Biomedical subjects

K Kroll

Publications and source records attributed to K Kroll.

At least 19 recordsLinked to original sources

PubMed2001

Altered serum sex steroids and vitellogenin induction in walleye (Stizostedion vitreum) collected near a metropolitan sewage treatment plant.

Several recent in situ studies have reported that domestic and mixed domestic/industrial sewage effluents contain one or more natural or anthropogenic estrogenic substances. Those studies examined caged or feral fish for the presence of the egg yolk precursor protein, vitellogenin (VTG), in the blood of male fish. We have previously reported that male, feral carp (Cyprinus carpio) obtained from the effluent channel of a major sewage treatment plant (STP) exhibited depressed serum testosterone (T) concentrations, as well as detectable levels of VTG. The present study examines male and female walleye (Stizostedion vitreum), a native species with a different life history and feeding habits, collected from the same Mississippi River locations below the St. Paul metropolitan STP. All male and female walleye collected from the effluent channel contained measurable levels of VTG in their blood. Males from that location also exhibited depressed serum T concentrations and elevated serum estradiol-17beta (E2) concentrations compared with males from the Snake River reference site. Males obtained from Mississippi River Navigational Pool #2 (MRP-2), 3-20 miles downstream of the STP also exhibited reduced serum T concentrations, but showed no alterations in E2 concentrations or the presence of VTG in the serum. Females collected at the STP site had greatly elevated serum E2 concentrations, but serum T concentrations were not different from females collected in the Snake River. Our results demonstrate that the St. Paul metropolitan STP continues to release an estrogenic effluent, capable of inducing VTG production and altering normal serum sex steroid concentrations in a commercially valuable, native fish, the walleye. Additional studies will be required to determine whether these observations portend long-term population level effects.

Animals↗

PubMed2000

Comparative estrogenicity of estradiol, ethynyl estradiol and diethylstilbestrol in an in vivo, male sheepshead minnow (Cyprinodon variegatus), vitellogenin bioassay.

An in vivo bioasssay for vitellogenin (VTG) synthesis was developed to screen individual chemicals or mixtures of chemicals for potentially estrogenic effects in a marine teleost model. An enzyme-linked immunosorbent assay (ELISA) was used to quantitate VTG synthesis in male sheepshead minnows (Cyprinodon variegatus) exposed to five concentrations of the natural estrogen (17beta-estradiol), a synthetic, steroidal pharmaceutical estrogen (17alpha-ethynyl estradiol), or a synthetic, non-steroidal, pharmaceutical estrogen (diethystilbestrol) for 16 days. At an exposure concentration of 20 ng/l, only diethystilbestrol elicited a vitellogenic response. At all test concentrations greater than 100 ng/l, VTG appeared in the plasma in a dose-dependent manner for the three estrogen treatments. Liver VTG mRNA measurements were also made, exhibiting no clear correlations between quantities, nor temporal appearance of the message and mature protein were apparent. This assay is short-term, relatively inexpensive, shows a direct response, and easily quantitated.

Journal Article↗

PubMed1999

Increased hypoxic stress decreases AMP hydrolysis in rabbit heart.

OBJECTIVE: AMP conversion to adenosine by cytosolic 5'nucleotidase (5NT) or to IMP by AMP deaminase determines the degree of nucleotide degradation, and thus ATP resynthesis, during reoxygenation. To elucidate the regulation of AMP hydrolysis during ischemia, data from 31P NMR spectroscopy and biochemical analyses were integrated via a mathematical model. Since 5NT is downregulated during severe underperfusion (5% flow), we tested 5NT regulation during less severe underperfusion (10% flow) and then made the perfusate hypoxic to see if the greater stress reactivated 5NT. METHODS: 31P NMR spectra and coronary venous effluents were obtained from Langendorff-perfused rabbit hearts subjected to two 30-min periods of underperfusion (10% flow); the second period with or without additional hypoxia (30% O2). Data were analyzed with a mathematical model describing the kinetics of myocardial energetics and metabolism. RESULTS: A single 30-min period of 10% flow causes downregulation of AMP hydrolysis and the data from the second period of underperfusion are best described by lower 5NT activity, even in the presence of extra hypoxia. Thirty percent less purines appear in the venous effluent than predicted by the phosphoenergetics (PCr and ATP) when IMP is not allowed to accumulate by the model, however the model indicates that a constant accumulation of IMP via AMP deaminase could explain the discrepancy between expected and measured purines in the venous effluent. CONCLUSIONS: While AMP hydrolysis to adenosine is prominent in early ischemia and acts to preserve cellular energy potential, during a second ischemic period, nucleotides are conserved by the stable inhibition of AMP hydrolysis. Furthermore, during 10% flow conditions, nucleotides are conserved, possibly via an IMP-accumulatory pathway.

