cGMP Production In Smooth Muscle Research Articles

Adipocytokine, progranulin, augments acetylcholine-induced nitric oxide-mediated relaxation through the increases of cGMP production in rat isolated mesenteric artery.

Progranulin (PGRN) is a novel adipocytokine with anti-inflammatory effects in vascular cells. The aim of this study was to clarify the effects of PGRN on reactivity of isolated blood vessel. Isometric contraction of rat isolated superior mesenteric artery was measured. Pre-treatment with PGRN (10-100ngmL-1 , 30min) had no effect on noradrenaline- or 5-hydroxytriptamine-induced contraction. On the other hand, pre-treatment with PGRN (100ngmL-1 ) augmented acetylcholine (ACh; 30nm)-induced endothelium-dependent relaxation. Pre-treatment with PGRN (100ngmL-1 ) augmented ACh (10μm)-induced nitric oxide (NO)-mediated relaxation in the presence of indomethacin (10μm), a cyclooxygenase inhibitor, and tetraethyl ammonium (10mm), a non-selective potassium channel blocker. In contrast, pre-treatment with PGRN (100ngmL-1 ) had no effect on ACh-induced endothelium-derived hyperpolarizing factor-mediated relaxation. Pre-treatment with PGRN (100ngmL-1 ) had no effect on ACh (10μm, 1min)-induced endothelial NO synthase phosphorylation (at Ser1177) as determined by Western blotting. Pre-treatment with PGRN (100ngmL-1 ) augmented an NO donor, sodium nitroprusside (SNP; 30nm-1μm)- but not a membrane-permeable cGMP analogue, 8-bromo-cGMP-induced relaxation. In the presence of 3-isobutyl-1-methylxanthine (100μm), a phosphodiesterase inhibitor, pre-treatment with PGRN (100ngmL-1 ) increased SNP (30nm, 5min)-induced cGMP production as determined by enzyme immunoassay. We for the first time demonstrate that PGRN augments ACh-induced NO-mediated relaxation through the increases of cGMP production in smooth muscle. These results indicate PGRN as a possible pharmacotherapeutic target against cardiovascular diseases including obesity-related hypertension.

Different regulatory effects of hydrogen sulfide and nitric oxide on gastric motility in mice

NO and H2S are gaseous signaling molecules that modulate smooth muscle motility. We aimed to identify expressions of enzymes that catalyze H2S and NO generation in mouse gastric smooth muscle, and determine relationships between endogenous H2S and NO in regulation of smooth muscle motility. Western blotting and immunocytochemistry methods were used to track expressions of neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS), cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) in gastric smooth muscles. Smooth muscle motility was recorded by isometric force transducers. cGMP production was measured by a specific radioimmunoassay. We found that CBS, CSE, eNOS, and nNOS were all expressed in mice gastric antral smooth muscle tissues, and in cultured gastric antral smooth muscle cells. AOAA significantly inhibited smooth muscle contractions in the gastric antrum, which was significantly recovered by NaHS, while PAG had no significant effect. l-NAME enhanced contractions. NaHS at low concentrations increased basal tension but decreased it at high concentrations. SNP significantly inhibited the contractions, which could be recovered by NaHS both in the absence and presence of CuSO4. ODQ did not block NaHS-induced excitatory effect, while IBMX partially blocked this effect. cGMP production in smooth muscle was significantly increased by SNP but was not affected by NaHS. All these results suggest that endogenous H2S and NO appear to play opposite roles in regulating gastric motility and their effects may be via separate signal transduction pathways. Intracellular H2S/NO levels may be maintained in a state of balance to warrant normal smooth muscle motility.

