Differential expression of renal nitric oxide synthase isoforms during pregnancy in rats

Enhanced [Ca2+]i in renal arterial smooth muscle cells of pregnant rats with reduced uterine perfusion pressure

Reduction of uterine perfusion pressure (RUPP) during late pregnancy has been suggested to trigger increases in renal vascular resistance and lead to hypertension of pregnancy. We investigated whether the increased renal vascular resistance associated with RUPP in late pregnancy reflects increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) and contraction of renal arterial smooth muscle. Single smooth muscle cells were isolated from renal interlobular arteries of normal pregnant Sprague-Dawley rats and a rat model of RUPP during late pregnancy. The cells were loaded with fura 2 and both cell length and [Ca(2+)](i) were measured. In cells of normal pregnant rats incubated in Hanks' solution (1 mM Ca(2+)), ANG II (10(-7) M) caused an initial increase in [Ca(2+)](i) to 414 +/- 13 nM, a maintained increase to 149 +/- 8 nM, and 21 +/- 1% cell contraction. In RUPP rats, the initial ANG II-induced [Ca(2+)](i) (431 +/- 18 nM) was not different from pregnant rats, but both the maintained [Ca(2+)](i) (225 +/- 9 nM) and cell contraction (48 +/- 2%) were increased. Membrane depolarization by 51 mM KCl and the Ca(2+) channel agonist BAY K 8644 (10(-6) M), which stimulate Ca(2+) entry from the extracellular space, caused maintained increases in [Ca(2+)](i) and cell contraction that were greater in RUPP rats than control pregnant rats. In Ca(2+)-free (2 mM EGTA) Hanks' solution, the ANG II- and caffeine (10 mM)-induced [Ca(2+)](i) transient and cell contraction were not different between normal pregnant and RUPP rats, suggesting no difference in Ca(2+) release from the intracellular stores. The enhanced maintained ANG II-, KCl- and BAY K 8644-induced [Ca(2+)](i) and cell contraction in RUPP rats compared with normal pregnant rats suggest enhanced Ca(2+) entry mechanisms of smooth muscle contraction in resistance renal arteries and may explain the increased renal vascular resistance associated with hypertension of pregnancy.

Pregnancy influence on the vascular interactions between nitric oxide and other endothelium-derived mediators in rat kidney

Peripheral vascular resistance and sensitivity to circulating pressor and vasoconstrictor agents are blunted during pregnancy. This has been mainly attributed to an increased production of endothelium-derived mediators. The objective of this work was to evaluate if pregnancy changes the relative participation of nitric oxide (NO) and prostaglandins (PG) in respect to the modulation of the increases in renal perfusion pressure induced by phenylephrine (Phe). Dose-response curves were made with gradually increasing doses of Phe using an isolated kidney preparation in the presence of a NO synthase (NOS) inhibitor (L-NAME, 1 microM), a PG-synthesis inhibitor (indomethacin, 1 microM), both, or neither. Also, renal cyclooxygenase (COX-1 and COX-2) and endothelial NOS (eNOS) expression was determined using PCR. The experiments were done in kidneys from nonpregnant and pregnant rats. Our results showed that the relative participation of renal vasoactive mediators seems to change during pregnancy. We found the presence of a COX-1-dependent vasoconstrictor in the middle of pregnancy that was not found in nonpregnant rats. Our results also suggest that there is increased participation of another renal vasodilator substance, the effect of which is observed when NO or PG synthesis is inhibited during late pregnancy. In addition, an apparent interaction between renal eNOS and COX-1 expression was observed: eNOS expression was diminished, while COX-1 was increased during the 2nd week of pregnancy. In contrast, in kidneys from the 3rd week of pregnancy, the expression of these two enzymes was similar.

Impact of pregnancy on underlying renal disease

Normal pregnancy involves marked renal vasodilation and large increases in glomerular filtration rate (GFR). Studies in rats reveal that the gestational renal vasodilation is achieved by parallel reductions in tone in afferent and efferent arterioles so GFR rises without a change in glomerular blood pressure. There is some evidence from animal studies that increased renal generation of nitric oxide (NO) may be involved. Although chronic renal vasodilation has been implicated in causing progression of renal disease in nonpregnant states by glomerular hypertension, there are no long-term deleterious effects of pregnancies on the kidney when maternal renal function is normal because glomerular blood pressure remains normal. When maternal renal function is compromised before conception, there are no long-term adverse effects on renal function in most types of renal disease, providing that the GFR is well maintained before conception. When serum creatinine exceeds approximately 1.4 mg/dL, pregnancy may accelerate the renal disease increases and when serum creatinine >2 mg/dL, the chances are greater than 1 in 3 that pregnancy will hasten the progression of the renal disease. The available animal studies suggest that glomerular hypertension does not occur despite diverse injuries. Thus, the mechanisms of the adverse interaction between pregnancy and underlying renal disease remain unknown.

