The effects of hindlimb unweighting on the capacitance of rat small mesenteric veins.

Microgravity is associated with an impaired cardiac output response to orthostatic stress. Mesenteric veins are critical in modulating cardiac filling through venoconstriction. The purpose of this study was to determine the effects of simulated microgravity on the capacitance of rat mesenteric small veins. We constructed pressure-diameter relationships from vessels of 21-day hindlimb-unweighted (HLU) rats and control rats by changing the internal pressure and measuring the external diameter. Pressure-diameter relationships were obtained both before and after stimulation with norepinephrine (NE). The pressure-diameter curves of HLU vessels were shifted to larger diameters than control vessels. NE (10(-4) M) constricted veins from control animals such that the pressure-diameter relationship was significantly shifted downward (i.e., to smaller diameters at equal pressure). NE had no effect on vessels from HLU animals. These results indicate that, after HLU, unstressed vascular volume may be increased and can no longer decrease in response to sympathetic stimulation. This may partially underlie the mechanism leading to the exaggerated fall in cardiac output and stroke volume seen in astronauts during an orthostatic stress after exposure to microgravity.     

Differential expression and localization of nitric oxide synthases in cirrhotic livers of bile duct-ligated rats.

Increased vascular nitric oxide (NO) production has been implicated in the pathogenesis of the hyperdynamic circulation in liver cirrhosis. This study investigated the expression of three isoforms of NO synthase (NOS) in rat cirrhotic livers. Cirrhosis was induced by chronic bile duct ligation (BDL). NOS enzyme activity was assessed by L-citrulline generation. Competitive RT-PCR was performed to detect the mRNA levels of NOS. In situ hybridization was done to localize NOS mRNA. Protein expression of NOS was evaluated by Western blotting and immunohistochemistry. The L-citrulline assay showed that constitutive NOS (cNOS) enzymatic activity was decreased, while inducible NOS (iNOS) activity was increased in BDL livers. Both endothelial NOS (eNOS) and neuronal NOS (nNOS) mRNA were detected in BDL and sham rats, but with enhanced expression in BDL rats. eNOS protein was redistributed with less expression in sinusoidal endothelial cells, but the total levels in liver were not changed. nNOS was induced in hepatocytes of BDL rats, in contrast to only a weak signal observed around some blood vessels in sham livers. Intense mRNA and protein expression of iNOS was induced in livers of BDL rats and was localized in hepatocytes, with no or a negligible amount in control livers. In conclusion, iNOS was induced in cirrhotic liver with its activity increased. In contrast, cNOS activity was impaired, regardless of unchanged eNOS protein levels and enhanced nNOS expression. These results suggest that all three types of NOS have a role in cirrhosis, but their expression and regulation are different.     

Low mercury concentrations cause oxidative stress and endothelial dysfunction in conductance and resistance arteries

Increased cardiovascular risk after mercury exposure has been described, but the underlying mechanisms are not well explored. We analyzed the effects of chronic exposure to low mercury concentrations on endothelium-dependent responses in aorta and mesenteric resistance arteries (MRA). Wistar rats were treated with mercury chloride (1st dose 4.6 microg/kg, subsequent dose 0.07 microg.kg(-1).day(-1) im, 30 days) or vehicle. Blood levels at the end of treatment were 7.97 +/- 0.59 ng/ml. Mercury treatment: 1) did not affect systolic blood pressure; 2) increased phenylephrine-induced vasoconstriction; 3) reduced acetylcholine-induced vasodilatation; and 4) reduced in aorta and abolished in MRA the increased phenylephrine responses induced by either endothelium removal or the nitric oxide synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME, 100 microM). Superoxide dismutase (SOD, 150 U/ml) and the NADPH oxidase inhibitor apocynin (0.3 mM) decreased the phenylephrine-induced contraction in aorta more in mercury-treated rats than controls. In MRA, SOD did not affect phenylephrine responses; however, when coincubated with l-NAME, the l-NAME effect on phenylephrine response was restored in mercury-treated rats. Both apocynin and SOD restored the impaired acetylcholine-induced vasodilatation in vessels from treated rats. Endothelial NOS expression did not change in aorta but was increased in MRA from mercury-treated rats. Vascular O2(-) production, plasmatic malondialdehyde levels, and total antioxidant status increased with the mercury treatment. In conclusion, chronic exposure to low concentrations of mercury promotes endothelial dysfunction as a result of the decreased NO bioavailability induced by increases in oxidative stress. These findings offer further evidence that mercury, even at low concentrations, is an environmental risk factor for cardiovascular disease.     

