Intravenous diadenosine tetraphosphate in dogs. Cardiovascular effects and influence on blood gases

Diadenosine tetraphosphate (AP4A) has a considerable vasodilating effect. Its dose was adjusted to decrease mean arterial pressure (MAP) by 20%, 40%, 50%, 60%, and 80% of the pretreatment value, and the effects on hemodynamics and gas exchange were evaluated. AP4A produced a dose-dependent decrease in MAP within the range of doses which decreased blood pressure by up to 60%. Heart rate remained constant at hypotension levels of 40% or less, but decreased significantly at hypotension levels of 50% or more. Cardiac output increased significantly at hypotension levels of 40% or less. Systemic vascular resistance (SVR) showed a significant decrease at that time. No significant changes were observed in central venous pressure and pulmonary capillary wedge pressure at any level of hypotension. Arterial oxygen tension and calculated pulmonary shunt ratio showed no change. Base excess and pH were decreased significantly with a 60% or 80% fall of blood pressure. In conclusion, AP4A seems to act on the resistance vessels and cause a decrease in SVR.

Role of vascular cell adhesion molecule 1/very late activation antigen 4 and intercellular adhesion molecule 1/lymphocyte function-associated antigen 1 interactions in antigen-induced eosinophil and T cell recruitment into the tissue

To determine the role of vascular cell adhesion molecule 1 (VCAM-1)/very late activation antigen 4 (VLA-4) and intercellular adhesion molecule 1 (ICAM-1)/lymphocyte function-associated antigen 1 (LFA-1) interactions in causing antigen-induced eosinophil and T cell recruitment into the tissue, we studied the effect of the in vivo blocking of VCAM-1, ICAM-1, VLA-4, and LFA-1 by pretreatment with monoclonal antibodies (mAb) to these four adhesion molecules on the eosinophil and T cell infiltration of the trachea induced by antigen inhalation in mice. The in vivo blocking of VCAM-1 and VLA-4, but not of ICAM-1 and LFA-1, prevented antigen-induced eosinophil infiltration into the mouse trachea. On the contrary, the in vivo blocking of VCAM-1 and VLA-4, but not of ICAM-1 and LFA-1, increased blood eosinophil counts after antigen challenge, but did not affect blood eosinophil counts without antigen challenge in sensitized mice. Furthermore, the expression of VCAM-1 but not ICAM-1 was strongly induced on the endothelium of the trachea after antigen challenge. In addition, pretreatment with anti-IL-4 mAb decreased the antigen-induced VCAM-1 expression only by 27% and had no significant effect on antigen-induced eosinophil infiltration into the trachea. The in vivo blocking of VCAM-1 and VLA-4 inhibited antigen-induced CD4+ and CD8+ T cell infiltration into the trachea more potently than that of ICAM-1 and LFA-1. In contrast, regardless of antigen challenge, the in vivo blocking of LFA-1, but not of ICAM-1, increased blood lymphocyte counts more than that of VCAM-1 and VLA-4. These results indicate that VCAM-1/VLA-4 interaction plays a predominant role in controlling antigen-induced eosinophil and T cell recruitment into the tissue and that the induction of VCAM-1 expression on the endothelium at the site of allergic inflammation regulates this eosinophil and T cell recruitment.

Chronic morphologic changes of skeletal muscle ventricles in circulation

Skeletal muscle ventricles (SMVs) were constructed either extrathoracically or intrathoracically in 44 dogs using the left latissimus dorsi muscle. These SMVs functioned as aortic counterpulsators for from several hours to 216 days. In this study, the relationship between the morphologic changes in the SMVs and their time course in the circulation was evaluated retrospectively. The average volume of the SMV chamber after it had been excised and fixed in formalin was 21.3 +/- 11.0 mL (mean +/- the standard deviation) for extrathoracic SMVs and 20.0 +/- 7.5 mL for intrathoracic SMVs. The volume of the SMV chamber did not correlate with the time course in the circulation. The SMV wall was mainly composed of three components: muscular, fibrous, and fatty aspects. The overall thickness of the wall appeared to be preserved over time in the circulation. However, the thickness of the muscular component tended to decrease over time. SMV rupture occurred in 15 dogs between postoperative days 4 and 39. All ruptures occurred at the suture line between the SMV and the vascular conduits. There was some degree of thrombus in 24 SMVs. Before SMVs can be applied clinically for the purpose of cardiac assist, problems with rupture and thrombus formation must be solved. A better understanding of the morphologic changes that take place in the SMV over time also is needed.