Preeclampsia. Part 2: experimental and genetic considerations

Preeclampsia-eclampsia is still one of the leading causes of maternal and fetal morbidity and mortality. Despite active research for many years, the etiology of this disorder exclusive to human pregnancy is an enigma. Recent evidence suggests there may be several underlying causes or predispositions leading to the signs of hypertension, proteinuria, and edema, findings that allow us to make the diagnosis of the "syndrome" of preeclampsia. Despite improved prenatal care, severe preeclampsia and eclampsia still occur. Although understanding of the pathophysiology of these disorders has improved, treatment has not changed significantly in over 50 years. Although postponement of delivery in selected women with severe preeclampsia improves fetal outcome to a degree, this is not done without risk to the mother. In the United States, magnesium sulfate and hydralazine are the most commonly used medications for seizure prophylaxis and hypertension in the intrapartum period. The search for the underlying cause of this disorder and for a clinical marker to predict those women who will develop preeclampsia-eclampsia is ongoing, with its prevention the ultimate goal. This review began with the clinical and pathophysiologic aspects of preeclampsia-eclampsia (Part 1). Now, in Part 2, the experimental observations, the search for predictive factors, and the genetics of this disorder are reviewed.

Role of cardiac eNOS expression during pregnancy in the coupling of myocardial oxygen consumption to cardiac work

We assessed whether pregnancy results in enhanced nitric oxide (NO)-mediated control of myocardial oxygen consumption. Rats were studied before (C), at 1 wk (1w) or 2 wk (2w) of pregnancy, and at 4 days after giving birth (-4d). Left ventricular endothelial NO synthase (eNOS) protein expression was determined by immunoblotting. Oxygen consumption of left ventricular tissue samples was measured in vitro in response to increasing doses of bradykinin with or without addition of the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Echocardiography indicated an increased cardiac output during pregnancy. Myocardial eNOS protein expression significantly increased by 46 +/- 9 and 39 +/- 8% at 1w and 2w, respectively, and returned to control levels at -4d. Bradykinin (10(-4) M) decreased cardiac oxygen consumption in a NO-dependent manner by 17 +/- 2% at C, by 21 +/- 2% at 1w, by 24 +/- 2% at 2w (P < 0.05 vs. C and -4d), and by 18 +/- 1% at -4d. Myocardial eNOS protein expression is transiently increased during pregnancy in rats, and this increase is associated with enhanced NO-dependent control of myocardial oxygen consumption at a time when cardiac output is increased.

Vascular mechanisms of increased arterial pressure in preeclampsia: lessons from animal models

Normal pregnancy is associated with reductions in total vascular resistance and arterial pressure possibly due to enhanced endothelium-dependent vascular relaxation and decreased vascular reactivity to vasoconstrictor agonists. These beneficial hemodynamic and vascular changes do not occur in women who develop preeclampsia; instead, severe increases in vascular resistance and arterial pressure are observed. Although preeclampsia represents a major cause of maternal and fetal morbidity and mortality, the vascular and cellular mechanisms underlying this disorder have not been clearly identified. Studies in hypertensive pregnant women and experimental animal models suggested that reduction in uteroplacental perfusion pressure and the ensuing placental ischemia/hypoxia during late pregnancy may trigger the release of placental factors that initiate a cascade of cellular and molecular events leading to endothelial and vascular smooth muscle cell dysfunction and thereby increased vascular resistance and arterial pressure. The reduction in uterine perfusion pressure and the ensuing placental ischemia are possibly caused by inadequate cytotrophoblast invasion of the uterine spiral arteries. Placental ischemia may promote the release of a variety of biologically active factors, including cytokines such as tumor necrosis factor-alpha and reactive oxygen species. Threshold increases in the plasma levels of placental factors may lead to endothelial cell dysfunction, alterations in the release of vasodilator substances such as nitric oxide (NO), prostacyclin (PGI(2)), and endothelium-derived hyperpolarizing factor, and thereby reductions of the NO-cGMP, PGI(2)-cAMP, and hyperpolarizing factor vascular relaxation pathways. The placental factors may also increase the release of or the vascular reactivity to endothelium-derived contracting factors such as endothelin, thromboxane, and ANG II. These contracting factors could increase intracellular Ca(2+) concentrations ([Ca(2+)](i)) and stimulate Ca(2+)-dependent contraction pathways in vascular smooth muscle. The contracting factors could also increase the activity of vascular protein kinases such as protein kinase C, leading to increased myofilament force sensitivity to [Ca(2+)](i) and enhancement of smooth muscle contraction. The decreased endothelium-dependent mechanisms of vascular relaxation and the enhanced mechanisms of vascular smooth muscle contraction represent plausible causes of the increased vascular resistance and arterial pressure associated with preeclampsia.