Adenosine↗

PubMed1999

Role of adenosine in local metabolic coronary vasodilation.

Adenosine has been postulated to mediate the increase in coronary blood flow when myocardial oxygen consumption is increased. The aim of this study was to evaluate the role of adenosine when myocardial oxygen consumption was augmented by cardiac paired-pulse stimulation without the use of catecholamines. In 10 anesthetized closed-chest dogs, coronary blood flow was measured in the left circumflex coronary artery, and myocardial oxygen consumption was calculated using the arteriovenous oxygen difference. Cardiac interstitial adenosine concentration was estimated from coronary venous and arterial plasma adenosine measurements using a previously described multicompartmental, axially distributed mathematical model. Paired stimulation increased heart rate from 55 to 120 beats/min, increased myocardial oxygen consumption 104%, and increased coronary blood flow 92%, but the estimated interstitial adenosine concentration remained below the threshold for coronary vasodilation. After adenosine-receptor blockade with 8-phenyltheophylline (8-PT), coronary blood flow and myocardial oxygen consumption were not significantly different from control values. Paired-pulse pacing during adenosine-receptor blockade resulted in increases in myocardial oxygen consumption and coronary blood flow similar to the response before 8-PT. Coronary venous and estimated interstitial adenosine concentration did not increase to overcome the adenosine blockade by 8-PT. These results demonstrate that adenosine is not required for the local metabolic control of coronary blood flow during pacing-induced increases in myocardial oxygen consumption.

Adenosine↗

PubMed1998

Downregulation of 5'-nucleotidase in rabbit heart during coronary underperfusion.

The hydrolysis of AMP to adenosine during acute coronary underperfusion is temporarily beneficial to myocardial survival yet may cause tissue injury during sustained underperfusion because of depletion of adenine nucleotides. We hypothesized that the enzyme mediating AMP hydrolysis, 5'-nucleotidase (5'-NT), is downregulated during sustained coronary underperfusion to prevent excessive loss of nucleotides. Langendorff-perfused rabbit hearts were subjected to two successive, identical 45-min periods of underperfusion (4-5% of baseline flow) separated by 20 min of reperfusion. Although coronary venous lactate efflux was comparable in the two periods, total coronary purine efflux during the second period of underperfusion was attenuated by 75%. Phosphorus nuclear magnetic resonance data showed that ATP fell 46% in the first period but fell only another 10% in the second period. Phosphocreatine levels fell comparably (75-78%) during both periods of underperfusion. Analysis using a mathematical model describing the kinetics of myocardial energetics revealed that the combined data set was best described by a lower activity of 5'-NT (52% decrease in maximal reaction velocity) during the second period of under-perfusion. Additional time course experiments showed that the decrease in 5'-NT activity was slow in onset, requiring approximately 20 min of underperfusion. The decrease in 5'-NT activity during sustained underperfusion may benefit tissue survival by limiting the depletion of myocardial adenine nucleotides. In conclusion, at the onset of coronary underperfusion, there is a high activity of 5'-NT, but later during sustained under-perfusion, 5'-NT is downregulated, resulting in decreased AMP hydrolysis to adenosine.

