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G S Marks

Publications and source records attributed to G S Marks.

At least 55 records · Page 3Linked to original sources
PubMed1996

Cytochrome P4503A is the major source of N-vinylprotoporphyrin IX formation after administration of 3-[2-(2,4,6-trimethylphenyl)thioethyl]-4-methylsydnone to untreated and dexamethasone-pretreated rats.

The sydnone, 3-[2-(2,4,6-trimethylphenyl)thioethyl]-4-methylsydnone (TTMS), which has previously been shown to cause mechanism-based inactivation of rat hepatic cytochrome P450 (P450) 1A and 3A, was shown to cause in vitro mechanism-based inactivation of rat P450s 2B1, 2C6, and 2C11, but not of P4502A1/2. Administration of TTMS to rats is known to cause degradation of rat hepatic P450 by heme N-alkylation yielding N-vinylprotoporphyrin IX (N-vinylPP). Pretreatment of rats with beta-naphthoflavone (beta NF) failed to increase hepatic N-vinylPP after TTMS administration. Because beta NF causes a marked increase in hepatic levels of P4501A, we conclude that P4501A of rat liver is not a quantitatively important source of N-vinylPP from TTMS. The increased formation of N-vinylPP in phenobarbital (PB)- and dexamethasone (DEX)-pretreated rats suggested that an inducible P450 isozyme (e.g. P4502B1/2, P4503A, or both) is/are an important contributor to N-vinylPP formation from TTMS. When troleandomycin (TAO) (a selective inhibitor of P4503A) was coadministered with TTMS, N-vinylPP formation was reduced to 25% of control in DEX-pretreated rats and to 34% of control in untreated (UT) rats, showing that P4503A was quantitatively the major source of N-vinylPP formation in UT- and DEX-pretreated rats. No significant differences were found in the formation of the ring A-substituted (NA), ring B-substituted (NB), ring C-substituted (NC), and ring D-substituted (ND) regioisomers of N-vinylPP among UT, beta NF-, PB-, or DEX-pretreated rats. Regioisomer data, in addition to data obtained with TAO, indicate that a single inducible form of P450, namely P4503A, is responsible for the bulk of N-vinylPP formation in UT and DEX-pretreated rat liver after TTMS administration.

Animals↗
PubMed1996

The apoprotein of cytochrome P450 3A2 does not selectively direct alkylation to one of four pyrrole rings of N-vinylprotoporphyrin IX.

A variety of porphyrinogenic xenobiotics cause mechanism-based inactivation of a number of rat hepatic cytochrome P450 isozymes. As a result, a mixture of four N-alkylprotoporphyin IX (N-alkylPP) regioisomers, with ferrochelatase-inhibitory properties, are formed. This study was designed to determine whether all four regioisomers are produced on the active site of a single P450 isozyme, or whether the apoprotein of individual P450 isozymes selectively directs the alkylation to one of four pyrrole nitrogen atoms of N-alkylPP. Administration of 3-[2-(2,4,6-trimethylphenyl)thioethyl]-4-methylsydnone (TTMS) to untreated and dexamethasone-pretreated rats results in the formation of four regioisomers of N-vinylprotoporphyrin IX (N-vinylPP). Following coadministration of TTMS with troleandomycin, N-vinylPP formation is reduced to 40 and 43% of control in untreated and dexamethasone-pretreated male rats. Since troleandomycin is a selective inhibitor of rat hepatic P450 3A, the difference in N-vinylPP regioisomer formation between control (TTMS alone) and TTMS plus troleandomycin coadministered rats represents the difference due to P450 3A. This allowed us to calculate that all four regioisomers of N-vinylPP are formed by P450 3A isozymes in both untreated and dexamethasone-pretreated male rats. Since untreated male rats express P450 3A2, but not P450 3A1, we conclude that the apoprotein of rat hepatic P450 3A2 does not selectively direct the alkylation to one of four pyrrole nitrogens of N-vinylPP.

Alkylation↗
PubMed1996

Cytochrome P450 and its interactions with the heme biosynthetic pathway.