TNF-alpha enhances contraction and inhibits endothelial NO-cGMP relaxation in systemic vessels of pregnant rats

Tumor necrosis factor-alpha (TNF-alpha) is elevated in the plasma of preeclamptic women and may have a role in pregnancy-induced hypertension. However, whether the hemodynamic effects of TNF-alpha reflect the direct effects on vascular reactivity is unclear. We tested the hypothesis that TNF-alpha impairs endothelium-dependent relaxation and enhances vascular contraction in systemic vessels of pregnant rats. We measured isometric contraction in aortic strips isolated from virgin and pregnant Sprague-Dawley rats (nontreated vs. treated for 2 h with 10-1,000 pg/ml TNF-alpha). In endothelium-intact vascular strips, TNF-alpha caused greater enhancement of phenylephrine (Phe) contraction in pregnant than virgin rats. TNF-alpha caused significant inhibition of ACh- and bradykinin-induced vascular relaxation and nitrite/nitrate production that were more prominent in pregnant than virgin rats. N(G)-nitro-L-arginine methyl ester [L-NAME, 100 microM, an inhibitor of nitric oxide (NO) synthase] or 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (ODQ, 1 microM, an inhibitor of cGMP production in smooth muscle) inhibited ACh relaxation and enhanced Phe contraction in nontreated but to a lesser extent in TNF-alpha-treated vessels, particularly those of pregnant rats. Endothelium removal enhanced Phe contraction in nontreated but not TNF-alpha-treated vessels, especially those of pregnant rats. Relaxation of Phe contraction with the NO donor sodium nitroprusside was not different between nontreated and TNF-alpha-treated vessels. Thus TNF-alpha enhances vascular contraction and inhibits endothelium-dependent NO-cGMP-mediated vascular relaxation in systemic vessels, particularly those of pregnant rats. The results support a direct role for TNF-alpha as a possible mediator of increased vascular resistance associated with pregnancy-induced hypertension.

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.

Renal 20-hydroxyeicosatetraenoic acid synthesis during pregnancy

We examined whether renal 20-hydroxyeicosatetraenoic acid (20-HETE) synthesis is altered during gestation. Renal microsomal arachidonic acid omega-hydroxylase activity increased by 50 and 48% in rats on days 12 and 19 of gestation, respectively. Renal microvessel 20-HETE synthesis increased by 50 and 82% in rats on days 6 and 12 of gestation, respectively, and returned to control levels at day 19 of gestation. In contrast, 20-HETE synthesis in isolated medullary thick ascending limb was unchanged from control levels on days 6 and 12 of gestation, but it increased twofold on day 19 of gestation. This increase on day 19 of gestation was associated with a twofold increase in urinary 20-HETE excretion, and it coincided with a 23-mmHg fall in blood pressure. Moreover, change in the rate of 20-HETE synthesis in microvessels was consistent with the level of expression of cytochrome P450 (CYP)4A proteins. Administration of the CYP4A inhibitor 1-aminobenzotriazole (ABT) for 2 days on day 12 of pregnancy or for 5 days starting on day 15 of pregnancy caused a transient but significant reduction in systolic blood pressure. ABT treatment also decreased urinary sodium, urinary 20-HETE, and renal and microvessel 20-HETE synthesis. This study, to our knowledge, is the first to demonstrate that 20-HETE synthesis in the kidney is altered in time- and site-specific manners during pregnancy. The localized pattern of changes suggests that there are distinct regulatory mechanisms for 20-HETE synthesis in the kidney during pregnancy.