Nitric Oxide Synthase Inhibition Promotes Carcinogen-Induced Preneoplastic Changes in the Colon of Rats

l-Arginine is metabolized either to polyamines through arginase and ornithine decarboxylase (ODC) activities or to citrulline and nitric oxide (NO, nitrogen monoxide) through the NO synthase (NOS) pathway. Polyamine levels and ODC activity are high in tumor cells. The aim of this study was to test whether N(G)-nitro-l-arginine methyl ester (l-NAME), an inhibitor of NOS, modulates colon carcinogenesis. Adult male Wistar rats were treated with azoxymethane (AOM, 15 mg/kg ip), a chemical carcinogen, once a week for 2 weeks. One week after the second injection the rats were randomly divided into two groups. One group (n = 8) received l-NAME (10 mg/kg body wt/day) in drinking water. The control group (n = 8) received tap water. After 5 weeks, the rats receiving l-NAME showed enhanced mean basal arterial blood pressure, decreased heart rate, and a significant decrease of the cGMP content in the colonic mucosa. In both groups, AOM induced the formation of colonic aberrant crypt foci (ACF). In l-NAME-treated rats, the number of ACF was higher than in controls by 47%. ODC activity was enhanced by 11-fold. S-Adenosyl-methionine-decarboxylase activity and putrescine concentration were significantly increased in the colonic mucosa of l-NAME-treated rats. The data suggest that l-NAME promotes carcinogen-induced preneoplastic changes in the colon by inhibiting NOS activity and by stimulating polyamine biosynthesis.     

Splenic hemodynamics and decreased endothelial nitric oxide synthase in the spleen of rats with liver cirrhosis

The enlarged spleen in liver cirrhosis is considered to play a role in the pathogenesis of portal hypertension, but the splenic hemodynamics and molecular mechanisms behind the phenomenon have not been elucidated. The present study aimed to examine the splenic hemodynamics associated with splenic microcirculation and congestion, and to determine the status of the endothelial nitric oxide synthase (eNOS) signaling pathway in the spleen of rats with liver cirrhosis. Liver cirrhosis was induced by bile duct ligation. In rats with bile duct ligation (BDL rats) and control rats, splenic blood flow was measured using a laser Doppler flowmeter, and splenic blood volume was measured using a near-infrared spectrophotometer. The expressions of eNOS and its upstream effectors, Akt, TNF-alpha and VEGF, in the spleen were also determined. Specific splenic blood flow was significantly decreased in BDL rats compared with control rats. Specific splenic blood volume was also decreased in BDL rats, while their total splenic blood volume, especially the deoxygenated volume, was significantly increased. The expressions of phosphorylated and total eNOS, and the eNOS phosphorylation ratio, were all significantly decreased in the spleen of BDL rats. The Akt phosphorylation ratio and TNF-alpha concentration were also decreased in the spleen of BDL rats although the expression of VEGF was increased. These findings suggest that the eNOS signaling pathway is suppressed in the spleen of cirrhotic rats, and may contribute to the measured decreases in specific blood flow and volume in the spleen of liver cirrhosis. Determination of the factors influencing the suppression of eNOS in the spleen may shed light on how liver cirrhosis results in hypodynamic intrasplenic circulation.     