5'-Nucleotidase↗

PubMed1998

Quantitation of presynaptic cardiac sympathetic function with carbon-11-meta-hydroxyephedrine.

UNLABELLED: The purpose of this study was to validate an axially distributed blood-tissue exchange model for the quantitation of cardiac presynaptic sympathetic nervous system function that could be applied to PET images. The model accounts for heterogeneity in myocardial blood flow, differences in transport rates of 11C-meta-hydroxyephedrine (mHED) across the capillary endothelium and/or neuronal membranes, the virtual volumes of distribution in the interstitial space and neuron and retention of mHED in the neuronal vesicles. METHODS: Multiple indicator outflow dilution and residue detection methods were used to measure the kinetics of radiolabeled intravascular space and interstitial space markers and 11C-mHED in isolated perfused rat heart at baseline and during norepinephrine neuronal transporter blockade with desipramine (DMI). The outflow dilution and residue detection data were modeled with a multiple pathway, four-region, axially distributed model of blood-tissue exchange describing flow in the capillary and exchange between regions using permeability-surface area products with units of clearance of milliliters per minute per gram. Meta-hydroxyephedrine may enter the nerve terminal via membrane transport, where it may be sequestered by first-order unidirectional uptake within vesicles. Release of mHED from the vesicles is modeled via exchange with the interstitial space. RESULTS: After intracoronary injection, mHED transport across the capillary endothelium and in the interstitial space closely followed that of sucrose. Subsequently, mHED was retained in the heart, whereas sucrose washed out rapidly. With DMI the outflow dilution curves more closely resembled those of sucrose. Model parameters reflecting capillary-interstitial kinetics and volumes of distribution were unchanged by DMI, whereas parameters reflecting the neuronal transporter process and volumes of distribution in the nerve terminal and vesicular sequestration were markedly decreased by DMI. Application of the model to a pilot set of canine PET images of mHED suggests the feasibility of this approach. CONCLUSION: Meta-hydroxyephedrine kinetics in the heart can be quantitated using an axially distributed, blood-tissue exchange model that accounts for heterogeneity of flow, reflects changes in neuronal function and is applicable to PET images.

Adrenergic Uptake Inhibitors↗

PubMed1997

Open-system kinetics of myocardial phosphoenergetics during coronary underperfusion.

A novel hypothesis is proposed and tested describing open-system kinetics for myocardial phosphoenergetics. The hypothesis is that during severe coronary underperfusion there is precise matching of the rates of ATP synthesis and hydrolysis, but despite the precise balance of ATP rates, there is a decrease in the concentration of ATP and an increase in the concentration of phosphocreatine (PCr) caused by the hydrolysis of AMP to adenosine. Isolated rabbit hearts were perfused using a crystalloid medium, and coronary flow was reduced by 95% from baseline for 45 min followed by reperfusion. Phosphorus nuclear magnetic resonance spectroscopy showed a rapid decrease in PCr concentration to 25% of baseline at the onset of underperfusion followed by a gradual increase in PCr to 42% of baseline, while ATP decreased continuously to 65% of baseline. The kinetics of PCr and ATP could only be described by the precise matching of the rates of ATP synthesis and ATP hydrolysis and an open adenylate system that included the decrease in cytosolic AMP concentration via the production and efflux of adenosine. To confirm the hypothesis of open-system kinetics, two independent predictions were tested in separate experiments: 1) total coronary venous purine efflux (adenosine+inosine+hypoxanthine) during underperfusion was equal to the decrease in ATP concentration, and 2) there was no increase in PCr during moderate coronary underperfusion (80% flow reduction). In conclusion, the open nature of the myocardial adenylate system causes mass action effects that exert novel control over PCr and ATP concentrations during coronary underperfusion. The open-system kinetics cause ATP to decrease and PCr to increase, even though there is precise matching of the rates of ATP synthesis and hydrolysis. Finally, the hydrolysis of AMP to adenosine may benefit tissue survival during ischemia by improving the free energy of ATP hydrolysis, thereby delaying or preventing calcium overload.

