Effects of acetaminophen and nonsteroidal anti-inflammatory drugs on progesterone production by porcine granulosa cells in vitro

We investigated the effects of a group of pharmaceutical agents commonly ingested by reproductive-aged women, acetaminophen and the nonsteroidal anti-inflammatory drugs (NSAID), on progesterone (P) production by cultures of highly differentiated porcine granulosa cells. These compounds were added to cultures over a dose range of 10(-8) to 10(-5) M and P, and cell protein was measured after 24 hours. P production was suppressed by acetaminophen, fenoprofen, and sulindac to a maximum of 81%, 76%, and 71% of control, respectively. P production was enhanced by butazolidin at all doses tested to a maximum of 140% of control. Granulosa cell protein was suppressed by butazolidin and salicylic acid to a maximum of 81% of controls. These data imply that acetaminophen and several NSAID have the potential for clinical reproductive toxicity with differing individual effects on reproductive tract tissues, suggesting further selective testing in vivo.     

Effects of adrenomedullin on rat cerebral arterioles

The effects of adrenomedullin on isolated rat intracerebral arterioles were investigated and compared with those of calcitonin gene-related peptide (CGRP) and amylin. Adrenomedullin produced dose-dependent vasodilation (maximum dilation 27.1±2.1% at 3×10⁻⁷ M, median effective dose (EC₅₀) 1.6×10⁻⁹ M). CGRP produced similar vasodilation (19.8±4.1%) at 10⁻⁷ M with a lower EC₅₀ of 2.8×10⁻¹¹ M. Amylin did not cause vasodilation at concentrations up to 10⁻⁶ M. Adrenomedullin-induced vasodilation was significantly suppressed by CGRP-(8–37). These data suggest that adrenomedullin is a potent vasodilator for arterioles in the cerebral microcirculation that acts through CGRP receptors.     

Hepatic toxicity of paraquat in primary cultures of rat hepatocytes

The aim of this work was to evaluate the hepatic effects of toxic and subtoxic doses of paraquat, using a primary culture of adult rat hepatocytes as an experimental model. Concentrations in culture ranged from 10⁻³ to 10⁻⁹ -paraquat. When added to cultures at the time of plating 10⁻³ -paraquat impaired hepatocyte spreading on the substratum and caused cell death which was preceded by a leakage of cytosolic enzymes (lactate dehydrogenase, glutamic-oxaloacetic transaminase). When added to 24-hr cultures, effects on the metabolism of the hepatocytes were observed at paraquat concentrations of 10⁻³ and 10⁻⁴ but not at lower concentrations. In comparison with controls, when paraquat was present at 10⁻³ , gluconeogenesis from fructose and lactate was inhibited by 40 and 58%, respectively, ureogenesis was inhibited by 16% and the albumin synthesis rate was reduced by 62%. The intracellular content of the reduced form of glutathione decreased by 33% and was parallelled by an increase in the oxidized form of glutathione. However, neither cytotoxic nor metabolic effects were observed in cells exposed to 10⁻⁵ , the concentration found in blood after acute intoxication with paraquat.     

Carbon film resistor electrode for amperometric determination of acetaminophen in pharmaceutical formulations

Flow injection analysis (FIA) with amperometric detection was employed for acetaminophen quantification in pharmaceutical formulations using a carbon film resistor electrode. This sensor exhibited sharp and reproducible current peaks for acetaminophen without chemical modification of its surface. A wide linear working range (8.0 × 10⁻⁷ to 5.0 × 10⁻⁴ mol L⁻¹) in phosphate buffer solution as well as high sensitivity (0.143 A mol⁻¹ L cm⁻²) and low submicromolar detection limit (1.36 × 10⁻⁷ mol L⁻¹) were achieved. The repeatability (R.S.D. for 10 successive injections of 5.0 × 10⁻⁶ and 5.0 × 10⁻⁵ mol L⁻¹ acetaminophen solutions) was 3.1 and 1.3%, respectively, without any memory effect between injections. The new procedure was applied to the analyses of commercial pharmaceutical products and the results were in good agreement with those obtained utilizing a spectrophotometric method. Consequently, this amperometric method has been shown to be very suitable for quality control analyses and other applications with similar requirements.     

