Peroxynitrite does not impair pulmonary and systemic vascular responses.

The effects of peroxynitrite (ONOO-) on vascular responses were investigated in the systemic and hindquarters vascular bed and in the isolated perfused rat lung. Intravenous injections of ONOO- decreased systemic arterial pressure, and injections of ONOO- into the hindquarters decreased perfusion pressure in a dose-related manner. Injections of ONOO- into the lung perfusion circuit increased pulmonary arterial perfusion pressure. Responses to ONOO- were rapid in onset, short in duration, and repeatable without exhibiting tachyphylaxis. Repeated injections of ONOO- did not alter systemic, hindquarters, or pulmonary responses to endothelium-dependent vasodilators or other vasoactive agonists and did not alter the hypoxic pulmonary vasoconstrictor response. Injections of sodium nitrate or nitrite or decomposed ONOO- had little effect on vascular pressures. Pulmonary and hindquarters responses to ONOO- were not altered by a cyclooxygenase inhibitor in a dose that attenuated responses to arachidonic acid. These results demonstrate that ONOO- has significant pulmonary vasoconstrictor, systemic vasodepressor, and vasodilator activity; that short-term repeated exposure does impair vascular responsiveness; and that responses to ONOO- are not dependent on cyclooxygenase product release.

Comparison of responses to novel nitric oxide donors in the feline pulmonary vascular bed.

Pulmonary vascular responses to the novel diazeniumdiolate nitric oxide (NO) donors diethylamine/NO, diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt, were investigated and compared in the intact-chest cat. Under conditions of controlled blood flow, when tone in the pulmonary vascular bed had been raised to a high steady level, intralobar injections of diethylamine/NO (0.3-10 microg), diethylenetriamine/NO (10-30 microg), spermine/NO (10-30 microg), sulfite/NO (10-30 microg), and angeli's salt (10-30 microg) caused dose-related decreases in lobar arterial pressure without changing left atrial pressure. In terms of relative vasodilator activity in the pulmonary vascular bed, the dose of the compounds that decreased lobar arterial pressure 4 mm Hg (ED(4) mm Hg) was significantly lower for diethylamine/NO compared to S-nitroso-N-acetylpenicillamine which was significantly less than diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt. The half-life of the vasodilator responses, as measured by 50% response recovery time, to diethylamine/NO, diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt was similar for doses with similar magnitudes of vasodilation, while the half-life to S-nitroso-N-acetylpenicillamine was significantly less than the diazeniumdiolate NO donors. The present data demonstrate that the diazeniumdiolate NO donors diethylamine/NO, diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt have potent but relatively short-lasting vasodilator activity in the pulmonary vascular bed of the cat.

Analysis of vasodilator responses to novel nitric oxide donors in the hindquarters vascular bed of the cat.

Controlled release of nitric oxide (NO*) may be useful in the treatment of a variety of vascular disorders. NO* donors of the diazeniumdiolate family with different rates of spontaneous NO* release have been synthesized. In the current study responses to seven diazeniumdiolate NO* donors (DEA/NO*, DETA/NO*, OXI/NO*, PIPERAZI/NO*, PROLI/NO*, SPER/NO*, and SULFI/NO*) were investigated in the hindquarters vascular bed of the cat. Intravenous injections of all NO* donors caused dose-dependent decreases in systemic arterial pressure and the rank order of potency was SNP > DEA/NO* > PIPERAZI/NO* > SPER/NO* > PROLI/NO* > OXI/NO*. Injections of all NO* donors into the hindlimb perfusion circuit caused dose-related decreases in hindquarters perfusion pressure that were similar to the order of potency in decreasing systemic arterial pressure. The rank order of the time required for the response to return to 50% of the maximal decrease in pressure (T(1/2)) and total duration of action of the NO* donors was SPER/NO* > PIPERAZI/NO* > DEA/NO* > OXI/NO* > DETA/NO* > PROLI/NO* > SULFI/NO*. After treatment with the NO* synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (100 mg/kg, i.v.), hindlimb vasodilator responses to the NO* donors were not significantly different, but vasodilator responses to acetylcholine were significantly reduced. After treatment with zaprinast (2 mg/kg, i.v.), a type V cyclic 3',5'-guanosine monophosphate-specific phosphodiesterase inhibitor, the duration of vasodilator responses to the NO* donors, as measured by T(1/2), was increased significantly, whereas the duration of the response to the beta2-adrenergic receptor agonist albuterol was unchanged. These data suggest that diazeniumdiolate NO* donors are endothelium-independent, directly stimulate soluble guanylate cyclase, and decrease vascular resistance by increasing cyclic 3',5'-guanosine monophosphate levels in the hindquarters vascular bed of the cat.

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.