An important factor in disruption of hepatic heme biosynthesis by porphyrinogenic drugs appears to be interaction with one or several cytochrome P450 isozymes. Clarification of the nature of the interaction between porphyrinogenic drugs and cytochrome P450 isozymes, as well as identification of the isozymes involved, will be helpful in extrapolating the results of animal experimentation to humans. Administration of griseofulvin to mice results in accumulation in the liver of two N-alkylated protoporphyrins (PPs). The major N-alkyl PP, N-griseofulvin PP, which is devoid of ferrochelatase-inhibitory activity, was shown to be the precursor of N-methyl PP, which is a potent ferrochelatase inhibitor. N-Griseofulvin PP was present predominantly as the Nc regioisomer rather than the anticipated NA regioisomer. Progesterone (PG) 6 beta-hydroxylase and androstenedione (AD) 6 beta-hydroxylase, diagnostic markers for cytochrome P450 3A1/2 activity in rat liver, were identified in chick embryo liver. The in ovo administration of 3,5-diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine (4-ethyl DDC) and 3-[2-(2,4,6-trimethylphenyl)thioethyl]-4-methylsydnone (TTMS) caused inactivation of chick embryo hepatic PG and AD 6 beta-hydroxylases. Ascorbate was shown to inhibit uroporphyrin accumulation in cultures of chick embryos treated with porphyrinogenic drugs and in the livers of an ascorbate-requiring rat strain treated with a porphyrinogenic combination of chemicals. Ascorbate appears to act by inhibiting oxidation of uroporphyrinogen to uroporphyrin. Avian hepatocytes were cultured in 48-well plates and directly assayed within the wells for the activity of 7-ethoxyresorufin O-deethylation (EROD), and for porphyrin and protein concentration by a fluorescence plate reader. Uroporphyrin was the main porphyrin to accumulate in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in chick embryos, pheasants, ducks, and herring gulls; heptacarboxylated porphyrin predominated in turkey hepatocytes. The EROD-inducing potential of complex mixtures of polyhalogenated aromatic hydrocarbons from herring gull eggs was assessed and compared with that of TCDD. A nuclear heme pool appears to regulate the transcription of the cytochrome P450 2B1/2B2 genes in rat liver, by modulating binding of a transcription factor(s) that appears to be involved in the transcriptional activation by phenobarbitone.

Animals↗
PubMed1996

Chick embryo liver microsomal steroid hydroxylations: induction by dexamethasone, phenobarbital, and glutethimide and inactivation following the in ovo administration of porphyrinogenic compounds.

Metabolites of [4-(14)C]androstenedione (AD) and [4-(14)C]progesterone (PG) were separated and quantitated following incubation with hepatic microsomes from chick embryos. PG 2 alpha-hydroxylase and AD 7 alpha-hydroxylase, which are diagnostic markers in rat liver for cytochrome P450 (P450) 2C11 and 2A1/2, respectively, were not identified in chick embryo liver. PG 6 beta-hydroxylase and AD 6 beta-hydroxylase, diagnostic markers for P450 3A1/2 activity in rat liver, were identified in chick embryo liver, and we were able to show that radiolabeled 6 beta-hydroxyprogesterone and 6 beta-hydroxyandrostenedione, the metabolites of PG and AD 6 beta-hydroxylase, respectively, were homogeneous and identical with authentic standards. Dexamethasone, phenobarbital, and glutethimide were found to be significant inducers of PG and AD 6 beta-hydroxylases in chick embryo liver. The in ovo administration of the porphyrinogenic compounds 3,5-diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine (4-ethyl DDC) and 3-[2-(2,4,6-trimethylphenyl)-thioethyl]-4-methylsydnone (TTMS) caused inactivation of chick embryo hepatic PG and AD 6 beta-hydroxylases. Therefore, we suggest that PG and AD 6 beta-hydroxylases may serve as diagnostic markers for a P450 3A-like isozyme in the chick embryo, and that this isozyme is one of the targets for inactivation by 4-ethyl DDC and TTMS.

Animals↗
PubMed1995

Inactivation of chick embryo hepatic cytochrome P450 1A, 2H and 3A following in ovo administration of 3,5-diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine and 3-[2-(2,4,6-trimethylphenyl)thioethyl]-4-methylsydnone.

