Bracken J. DeWitt

Comparison of responses to adrenomedullin and calcitonin gene-related peptide in the pulmonary vascular bed of the cat

Pulmonary vascular responses to the newly discovered hypotensive peptide, adrenomedullin, were compared with responses to the structurally related peptides, calcitonin gene-related peptide (CGRP) and amylin, 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 adrenomedullin (0.03-1 nmol), CGRP (0.1-3 nmol), and amylin (0.1 and 0.3 nmol) 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 peptide that decreased lobar arterial pressure 7.5 mm Hg (ED7.5 mm Hg) was significantly lower for adrenomedullin than for CGRP. The duration of the pulmonary vasodilator responses to CGRP was longer than for adrenomedullin, and both peptides decreased systemic arterial pressure when injected into the perfused lobar artery in the higher doses studied. The present data demonstrate that synthetic human adrenomedullin and CGRP have potent but relatively short-lasting vasodilator activity in the pulmonary vascular bed. These data show also that amylin, a structurally related pancreatic peptide, also has significant pulmonary vasodilator activity.

Synthetic human adrenomedullin and ADM15-52 have potent short-lasting vasodilator activity in the pulmonary vascular bed of the cat

Responses to synthetic human adrenomedullin, a novel hypotensive peptide localized in several organ systems, including the lung, and the carboxy terminal 15-52 amino acid fragment of adrenomedullin (ADM15-52) were investigated in the pulmonary vascular bed of the intact-chest cat. Under constant flow conditions when baseline tone in the pulmonary vascular bed was raised to a high steady level, injections of adrenomedullin and ADM15-52 into the perfused lobar artery in doses of 0.1-1 nmol, caused significant dose-related decreases in lobar arterial pressure. Since left atrial pressure was unchanged, the decreases in lobar arterial pressure reflect decreases in pulmonary lobar vascular resistance. Adrenomedullin and ADM15-52 exhibited similar vasodilator activity and were approximately 3-fold more potent than bradykinin in the pulmonary vascular bed of the cat. Pulmonary vasodilator responses to adrenomedullin and ADM15-52 were rapid in onset and lasted for 150-200 sec, depending on the dose of the peptide injected. The present results demonstrate that synthetic human adrenomedullin and ADM15-52 possess potent, short-lasting vasodilator activity in the pulmonary vascular bed of the cat and suggest that amino acids 15-52 in the peptide are important for the expression of vasodilator activity in the pulmonary vascular bed of the cat.

des-Arg9-bradykinin produces tone-dependent kinin B1 receptor-mediated responses in the pulmonary vascular bed.

Responses to des-Arg9-bradykinin, a selective kinin B1 receptor agonist, were characterized in the pulmonary vascular bed of the intact-chest cat. Injections of des-Arg9-bradykinin into the perfused lobar artery under low-resting tone conditions caused dose-related increases in lobar arterial pressure; whereas in the same experiment under elevated tone conditions, injections of the B1 agonist caused dose-related decreases in lobar arterial pressure. Vasoconstrictor responses to des-Arg9-bradykinin under low-tone conditions and vasodilator responses under elevated-tone conditions were antagonized by des-Arg9,[Leu8]-bradykinin, a kinin B1 receptor antagonist, whereas responses under low- and high-tone conditions were not altered by Hoe 140, a kinin B2 receptor antagonist. Vasoconstrictor responses to des-Arg9-bradykinin under low-tone conditions were attenuated by phentolamine, prazosin, and reserpine but not by sodium meclofenamate, suggesting that release of catecholamines and activation of alpha-adrenergic receptors are involved. Pulmonary vasodilator responses under elevated-tone conditions were inhibited by N omega-nitro-L-arginine methyl ester, suggesting that des-Arg9-bradykinin stimulates the release of nitric oxide, whereas meclofenamate and U-37883A, a nonsulfonylurea ATP-sensitive K+ channel antagonist, did not alter vasodilator responses to the B1 receptor agonist. These results suggest that vasoconstrictor responses to des-Arg9-bradykinin under low-tone conditions are mediated by the activation of kinin B1 receptors, the release of catecholamines within the lung, and the activation of alpha-adrenergic receptors, whereas vasodilator responses under elevated tone conditions are mediated by activation of B1 receptors and the release of nitric oxide from the endothelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of responses to pituitary adenylate cyclase activating peptides 38 and 27 in the pulmonary vascular bed of the cat

Responses to pituitary adenylate cyclase activating polypeptide (PACAP)-38 were investigated and compared with responses to PACAP-27 and vasoactive intestinal polypeptide (VIP) in the pulmonary vascular bed of the intact-chest cat under constant flow conditions. Under low resting tone baseline conditions, injections of PACAP-38 had little or no effect on lobar arterial pressure; however, when tone in the pulmonary vascular bed was raised to a high steady level (35-40 mm Hg) with U46619, intralobar injections of PACAP-38 caused dose-related decreases in lobar arterial pressure without altering left atrial pressure. The peptide induced biphasic changes in systemic arterial pressure. PACAP-38 was more potent than VIP in decreasing lobar arterial pressure, and both peptides were significantly less potent than PACAP-27 in dilating the pulmonary vascular bed. The present data show that PACAP-38 has significant vasodilator activity in the pulmonary vascular bed of the cat, and that the 27 amino acid form of the peptide is approximately 3-fold more potent than PACAP-38.

