In vitro, animal, and human characterization of OPTISON infusions for myocardial contrast echocardiography.

UNLABELLED: Traditionally, performing myocardial contrast echocardiography with OPTISON required maximal bolus dosing. However, sustained and consistent opacification of the myocardium would be preferable for perfusion imaging. METHODS: Images of 5 anesthetized dogs and 6 human volunteers were obtained with a second harmonic ultrasound system during bolus administration of OPTISON and 2 infusion techniques. One infusion technique used diluted OPTISON, and the other used the buoyant properties of OPTISON microspheres by placing the contrast agent between an infusion source and the intravenous site in a vertically oriented extension line (ELT). Myocardial intensities and in vitro microsphere characteristics were analyzed to assess the consistency of microsphere delivery over time. RESULTS: In addition to providing higher myocardial opacification intensity than diluted infusions, ELT infusions provided consistent microsphere concentration, phantom enhancement, and near-peak bolus-level myocardial opacification for 7 to 15 minutes. The myocardial intensity at 3 and 5 minutes in human subjects during ELT infusions (30 mL/h; 2.5 mL) was lower (220 arbitrary units [au] and 165 au, respectively) but not significantly different (P =.3 and.1, respectively) than the peak myocardial intensity (265 au) after bolus administration. CONCLUSION: This new ELT infusion method provides an acceptable alternative to bolus administration of OPTISON for prolonged myocardial opacification.

Physiologically based pharmacokinetic model for fluorocarbon elimination after the administration of an octafluoropropane-albumin microsphere sonographic contrast agent.

A physiologically based pharmacokinetic model was developed to evaluate the kinetics of one of the newest sonographic contrast agents available, FS069 or Optison. This material consists of octafluoropropane gas encapsulated in proteinaceous microspheres, injected intravenously for use as a myocardial contrast agent in humans. This model has six compartments: two lung compartments (alveolar and dead volume), and compartments for the heart, slowly perfused tissue, richly perfused tissue, and gastrointestinal tract. The model was developed to determine the distribution and excretion of the octafluoropropane in the body. Despite the high affinity of octafluoropropane for tissue, the model predicted that nearly 100% of the material would be exhaled from the lungs within 6 min. The model verified the results of a phase I clinical trial with 10 healthy subjects. Ventilation rate was found to play a critical role in the complete excretion of this contrast agent. The physiologically based pharmacokinetic model was a useful tool for evaluating the safety of FS069. This model can be used a basis for developing similar models for other types of contrast agents.

Lack of bioeffects of ultrasound energy after intravenous administration of FS069 (Optison) in the anesthetized rabbit.

The current study was designed to provide a sensitive in vivo model to maximize the potential bioeffects (measured by hemolysis) of B-mode ultrasound energy in combination with FS069 (Optison). B-mode ultrasound energy was delivered to anesthetized male New Zealand white rabbits with a phased array 5 MHz transducer on a Hewlett-Packard Sonos 1500 ultrasonograph, with transmit level set to maximum (40 dB, approx 135 W/cm2). FS069 (Optison), latex particles in human albumin, or human albumin alone (vehicle) was infused via an ear vein at 0.6 mL/kg. No statistically significant changes were noted in serum free hemoglobin or lactate dehydrogenase either over time or between groups.

Detection of myocardial perfusion defects by contrast echocardiography in the setting of acute myocardial ischemia with residual antegrade flow.