Nitric oxide synthase upregulation and the predelivery blood pressure decrease in spontaneously hypertensive rats

OBJECTIVE

The pregnant spontaneously hypertensive rat (SHR) exhibits a decrease in arterial blood pressure shortly before delivery; however, the mechanisms are unknown. Nitric oxide may be involved.

DESIGN

Blood pressure in stroke-prone SHR (SHRSP) and Wistar-Kyoto control rats (WKY) was telemetrically measured. Four groups were studied: pregnant and non-pregnant WKY and SHRSP rats, respectively. Mean blood pressure in pregnant SHRSP rats decreased from 148 +/- 2 mmHg at conception to 120 +/- 4 mmHg at day 15, compared to 112 +/- 1 mmHg in pregnant WKY rats. At delivery, we determined the vasodilatory responses of isolated preconstricted aortic strips.

RESULTS

Vasodilatory responses from late-term SHRSP rats were significantly greater following acetylcholine than either those from non-pregnant SHRSP or pregnant and non-pregnant WKY rats (acetylcholine IC50: 5, 22.8, 398, 1000 nmol/l, respectively), while contractile responses to increasing doses of norepinephrine were not different. Similar results were obtained with substance P. Indomethacin had no effect on the relaxation responses. Relaxation in response to sodium nitroprusside was not different in the groups. Western blot analysis showed that endothelial nitric oxide synthase (eNOS) levels were significantly increased in the pregnant SHRSP vessels compared to non-pregnant SHRSP, pregnant WKY, and non-pregnant WKY vessels.

CONCLUSION

Increased NOS may explain the blood pressure decrease during late pregnancy in genetically hypertensive rats.

Reduced endothelial NO-cGMP vascular relaxation pathway during TNF-alpha-induced hypertension in pregnant rats

Placental ischemia during pregnancy is thought to release cytokines such as tumor necrosis factor-alpha (TNF-alpha), which may contribute to the increased vascular resistance associated with pregnancy-induced hypertension. We have reported that a chronic twofold elevation in plasma TNF-alpha increases blood pressure in pregnant but not in virgin rats; however, the vascular mechanisms are unclear. We tested the hypothesis that increasing plasma TNF-alpha during pregnancy impairs endothelium-dependent vascular relaxation and enhances vascular reactivity. Active stress was measured in aortic strips of virgin and late-pregnant Sprague-Dawley rats untreated or infused with TNF-alpha (200 ng x kg(-1) x day(-1) for 5 days) to increase plasma level twofold. Phenylephrine (Phe) increased active stress to a maximum of 4.2 +/- 0.4 x 10(3) and 9.9 +/- 0.7 x 10(3) N/m2 in control pregnant and TNF-alpha-infused pregnant rats, respectively. Removal of the endothelium enhanced Phe-induced stress in control but not in TNF-alpha-infused pregnant rats. In endothelium-intact strips, ACh caused greater relaxation of Phe contraction in control than in TNF-alpha-infused pregnant rats. Basal and ACh-induced nitrite/nitrate production was less in TNF-alpha-infused than in control pregnant rats. Pretreatment of vascular strips with 100 microM N(G)-nitro-L-arginine methyl ester, to inhibit nitric oxide (NO) synthase, or 1 microM 1H-[1,2,4]oxadiazolo[4,3-]quinoxalin-1-one, to inhibit cGMP production in smooth muscle, inhibited ACh-induced relaxation and enhanced Phe-induced stress in control but not in TNF-alpha-infused pregnant rats. Phe contraction and ACh relaxation were not significantly different between control and TNF-alpha-infused virgin rats. Thus an endothelium-dependent NO-cGMP-mediated vascular relaxation pathway is inhibited in late-pregnant rats infused with TNF-alpha. The results support a role for TNF-alpha as one possible mediator of the increased vascular resistance associated with pregnancy-induced hypertension.

Preeclampsia: linking placental ischemia with cardiovascular-renal dysfunction

Placental ischemia during preeclampsia is thought to lead to widespread activation/dysfunction of the maternal vascular endothelium. This results in enhanced formation of endothelin and thromboxane and decreased formation of nitric oxide and prostacyclin. These endothelial abnormalities, in turn, cause hypertension by impairing renal pressure natriuresis and increasing total peripheral resistance.