Myogenic responses and compliance of mesenteric and splenic vasculature in the rat

In the rat, the spleen is a major site of fluid efflux out of the blood. By contrast, the mesenteric vasculature serves as a blood reservoir. We proposed that the compliance and myogenic responses of these vascular beds would reflect their different functional demands. Mesenteric and splenic arterioles ( approximately 150-200 microm) and venules (<250 microm) from rats anesthetized with pentobarbital sodium were mounted in a pressurized myograph. Mesenteric arterial diameter decreased from 146 +/- 6 to 133 +/- 6 microm on raising intraluminal pressures from 80 to 120 mmHg. This response was enhanced in the presence of N(omega)-nitro-l-arginine methyl ester (l-NAME; 139 +/- 6 to 112 +/- 7 microm). There was no such myogenic response in the splenic arterioles, except in the presence of l-NAME (194 +/- 4 to 164 +/- 4.2 microm). We propose that, whereas mesenteric arterioles exhibit myogenic responses, this is normally masked by NO-mediated dilation in the splenic vessels. The mesenteric venules were highly distensible (active, 184 +/- 15 to 320 +/- 30.9 microm; passive in Ca(2+)-free media, 209 +/- 31 to 344 +/- 27 microm; 4-8 mmHg) compared with the splenic vessels (active, 169 +/- 11 to 184 +/- 16 microm; passive, 187 +/- 12 to 207 +/- 17 microm). We conclude that, in response to an increase in perfusion pressure, mesenteric arterial diameter would decrease to limit the changes in flow and microvascular pressure. In addition, mesenteric venous capacitance would increase. By contrast, splenic arterial diameter would increase, while there would be little change in venous diameter. This would enhance the increase in intrasplenic microvascular pressure and increase fluid extravasation.     

Orthostasis fails to produce active limb venoconstriction in adolescents.

Orthostasis is characterized by translocation of blood from the upper body and thorax into dependent venous structures. Although active splanchnic venoconstriction is known to occur, active limb venoconstriction remains controversial. Based on prior work, we initially hypothesized that active venoconstriction does occur in the extremities during orthostasis in response to baroreflex activation. We investigated this hypothesis in the arms and legs of 11 healthy volunteers, aged 13-19 yr, using venous occlusion strain gauge plethysmography to obtain the forearm and calf blood flows and to compute the capacitance vessel volume-pressure compliance relation. Subjects were studied supine and at -10, +20, and +35 degrees to load the baroreflexes. With +20 degrees of tilt, blood flow decreased and limb arterial resistance increased significantly (P < 0.05) compared with supine. With +35 degrees of tilt, blood flow decreased, limb arterial resistance increased, and heart rate increased, indicating parasympathetic withdrawal and sympathetic activation with arterial vasoconstriction. The volume-pressure relation was unchanged by orthostatic maneuvers. The results suggest that active venoconstriction in the limbs is not important to mild orthostatic response.     

Repeated pregnancies (multiparity) increases venous tone and reduces compliance

In humans, multiparity (repeated pregnancy) is associated with increased risk of cardiovascular disease. In rats, multiparity increases the pressor response to phenylephrine and to acute stress, due in part to changes in tone of the splanchnic arterial vasculature. Given that the venous system also changes during pregnancy, we studied the effects of multiparity on venous tone and compliance. Cardiovascular responses to volume loading (2 ml/100 g body wt), and mean circulatory filling pressure (MCFP, an index of venomotor tone) were measured in conscious, repeatedly bred (RB), and age-matched virgin rats. In addition, passive compliance and venous reactivity of isolated mesenteric veins were measured by pressure myography. There was a greater increase in mean arterial pressure after volume loading in RB rats (+7.2 +/- 2.5 mmHg, n = 8) than virgin rats (-1.4 +/- 1.7 mmHg, n = 7) (P < 0.05). The increase in MCFP in response to norepinephrine (NE) was also greater in RB rats [half maximal effective dose (ED(50)) 3.1 +/- 0.5 nmol.kg(-1).min(-1), n = 6] than virgins (ED(50): 12.1 +/- 2.7 nmol.kg(-1).min(-1), n = 6) (P < 0.05). Pressure-induced changes in passive diameter were lower in isolated mesenteric veins from RB rats (29.3 +/- 1.8 microm/mmHg, n = 6) than from virgins (36.9 +/- 1.3 microm/mmHg, n = 6) (P < 0.05). Venous reactivity to NE in isolated veins was also greater in RB rats (EC(50): 2.68 +/- 0.37x10(-8) M, n = 5) than virgins (EC(50): 4.67 +/- 0.93 x 10(-8) M, n = 8). We conclude that repeated pregnancy induces a long-term reduction in splanchnic venous compliance and augments splanchnic venous reactivity and sympathetic tonic control of total body venous tone. This compromises the ability of the capacitance (venous) system to accommodate volume overloads and to buffer changes in cardiac preload.     