Animals↗

PubMed1997

Role of adenosine in norepinephrine-induced coronary vasodilation.

Adenosine has been postulated to be the physiological transmitter coupling increases in coronary blood flow to increases in myocardial metabolism. The purpose of this experiment was to evaluate the role of adenosine in the coronary hyperemia due to norepinephrine. In 11 anesthetized, closed-chest canine preparations, the left main coronary artery was cannulated and perfused with blood at 100 mmHg. Coronary blood flow and myocardial oxygen consumption were measured, and interstitial adenosine concentration was estimated from arterial and coronary venous measurements using a distributed model. Adenosine receptor blockade with 8-phenyltheophylline (8-PT) was used to shift the adenosine dose-response curve 12-fold. During intracoronary norepinephrine infusion, coronary blood flow and myocardial oxygen consumption increased similarly before and after 8-PT, demonstrating a lack of an effect from the adenosine receptor blockade. Before 8-PT, estimated interstitial adenosine increased to a vasoactive concentration (220 nM); however, the temporal correlation with coronary blood flow was poor. After 8-PT, a similar increase in estimated interstitial adenosine was found, demonstrating that there was no augmentation in adenosine concentration to overcome the adenosine receptor blockade. Thus adenosine could not be responsible for the increase in coronary blood flow after adenosine receptor blockade and therefore is not required for norepinephrine-induced hyperemia.

Adenosine↗

PubMed1997

K+ATP channels and adenosine are not necessary for coronary autoregulation.

Autoregulation is defined as the intrinsic ability of an organ to maintain constant flow in the face of changing perfusion pressure. The present study evaluated the role of several potential mediators of coronary autoregulation: interstitial adenosine, ATP-sensitive K+ (K+ATP) channels, and myocardial oxygen and carbon dioxide tensions as reflected by coronary venous oxygen and carbon dioxide tensions. The left main coronary artery was cannulated, and blood was perfused at controlled pressures in closed-chest dogs. Interstitial adenosine concentration was estimated from arterial and venous adenosine concentrations with a previously described mathematical model. Autoregulation of coronary blood flow was observed between 100 and 60 mmHg. Glibenclamide, an inhibitor of K+ATP channels, reduced coronary blood flow by 19% at each perfusion pressure, but autoregulation was preserved. After stepwise reductions in coronary pressure to values > or = 70 mmHg, adenosine concentrations did not increase above basal levels. Adenosine concentration was elevated at 60 mmHg, suggesting a role for adenosine at the limit of coronary autoregulation. Adenosine is not required because glibenclamide, an inhibitor of adenosine-mediated vasodilation, did not reduce autoregulation or increase adenosine concentration. Coronary venous oxygen and carbon dioxide tensions were little changed during autoregulation before the inhibition of K+ATP channels and adenosine vasodilation with glibenclamide. However, coronary venous carbon dioxide tension rose progressively with decreasing coronary pressure after glibenclamide. The increase in carbon dioxide indirectly suggests that carbon dioxide-mediated vasodilation compensated for the loss of K+ATP-channel function. In summary, neither K+ATP channels nor adenosine is necessary to maintain coronary flow in the autoregulatory range of coronary arterial pressure from 100 to 60 mmHg.

ATP-Binding Cassette Transporters↗

PubMed1997

Hypoxia-induced inhibition of adenosine kinase potentiates cardiac adenosine release.