Validation of whole chick embryo cultures, whole rat embryo cultures and aggregating embryonic brain cell cultures using six pairs of coded compounds

A comparative study was performed to assess the effects of six pairs of coded compounds using cultures of whole chick and rat embryos as well as aggregating brain cell cultures. Developed originally for basic studies in developmental biology, these three culture systems have been adapted for the screening of chemicals in the field of prenatal toxicology. Chick and rat embryos were cultured for 2 days during the early stages of organogenesis. Aggregating cell cultures were prepared from early foetal rat telecephalon and grown for 14 days in a chemically defined medium. Concentration-response relationships were established by treating whole embryos in vitro for 2 days, and aggregating brain cell cultures for 9 days. After decoding the compounds, the results showed that, in the three test systems, specific effects were induced at comparable concentration levels. Similar compound-related malformations could be observed in both chick and rat whole embryo cultures. In aggregating brain cell cultures, neuron- and glia-specific effects could be distinguished. Based on the results obtained in the three in vitro systems, the following concentration ranges were determined for the teratogenic/toxic potencies of the test compounds (in mol/litre): <10⁻⁶: retinoids (Ro 13-6307, Ro 1-5488), 6-aminonicotinamide, ketoconazole; 10⁻⁶−10⁻³: 4-hydroxypyridine, sulfadiazine, sulfanilamide, caffeine, theophylline, metronidazole, methoxyacetic acid; >10⁻³: methoxyethanol. In general, the three in vitro test systems were found to provide concordant and complementary data on the toxicity and teratogenicity of a given compound. These data were also comparable with those available from in vivo studies. It is therefore concluded that such a test battery could contribute significantly to risk assessment and to the reduction of in vivo experimentation in reproductive toxicology.     

JNK1 is required for sulindac-mediated inhibition of cell proliferation and induction of apoptosis in vitro and in vivo

Our previous studies demonstrated that sulindac, a non-steroidal anti-inflammatory drug, suppressed intestinal tumor formation in mouse, which is linked to the induction of wild-type p53-activated fragment 1 (p21WAF1, or p21). Here we showed that sulindac also required c-Jun N-terminal Kinase 1 (JNK1) to inhibit cell proliferation and induce apoptosis in vitro and in vivo. First, sulindac inhibited cell proliferation and induced apoptosis in colon cancer cell lines HCT116 with wild-type p21 or null p21, which were p21-dependent and were also associated with the induction of p21 and phosphorylation of JNK1. Second, sulindac increased apoptosis in JNK1^+/+ and JNK1^−/− mouse embryonic fibroblast (MEF) cells, but, the increase of apoptosis in JNK1^+/+ cells was more than that in JNK1^−/− cells. More interestingly, sulindac significantly inhibited cell proliferation in JNK1^+/+ cells, but the inhibition in JNK1^−/− cells markedly decreased. Further studies indicated that JNK1 was dramatically induced by sulindac in the JNK1^+/+ cells which correlated with the induction of p21. However, the induction of p21 in JNK1^−/− cells was less than that in JNK1^+/+ cells. Finally, we determined the expression of JNK1 in the intestinal mucosa of Apc^+/−, p21^+/+ mice, and found that sulindac significantly induced JNK1 phosphorylation, corresponding to the induction of p21, both in mRNA and protein levels. Our data indicates that sulindac-mediated proliferation inhibition and apoptosis induction were not only p21-dependent, but also required JNK1.     

KATP channels do not mediate vasodilation by 3-morpholinosydnonimine in goat coronary artery

The present study investigated the role of ATP-sensitive potassium (K_ATP) channels in mediating relaxation to the nitric oxide (NO) donor, 3-morpholinosydnonimine (SIN-1) in goat coronary arteries. SIN-1 (10⁻⁸–10⁻⁵ M) caused concentration-dependent relaxations of the coronary artery ring segments contracted with K⁺ (30 mM) with an EC₅₀ of 6.61×10⁻⁷ M. Methylene blue (3×10⁻⁶ M) caused a rightward shift in the concentration–response curve of SIN-1 (10⁻⁸–3×10⁻⁵ M) with a corresponding increase in the EC₅₀ (3.62×10⁻⁶ M) of the nitrovasodilator. While the K_ATP channel blocker, glibenclamide (1 and 3×10⁻⁶ M) caused dose-dependent inhibition of vasorelaxations produced by pinacidil (10⁻⁸–10⁻⁴ M), it had no effect on the vasodilations elicited by SIN-1 (10⁻⁸–10⁻⁵ M) in the coronary arterial smooth muscle. Increasing the extracellular K⁺ concentration from 30 mM to 80 mM to reduce the K⁺ gradient across the cell membrane, inhibited the relaxations elicited by pinacidil (10⁻⁸–10⁻⁴ M). On the other hand, SIN-1 (10⁻⁸–10⁻⁵ M)-induced relaxations were potentiated in high K⁺ (80 mM) compared to those observed at K⁺ (30 mM). These results suggest that goat coronary artery vasodilations caused by the NO donor, SIN-1, do not involve K_ATP channels.     

