Spectral Characteristics and Molecular Structure of (E)-1-(4-Chlorophenyl)-3-(4-(Dimethylamino)Phenyl)Prop-2-en-1-One (DAP)

In this work, a laser dye of (E)-1-(4-chlorophenyl)-3-(4-(dimethylamino)phenyl)prop-2-en-1-one (DAP) was synthesized and examined as a new laser medium. The compound DAP’s photophysical properties were investigated under the influence of solvents, concentrations, and pump power excitations. The absorption spectra showed a single band, and the shape of the spectra remained the same, regardless of the optical density. The fluorescence spectra showed a band around 538 nm; its intensity was inversely proportional to the concentration. DAP exhibits dual amplified spontaneous emission (ASE) bands at 545 and 565 nm under suitable pump power laser excitation and concentration. The results revealed that the ASE band at 565 nm is affected by solvents polarity, concentrations and pump power energies. This band could be attributed to the combination of two excited molecules and the solvent between them (superexciplex). Moreover, the molecular structure, the energy bandgap, and the total energy of DAP was calculated using density functional theory.     

Lipoprotein size and atherosclerosis susceptibility in Apoe(-/-) and Ldlr(-/-) mice

Two hypercholesterolemic mouse models, the apo-E-deficient mouse (Apoe(-/-)) and the LDL receptor-deficient mouse (Ldlr(-/-)), have been used extensively as animal models of atherogenesis. Total plasma cholesterol levels in chow-fed Apoe(-/-) mice are much higher than in Ldlr(-/-) mice. In a recent study, we managed to even-up the cholesterol levels in Apoe(-/-) mice and Ldlr(-/-) mice by making both models homozygous for the Apob(100) (apo B-100-only) allele. On a chow diet, apo-E-deficient apo B-100-only mice (Apoe(-/-)Apob(100/100)) and LDL receptor-deficient apo B-100-only mice (Ldlr(-/-)Apob(100/100)) had similar total plasma cholesterol levels ( approximately 300 mg/dL). The plasma of Ldlr(-/-)Apob(100/100) mice contained large numbers of small lipoproteins, whereas the plasma of Apoe(-/-)Apob(100/100) mice contained much lower levels of much larger lipoproteins. Interestingly, the Ldlr(-/-)Apob(100/100) mice developed far more extensive atherosclerotic lesions than the Apoe(-/-)Apob(100/100) mice. The finding of substantially more atherosclerosis in Ldlr(-/-)Apob(100/100) mice than in Apoe(-/-)Apob(100/100) mice, despite nearly identical cholesterol levels, suggests that large numbers of small apo B-100-containing lipoproteins are far more atherogenic than lower numbers of large apo B-100-containing lipoproteins.     

Evaluation of 2-(methylaminosulfonyl)-1-(arylsulfonyl)hydrazines as anticancer agents

Seven new 2-(methylaminosulfonyl)- 1-(arylsulfonyl)hydrazines were prepared and evaluated as potential antitumor agents in vivo against murine Ehrlich ascites carcinoma (EAC). Borderline in vivo activity in EAC was exhibited by two compounds. All of them were screened in vitro against a battery of human tumor cell lines at the National Cancer Institute (NCI), USA. One of them, namely compound 2f(NSC No. 649 752) displayed highly significant specificity in two different cell lines as non-small cell lung cancer line HOP-18 and in CNS cancer line SNB-19. The compounds assessed in vitro for anti-HIV activity also at the NCI, however, have not reached the criteria of significant activity. The alkylating activity of the compounds was determined by measuring the absorbance of the alkylated product of 4-(4-nitrobenzyl)pyridine. It was found that they are capable of acting as chemical alkylating agents.     

Adrenocorticotropin(1-10) and -(11-24) promote adrenal steroidogenesis by different mechanisms

ACTH1-10 and ACTH11-24 each elicit cortisol secretion submaximally in freshly dispersed or cultured beef adrenal cortical cells. The combination of ACTH1-10 and ACTH11-24 promotes cortisol release to the maximal level elicited by ACTH1-24. Maximal cortisol release by ACTH11-24, but not by ACTH1-24 or ACTH1-10, was enhanced by forskolin. The calcium channel blockers nifedipine and verapamil inhibited cortisol release by ACTH1-10, ACTH1-24 or ACTH11-24, suggesting calcium influx to be essential for steroid secretion regardless of the secretagogue. Vanadium, in a dose-dependent manner, inhibited cortisol secretion elicited by ACTH1-24 and ACTH1-10 but not that caused by ACTH11-24. These results suggest that there are at least two receptors mediating ACTH1-24-dependent steroid secretion. One class of receptor recognizes ACTH1-10 but not ACTH11-24 and is linked to the cAMP messenger pathway.     