Nitric oxide synthase gene knockout mice do not become hypertensive during pregnancy

OBJECTIVE

The purpose of this study was to test whether omitting the vasodilator nitric oxide that is derived from any 1 of the 3 isoforms of nitric oxide synthase results in hypertension during pregnancy.

STUDY DESIGN

We measured systolic blood pressure before, during, and after pregnancy using an automated tail cuff method in 3 mutant (gene knockout) mouse strains in which the gene for neuronal nitric oxide, inducible nitric oxide, or endothelial nitric oxide was disrupted by gene targeting.

RESULTS

In neuronal nitric oxide gene knockout mice (n = 10), blood pressure was 100 +/- 3 mm Hg, not significantly different from 101 +/- 3 mm Hg in matched wild-type control mice (n = 10). Pregnancy did not change blood pressure or heart rate in either group. In inducible nitric oxide gene knockout mice (n = 9), blood pressure was 110 +/- 3 mm Hg, the same as in the wild-type control mice (110 +/- 2 mm Hg; n = 14). Blood pressure was unaffected by pregnancy in either group of mice. However, heart rate was significantly less in knockout mice (647 +/- 11 beats/min vs 666 +/- 9 beats/min; P <.005); this difference persisted through pregnancy. In endothelial nitric oxide gene knockout mice (n = 8), blood pressure was higher before pregnancy (114 +/- 4 mm Hg vs 103 +/- 4 mm Hg; P <.05) than in wild-type control mice (n = 9), but this difference disappeared during pregnancy, returning only after delivery. Heart rates were not different before pregnancy and were unaffected by pregnancy.

CONCLUSION

There was no apparent increase in systolic blood pressure in any of the 3 nitric oxide synthase gene knockout strains during pregnancy compared to the wild-type control mice. This suggests that, at least in the mouse, genetic deficiency of any 1 isoform of nitric oxide synthase does not result in pregnancy-induced hypertension.

Role of neuronal nitric oxide synthase in mediating renal hemodynamic changes during pregnancy

Renal plasma flow (RPF) and glomerular filtration rate (GFR) are markedly increased during pregnancy. We recently reported that the renal hemodynamic changes observed during pregnancy in rats are associated with enhanced renal protein expression of neuronal nitric oxide synthase (nNOS). The purpose of this study was to determine the role of nNOS in mediating renal hemodynamic changes observed during pregnancy. To achieve this goal, we examined the effects of the nNOS inhibitor 7-nitroindazole (7-NI) on kidney function in normal conscious, chronically instrumented virgin (n = 6) and pregnant rats (n = 9) at day 16 of gestation. Infusion of 7-NI had no effect on RPF (4.7 +/- 0.7 vs. 4.8 +/- 0.9 ml/min), GFR (2.2 +/- 0.2 vs. 2.5 +/- 0.4 ml/min), or mean arterial pressure (MAP; 127 +/- 7 vs. 129 +/- 10 mmHg) in virgin rats. In contrast, 7-NI infused into pregnant rats decreased RPF (8.9 +/- 1.6 vs. 6.5 +/- 1.4 ml/min) and GFR (4.4 +/- 0.7 vs. 3.3 +/- 0.7 ml/min) while having no effect on MAP (123 +/- 4 vs. 123 +/- 3 mmHg). In summary, inhibition of nNOS in pregnant rats at midgestation results in significant decreases in RPF and GFR. nNOS inhibition in virgin rats had no effect on renal hemodynamics. These data suggest that nNOS may play a role in mediating the renal hemodynamic changes that occur during pregnancy.

Chronic NOS inhibition reverses systemic vasodilation and glomerular hyperfiltration in pregnancy