A novel adipocytokine, nesfatin-1 modulates peripheral arterial contractility and blood pressure in rats

Nesfatin-1 is a novel adipocytokine which exerts not only anorexigenic but also hypertensive roles through acting on hypothalamus melanocortin-3/4 receptors. Although it is logical to hypothesize that nesfatin-1 could also affect the contractile reactivity of peripheral blood vessels, it still remains to be examined. The present study was performed to test the hypothesis. In both endothelium-intact and -denuded mesenteric artery of rats, acute treatment with nesfatin-1 (10nM, 30min pretreatment) had no influence on the noradrenaline- and 5-hydroxytryptamine-induced concentration-dependent contractions. Chronic treatment of mesenteric artery with nesfatin-1 (10nM, 3days) using organ-culture method had also no influence on the agonists-induced contractions. In contrast, nesfatin-1 (10nM, 30min) significantly inhibited the sodium nitroprusside (SNP)-induced relaxations of smooth muscle in mesenteric artery. A membrane permeable cyclic GMP (cGMP) analog, 8-bromo-cGMP-induced relaxations were not affected by nesfatin-1. Consistently, the SNP-induced cGMP production in smooth muscle was impaired by nesfatin-1. Intravenous application of nesfatin-1 to rats not only increased blood pressure but also impaired the SNP-induced decreases in blood pressure. The present study for the first time reveals that nesfatin-1 affects peripheral arterial blood vessel and inhibits the nitric oxide donor-induced smooth muscle relaxations via impairing the cGMP production. The results are the first to demonstrate that nesfatin-1 modulates blood pressure through directly acting on peripheral arterial resistance.

Interleukin-6 impairs endothelium-dependent NO-cGMP-mediated relaxation and enhances contraction in systemic vessels of pregnant rats.

IL-6 is elevated in plasma of preeclamptic women, and twofold elevation of plasma IL-6 increases vascular resistance and arterial pressure in pregnant rats, suggesting a role of the cytokine in hypertension of pregnancy. However, whether the hemodynamic effects of IL-6 reflect direct effects of the cytokine on the mechanisms of vascular contraction/relaxation is unclear. The purpose of this study was to test the hypothesis that IL-6 directly impairs endothelium-dependent relaxation and enhances vascular contraction in systemic vessels of pregnant rats. Active stress was measured in aortic strips isolated from virgin and late pregnant Sprague-Dawley rats and then nontreated or treated for 1 h with IL-6 (10 pg/ml to 10 ng/ml). In endothelium-intact vascular strips, phenylephrine (Phe, 10(-5) M) caused an increase in active stress that was smaller in pregnant (4.2 +/- 0.3) than virgin rats (5.1 +/- 0.3 x 10(4) N/m(2)). IL-6 (1,000 pg/ml) caused enhancement of Phe contraction that was greater in pregnant (10.6 +/- 0.7) than virgin rats (7.5 +/- 0.4 x 10(4) N/m(2)). ACh and bradykinin caused relaxation of Phe contraction and increases in vascular nitrite production that were greater in pregnant than virgin rats. IL-6 caused reductions in ACh- and bradykinin-induced vascular relaxation and nitrite production that were more prominent in pregnant than virgin rats. Incubation of endothelium-intact strips in the presence of N(omega)-nitro-L-arginine methyl ester (10(-4) M) to inhibit nitric oxide (NO) synthase, or 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (ODQ, 10(-5) M) to inhibit cGMP production in smooth muscle, inhibited ACh-induced relaxation and enhanced Phe-induced stress in nontreated but to a lesser extent in IL-6-treated vessels, particularly those of pregnant rats. Removal of the endothelium enhanced Phe-induced stress in nontreated but not IL-6-treated vessels, particularly those of pregnant rats. In endothelium-denuded strips, relaxation of Phe contraction with sodium nitroprusside, an exogenous NO donor, was not different between nontreated and IL-6-treated vessels of virgin or pregnant rats. Thus IL-6 inhibits endothelium-dependent NO-cGMP-mediated relaxation and enhances contraction in systemic vessels of virgin and pregnant rats. The greater IL-6-induced inhibition of vascular relaxation and enhancement of contraction in systemic vessels of pregnant rats supports a direct role for IL-6 as one possible mediator of the increased vascular resistance associated with hypertension of pregnancy.

