Methylene blue selectively inhibits pulmonary vasodilator responses in cats

The effects of methylene blue on vascular tone and the responses to pressor and depressor substances were investigated in the constricted feline pulmonary vascular bed under conditions of controlled blood flow and constant left atrial pressure. When tone was elevated with U46619, intralobar injections of acetylcholine, bradykinin, nitroglycerin, isoproterenol, epinephrine, and 8-bromoguanosine-3',5'-cyclic monophosphate (8-bromo-cGMP) dilated the pulmonary vascular bed. Intralobar infusions of methylene blue elevated lobar arterial pressure without altering base-line left atrial or aortic pressure, heart rate, or cardiac output. When methylene blue was infused in concentrations that raised lobar arterial pressure to values similar to those attained during U46619 infusion, the pulmonary vasodilator responses to acetylcholine, bradykinin, and nitroglycerin were reduced significantly, whereas vasodilator responses to isoproterenol, epinephrine, and 8-bromo-cGMP were not altered. Moreover, the pressor responses to angiotensin II and BAY K 8644 during U46619 infusion and during methylene blue infusion were similar. The enhancing effects of methylene blue on vascular tone and inhibiting effects of this agent on responses to acetylcholine, bradykinin, and nitroglycerin were reversible. These responses returned to control value when tone was again increased with U46619, 30-45 min after the methylene blue infusion was terminated. The present data are consistent with the hypothesis that cGMP may play a role in the regulation of tone in the feline pulmonary vascular bed and in the mediation of vasodilator responses to the endothelium-dependent vasodilators, acetylcholine and bradykinin, and to nitrogen oxide-containing vasodilators such as nitroglycerin.     

Selective pulmonary vasodilation with ATP-MgCl2 during pulmonary hypertension in lambs

We investigated the effects of infusions of ATP-MgCl2 on the circulation in 11 spontaneously breathing newborn lambs during pulmonary hypertension induced either by the infusion of U-46619, a thromboxane A2 mimetic, or by hypoxia. During pulmonary hypertension induced by U-46619, ATP-MgCl2 (0.01-1.0 mg.kg-1.min-1) caused a significant dose-dependent decrease in pulmonary arterial pressure (12.4-40.7%, P less than 0.05), while systemic arterial pressure decreased only at the highest doses (P less than 0.05). Left atrial infusions of ATP-MgCl2 caused systemic hypotension without decreasing pulmonary arterial pressure. During hypoxia-induced pulmonary hypertension, ATP-MgCl2 caused a similar significant dose-dependent decrease in pulmonary arterial pressure (12.0-41.1%, P less than 0.05), while systemic arterial pressure decreased only at high doses (P less than 0.05). Regression analysis showed selectivity of the vasodilating effects of ATP-MgCl2 for the pulmonary circulation during pulmonary hypertension induced either by U-46619 or hypoxia. ATP-MgCl2 is a potent vasodilator with a rapid metabolism that allows for selective vasodilation of the vascular bed first encountered (pulmonary or systemic). We conclude that infusions of ATP-MgCl2 may be clinically useful in the treatment of children with pulmonary hypertension.     

N omega-nitro-L-arginine methyl ester selectively inhibits pulmonary vasodilator responses to acetylcholine and bradykinin.

The effects of N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of endothelium-derived relaxing factor (EDRF) production, on vascular tone and responses were investigated in the pulmonary vascular bed of the intact-chest cat under conditions of controlled blood flow and constant left atrial pressure. When pulmonary vascular tone was elevated with U-46619, intralobar injections of acetylcholine, bradykinin, sodium nitroprusside, isoproterenol, prostaglandin E1 (PGE1), lemakalim, and 8-bromo-guanosine 3',5'-cyclic monophosphate (8-bromo-cGMP) dilated the pulmonary vascular bed. Intravenous administration of L-NAME elevated lobar arterial and systemic arterial pressures without altering left atrial pressure. When U-46619 was infused after L-NAME to raise lobar arterial pressure to levels similar to those attained during the control period, vasodilator responses to acetylcholine and bradykinin were reduced significantly, whereas responses to PGE1, lemakalim, and 8-bromo-cGMP were not altered, and responses to nitroprusside were increased. There was a small effect on the response to the highest dose of isoproterenol, and pressor responses to BAY K 8644 and angiotensin II were not altered. These results are consistent with the hypothesis that EDRF production may involve the formation of nitric oxide or a nitroso compound from L-arginine and that EDRF production may have a role in the regulation of tone and in the mediation of responses to acetylcholine and bradykinin in the pulmonary vascular bed of the cat.     