Effects of papaverine on isolated rabbit papillary muscle

The effect of papaverine on the positive inotropic response to isoprenaline and to calcium was studied on the rabbit isolated papillary muscle; theophylline and the calcium antagonistic D600 were used for comparison. The dose—response curve for isoprenaline was shifted to the left by papaverine (3 × 10⁻⁶ to 3 × 10⁻⁵ M), in a dose-dependent manner, while that for calcium was not affected by the same concentration. In this respect papaverine was about 30 times more potent than theophylline. In the presence of papaverine isoprenaline induced arrhythmic contractions of the papillary muscle: the incidence of arrhythmic contractions correlated to the concentration of papaverine. Papaverine 10⁻⁵ to 10⁻⁴ M caused only a positive inotropic response whereas 3 × ⁻¹⁰ to 10⁻³ M induced a biphasic response, i.e., after a positive inotropic effect followed a negative one. In the presence of 3 × 10⁻⁴ M papaverine isoprenaline failed to cause a positive inotropic response but exclusively induced arrhythmic contractions. Calcium, on the other hand, readily antagonized the negative inotropic effectof papaverine (3 × 10⁻⁴ M) and caused a contracture of the papillary muscle. The results indicate that papaverine (3 × 10⁻⁶ to 10⁻⁵ M) like theophylline (10⁻⁴ to 10⁻³ M) produces its effect by phosphodiesterase inhibition and thereby specifically potentiates the response through β-adrenoceptor stimulation. In higher concentrations (3 × 10⁻⁴ to 10⁻³ M) it act as a calcium antagonistic, like D600, and furthermore may interact with calcium moving through myocardial cell membranes to cause a contracture via a mechanism which it shares with theophylline.     

8-isoprostaglandin E(2) activates Ca(2+)-dependent K(+) current via cyclic AMP signaling pathway in murine renal artery

The inhibitory pathway of 8-isoprostaglandin E₂ was investigated in murine renal arterial smooth muscle. K⁺ current was augmented in a concentration-dependent fashion, with an average increase of 123 ± 28% (n = 6) following application of 10^− 5 M 8-isoPGE₂. This augmentation was observed in the presence of 4-aminopyridine (4-AP, 10^− 3 M) but not that of charybdotoxin (ChTx, 10^− 7 M). Fluorimetric recordings showed marked concentration-dependent increase of cytosolic Ca²⁺ levels by 8-isoPGE₂, while an enzyme-linked immunosorbent assay (ELISA)-based cyclic AMP assay showed increased cAMP levels by 10^− 7 M 8-isoPGE₂ challenge. The isoprostane-induced augmentation was prevented by the ryanodine receptor blocker ruthenium red (10^− 5 M) or the adenylate cyclase blocker SQ 22536 (10^− 4 M). The protein kinase A (PKA) inhibitor H89 (10^− 5 M) inhibited resting K⁺ currents (78 ± 5%, n = 5) but did not prevent 8-isoPGE₂ from augmenting the remaining K⁺ current. We conclude that 8-isoPGE₂ enhances Ca²⁺-dependent K⁺ currents in murine renal artery through a cAMP-dependent pathway which may involve internally sequestered Ca²⁺.     

Effects of branched-chain amino acids on DNA synthesis and proliferation in primary cultures of adult rat hepatocytes

We investigated the effects of branched-chain amino acids on DNA synthesis and proliferation in primary cultures of adult rat hepatocytes. Of the branched-chain amino acids, only leucine (10⁻⁵–10⁻³ M) induced hepatocyte DNA synthesis and proliferation in a time- and dose-dependent manner. The addition of valine or isoleucine on its own had no significant effects on the hepatocyte DNA synthesis and proliferation. When combined, isoleucine competitively antagonized leucine-stimulated hepatocyte mitogenesis. U73122 (10⁻⁶ M), AG1478 (10⁻⁷ M), wortmannin (10⁻⁷ M), PD98059 (10⁻⁶ M) and rapamycin (10 ng/ml) inhibited the ability of leucine to stimulate the hepatocyte DNA synthesis and proliferation, suggesting that phospholipase C, tyrosine kinase, phosphatidylinositol 3-kinase, mitogen-activated protein (MAP) kinase, and p70 S6 kinase are involved in leucine signaling. The mitogenic effects of leucine are completely abolished by the addition of anti-transforming growth factor- (TGF-) antibody to the culture medium. Furthermore, leucine stimulated TGF- secretion into the culture medium and the leucine effect was inhibited by U73122. Isoleucine alone had no significant effect on TGF- secretion but this agent blocked leucine-induced TGF- secretion. The results suggest that leucine triggers TGF- secretion through a putative leucine receptor. The secreted TGF- then stimulates hepatocyte DNA synthesis and proliferation through activation of TGF- receptor to induce tyrosine kinase/MAP kinase activity and other downstream growth-related signal transducers.     

