GNB3 C825T Polymorphism and Myocardial Recovery in Peripartum Cardiomyopathy: Results of the Multicenter Investigations of Pregnancy-Associated Cardiomyopathy Study.

BACKGROUND: Black women are at greater risk for peripartum cardiomyopathy (PPCM). The guanine nucleotide-binding proteins ß-3 subunit (GNB3) has a polymorphism C825T. The GNB3 TT genotype more prevalent in blacks is associated with poorer outcomes. We evaluated GNB3 genotype and myocardial recovery in PPCM. METHODS AND RESULTS: A total of 97 women with PPCM were enrolled and genotyped for the GNB3 T/C polymorphism. Left ventricular ejection fraction (LVEF) was assessed by echocardiography at entry, 6 and 12 months postpartum. LVEF over time in subjects with the GNB3 TT genotype was compared with those with the C allele overall and in black and white subsets. The cohort was 30% black, age 30+6, LVEF 0.34+0.10 at entry 31+25 days postpartum. The % GNB3 genotype for TT/CT/CC=23/41/36 and differed markedly by race (blacks=52/38/10 versus whites=10/44/46, P<0.001). In subjects with the TT genotype, LVEF at entry was lower (TT=0.31+0.09; CT+CC=0.35+0.09, P=0.054) and this difference increased at 6 (TT=0.45+0.15; CT+CC=0.53+0.08, P=0.002) and 12 months (TT=0.45+0.15; CT+CC=0.56+0.07, P<0.001.). The difference in LVEF at 12 months by genotype was most pronounced in blacks (12 months LVEF for GNB3 TT=0.39+0.16; versus CT+CC=0.53+0.09, P=0.02) but evident in whites (TT=0.50++0.11; CT+CC=0.56+0.06, P=0.04). CONCLUSIONS: The GNB3 TT genotype was associated with lower LVEF at 6 and 12 months in women with PPCM, and this was particularly evident in blacks. Racial differences in the prevalence and impact of GNB3 TT may contribute to poorer outcomes in black women with PPCM.

Molecular mechanisms regulating the vascular prostacyclin pathways and their adaptation during pregnancy and in the newborn.

Prostacyclin (PGI(2)) is a member of the prostanoid group of eicosanoids that regulate homeostasis, hemostasis, smooth muscle function and inflammation. Prostanoids are derived from arachidonic acid by the sequential actions of phospholipase A(2), cyclooxygenase (COX), and specific prostaglandin (PG) synthases. There are two major COX enzymes, COX1 and COX2, that differ in structure, tissue distribution, subcellular localization, and function. COX1 is largely constitutively expressed, whereas COX2 is induced at sites of inflammation and vascular injury. PGI(2) is produced by endothelial cells and influences many cardiovascular processes. PGI(2) acts mainly on the prostacyclin (IP) receptor, but because of receptor homology, PGI(2) analogs such as iloprost may act on other prostanoid receptors with variable affinities. PGI(2)/IP interaction stimulates G protein-coupled increase in cAMP and protein kinase A, resulting in decreased [Ca(2+)](i), and could also cause inhibition of Rho kinase, leading to vascular smooth muscle relaxation. In addition, PGI(2) intracrine signaling may target nuclear peroxisome proliferator-activated receptors and regulate gene transcription. PGI(2) counteracts the vasoconstrictor and platelet aggregation effects of thromboxane A(2) (TXA(2)), and both prostanoids create an important balance in cardiovascular homeostasis. The PGI(2)/TXA(2) balance is particularly critical in the regulation of maternal and fetal vascular function during pregnancy and in the newborn. A decrease in PGI(2)/TXA(2) ratio in the maternal, fetal, and neonatal circulation may contribute to preeclampsia, intrauterine growth restriction, and persistent pulmonary hypertension of the newborn (PPHN), respectively. On the other hand, increased PGI(2) activity may contribute to patent ductus arteriosus (PDA) and intraventricular hemorrhage in premature newborns. These observations have raised interest in the use of COX inhibitors and PGI(2) analogs in the management of pregnancy-associated and neonatal vascular disorders. The use of aspirin to decrease TXA(2) synthesis has shown little benefit in preeclampsia, whereas indomethacin and ibuprofen are used effectively to close PDA in the premature newborn. PGI(2) analogs have been used effectively in primary pulmonary hypertension in adults and have shown promise in PPHN. Careful examination of PGI(2) metabolism and the complex interplay with other prostanoids will help design specific modulators of the PGI(2)-dependent pathways for the management of pregnancy-related and neonatal vascular disorders.