Comparison of the hemodynamic effects of nitric oxide and endothelium-dependent vasodilators in intact lungs

The effects of endothelium-dependent vasodilation on pulmonary vascular hemodynamics were evaluated in a variety of in vivo and in vitro models to determine 1) the comparability of the hemodynamic effects of acetylcholine (ACh), bradykinin (BK), nitric oxide (NO), and 8-bromo-guanosine 3',5'-cyclic monophosphate (cGMP), 2) whether methylene blue is a useful inhibitor of endothelium-dependent relaxing factor (EDRF) activity in vivo, and 3) the effect of monocrotaline-induced pulmonary hypertension on the responsiveness of the pulmonary vasculature to ACh. In isolated rat lungs, which were preconstricted with hypoxia, ACh, BK, NO, and 8-bromo-cGMP caused pulmonary vasodilation, which was not inhibited by maximum tolerable doses of methylene blue. Methylene blue did not inhibit EDRF activity in any model, despite causing increased pulmonary vascular tone and responsiveness to various constrictor agents. There were significant differences in the hemodynamic characteristics of ACh, BK, and NO. In the isolated lung, BK and NO caused transient decreases of hypoxic vasoconstriction, whereas ACh caused more prolonged vasodilation. Pretreatment of these lungs with NO did not significantly inhibit ACh-induced vasodilation but caused BK to produce vasoconstriction. Tachyphylaxis, which was agonist specific, developed with repeated administration of ACh or BK but not NO. Tachyphylaxis probably resulted from inhibition of the endothelium-dependent vasodilation pathway proximal to NO synthesis, because it could be overcome by exogenous NO. Pretreatment with 8-bromo-cGMP decreased hypoxic pulmonary vasoconstriction and, even when the hypoxic pressor response had largely recovered, subsequent doses of ACh and NO failed to cause vasodilation, although BK produced vasoconstriction. These findings are compatible with the existence of feedback inhibition of the endothelium-dependent relaxation by elevation of cGMP levels. Responsiveness to ACh was retained in lungs with severe monocrotaline-induced pulmonary hypertension. Many of these findings would not have been predicted based on in vitro studies and illustrate the importance for expanding studies of EDRF to in vivo and ex vivo models.     

TNF-alpha augments pulmonary vasoconstriction via the inhibition of nitrovasodilator activity.

We tested the hypothesis that tumor necrosis factor-alpha (TNF-alpha) increases pulmonary vasoconstriction by decreases in nitric oxide- (NO) dependent vasodilation. Lungs were isolated from guinea pigs 18 h after intraperitoneal injection of either TNF-alpha (1.60 x 10(5) U/kg) or control. U-46619 (365 mM/min) caused increases in pulmonary arterial and capillary pressures, pulmonary arterial and venous resistances, and lung weight. TNF-alpha augmented the U-46619-induced increases in pulmonary arterial and capillary pressures, pulmonary arterial and venous resistances, and lung weight. Methylene blue (1 microM), which inhibits the activation of soluble guanylate cyclase by NO, had an effect similar to TNF-alpha on the pulmonary response to U-46619 alone but was not additive to the effect of TNF-alpha. NG-monomethyl-L-arginine (270 microM), an inhibitor of NO generation, also enhanced the response to U-46619. Lung effluent levels of nitrite, the oxidation product of NO, were reduced after treatment with either TNF-alpha or NG-monomethyl-L-arginine compared with U-46619 alone. In addition, lungs isolated after TNF-alpha treatment showed decreased vasodilation in response to acetylcholine (10(-8)-10(-5) M) compared with control; however, vasodilation in response to L-arginine (10 mM) and nitroprusside (10(-6.3) and 10(-6) M), agents that promote NO release, was not decreased in TNF-alpha-treated lungs. The data indicate that TNF-alpha induces an increase in vascular constriction in response to U-46619 and a decrease in vasodilation in response to acetylcholine. The mechanism for the TNF-alpha-induced alteration in pulmonary vascular reactivity may be decreased generation of NO.     

