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B E McLaughlin

Publications and source records attributed to B E McLaughlin.

13 recordsLinked to original sources
PubMed1992

Carbon monoxide does not inhibit glyceryl trinitrate biotransformation by or relaxation of aorta.

Carbon monoxide (CO) was employed to assess the role of ferrous hemoproteins in the vasodilation and biotransformation of glyceryl trinitrate (GTN) in rabbit aortic strips. These tissues were contracted submaximally with phenylephrine, exposed to CO for 5 min, and then incubated with 0.5 microM [1,3(14) C]GTN in the presence of CO for 2 min or 30 s. The [14C]GTN-induced relaxation of the strips was recorded, and [14C]GTN biotransformation to [14C]glyceryl dinitrate metabolites by the tissues was determined by thin-layer chromatographic-liquid scintillation spectrometric analysis. CO treatment inhibited neither GTN-induced relaxation nor GTN biotransformation to glycerol dinitrate metabolites. These results indicate that ferrous hemoproteins are probably not involved in the biotransformation of GTN that is associated with relaxation of the rabbit aortic strips.

Animals↗
PubMed1992

Direct evidence for nitric oxide formation from glyceryl trinitrate during incubation with intact bovine pulmonary artery.

It has been proposed that the mechanism of the vasodilator action of glyceryl trinitrate (GTN) involves biotransformation to nitric oxide. A sensitive chemiluminescence method for nitric oxide determination was used to test this hypothesis. In four experiments, bovine pulmonary artery (BPA) was incubated with GTN (0.1 mM) in Krebs' solution (2 mL) containing 30 mM KCl, and in anaerobic conditions using 95% Ar - 5% CO2, in a sealed micro-Fernbach flask (6.2-mL volume). After incubation for 2, 5, 10, or 20 min at 37 degrees C, 400-microL aliquots of headspace gas were removed and injected into a redox chemiluminescence detector. Nitric oxide formation was first measurable at 5 min (76 +/- 53 pmol/g wet wt. BPA), and increased with incubation time (174 +/- 46 pmol/g wet wt. BPA after 10 min and 310 +/- 67 pmol/g wet wt. BPA after 20 min). This is the first direct chemical measurement of nitric oxide formation during interaction of GTN with vascular smooth muscle. These data support the concept that GTN is a nitrovasodilator prodrug acting via the formation of nitric oxide.

Animals↗
PubMed1992

Biotransformation of glyceryl trinitrate by rat brain homogenate.

Incubation of glyceryl trinitrate (GTN) with 5% (w/v) rat brain homogenate (RBH) resulted in biotransformation of the organic nitrate vasodilator drug to a mixture of glyceryl-1,2-dinitrate (1,2-GDN) and glyceryl-1,3-dinitrate (1,3-GDN). Heating of the RBH at 100 degrees C for 5 min and (or) pretreatment with 5 mM N-ethylmaleimide at 37 degrees C for 10 min demonstrated that about two-thirds of the GTN biotransformation activity was due to a sulfhydryl-dependent enzymatic process resulting in the predominant formation of 1,2-GDN, and that the remaining biotransformation activity was due to a sulfhydryl-dependent nonenzymatic process resulting in the selective formation of 1,3-GDN. In a preliminary experiment, nitric oxide formation was observed during the incubation of GTN with RBH under anaerobic conditions. These data support the idea that some of the therapeutic and adverse effects of GTN are mediated through its action in the central nervous system.

Animals↗
PubMed1991

Quantitation of nitric oxide formation from nitrovasodilator drugs by chemiluminescence analysis of headspace gas.

A rapid and reliable method has been developed for the quantitation of nitric oxide by chemiluminescence analysis of headspace gas. Aqueous nitric oxide standards are used to calibrate the method. There is a linear relationship between the amount of nitric oxide and the redox chemiluminescence detector response over the range of 52-2445 pmol of nitric oxide in 2.0 mL of deionized water contained in a sealed 6.2-mL flask. The intra-day and inter-day coefficient of variation values of the method do not exceed 4% and 9%, respectively. The lower limit of quantitative sensitivity and the lower limit of qualitative detection are 52 pmol and 26 pmol of nitric oxide, respectively. This method has been used to measure nitric oxide formation during the incubation of glyceryl trinitrate or sodium nitroprusside in the presence of cysteine. This method has two major advantages over the currently available procedures for the quantitation of nitric oxide, viz., no artifactual formation of nitric oxide during sample preparation and decreased instrumental contamination.