The development of a valveless cardiac assist device attached to the ventricular apex

Konstantinov et al, in October, 1991, published a novel way to bridge a patient for heart transplantation. They proposed to cut off both ventricles high under the atrioventricular groove, leaving the atria, aorta, and pulmonary artery and their valves intact and to attach pneumatically driven, valveless pulsating pouches to assist the heart until a donor could be found. The removal of the ventricles just below the atrioventricular groove is called the "high cut"; it, however, destroys the chordae tendineae rendering the mitral and tricuspid valves insufficient. These have to be replaced by tissue inflow valves. We chose to cut off the ventricles at a lower level (the "low cut") to leave the papillary muscles on both sides intact, thereby saving the integrity of the mitral and tricuspid valves. Pulsating pouches were made to fit the heart at this lower level. They can be easily connected to the remaining heart after a specially disigned cuff has been sutured over the ventricular stumps. The pouches were pumped during the systole of the natural heart, but the myocardium may have to be electrically stimulated during systole to prevent undue distension. If the turgor is too weak to prevent distension, a sleeve over the ventricles is provided. To find the best location for these pouches, human cadaver implantations were done and the pre peritoneal cavity was found to be the most suitable. In vitro testing to determine how much flow could be pumped was done by attaching the pouches to fresh pig hearts and connecting them to a double sided mock circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

FR901228, a novel antitumor bicyclic depsipeptide produced by Chromobacterium violaceum No. 968. I. Taxonomy, fermentation, isolation, physico-chemical and biological properties, and antitumor activity

A novel antitumor bicyclic depsipeptide, FR901228, was isolated from a broth culture of Chromobacterium violaceum No. 968 as colorless prisms and the molecular formula was determined as C24H36N4O6S2. This antibiotic reverted the transformed morphology of a Ha-ras transformant to normal, and exhibited prominent antitumor activities against murine and human tumor cell lines both in vitro and in vivo.

Characterization of a taxol-resistant human small-cell lung cancer cell line

Taxol is a novel anticancer agent with activity against a broad range of tumors. It has a unique ability to stabilize polymerized tubulin into microtubule bundles within the cell. We have established a taxol-resistant human small-cell lung cancer cell line (H69/Txl) by exposing H69 cells to stepwise increases in taxol concentration. The resistance of H69/Txl cells to taxol was 4.7-fold that of the original H69 cells: the IC50 values for H69 and H69/Txl were 113.7 +/- 56.54 nM and 538.7 +/- 214.7 nM by the tetrazolium dye assay, respectively. Removal of the drug from the medium resulted in a 38% decrease in the growth rate of H69/Txl as compared with that in the presence of 30 nM taxol, suggesting that the growth of H69/Txl was partially dependent on taxol. H69/Txl showed higher sensitivity to vinca alkaloids such as vindesine, vincristine and vinblastine than the parental H69. There was no significant difference in intracellular [3H]taxol content between H69 and H69/Txl cells. No MDR-1 mRNA was detected in H69/Txl by the reverse transcription polymerase chain reaction. There was no significant difference of total and polymerized tubulin content between H69 and H69/Txl cells. Altered mobility of one of the alpha-tubulin isoforms in H69/Txl was revealed by using isoelectric focusing and Western blotting with anti-alpha-tubulin antibody. In H69, two alpha-tubulin isoforms were observed, whereas three were evident in H69/Txl, two of them comigrating with the isoforms of H69 and the other being more acidic. We observed the increased acetylation of alpha-tubulin in H69/Txl cells as compared with that in H69 cells. The acetylation of alpha-tubulin may be responsible for the taxol resistance and/or taxol-dependent growth of H69/Txl.