Akt and MAPK signaling mediate pregnancy-induced cardiac adaptation.

Although the signaling pathways underlying exercise-induced cardiac adaptation have been extensively studied, little is known about the molecular mechanisms that result in the response of the heart to pregnancy. The objective of this study was to define the morphological, functional, and gene expression patterns that define the hearts of pregnant mice, and to identify the signaling pathways that mediate this response. Mice were divided into three groups: nonpregnant diestrus control, midpregnancy, and late pregnancy. Both time points of pregnancy were associated with significant cardiac hypertrophy. The prosurvival signaling cascades of Akt and ERK1/2 were activated in the hearts of pregnant mice, while the stress kinase, p38, was decreased. Given the activation of Akt in pregnancy and its known role in cardiac hypertrophy, the hypertrophic response to pregnancy was tested in mice expressing a cardiac-specific activated (myristoylated) form of Akt (myrAkt) or a cardiac-specific constitutively active (antipathologic hypertrophic) form of its downstream target, glycogen synthase kinase 3ß (caGSK3ß). The pregnancy-induced hypertrophic responses of hearts from these mice were significantly attenuated. Finally, we tested whether pregnancy-associated sex hormones could induce hypertrophy and alter signaling pathways in isolated neonatal rat ventricular myocytes (NRVMs). In fact, progesterone, but not estradiol treatment increased NRVM cell size via phosphorylation of ERK1/2. Inhibition of MEK1 effectively blocked progesterone-induced cellular hypertrophy. Taken together, our study demonstrates that pregnancy-induced cardiac hypertrophy is mediated by activation of Akt and ERK1/2 pathways.

Angiogenin and hemoxygenase in pregnancy: influence of hypertension.

The pathophysiology of hypertension and preeclampsia involves angiogenesis and endothelial damage/dysfunction, as shown by abnormal growth factors (vascular endothelial growth factor [VEGF], and its receptor sFlt-1) and von Willebrand factor (vWf) in the plasma. Angiogenin and hemoxygenase are abnormal in hypertension and angiogenesis but data on pregnancy are scant. We hypothesized altered angiogenin and hemoxygenase in 38 hypertensive pregnant women (HTPW) compared to 38 normotensive pregnant women (NTPW) and 50 nonpregnant controls (NonPCs). Plasma markers were measured by enzyme-linked immunosorbent assay (ELISA). Hypertensive pregnant women had lower VEGF than NonPCs (P < .01), vWf was raised in both pregnant groups (P < .01), but sFlt-1 was no different. Both angiogenin and hemoxygenase were lower in NTPW compared to NonPCs (both p<0.02). In both pregnancy groups, angiogenin correlated with vWf (r > .33, P < .05), but in NonPCs this was not significant (r = .13, P = .367). These changes may reflect differences in endothelial cell physiology and pathology in the hypertension in pregnancy.

[Severe increase in alkaline phosphatase levels during pregnancy]. / Svært forhøjet alkalisk fosfatase-niveau i graviditeten.

In pregnancy the maternal serum alkaline phosphatase (AP) level increases twofold. If AP values rise above this level, diseases should be considered. We report a case of a 29 year-old pregnant woman with a ninefold increase in the serum AP level due to an increase in the placental level. In the last trimester she had a deep venous thrombosis and lung emboli, which is, however, not shown to correlate to a rise in the AP level. She delivered uncomplicated at term. The aim of this case report is to show the increase of the AP level in pregnancy, to show that there are different isozymes of AP, and to show the importance of investigating a serum AP level, which is increased more than twofold.