3-Deazaadenosine inhibits vasa vasorum neovascularization in aortas of ApoE(-/-)/LDL(-/-) double knockout mice

BackgroundAtherosclerosis and inflammation/angiogenesis are strongly associated including growth of vasa vasorum (VV) and plaque neovascularization, but a causative role for neovascularization has still not been established. Hence, we investigated the effect of 3-deazaadenosine (c³Ado), an anti-inflammatory and anti-proliferative drug, on plaque progression and VV neovascularization in apoE^?/?/LDL^?/? double knockout mice.MethodsThe arterial trees from apoE^?/?/LDL^?/? mice with, or without c³Ado at the age of 16 weeks (n = 10), 18 weeks (n = 8) and 20 weeks (n = 7) were infused in situ with Microfil, and the aortas harvested and scanned with micro-CT (12 μm cubic voxel). We characterized plaque volume and VV luminal volume along the descending aorta using Analyze 6.0 software. Cellular effects of c³Ado on human endothelial and vascular smooth muscle cells were investigated in cell cultures and on nylon cDNA expression arrays.ResultsLesions spatially connected to VV increased from 16 to 20 weeks significantly (p < 0.001). The volume of atherosclerotic lesions was significantly reduced in animals treated with c³Ado (p < 0.01). This was accompanied by a significant decrease of vasa vasorum neovascularization along the descending aorta (p < 0.01). Using nylon cDNA expression arrays, we identified the regulation of anti-proliferative, anti-inflammatory genes in human smooth muscle cells which might be involved in the anti-angiogenic effects of c³Ado. Moreover, c³Ado dose-dependently prevented the proliferation and migration of human coronary artery endothelial cells in vitro.ConclusionThe smaller lesion volume in animals treated with c³Ado was closely associated with a reduced VV neovascularization, suggesting a direct relationship between lesion growth and VV development.     

1,2-Bis(methylsulfonyl)-1-(2-chloroethyl)-2-[[1-(4-nitrophenyl)ethoxy]carbonyl]hydrazine: an anticancer agent targeting hypoxic cells

To target malignant cells residing in hypoxic regions of solid tumors, we have designed and synthesized prodrugs generating the cytotoxic alkylating species 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine (90CE) after bioreductive activation. We postulate that one of these agents, 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-[[1-(4-nitrophenyl)ethoxy]carbonyl]hydrazine (KS119), requires enzymatic nitro reduction to produce 90CE, whereas another agent, 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-[(4-nitrobenzyloxy)carbonyl]hydrazine (PNBC), can also be activated by nucleophilic attack by thiols such as glutathione (GSH)/GST. We demonstrated that these agents selectively kill hypoxic EMT6 mouse mammary carcinoma and CHO cells. In hypoxia, 50 microM KS119 produced 5 logs of kill of EMT6 cells without discernable cytotoxicity in air; similar effects were observed with CHO cells. PNBC was less efficacious against hypoxic tumor cells and also had some toxicity to aerobic cells, presumably because of GST/thiol activation, making PNBC less interesting as a selective hypoxic-cell cytotoxin. BALB/c mice with established EMT6 solid tumors were used to demonstrate that KS119 could reach and kill hypoxic cells in solid tumors. To gain information on bioreductive enzymes involved in the activation of KS119, cytotoxicity was measured in CHO cell lines overexpressing NADH:cytochrome b5 reductase (NBR), NADPH:cytochrome P450 reductase (NPR), or NADPH: quinone oxidoreductase 1 (NQO1). Increased cytotoxicity occurred in cells overexpressing NBR and NPR, whereas overexpressed NQO1 had no effect. These findings were supported by enzymatic studies using purified NPR and xanthine oxidase to activate KS119. KS119 has significant potential as a hypoxia-selective tumor-cell cytotoxin and is unlikely to cause major toxicity to well oxygenated normal tissues.     