Muscle- and pneumatic-powered counterpulsating LVADs: a pilot study

There is a worldwide interest in supporting the failing heart with a skeletal muscle by either wrapping it around the natural heart (dynamic cardiomyoplasty) or by constructing a skeletal muscle ventricle (SMV) used for counterpulsation. Conventional cardiomyoplasty in many clinics carries an operative mortality rate of 15-20% partly because it requires 6 weeks to train the muscle to contract continually. A flexible, pear-shaped blood pump with an inflatable air chamber was designed and made around which a muscle can be wrapped. The advantage of our design is that it can also be driven by pneumatic power, immediately supporting the circulation of a seriously ill patient while that patient is still on the operating table. After a period of time to allow for revascularization and the subsequent training of the muscle, the external pneumatic power can be gradually discontinued. Then the assisted patient becomes tether-free. If, at any time, the muscle power fails, the pneumatic-powered mechanism can be reactivated. In the preferred approach, the blood pump is connected to the aorta for diastolic counterpulsation. A muscle can either be wrapped around the blood pump directly, or around one of two separate muscle pouches connected to the blood pump. To facilitate surgery, a large pouch is inserted under the musculus latissimus dorsi, which is connected to a blood pump. When stimulated, the muscle will contract over the pouch compressing it and providing power to the blood pump. If it is found that the pressure generated in the pouch cannot meet the aortic blood pressure, it can be augmented by using a pressure amplifier.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effects of 9-cis retinoic acid on hematopoiesis in vitro]

9-cis retinoic acid (cRA) is a high affinity ligand for RXR and binds efficiently to RAR. cRA in general was more potent than all-trans RA (tRA) in suppressing clonal growth and inducing differentiation of HL-60 and human leukemic cells. At very low concentrations, retinoid stimulate proliferation of leukemic cells rather than induce their differentiation. Also, cRA in combination with tRA could induce differentiation of RA resistant HL-60 cells. Steady-state levels of RAR-alpha mRNA in HL-60 cells were not affected by either cRA or tRA. In contrast, cRA, but not tRA could reduced RXR-alpha mRNA accumulation in dose-dependent manner. The loss of partner for RAR may result in differential gene regulation through the retinoid pathway. These differences in regulation of RAR and RXR mRNA might be of physiological significance.

Cloning and expression in Escherichia coli of the gene encoding the Proteus vulgaris chondroitin ABC lyase

The structural gene encoding chondroitin ABC lyase from Proteus vulgaris was cloned and sequenced. This gene consists of a single open reading frame of 3,063 bp, including a sequence (72 bp) for a possible secretory protein leader peptide, preceded by a Shine-Dalgarno ribosomal binding site. Promoter-like and rho-independent terminator sequences were detected upstream and downstream of the open reading frame, respectively. The G+C content of the coding region was 38.6%. The transcription startpoint was located 41-bp upstream of the initiation codon (ATG). Chondroitin ABC lyase is composed of 997 amino acids, and has a relative molecular mass of 112,635. When the 5.2-kb fragment containing the 1.2-kb upstream from the gene was inserted into pSTV29, and cloned in Escherichia coli, chondroitin ABC lyase was induced in the medium containing chondroitin-6-sulfate as the carbon source. On the other hand, when a 4.2-kb fragment containing only 0.2 kb upstream was inserted into pSTV29(pCHS delta 6), and pCHS delta 6 was introduced into E. coli, the enzyme was constitutively produced, even in medium containing glucose as the carbon source. By immunoblot analysis, the polypeptide synthesized by E. coli cells carrying pCHS delta 6 appeared to be the same as that of the purified chondroitin ABC lyase from P. vulgaris.

DNFB contact sensitivity (CS) in BALB/c and C3H/He mice: requirement for early-occurring, early-acting, antigen-specific, CS-initiating cells with an unusual phenotype (Thy-1+, CD5+, CD3-, CD4-, CD8-, sIg-, B220+, MHC class II-, CD23+, IL-2R-, IL-3R+, Mel-14-, Pgp-1+, J11d+, MAC-1+, LFA-1+, and Fc gamma RII+)