Rat hepatic cytochrome P450 (P450) isozymes 1A1, 2C6, 2C11, 3A1 and 3A2 are targets for mechanism-based inactivation by the porphyrinogenic compound 3,5-diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine (4-ethyl DDC). It is of interest to determine whether similar P450 isozymes are targets of porphyrinogenic drugs in the chick embryo liver. The chick embryo expresses P450 2H1/2 isozymes, which are similar to the rat P450 2B1/2 isozymes, a polycyclic aromatic hydrocarbon-inducible P450 1A isozyme, and a pregnenolone 16 alpha-carbonitrile-inducible P450 3A isozyme. We have found previously that chick embryo hepatic P450 1A and 3A isozymes are targeted for in vitro mechanism-based inactivation by 4-ethyl DDC and by the sydnone 3-[2-(2,4,6-trimethylphenyl)thioethyl]-4-methylsydnone (TTMS). Marked differences have been observed between the in vitro and in vivo effects of porphyrinogenic drugs on P450 isozymes. Thus, the first objective of this study was to determine whether chick embryo hepatic P450 1A and 3A isozymes are subject to in ovo inactivation by these porphyrinogenic compounds. Our second objective was to determine whether the chick embryo hepatic P450 2H isozyme(s) was subject to in ovo and in vitro inactivation by 4-ethyl DDC and TTMS. Using hepatic microsomes prepared from beta-naphthoflavone-, dexamethasone-, phenobarbital-, and glutethimide-induced 19-day-old chick embryos, we found that total P450 content was decreased significantly in microsomes prepared from all treatment groups following in ovo administration of 4-ethyl DDC and TTMS. Moreover, in ovo administration of both 4-ethyl DDC and TTMS caused a significant decrease of 7-ethoxyresorufin O-deethylase, erythromycin N-demethylase, and benzphetamine N-demethylase activities, which are selective catalytic markers for chick embryo hepatic P450 1A, 3A and 2H isozymes, respectively. In addition, in vitro administration of 4-ethyl DDC and TTMS caused mechanism-based inactivation of benzphetamine N-demethylase activity in microsomes from phenobarbital- and glutethimide-treated chick embryos, showing that the chick embryo hepatic P450 2H isozyme is a target for mechanism-based inactivation. Therefore, it was concluded that the chick embryo hepatic P450 1A, 2H and 3A isozymes serve as targets for both in ovo and in vitro mechanism-based inactivation by 4-ethyl DDC and TTMS.

Alkylation↗
PubMed1995

Heme oxygenase activity in the adult rat aorta and liver as measured by carbon monoxide formation.

Rat aorta was homogenized and the 13000 x g supernatant fraction was tested for heme oxygenase (HO) activity by using a sensitive gas chromatographic method to measure carbon monoxide (CO), one of the products of the HO reaction. The rate of NADPH-dependent CO formation, an index of HO activity, was 1.41 +/- 0.40 nmol CO.mg(-1)protein. h(-1) in the rat aorta supernatant fraction and 2.05 +/- 0.55 nmol CO.mg(-1) protein.h(-1) in the rat liver 13000 x g supernatant fraction, a tissue known to contain HO activity. Chromium mesoporphyrin (0.05 mM), an inhibitor of rat liver HO, significantly decreased HO activity by 26% in the aorta supernatant fraction and 50% in the liver supernatant fraction. On the basis of the results of this study, which demonstrated HO-catalyzed CO formation in aortic tissue, and previous observations that CO relaxes vascular smooth muscle, we suggest that a physiological role for CO in vascular smooth muscle relaxation should be further investigated.

Animals↗
PubMed1995

Sulfhydryl involvement in nitric oxide sequestration and nitric oxide induced guanylyl cyclase activation in vascular smooth muscle.

