Biomedical subjects

M Hecker

Publications and source records attributed to M Hecker.

At least 145 records · Page 8Linked to original sources

PubMed1995

Cloning, nucleotide sequence, and regulation of katE encoding a sigma B-dependent catalase in Bacillus subtilis.

A sigma B-dependent stress gene of Bacillus subtilis was localized downstream of the licS gene. The predicted amino acid sequence exhibited a significant similarity to the sequence of the katE-encoded catalase HPII of Escherichia coli, and we designated it the open reading frame katE. In a B. subtilis katE mutant, catalase 2 could not be detected. The amount of katE-specific mRNA was increased after heat, salt, or ethanol stress or after glucose starvation in a sigma B-dependent manner. As in E. coli, the transcription of the katE gene in B. subtilis was unaffected by the addition of H2O2 to exponentially growing cells. In contrast, the katA gene encoding catalase 1 of B. subtilis showed an induction pattern different from that of katE; katA expression was strongly increased by oxidative stress. The similarity between E. coli sigma S-dependent genes and B. subtilis sigma B-dependent genes suggests that both may confer multiple stress resistance to stationary-phase cells.

Amino Acid Sequence↗

PubMed1994

Characterization of endothelium-derived hyperpolarizing factor as a cytochrome P450-derived arachidonic acid metabolite in mammals.

1. In addition to nitric oxide (NO) and prostacyclin (PGI2) an as yet unidentified endothelium-derived hyperpolarizing factor (EDHF) contributes to the dilator effect of bradykinin in different vascular beds. We have investigated the nature and mechanism of action of this factor in freshly isolated bovine and porcine coronary artery segments which were preconstricted with the thromboxane mimetic U46619 (9,11-dideoxy-11 alpha, 9 alpha-epoxymethano-prostaglandin F2 alpha, 10-30 nM). 2. The concentration-response curve of bradykinin was significantly shifted to the right after inhibition of NO synthesis with NG-nitro-L-arginine (L-NNA, 30 microM), whereas cyclo-oxygenase blockade with diclofenac (1 microM) had no effect. Preconstriction of the segments with potassium chloride (40-60 mM) completely abrogated the NO/PGI2-independent dilator response to bradykinin. In sandwich bioassay experiments, both the luminal and abluminal release of NO, but not that of EDHF, was readily detectable. 3. Inhibitors of Ca(2+)-activated K+ channels (K+Ca), such as apamin (1 microM) and tetrabutylammonium (TBA, 3 mM), strongly attenuated the EDHF-mediated bradykinin-induced relaxation, while glibenclamide (3 microM), an inhibitor of K+ATP channels, had no effect. 4. These relaxations were also significantly inhibited by the phospholipase A2 inhibitor, quinacrine (30 microM), and the cytochrome P450 inhibitors, SKF525a (30-100 microM) and clotrimazole (100 microM). Moreover, incubation of endothelium-denuded coronary artery rings with a cytochrome P450-derived arachidonic acid metabolite, 11,12-epoxyeicosatetraenoic acid, elicited a concentration-dependent (1-10 microM) dilatation which was abolished both in the presence of TBA (3 mM) and following preconstriction of the segments with potassium chloride instead of U46619.(ABSTRACT TRUNCATED AT 250 WORDS)

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1994

Subcellular localization and characterization of nitric oxide synthase(s) in endothelial cells: physiological implications.

Endothelial cells (EC) contain a constitutive Ca2+/calmodulin-dependent nitric oxide (NO) synthase (cNOS) which plays an important role in the local control of vascular tone. We compared the subcellular distribution of this enzyme in cultured and freshly isolated pig EC by determination of specific cNOS activity and immunoblot analysis. Similar studies were also performed with cultured and freshly isolated bovine and cultured human EC. Enzyme activity was predominantly (> 70%) associated with the particulate fraction of all EC types tested and was highest in freshly isolated porcine EC. Both specific cNOS activity and immunoreactivity were substantially higher (> 3-fold) in the microsomal as compared with the soluble fraction of all EC types tested. In freshly isolated pig EC, these two fractions also differed in terms of their Ca(2+)-dependency, pH optimum and inhibitor specificity. EC may thus contain either two different cNOS isoenzymes or a single enzyme, the conformation of which differs between the soluble and membrane-bound state. Moreover, detailed subcellular fractionation of freshly isolated pig EC revealed that the distribution of cNOS activity closely resembled that of the plasma membrane marker 5'-nucleotidase, suggesting that most, if not all, of the cNOS activity in these cells is associated with the plasma membrane. This localization might render the enzyme more susceptible to activation by physical stimuli, such as a shear stress-induced change in the fluidity of the plasma membrane. Moreover, the continuous exposure to shear stress in vivo may also upregulate cNOS expression in EC, since specific enzyme activity, immunoreactivity and basal NO release were significantly higher in freshly isolated EC as compared with cultured EC.