[Methyldopa-induced acute reactive hepatitis in pregnancy, drug-metabolizing capacity of the liver]. / Methyldopa által indukált akut reaktív hepatitis terhességben, a máj gyógyszer-metabolizáló képességének alakulása.

Alpha-methyldopa is a regularly used antihypertensive drug during pregnancy. Methyldopa, which decreases the sympathoadrenal system, is the first drug of choice since decades. The reactive hepatitis is not frequent, but known serious side effect of alpha-methyldopa. In non-pregnant women the estimated rate of manifest hepatotoxicity is 2.5-10%. In our case, gestation hypertension developed at the 21st gestation week of a 35 year-old pregnant woman. Oral methyldopa, a central alpha adrenergic blocker therapy was introduced. On the 23rd gestation week acute hepatitis developed. During differential diagnosis of hepatitis, the etiology of methyldopa was taken into account. Viral and autoimmune origin was rolled out. No fetal aberration was found during ultrasound examination. The function of drug metabolizing function from blood was measured by CYP phenotyping (CYP gene expression analysis). CYP3A4 enzyme plays a primary role in the metabolism of nifedipine. Antihypertensive therapy was changed from methyldopa to nifedipine. Nifedipine dosage was based on the value of CYP3A4 gene expression. With the reduced nifedipine therapy (30 mg daily), blood pressure was successfully under control. The diagnosis of alpha-methyldopa induced hepatitis was based on anamnesis, clinical picture and the results of chemical and radiological examination and confirmed by the level of drug-metabolizing capacity. The gestation hepatotoxicity of alpha-methyldopa was reported first in 1969 by Elkington Smith, who suggested the monitoring of serum aminotransferase during alpha-methyldopa therapy in pregnancy in their case report. Our case report confirms that monitoring of serum aminotransferase level is still valuable when treating a pregnant woman with alpha-methyldopa.

[Development of oxidative stress in complicated pregnancy].

The changes in the blood activity of antioxidative defense system enzymes were evaluated in pregnant and non-pregnant women with arterial hypertension (AH). The directionality of revealed changes may be regarded ambiguously. Specifically, the detected dysregulation of first-line antioxidative defense enzymes leads to the accumulation of different forms of active oxygen metabolites that are involved in the development of the molecular basis of the pathogenesis of AH. However, activation of peroxidation processes not only ensures the molecular mechanism of cellular damage, but also aims at developing compensatory and adaptive reactions. The degree of these impairments is likely to be affected by the influence of oxidative stress starting from the cell to organism level--the formation of a metabolic compensation or decompensation phase in arterial hypertension.

NTPDase and 5'-nucleotidase activities in platelets of human pregnants with a normal or high risk for thrombosis.

The nucleotide degrading enzymes, ectonucleotidases, present on the platelet surface of human pregnant with a normal (without complications) or high risk for thrombosis (hypertension and gestational diabetes) were studied. NTPDase (E.C. 3.6.1.5, CD39) and 5'-nucleotidase (E.C. 3.1.3.5, CD73) activities of four patient groups, non-pregnant (NP, n = 18), pregnant without complications (P, n = 25), pregnant with hypertension (HP, n = 15) and pregnant with gestational diabetes mellitus (GDP, n = 10), were analyzed. Increased NTPDase activities were observed in the groups P (37.0%, S.D. = 2.03 and 34.0%, S.D. = 3.19), HP (40.0%, S.D. = 3.32 and 56.0%, S.D. = 3.25) and GDP (23.0%, S.D. = 2.30 and 42.0%, S.D. = 2.26) in comparison to the control group NP (p < 0.01, S.D. = 1.92 and S.D. = 2.48) when ATP and ADP were used as substrate, respectively. AMP was used as substrate to determine the 5'-nucleotidase activities, which showed to be elevated in the groups P (45.0%, S.D. = 1.73), HP (54.0%, S.D. = 2.64) and GDP (68.0%, S.D. = 1.69) when compared to the control group NP (p < 0.01, S.D. = 1.26). However, no statistically significant differences were observed between the groups P, HP and GDP. As a consequence, the enhanced ATP, ADP and AMP hydrolysis was ascribed to the pregnancy itself, independent of a normal or high risk for thrombosis. The enhanced NTPDase and 5'-nucleotidase activities in platelets suggest that these enzymes are involved in the thromboregulation process in the pregnancy.