The chronic role of nitric oxide (NO), independent of prostaglandin synthesis, in the primary peripheral vasodilation, increased glomerular filtration rate (GFR), and renal plasma flow (RPF) in normal pregnancy remains to be defined. The purpose of the present study was to chronically inhibit NOS to return systemic vascular resistance (SVR), cardiac output (CO), GFR, and RPF to nonpregnant values. Pregnant rats received the nitric oxide synthase (NOS) inhibitor, nitro-L-arginine methyl ester (L-NAME), orally from gestational days 7 through 14. Results were compared with nonpregnant and untreated pregnant rats. At 14 days gestation, CO significantly increased in pregnant vs. nonpregnant rats (187 +/- 17 vs. 125 +/- 10 ml/min, P < 0.05) as SVR decreased (0.64 +/- 0.08 vs. 1.08 +/- 0.08 mmHg. ml(-1). min, P < 0.05) and mean arterial pressure was unchanged (117 +/- 5 vs. 125 +/- 2 mmHg, not significant). Pregnant rats also demonstrated increased GFR (3,015 +/- 33 vs. 2,165 +/- 136 microl/min, P < 0.01) and RPF (7,869 +/- 967 vs. 5,507 +/- 290 microl/min, P < 0.05) vs. nonpregnant rats. L-NAME-treated pregnant rats had values for CO (118 +/- 7 ml/min), SVR (1.09 +/- 0.07 mmHg. ml(-1). min), GFR (2,264 +/- 150 microl/min), and RPF (5,777 +/- 498 microl/min), which were no different than nonpregnant animals. In summary, similar to human pregnancy, primary peripheral vasodilation occurs early in rat pregnancy. Furthermore, the hyperdynamic circulation and glomerular hyperfiltration of normal rat midterm pregnancy can be chronically reversed by NOS inhibition. These findings suggest a role for endothelial damage and decreased NO in the pathogenesis of preeclampsia.

[Ca(2+)](i) signaling in renal arterial smooth muscle cells of pregnant rat is enhanced during inhibition of NOS

Vascular resistance and arterial pressure are reduced during normal pregnancy, but dangerously elevated during pregnancy-induced hypertension (PIH), and changes in nitric oxide (NO) synthesis have been hypothesized as one potential cause. In support of this hypothesis, chronic inhibition of NO synthesis in pregnant rats has been shown to cause significant increases in renal vascular resistance and hypertension; however, the cellular mechanisms involved are unclear. We tested the hypothesis that the pregnancy-associated changes in renal vascular resistance reflect changes in contractility and intracellular Ca(2+) concentration ([Ca(2+)](i)) of renal arterial smooth muscle. Smooth muscle cells were isolated from renal interlobular arteries of virgin and pregnant Sprague-Dawley rats untreated or treated with the NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME; 4 mg. kg(-1). day(-1) for 5 days), then loaded with fura 2. In cells of virgin rats incubated in Hanks' solution (1 mM Ca(2+)), the basal [Ca(2+)](i) was 86 +/- 6 nM. Phenylephrine (Phe, 10(-5) M) caused a transient increase in [Ca(2+)](i) to 417 +/- 11 nM and maintained an increase to 183 +/- 8 nM and 32 +/- 3% cell contraction. Membrane depolarization by 51 mM KCl, which stimulates Ca(2+) entry from the extracellular space, caused maintained increase in [Ca(2+)](i) to 292 +/- 12 nM and 31 +/- 2% contraction. The maintained Phe- and KCl-induced [Ca(2+)](i) and contractions were reduced in pregnant rats but significantly enhanced in pregnant rats treated with L-NAME. Phe- and KCl-induced contraction and [Ca(2+)](i) were not significantly different between untreated and L-NAME-treated virgin rats or between untreated and L-NAME + L-arginine treated pregnant rats. In Ca(2+)-free Hanks', application of Phe or caffeine (10 mM), to stimulate Ca(2+) release from the intracellular stores, caused a transient increase in [Ca(2+)](i) and a small cell contraction that were not significantly different among the different groups. Thus renal interlobular smooth muscle of normal pregnant rats exhibits reduction in [Ca(2+)](i) signaling that involves Ca(2+) entry from the extracellular space but not Ca(2+) release from the intracellular stores. The reduced renal smooth muscle cell contraction and [Ca(2+)](i) in pregnant rats may explain the decreased renal vascular resistance associated with normal pregnancy, whereas the enhanced cell contraction and [Ca(2+)](i) during inhibition of NO synthesis in pregnant rats may, in part, explain the increased renal vascular resistance associated with PIH.