Immunization of mice for contact sensitivity induces two different antigen-specific Thy-1+ cell activities that are required to act in sequence for elicitation of contact sensitivity. In this study, 2,4-dinitro-1-fluorobenzene contact sensitivity responses in BALB/c and C3H/He mice demonstrated the importance of early-acting and antigen-specific contact sensitivity-initiating cells to recruit the classical, late-acting contact sensitivity effector T cells. Employing in vitro treatment of sensitized cells with monoclonal antibodies to cell surface determinants and then incubation in complement, prior to adoptive cell transfer, the contact sensitivity-initiating cells were shown to have a surface phenotype that is quite unusual for antigen-specific cells [Thy-1+, CD5+, CD3-, CD4-, CD8-, sIg-, B220+, major histocompatibility complex class II-, CD23+, IL-2R-, IL-3R+, Mel-14-, CD44+ (Pgp-1+), J11d+ (HSA+), MAC-1+, LFA-1+, and Fc gamma IIR+], and is quite different from the late-acting, contact sensitivity-effector T cells (Thy-1+, CD5+, CD3+, CD4+, CD8-, sIg-, B220-, major histocompatibility complex class II-, CD23-, IL-2R+, IL-3R-, and CD44- (Pgp-1-), J11d-(HSA-), MAC-1-, LFA-1+, Fc gamma IIR-). Contact sensitivity initiation was required for elicitation of late 24-h 2,4-dinitro-1-fluorobenzene contact sensitivity responses, in both BALB/c and C3H/He mice. Moreover, relatively high doses of some monoclonal antibodies [anti-B220 (CD45RA) and anti-CD23 (IgE Fc epsilon II receptor)] were necessary to completely eliminate all contact sensitivity-initiating cells that permitted expression of late contact sensitivity-effector T-cell activity. In contrast, high doses of monoclonal antibody specific for surface determinants of late-acting contact sensitivity effector T cells (anti-CD3 and anti-CD4), when used in high doses similar to anti-B220 and anti-CD23, had no effect on contact sensitivity-initiating cell activity. Our results indicate that two very different antigen-specific Thy-1+ cells are necessary to elicit 2,4-dinitro-1-fluorobenzene contact sensitivity in BALB/c and C3H/He mice.

Cytotoxic lymphocyte granzymes trigger a target cell internal disintegration pathway leading to cytolysis and DNA breakdown

Two approaches have been used to assess the hypothesis that granzymes secreted by cytotoxic lymphocytes act within the target cells to trigger an internal disintegration pathway leading to target cell lysis. The lytic properties of several clones of rat basophilic leukemia cells transfected with either cytolysin (perforin) alone (RBL-cy) or a combination of cytolysin and granzyme A (RBL-cy-gza) were compared with cloned CTL. Analysis of the kinetics of target cell 125I-DNA vs 51Cr release with three tumor targets showed negligible DNA release with RBL-cy, less extensive 125I-DNA release relative to 51Cr release with RBL-cy-gza effector cells, whereas CTL caused greater or equal DNA release than 51Cr release at all time points. Using three different tumor target cells, comparison of RBL-cy-gza and RBL-cy clones in multiple experiments shows that RBL-cy-gza are on average more than threefold more lytic than RBL-cy. This distinction was not seen with red cell targets, in which an internal disintegration pathway does not operate. A second approach to this issue consisted of cytoplasmic loading of tumor target cells with aprotinin, a macromolecular protease inhibitor known to inhibit granzyme A and probably other granzymes. Although the control BSA-loaded target cells were essentially identical to nonloaded targets in all cases, aprotinin-loaded targets showed substantially lower release of both 51Cr and 125I-DNA with both CTL and RBL-cy-gza effector cells. In contrast, aprotinin-loaded targets were lysed with the same efficiency as control targets by RBL-cy effector cells. We conclude that secreted granzymes contribute to target lysis by triggering a target cell internal disintegration pathway that leads to both lysis and DNA breakdown.

Cardiomyoplasty: probable mechanism of effectiveness using the pressure-volume relationship

The mechanism of effectiveness of cardiomyoplasty was evaluated in the setting of chronic left ventricular dysfunction in terms of the pressure-volume relationship. The distal branches of the left coronary artery were ligated in 12 sheep. Seven sheep died and the 5 survivors underwent cardiomyoplasty using a left latissimus dorsi graft 10 to 12 weeks later. These muscle grafts were then electrically conditioned for 2 months. The systemic pressure and cardiac output were not different between the postinfarction and postcardiomyoplasty period with the pacemaker off or on. However, the pressure-volume loops were altered by cardiomyoplasty in all 5 animals. Emax, which is an index of ventricular contractility, increased after cardiomyoplasty from 2.66 +/- 0.92 to 4.59 +/- 1.73 mm Hg/mL (mean +/- the standard deviation; p < 0.05), but did not change between the pacemaker off and on situations. The pressure-volume area, which strongly correlates with myocardial oxygen consumption, decreased after cardiomyoplasty (1,932 +/- 615 mm Hg.mL), compared with before cardiomyoplasty (3,776 +/- 1,201 mm Hg.mL) (p < 0.05), but did not change between pacemaker off and on. The probable mechanism responsible for the effectiveness of cardiomyoplasty is an "active" support or constraint of the damaged myocardium by the latissimus dorsi and the prevention of further ventricular dilation. This suggests that left ventricular systolic function can be augmented by cardiomyoplasty, but that it is a secondary mechanism of action.