Cysteine↗
PubMed1991

Does carbon monoxide have a physiological function?

Recently endothelium-derived relaxing factor (EDRF) has been identified as nitric oxide. The source of the nitric oxide is L-arginine, and the L-arginine-nitric oxide pathway has been proposed to function as a widespread transduction mechanism for the regulation of cell function and communication. Gerald Marks and colleagues suggest that carbon monoxide, which is formed endogenously from heme catabolism and which shares some of the chemical and biological properties of nitric oxide, may play a similar role. This would be achieved by carbon monoxide binding to the iron atom of the heme moiety of soluble guanylyl cyclase and to the iron-sulfur centers of macrophage enzymes.

Animals↗
PubMed1991

Interaction of glyceryl trinitrate and sodium nitroprusside with bovine pulmonary vein homogenate and 10,000 x g supernatant: biotransformation and nitric oxide formation.

The current proposed mechanism of action of nitrovasodilator drugs involves biotransformation to nitric oxide, which is postulated to be the active vasodilator substance. Our objective was to determine whether nitric oxide was formed from two prototype nitrovasodilator drugs, glyceryl trinitrate (GTN) and sodium nitroprusside (SNP), after incubation with bovine pulmonary vein (BPV) preparations. GTN or SNP was incubated in an argon atmosphere with phosphate buffer, BPV homogenate, or the 10,000 x g supernatant fraction of the homogenate. Nitric oxide formation, as determined by a chemiluminescence-headspace gas method, was measurable following the incubation of SNP with BPV homogenate and 10,000 x g supernatant. There was no detectable formation of nitric oxide from the incubation of GTN with the two BPV preparations, although GTN was biotransformed to glyceryl dinitrate, as determined by gas-liquid chromatography. There was decreased recovery of nitric oxide during the incubation of authentic nitric oxide with the two BPV preparations as compared with buffer. In conclusion, formation of nitric oxide was measured for the interaction of SNP, but not GTN, with BPV preparations. However, the data do not exclude the possible formation of nitric oxide from GTN, as nitric oxide was shown to be sequestered or transformed by the BPV preparations.

Animals↗
PubMed1990

Biotransformation of glyceryl trinitrate and elevation of cyclic GMP precede glyceryl trinitrate-induced vasodilation.

In this study, we examined glyceryl trinitrate (GTN) biotransformation and cyclic GMP elevation in vascular smooth muscle before onset of GTN-induced relaxation. Isolated rabbit aortic strips (RAS) and strips of bovine pulmonary artery (BPA) and bovine pulmonary vein (BPV) were contracted submaximally and incubated with [3H]GTN. Before onset of GTN-induced vasodilation, the tissues were freeze-clamped and then analyzed for GTN, glyceryl-1,2-dinitrate (1,2-GDN), and glyceryl-1,3-dinitrate (1,3-GDN) and for cyclic GMP. Before onset of relaxation of RAS, BPA, and BPV, there was significant biotransformation of GTN to GDN and significant elevation of cyclic GMP. There was significantly greater biotransformation of GTN and elevation of cyclic GMP by BPV than by BPA incubated with the same concentration of GTN, which was temporally related with the more rapid onset of relaxation induced in BPV than in BPA. These results are consistent with the hypothesis that the magnitude of GTN biotransformation before vasodilation is the important determinant of subsequent tissue relaxation. In GTN biotransformation before vasodilation, there was preferential formation of 1,2-GDN. These data indicate that the mechanism of GTN biotransformation to 1,2-GDN is related to elevation of cyclic GMP and subsequent vasodilation.

Animals↗
PubMed1989

Differential biotransformation of glyceryl trinitrate by red blood cell-supernatant fraction and pulmonary vein homogenate.