ICAM-1 deficiency reduces atherosclerotic lesions in double-knockout mice (ApoE(-/-)/ICAM-1(-/-)) fed a fat or a chow diet

Intercellular adhesion molecule (ICAM)-1, a major adhesion molecule, plays a critical role in the homing of leukocytes to sites of atherosclerotic lesions. However, very little is known on the role of ICAM-1 in initiating and perpetuating vascular lesions in ApoE(-/-) mice fed a chow or a fat diet. This study has investigated the mean aortic lesions in mice (C57BL6 background) with a single-knockout (ApoE(-/-)) or double-knockout (DKO; ApoE(-/-), ICAM-1(-/-)) fed a chow or a fat diet over a period of 3, 6, 15, and 20 weeks. A 3-fold reduction in lesion size was observed at all time points in DKO mice fed a chow diet. However, in DKO mice fed a fat diet, a marked reduction in the aortic lesion was observed at 3 and 15 weeks, which did not reach a significant level at 6 and 20 weeks. This study shows in essence that DKO mice are protected from developing significant lesions for up to 6 weeks when fed a chow diet and from 3 to 6 weeks when fed a fat diet. After 6 weeks, the lesion size of the DKO mice follows that of the single-knockout mice when fed a chow diet and gets to the same level in mice fed a fat diet. Plasma cholesterol levels were not altered as a result of ICAM-1 deficiency. These studies show that ICAM-1 is implicated in the formation and progression of atherosclerotic lesions.     

(E)-5-(2-Bromovinyl)-2''-deoxyuridine: a potent and selective anti-herpes agent.

Of a series of five newly synthesized 2'-deoxyuridine derivatives, including 5-vinyl-dUrd, 5-ethynyl-dUrd, 5-(1-chlorovinyl)-dUrd, (E)-5-(2-bromovinyl)-dUrd, and (E)-5-(2-iodovinyl)-dUrd, the last two compounds were found to exert a marked inhibitory effect on the replication of herpes simplex virus type 1 [ID50 (mean inhibitory dose), 0.004-0.02 microgram/ml]. Both (E)-5-(2-bromovinyl)-dUrd and (E)-5-(2-iodovinyl)-dUrd were highly selective in their anti-herpes activity in that they did not affect the growth or metabolism of the host (primary rabbit kidney) cells unless drug concentrations were used that were 5,000- to 10,000-fold greater than those required to inhibit virus multiplication. In this sense (E)-5-(2-bromovinyl)-dUrd and (E)-5-(2-iodovinyl)-dUrd proved more selective in their activity against herpes simplex virus type 1 than all other anti-herpes compounds that have been described so far. In animal model systems (namely, cutaneous herpes infections of athymic nude mice), (E)-5-(2-bromovinyl)-dUrd suppressed the development of herpetic skin lesions and mortality therewith associated, whether the compound was administered topically or systemically. Under the same conditions, the standard anti-herpes drug 5-iodo-dUrd (Idoxuridine) offered little, if any, protection. Although the precise mechanism of action of (E)-5-(2-bromovinyl)-dUrd and (E)-5-(2-iodovinyl)-dUrd remains to be established, preliminary findings indicate that they do not specifically act at the thymidylate synthetase step.     

Antitumor activity of 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) and 1-(2-chloroethyl)-3-(4-methyl-cyclohexyl)-1-nitrosourea (MeCCNU) on yoshida sarcoma ascites cells implanted into the colon wall of rats

Summary Three thousand Yoshida sarcoma cells were inoculated into the wall of the descending colon of each of 120 male Sprague-Dawley rats. On day 8 after the tumor implantation, the animals were at random divided into four groups of 30 rats each. The effect of cyclophosphamide (70 mg/kg), BCNU (25 mg/kg), and methyl-CCNU (45 mg/kg) after single i.p. application was investigated. The Yoshida sarcoma transplanted into the colon is sensitive to all three chemotherapeutic drugs. At the doses given cyclophosphamide showed the best results. The two nitrosoureas had a comparable antitumor activity but methyl-CCNU showed a more distinct toxic effect.The introduction of this model for testing new cytostatics in animal experiments is discussed.     