Pulmonary vasodilation with structurally altered pulmonary vessels and pulmonary hypertension

To evaluate pulmonary vasodilation in a structurally altered pulmonary vascular bed, we gave endothelium-dependent (acetylcholine) and endothelium-independent [sodium nitroprusside, prostaglandin I2 (PGI2)] vasodilators in vivo and to isolated lobar pulmonary arteries from neonatal calves with severe pulmonary hypertension. Acetylcholine, administered by pulmonary artery infusion, decreased pulmonary arterial pressure from 120 +/- 7 to 71 +/- 6 mmHg and total pulmonary resistance from 29.4 +/- 2.6 to 10.4 +/- 0.9 mmHg.l-1.min without changing systemic arterial pressure (90 +/- 5 mmHg). Although both sodium nitroprusside and PGI2 lowered pulmonary arterial pressure to 86 +/- 4 and 96 +/- 4 mmHg, respectively, they also decreased systemic arterial pressure to 65 +/- 4 and 74 +/- 3 mmHg, respectively. Neither sodium nitroprusside nor PGI2 was as effective as acetylcholine at lowering total pulmonary resistance (18.0 +/- 3.6 and 19.1 +/- 2.2 mmHg.l-1.min, respectively). Right-to-left cardiac shunt through the foramen ovale was decreased by acetylcholine from 1.6 +/- 0.4 to 0.1 +/- 0.2 l/min but was not changed by sodium nitroprusside or PGI2. Isolated lobar pulmonary arteries from pulmonary hypertensive calves did not relax in response to acetylcholine, whereas isolated pulmonary arteries from age-matched control calves did relax in response to acetylcholine. Control and pulmonary hypertensive lobar pulmonary arteries relaxed equally well in response to sodium nitroprusside. We concluded that acetylcholine vasodilation was impaired in vitro in isolated lobar pulmonary arteries but was enhanced in vivo in resistance pulmonary arteries in neonatal calves with pulmonary hypertension.     

Inhibition of phosphodiesterase 1 augments the pulmonary vasodilator response to inhaled nitric oxide in awake lambs with acute pulmonary hypertension

Phosphodiesterase 1 (PDE1) modulates vascular tone and the development of tolerance to nitric oxide (NO)-releasing drugs in the systemic circulation. Any role of PDE1 in the pulmonary circulation remains largely uncertain. We measured the expression of genes encoding PDE1 isozymes in the pulmonary vasculature and examined whether or not selective inhibition of PDE1 by vinpocetine attenuates pulmonary hypertension and augments the pulmonary vasodilator response to inhaled NO in lambs. Using RT-PCR, we detected PDE1A, PDE1B, and PDE1C mRNAs in pulmonary arteries and veins isolated from healthy lambs. In 13 lambs, the thromboxane A(2) analog U-46619 was infused intravenously to increase mean pulmonary arterial pressure to 35 mmHg. Four animals received an intravenous infusion of vinpocetine at incremental doses of 0.3, 1, and 3 mg.kg(-1).h(-1). In nine lambs, inhaled NO was administered in a random order at 2, 5, 10, and 20 ppm before and after an intravenous infusion of 1 mg.kg(-1).h(-1) vinpocetine. Administration of vinpocetine did not alter pulmonary and systemic hemodynamics or transpulmonary cGMP or cAMP release. Inhaled NO selectively reduced mean pulmonary arterial pressure, pulmonary capillary pressure, and pulmonary vascular resistance index, while increasing transpulmonary cGMP release. The addition of vinpocetine enhanced pulmonary vasodilation and transpulmonary cGMP release induced by NO breathing without causing systemic vasodilation but did not prolong the duration of pulmonary vasodilation after NO inhalation was discontinued. Our findings demonstrate that selective inhibition of PDE1 augments the therapeutic efficacy of inhaled NO in an ovine model of acute chemically induced pulmonary hypertension.     