Amino Acid Oxidoreductases↗

PubMed1994

Subcellular localization and characterization of neuronal nitric oxide synthase.

In contrast to the predominantly particulate, Ca2+/calmodulin-dependent nitric oxide (NO) synthase in endothelial cells, the corresponding neuronal isoenzyme is considered to be mainly soluble, presumably owing to the lack of a posttranslational myristoylation. However, preliminary findings from this and other laboratories suggest that a substantial portion of the neuronal NO synthase activity may in fact be membrane bound. We have therefore investigated the distribution of this enzyme among subcellular fractions of the rat and rabbit cerebellum in more detail. Up to 60% of the total NO synthase activity was found in the particulate fraction and, according to density gradient ultracentrifugation, associated mainly with the endoplasmic reticulum fraction. There was no apparent difference between the soluble and particulate enzymes with respect to their specific activity, Ca2+ and pH dependency, inhibitor sensitivity, or immunoreactivity, suggesting that both rat and rabbit cerebella contain a single Ca2+/calmodulin-dependent NO synthase. The inhibition by the cytochrome P450 inhibitor SKF-525A of the NO synthase activity in these subcellular fractions (IC50 = 90 microM) and the fact that mammalian cytochrome P450 enzymes are endoplasmic reticulum-bound proteins support the notion that the cerebellar NO synthase is a cytochrome P450-type hemoprotein. Moreover, the aforementioned findings suggest that posttranslational myristoylation may not be the only factor determining the intracellular localization of NO synthase.

Amino Acid Oxidoreductases↗

PubMed1994

Analysis of the induction of general stress proteins of Bacillus subtilis.

In Bacillus subtilis stress proteins are induced in response to different environmental conditions such as heat shock, salt stress, glucose and oxygen limitation or oxidative stress. These stress proteins have been previously grouped into general stress proteins (Gsps) and heat-specific stress proteins (Hsps). In this investigation the N-terminal sequences of 13 stress proteins of B. subtilis were determined. The quantification of the mRNA and the analysis of the protein synthesis pattern support the initial hypothesis that the chaperones DnaK and GroEL are Hsps in B. subtilis. In contrast, the recently described proteins GsiB, Ctc and RsbW belong to a class of Gsps that are induced by various stresses including heat shock. The main part of the Gsps described in this study failed to be induced in the sigB deletion mutant ML6 in response to heat shock. However, all the five Hsps were induced in this mutant in response to heat shock. These data indicate that SigB plays a crucial role in the induction of general stress genes, but is dispensable for the induction of Hsps.

Amino Acid Sequence↗

PubMed1994

Regulation of xylanolytic enzymes in Bacillus subtilis.

The synthesis of the xylanolytic enzymes beta-xylanase and beta-xylosidase of Bacillus subtilis was studied. In contrast to many catabolic extracellular enzymes, beta-xylanase was synthesized constitutively during exponential growth and was not repressed by glucose. beta-Xylosidase synthesis was induced 100-fold by xylose and repressed 100-fold by glucose. Carbon catabolite repression was abolished in a ccpA mutant. Titration experiments using a multicopy operator sequence responsible for carbon catabolite repression indicated that the gene encoding beta-xylosidase is part of the same carbon catabolite repression regulon as the amyE and bgIS genes.

Bacillus subtilis↗

PubMed1994

Potentiation by ACE inhibitors of the dilator response to bradykinin in the coronary microcirculation: interaction at the receptor level.