Acute myeloid leukaemia with an unusual phenotype: myeloperoxidase (+), CD13 (-), CD14 (-) and CD33 (-)

We herein describe an unusual case of acute myeloid leukaemia (AML) showing strong cytochemical reactivity for myeloperoxidase (MPO) but surprisingly no reactivity using flow cytometry for any of the lineage-specific cell surface markers, i.e. myelomonocytic antigens CD13, CD14 and CD33; or B-lymphoid antigens CD19, CD20 and immunoglobulins; or T-lymphoid antigens CD2, CD3 and CD5. The strong reactivity for MPO and the complete absence of reactivity for CD13 and CD14 was verified by an independent assay involving alkaline phosphatase-anti-alkaline phosphatase (APAAP). Our case is of interest for at least two reasons: First, a poorly differentiated variant of AML (negative for MPO but positive for one or more of the myeloid-lineage CD antigens) has been designated FAB M0. In terms of the expression of phenotypic markers, our case may be considered as an 'MPO (+), CD antigen (-) AML'. The CD antigens are known to be expressed very early during myeloid differentiation whereas MPO (in its functional form) is viewed as being expressed relatively late in the process. It is therefore intriguing from a biological standpoint why the supposedly early antigens (CD33 and CD13) remain unexpressed; this may represent an example of 'asynchronous differentiation' in leukaemia. Second, from a practical standpoint, the use of immunophenotyping as a first-line diagnosis would fail to detect such cases. This case strengthens the notion that immunophenotyping by flow cytometry does not eliminate the necessity of performing peroxidase cytochemical staining.     

Effect of an oral astaxanthin prodrug (CDX-085) on lipoprotein levels and progression of atherosclerosis in LDLR(-/-) and ApoE(-/-) mice

Oxidative stress and inflammation are key promoters of atherosclerosis and myocardial damage. When orally administered, the novel astaxanthin prodrug CDX-085 delivers high levels of the xanthophyll antioxidant astaxanthin that protects LDL from oxidation and reduces primary thrombosis. In this study, we analyzed whether delivery of astaxanthin from administration of the CDX-085 prodrug reduces plasma lipoprotein levels and the progression of atherosclerosis in low-density lipoprotein receptor negative (LDLR^?/?) and apolipoprotein E deficient (ApoE^?/?) mice.MethodsRelative circulating levels of astaxanthin derived from CDX-085 administration compared to administration of pure astaxanthin was initially evaluated in a canine model. In mouse Study #1, 16 wild-type and 16 LDLR^?/? mice on 0.5% cholesterol diet supplemented with either 0.0%, 0.08%, 0.2% and 0.4% CDX-085 were used to assess plasma levels and lipoprotein biodistribution measured by FPLC after 4 weeks treatment. In Study #2, 36 male LDLR^?/? mice were randomized to a 0.5% cholesterol chow diet (CHOW group, n = 12) or 0.5% cholesterol chow fortified with 0.08% CDX-085 (n = 12) or 0.5% cholesterol chow with 0.4% CDX-085 (n = 12) for 12 weeks. In Study #3, 34 male ApoE^?/? mice were randomized in the same fashion as the Study #2 and fed similar diets for 9 weeks.ResultsCDX-085 administration was shown to result in significantly higher levels of circulating astaxanthin (p < 0.001 ANOVA) over a 72 h period compared to pure, non-esterified astaxanthin in a single-dose pharmacokinetic study in beagles. In Study #1, plasma astaxanthin levels were 5–9-fold higher in LDLR^?/? mice compared to wild-type mice. Astaxanthin was highly distributed among all lipoprotein fractions, generally reflecting cholesterol content of lipoproteins. In Study #2, administration of CDX-085 resulted in significantly lower total cholesterol levels (528 ± 68 mg/dL vs. 550 ± 67 mg/dL vs. 602 ± 80 mg/dL, p = 0.047) and aortic arch atherosclerosis (9.0 ± 4.2% vs. 9.8 ± 3.5% vs. 13.2 ± 3.6%, p = 0.023) in the 0.4% CDX-085 group compared to the 0.08% CDX-085 and CHOW groups, respectively. In ApoE^?/? mice, a 72% reduction in triglycerides in the 0.4% CDX-085 group and 50% reduction in the 0.08% CDX-085 groups was noted compared to CHOW group (final levels 17 ± 11 mg/dL vs. 30 ± 15 mg/dL vs. 60 ± 32 mg/dL, respectively, p = 0.001).ConclusionOral administration of the novel astaxanthin prodrug CDX-085 shows that it distributes among lipoproteins. CDX-085 lowers total cholesterol and aortic arch atherosclerosis in LDLR^?/? mice and triglyceride levels in ApoE^?/? mice and shows promise for further evaluation in human studies.     