The endothelium-dependent and the endothelium-independent vasodilators in the isolated, perfused guinea pig heart.

The endothelium-dependent (acetylcholine, bradykinin, substance P) and the endothelium-independent (gliceryl trinirate, 3-morpholinsydnominine, sodium nitroprusside) vasodilators were studied in the Langendorff-perfused heart of the guinea pig. The involvement of prostanoids and EDRF in the endothelium-dependent responses were assessed by using indomethacin, an inhibitor of cyclooxygenase, and NG-nitro-L-Arginine, an inhibitor of NO synthase. The endothelium-independent agents were used as reference compounds. Both indomethacin and NG-nitro-L-Arginine elevated significantly baseline coronary perfusion pressure, indicating that prostanoids (most likely PGI2 and PGE2) and EDRF modulate the resting tone of the guinea pig coronary circulation. NG-nitro-L-Arginine, but not indomethacin, considerably reduced receptor-stimulated responses. It is concluded that acetylcholine, bradykinin or substance P-induced vasodilation is mediated by EDRF. In contrast, prostanoids do not contribute to endothelium-dependent responses. In addition, short-term tachyphylaxis to bolus injection of gliceryl trinitrate but not of sodium nitroprusside was demonstrated, suggesting that this preparation may be of value for studying nitrate tolerance.     

Differential effects of general anesthesia on cGMP-mediated pulmonary vasodilation.

We investigated the effects of an intravenous (pentobarbital sodium) and an inhalational (halothane) general anesthetic on guanosine 3',5'-cyclic monophosphate- (cGMP) mediated pulmonary vasodilation compared with responses measured in the conscious state. Multipoint pulmonary vascular pressure-flow plots were generated in the same nine dogs in the fully conscious state, during pentobarbital sodium anesthesia (30 mg/kg iv), and during halothane anesthesia (approximately 1.2% end tidal). Continuous intravenous infusions of bradykinin (2 micrograms.kg-1.min-1) and sodium nitroprusside (5 micrograms.kg-1.min-1) were utilized to stimulate endothelium-dependent and -independent cGMP-mediated pulmonary vasodilation, respectively. In the conscious state, both bradykinin and nitroprusside decreased (P less than 0.01) the pulmonary vascular pressure gradient (pulmonary arterial pressure-pulmonary arterial wedge pressure) over the entire range of flows studied; i.e., bradykinin and nitroprusside caused active flow-independent pulmonary vasodilation. Pulmonary vasodilator responses to bradykinin (P less than 0.01) and nitroprusside (P less than 0.05) were also observed during pentobarbital anesthesia. In contrast, during halothane anesthesia, the pulmonary vasodilator responses to both bradykinin and nitroprusside were abolished. These results indicate that, compared with the conscious state, cGMP-mediated pulmonary vasodilation is preserved during pentobarbital anesthesia but is abolished during halothane anesthesia.     

Pulmonary vasodilator responses to vasoactive intestinal peptide in the cat

We investigated the effects of vasoactive intestinal peptide (VIP) in the feline pulmonary vascular bed under conditions of controlled pulmonary blood flow when pulmonary vascular tone was at base-line levels and when vascular resistance was elevated. Under base-line conditions, VIP caused small but significant reductions in lobar arterial pressure without affecting left atrial pressure. Decreases in lobar arterial pressure in response to VIP were greater and were dose related when lobar vascular resistance was increased by intralobar infusion of U 46619, a stable prostaglandin endoperoxide analogue. Acetylcholine and isoproterenol also caused significant decreases in lobar arterial pressure under base-line conditions, and responses to these agents were enhanced when lobar vascular tone was elevated. Moreover, when doses of these agents are expressed in nanomoles, acetylcholine and isoproterenol were more potent than VIP in decreasing lobar arterial pressure. Responses to VIP were longer in duration with a slower onset than were responses to acetylcholine or isoproterenol. Pulmonary vasodilator responses to VIP were unchanged by indomethacin, atropine, or propranolol. The present data demonstrate that VIP has vasodilator activity in the pulmonary vascular bed and that responses are dependent on the existing level of vasoconstrictor tone. These studies indicate that this peptide is less potent than acetylcholine or isoproterenol in dilating the feline pulmonary vascular bed and that responses to VIP are not dependent on a muscarinic or beta-adrenergic mechanism or release of a dilator prostaglandin.     