No association of the Asp298 variant of the endothelial nitric oxide synthase gene with preeclampsia.

BACKGROUND: Preeclampsia, the most common serious complication of pregnancy, is characterized by vasoconstriction, dysfunction of the vascular endothelium, and hypertension. Unidentified genetic factors and impaired nitric oxide (NO)-mediated vasodilation are thought to contribute to the development of the syndrome. Polymorphisms of the endothelial nitric oxide synthase (eNOS) gene affect NO production and have been associated with hypertension and preeclampsia in a Japanese population. METHODS: We compared the frequency of the Glu298Asp eNOS polymorphism in 397 Hispanic and white normotensive pregnant control subjects with the gene frequencies in 64 women with preeclampsia (systolic blood pressure >140 mm Hg or diastolic blood pressure >90 mm Hg, on at least two occasions 6 hours apart, and proteinuria >0.3 g/L or a dipstick proteinuria reading of 2+). RESULTS: Preeclampsia was not associated with the presence of Asp at position 298 of eNOS. CONCLUSIONS: In contrast to the findings in Japanese women, preeclampsia was not associated with the Asp variant of eNOS in an American population.

[Urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion in women with pregnancy complicated with hypertension]. / Aktywnosc N-acetylo-beta-D-glukozaminidazy (NAG) w moczu u kobiet w ciazy powiklanej nadcisnieniem tetniczym.

OBJECTIVES: Hypertensive disorders in pregnancy are one of the major mortality risk factors for mother and fetus. Although pathomechanisms of hypertension are extreme complex, the involvement of kidneys usually occurs. N-acetyl-beta-D-glucosaminidase (NAG) is a lysosomal enzyme which is located in renal tubular cells. Therefore an elevation of urinary NAG activity serves as a marker of tubular cell damage. AIM: Evaluation of renal tubular damage in pregnant women with different types of hypertension by determination of urinary NAG activity. MATERIAL AND METHODS: The study comprised 84 pregnant women in third trimester, divided according to type of hypertension into 3 subgroups: pregnancy induced hypertension (n = 58), preeclampsia (n = 13) and chronic hypertension (n = 13). The control group comprised 36 healthy pregnant women. Urinary NAG activity was measured in the second morning urine samples by colorimetric method and the results were expressed as NAG/creatinine ratios (NAG/Cr). RESULTS: The highest NAG/Cr ratios were found in women with preeclampsia (median-1.520 U/mmol) and in women with pregnancy induced hypertension (median-0.874 U/mmol) and both results differed significantly from those in controls (median-0.782 U/mmol). There was slight positive correlation between NAG/Cr ratios and systolic blood pressure (r = 0.225, p < 0.05). CONCLUSIONS: Hypertension in pregnancy may lead to renal tubular damage, however clinical significance of this phenomenon requires further studies.

Placental 11beta-hydroxysteroid dehydrogenase in Dahl and spontaneously hypertensive rats.