In the present study, the role of vascular smooth muscle sulhydryl groups was investigated with respect to sequestration of nitric oxide (NO) and activation of soluble guanylyl cyclase by NO. Vascular smooth muscle 100,000 x g supernatant (soluble) fraction was prepared in phosphate buffer, using the medial layer of bovine pulmonary artery. The soluble fraction was incubated with 100 pmol NO for 5 min in a sealed flask at 37 degree C under anerobic conditions in the presence or absence of the sulfhydryl reagent, N-ethylmaleimide (NEM, 5 mM). NO sequestration by the soluble fraction was measured as an indicator of NO binding. Total thiol content was measured in the soluble fraction with and without exposure to NEM. Guanylyl cyclase activity was measured in the soluble fraction with and without exposure to NO and a combination of NO and NEM. NEM decreased total thiol content in the soluble fraction from 103.59 nmol/mL to undetectable levels, and decreased guanylyl cyclase activity to below basal levels. The percentage of NO sequestered by the soluble fraction was inhibited by NEM by approximately 25% from a control value of 26.52 +/- 9.39 to 18.72 +/- 8.52, n = 13, p < 0.05. The data indicate that sulfhydryl groups are essential for guanylyl cyclase activation by NO, and are also involved in the sequestration of NO by the vascular smooth muscle soluble fraction.

Animals↗
PubMed1995

Time-dependent increase in nitric oxide formation concurrent with vasodilation induced by sodium nitroprusside, 3-morpholinosydnonimine, and S-nitroso-N-acetylpenicillamine but not by glyceryl trinitrate.

Nitrovasodilators is a term used to describe a diverse group of agents believed to exert their vasodilator effect by a common mechanism, namely formation of nitric oxide. The objective of the present study was to test this concept by comparing the magnitude of nitric oxide formation from four representative nitrovasodilators incubated in the presence of rabbit aortic strips (RAS) with the magnitude of nitrovasodilator-induced relaxation of RAS, over the time course of relaxation. The RAS were incubated in anaerobic condition with 100 microM either sodium nitroprusside, glyceryl trinitrate (GTN), 3-morpholinosydnonimine, or S-nitroso-N-acetylpenicillamine in Krebs' solution. Relaxation of RAS by each of the four drugs started at approximately 10 sec and increased with incubation time. Formation of nitric oxide was measurable using a chemiluminescence-headspace-gas method at 0.5 min with sodium nitroprusside, 3-morpholinosydnonimine, and S-nitroso-N-acetylpenicillamine, and formation increased concurrently with relaxation of RAS. In contrast, formation of nitric oxide from GTN was not measurable until 5 min, at which time GTN-induced relaxation of RAS was nearly complete. These data support the concept that sodium nitroprusside, 3-morpholinosydnonimine, and S-nitroso-N-acetylpenicillamine are nitrovasodilator drugs acting via formation of nitric oxide. However, the present study suggests that the mechanism of action for GTN-induced vasodilation may involve the formation of a nitric oxide-adduct, such as a nitrosothiol, rather than nitric oxide per se.

Animals↗
PubMed1994

Evidence for mechanism-based inactivation of rat and chick embryo hepatic cytochrome P4501A and P4503A by dihydropyridines, sydnones, and dihydroquinolines.

Rat hepatic P4501A1 and 3A1/2 have been shown previously to be targets for mechanism-based inactivation by the 4-alkyl analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC), namely, 4-ethyl DDC and 4-isopropyl DDC. In this study we have shown that rat hepatic P4501A and P4503A are targets for mechanism-based inactivation by the sydnones, 3-[2-(2,4,6-trimethylphenyl)thioethyl]-4-methylsydnone (TTMS) and 3-(2-phenylethyl)-4-methylsydnone (PEMS). The dihydroquinoline, 2,4-diethyl-2-methyl-1,2-dihydroquinoline (DMDQ), caused mechanism-based inactivation of rat hepatic P4501A but not of P4503A. The P4501A isozyme(s) of chick embryo liver was found to share the ability of rat liver P4501A to serve as a target for mechanism-based inactivation by the dihydropyridines, 4-ethyl DDC and 4-isopropyl DDC, the sydnones, TTMS and PEMS, and the dihydroquinoline, DMDQ. A P4503A-like isozyme of chick embryo liver shared the ability of the rat liver P4503A isozyme(s) to serve as a target for mechanism-based inactivation by the dihydropyridines, 4-ethyl DDC and 4-isopropyl DDC, and the sydnone, TTMS, but not of the sydnone PEMS. The dihydropyridine, DDC, was found to serve as a mechanism-based inactivator of the chick embryo P4501A isozyme(s), but not of the P4503A isozyme(s), in contrast to its previously reported inactivity with both the rat hepatic P4501A1 and 3A1/2 isozymes.

