KP. Acute blockade of nitric oxide synthase inhibits renal vasodilation and hyperfiltration during pregnancy in chronically instrumented conscious rats. J Clin Invest. 1995; 96 : 482 –490.[Medline] [Order article via Infotrieve]

27. Danielson LA, Conrad KP. Prostaglandins maintain renal vasodilation and hyperfiltration during chronic nitric oxide synthase blockade in conscious pregnant rats. Circ Res. 1996; 79 : 1161 –1166.[Abstract/Free Full Text]

28. Novak J, Reckelhoff JF, Bumgarner L, Cockrell K, Kassab S, Granger JP. Role of nitric oxide in mediating the reduced sensitivity of the renal circulation to angiotensin II in rats. Hypertension. 1997; 30 : 580 –584.[Abstract/Free Full Text]

29. Chu ZM, Beilin LJ. Mechanisms of vasodilation in pregnancy: studies of the role of prostaglandins and nitric oxide in changes of vascular reactivity in the in situ blood perfused mesentry of pregnant rats. Br J Pharmacol. 1993; 109 : 322 –329.[Medline] [Order article via Infotrieve]

30. Davidge ST, McLaughlin MK. Endogenous modulation of the blunted adrenergic response in resistance-sized mesentric arteries from the pregnant rat. Am J Obstet Gynecol. 1992; 167 : 1691 –1698.[Medline] [Order article via Infotrieve]

31. Pascoal IF, Lindheimer MD, Nalbantian-Brandt C, Umans GJ. Con traction and endothelium-dependent relaxation in mesentric microvessels from pregnant rats. Am J Physiol. 1995; 269 : H1899 –H1904.[Medline] [Order article via Infotrieve]

32. Ahokas RA, Sibai BM. Endothelium-derived relaxing factor inhibition augments vascular angiotensin II reactivity in the pregnant rat hindlimb. Am J Obstet Gynecol. 1992; 167 : 1053 –1058.[Medline] [Order article via Infotrieve]

33. Yallampalli C, Byam-Smith M, Nelson SO, Garfield RE. Steroid hormones modulate the production of nitric oxide and cGMP in the rat uterus. Endocrinology. 1994; 134 : 1971 –1974.[Abstract/Free Full Text]

34. Weiner CP, Lizasoain I, Baylis SA, Knowles RG, Chades IG, Moncada S. Induction of calcium-dependent nitric oxide synthase by sex hormones. Proc Natl Acad Sci U S A. 1994; 91 : 5212 –5216.[Abstract/Free Full Text]

35. Ni Y, Meyer M, Osol G. Gestation increases nitric oxide-mediated vasodilation in rat uterine arteries. Am J Obstet Gynecol. 1997; 176 : 856 –864.[Medline] [Order article via Infotrieve]

36. Furfine ES, Harmon MF, Paith JE, Carvet EP. Selective inhibition of constitutive nitric oxide synthase by L-nitroarginine. Biochemistry. 1993; 32 : 8512 –8517.[Medline] [Order article via Infotrieve]

37. Lyall F, Young A, Greer IA. Nitric oxide concentrations are increased in the fetoplacental circulation in preeclampsia. Am J Obstet Gynecol. 1995; 173 : 714 –718.[Medline] [Order article via Infotrieve]

38. Magness RR, Shaw CE, Phernetton TM, Zheng J, Bird IM. Endothelial vasodilator production by uterine and systemic arteries. II. Pregnancy effects on NO synthase expression. Am J Physiol. 1997; 272 : H1730 –H1740.[Medline] [Order article via Infotrieve]

39. Magness RR, Rosenfeld CR, Hassan A, Shaul PW. Endothelial vasodilator production by uterine and systemic arteries: effects of ANG II on PGI₂ and NO in pregnancy. Am J Physiol. 1997; 272 : H1730 –H1740.[Medline] [Order article via Infotrieve]

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