Studies in normotensive rats showed that excessive fetal exposure to maternal glucocorticoids retards growth and programs hypertension in later life. This excessive exposure is proposed to occur due to a reduction of the placental barrier to maternal glucocorticoids that is provided by 11beta-hydroxysteroid dehydrogenase (11betaHSD). To assess the possible alterations of glucocorticoid placental barrier in two genetic models of hypertension - spontaneously hypertensive (SHR) and Dahl salt-sensitive rats (DS) and their normotensive counterparts Wistar-Kyoto (WKY) and Dahl salt-resistant rats (DR)-we performed real-time reverse transcriptase-polymerase chain reaction analysis and bioactivity measurements of placental 11betaHSD in the last third of gestation. Whereas 11betaHSD2 mRNA expression was not different among the investigated strains, 11betaHSD1 mRNA abundance was 2.4 times higher in WKY than in SHR and 9.6 times higher in DS than in DR placentae. The 11betaHSD2 activity studies performed in placental homogenates revealed activity that did not differ among the strains. Concomitant with 11betaHSD1 mRNA expression 11-oxoreductase activity was clearly evident in all strains and was higher in WKY and DS rats than in SHR and DR, respectively. Nevertheless, the net 11betaHSD activity of tissue fragments (11beta-dehydrogenase minus 11-oxoreductase) was tended toward dehydrogenase action, ie, toward corticosterone inactivation and was significantly lower in DS than in DR rats. The 11beta-dehydrogenase/11-oxoreductase ratio was less than 2:1 in SHR and WKY rats, whereas this ratio was 9:1 in DR and 4.5:1 in DS rats. These data suggest that the placental glucocorticoid barrier is not decreased in SHR rats in comparison with normotensive WKY but is lower in DS than in DR counterparts. It cannot be excluded, therefore, that the placental glucocorticoid barrier in Dahl rats influences the pathways that might lead to the sensitivity of blood pressure to high salt intake in later life.

Association between a variant of the glutathione S-transferase P1 gene (GSTP1) and hypertension in pregnancy in Japanese: interaction with parity, age, and genetic factors.

Hypertension in pregnancy (HP), including preeclampsia (PE), is known to be a multifactorial disease. Recently, an Ile105Val variant of the glutathione S-transferase P1 gene ( GSTP1) was shown to be associated with PE in The Netherlands. We therefore performed an association study of the Ile105Val variant comparing 131 patients with HP and 327 normal pregnant controls in Japan. We analyzed the data in the context of other risk factors before pregnancy. The frequency of the Ile/Val+Val/Val genotype of the GSTP1 was not significantly different between the HP (26%) patients and the controls (28%). However, in primiparous patients, the frequency was significantly different in elderly pregnancy (63% in severe HP vs. 18% in controls; P < 0.05), in the subgroup with the MM+MT genotypes of the angiotensinogen gene (50% in severe HP vs. 26% in controls; P < 0.05), and in the subgroup with the GA+AA genotypes of the endothelial nitric oxide synthase gene (42% in severe HP vs. 13% in controls; P < 0.05). These results suggest that this variant of the GSTP1 may play a role in the manifestation of HP together with other independently and/or synergistically acting factors, particularly in primiparous pregnancy.

[Expression of nicotinamide edenine dinucleotide dehydrogenase gene in placenta of patients with pregnancy induced hypertension].

OBJECTIVE: To investigate the expression of nicotinamide edenine dinucleotide (NADH) dehydrogenase gene in the placenta of patients with pregnancy induced hypertension (PIH) and the role of NADH dehydrogenase in PIH pathogenesis. METHODS: Using (32)P dATP labeled human NADH dehydrogenase cDNA probe, the expression of NADH dehydrogenase gene in placental tissues of 10 normal late pregnant (NLP) women and 10 PIH patients was detected by dot blot. Mean A of each hybridization dot was measured by image analysis system to compare NADH dehydrogenase mRNA level in PIH placentae with that in NLP placenta. RESULTS: The NADH dehydrogenase gene values in patients with PIH and NLP were 21 +/- 6 and 56 +/- 16. The level of NADH dehydrogenase mRNA in PIH placenta was significantly higher than that in normal placenta (P < 0.05). CONCLUSION: Elevated expression of NADH dehydrogenase gene may play a role in PIH pathogenesis.