Animals↗
PubMed1994

The history of pharmacology in Canada.

Pharmacology training in Canada was initiated at McGill University in Montréal in 1824, and there are now 17 pharmacology departments in Canada offering graduate training to more than 500 students. In this article, Gerald Marks reviews the growth of pharmacology in Canada since the early 19th century in both academic establishments and in the pharmaceutical industry.

Canada↗
PubMed1994

Nitric oxide formation from glyceryl trinitrate by rabbit aortic strip: detection by rabbit taenia coli concurrent with vasorelaxation.

1. The purpose of the present study was to assay NO formation from GTN biotransformation by the rabbit aortic strip (RAS) at times concurrent with its vasorelaxation. Such an assay is an important test of the prodrug hypothesis where it is postulated that glyceryl trinitrate (GTN) is biotransformed to nitric oxide (NO), the active species that initiates vascular smooth muscle relaxation. To test such a hypothesis, we propose that a sample of smooth muscle, poorly responsive to GTN, yet sensitive to the effects of NO could be used to detect RAS production of NO from GTN. 2. Muscle strips of rabbit taenia coli (RTCS) and RAS in close apposition, were mounted in tissue baths, and muscle relaxation was recorded with isometric force transducers. Tissues were submaximally precontracted with 30-35 mM K+ depolarizing solution and exposed to increasing concentrations of GTN (0.1 nM-10 microM). 3. EC25 for GTN-induced relaxation of RTCS in the presence of RAS was significantly decreased to that for RTCS in the absence of RAS (5.9 +/- 3.0 x 10(-8) M and 5.5 +/- 3.7 x 10(-6) M, respectively). Mean maximal levels of GTN-induced relaxation of similarly precontracted RTCS also differed in the presence and absence of RAS, viz., 80.8 +/- 2.1% and 29.8 +/- 8.3% respectively. 4. RTCS was found to relax upon administration of NO gas bubbled through the incubation medium. Analysis of tissue bath medium revealed that the NO concentration to which RTCS was exposed attained a maximum of 33 nM. Relaxation of RTCS by NO gas was inhibited by 1 microM reduced haemoglobin. 5. For GTN-incubation with intestinal and vascular smooth muscle preparations, NO formation was greater with RAS compared to RTCS. Thus, in the two-issue bioassay, the RAS was the predominant source of NO formation from GTN. 6. Reduced deoxyhaemoglobin (1 microM), a potent extracellular NO scavenger, was found to decrease the augmented GTN-induced relaxation in the RTCS-RAS sandwich preparation from 17.3 +/- 1.8% to 8.0 +/- 0.8%. The augmented RTCS response was restored upon washout and subsequent addition of GTN, in the absence of reduced Hb.7 These data indicate that nitric oxide or a closely related NO-donor is produced by vascular biotransformation of GTN as seen by the increased sensitivity of RTCS to GTN when in the presence of RAS. The results of this bioassay thus support the GTN-NO prodrug hypothesis.

Animals↗
PubMed1994

Mechanism-based inactivation of hepatic cytochrome P450 2C6 and P450 3A1 following in vivo administration of 3,5-diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine to rats: differences from previously observed in vitro results.

Using progesterone 21-hydroxylase as a selective substrate for P450 2C6 in phenobarbital-treated male rats, and androstenedione and progesterone 6 beta-hydroxylases as well as erythromycin N-demethylase as selective markers for P450 3A1 in dexamethasone-treated female rats, we have shown that these P450 isozymes undergo mechanism-based inactivation after in vivo administration of 3,5-diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine (4-ethyl DDC). These results differ from our previous studies where no inactivation was observed after in vitro administration of 4-ethyl DDC to rat hepatic microsomes. We show that the differences between the in vivo and in vitro effects of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) analogues are due to the presence of residual 4-ethyl DDC in the in vitro experiments causing time-independent competitive inhibition and obscuring observation of mechanism-based inactivation.