Pulmonary vasodilation by inhaled nitric oxide after endothelial injury.

Inhaled nitric oxide gas (NO) has recently been shown to reverse experimentally induced pulmonary vasoconstriction. To examine the effect of free radical injury and methylene blue exposure on inhaled NO-induced pulmonary vasodilation we studied ventilated rabbit lungs perfused with Krebs solution containing 3% dextran and indomethacin. When NO gas (120 ppm) was added to the inhaled mixture for 3 min, the elevated pulmonary arterial perfusion pressure (Ppa) induced by the thromboxane analogue U-46619 was significantly reduced [8 +/- 2 (SE) mmHg]. Acetylcholine similarly reduced Ppa (9 +/- 1 mmHg). After free radical injury and methylene blue exposure, inhaled NO again produced significant vasodilation (5 +/- 1 and 9 +/- 2 mmHg, respectively), but acetylcholine resulted in an increase in Ppa (-9 +/- 3 and -4 +/- 1 mmHg, respectively). These data demonstrate that pulmonary vasodilation produced by inhaled NO is unaffected by free radical injury or methylene blue in the intact lung despite concomitant reversal of acetylcholine-induced vasodilation.     

L-NAME enhances responses to atrial natriuretic peptide in the pulmonary vascular bed of the cat.

This study investigated the hypothesis that atrial natriuretic peptide (ANP) responses are mediated by particulate guanylate cyclase in the pulmonary vascular bed of the cat. When tone in the pulmonary vascular bed was raised to a high steady level with the thromboxane mimic U-46619, injections of ANP caused dose-related decreases in lobar arterial pressure. After administration of HS-142-1, an ANP-A- and ANP-B-receptor antagonist, vasodilator responses to ANP were reduced. The nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) enhanced ANP vasodilator responses, suggesting that inhibition of NO modulates ANP responses. L-NAME administration with constant 8-bromo-cGMP infusion attenuated the increased vasodilator response to ANP, suggesting that supersensitivity to ANP occurs upstream to activation of a cGMP-dependent protein kinase. In pulmonary arterial rings, ANP produced concentration-related vasorelaxant responses with and without endothelium. Methylene blue, L-NAME, or N(omega)-monomethyl-L-arginine did not alter ANP vasorelaxant responses. These data show that ANP supersensitivity observed in the intact pulmonary vascular bed is not seen in isolated pulmonary arterial segments, suggesting that it may only occur in resistance vessel elements. These results suggest that ANP responses occur through activation of ANP-A and/or -B receptors in an endothelium-independent manner and are modulated by NO in resistance vessel elements in the pulmonary vascular bed of the cat.     

Acetylcholine's effect on vascular resistance and compliance in the pulmonary circulation

Acetylcholine's effect on the distribution of vascular resistance and compliance in the canine pulmonary circulation was determined under control and elevated vascular tone by the arterial, venous, and double occlusion techniques in isolated blood-perfused dog lungs at both constant flow and constant pressure. Large and small blood vessel resistances and compliances were studied in lungs given concentrations of acetylcholine ranging from 2.0 ng/ml to 200 micrograms/ml. The results of this study indicate that acetylcholine dilates large arteries at low concentrations (less than or equal to 20 ng/ml) and constricts small and large veins at concentrations of at least 2 micrograms/ml. Characterization of acetylcholine's effects at constant pulmonary blood flow indicates that 1) large artery vasodilation may be endothelial-derived relaxing factor-mediated because the dilation is blocked with methylene blue; 2) a vasodilator of the arachidonic acid cascade (blocked by ibuprofen), probably prostacyclin, lessens acetylcholine's pressor effects; 3) when vascular tone was increased, acetylcholine's hemodynamic effects were attenuated; and 4) acetylcholine decreased middle compartment and large vessle compliance under control but not elevated vascular tone. Under constant pressure at control vascular tone acetylcholine increases resistance in all segments except the large artery, and at elevated vascular tone the pressor effects were enhanced, and large artery resistance was increased.     