Effects of PKC isozyme inhibitors on constrictor responses in the feline pulmonary vascular bed.

The effects of Gö-6976, a Ca(2+)-dependent protein kinase C (PKC) isozyme inhibitor, and rottlerin, a PKC-delta isozyme/calmodulin (CaM)-dependent kinase III inhibitor, on responses to vasopressor agents were investigated in the feline pulmonary vascular bed. Injections of angiotensin II, norepinephrine (NE), serotonin, BAY K 8644, and U-46619 into the lobar arterial constant blood flow perfusion circuit caused increases in pressure. Gö-6976 reduced responses to angiotensin II; however, it did not alter responses to serotonin, NE, or U-46619, whereas Gö-6976 enhanced BAY K 8644 responses. Rottlerin reduced responses to angiotensin II and NE, did not alter responses to serotonin or U-46619, and enhanced responses to BAY K 8644. Immunohistochemistry of feline pulmonary arterial smooth muscle cells demonstrated localization of PKC-alpha and -delta isozymes in response to phorbol 12-myristate 13-acetate and angiotensin II. Localization of PKC-alpha and -delta isozymes decreased with administration of Gö-6976 and rottlerin, respectively. These data suggest that activation of Ca(2+)-dependent PKC isozymes and Ca(2+)-independent PKC-delta isozyme/CaM-dependent kinase III mediate angiotensin II responses. These data further suggest that Ca(2+)-independent PKC-delta isozyme/CaM-dependent kinase III mediate responses to NE. A rottlerin- or Gö-6976-sensitive mechanism is not involved in mediating responses to serotonin and U-46619, but these PKC isozyme inhibitors enhanced BAY K 8644 responses in the feline pulmonary vascular bed.

Comparison of responses to siguazodan, rolipram, and zaprinast in the feline pulmonary vascular bed.

The present study was undertaken to investigate and compare responses to the cyclic nucleotide phosphodiesterase inhibitors siguazodan (type III, guanosine 3',5'-cyclic monophosphate (cGMP)-inhibited adenosine 3',5'-cyclic monophosphate (cAMP)), rolipram (type IV, cAMP-specific), and zaprinast (type V, cGMP-specific) in the feline pulmonary vascular bed. When tone in the pulmonary vascular bed was raised to a high steady level with a constant infusion of the thromboxane mimic U46619 (9,11-dideoxy-11, alpha9alpha-epoxymethano prostaglandin F(2alpha)), intralobar injections of the three phosphodiesterase inhibitors caused dose-related decreases in lobar arterial pressure. In terms of relative vasodilator activity, rolipram was more potent at higher doses than siguazodan, which was more potent than zaprinast. The duration of the pulmonary vasodilator response to zaprinast was shorter than for siguazodan or rolipram. Furthermore, siguazodan and rolipram, but not zaprinast, decreased systemic arterial pressure when injected into the perfused lobar artery in the range of doses studied. The present data demonstrate that the three phosphodiesterase inhibitors have potent, long-lasting vasodilator activity in the pulmonary vascular bed of the cat. These data suggest that there is rapid turnover of cAMP and cGMP in the pulmonary circulation and indicate that phosphodiesterase enzyme types III, IV, and V may play an important role in the regulation of vasomotor tone in the feline lung.

L-163,491 is a partial angiotensin AT(1) receptor agonist in the hindquarters vascular bed of the cat.

Responses to the nonpeptide angiotensin II agonist 5, 7-Dimethyl-2-ethyl-3-[[2'-([butyloxycarbonyl) aminosulfonyl]-5'-(3-methyoxybenzyl)-[1, 1'-biphenyl]-4-yl]methyl]-3H-imidazo[4,5-b]pyridine (L-163,491) were investigated and compared with responses to angiotensin II, angiotensin IV and norepinephrine in the hindquarters vascular bed of the cat under constant-flow conditions. Injections of L-163,491 into the hindquarter perfusion circuit caused dose-related increases in hindquarters perfusion pressure. In relative terms, angiotensin II was more potent than norepinephrine, which was more potent than angiotensin IV and L-163,491 in increasing hindlimb vascular resistance. The slope of the dose-response curve for L-163,491 was flat, while the apparent affinity of the compound for angiotensin AT(1) receptors was slightly greater than angiotensin IV. Responses to L-163,491 were inhibited by the angiotensin AT(1) receptor antagonist DuP 532 (2-propyl-4-pentafluoroethyl-1-[2'-(1H-tetrazol-5-yl)bipheny l-4-yl)me thyl]imidazole-5-carboxylic acid) and were not altered by the angiotensin AT(2) receptor antagonist PD123,319 (S(+)-1-[[4-(Dimethylamino)-3-methylphenyl]methyl]-5-(diphenylacetyl+ ++) -4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid ditribluoroacetate). However, the increase in hindlimb perfusion pressure in response to angiotensin II and angiotensin IV was significantly decreased following injection of L-163,491. These data suggest that the nonpeptide angiotensin analog L-163,491 has partial agonist activity, which is dependent on the stimulation of angiotensin AT(1) receptors in the hindquarters vascular bed of the cat.