Xanthine oxidase activation in mild gestational hypertension.

OBJECTIVE: We hypothesized that activation of the xanthine oxidase (XO) enzyme system is a potential source of free radicals in pregnancy-induced hypertension (PIH). METHODS: A prospective observational study was carried out on 16 pregnant women who met the criteria of gestational hypertension [rise in blood pressure (BP) of 30 mm Hg systolic or 15 mm Hg diastolic after 20 weeks gestation or BP>140/90 mm Hg if earlier pressure is unknown] without proteinuria or any signs of renal impairment. Fourteen women with a clinically normal pregnancy matched for maternal age, parity, and gestational age acted as pregnant controls. Nonpregnant control women were members of the laboratory staff ( n=15). MAIN OUTCOME MEASURES: Concentrations of free sulfhydryl (SH) groups, purine catabolites, lipid peroxidation products in plasma, and blood carboxyhemoglobin levels were used to follow oxidative stress and potential hemolysis. A noninvasive measurement of functional XO activity was carried out (i.e., the urinary ratio of the two metabolites of caffeine was estimated). RESULTS: A pronounced oxidative stress was demonstrated in plasma samples of patients with hypertension by the elevated concentrations of uric acid and lipid peroxidation products. A reduced level of free sulfhydryl groups and an increased concentration of hypoxanthine (HX) were shown in normotensive pregnant individuals. The XO activity index was substantially higher in overweight pregnant subjects with mild hypertension [0.849+/-0.096 ( p<0.01)] than in normotensive pregnant women or in age-matched nonpregnant subjects [0.596+/-0.105, 0.542+/-0.049 (means+/-SD), respectively]. CONCLUSIONS: Our study of mildly hypertensive pregnant subjects provides additional evidence of the putative role of XO activation as a source of free radicals in the early stage of endothelial dysfunction.

Tumor necrosis factor-alpha-induced hypertension in pregnant rats results in decreased renal neuronal nitric oxide synthase expression.

BACKGROUND: Preeclampsia is associated with increases in plasma levels of tumor necrosis factor-alpha (TNF-alpha), a cytokine known to contribute to endothelial dysfunction. We recently reported that a twofold elevation in plasma TNF-alpha produces significant reductions in renal function and hypertension in pregnant rats. The purpose of this study was to determine the role of the nitric oxide (NO) system in TNF-alpha-induced hypertension in pregnant rats. METHODS: Tumor necrosis factor-alpha (50 ng/day) was chronically infused starting at day 14 of gestation. Mean arterial pressure, 24-h urinary nitrite/nitrate excretion, and renal nitric oxide synthase (NOS) protein expression by Western blot analysis was measured at day 19 of gestation. RESULTS: A twofold increase in plasma TNF-alpha levels in pregnant rats resulted in a significant increase in arterial pressure (97 +/- 3.6 v 116 +/- 2.1 mm Hg, pregnant versus TNF-alpha pregnant, respectively, P < .05), but no significant change in urinary nitrite/nitrate excretion (22.0 +/- 1.9 v 20.8 +/- 2.5 micromol/24 h, pregnant versus TNF-alpha pregnant, respectively), a measure of whole body NO production. As abnormalities in renal production of NO would not be reflected in the measure of whole body NO production, changes in renal NOS protein levels were determined. The protein expression of both neuronal (nNOS) and inducible (iNOS) nitric oxide synthase were significantly decreased in the medulla of TNF-alpha pregnant rats (nNOS: 10.6 +/- 0.7 v 8.2 +/- 0.8 densitometric units, P < .05; and iNOS: 19.2 +/- 0.9 v 15.4 +/- 0.8 densitometric units, P < .05, pregnant versus TNF-alpha pregnant, respectively). CONCLUSION: The hypertension associated with a chronic twofold increase in TNF-alpha in pregnant rats is associated with significant decreases in renal nNOS and iNOS protein production.

11 beta-hydroxysteroid dehydrogenase (11 beta-HSD-II) activity in human placenta: its relationship to placental weight and birth weight and its possible role in hypertension.