Pulmonary and systemic vasodilator responses to the soluble guanylyl cyclase activator, BAY 60-2770, are not dependent on endogenous nitric oxide or reduced heme

4-({(4-Carboxybutyl)[2-(5-fluoro-2-{[4'-(trifluoromethyl)biphenyl-4-yl]methoxy}phenyl)ethyl]amino}methyl)benzoic acid (BAY 60-2770) is a nitric oxide (NO)-independent activator of soluble guanylyl cyclase (sGC) that increases the catalytic activity of the heme-oxidized or heme-free form of the enzyme. In this study, responses to intravenous injections of the sGC activator BAY 60-2770 were investigated under baseline and elevated tone conditions induced by the thromboxane mimic U-46619 when NO synthesis was inhibited by N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME), when sGC activity was inhibited by 1H-[1,2,4]-oxadizaolo[4,3]quinoxaline-1-one (ODQ), an agent that oxidizes sGC, and in animals with monocrotaline-induced pulmonary hypertension. The intravenous injections of BAY 60-2770 under baseline conditions caused small decreases in pulmonary arterial pressure, larger decreases in systemic arterial pressure, and no change or small increases in cardiac output. Under elevated tone conditions during infusion of U-46619, intravenous injections of BAY 60-2770 caused larger decreases in pulmonary arterial pressure, smaller decreases in systemic arterial pressure, and increases in cardiac output. Pulmonary vasodilator responses to BAY 60-2770 were enhanced by L-NAME or by ODQ in a dose that attenuated responses to the NO donor sodium nitroprusside. ODQ had no significant effect on baseline pressures and attenuated pulmonary and systemic vasodilator responses to the sGC stimulator BAY 41-8543 2-{1-[2-(fluorophenyl)methyl]-1H-pyrazolo[3,4-b]pyridin-3-yl}-5(4-morpholinyl)-4,6-pyrimidinediamine. BAY 60-2770 and sodium nitroprusside decreased pulmonary and systemic arterial pressures in monocrotaline-treated rats in a nonselective manner. The present data show that BAY 60-2770 has vasodilator activity in the pulmonary and systemic vascular beds that is enhanced by ODQ and NOS inhibition, suggesting that the heme-oxidized form of sGC can be activated in vivo in an NO-independent manner to promote vasodilation. These results show that BAY 60-2770 and sodium nitroprusside decreased pulmonary and systemic arterial pressures in monocrotaline-treated rats, suggesting that BAY 60-2770 does not have selective pulmonary vasodilator activity in animals with monocrotaline-induced pulmonary hypertension.     

K+ channel pulmonary vasodilation in fetal lambs: role of endothelium-derived nitric oxide.