Role of oxidative stress in age-related reduction of NO-cGMP-mediated vascular relaxation in SHR.

The incidence of hypertension increases during the late stages of aging; however, the vascular mechanisms involved are unclear. We investigated whether the late stages of aging are associated with impaired nitric oxide (NO)-mediated vascular relaxation and enhanced vascular contraction and whether oxidative stress plays a role in the age-related vascular changes. Aging (16 mo) male spontaneously hypertensive rats (SHR) nontreated or treated for 8 mo with the antioxidant tempol (1 mM in drinking water) or vitamin E (E; 5,000 IU/kg chow) and vitamin C (C; 100 mg. kg-1. day-1 in drinking water) and adult (12 wk) male SHR were used. After the arterial pressure was measured, aortic strips were isolated from the rats for measurement of isometric contraction. The arterial pressure and phenylephrine (Phe)-induced vascular contraction were enhanced, and the ACh-induced vascular relaxation and nitrite/nitrate production were reduced in aging compared with adult rats. In aging rats, the arterial pressure was nontreated (188 +/- 4), tempol-treated (161 +/- 6), and E + C-treated (187 +/- 1 mmHg). Phe (10-5 M) caused an increase in active stress in nontreated aging rats (14.3 +/- 1.0) that was significantly (P < 0.05) reduced in tempol-treated (9.0 +/- 0.7) and E + C-treated rats (9.8 +/- 0.6 x 104 N/m2). ACh produced a small relaxation of Phe contraction in nontreated aging rats that was enhanced (P < 0.05) in tempol- and E + C-treated rats. l-NAME (10-4 M), inhibitor of NO synthase, or ODQ (10-5 M), inhibitor of cGMP production in smooth muscle, inhibited ACh relaxation and enhanced Phe contraction in tempol- and E + C-treated but not the nontreated aging rats. ACh-induced vascular nitrite/nitrate production was not different in nontreated, tempol- and E + C-treated aging rats. Relaxation of Phe contraction with sodium nitroprusside, an exogenous NO donor, was smaller in aging than adult rats but was not different between nontreated, tempol- and E + C-treated aging rats. Thus, during the late stages of aging in SHR rats, an age-related inhibition of a vascular relaxation pathway involving not only NO production by endothelial cells but also the bioavailability of NO and the smooth muscle response to NO is partially reversed during chronic treatment with the antioxidants tempol and vitamins E and C. The data suggest a role for oxidative stress in the reduction of vascular relaxation and thereby the promotion of vascular contraction and hypertension during the late stages of aging.

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.

Reduced endothelial NO-cGMP vascular relaxation pathway during TNF-α-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.

High-salt diet enhances vascular reactivity in pregnant rats with normal and reduced uterine perfusion pressure.