To elucidate the physiological role of the AMP-adenosine metabolic cycle and to investigate the relation between AMP and adenosine formation, the O2 supply of isolated guinea pig hearts was varied (95% to 10% O2). The net adenosine formation rate (AMP-->adenosine) and coronary venous effluent adenosine release rate were measured; free cytosolic AMP was determined by 31P-nuclear magnetic resonance. Switching from 95% to 40% O2 increased free AMP and adenosine formation 4-fold, whereas free cytosolic adenosine and venous adenosine release rose 15- to 20-fold. In the AMP range from 200 to 3000 nmol/L, there was a linear correlation between free AMP and adenosine formation (R2 = .71); however, adenosine release increased several-fold more than formation. At 95% O2, only 6% of the adenosine formed was released; however, this fraction increased to 22% at 40% O2, demonstrating reduced adenosine salvage. Selective blockade of adenosine deaminase and adenosine kinase indicated that flux through adenosine kinase decreased from 85% to 35% of adenosine formation in hypoxia. Mathematical model analysis indicated that this apparent decrease in enzyme activity was not due to saturation but to the inhibition of adenosine kinase activity to 6% of the basal levels. The data show (1) that adenosine formation is proportional to the AMP substrate concentration and (2) that hypoxia decreases adenosine kinase activity, thereby shunting myocardial adenosine from the salvage pathway to venous release. In conclusion, because of the normal high turnover of the AMP-adenosine metabolic cycle, hypoxia-induced inhibition of adenosine kinase causes the amplification of small changes in free AMP into a major rise in adenosine. This mechanism plays an important role in the high sensitivity of the cardiac adenosine system to impaired oxygenation.

Adenosine↗

PubMed1996

Proteins of cytosol and amniotic fluid increase the voltage dependence of human type-1 porin.

Heat-stable proteins from human and porcine cytosol and human amniotic fluid were found to increase the voltage dependence of human type-1 porin reconstituted in planar phospholipid bilayers. Purification processes revealed that these regulatory molecules were characterized by anionic charge and apparent molecular weights of between 23 and 64 kDa. The human cytosol proteins exerted inhibitory activity only when added to the compartment with applied negative potential. The observed increase in voltage dependence of porin was due to the presence of specific proteins in cytosol and amniotic fluid, since human cerebral spinal fluid in comparable amounts had no significant effect on the channel properties. Furthermore, other anionic proteins and polypeptides investigated demonstrated no inhibitory activity, indicating that anionic charge alone could not mimic the molecular properties of the regulatory proteins. With respect to the well-documented expression of porin in the plasma membrane of various cells and species, the presented data give first clues for a biochemical regulation of the channel in this compartment.

Amniotic Fluid↗

PubMed1996

The divergent domains of the NEFA and nucleobindin proteins are derived from an EF-hand ancestor.

The human protein NEFA (DNA binding, EF-hand, Acidic region) has previously been isolated from a KM3 cell line and immunolocalized on the plasma membrane, in the cytoplasma, and in the culture medium. Sequence analysis of a cDNA clone encoding NEFA identified a hydrophilic domain, two EF-hands, and a leucine zipper at the C-terminus. These characters are shared with nucleobindin (Nuc). In this paper we have further characterized NEFA and probed its evolutionary origins. Circular dichroism (CD) spectra of recombinant NEFA indicated a helical content of 51% and showed that the EF-hands are capable of binding Ca2+. Experiments with recombinant NEFA and synthesized peptides revealed that the leucine zipper cannot form a homodimer. The leucine zipper may allow heterodimer formation of NEFA and an unknown protein. Phylogenetic analyses suggest that this protein is derived from a four-domain EF-hand ancestor with subsequent duplications and fusions. The leucine zipper and putative DNA-binding domains of NEFA have evolved secondarily from existing EF-hand sequences. These analyses provide insights into how complex proteins may originate and trace the precursor of NEFA to the common ancestor of eukaryotes.

Amino Acid Sequence↗

PubMed1996

Effect of glucose on uptake of radiolabeled glucose, 2-DG, and 3-O-MG by the perfused rat liver.