Cytotoxic lymphocyte granzymes trigger a target cell internal disintegration pathway leading to cytolysis and DNA breakdown

Two approaches have been used to assess the hypothesis that granzymes secreted by cytotoxic lymphocytes act within the target cells to trigger an internal disintegration pathway leading to target cell lysis. The lytic properties of several clones of rat basophilic leukemia cells transfected with either cytolysin (perforin) alone (RBL-cy) or a combination of cytolysin and granzyme A (RBL-cy-gza) were compared with cloned CTL. Analysis of the kinetics of target cell 125I-DNA vs 51Cr release with three tumor targets showed negligible DNA release with RBL-cy, less extensive 125I-DNA release relative to 51Cr release with RBL-cy-gza effector cells, whereas CTL caused greater or equal DNA release than 51Cr release at all time points. Using three different tumor target cells, comparison of RBL-cy-gza and RBL-cy clones in multiple experiments shows that RBL-cy-gza are on average more than threefold more lytic than RBL-cy. This distinction was not seen with red cell targets, in which an internal disintegration pathway does not operate. A second approach to this issue consisted of cytoplasmic loading of tumor target cells with aprotinin, a macromolecular protease inhibitor known to inhibit granzyme A and probably other granzymes. Although the control BSA-loaded target cells were essentially identical to nonloaded targets in all cases, aprotinin-loaded targets showed substantially lower release of both 51Cr and 125I-DNA with both CTL and RBL-cy-gza effector cells. In contrast, aprotinin-loaded targets were lysed with the same efficiency as control targets by RBL-cy effector cells. We conclude that secreted granzymes contribute to target lysis by triggering a target cell internal disintegration pathway that leads to both lysis and DNA breakdown.

Degradation of a polymerase chain reaction (PCR) product by heat-stable deoxyribonuclease (DNase) produced from Yersinia enterocolitica

When crude deoxyribonucleic acid (DNA) preparations by boiling were used for the polymerase chain reaction (PCR) from pathogenic and non-pathogenic Yersinia enterocolitica strains, the amplified products were degraded after their storage at 4 C. The degradation of products was prevented by the addition of ethylenediaminetetraacetate (EDTA) or treatment with proteinase K. These findings indicate that Y. enterocolitica produced heat-stable deoxyribonuclease (DNase). Proteinase K treatment would be recommended to prevent heat-stable DNase contamination in the DNA preparations for PCR from Y. enterocolitica strains.

Chronic salicylate intoxication and rhabdomyolysis in a patient with scleroderma and Sjögren's syndrome

A 44-year-old woman with scleroderma and Sjögren's syndrome developed altered consciousness, acute renal failure, and rhabdomyolysis. She had no history of trauma, seizures, alcohol abuse, hyperthermia, or other possible causative factors for rhabdomyolysis. A high serum salicylate level indicated a diagnosis of salicylate intoxication. Medical history after recovery revealed chronic salicylate ingestion for severe headaches. This is possibly the first reported case of rhabdomyolysis caused by chronic salicylate intoxication. Continuous hemodiafiltration early in hospitalization was an effective treatment.

Immunohistochemical study of graft-versus-host reaction (GVHR)-type drug eruptions

Skin biopsies of graft-versus-host reaction (GVHR)-type drug eruptions in the acute phase were compared immunohistochemically with those in the chronic phase and also with non-GVHR type drug eruptions in the acute phase. Predominance of CD8+ T cells in the epidermal infiltrates, reduction in the number of epidermal OKT6+ dendritic cells (Langerhans cells), and increased expression of HLA-DR and ICAM-1 on keratinocytes were observed in the acute phase of GVHR-type, but not in either the chronic phase of GVHR-type or the acute non-GVHR type. These findings were similar to those of previous reports on skin lesions of acute GVH disease (GVHD) seen after bone marrow transplantation. Therefore, immunohistochemistry is not useful for differential diagnosis between acute GVHR-type drug eruptions and acute cutaneous GVHD. These findings also indicate that similar immunomechanisms may be involved in the pathogenesis of both GVHR-type drug eruptions and cutaneous GVHD.