Phosphoramidon blocks the pressor activity of porcine big endothelin-1-(1-39) in vivo and conversion of big endothelin-1-(1-39) to endothelin-1-(1-21) in vitro.

In porcine aortic endothelial cells, the 21-amino acid peptide endothelin-1 (ET-1) is formed from a 39-amino acid intermediate called "big endothelin-1" (big ET-1) by a putative ET-converting enzyme (ECE) that cleaves the 39-mer at the bond between Trp-21 and Val-22. Since big ET-1 has only 1/100-1/150th the contractile activity of ET-1, inhibition of ECE should effectively block the biological effects of ET-1. Big ET-1 injected intravenously into anesthetized rats produces a sustained pressor response that presumably is due to conversion of big ET-1 into ET-1 by ECE. We determined the type of protease activity responsible for this conversion by evaluating the effectiveness of protease inhibitors in blocking the pressor response to big ET-1 in ganglion-blocked anesthetized rats. The serine protease inhibitor leupeptin, the cysteinyl protease inhibitor E-64, and the metalloprotease inhibitors captopril and kelatorphan were all ineffective at blocking the pressor response to big ET-1. However, the metalloprotease inhibitors phosphoramidon and thiorphan dose-dependently inhibited the pressor response to big ET-1, although phosphoramidon was substantially more potent than thiorphan. None of the inhibitors blocked the pressor response to ET-1 and none had any effect on mean arterial pressure when administered alone. In a rabbit lung membrane preparation, ECE activity was identified that was blocked by the metalloprotease inhibitors phosphoramidon and 1,10-phenanthroline in a concentration-dependent manner. This enzyme converted big ET-1 to a species of ET that comigrated on HPLC with ET-1 and produced an ET-like contraction in isolated rat aortic rings. Our results suggest that the physiologically relevant ECE is a metalloprotease.     

Effects of GLP-1-(7-36)NH2, GLP-1-(7-37), and GLP-1- (9-36)NH2 on intravenous glucose tolerance and glucose-induced insulin secretion in healthy humans

Glucagon-like peptide 1 (GLP-1) is an insulin secretagogue synthesized in the intestine and released in response to meal ingestion. It is secreted primarily in two forms, GLP-1-(7-37) and GLP-1-(7-36)NH(2), both of which bind to a specific GLP-1 receptor (GLP-1r) on the pancreatic beta-cell and augment glucose-stimulated insulin secretion. Once secreted, GLP-1-(7-36)NH(2) is rapidly metabolized to GLP-1-(9-36)NH(2), which is the predominant form of GLP-1 in postprandial plasma because of its relatively slower clearance. Although no clear biological role for GLP-1-(9-36)NH(2) in humans has been identified, recent studies in animals suggest two potential effects: to antagonize the effects of intact GLP-1 and to promote glucose disappearance in peripheral tissues. In the studies reported here we compared the independent effects of GLP-1-(7-36)NH(2), GLP-1-(7-37), and GLP-1-(9-36)NH(2) on parameters of iv glucose tolerance and determined whether GLP-1-(9-36)NH(2) inhibits the insulinotropic actions of GLP-1. Ten healthy subjects underwent 4 separate frequently sampled iv glucose tolerance tests during infusions of GLP-1-(7-37), GLP-1-(7-36)NH(2), GLP-1-(9-36)NH(2), or saline. Results from the iv glucose tolerance test were used to obtain indexes of beta-cell function (acute insulin response to glucose) and iv glucose tolerance (glucose disappearance constant), and the minimal model of glucose kinetics was used to obtain indexes of glucose effectiveness and insulin sensitivity. Compared with control studies, both GLP-1-(7-36)NH(2) and GLP-1-(7-37) significantly increased acute insulin response to glucose, glucose disappearance constant, glucose effectiveness, and glucose effectiveness at zero insulin, but did not change the insulin sensitivity index. In contrast, none of the parameters of glucose tolerance was measurably affected by GLP-1-(9-36) amide. In a second set of experiments, 10 healthy subjects had glucose-stimulated insulin secretion measured during an infusion of GLP-1-(7-36)NH(2) alone or with a simultaneous infusion of GLP-1-(9-36)NH(2) that increased plasma levels approximately 10-fold over those produced by unmetabolized GLP-1. Augmentation of glucose-stimulated insulin secretion by GLP-1-(7-36)NH(2) was not altered by the coadministration of GLP-1-(9-36)NH(2). Based on these results we conclude that GLP-1-(9-36)NH(2) does not regulate insulin release or glucose metabolism in healthy humans.     