High-salt (HS) diet is often associated with increased vascular resistance and arterial pressure; however, the effects of HS intake on the vascular control mechanisms of arterial pressure during pregnancy are unclear. We investigated whether a HS diet during pregnancy is associated with increases in vascular reactivity. Active stress was measured in aortic strips of virgin and normal pregnant Sprague-Dawley rats and a hypertensive pregnant rat model produced by reduction in uterine perfusion pressure (RUPP), fed either normal-sodium (NS, 1%) or HS diet (8%) for 7 days. In endothelium-intact strips, phenylephrine (Phe) caused a concentration-dependent contraction that was greater in RUPP rats than in normal pregnant or virgin rats and was significantly enhanced in pregnant/HS and RUPP/HS rats compared with pregnant/NS and RUPP/NS rats, respectively. Removal of the endothelium enhanced the Phe-induced stress slightly in virgin rats and significantly in pregnant/NS but not in pregnant/HS, RUPP/NS, or RUPP/HS. In endothelium-intact strips, acetylcholine (ACh) caused a concentration-dependent relaxation that was reduced in RUPP/NS (max, 31%) compared with pregnant/NS rats (max, 75%). ACh relaxation was further reduced in pregnant/HS rats compared with pregnant/NS rats and in RUPP/HS rats compared with RUPP/NS rats. Pretreatment of endothelium-intact strips with N(G)-nitro-L-arginine methyl ester (L-NAME, 10(-4) mol/L), to inhibit NO synthase, or with 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (ODQ, 10(-6) mol/L), to inhibit cGMP production in smooth muscle, inhibited ACh-induced relaxation and enhanced Phe-induced contraction in pregnant/NS rats but not in pregnant/HS, RUPP/NS, or RUPP/HS rats. Basal and ACh-induced nitrite/nitrate production from aortic strips showed significant reduction in pregnant/HS rats compared with pregnant/NS rats but not in RUPP/HS rats compared with RUPP/NS rats. Sodium nitroprusside, an exogenous NO donor, caused relaxation of Phe contraction that was similar in virgin or pregnant rats on an NS or HS diet but was significantly reduced in RUPP/HS rats (ED(50) 6x10(-8) mol/L) compared with RUPP/NS rats (ED(50) 6x10(-9) mol/L). Thus, a HS diet in normal pregnant and RUPP rats is associated with increases in vascular reactivity. The enhanced vascular reactivity with the HS diet is possibly related to abnormalities in NO synthesis/release from the endothelium in normal pregnant rats and an additional decrease in the sensitivity of the smooth muscle to relaxation by NO in pregnant rats with reduced uterine perfusion pressure.

Role of endothelin B receptors in enhancing endothelium-dependent nitric oxide-mediated vascular relaxation during high salt diet.

High salt diet is often associated with increases in blood pressure, and the state of activation of endothelium-dependent vascular relaxation pathways is critical under these conditions. Basal activation of endothelial endothelin B (ET(B)) receptors by endothelin has been suggested to stimulate the release of factors that promote vascular relaxation. However, whether ET(B) receptors play a role in enhancing endothelium-dependent vascular relaxation during high salt diet is unclear. In this study, we investigated whether chronic treatment with an ET(B) receptor antagonist is associated with impaired endothelium-dependent vascular relaxation and enhanced vascular reactivity particularly during high salt diet. Isometric contraction was measured in aortic strips isolated from male Sprague-Dawley rats on normal sodium (NS, 1%) and high sodium diet (HS, 8%) for 7 days and untreated or treated with the ET(B) receptor antagonist A-192621 (30 mg/kg per day) for 5 days. The mean arterial pressure was (in mm Hg) 122+/-3 in NS, 132+/-3 in HS, 144+/-2 in NS/ET(B) antagonist, and 171+/-12 in HS/ET(B) antagonist rats. In endothelium-intact strips, phenylephrine (Phe, 10(-5) mol/L) increased active stress to 7.6+/-1.0x10(3)N/m(2) in NS rats and 8.2+/-0.9x10(3)N/m(2) in HS rats. Phe (10(-5) mol/L) -induced stress was significantly greater in NS/ET(B) antagonist (11.3+/-0.9x10(3)N/m(2)) than NS and far greater in HS/ET(B) antagonist (14.1+/-0.1.2x10(3)N/m(2)) than HS rats. Also, Phe was more potent in NS/ET(B) antagonist and HS/ET(B) antagonist rats (ED(50)=0.3x10(-7) and 0.15x10(-7) mol/L) than in NS and HS rats (ED(50)=0.8x10(-7) and 0.7x10(-7) mol/L). Removal of the endothelium enhanced Phe-induced contraction significantly in NS and to a greater extent in HS, but not in NS/ET(B) antagonist or HS/ET(B) antagonist rats. In endothelium-intact strips, acetylcholine (ACh) caused relaxation of Phe contraction that was less in NS/ET(B) antagonist than NS and far less in HS/ET(B) antagonist than HS rats. Pretreatment of endothelium-intact strips with L-NAME (10(-4) mol/L), to inhibit nitric oxide (NO) synthase, or with methylene blue (10(-5) mol/L) or 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (ODQ, 10(-6) mol/L), to inhibit cGMP production in smooth muscle, inhibited ACh-induced relaxation and enhanced Phe-induced contraction significantly in NS and HS, slightly in NS/ET(B) antagonist, but not in HS/ET(B) antagonist rats. Measurement of basal and ACh-induced nitrite/nitrate production from aortic strips showed a significant reduction in NS/ET(B) antagonist compared with NS, and a greater reduction in HS/ET(B) antagonist compared with HS rats. Relaxation of Phe contraction with sodium nitroprusside was not significantly different among the different groups of rats. Thus, an endothelial ET(B) receptor-mediated pathway of vascular relaxation involving release of NO seems to be active under basal conditions and may protect against excessive vasoconstriction and increased blood pressure particularly during high salt diet.