Blood volume, the venous system, preload, and cardiac output

Cardiac output is determined by heart rate, by contractility (maximum systolic elastance, Emax) and afterload, and by diastolic ventricular compliance and preload. These relationships are illustrated using the pressure-volume loop. Diastolic compliance and Emax place limits determined by the heart within which the pressure-volume loop must lie. End-diastolic and end-systolic pressures and hence the exact position of the loop within these limits are determined by the peripheral circulation. In the presence of minimal sympathetic tone, some 60% of total blood volume is hemodynamically inactive and constitutes a blood volume reserve (the unstressed volume). The remainder of the blood volume (the stressed volume) and the compliance of the venous system determine the venous pressure. This venous pressure together with venous resistance determines venous return, right atrial pressure, cardiac preload, and hence cardiac output. Venoconstriction causes conversion of unstressed volume to the stressed volume, the blood volume reserve is converted into hemodynamically active blood volume. After hemorrhage this replaces the lost stressed volume, while in other situations where total blood volume is not reduced, it allows a sustained increase in cardiac output. The major blood volume reserve is in the splanchnic bed: the liver and intestine, and in animals but not man, the spleen. A major unsolved problem is how the conversion of unstressed volume to stressed volume by venoconstriction is reflexly controlled.     

Endothelin in the splanchnic vascular bed of DOCA-salt hypertensive rats

Vascular capacitance is reduced by endothelin-1 (ET-1) in deoxycorticosterone (DOCA)-salt hypertensive rats. This may contribute to hypertension development. Because the splanchnic blood vessels (especially veins) are important in determining vascular capacitance, we tested the hypothesis that ET-1 levels in the splanchnic vasculature are elevated in hypertensive DOCA-salt compared with normotensive rats. Tissue ET-1 content was measured by ELISA in aorta, vena cava, superior mesenteric artery and vein, and small mesenteric arteries and veins from normotensive sham-operated (sham) and 4-wk DOCA-salt rats. We also determined ET-1 concentration in aortic and portal venous blood (draining the nonhepatic splanchnic organs) in anesthetized and conscious sham and DOCA-salt rats before and after acute blockade of ETB receptor-mediated plasma clearance of ET-1. Results showed a higher ET-1 content in veins than in arteries of similar size. However, ET-1 content was similar in vessels from sham and DOCA-salt rats, except in aorta and superior mesenteric artery, where ET-1 content was greater in DOCA-salt rats. ET-1 concentration was significantly higher in portal venous than in aortic blood, indicating net nonhepatic splanchnic release (nNHSR) of ET-1. However, nNHSR of ET-1 was similar in sham and DOCA-salt rats. Although nNHSR of ET-1 increased significantly after ETB receptor blockade in sham rats, it was completely unchanged in DOCA-salt rats. These data suggest that, despite the absence of ETB receptor-mediated plasma clearance of ET-1, neither the venous peptide content nor the net release of ET-1 is increased in the splanchnic vasculature of DOCA-salt rats. These results argue against the hypothesis that increased venomotor tone in DOCA-salt hypertension is caused by increased ET-1 concentration around splanchnic venous smooth muscle cells.     

Haemodynamic effects of angiotensin II in conscious, non-ascitic cirrhotic rats

The effect of angiotensin II (AII) on systemic and regional haemodynamics was studied in 18 control and 18 cirrhotic, non-ascitic conscious rats (CCl4/phenobarbital model). Cirrhotic rats were found to retain sodium and to have normal plasma renin and plasma aldosterone concentrations when compared with control animals. Cirrhotic rats showed an enhanced cardiac output (34.4 +/- 0.5 vs. 27.5 +/- 2.0 ml/min in controls) and decreased peripheral resistances (2.96 +/- 0.25 vs. 3.95 +/- 0.31 mm Hg/min/100 g/ml in controls) under basal conditions. When AII was administered cardiac output decreased by 10.7 +/- 1.2% in cirrhotic rats, whereas it increased in control animals (11.2 +/- 2%, p less than 0.005). The AII-induced increase in arterial pressure was lower in cirrhotic than in control rats. The renal blood supply was particularly impaired by AII in cirrhotics, with a maintained flow to other organs (muscle, testes). It is concluded that the response to AII is disturbed in rats with hepatic cirrhosis even in a stage without ascites and with plasma renin and aldosterone concentrations similar to those of control animals.     