[Studies on hypogeusia in hyperemesis gravidarum]

We measured changes in gustatory sensitivities and gustation threshold levels and those of some trace elements, vitamin E and lipids in the serum of 38 patients suffering from hyperemesis gravidarum, 12 normal pregnant women in the first trimester and 22 healthy non-pregnant women by means of filter discs and an electrogusto meter (EGM) and we obtained the following results. 1. Gustatory sensitivity to sweetness was found to be significantly lowered in the patients with hyperemesis gravidarum when tested with filter discs (p < 0.05). 2. Gustation threshold levels were significantly lowered in the patients with hyperemesis gravidarum and the normal pregnant women tested with the EGM (p < 0.01). 3. There was considerable heterogeusia of women in the patients with hyperemesis gravidarum (p < 0.05). 4. Zn and Mg in serum decreased (p < 0.01), but Cu increased significantly in the patients with hyperemesis gravidarum and the normal pregnant women (p < 0.01). 5. Total cholesterol and phospholipid in serum significantly decreased, but lipid peroxide in serum significantly increased in the patients with hyperemesis gravidarum (p < 0.01). These results suggested that the gustatory test was helpful in investigating hyperemesis gravidarum and that biological defense systems (scavenger systems) to free radicals were damaged in patients with hyperemesis gravidarum.

Complete amino acid sequence of biliverdin-IX beta reductase from human liver

The amino acid sequence of biliverdin-IX beta reductase (EC1.3.1.24) from human liver was determined by automated Edman degradation of peptides generated by enzymatic and chemical cleavages. The enzyme was a single polypeptide chain of 204 amino acid residues, and its amino acid sequence had no significant homology to that of rat liver biliverdin-IX alpha reductase. Biliverdin-IX alpha reductase from human liver had intense homology to the rat enzyme. Cysteinyl residues are essential for the enzymatic activity of biliverdin-IX alpha, but nonessential for that of biliverdin-IX beta reductase. The results strongly indicate that the two enzymes, biliverdin-IX alpha reductase and biliverdin-IX beta reductase, are distinct in enzymatic action mechanisms as well as ancient origins of gene.

Effects of novel retinoic acid compound, 9-cis-retinoic acid, on proliferation, differentiation, and expression of retinoic acid receptor-alpha and retinoid X receptor-alpha RNA by HL-60 cells

Retinoic acid modulates proliferation and differentiation of a wide variety of normal and leukemic cells through two distinct families of transcriptional factors: the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs). A stereoisomer of retinoic acid, 9-cis-retinoic acid, is a high-affinity ligand for RXR and binds efficiently to RAR. In contrast, all-trans-retinoic acid interacts 40-fold less efficiently with RXR as compared with RAR. To clarify the biologic role of retinoic acid compounds (all-trans,- 9-cis-, and 13-cis-retinoic acid) in hematopoietic cells, we studied their effects on clonal growth, differentiation, and expression of RAR-alpha and RXR-alpha genes in HL-60 cells. At very low concentrations (10(-15) to 10(-12) mmol/L), each retinoid enhanced clonal growth of HL-60 cells. These concentrations of the retinoids had no capacity to induce differentiation of leukemic cells as measured by ability either to reduce nitroblue tetrazolium and to express CD11b antigens, suggesting that retinoids at very low concentrations may stimulate proliferation of leukemic cells rather than induce their differentiation. These findings may help explain why patients with acute promyelocytic leukemia may relapse while receiving retinoic acids. With continuous therapy, retinoids are metabolized rapidly with increased urinary excretion, lowering their plasma levels to a range that may stimulate proliferation without inducing differentiation of leukemic cells. In contrast, we found that at higher concentrations (> or = 10(-11) mmol/L) each retinoid inhibited clonal growth, reduced c-myc RNA levels, and induced differentiation of HL-60 cells. 9-cis-retinoic acid was a slightly more potent inducer of differentiation than all-trans-retinoic acid; the mechanism for this increased potency and its clinical potential requires additional studies. Steady-state levels of RAR-alpha mRNA in HL-60 cells were not affected by either 9-cis- and all-trans-retinoic acid. In contrast, 9-cis-retinoic acid, but not all-trans-retinoic acid, reduced RXR-alpha mRNA accumulation in a dose-dependent manner.