1. To examine the possibility that angiotensin-converting enzyme (ACE) inhibitors modulate the action of bradykinin at the receptor level, their effect on the dilator response to bradykinin was studied in the isolated saline-perfused heart of the rabbit. 2. Continuous infusion of bradykinin (10 nM) elicited a transient decrease in coronary perfusion pressure (CPP) and increased prostacyclin (PGI2) release which returned to baseline values within 30 min. 3. Subsequent co-infusion of ramiprilat (> or = 10 nM) or moexiprilat, but not of the less potent ACE inhibitor n-octyl-ramipril (RA-octyl), caused another fall in CPP and an increase in PGI2 release, the magnitude and time course of which were almost identical to the first response to bradykinin. No change in CPP or PGI2 release was observed when the ACE inhibitors were administered in the absence of exogenous bradykinin. 4. Infusion of D-Arg[Hyp3]-bradykinin (10 nM), a specific B2-receptor agonist which was significantly more resistant to degradation by ACE than bradykinin, produced virtually identical changes in CPP and PGI2 release when compared to bradykinin. Subsequent co-infusion of ramiprilat was similarly effective in restoring the fall in CPP and increase in PGI2 release elicited by D-Arg[Hyp3]-bradykinin as in the presence of bradykinin. 5. In concentrations which should block the degradation of bradykinin by ACE in the coronary vascular bed, two ACE substrates, hippuryl-L-histidyl-L-leucine (0.2 mM) and angiotensin I (0.3 microM), were unable to elicit a significant change in CPP or PGI2 release while ramiprilat and another ACE inhibitor, quinaprilat, were still active in the presence of these substrates. 6. To reveal the potential B2-receptor action of ramiprilat, its effect on the constrictor response to bradykinin was studied in the rabbit isolated jugular vein. Ramiprilat (0.1 MicroM), but not RA-octyl (1 MicroM),potentiated the endothelium-independent, B2-receptor-mediated constrictor response to bradykinin, but not that to the thromboxane-mimetic U46619 (9,11-dideoxy-ll alpha,9 alpha-epoxymethano-prostaglandin F2.).Moreover, ramiprilat but not RA-octyl caused a concentration-dependent, B2-receptor antagonist sensitive increase in tone when administered alone.7. These findings suggest that an interaction of ACE inhibitors with the B2-receptor or its signal transduction pathway rather than an accumulation of bradykinin within the vascular wall is responsible for the restoration of the endothelial response to bradykinin (dilatation, PGI2 release) in the coronary vascular bed of the rabbit.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1994

Release of nitric oxide by angiotensin-(1-7) from porcine coronary endothelium: implications for a novel angiotensin receptor.

The angiotensin I (AI) metabolite, A(1-7), elicited a concentration-dependent dilator response (ED50 > or = 2 microM) in porcine coronary artery rings which was markedly attenuated by the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine, and abolished after removal of the endothelium. This effect of the heptapeptide was not mimicked by AII, AIII or A(3-8) at comparable concentrations. The A(1-7)-induced relaxation was not affected by AT1 or AT2 receptor blockade or cyclo-oxygenase inhibition, but was attenuated by the B2 receptor antagonist, Hoe 140, and augmented by the angiotensin-converting enzyme (ACE) inhibitor, quinaprilat. These findings suggest that the relaxation to A(1-7) was mediated by the release of NO from the coronary endothelium through activation of an, as yet unidentified, AT receptor, the occupation of which also seems to stimulate the release of vasoactive kinins. Since A(1-7) accumulates during ACE inhibition, this mechanism may contribute to the coronary dilator effect of ACE inhibitors in vivo.

Amino Acid Sequence↗

PubMed1994

Display of the characteristics of endothelium-derived hyperpolarizing factor by a cytochrome P450-derived arachidonic acid metabolite in the coronary microcirculation.

1. In addition to nitric oxide (NO) and prostacyclin (PGI2) an endothelium-derived factor, which hyperpolarizes vascular smooth muscle cells via activation of K+ channels, contributes to the dilator effect of bradykinin in different vascular beds. Since this so-called endothelium-derived hyperpolarizing factor (EDHF) also seems to play an important role in the coronary circulation, we investigated its nature and mechanism of action in the rat isolated perfused heart (Langendorff preparation). 2. Bolus injections of bradykinin (1, 10, and 100 pmol) elicited a transient dose-dependent dilator response (e.g., 12 +/- 2% decrease in coronary perfusion pressure (CPP) at 10 pmol bradykinin, n = 41). Administration of the cyclo-oxygenase inhibitor, diclofenac (1 microM), augmented the bradykinin-induced dilation approximately twofold (n = 9 P < 0.01). Combined treatment with the NO synthase inhibitor, NG-nitro-L-arginine (30 microM) and diclofenac (1 microM) significantly reduced the duration, but increased the amplitude of the dilator response to bradykinin (27 +/- 2% decrease in CPP, n = 24, P < 0.01). 3. The abolition of this NG-nitro-L-arginine/diclofenac-insensitive dilator response to bradykinin by tetrabutylammonium (0.3 mM), an inhibitor of Ca(2+)-dependent K+ channels (4 +/- 1% decrease in CPP, n = 6, P < 0.01), supports the view that the dilator compound released in the coronary microcirculation is EDHF. 4. This EDHF-type dilation was reversibly inhibited by the phospholipase A2 inhibitor, quinacrine (3 microM, 9 +/- 3% decrease in CPP, n = 6, P < 0.01) and by the cytochrome P450 inhibitor SKF525a (3 microM, 6 +/- 1% decrease in CPP, n = 6, P < 0.01). 5. Tetrabutylammonium, quinacrine or SKF 525a did not affect the endothelium-independent dilator response to sodium nitroprusside (1 nmol), indicating that these compounds did not affect smooth muscle relaxation in a non-specific manner.6. These findings suggest that in the coronary microcirculation bradykinin stimulates the release of a cytochrome P450-derived arachidonic acid metabolite, which exhibits the characteristic features of EDHF.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1994