To define the role and mechanism of action of K+ channels in regulating fetal pulmonary vascular tone, we studied the hemodynamic effects of pinacidil (a K+ channel activator) and glibenclamide (a K+ channel blocker). The effects of pinacidil were compared with those of acetylcholine [an endothelium-derived relaxing factor- (EDRF) dependent pulmonary vasodilator] and 8-bromoguanosine 3',5'-cyclic monophosphate (8-bromo-cGMP, an EDRF-independent pulmonary vasodilator) before and after treatment with N omega-nitro-L-arginine [a competitive inhibitor of an EDRF, endothelium-derived nitric oxide (EDNO), synthesis], or L-arginine (the substrate for the formation of EDNO). In 14 unanesthetized fetal lambs in utero, catheters were inserted into the fetal pulmonary artery, descending aorta, left atrium, and superior vena cava to measure pressures and administer drugs. An ultrasonic flow transducer was placed around the left pulmonary artery to measure flow (QP) continuously. In eight animals, pinacidil, acetylcholine, and 8-bromo-cGMP caused similar acute maximal increases in QP of 128, 137, and 155 ml/min, respectively. After a 60-min infusion of N omega-nitro-L-arginine (2.07 +/- 0.27 mg.kg-1.min-1), the increase in QP caused by acetylcholine and pinacidil was significantly attenuated, by 84 and 68%, respectively, with only a 10% attenuation of the increase in QP caused by 8-bromo-cGMP. In six additional N omega-nitro-L-arginine-pretreated fetal lambs, infusion of L-arginine (32.2 +/- 4.3 mg.kg-1.min-1) restored the vasodilatory effects of acetylcholine and pinacidil. A 20-min infusion of glibenclamide (n = 6; 0.64 +/- 0.07 mg.kg-1.min-1) blocked the vasodilation by pinacidil but not acetylcholine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise restores coronary vascular function independent of myogenic tone or hyperglycemic status in db/db mice

Regulation of coronary function in diabetic hearts is an important component in preventing ischemic cardiac events but remains poorly studied. Exercise is recommended in the management of diabetes, but its effects on diabetic coronary function are relatively unknown. We investigated coronary artery myogenic tone and endothelial function, essential elements in maintaining vascular fluid dynamics in the myocardium. We hypothesized that exercise reduces pressure-induced myogenic constriction of coronary arteries while improving endothelial function in db/db mice, a model of type 2 diabetes. We used pressurized mouse coronary arteries isolated from hearts of control and db/db mice that were sedentary or exercised for 1 h/day on a motorized exercise-wheel system (set at 5.2 m/day, 5 days/wk). Exercise caused a approximately 10% weight loss in db/db mice and decreased whole body oxidative stress, as measured by plasma 8-isoprostane levels, but failed to improve hyperglycemia or plasma insulin levels. Exercise did not alter myogenic regulation of arterial diameter stimulated by increased transmural pressure, nor did it alter smooth muscle responses to U-46619 (a thromboxane agonist) or sodium nitroprusside (an endothelium-independent dilator). Moderate levels of exercise restored ACh-simulated, endothelium-dependent coronary artery vasodilation in db/db mice and increased expression of Mn SOD and decreased nitrotyrosine levels in hearts of db/db mice. We conclude that the vascular benefits of moderate levels of exercise were independent of changes in myogenic tone or hyperglycemic status and primarily involved increased nitric oxide bioavailability in the coronary microcirculation.     

Atriopeptin II relaxes and elevates cGMP in bovine pulmonary artery but not vein

Atriopeptin II, a 23-amino acid synthetic peptide fragment of atrial natriuretic factor, caused an endothelium-independent relaxation of isolated precontracted rings of bovine intrapulmonary artery that was accompanied by the concomitant accumulation of guanosine 3',5'-cyclic monophosphate (cGMP) but not adenosine 3',5'-cyclic monophosphate. In contrast, rings of intrapulmonary vein were unaffected by atriopeptin II whether or not endothelium was present. Whereas methylene blue, an inhibitor of soluble guanylate cyclase, abolishes endothelium-dependent and independent arterial relaxation and cGMP accumulation in response to acetylcholine and glyceryl trinitrate, respectively, methylene blue failed to alter these responses to atriopeptin II. Similarly, the effects of atriopeptin II were unaltered by propranolol, indomethacin, or atropine. These results indicate that relaxation elicited by atriopeptin II may be selective for arterial smooth muscle receptors, does not require endothelial cells, and does not involve the soluble form of guanylate cyclase, although cGMP accumulation is stimulated.     