In the transition from the fasting to the fed state, plasma glucose levels rise, and the liver converts from an organ producing glucose to one of storage. To determine the effect of glucose on hepatic glucose uptake, radiolabeled glucose, 2-deoxyglucose, and 3-O-methylglucose were injected into perfused rat livers during different nontracer glucose levels, and the concentrations in the outflow were measured. A mathematical model was developed that described the behavior of the injected compounds as they traveled through the liver and was used to simulate and fit the experimental results. The rates of membrane transport, glucokinase, glucose-6-phosphatase, and the consumption of glucose 6-phosphate were estimated. Membrane transport for all of the tracers decreased as nontracer glucose increased, demonstrating competitive inhibition of the glucose transporter. In contrast, the consumption of injected [2-14C]glucose increased when glucose was elevated, demonstrating that glucose caused an activation of enzyme activity that overcame the competitive inhibition of transport and phosphorylation. When glucose was elevated, the rate coefficient of glucokinase did not decrease, indicating that glucokinase was stimulated by glucose. Both changes would lead to the increased glycogen synthesis and decreased glucose production rate observed in vivo during the fasted-to-fed transition.

3-O-Methylglucose↗

PubMed1996

Adenosine kinetics in canine coronary circulation.

Adenosine kinetics in the coronary circulation were investigated in anesthetized closed-chest dogs by analysis of multiple-indicator dilution experiments. During simultaneous intracoronary bolus injections of 125I-labeled albumin, [14C]sucrose, and [3H]adenosine, dilution curves were measured by automated sampling of coronary venous blood, using high-performance liquid chromatography and isotope detection techniques. Under control conditions, only 1% of the injected [3H]adenosine was detected in coronary venous samples, compared with the reference tracer, [14C]sucrose, and the peak of the adenosine dilution curve preceded those of the reference tracers by 2-4 s. Optimized model fits to the control adenosine curves required the combination of high ratios of the capillary endothelial cell membrane permeability-surface area product to flow (5.3) and endothelial cell consumption capacity to flow (23), in addition to a broad heterogeneity of flow. Dilution curves were measured under control conditions and during increased coronary flow (nitroglycerin), inhibition of the enzyme adenosine kinase (iodotubercidin), and blockade of membrane adenosine transport (dipyridamole). Reliability of the parameter estimates was confirmed using residual analysis, sensitivity function analysis, and Monte Carlo simulation techniques. Accuracy of the model was confirmed in separate experiments in which nontracer adenosine was infused into the coronary artery and the model prediction of coronary venous adenosine concentrations was compared with measured values. Using published measurements of coronary blood flow and arterial and coronary venous plasma adenosine concentrations in open-chest dogs, the estimated in vivo interstitial adenosine concentration is 100-220 nM.

Adenosine↗

PubMed1996

Modeling regional myocardial flows from residue functions of an intravascular indicator.

The purpose of the present study was to determine the accuracy and the sources of error in estimating regional myocardial blood flow and vascular volume from experimental residue functions obtained by external imaging of an intravascular indicator. For the analysis, a spatially distributed mathematical model was used that describes transport through a multiple-pathway vascular system. Reliability of the parameter estimates was tested by using sensitivity function analysis and by analyzing "pseudodata": realistic model solutions to which random noise was added. Increased uncertainty in the estimates of flow in the pseudodata was observed when flow was near maximal physiological values, when dispersion of the vascular input was more than twice the dispersion of the microvascular system for an impulse input, and when the sampling frequency was < 2 samples/s. Estimates of regional blood volume were more reliable than estimates of flow. Failure to account for normal flow heterogeneity caused systematic underestimates of flow. To illustrate the method used for estimating regional flow, magnetic resonance imaging was used to obtain myocardial residue functions after left atrial injections of polylysine-Gd-diethylenetriaminepentaacetic acid, an intravascular contrast agent, in anesthetized chronically instrumental dogs. To test the increase in dispersion of the vascular input after central venous injections, magnetic resonance imaging data obtained in human subjects were compared with left ventricular blood pool curves obtained in dogs. It is concluded that if coronary flow is in the normal range, when the vascular input is a short bolus, and the heart is imaged at least once per cardiac cycle, then regional myocardial blood flow and vascular volume may be reliably estimated by analyzing residue functions of an intravascular indicator, providing a noninvasive approach with potential clinical application.

Animals↗

PubMed1996

Quantitative relation between interstitial adenosine concentration and coronary blood flow.