Stress induction of clpC in Bacillus subtilis and its involvement in stress tolerance.

A member of the clpC subfamily of stress response-related Clp ATPases was cloned from Bacillus subtilis. The B. subtilis clpC gene was induced in response to various stresses, including heat shock. Its product was identified as a general stress protein (Gsp12) described previously. A dramatic increase in the amount of clpC mRNA immediately after exposure to multiple stresses suggested regulation on a transcriptional level. Induction by heat shock was independent of the alternative sigma factor SigB, indicating a new mechanism of heat shock induction in B. subtilis. A clpC insertional mutant had an impaired tolerance for heat shock and salt stress. Furthermore, the mutation triggered the formation of elongated cells, a phenomenon particularly pronounced during stress.

Adaptation, Biological↗

PubMed1994

Cloning, nucleotide sequence, and expression of the Bacillus subtilis lon gene.

The lon gene of Escherichia coli encodes the ATP-dependent serine protease La and belongs to the family of sigma 32-dependent heat shock genes. In this paper, we report the cloning and characterization of the lon gene from the gram-positive bacterium Bacillus subtilis. The nucleotide sequence of the lon locus, which is localized upstream of the hemAXCDBL operon, was determined. The lon gene codes for an 87-kDa protein consisting of 774 amino acid residues. A comparison of the deduced amino acid sequence with previously described lon gene products from E. coli, Bacillus brevis, and Myxococcus xanthus revealed strong homologies among all known bacterial Lon proteins. Like the E. coli lon gene, the B. subtilis lon gene is induced by heat shock. Furthermore, the amount of lon-specific mRNA is increased after salt, ethanol, and oxidative stress as well as after treatment with puromycin. The potential promoter region does not show similarities to promoters recognized by sigma 32 of E. coli but contains sequences which resemble promoters recognized by the vegetative RNA polymerase E sigma A of B. subtilis. A second gene designated orfX is suggested to be transcribed together with lon and encodes a protein with 195 amino acid residues and a calculated molecular weight of 22,000.

ATP-Dependent Proteases↗

PubMed1994

Intracellular alkalinization induced by bradykinin sustains activation of the constitutive nitric oxide synthase in endothelial cells.

The transient increase in [Ca2+]i in endothelial cells after stimulation with bradykinin can account for the initiation but not the sustained production of nitric oxide (NO). Therefore, we investigated whether this sustained activation of the constitutive NO synthase (cNOS) could be mediated by an increase in pHi, which is induced by an activation of the Na(+)-H+ exchanger rather than an increase in [Ca2+]i. Cultured human endothelial cells grown on coverslips were loaded with either C.SNAFL-2 or fura 2-AM for fluorometric analysis of either pHi or [Ca2+]i. NO release was assayed by the ability of effluent from endothelial cells to stimulate purified soluble guanylyl cyclase. The pH dependence of a microsomal cNOS preparation was determined by assay of L-[3H]citrulline formation from L-[3H]arginine. Bradykinin (10 nmol/L) induced a biphasic change in endothelial pHi consisting of an initial acidification followed by a prolonged alkalinization above resting values. Inhibition of the Na(+)-H+ exchanger using HOE 694 (10 mumol/L) prevented this increase in pHi. The L-citrulline assay revealed a twofold increase in cNOS activity on increasing pH from 6.7 to 7.4, an optimum at pH 7.5, and a complete abolition of activity at pH 8.6. Endothelial production of NO 15 minutes after starting the infusion of bradykinin was maintained at significantly higher levels in control cells compared with cells pretreated with HOE 694. The latter effect cannot be accounted for by an increase in intracellular Ca2+, since [Ca2+]i levels were not significantly different between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗

PubMed1994

Mechanisms involved in the angiotensin II-independent hypotensive action of ACE inhibitors.