Nitric oxide dysfunction in the pathophysiology of preeclampsia

Researchers disagree as to the importance of nitric oxide (NO) in preeclampsia. Many researchers have alluded to NO's possible primary or secondary role in the development of preeclampsia, but few have correlated the dysfunction of nitric oxide production with the other metabolic derangements seen in this condition. This paper will review the evidence that the primary dysfunction in preeclampsia is a relative deficiency of available NO (secondary to oxidative degradation) and an excess of peroxynitrite (ONOO(-)). The combination of a deficiency of NO and an increase in ONOO(-) can directly or indirectly initiate the vast majority of physiological and serological changes associated with preeclampsia, such as blood pressure, increased glomerular filtration rate, proteinuria, platelet dysfunction, increased thromboxane and endothelin, and a decrease in prostacyclin. Understanding the complex role of nitric oxide in this condition may explain why previous interventions have been unsuccessful and suggest possible strategies for prevention and treatment in the future.

Intrauterine endotoxin infusion in rat pregnancy induces preterm delivery and increases placental prostaglandin F2alpha metabolite levels

OBJECTIVE

This study was designed to examine the effects of intrauterine endotoxin (lipopolysaccharide) on rat pregnancy.

STUDY DESIGN

Pregnant Sprague-Dawley rats (N = 26) were implanted with uterine catheters on day 15 or 16 of a 22-day gestation. Animals were randomly assigned to receive either lipopolysaccharide (25 or 50 microg) or sodium chloride solution (1 mL) on day 17 and then were either sacrificed on day 19 or observed until delivery. Placentas were harvested at the time of death, homogenates were prepared, and prostaglandin F(2)(alpha) metabolite levels were determined by means of radioimmunoassay. Data were analyzed by analysis of variance, Student-Newman-Keuls, and Mann-Whitney tests.

RESULTS

Lipopolysaccharide-treated groups (25 and 50 microg) displayed a shorter interval to delivery (mean +/- SE, 82 +/- 13 and 63 +/- 8 hours, respectively) than control animals (117 +/- 3 hours). Pups of lipopolysaccharide-treated (25 and 50 microg) female animals had lower live birth weights (4.92 +/- 0.01 and 5.12 +/- 0. 24 g, respectively) compared with control animals (6.04 +/- 0.07 g). Placental homogenates from lipopolysaccharide-treated female animals contained higher levels of prostaglandin F(2)(alpha) metabolite (1567 +/- 64 and 1475 +/- 59 pg/mL) than those from sodium chloride solution-infused control animals (804 +/- 68 pg/mL).

CONCLUSION

Bacterial products induce the preterm delivery of low-birth-weight pups in rats, possibly by increasing local prostaglandin biosynthesis.

Pregnancy-associated reduction in vascular protein kinase C activity rebounds during inhibition of NO synthesis

Vascular reactivity has been shown to be reduced during pregnancy and to be enhanced during chronic inhibition of nitric oxide (NO) synthesis in pregnant rats; however, the cellular mechanisms involved are unclear. The purpose of this study was to investigate whether the pregnancy-induced changes in vascular reactivity are associated with changes in the amount and/or activity of vascular protein kinase C (PKC). Active stress as well as the amount and activity of PKC was measured in deendothelialized thoracic aortic strips from virgin and pregnant rats untreated or treated with the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). In virgin rats, the PKC activator phorbol 12,13-dibutyrate (PDBu, 10(-6) M) and the alpha-adrenergic agonist phenylephrine (Phe, 10(-5) M) caused significant increases in active stress and PKC activity that were inhibited by the PKC inhibitors staurosporine and calphostin C. Western blot analysis in aortic strips of virgin rats showed significant amount of the alpha-PKC isoform. Both PDBu and Phe caused significant translocation of alpha-PKC from the cytosolic to the particulate fraction. Compared with virgin rats, the PDBu- and Phe-stimulated active stress and PKC activity as well as the amount and the PDBu- and Phe-induced translocation of alpha-PKC were significantly reduced in late pregnant rats but significantly enhanced in pregnant rats treated with L-NAME. The PDBu- and Phe-induced changes in active stress and the amount, distribution, and activity of alpha-PKC in virgin rats treated with L-NAME were not significantly different from that in virgin rats, whereas the changes in pregnant rats treated with L-NAME + the NO synthase substrate L-arginine were not significantly different from that in pregnant rats. These results provide evidence that a PKC-mediated contractile pathway in vascular smooth muscle is reduced during pregnancy and significantly enhanced during chronic inhibition of NO synthesis. The results suggest that one possible mechanism of the pregnancy-associated changes in vascular reactivity may involve changes in the amount and activity of the alpha-PKC isoform.