It has been assumed that low birth weight and high placenta weight were key factors for predicting hypertension in human adulthood. A deficiency in placental 11 beta-HSD-II enzyme activity was supposed to be the underlying cause. To possibly establish 11 beta-HSD-II as a leading factor, we determined 11 beta-HSD-II activities in 133 healthy pregnancies, 21 proteinuric pregnancies complicated by pregnancy-induced hypertension (PIH), 26 non proteinuric PIH pregnancies and 15 pregnancies complicated by fetal growth restriction (32nd-41st gestational week). We could not identify differences in 11 beta-HSD-II activity between pregnancies with the rare combination of small babies with big placentas and others (p = 0.59; Kruskal-Wallis test). And although there was no correlation between 11 beta-HSD-II activity and birth weight, in the control gestational age correlated with 11 beta-HSD-II activity (r = 0.22; p < 0.05; Spearman). 11 beta-HSD-II activity in the proteinuric PIH group was significantly higher than in the controls (11.7 pmol/min/mg prot.; range 10-13.2 vs. 7.9; range 7.0-9.1; p < 0.05). The lowest, but not significant, enzyme activities were in the IUGR group (5.8 pmol/min/mg prot.; range 4.0-9.2). In this group, analysis of variance detected a correlation between enzyme activity and placental weight. In conclusion, we could not confirm that placental 11 beta-HSD-II deficiencies act as an indicator for the risk of adult hypertension in small fetuses with large placentas. However, in growth restriction 11 beta-HSD-II activity might play a role. To clarify the influence in this group, further research is needed. Increased 11 beta-HSD-II activities with gestational age in the control may serve to sustain fetal adrenal steroid genesis and to prepare the fetus for autonomic life.

Effects of nitric oxide synthase inhibition on angiotensin receptors and metabolism in the pregnant hypertensive rat.

Endothelial dysfunction and a consequent decrease in nitric oxide production have been implicated in the pathogenesis of pre-eclampsia. A prominent feature of the pre-eclamptic syndrome is a loss of the pregnancy-induced refractoriness to infused pressor agents, such as angiotensin. In this study, we sought to determine whether a decrease in nitric oxide production might be linked via changes in angiotensin II receptors and angiotensin II metabolism to changes in pressor sensitivity to infused angiotensin II. Pregnant and non-pregnant spontaneously hypertensive rats (SHRs) were randomly allocated to receive 5 mg x kg(-1) x day(-1) N(G)-nitro-L-arginine methyl ester (L-NAME) in the drinking water or drinking water alone from days 7 to 14 of gestation. Steady-state metabolic clearance studies of angiotensin II were then performed, or tissues were harvested for angiotensin II receptor studies. Treatment with L-NAME caused an increase in systolic pressure (P<0.001) in both pregnant and non-pregnant rats, while urinary protein excretion increased only in the pregnant SHRs (P<0.001). Plasma angiotensin II levels were significantly increased in the L-NAME-treated SHRs compared with controls (non-pregnant, P<0.0005; pregnant, P<0.01). The metabolic clearance rate of angiotensin II was decreased by L-NAME treatment in non-pregnant SHRs (P<0.05), but was increased by L-NAME treatment in the pregnant rats (P<0.01). In the aorta, the angiotensin II receptor number increased after treatment with L-NAME in both non-pregnant (P<0.0005) and pregnant (P<0.05) SHRs, and the dissociation constant increased in the non-pregnant SHRs (P<0.005). Thus treatment of SHRs with L-NAME increased blood pressure, as well as the circulating angiotensin II concentration and vascular angiotensin II receptor expression. However, treatment with L-NAME did not affect pressor sensitivity to infused angiotensin II. We conclude, therefore, that although a decrease in nitric oxide production is associated with changes in angiotensin II concentrations and receptor numbers, it does not induce changes in pressor sensitivity to infused angiotensin II in the SHR.