1. The blood pressure-lowering and cardioprotective actions of angiotensin converting enzyme (ACE) inhibitors are thought to be based primarily on a reduction in vascular angiotensin II (Ang-II) formation. However, since ACE also degrades the potent endothelium-dependent vasodilator bradykinin, it has been proposed that the local accumulation of this peptide represents an additional mechanism by which ACE inhibitors exert their cardiovascular effects. 2. Incubation of endothelial cells with ACE inhibitors indeed causes an enhanced formation of nitric oxide (NO) and prostacyclin (PGI2) which can be completely blocked by the B2-kinin receptor antagonist Hoe 140, suggesting that the vascular endothelium is capable of generating vasoactive kinins from an endogenous source. 3. Moreover, ACE inhibitors not only prevent the breakdown of bradykinin but, by virtue of an as yet unidentified mechanism, also enhance the potency of bradykinin at the receptor level and reverse the desensitization of the B2-kinin receptor following continuous exposure to bradykinin. Both of these effects may enhance or sustain the bradykinin-induced formation of NO and PGI2 by the endothelium. 4. Furthermore, ACE inhibition leads to the accumulation of Ang-I which can be metabolised to Ang-(1-7) by another endothelial enzyme, neutral endopeptidase 24.11. By activating an as yet unidentified angiotensin receptor, Ang-(1-7), but not other known angiotensin peptides, stimulates endothelial NO release in porcine coronary arteries as well as in the isolated perfused rat heart. This effect is, albeit to a different degree, dependent on the release of vasoactive kinins from the endothelium. The shift in Ang-I metabolism towards an enhanced formation of Ang-(1-7) in the presence of an ACE inhibitor may thus contribute to the hypotensive action of this class of compounds as well.

Angiotensin II↗

PubMed1994

[Endothelial mechanisms in vasomotor effects of ACE inhibitors].

The beneficial cardiovascular effects of ACE inhibitors are thought to be based primarily on a reduction in vascular angiotensin II formation. However, since ACE also degrades the potent endothelium-dependent vasodilator bradykinin, it has been proposed that the local accumulation of this peptide in the vascular wall represents an additional mechanism by which ACE inhibitors exert their cardiovascular effects. In this context it has been demonstrated that incubation of cultured endothelial cells with ACE inhibitors leads to an enhanced formation of nitric oxide (NO) and prostacyclin (PGI2). This effect is believed to be the consequence of an accumulation of endothelium-derived bradykinin in the vicinity of the endothelial cells. Moreover, by virtue of an as yet unidentified mechanism, ACE inhibitors may also enhance the potency of bradykinin at the receptor level and/or activate the B2-kinin receptor following pre-exposure to bradykinin. Both of these effects may enhance or sustain the bradykinin-induced formation of NO and PGI2 by the endothelium. ACE inhibition also leads to the accumulation of angiotensin I which can be metabolized to angiotensin-(1-7) by another endothelial enzyme, the neutral endopeptidase 24.11. Activating an as yet unidentified receptor, angiotensin-(1-7) (but not other known angiotensin peptides) stimulates endothelial NO release in coronary arteries from different species as well as in the isolated perfused rat heart. This effect also seems to involve the release of vasoactive kinins from the endothelium. The shift in angiotensin I metabolism towards an enhanced formation of angiotensin-(1-7) in the presence of an ACE inhibitor may thus also contribute to the hypotensive action of this class of compounds.

Angiotensin I↗

PubMed1994

Control of nitric oxide and prostacyclin synthesis in endothelial cells.

Endothelial cells produce a variety of factors involved in the control of vascular tone, platelet activation and cell growth, the most important being nitric oxide (NO) and prostacyclin (PGI2). Although continuously produced in small amounts, synthesis and release of these autacoids are enhanced by mechanical (e.g. fluid shear stress) and humoral stimuli (e.g. acetylcholine, bradykinin, histamine). By counteracting neuro- and myogenic vasoconstriction, the continuous release of NO and PGI2 from the vascular endothelium represents a sensitive and highly effective local system for the maintenance of an adequate blood flow to the organs. This overview resumes current knowledge concerning the intracellular pathways which link endothelial cell activation by receptor-dependent and -independent stimuli to the formation of NO and PGI2.