Although myocardial contrast echocardiography accurately demarcates area at risk during total coronary occlusion, the ability of MCE to delineate area at risk in the presence of residual antegrade flow is unknown. We hypothesized that perfusion defects in myocardial segments supplied by severe coronary stenoses with residual antegrade flow could be detected by MCE using intravenous FS069. We studied 13 open-chest dogs using an intravenous injection of FS069 during intermittent harmonic imaging. Images were collected at baseline, during acute ischemia with residual antegrade flow, physiologic hyperemia (release of stenosis), and total coronary occlusion. Regional myocardial blood flow was assessed using colored microspheres. MCE risk area during acute ischemia with residual antegrade flow and total occlusion was planimetered and compared with pathologic risk area (area unstained by monastral blue). Background-subtracted peak videointensity in the risk area was assessed for all flow states. Regional myocardial blood flow confirmed expected flow states, being significantly greater during physiologic hyperemia (4.16 +/- 1.22 ml/min/g) than at baseline (0.71 +/- 0.19 ml/min/g) and significantly diminished during coronary stenosis with residual antegrade flow (0.20 +/- 0.16 ml/min/g) and total occlusion (0.09 +/- 0.06 ml/min/g; p < 0.0001). Myocardial risk area by MCE during coronary stenosis with residual antegrade flow correlated well with pathologic risk area determined by monastral blue staining (r = 0.86). Peak videointensity during coronary stenosis (111 +/- 27) was significantly less than at baseline (157 +/- 50) but greater than during total occlusion (81 +/- 34; p < 0.0001). In conclusion, intravenous FS069 in conjunction with intermittent harmonic imaging delineates area at risk in ischemic myocardium supplied by a coronary stenoses with residual antegrade flow. The presence of a perfusion defect on MCE does not necessarily imply that the coronary artery is totally occluded.

Role of alpha 1-adrenoceptors and 5-HT2 receptors in serotonin-induced contraction of rat prostate: autoradiographical and functional studies.

Urinary obstruction from benign prostatic hyperplasia is a common clinical problem possibly associated with excessive prostatic constriction around the urethra. These studies compared adrenergic and serotonergic functional activity to specific alpha 1 and serotonin (5-hydroxytryptamine; 5-HT) binding sites in the rat prostate. Isolated, left ventral lobes of the rat prostate were removed and examined for in vitro contraction. Norepinephrine-induced contraction of the rat prostate was competitively blocked by prazosin with an apparent antagonist dissociation constant (pKB) of 8.13. 5-HT also contracted the rat prostate. However, in the presence of prazosin, maximum 5-HT contraction was reduced by half suggesting that high concentrations of 5-HT can activate alpha 1 receptors in the prostate. The concentration-response curve to 5-HT in the presence of 1 microM prazosin was competitively inhibited by the 5-HT2 receptor antagonist LY53857 (6-methyl-1-(1-methylethyl)ergoline-8-carboxylic acid 2-hydroxyl-1-methylpropylester (Z)-2-butenedioate (1:1)) (pKB = 9.02). Autoradiographic studies with [125I]LSD (2-iodo-lysergic acid diethylamide) documented the presence of 5-HT2 receptors since significant displacement of the radioligand occurred with 5-HT and LY53857, but not with prazosin. The alpha 1-adrenoceptor ligand [125I]HEAT ([beta-(4-hydroxy-3-iodophenyl)ethylaminomethyl]-tetralone) confirmed the presence of alpha 1-adrenoceptors in the rat prostate since significant displacement of the radioligand occurred with prazosin, but not 5-HT or LY53857. The inability of prazosin to displace [125I]LSD and the inability of 5-HT to displace [125I]HEAT suggest that 5-HT cannot directly interact with alpha 1-adrenoceptors in the prostate.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelets and alpha-naphthylisothiocyanate-induced liver injury.