We have demonstrated previously that glyceryl trinitrate (GTN) undergoes biotransformation to two glyceryl dinitrate (GDN) metabolites in the human red blood cell-supernatant fraction (RBC-SF) by hemoglobin-mediated and sulfhydryl-dependent enzymatic mechanisms. In the present study, we have shown that biotransformation of GTN in rabbit RBC-SF yields a glyceryl-1,2-dinitrate (1,2-GDN)/glyceryl-1,3-dinitrate (1,3-GDN) ratio of 5.3. Following inhibition of hemoglobin-mediated biotransformation of GTN by carbon monoxide (CO), the 1,2-GDN/1,3-GDN ratio was 2.1. Following inhibition of sulfhydryl-dependent biotransformation by N-ethylmaleimide (NEM), the 1,2-GDN/1,3-GDN ratio was 30.0. We have demonstrated previously that for GTN-induced vasodilation of isolated bovine pulmonary vein (BPV), the 1,2-GDN/1,3-GDN ratio was 7.1, which indicated that a hemoprotein-dependent process was involved in GTN biotransformation. To determine if this was the case, the biotransformation of GTN (0.51 microM) was studied in BPV homogenates; 31.1 pmol GDN/mg BPV protein was formed in 20 min. The 1,2-GDN/1,3-GDN ratio was 1.1, which indicated that hemoprotein-mediated biotransformation did not occur. This conclusion was supported by the fact that CO did not inhibit GTN biotransformation. GTN biotransformation by BPV homogenate was inhibited 62% by NEM, 89% by boiling of the homogenate, and almost completely by boiling plus NEM. These results indicated that biotransformation of GTN by the BPV homogenate involved in a combination of enzymatic and nonenzymatic processes that were mostly sulfhydryl dependent. It is concluded that the mechanism for GTN biotransformation in isolated intact BPV, which yielded preferential formation of 1,2-GDN, was rendered nonfunctional upon tissue homogenization.

Animals↗
PubMed1989

Biotransformation of glyceryl trinitrate and isosorbide dinitrate in vascular smooth muscle made tolerant to organic nitrates.

It has been proposed that organic nitrates are prodrugs and biotransformation to a pharmacologically active metabolite (i.e., nitric oxide) must occur before the onset of vasodilation. If this postulated mechanism is correct, tolerance to organic nitrate-induced vasodilation might involve decreased biotransformation of organic nitrates by vascular smooth muscle. In this study, biotransformation of isosorbide dinitrate (ISDN) and glyceryl trinitrate (GTN) was estimated by measuring isosorbide mononitrate (ISMN) and glyceryl dinitrate (GDN), respectively, rather than the nitrate anion, because of a more sensitive method for measurement of ISMN and GDN. To test this hypothesis, isolated rabbit aortic strips (RAS) were made tolerant in vitro by incubation with 500 microM GTN or ISDN for 1 h. After a washout period and submaximal contraction with phenylephrine, the tissues were incubated with either 2.0 microM [14C]ISDN or 0.5 microM [14C]GTN for 2 min. ISDN- or GTN-induced relaxation of RAS was monitored and tissue parent drug and metabolite contents were determined by thin-layer chromatography and liquid scintillation spectrometry. ISDN- and GTN-induced relaxation of RAS and the metabolite concentrations were significantly less for both GTN- and ISDN-tolerant tissue compared with nontolerant tissue. These results are consistent with the hypothesis that organic nitrate biotransformation is required for organic nitrate-induced vasodilation.

Animals↗
PubMed1988

Nitric oxide-induced vasodilation of organic nitrate-tolerant rabbit aorta.

It is postulated that the organic nitrate vasodilator agents, including glyceryl trinitrate (GTN) and isosorbide dinitrate (ISDN), are prodrugs, such that biotransformation to the active inorganic metabolite, nitric oxide (NO), occurs prior to the onset of vasodilation. Furthermore, it is proposed that organic nitrate tolerance in vascular tissue involves decreased formation of NO. To test this latter hypothesis, we examined vasodilation induced by NO, GTN, and ISDN in non-tolerant, GTN-tolerant, and ISDN-tolerant rabbit aortic rings (RARs). Isolated RARs were contracted submaximally with phenylephrine; the time of onset of relaxation and percent relaxation of tissue were determined in response to NO (0.3 microM), GTN (0.03 microM), and ISDN (0.12 microM) before and after a 1-h treatment with 500 microM GTN, 500 microM ISDN, or buffer only. The data demonstrated that the response to NO was not changed in GTN-tolerant and ISDN-tolerant tissues, in which there was virtually no GTN-induced or ISDN-induced relaxation. These results are consistent with the postulate that organic nitrate vasodilator drugs must undergo biotransformation to NO before vasodilation can occur and that the mechanism of organic nitrate tolerance involves decreased formation of NO.