Animals↗

PubMed1993

Cloning and characterization of heat-inducible promoters of Bacillus subtilis.

Heat-inducible DNA fragments of Bacillus subtilis were cloned with two different promoter probe vectors. The increased synthesis of the reporter enzymes seemed to be due to a transient increase in the transcription of the encoding genes. The structure of the heat-sensitive promoters resembles the consensus sequence of promoters recognized by the vegetative form of RNA polymerase of B. subtilis. Our results support data in literature that the heat shock response of B. subtilis is regulated by a different mechanism than in Escherichia coli, where alternative sigma factors direct the transcription of heat shock genes.

Bacillus subtilis↗

PubMed1993

Modulation of endothelial autacoid release by protein kinase C: feedback inhibition or non-specific attenuation of receptor-dependent cell activation?

Receptor-mediated elevations of intracellular Ca2+ in endothelial cells may be controlled by a negative feedback mechanism through activation of protein kinase C (PKC). To test this hypothesis, we studied the effects of an activation or inhibition of PKC on the release of nitric oxide (NO) and prostacyclin (PGI2) from cultured bovine and porcine aortic endothelial cells (EC). Preincubation with the PKC activators phorbol-12-myristate-13-acetate (PMA) (3-300 nM) or 1-oleyl-2-acetyl-glycerol (OAG) (30 microM) significantly attenuated the release of NO and PGI2 from EC stimulated with bradykinin (0.3-30 nM), whereas phorbol-12,13-didecanoate (PDD) (30-300 nM), which does not activate PKC, had no effect. UCN-01 (10 nM), a specific PKC inhibitor, significantly augmented the bradykinin-stimulated release of NO from EC. These effects were correlated with a reduced (PMA) or enhanced (UCN-01) elevation of intracellular Ca2+ in response to bradykinin in both types of EC. Neither the PKC activators nor the inhibitor had any effect on resting intracellular Ca2+ or basal endothelial autacoid release. Several isoforms of PKC (namely PKC alpha, PKC delta, PKC epsilon, and PKC zeta) were detected in bovine, human, and porcine EC by immunoblotting analysis with isotype-specific anti-PKC antibodies, which, except PKC epsilon, were predominantly located in the cytosol. Incubation of bovine EC with PMA elicited a significant increase in membrane-bound PKC alpha immunoreactivity, whereas there was no translocation of PKC alpha from the cytosolic to the membrane fraction with bradykinin. As determined by histone phosphorylation, PKC activity was similarly reduced in the cytosol, but increased in the membrane fraction of bovine EC exposed to PMA, whereas bradykinin had no significant effect. These findings indicate that endothelial autacoid release can be modulated by activators and inhibitors of PKC. However, stimulation of EC with bradykinin does not lead to a detectable activation of PKC, suggesting that PKC does not exert a negative feedback in the signal transduction pathway of this receptor-dependent agonist.

Autacoids↗

PubMed1993

Dual action of angiotensin II on coronary resistance in the isolated perfused rabbit heart.

We studied the functional role of angiotensin II (AII) receptor subtypes and vasodilatory endothelial autacoid release in response to AII in isolated perfused rabbit hearts. AII infusion induced biphasic changes in coronary perfusion pressure (CPP): an initial increase was followed by a decrease until a plateau was reached. At higher concentrations of AII (> or = 10 nmol/l) this plateau phase was lower than the initial CPP level. AII infusion elicited inverse changes in peak left ventricular pressure (LVP): coronary constriction was associated with a transient decline, and during the plateau phase LVP was clearly increased. AII also moderately augmented prostacyclin (PGI2) release from the coronary vascular bed. The AII-induced changes in CPP, LVP, and PGI2 release were effectively inhibited by the AT1 receptor subtype antagonist ICI D8731 (30 nmol/l), but not by the AT2 receptor antagonist CGP 42112 (30 nmol/l). The adenosine A1 receptor antagonist 8-phenyltheophylline (0.1 mumol/l) attenuated the decline in CPP following the constriction phase without affecting the changes in LVP during AII infusion. The cyclooxygenase inhibitor diclofenac (1 mmol/l) had no effect on the AII-induced changes in CPP, whereas the nitric oxide-synthase inhibitor NG-nitro-L-arginine (30 mumol/l) markedly potentiated the vasoconstriction but was without effect on the plateau phase of the response. In contrast to AII, the thromboxane analogue U46619 elicited sustained increases in CPP which were associated with slight decreases in LVP.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