Stimulation of the AT2 receptor reduced atherogenesis in ApoE(-/-)/AT1A(-/-) double knock out mice

AT1 receptor blockers (ARB) and in part ACE inhibitors (ACI) potentially exert beneficial effects on atherogenesis independent of AT1 receptor inhibition. These pleiotropic effects might be related to angiotensin II mediated activation of the AT2 receptor. To analyze this hypothesis we investigated the development of atherosclerosis and the role of ACIs and ARBs in apolipoprotein E-deficient (ApoE(-/-)) mice and in ApoE/AT1A receptor double knockout mice (ApoE(-/-)/AT1A(-/-)). ApoE(-/-) mice and ApoE(-/-)/AT1A(-/-) mice were fed cholesterol-rich diet for 7 weeks. Vascular oxidative stress, endothelial dysfunction, and atherosclerotic lesion formation were evident in ApoE(-/-) mice, but were markedly reduced in ApoE(-/-)/AT1A(-/-) mice. Concomitant treatment of ApoE(-/-)/AT1A(-/-) mice with either telmisartan or ramipril had no additional effect on blood pressure, vascular oxidative stress, AT2 receptor expression, and endothelial function. Remarkably, atherosclerotic lesion formation was increased in ramipril treated ApoE(-/-)/AT1A(-/-) mice compared to untreated ApoE(-/-)/AT1A(-/-) mice whereas pharmacological AT1 receptor inhibition with telmisartan had no additional effect on atherogenesis. Moreover, chronic AT2 receptor inhibition with PD123,319 significantly increased plaque development in ApoE(-/-)/AT1A(-/-) mice. In additional experiments, direct AT2 receptor stimulation reduced atherogenesis in ApoE(-/-)/AT1A(-/-) mice. Taken together, our data demonstrate a relevant antiatherosclerotic role of the AT2 receptor in atherosclerotic mice and provide novel insight in RAS-physiology.     

Inotropic and lusitropic effects of MCI-154 (6-[4-(4- pyridyl)aminophenyl]-4,5-dihydro-3(2H)-pyridazinone) on human myocardium

We studied the inotropic and lusitropic responses to MCI-154 in 12 right or left ventricular trabeculae carneae isolated from 7 organ donors (non-cardiac) without known cardiovascular disease who met accepted criteria for brain death. Isometric tension was recorded from muscles superfused with a physiologic salt solution at 30 degrees C, and stimulated to contract at three-second intervals. Concentration-response curves were developed over a range of MCI-154 organs bath concentrations (10(-7) M to 3 x 10(-4) M; n = 9). Six experiments were conducted using 10(-6) M carbachol, a muscarinic agonist, in the presence of a maximally effective concentration of MCI-154 to test for dependence of tension development on cyclic adenosine monophosphate. Three experiments were conducted with MCI-154, 3 x 10(-5) M, in muscles loaded with the bioluminescent calcium indicator aequorin. MCI-154 produced a concentration-dependent rise in peak tension in the human muscle (positive inotropic effect), equivalent to 70% of the maximal response to calcium (P less than 0.001). Relaxation was enhanced (positive lusitropic effect), as evidenced by a fall in the time to 80% relaxation from 311 +/- 13 ms (baseline) to 248 +/- 15 ms at 10(-5) M (P less than 0.01). Aequorin studies showed the increase in tension to be accompanied by large increases in cystolic calcium, the principal mechanism of action. Carbachol caused MCI-154--induced maximum peak tension to decrease by 5 +/- 1%. While not excluding a cyclic adenosine monophosphate--mediated MCI action, this modest carbachol inhibition suggests the existence of additional mechanism(s) of action. MCI-154 had a negative lusitropic effect at high concentrations (greater than 10(-4)M) which may have been due to intracellular calcium overload, evidenced by the large amplitude aequorin signals. This does not exclude sensitization of the myofilaments to calcium as a possibility. Extrapolated to the in vivo setting, these experiments suggest that MCI-154 may be an effective positive inotropic agent in man.