Animals↗
PubMed1994

Inhibition of nitrovasodilators by pyocyanin and methylene blue is dissociated from nitric oxide formation.

The phenazine pigment pyocyanin (Pyo), like methylene blue (MB), inhibits vascular relaxation induced by organic nitrates. These nitrovasodilators are pro-drugs that have in common the ability to generate nitric oxide (NO). In this study, we characterized responses of rabbit isolated aortic ring to 3-morpholinosydnonimine (SIN-1), S-nitroso-N-acetylpenicillamine (SNAP), sodium nitroprusside, glyceryl trinitrate (GTN), and isosorbide dinitrate in the presence and absence of 10 microM Pyo. We also examined the effect of Pyo (1 and 10 microM) and MB (1 and 10 microM) on vasorelaxation induced by authentic NO, and finally we tested the effects of Pyo and MB on the tissue-independent formation of NO from SIN-1, SNAP, and sodium nitroprusside, using the chemiluminescence--headspace gas method. Pyo (10 microM) surmountably inhibited aortic responses to GTN, isosorbide dinitrate, SIN-1, and SNAP with a characteristic rightward shift of the dose-response curve; the apparent EC50 of these drugs for relaxation of phenylephrine-contracted aorta was increased 18-, 4-, 13-, and 15-fold, respectively. Pyo (1 and 10 microM) and MB (10 microM) inhibited NO-induced vasorelaxation at the EC50 of NO by 35, 72, and 56%. In contrast, Pyo did not inhibit sodium nitroprusside induced vasodilation. For a 10-min incubation, 10 microM Pyro or MB increased NO production from SNAP 1.8- and 2.9-fold, respectively, and increased NO production from SIN-1 by 3.8- and 7.1-fold, respectively. Neither Pyo nor MB enhanced NO formation from sodium nitroprusside. These data indicate that Pyo and MB inhibit nitrovasodilator-induced relaxation of aortic ring by interfering with the action of NO, subsequent to its formation.

Animals↗
PubMed1994

Nitric oxide actions in paraventricular nucleus: cardiovascular and neurochemical implications.

We have examined potential functions of nitric oxide (NO) within the paraventricular nucleus (PVN) in urethan-anesthetized male Sprague-Dawley rats. Initial experiments demonstrated microinjection of 50 pmol of the NO donor, sodium nitroprusside (SNP), directly into the PVN resulted in significant decreases in mean blood pressure (BP) (-3,312 +/- 1,189 mmHg/s over 300-s response time; P < 0.05). To determine whether such effects were attributable to SNP-induced NO release, NO was administered into PVN directly by bilateral microdialysis of NO-containing artificial cerebrospinal fluid (NO-aCSF), a process that results in delivery of approximately 50 pmol NO.PVN-1 x min-1. Such microdialysis resulted in significant decreases in BP (-5,121 +/- 817 mmHg/s over 1,200-s response time; P < 0.005), while aCSF microdialysis was without effect (1,298 +/- 1,071 mmHg/s over 1,200-s response time; P > 0.1). Amino acid concentrations were measured in dialysates collected during perfusion of the same PVN sites with either aCSF or NO-aCSF by high-performance liquid chromatography (HPLC) analysis. NO-aCSF induced significant increases in aspartate (aCSF 31 +/- 7 pmol/30 min; NO-aCSF 134 +/- 33 pmol/30 min; P < 0.05), glutamate (aCSF 36 +/- 5 pmol/30 min; NO-aCSF 417 +/- 108 pmol/30 min; P < 0.02), gamma-aminobutyric acid (aCSF 4.1 +/- 0.7 pmol/30 min; NO-aCSF 104 +/- 29 pmol/30 min; P < 0.02), and taurine (aCSF 34 +/- 3 pmol/30 min; NO-aCSF 117 +/- 24 pmol/30 min; P < 0.01) concentrations, while alanine, glutamine, and serine concentrations were unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1994

The effects of hypothermic and normothermic cardiopulmonary bypass on glyceryl trinitrate activity.