Administration of alpha-naphthylisothiocyanate (ANIT) to rats results in periportal cholangiolitic hepatopathy. Inflammation is a hallmark of the liver injury, and expression of toxicity is dependent on blood neutrophils. The role of other cellular mediators of inflammation in ANIT-induced hepatic insult is unknown. We hypothesized that platelets participate in the expression of ANIT hepatotoxicity. To test this, circulating platelets were decreased by administration of anti-rat platelet serum (PAb) prior to treatment of rats with ANIT. The PAb treatment regimen effectively reduced circulating thrombocytes over the course of the experiment. Twenty-four hours after oral ANIT administration, rats were euthanized and liver injury was estimated by increases in serum alanine aminotransferase (ALT) and gamma-glutamyltransferase (GGT) activities. Cholestasis was assessed by measurement of serum total bilirubin concentration and bile flow. Reduction in platelet numbers was associated with attenuation of the increases in plasma ALT activity and bilirubin concentration seen after ANIT administration. However, PAb treatment did not attenuate the increase in plasma GGT, a marker of biliary epithelial cell injury. ANIT-induced changes in platelet function were assessed by evaluating platelet aggregation responses in platelet-rich plasma from rats treated with ANIT in vivo. ANIT treatment modestly decreased ex vivo platelet aggregation in response to ADP and collagen stimuli. To address further the role of platelet-derived cyclooxygenase products in ANIT hepatotoxicity, rats were treated with aspirin or ibuprofen. Neither pretreatment ameliorated ANIT-induced hepatic insult. These results suggest that platelets contribute to the expression of ANIT-induced liver injury, but they do not appear to act through the production of cyclooxygenase metabolites.

Cardiovascular and thrombosis pathology associated with cocaine use.

After decades of focus on the effects of cocaine abuse on the central nervous system (CNS), the cardiovascular toxicity of cocaine is just beginning to be appreciated. The most common cardiovascular pathologies associated with cocaine use include: cardiomyopathy, left ventricular dysfunction, myocarditis, arrhythmia, hypertension, myocardial infarction, stroke, arterial thrombosis, deep vein thrombosis, and gastrointestinal, renal, and skeletal muscle ischemia. This article reviews the above pathologies with speculations on the mechanisms by which cocaine produces cardiovascular tissue damage.

Presence of beta- but not alpha-adrenoceptors in the rat jugular vein: autoradiographical evidence.

Previous functional studies with the rat jugular vein have shown alpha-adrenergically mediated contraction was minimal to nonexistent, yet this tissue relaxed in response to norepinephrine via beta 1 and to isoproterenol via beta 2-receptor activation. Unlike the rat jugular vein, the rat aorta markedly contracted to norepinephrine and relaxed to beta-adrenoceptor stimulation. This study qualitatively examined the alpha- and beta-receptor distributions in the rat jugular vein, as compared to the rat aorta, with autoradiographical methods. Cross-sections of blood vessels were labelled with the alpha-receptor ligand, [125I]HEAT ([beta-(4-hydroxy-3-iodophenyl)-ethyl-aminomethyl]-tetralone) and the beta-receptor ligand, [125I]ICYP (iodo-cyanopindolol), and subsequently were opposed to emulsion coated coverslips. Specific binding of both alpha- and beta-receptors was demonstrated in the rat aorta. While specific beta-receptor binding was demonstrated in the rat jugular vein, this tissue showed no detectable alpha-receptors. These autoradiographic studies indicate that the lack of alpha-adrenergically mediated contraction in the rat jugular vein is likely due to a virtual absence of alpha-receptor binding sites, rather than poor functional alpha-receptor coupling.

Characterization of rat platelet serotonin receptors with tryptamine agonists and the antagonists: ketanserin and SCH 23390.

Current literature suggests that the platelet 5-HT2 receptor, thought to be the only active platelet serotonin (5-HT) receptor, may be both heterogeneous and not the sole 5-HT receptor subtype on platelet membranes. The present studies used more selective tryptamine agonists, and the antagonists ketanserin and SCH 23390 to characterize rat platelet 5-HT receptors in vitro. The present studies also addressed anticoagulant effects (citrate versus heparin) on platelet 5-HT aggregation in the rat. 5-HT was less potent at enhancing ADP-induced aggregation in heparinized rat platelet rich plasma (PRP) as compared to citrated PRP. However, potency and maximum aggregation to ADP were greater in heparinized platelets. In citrated rat PRP, the selective tryptamine agonists, 5-carboxamidotryptamine (5-CT) and 2-CH3-5-HT, produced little change in the baseline ADP-induced aggregation and induced platelet shape change only in higher concentrations (greater than 1 microM). In contrast, alpha-CH3-5-HT-induced shape change and enhancement of ADP aggregation were superimposable with that of 5-HT itself suggesting 5-HT2 receptor activation. The antagonists, ketanserin and SCH 23390, inhibited 5-HT enhancement of ADP-induced aggregation with affinity constants consistent with the presence of 5-HT2 receptors as well. Studies with heparinized rat PRP did not unmask activity to 5-CT or 2-CH3-5-HT. Thus, although reports of multiple platelet 5-HT receptors exist, the only detectable, functional 5-HT receptor to enhance aggregation in rat platelets was probably of the 5-HT2 type.