Effects of CD-832, a dihydropyridine derivative with a nitrate ester moiety, on rabbit femoral artery and vein

We investigated the effects of CD-832 ((4R)-(−)-2-(nicotinoyl-amino)ethyl 3-nitroxypropyl 1,4-dihydro-2,6-dimethyl-4,3-nitrophenyl, 3,5-pyridine dicarboxylate), a dihydropyridine derivative with a nitrate ester moiety, on contractile responses in rabbit femoral arteries and veins. CD-832 (10⁻⁸ to 10⁻⁶ M) and nifedipine inhibited the 64 mM KCl-induced and 10⁻⁶ M norepinephrine-induced contractions of rabbit femoral arteries, while nitro compounds had no effect on the contractions. CD-832 (10⁻⁸ to 10⁻⁶ M) and nitro compounds inhibited the 10⁻⁶ M norepinephrine-induced contractions in rabbit femoral veins, while other Ca²⁺ channel antagonists had little effect. The inhibitory effects of CD-832 (10⁻⁷ M) on norepinephrine-induced contractions were antagonized by treatment with methylene blue (10⁻⁵ M). These results indicate that CD-832 potently relaxes venous smooth muscle, and that it may be a useful agent for the treatment of angina pectoris.     

Nitric oxide modulates angiotensin II-induced endothelial vasoconstrictor prostanoid release

This study investigated the modulation of angiotensin II-induced endothelial prostanoid release in rabbit aortic rings. Two cumulative dose response curves with 90-min washing interval were performed. Incubation with l-N^G-nitroarginine methyl ester (l-NAME) 10^− 4 M increased angiotensin II maximal contractile response (E_max). This effect was reversed by indomethacin 10^− 5 M, diphenyliodinum 10^− 5 M, Tempol 10^− 5 M or ascorbic acid 10^− 4 M in both cumulative dose response curves and by SQ 29548 10^− 6 M in the second cumulative dose response curve. When segments were treated with tetraethylamonium 10^− 3 M but not with glibenclamide 10^− 5 M during the washing period, l-NAME recovered its ability to enhance the E_max in arteries incubated with SQ 29548. Conclusions: nitric oxide modulates angiotensin II-induced endothelial release of cyclooxygenase-dependent eicosanoids, one of which acts through thromboxane A₂/prostaglandin H₂ receptors and would decrease K_Ca channel activity. An increase in free radical production may account for the enhancement of such prostanoid release. Furthermore, it was found that in the present conditions, the release of the hyperpolarizing factor would improve in order to maintain the vascular tone.     

Single-dose topical exposure to the pyrethroid insecticide, permethrin in C57BL/6N mice: effects on thymus and spleen

Immunomodulatory effects of single topical exposure to permethrin were evaluated in 5-week-old female C57BL/6N mice. Mice exposed to 5–25 μl permethrin (equivalent to 220–1100 mg/kg body weight) on shaved interscapular skin were evaluated for altered body weight; splenic and thymic organ weight and cellularity; thymocyte cell surface expression, cellular apoptosis; splenic macrophage phagocytosis and hydrogen peroxide production; splenic B cell antibody production and T cell cytolytic activity; and mitogen-induced proliferation of splenocytes and thymocytes after in vivo or in vitro permethrin exposure. Topical permethrin application (25 μl) caused 32% inhibition of splenic T cell proliferation; in vitro exposure to permethrin also diminished splenocyte proliferation by 72% at 25 μ and 86% at 100 μ . permethrin did not appear to affect other leukocyte functional assays. Dose-related decreases in thymic cellularity of 52 and 80% were seen in mice exposed to 15 and 25 μl permethrin, respectively. Apoptosis was significantly increased in CD4⁻8⁻ and CD4⁻8⁺ thymocytes, and the CD4⁺CD8⁺ thymocyte subpopulation was most severely diminished, suggesting possible chemical-induced apoptotic mechanism of thymic atrophy. Permethrin also caused splenic hypocellularity by 31% at 15 μl, and by 50% at 25 μl, an effect that may relate to inhibited proliferation or reduced seeding from the hypocellular thymus.     