Angiotensin II-induced venoconstriction involves both AT1 and AT2 receptors and is counterbalanced by nitric oxide

The venoconstrictor effect of Angiotensin II (Ang II) was investigated in the rat mesenteric venules and portal vein. Mesenteric venules were perfused at a constant rate and reactivity to Ang II (0.1 nmol) was evaluated as changes in the perfusion pressure. Rings of portal vein were mounted in organ baths and curves to Ang II (0.1–100 nmol/L) were generated. In venules, Ang II-contraction (10.6 ± 1.1 mmHg) was abolished by losartan (0.9 ± 0.3 mmHg^*), reduced by PD 123,319 (5.8 ± 0.9 mmHg^*), increased by l-NAME (16.5 ± 1.8 mmHg^*) and not altered by indomethacin. In portal veins, curves to Ang II (−log EC50: 8.9 ± 0.1 mol/L) were shifted to the right by losartan (−log EC50: 7.5 ± 0.1 mol/L^*) and by PD 123,319 (−log EC50: 8.0 ± 0.1 mol/L^*). l-NAME increased the maximal response to Ang II (E_max: 0.91 ± 0.1 g versus 1.62 ± 0.3 g^*) and indomethacin had no effect. In conclusion, Ang II induces venoconstriction by activating AT1 and AT2 receptors. Data obtained with l-NAME provide evidence that the basal nitric oxide release from the endothelium of the venous system can modulate the Ang II-induced venoconstriction.     

Endocannabinoids acting at vascular CB1 receptors mediate the vasodilated state in advanced liver cirrhosis.

Advanced cirrhosis is associated with generalized vasodilation of unknown origin, which contributes to mortality. Cirrhotic patients are endotoxemic, and activation of vascular cannabinoid CB1 receptors has been implicated in endotoxin-induced hypotension. Here we show that rats with biliary cirrhosis have low blood pressure, which is elevated by the CB1 receptor antagonist SR141716A. The low blood pressure of rats with CCl4-induced cirrhosis was similarly reversed by SR141716A, which also reduced the elevated mesenteric blood flow and portal pressure. Monocytes from cirrhotic but not control patients or rats elicited SR141716A-sensitive hypotension in normal recipient rats and showed significantly elevated levels of anandamide. Compared with non-cirrhotic controls, in cirrhotic human livers there was a three-fold increase in CB1 receptors on isolated vascular endothelial cells. These results implicate anandamide and vascular CB1 receptors in the vasodilated state in advanced cirrhosis and indicate a novel approach for its management.     

Effect of portacaval surgical anastomosis on systemic and splanchnic hemodynamics in portal hypertensive, cirrhotic rats

The effect of surgical end-to-side portacaval anastomosis (PCSA) on systemic and splanchnic circulation has been studied in cirrhotic rats with portal hypertension (CCl4-phenobarbital method) and in control animals. Hemodynamics have been measured using the microsphere technique, with a reference sample for the systemic hemodynamic measurements, and intrasplenic injection for portal systemic shunting rate measurements. Compared with controls, sham-operated (SO) cirrhotic rats showed a hyperdynamic circulation with increased cardiac output (CO) and decreased mean arterial pressure and peripheral resistances. PCSA in control rats induced only a small change in systemic hemodynamics, with parallel decreases in arterial pressure and peripheral resistances, and a small, nonsignificant increase in CO. In cirrhotic rats, PCSA induced a decrease of CO to values similar to those of control rats, with an increase in total peripheral resistances. PCSA induced an increase in hepatic arterial blood flow in control and in cirrhotic rats, portal pressure becoming in this latter group not different from that of control rats. Blood flow to splanchnic organs was higher in SO cirrhotic than in SO control animals. Thus portal venous inflow was also increased in SO cirrhotic rats. PCSA induced an increase in portal venous inflow in control rats, which was only significant in cirrhotic rats when expressed as a percentage of CO. In SO control animals, a significant correlation was observed between total peripheral resistances and splanchnic arteriolar resistances and between CO and splanchnic blood flow. These correlations were not observed in cirrhotic rats. These results do not support the hypothesis that hyperdynamic circulation shown by cirrhotic rats is based on increases in splanchnic blood flow and (or) massive portal systemic shunting.     