Attenuation of endothelium-dependent relaxation in mesenteric artery during noise-induced hypertension

The present study was designed to determine whether there is a causal relationship between noise-induced hypertension and changes of endothelial function. Rats were exposed to noise stress (100 dB, 1 kHz, 4 h/day, 6 days/week) for 1–4 weeks. The systolic blood pressure was significantly increased after rats were exposed to noise stress for 3 weeks. The relaxant responses of isolated mesenteric arterial rings to endothelium-dependent vasodilators (A23187 and acetylcholine) in noise-treated rats were significantly less than those in control rats. This difference in response to acetylcholine still existed in the presence of methylene blue or N-nitro-L-arginine. On the other hand, the responses to the endothelium-independent vasodilator nitroglycerin were not affected in rats exposed to noise stress. The attenuation to endothelium-dependent vasodilators during noise stress may result in increasing peripheral vascular resistance and thus elevate blood pressure. This indicates that noise-induced hypertension may be partly due to the alterations of endothelial activity.     

rhVEGF treatment preserves pulmonary vascular reactivity and structure in an experimental model of pulmonary hypertension in fetal sheep

We have previously shown that lung VEGF expression is decreased in a fetal lamb model of PPHN and that VEGF165 inhibition causes severe pulmonary hypertension in fetal lambs. Therefore, we hypothesized that treatment with rhVEGF165 would preserve endothelium-dependent vasodilation and reduce the severity of pulmonary vascular remodeling in an experimental model of PPHN. We studied the effects of daily intrapulmonary infusions of rhVEGF after partial ligation of the ductus arteriosus (DA). We performed surgery in 24 late-gestation fetal lambs and placed catheters in the main pulmonary artery, left atrium, and aorta for pressure measurements and in the left pulmonary artery for drug infusions. A pressure transducer was placed around the LPA to measure blood flow to the left lung (Qp), and the DA was surgically constricted to induce pulmonary hypertension. rhVEGF165 or vehicle was infused for 7 or 14 days. ACh or 8-BrcGMP was infused on days 2 and 13 to assess endothelium-dependent and -independent vasodilation, respectively. ACh-induced vasodilation was reduced in PPHN lambs after 14 days (change in Qp from baseline, 106% vs. 11%). In contrast, the response to ACh was preserved in lambs treated with rhVEGF (change in Qp, 94% vs. 90%). Pulmonary vasodilation to 8-BrcGMP was not altered in PPHN lambs or enhanced by VEGF treatment. rhVEGF treatment increased expression of lung eNOS protein and decreased pulmonary artery wall thickness by 34% vs. PPHN lambs. We conclude that VEGF165 preserves endothelium-dependent vasodilation, upregulates eNOS expression, and reduces the severity of pulmonary vascular remodeling in experimental PPHN.     

Differential effects of PACAP and VIP on the pulmonary and hindquarters vascular beds of the cat.

Responses to pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide derived from ovine hypothalamus with 68% sequence homology with vasoactive intestinal polypeptide (VIP), were investigated in the pulmonary and hindquarters vascular beds of the anesthetized cat under conditions of controlled blood flow. Injection of the peptide into the perfused lung lobe under elevated tone conditions produced dose-dependent decreases in lobar arterial pressure that were accompanied by biphasic changes in systemic arterial pressure characterized by an initial decrease followed by a secondary increase in pressure. When compared with other vasodilator agents in the pulmonary vascular bed, the relative order of potency was isoproterenol greater than PACAP greater than acetylcholine greater than calcitonin gene-related peptide greater than VIP. In the hindquarters vascular bed, intra-arterial injections of PACAP produced biphasic changes in hindquarters perfusion pressure characterized by initial decreases followed by secondary increases, which were accompanied by biphasic changes in systemic arterial pressure. In terms of relative vasodilator activity in the hindlimb, the order of relative potency was isoproterenol greater than acetylcholine greater than calcitonin gene-related peptide greater than VIP greater than PACAP. PACAP was the only agent that caused a secondary vasoconstrictor response in the hindlimb and produced biphasic changes in systemic arterial pressure. D-Phe2-VIP, a VIP receptor antagonist, blocked the hindquarters vasodilation in response to VIP but had no effect on responses to PACAP. The present investigation shows that PACAP produces pulmonary vasodilation, as well as dilation, and vasoconstriction in the systemic (hindlimb) vascular bed.(ABSTRACT TRUNCATED AT 250 WORDS)