The effect of exogenous and endogenous adenosine in controlling coronary flow was determined using an axially distributed mathematical model of the myocardium to estimate interstitial adenosine concentration from coronary arterial and venous adenosine values. The left main coronary artery was perfused at constant pressure in closed-chest, anesthetized dogs, and exogenous adenosine was infused intracoronary to increase coronary flow. Basal interstitial adenosine was 92 nmol/L, just at the threshold for increasing coronary flow. An increase in interstitial adenosine concentration of only 62% was sufficient to increase coronary flow from 5% to 50% of maximal flow. The possible contribution of an endothelial dilator secondary to activation of adenosine receptors on endothelial cells was tested by comparing the response to exogenous intracoronary adenosine infusion with increases in endogenous adenosine produced by inhibition of adenosine kinase and adenosine deaminase. If adenosine increases coronary flow by an endothelial mechanism, then the interstitial ED50 of exogenous adenosine would be lower than that for endogenous adenosine due to the postulated additional endothelial dilator. The interstitial ED50 for exogenous adenosine was 156 nmol/L, not different from the endogenous ED50 of 150 nmol/L. In conclusion, basal interstitial adenosine concentration is at the threshold of a remarkably steep dose-response curve for increasing coronary blood flow. No evidence was found for an endothelium-mediated vasodilator mechanism secondary to adenosine receptor activation of endothelial cells in vivo. The steep adenosine dose-response curve indicates that measurements of adenosine concentration should be interpreted with caution, because small changes in adenosine concentration cause large changes in coronary flow.

Adenosine↗

PubMed1996

A Xenopus nodal-related gene that acts in synergy with noggin to induce complete secondary axis and notochord formation.

Using a paracrine assay to screen for signaling proteins that could respecify ectodermal tissue, we isolated a Xenopus gene related to the mouse gene nodal, a member of the TGFbeta superfamily. The gene is expressed in three regions in the early Xenopus embryo: first in the gastrula organizer, then in two stripes of cells flanking the posterior notochord in late neurulae, and finally in lateral plate mesoderm restricted to the left side of tailbud-stage embryos. Ectopic expression of the gene induces muscle formation in ectodermal explants and partial secondary axes in whole embryos. Together with noggin, another secreted protein also present in the organizer, it induces notochord formation in ectodermal explants and complete secondary axes in whole embryos. These results suggest that the nodal-related gene may act together with noggin to induce axial pattern during gastrulation and also may play a role in left-right asymmetry generation in the post-gastrula embryo.

Animals↗

PubMed1995

EDRF and norepinephrine-induced vasodilation in the canine coronary circulation.

Experiments were performed to characterize the role of endothelium-derived relaxing factor (EDRF) in coronary vasodilation caused by norepinephrine. The circumflex or left anterior descending coronary artery was cannulated and pump perfused with constant pressure or constant flow in closed-chest anesthetized dogs. Prostaglandin synthesis was blocked with ibuprofen. During constant-pressure perfusion, EDRF inhibition with intracoronary N omega-nitro-L-arginine (L-NNA) did not affect the vasodilation due to nitroglycerin (an endothelium-independent process). However, L-NNA did significantly inhibit (P < 0.001) the vasodilation due to acetylcholine (an endothelium-dependent process). In response to bolus injections of norepinephrine, EDRF inhibition with L-NNA significantly reduced coronary vasodilation (P < 0.001). This inhibition was partially reversed with L-arginine infusion. To determine whether an increase in shear stress due to an increase in flow was the stimulus for EDRF release, experiments were performed during constant-flow conditions. Vasodilation caused by nitroglycerin was not inhibited by L-NNA, but EDRF inhibition did blunt acetylcholine-induced vasodilation significantly (P < 0.001) during constant-flow perfusion. During EDRF inhibition with L-NNA, vasodilation due to norepinephrine was not significantly altered when coronary flow was held constant (P = 0.19). In conclusion, EDRF plays a role in norepinephrine-induced coronary vasodilation that is largely flow dependent.

Acetylcholine↗