Enforced exercise, but not acute temperature elevation, decreases venous capacitance in the stenothermal Antarctic fish Pagothenia borchgrevinki

The venous haemodynamic response to enforced exercise and acute temperature increase was examined in the Antarctic fish Pagothenia borchgrevinki (borch) to enable comparisons with the existing literature for temperate species, and investigate if the unusual cardiovascular response to temperature changes previously observed in the borch can be linked to an inability to regulate the venous vasculature. Routine central venous blood pressure (P (cv)) was 0.08 kPa and the mean circulatory filling pressure (P (mcf); an index of venous capacitance) was 0.14 kPa. Acute warming from 0 to 2.5 and 5 degrees C increased heart rate (f (H)), while dorsal aortic blood pressure (P (da)) decreased. P (mcf) did not change, while P (cv) decreased significantly at 5 degrees C. This contrasts with the venoconstriction previously observed in rainbow trout in response to increased temperature. Exercise resulted in small increases in P (mcf) and P (cv), a response that was abolished by alpha-adrenoceptor blockade. This study demonstrates that the heart of P. borchgrevinki normally operates at positive filling pressures (i.e. P (cv)) and that venous capacitance can be actively regulated by an alpha-adrenergic mechanism. The lack of decrease in venous capacitance during warming may suggest that a small increase in venous tone is offset by a passive temperature-mediated increase in compliance.     

Increased EETs participate in peripheral endothelial dysfunction of cirrhosis

The hyperdynamic circulation of cirrhosis participates in the pathophysiology of portal hypertension. P450-dependent epoxyeicosatrienoic acids (EET) are potent vasodilators. We evaluated plasma levels of EETs in cirrhotic patients and the effect of epoxygenase and nitric oxide synthase (NOS) inhibition on skin blood flow, measured by laser Doppler flowmetry, in normal subjects and cirrhotic patients with and without ascites. Free plasma EETs were increased in cirrhotic patients compared to normal subjects, while the ratio between 8,9-, 11,12-, and 14-15-EET was the same. In cirrhotic patients without ascites, skin blood flow was significantly increased compared to normal subjects. In patients with ascites skin blood flow was significantly reduced compared to control subjects and patients without ascites. Inhibition of epoxygenase with miconazole and of NOS with L-NG-Nitroarginine methyl ester (L-NAME) decreased basal skin flow in normal subjects and in cirrhotic patients, the effect being higher in cirrhotic patients. Miconazole caused a further decrease in flow when administered with L-NAME, both in normal subjects and in cirrhotic patients. In conclusion, EETs participate in the control of peripheral circulation of normal subjects and in the pathophysiology of peripheral vasodilatation of cirrhotic patients with ascites.     

Endocannabinoids acting at CB1 receptors mediate the cardiac contractile dysfunction in vivo in cirrhotic rats

Advanced liver cirrhosis is associated with hyperdynamic circulation consisting of systemic hypotension, decreased peripheral resistance, and cardiac dysfunction, termed cirrhotic cardiomyopathy. Previous studies have revealed the role of endocannabinoids and vascular CB(1) receptors in the development of generalized hypotension and mesenteric vasodilation in animal models of liver cirrhosis, and CB(1) receptors have also been implicated in the decreased beta-adrenergic responsiveness of isolated heart tissue from cirrhotic rats. Here we document the cardiac contractile dysfunction in vivo in liver cirrhosis and explore the role of the endocannabinoid system in its development. Rats with CCl(4)-induced cirrhosis developed decreased cardiac contractility, as documented through the use of the Millar pressure-volume microcatheter system, low blood pressure, and tachycardia. Bolus intravenous injection of the CB(1) antagonist AM251 (3 mg/kg) acutely increased mean blood pressure, as well as both load-dependent and -independent indexes of systolic function, whereas no such changes were elicited by AM251 in control rats. Furthermore, tissue levels of the endocannabinoid anandamide increased 2.7-fold in the heart of cirrhotic compared with control rats, without any change in 2-arachidonoylglycerol levels, whereas, in the cirrhotic liver, both 2-arachidonoylglycerol (6-fold) and anandamide (3.5-fold) were markedly increased. CB(1)-receptor expression in the heart was unaffected by cirrhosis, as verified by Western blotting. Activation of cardiac CB(1) receptors by endogenous anandamide contributes to the reduced cardiac contractility in liver cirrhosis, and CB(1)-receptor antagonists may be used to improve contractile function in cirrhotic cardiomyopathy and, possibly, in other forms of heart failure.     