Role of Enothelin B Receptors in Enhancing Endothelium-Dependent No-Mediated Vascular Relaxation During High Salt Diet

P21 Basal stimulation of endothelial endothelin B (ET B ) receptors and the ensuing release of endothelium-derived relaxing factors has been hypothesized to protect against excessive vasoconstriction and increased blood pressure particularly during high salt diet. To test this hypothesis, we investigated whether chronic infusion of ET B receptor antagonist is associated with impaired endothelium-dependent vascular relaxation and enhanced vascular reactivity particularly with high salt diet. Active stress was measured in aortic strips isolated from male Sprague-Dawley rats on normal sodium (NS, 1%) and high sodium diet (HS, 8%) for 7 days and untreated or infused with the ET B receptor antagonist A-192621 (30 mg/kg/day) for 5 days. In endothelium-intact strips, phenylephrine (Phe,10 -5 M) increased stress to 6.9±.3 in NS and to 7.2±.4x10 3 N/m 2 in HS rats. The Phe-induced stress in NS/ET B (8.6±.5) and HS/ET B rats (12.5±.4x10 3 N/m 2 ) was significantly &gt; NS and HS rats. Removal of the endothelium significantly enhanced Phe-induced stress in NS and HS, and only slightly in NS/ET B but not in HS/ET B rats. In endothelium-intact strips, acetylcholine (ACh) induced relaxation of Phe contraction was in NS &gt; HS &gt; NS/ET B &gt; HS/ET B rats with an ED 50 of 0.3x10 -6 , 0.4x10 -6 , 0.7x10 -6 and 1.1x10 -6 M, respectively. Pretreatment of endothelium-intact strips with L-NAME (10 -4 M), to inhibit nitric oxide (NO) synthase, or methylene blue (10 -5 M), to inhibit cGMP production in smooth muscle, significantly inhibited ACh-induced relaxation and enhanced Phe-induced stress in NS and HS, and only slightly in NS/ET B but not in HS/ET B rats. Measurement of basal and ACh-induced nitrite/nitrate production from aortic strips showed a significant decrease in NS/ET B and HS/ET B compared to NS and HS rats. Relaxation of Phe contraction with sodium nitroprusside was not significantly different among the different groups of rats. Thus, an endothelial ET B receptor-mediated pathway of vascular relaxation involving release of NO is active under basal conditions and may protect against excessive vasoconstriction and increased blood pressure particularly during high salt diet.

Decreased Endothelium-Dependent Vascular Relaxation During Reduction of Uterine Perfusion Pressure in Pregnant Rat