LY53857, a 5HT2 receptor antagonist, delays occlusion and inhibits platelet aggregation in a rabbit model of carotid artery occlusion.

The present study was designed to evaluate the effectiveness of the ergoline 5HT2 receptor antagonist, LY53857 in a rabbit model of vascular arterial occlusion. LY53857 (1 and 10 microM) inhibited serotonin amplified platelet aggregation responses to threshold concentrations of ADP in rabbit platelets in vitro. LY53857 (1 microM) not only inhibited the serotonin component of rabbit platelet aggregation, but also inhibited in vitro aggregation induced by ADP (48.7 +/- 16.7% inhibition), collagen (76.1 +/- 15.9% inhibition) and U46619 (65.2 +/- 12.3% inhibition). The effectiveness of this ergoline 5HT2 receptor antagonist in blocking aggregation to ADP, collagen and U46619 may be related to its ability to inhibit a serotonin component of platelet aggregation since rabbit platelets possess high concentrations of serotonin that may be released during aggregation produced by other agents. Based on the effectiveness of LY53857 to inhibit rabbit platelet aggregation, we explored the ability of LY53857 to extend the time to carotid artery occlusion in rabbits following electrical stimulation of the artery. Reproducible carotid artery occlusion was induced in rabbits by moderate stenosis coupled to arterial cross clamping, followed by electrical stimulation. With this procedure, occlusion occurred at 47.0 +/- 7 min (n = 30) after initiation of the electrical stimulation. Animals pretreated with LY53857 (50 to 500 micrograms/kg i.v.) showed a delay in the time to carotid artery occlusion (at 100 micrograms/kg i.v. occlusion time extended to 164 +/- 16 min). Furthermore, ex vivo platelet aggregation from animals treated with LY53857 (300 micrograms/kg i.v.) resulted in 40.5% inhibition of platelet aggregation in response to the combination of ADP (1 microM) and serotonin (1 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of two different arterial tissues suggests possible 5-hydroxytryptamine2 receptor heterogeneity.

A comparison of activities and affinities of several known and novel compounds in the isolated rat thoracic aorta (RA) and the rabbit femoral artery (RFA) was undertaken to evaluate these two tissues for use in screening for functional 5-hydroxytryptamine2 (5-HT2) receptor activity. Affinities for 5-HT and for ketanserin against 5-HT-elicited contractions in both vascular tissues suggested the presence of homogeneous 5-HT2 receptors with values consistent with other reported 5-HT2 receptor preparations. However, further studies showed compounds which exhibited either partial agonism in the RFA and competitive antagonism of 5-HT in the RA, or antagonism of 5-HT in both arteries with different affinities. Affinity constants calculated from the isolated vascular tissue studies were compared with affinity constants calculated for inhibition of [3H]ketanserin binding in the frontal cortices of both the rat and the rabbit. There were no significant differences between the pKi values in the rat and the rabbit cortical membranes or between these pKi's in either species and the pA2 values in the RA. Several of the affinities for both the partial agonists and the antagonists in the RFA were significantly different from the binding pKi and the pA2 values in the RA. These findings suggest identity between the [3H]ketanserin binding site in the cortices of both species and the 5-HT2 receptor in the RA; however, the contractile 5-HT receptor in the RFA, although showing some characteristics of a 5-HT2 receptor, is significantly different. We suggest that there may be functional subtypes of the vascular 5-HT receptor.