Alterations in Perivascular Sympathetic and Nitrergic Innervation Function Induced by Late Pregnancy in Rat Mesenteric Arteries

Background and Purpose

We investigated whether pregnancy was associated with changed function in components of perivascular mesenteric innervation and the mechanism/s involved.

Experimental Approach

We used superior mesenteric arteries from female Sprague-Dawley rats divided into two groups: control rats (in oestrous phase) and pregnant rats (20 days of pregnancy). Modifications in the vasoconstrictor response to electrical field stimulation (EFS) were analysed in the presence/absence of phentolamine (alpha-adrenoceptor antagonist) or L-NAME (nitric oxide synthase-NOS- non-specific inhibitor). Vasomotor responses to noradrenaline (NA), and to NO donor DEA-NO were studied, NA and NO release measured and neuronal NOS (nNOS) expression/activation analysed.

Key Results

EFS induced a lower frequency-dependent contraction in pregnant than in control rats. Phentolamine decreased EFS-induced vasoconstriction in segments from both experimental groups, but to a greater extent in control rats. EFS-induced vasoconstriction was increased by L-NAME in arteries from both experimental groups. This increase was greater in segments from pregnant rats. Pregnancy decreased NA release while increasing NO release. nNOS expression was not modified but nNOS activation was increased by pregnancy. Pregnancy decreased NA-induced vasoconstriction response and did not modify DEA-NO-induced vasodilation response.

Conclusions and Implications

Neural control of mesenteric vasomotor tone was altered by pregnancy. Diminished sympathetic and enhanced nitrergic components both contributed to the decreased vasoconstriction response to EFS during pregnancy. All these changes indicate the selective participation of sympathetic and nitrergic innervations in vascular adaptations produced during pregnancy.     

Effect of nitric oxide synthase inhibition on mitochondrial biogenesis in rat skeletal muscle.

The purpose of this study was to determine whether nitric oxide synthase (NOS) inhibition decreased basal and exercise-induced skeletal muscle mitochondrial biogenesis. Male Sprague-Dawley rats were assigned to one of four treatment groups: NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME, ingested for 2 days in drinking water, 1 mg/ml) followed by acute exercise, no l-NAME ingestion and acute exercise, rest plus l-NAME, and rest without l-NAME. The exercised rats ran on a treadmill for 53 +/- 2 min and were then killed 4 h later. NOS inhibition significantly (P < 0.05; main effect) decreased basal peroxisome proliferator-activated receptor-gamma coactivator 1beta (PGC-1beta) mRNA levels and tended (P = 0.08) to decrease mtTFA mRNA levels in the soleus, but not the extensor digitorum longus (EDL) muscle. This coincided with significantly reduced basal levels of cytochrome c oxidase (COX) I and COX IV mRNA, COX IV protein and COX enzyme activity following NOS inhibition in the soleus, but not the EDL muscle. NOS inhibition had no effect on citrate synthase or beta-hydroxyacyl CoA dehydrogenase activity, or cytochrome c protein abundance in the soleus or EDL. NOS inhibition did not reduce the exercise-induced increase in peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha) mRNA in the soleus or EDL. In conclusion, inhibition of NOS appears to decrease some aspects of the mitochondrial respiratory chain in the soleus under basal conditions, but does not attenuate exercise-induced mitochondrial biogenesis in the soleus or in the EDL.