Reduction in uterine perfusion and the ensuing placental ischemia during late pregnancy have been proposed to trigger increases in systemic vascular resistance and pregnancy-induced hypertension; however, the intermediary mechanisms involved are unclear. The purpose of the present study was to test the hypothesis that reduced uterine perfusion pressure during late pregnancy is associated with impaired endothelium-dependent vascular relaxation and, consequently, enhanced systemic vascular reactivity. Active stress was measured in aortic strips isolated from late pregnant Sprague-Dawley rats and a hypertensive pregnant rat model produced through the long-term reduction in uterine perfusion pressure (RUPP). Phenylephrine (Phe, 10(-5) mol/L) caused an increase in active stress to 4.5+/-0.4x10(3) N/m(2) in normal pregnant rats and a larger increase to 9.4+/-0. 7x10(3) N/m(2) in RUPP rats. Removal of the endothelium significantly enhanced Phe-induced stress in pregnant (6.4+/-0. 6x10(3) N/m(2)) but not RUPP (9.95+/-0.95x10(3) N/m(2)) rats. In endothelium-intact strips, acetylcholine (ACh) was more potent in inducing relaxation of Phe contraction in pregnant (ED(50) 0. 1x10(-6) mol/L) than in RUPP (ED(50) 1.2x10(-6) mol/L) rats. Pretreatment of endothelium-intact strips with N(G)-nitro-L-arginine methyl ester(100 micromol/L), to inhibit nitric oxide (NO) synthase, significantly inhibited ACh-induced relaxation and enhanced Phe-induced stress in pregnant (6.2+/-0.5x10(3) N/m(2)) but not RUPP (9.5+/-0.85x10(3) N/m(2)) rats. Pretreatment of endothelium-intact strips with methylene blue (10 micromol/L), to inhibit cGMP production in smooth muscle, also inhibited ACh-induced relaxation and enhanced Phe-induced stress in pregnant (6.9+/-0.65x10(3) N/m(2)) but not RUPP (9.3+/-0.7x10(3) N/m(2)) rats. In endothelium-denuded strips, relaxation of Phe contraction with the exogenous NO donor sodium nitroprusside was not significantly different between pregnant and RUPP rats. These results suggest that an endothelium-dependent relaxation pathway involving the release of NO from endothelial cells and increased cGMP production in smooth muscle is inhibited in systemic vessels of late pregnant rats with reduced uterine perfusion pressure and may in part explain the increased vascular resistance in pregnancy-induced hypertension.

Endothelium-Derived Relaxing Factor: Presence in Pulmonary and Systemic Arteries of the Newborn Guinea Pig

Endothelium-derived relaxing factor (EDRF), believed to be nitric oxide or a compound that releases nitric oxide, is a potent vasodilator produced by some arteries in response to acetylcholine (ACh) and bradykinin (BK). ACh and BK are potent dilators of perinatal pulmonary and systemic arteries. The objectives of this study were to determine if EDRF is present in newborn vessels and if EDRF mediates the vasodilator actions of ACh and BK. Arterial rings from newborn guinea pigs, 1 to 3 d old, were obtained from a branch of the main pulmonary artery and the descending aorta for isometric force bioassays. At their optimal resting tension, the rings were preconstricted with phenylephrine 10(-5) M in Krebs-Henseleit solution before adding incremental doses of ACh or BK. If the endothelium was intact, ACh (10(-5) M) relaxed pulmonary arteries and aortas (64 +/- 7%, 72 +/- 9% relaxation, respectively, mean +/- SE). ACh-induced relaxation (ACh 10(-5) M) in the pulmonary artery and aorta, respectively, was significantly (p less than 0.05) attenuated by 1) endothelial removal (11 +/- 9%, 28 +/- 10%) by rubbing the ring lumen; 2) methylene blue, 10(-6) M, (6 +/- 8%, 7 +/- 3%) that inhibits EDRF-associated cGMP production in smooth muscle; and 3) methemoglobin, 10(-5) M, (13 +/- 9%, 17 +/- 7%) that binds EDRF. The results for BK were similar to ACh for the pulmonary artery but BK did not relax the aorta. Indomethacin diminished relaxation of the pulmonary artery and aorta to the submaximal dose (10(-5) M) of ACh but indomethacin did not effect the relaxation to ACh 10(-4) M or BK. We conclude that EDRF is produced in the guinea pig pulmonary artery and descending aorta at birth and that EDRF is a mediator of the vasodilator actions of ACh and BK. Vasodilation by ACh may also involve activation of the cyclooxygenase pathway.