Animals↗
PubMed1988

Mechanism of glyceryl trinitrate-induced vasodilation. I. Relationship between drug biotransformation, tissue cyclic GMP elevation and relaxation of rabbit aorta.

This study was conducted to test the hypothesis that biotransformation of glyceryl trinitrate (GTN) is involved in GTN-induced relaxation of vascular smooth muscle. The temporal relationship between GTN biotransformation, elevation of cyclic GMP content and vasodilation in rabbit aortic strips (RAS) was determined. Isolated RAS were contracted submaximally with phenylephrine, and then were incubated with 0.62 microM [3H]GTN in a 30-sec time course study. GTN-induced relaxation (inhibition of phenylephrine-induced tone) of RAS was monitored; tissue cyclic GMP content was measured by radioimmunoassay; and GTN, glyceryl-1,2-dinitrate (1,2-GDN) and glyceryl-1,3-dinitrate (1,3-GDN) concentrations in RAS were measured by thin-layer chromatography and liquid scintillation spectrometry. There was time-dependent biotransformation of GTN to GDN by the RAS and a time-dependent increase in cyclic GMP content in the RAS. Statistically significant (P less than .05) biotransformation of GTN and elevation of cyclic GMP content in the tissue occurred at 10 sec, whereas the onset of GTN-induced relaxation of RAS occurred at 12 sec. During the tissue biotransformation of GTN, there was preferential formation of 1,2-GDN compared with 1,3-GDN, with 1,2-GDN/1,3-GDN ratio of 3.0/1 at 10 sec, 5.3/1 at 20 sec and 5.8/1 at 30 sec. The results of this study are consistent with the hypothesis that GTN is a prodrug, such that biotransformation to an active metabolite is involved in GTN-induced relaxation of vascular smooth muscle. The data also indicate that the mechanisms of GTN biotransformation and GTN-induced activation of guanylate cyclase may be related intimately.

Animals↗
PubMed1986

Biotransformation of glyceryl trinitrate occurs concurrently with relaxation of rabbit aorta.

This study was conducted to test the hypothesis that biotransformation of glyceryl trinitrate (GTN) is involved in GTN-induced relaxation of vascular smooth muscle. Isolated rabbit aortic strips (RAS) were contracted submaximally with phenylephrine (PE) and then were incubated with 0.5 microM [14C]GTN in a time course study. GTN-induced relaxation (inhibition of PE-induced tone) of RAS was monitored and tissue GTN and glyceryl-1,2- and 1,3-dinitrate (GDN) concentrations were measured by thin-layer chromatography and liquid scintillation spectrometry at 0.5, 1, 2 and 20 min after incubation. Biotransformation of GTN to GDN occurred during GTN-induced relaxation of RAS. The tissue GDN concentration was dependent on the time duration of incubation with GTN and was related to the magnitude of GTN-induced tissue relaxation. At the 20-min interval, the GDN concentration in the incubation medium indicated appreciable efflux of GDN metabolites from the RAS. In the biotransformation of GTN by RAS, there was about 4-fold preferential formation of 1,2-GDN compared with 1,3-GDN. RAS were made tolerant to GTN in vitro by incubation with 500 microM GTN for 1 hr. After washing, GTN-tolerant and nontolerant (incubation with vehicle for 1 hr) RAS were contracted submaximally with PE, and then were incubated with 0.5 microM [14C]GTN for 2 min. GTN-induced relaxation of RAS and tissue GDN concentration were significantly less for GTN-tolerant tissue compared with nontolerant tissue. Tissue GTN concentration was similar for both GTN-tolerant and nontolerant RAS, which indicated that the tissue uptake of GTN was similar and that GTN biotransformation was diminished in tolerant tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