Glyceryl trinitrate (GTN) is used to control arterial blood pressure during cardiopulmonary bypass (CPB) procedures, but its effects are often decreased during the period of extracorporeal support. The plasma and urine concentrations of GTN and glyceryl-1,2-dinitrate (1,2-GDN) and glyceryl-1,3-dinitrate (1,3-GDN) for male and female patients who received GTN during hypothermic CPB, and male and female patients who were given GTN during normothermic CPB, were measured by gas-liquid chromatography. During hypothermic CPB, the male and female subjects experienced significant decreases in GTN clearance (P < 0.05), 66% and 52%, respectively. Neither the males nor the females who underwent normothermic CPB experienced any significant change in GTN clearance. These results suggest that the lower core temperature during hypothermic CPB may decrease the biotransformation of GTN to GDNs and nitric oxide, thereby resulting in less dilation of blood vessels. Furthermore, the males in the hypothermic CPB group had significantly greater urinary concentrations of 1,3-GDN and 1,2-GDN than the females (P < 0.05), and the normothermic CPB males had a significantly greater urinary concentration of 1,2-GDN than the females in that group. The normothermic CPB males also had significantly higher plasma concentration of GTN at two time points, and 1,3-GDN at one time point, than the females. These data suggest that there may be a gender difference in GTN biotransformation.

Aged↗
PubMed1994

Heme oxygenase: the physiological role of one of its metabolites, carbon monoxide and interactions with zinc protoporphyrin, cobalt protoporphyrin and other metalloporphyrins.

In 1991, we postulated that carbon monoxide, which is formed endogenously from heme catabolism catalyzed by heme oxygenase and shares some of the chemical and biological properties of nitric oxide, may play a role similar to that of nitric oxide as a widespread signal transduction mechanism for the regulation of cell function and communication. We review the experimental evidence that tests this postulate. Carbon monoxide appears to be involved in the neurophysiological phenomenon of long-term potentiation, which appears to play a key role in memory and learning. Zinc protoporphyrin, an inhibitor of heme oxygenase, prevents induction of long-term potentiation. Zinc protoporphyrin is an endogenous substance, the levels of which are increased in iron deficiency states and in lead poisoning, and by inhibiting heme oxygenase may modulate long-term potentiation and memory. It has been shown that, when cobalt protoporphyrin is injected into the medial nuclei of the rat hypothalamus, weight loss occurs. These nuclei contain heme oxygenase, and we postulate that weight loss is due to cobalt protoporphyrin induction of heme oxygenase and increased formation of carbon monoxide, which serves as a signal transduction mechanism in the medial hypothalamus to suppress appetite.

Animals↗
PubMed1993

A novel method for detection of nitric oxide binding sites by using a chemiluminescence-headspace gas technique.

Nitric oxide (NO) is important in many physiological, pharmacological, and pathological processes. According to current concepts, guanylyl cyclase is considered to be a receptor for NO in vascular and nonvascular smooth muscle and other tissues. Since there are no suitable radioisotopes of oxygen and nitrogen available for conventional radioligand-receptor binding studies for NO, a novel method was developed to identify NO binding site(s). A chemiluminescence-headspace gas assay was utilized to measure the sequestration of NO in biological systems, and this was used as an index of NO binding. In the present report, myoglobin (a hemoprotein, Mb) was used as a prototype macromolecule to develop the binding assay for subsequent application to studies of putative NO receptors. Solutions containing various concentrations of Mb were incubated with NO in sealed micro-Fernbach flasks at 37 degrees C in an argon atmosphere for 30 min; NO remaining in the headspace gas was analyzed by means of the chemiluminescence assay. The magnitude of NO sequestration was dependent on Mb concentration, and 5 nM Mb was the lowest Mb concentration for which NO sequestration was measurable. Application of the method to the measurement of NO sequestration by bovine serum albumin (BSA) and pulmonary artery medial layer homogenate (BPA-M) revealed that the lowest BSA concentration at which NO sequestration was measurable was 1.6 microM, which was 320 times greater than that for Mb. Applicability of the method to address the question of putative NO receptors was indicated by significant NO sequestration after incubation with 20% (w/v) homogenate of BPA-M, which is responsive to NO and putative NO prodrugs.

Animals↗