Pulmonary Vascular Responses to Ma Huang Extract

OBJECTIVE To test the hypothesis that ma huang induces a pressor response in the pulmonary vascular bed of the cat by activating alpha(1)-adrenergic receptors DESIGN Prospective vehicle-controlled study. SETTING Research laboratory at Texas Tech University School of Medicine, Lubbock, TX. SUBJECTS Intact chest preparation; adult mongrel cats. INTERVENTIONS The effects of phentolamine, a nonselective alpha receptor blocker, and prazosin, an alpha(1) selective antagonist, were investigated on pulmonary arterial responses to ma huang, phenylepherine, norepinephrine, and U-46619, a thromboxane A(2) mimic. MEASUREMENTS AND MAIN RESULTS Lobar arterial perfusion pressure was continuously monitored, electronically averaged, and recorded with constant flow in the isolated left lower lobe vascular bed of the cat. Phentolamine and prazosin significantly reduced vasoconstrictor pulmonary perfusion pressure increases induced by ma huang. CONCLUSIONS Ma huang has significant vasopressor activity in the pulmonary vascular bed of the cat mediated predominantly by alpha(1)-adrenergic receptor activation.

Differential effects of glibenclamide on responses to thromboxane A2 mimic, U46619, in the pulmonary and hindquarters vascular beds of the cat

The inhibitory effects of the oral sulfonylurea, glibenclamide, on vasoconstrictor responses to the thromboxane A2 mimic, U46619, were investigated in the pulmonary and hindquarters vascular beds of the cat under constant flow conditions. When lobar arterial tone was at resting conditions (14 +/- 2 mm Hg), intralobar injections of U46619, prostaglandin F2alpha, prostaglandin D2, angiotensin II, norepinephrine, and BAY K 8644 caused dose-related increases in lobar arterial pressure without altering left atrial pressure. Following an intralobar infusion of glibenclamide (5 mg/kg), vasoconstrictor responses to U46619, prostaglandin F2alpha and prostaglandin D2 were significantly reduced, whereas vasoconstrictor responses to norepinephrine and angiotensin II were not altered and responses to BAY K 8644 were significantly enhanced. When tone in the pulmonary vascular bed was raised to a high steady level (36 +/- 3 mm Hg), glibenclamide in a dose of 5 mg/kg i.a. markedly attenuated responses to injections of U46619 and reduced the vasodilator responses to the K+-ATP channel opener, levcromakalim, whereas responses to acetylcholine and S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide donor, were not changed. In the hindquarters vascular bed of the cat, administration of glibenclamide in a dose of 5 mg/kg i.a. had no significant effect on vasoconstrictor responses to U46619, norepinephrine or angiotensin II. Hindquarters vasodilator responses to levcromakalim, but not to nitric oxide, were decreased significantly following administration of glibenclamide. These data suggest that glibenclamide, in addition to inhibiting K+-ATP channels, has thromboxane A2 receptor blocking activity in the pulmonary vascular bed of the cat. These data also suggest that vasoconstrictor responses to U46619 may be mediated by different thromboxane A2 receptors with different binding affinities in the pulmonary and in the hindquarters vascular beds of the cat.

Analysis of thromboxane receptor-mediated responses in the feline pulmonary vascular bed.

OBJECTIVE Current evidence suggests that thromboxane plays a role in pathophysiologic processes in the lung. Efforts to find effective, specific therapy to modify these effects have led to the development of a new class of thromboxane receptor blockers. This present investigation examined the selectivity and duration of the inhibitory effects of one of these novel agents in the pulmonary vascular bed of anesthetized cats. DESIGN Prospective, randomized, controlled study with repeated measures. SETTING University research laboratory. SUBJECTS Twenty-nine adult cats obtained from the Tulane University School of Medicine vivarium. INTERVENTIONS The effects of GR32191, a thromboxane receptor antagonist, were investigated under constant-flow conditions in the intact-chest cat, using a triple-lumen, 6-Fr, balloon perfusion catheter that was placed by means of fluoroscopic guidance. Data were analyzed using a paired or unpaired t-test or analysis of variance. A p < .05 was considered statistically significant. MEASUREMENTS AND MAIN RESULTS Aortic, left atrial, and left lobar arterial pressures were measured. After administration of GR32191 (0.25 and 1.0 mg/kg iv), pulmonary vasoconstrictor responses to U46619, a thromboxane mimic, were significantly decreased. Blockade was overcome with higher doses of the thromboxane mimic. GR32191 was without significant effect on the responses to prostaglandin (PG) D2, PGF2 alpha, serotonin, the calcium-channel agonist BAY K8644, or norepinephrine. Additionally, GR32191 did not alter baseline vascular pressures. Responses to U46619 returned to 50% of control value 90 mins after administration of 0.25 mg/kg of U46619. Responses to GR32191 returned to 50% of control value 180 mins after administration of 1.0 mg/kg of GR32191. These data suggest that GR32191 selectively blocks thromboxane A2 receptor-mediated responses in a competitive and reversible manner in the pulmonary vascular bed of the cat. CONCLUSIONS These results are consistent with the hypothesis that discrete thromboxane A2 receptors, unrelated to receptors activated by PGF2 alpha or PGD2, are present in the feline pulmonary vascular bed. Specific thromboxane receptor antagonists, such as GR32191, could be useful therapeutic agents in the treatment of pulmonary hypertensive and thromboembolic disorders.