Adenosine alters the vascular effects of a diacylglycerol analogue and polymyxin B

Endothelium-denuded rat aorta rings were used to study the possible relationship between protein kinase C and the mechanism of adenosine-induced smooth muscle relaxation. Adenosine (5 × 10⁻⁴M) partially relaxed the aortic rings contracted by either a depolarising amount of KCl (4 × 10⁻² M) or activation of protein kinase C with l-oleoyl-2- acetyl-sn-glycerol (10⁻⁶ M). The same amount of adenosine blocked the further relaxation obtained in the presence of polymyxin B (5 × 10⁻⁵ M), a protein kinase C blocking agent. These results suggest a possible interaction in vascular smooth muscle between adenosine and protein kinase C.     

Effect of temperature on limitation by MK-801 of firing of action potentials by spinal cord neurons in cell culture

The anticonvulsant, MK-801, limited sustained high frequency repetitive firing of sodium-dependent action potentials by mouse spinal cord neurons in monolayer dissociated cell culture. Limitation was voltage- and temperature-dependent and was accompanied by decreasing rate of rise of action potentials until firing ceased during the 400 ms depolarizations. The IC₅₀ for limitation was 2 × 10⁻⁷ M at 37°C, 6.4 × 10⁻⁷ M at 35°C, and 4 × 10⁻⁵ M at 23°C. The relationship between the percentage of neurons capable of sustained repetitive firing and MK-801 concentration at 33°C was biphasic. The first phase (about 50%) of limitation had IC_50a = 1.5 × 10⁻⁷ M, and the second had IC_50b = 2 × 10⁻⁴ M; the midpoint of the connecting plateau was 10⁻⁵ M. At temperatures below 37°C, the current needed to achieve maximal firing increased. The maximal rate of rise, maximal firing frequency and sensitivity to MK-801 of action potentials elicited by 1 ms stimuli decreased at temperatures below 37°C. Passive membrane properties were unchanged. Slow firing and a temperature-sensitive conformational change in voltage-activated sodium channels could account for the higher concentrations of MK-801 required to block sodium-dependent action potentials at temperatures below 37°C.     

Effects of EDTA on signal stability during electrochemical detection of acetaminophen

The use of EDTA in the medium to avoid the passivation of a solid electrode during electrochemical analysis of acetaminophen is presented in this work. The performance of this system was investigated with respect to pH, applied potential and supporting electrolyte concentration. The major advantage in using EDTA in the supporting electrolyte is the significant increase in sensitivity, precision and stability of the measurements, when compared to the system in absence of the chelating agent. The sensitivity increases 5.5 times (21.5 and 3.9 mA l mol⁻¹ in the presence and the absence of EDTA, respectively), the repeatability (n=20) is 3.5 times better, expressed by within-run-precision of 4.0% for 6.0×10⁻⁵ mol l⁻¹ acetaminophen in the presence of EDTA while, in its absence, the within-run-precision was higher than 14%. Moreover, the system showed excellent stability, allowing more than 120 measurements with no significant changes.     

Opposite effects of Bay k 8644 and nicardipine on the inhibitory effect of Ca on rat myometrium

The effect of Ca²⁺ on the oxytocin-induced, sustained contraction of rat uterine muscle in Ca-free medium after prolonged incubation with 3 mM EGTA (Ca-free contraction) was investigated. A micromolar concentration of Ca²⁺ caused phasic contraction followed by relaxation while a submicromolar concentration caused relaxation only. Cumulative addition of Ca²⁺ (10⁻⁸-3×10⁻⁶ M) caused dose-dependent relaxation (Ca reversal). This relaxation was inhibited by nicardipine and enhanced by Bay k 8644, and the effects of these two drugs were potentiated in 45.6 mM K⁺ medium. It is concluded that the inhibitory effect of Ca²⁺ on Ca-free contraction is caused by the influx of a minute amount of Ca²⁺. Thus, Ca²⁺ has dual actions in the cell: activation at concentrations higher than 10⁻⁶ M, and inhibition alone at concentrations lower than 10⁻⁷ M.     