Analysis of responses of garlic derivatives in the pulmonary vascular bed of the rat.

Allicin, an extract from garlic, has been shown to be a systemic and pulmonary arterial vasodilator that acts by an unknown mechanism. In the present experiments, pulmonary vascular responses to allicin (10-100 microg), allyl mercaptan (0.3-1 mg), and diallyl disulfide (0.3-1 mg) were studied in the isolated lung of the rat under constant-flow conditions. When baseline tone in the pulmonary vascular bed of the rat was raised to a high-steady level with the thromboxane A(2) mimic U-46619, dose-related decreases in pulmonary arterial pressure were observed. In terms of the mechanism of action of allicin vasodilator activity in the rat, responses to allicin were not significantly different after administration of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester, the K(ATP)(+) channel antagonist U-37883A, or the cyclooxygenase inhibitor sodium meclofenamate, or when lung ventilation was interrupted. These data show that allicin has significant vasodilator activity in the pulmonary vascular bed of the rat, whereas allyl mercaptan and diallyl disulfide produced no significant changes in pulmonary arterial perfusion pressure. The present data suggest that pulmonary vasodilator responses to allicin are independent of the synthesis of nitric oxide, ATP-sensitive K(+) channels, activation of cyclooxygenase enzyme, or changes in bronchomotor tone in the pulmonary vascular bed of the rat.

Capillary recruitment and transit time in the rat lung.

Increasing pulmonary blood flow and the associated rise in capillary perfusion pressure cause capillary recruitment. The resulting increase in capillary volume limits the decrease in capillary transit time. We hypothesize that small species with relatively high resting metabolic rates are more likely to utilize a larger fraction of gas-exchange reserve at rest. Without reserve, we anticipate that capillary transit time will decrease rapidly as pulmonary blood flow rises. To test this hypothesis, we measured capillary recruitment and transit time in isolated rat lungs. As flow increased, transit time decreased, and capillaries were recruited. The decrease in transit time was limited by an increase in the homogeneity of the transit time distribution and an increased capillary volume due, in part, to recruitment. The recruitable capillaries, however, were nearly completely perfused at flow rates and pressures that were less than basal for the intact animal. This suggests that a limited reserve of recruitable capillaries in the lungs of species with high resting metabolic rates may contribute to their inability to raise O2 consumption manyfold above basal values.

Responses to L-163,491, a nonpeptide angiotensin II mimic, in the pulmonary vascular bed of the cat.

Pulmonary vascular responses to 5,7-dimethyl-2-ethyl-3-[[2'-[butyloxycarbonyl)amino-sulfonyl]-5'-(3-meth oxybenzyl)-[1,1'-biphenyl]-4-yl]methyl]-3H-imidazo[4,5-b]pyridine (L-163,491), a novel nonpeptide angiotensin agonist, and angiotensin IV, the 3-8 amino acid fragment of angiotensin, were compared with responses to angiotensin II. Responses were investigated in the intact-chest cat under conditions of controlled blood flow and intralobar injections of angiotensin II, L-163,491, and angiotensin IV caused dose-related increases in lobar arterial pressure. When comparable in lobar arterial pressure of the three agents were examined, L-163,491 was approximately 3-fold less potent than angiotensin IV and approximately 100-fold less potent than angiotensin II when doses are expressed on a nmol basis. DuP 532, 2-propyl-4-pentafluoroethyl-1-([2'-(1H-tetrazol-5-yl)bipheny l-4]-methyl)imidazole-5-carboxylic acid, an angiotensin II AT1 receptor antagonist, reduced pulmonary vasoconstrictor responses to angiotensin II, angiotensin IV and L-163,491, but did not significantly change pressor responses to serotonin, norepinephrine, or the thromboxane A2 mimic, U46619. PD 123319, an angiotensin II subtype 2 receptor antagonist, did not significantly change pressor responses to L-163,491, angiotensin II, or angiotensin IV. Captopril, the angiotensin-converting enzyme inhibitor, decreased pulmonary vasoconstrictor responses to angiotensin I and enhanced vasodilator responses to bradykinin, but did not significantly change pressor responses to L-163,491. These data show that L-163,491 significant angiotensin AT1 receptor-mediated vasoconstrictor activity in the pulmonary vascular bed of the cat. These data also show the nonpeptide agonist has 3-fold less activity compared to angiotensin IV and is approximately 100-fold less potent than angiotensin II in the feline pulmonary vascular bed.