Influence of HOE 140, A Bradykinin Receptor Antagonist, in the Isolated Mesenteric Vascular Bed of the Rat.

The inhibitory effects of HOE 140 (D-Arg-[Hyp3,Thi5,D-Tic7, Oic8]bradykinin), a novel bradykinin B2-receptor antagonist, on mesenteric vascular bed vasodilator responses to bradykinin (BK) were investigated under constant-flow conditions in the isolated blood-perfused rat mesenteric vascular bed. During baseline conditions, injections of BK produced dose-related decreases in mesenteric arterial perfusion pressure which were reproducible with respect to time. HOE 140, in a dose of 50 μg/kg intravenously, decreased vasodilator responses to BK but had no significant effect on mesenteric vasodilator responses to albuterol, acetylcholine, levcromakalim, or to nitroglycerin. These results suggest that BK has significant vasodilator actions which are mediated by the activation of kinin B2-receptors in the mesenteric vascular bed of the rat. HOE 140 caused a significant increase in baseline mesenteric arterial perfusion pressure. These data indicate that HOE 140 is a highly selective, BK B2-receptor antagonist in the mesenteric vascular bed of the rat, and the elevation of baseline mesenteric arterial tone by HOE 140 suggests that BK plays a role in maintaining normal vascular tone in the mesenteric circulation. These results also suggest that HOE 140 is a useful probe for studying the role of BK in the mesenteric vascular bed under physiologic and pathophysiologic conditions.

Inhibitory Effects of LY301875 on Responses to Angiotensin Peptides in Pulmonary Vascular Bed of the Cat.

The effects of the nonpeptide angiotensin receptor antagonist LY301875 on responses to angiotensin II, angiotensin III, and angiotensin IV were investigated in the pulmonary vascular bed of the intact cat chest. Under conditions of controlled blood flow, injections of the angiotensin peptides into the perfused lobar artery caused dose-related increases in lobar arterial pressure, and LY301875 decreased pressor responses to angiotensin II, angiotensin III, and angiotensin IV. The duration of the blockade was related to the dose of the antagonist, and LY301875 had no significant effect on pressor responses to U-46619, norepinephrine, serotonin or BAY K 8644. LY301875 caused minimal decreases on mean baseline systemic arterial pressures and did not significantly affect lobar arterial pressure in the cat. These results indicate that LY301875 is a potent selective long-acting angiotensin receptor antagonist and suggest that this agent may be useful in the investigation of the role of angiotensin peptides in physiological and pathophysiological processes in the pulmonary vascular bed.

Comparative Effects of Nω-Nitro-L-Arginine, Nω-Nitro-L-Arginine Methyl Ester, and Nω-Nitro-L-Arginine Benzyl Ester on Vasodilator Responses to Acetylcholine and Substance P

Recent evidence suggests that the endothelium-derived relaxing factor first described by Furchgott and Zawadski (1980) is nitric oxide or a labile nitroso derivative. Nitric oxide is formed from L-arginine in cultured endothelial cells, and NG-monomethyl-L-arginine (L-NMMA) was the first L-arginine analog shown to inhibit nitric oxide formation (Moncada et al., 1989). Since the discovery that L-NMMA inhibits nitric oxide synthase, a number of L-arginine analogs that block nitric oxide release have been developed (Ishii et al., 1990; Moore et al., 1990). The use of these compounds has provided important information on the role of nitric oxide in the regulation of cardiovascular function in in vivo experiments (Bellan et al., 1991;1993; McMahon et al, 1991; McMahon and Kadowitz, 1992,1993). Experiments with nitric oxide synthase inhibitors, including Nω-nitro-L-arginine (L-NA) and Nω-nitro-L-arginine methyl ester (L-NAME), have provided evidence that nitric oxide is involved in maintaining the pulmonary and peripheral vascular bed in a dilated state and in mediating vasodilator responses to acetylcholine, bradykinin, substance P, and other nitric oxide releasing agents (Bellan et al., 1991,1993; McMahon et al., 1991; McMahon and Kadowitz, 1993). However, recent studies have shown that L-NAME and other alkyl esters of L-NA are muscarinic receptor antagonists and suggest that these compounds are poor choices as nitric oxide synthase inhibitors in studies in which muscarinic receptors are not blocked (Buxton et al., 1992). Although L-NAME has been reported to inhibit responses to acetylcholine, bradykinin, and substance P in the pulmonary vascular bed of the cat, other studies show that L-NAME does not inhibit responses to endothelium-dependent vasodilator agents (Lippton et al., 1992).