Determination of salbutamol in syrups by capillary electrophoresis with contactless conductivity detection (CE-C(4)D)

This paper describes the separation and quantification of salbutamol in pharmaceutical products (salbutamol syrups) by capillary electrophoresis (CE) with contactless conductivity detection (C⁴D). The system was studied by micellar electrokinetic capillary chromatography (MEKC) and free solution capillary electrophoresis (FSCE), being the latter chosen in function of best resolution and sensitivity in comparison with the MEKC method. CE-C⁴D was applied to analysis of salbutamol in syrups utilizing 1.0 × 10⁻² mol L⁻¹ acetic acid/sodium acetate buffer (pH 4.9) as running electrolyte. Tetraethylammonium (TEA) solution was used as internal standard. The results obtained include a linear dynamic range from 7.0 × 10⁻⁵ to 3.0 × 10⁻⁴ mol L⁻¹ and good repeatability (R.S.D. = 4.7% for n = 10 for a 7.0 × 10⁻⁵ mol L⁻¹ salbutamol solution). The detection limit was calculated as 1.0 × 10⁻⁵ mol L⁻¹ and the limit of quantification was estimated as 3.3 × 10⁻⁵ mol L⁻¹. For syrups analysis the reproducibility presented deviations between 1.5% and 2.5% (three different days) obtained for measurements in triplicate.     

Vascular smooth muscle relaxation induced by epidermal growth factor is endothelium-dependent

Epidermal growth factor (EGF) is released from platelets during aggregation. Because we thought that EGF played a role in vascular tone, we investigated its vascular reactivity using isolated rat aortic strips with and without the endothelium. In the presence of endothelium, EGF relaxed vascular smooth muscle precontracted with 40 mM K⁺, 10⁻⁵ M prostaglandin F₂ or 10⁻⁶ M norepinephrine. The relaxation induced by EGF was more prominent on the prostaglandin F₂- and norepinephrine-induced contractions than on the K⁺-induced contraction. Atropine (10⁻⁵ M) and aspirin (10⁻⁵ M) had no effect on the EGF-induced relaxation, but methylene blue (10⁻⁵ M) partly abolished the relaxation evoked by EGF. These results suggest that EGF relaxes vascular smooth muscle in the presence of the endothelium. They also suggest that EGF has an effect on the endothelium to produce relaxing factor independent of cyclooxygenase; the releasing factor activates soluble guanylate cyclase, resulting in relaxation of vascular smooth muscle through the production of cyclic GMP.     

Cardiac inotropic vs. chronotropic selectivity of isradipine, nifedipine and clevidipine, a new ultrashort-acting dihydropyridine

Cardiac effects of clevidipine, a new ultrashort-acting dihydropyridine Ca²⁺ channel antagonist were investigated in Langendorff-perfused rat hearts and compared to those of nifedipine and isradipine. The aim was to determine and compare the negative inotropic vs. chronotropic potency of these drugs. The hearts were perfused with oxygenated Krebs–Henseleit buffer at a perfusion pressure of 90 cm H₂O. After stabilization, one concentration of each drug was administered for 45 min followed by a higher concentration for an additional 45 min. The concentrations of each drug in this study were 10⁻⁹, 3×10⁻⁹, 10⁻⁸, 10⁻⁷, 10^−6.5 and 10⁻⁶ M for clevidipine and nifedipine, and 10⁻¹⁰, 3×10⁻¹⁰, 10⁻⁹, 10⁻⁸, 10^−7.5 and 10⁻⁷ M for isradipine. Each concentration of each drug was tested in six hearts. Coronary flow, left ventricular dP/dt max, left ventricular systolic pressure and heart rate were recorded when the hearts were beating spontaneously and during pacing at a constant rate for 1 min. Spontaneous heart rate and atrio-ventricular conduction were not affected by clevidipine at any of the concentrations studied, while nifedipine and isradipine caused a concentration-dependent decrease. These two drugs caused atrio-ventricular block at high concentrations. All three compounds reduced cardiac contractility in a concentration-dependent manner. When isradipine was administered, at a given concencentration, heart rate and contractility decreased proportionately. When clevidipine or nifedipine was given, at a given concentration, the proportionate reduction in left ventricular dP/dt max was greater than that in heart rate, resulting in a high inotropic vs. chronotropic selectivity. It is concluded that in contrast to nifedipine and isradipine, clevidipine does not impair atrio-ventricular conduction. Like nifedipine, clevidipine is selective for inotropic vs. chronotropic cardiac effects.