Search PubMed⌕ Search

Biomedical subjects

M Marusić

Publications and source records attributed to M Marusić.

At least 19 recordsLinked to original sources

Good editorial practice: editors as educators.

There may be valuable research going on in the developing and financially less-privileged countries, but it usually does not reach international visibility, in spite of a large number of scientific journals in these countries. Such journals are not only invisible but, by perpetuating a vicious circle of inadequacy, may be directly damaging to the local science and research culture. We call for an international action to help journal editors in less privileged countries. International associations of editors may be leaders of these activities by defining, promoting, and perhaps controlling good editorial practice, as a main criterion for international recognition of a journal. However, the editors of small journals have the power and moral obligation to become a stronghold of quality and advancement in their scientific community. Their educational "tools" are editorial integrity and author-friendly policy. Editors can teach the authors study design, statistical analysis, precision, punctuality, research integrity, style and format of writing, and other aspects of scientific communication. The editors of "big", mainstream scientific journals can act as global educators, teaching and providing guidance to editors of small journals. The editors from developed countries as leaders, and editors from less advantageous environments as teachers are the key figures in shaping research communication in less privileged scientific communities.

Croatia↗

Appointment of statistical editor and quality of statistics in a small medical journal.

AIM: To test if the appointment of a statistical editor improves the quality of manuscripts published in a small general medical journal. METHODS: Retrospective review of all manuscripts containing statistical data published in the Croatian Medical Journal between 1992 and 2000 (n=241). Statistical analysis and its presentation were assessed by a single observer. RESULTS: Before the appointment of statistical editor in 1996, 97 manuscripts with statistical data were published. Statistics was not satisfactory in 52 (54%) of them, including 26 definite errors in analysis and 43 in presentation. After the appointment of statistical editor, 144 manuscripts containing statistical data were published. Statistics was not satisfactory in 91 (63%) of them, with 51 definite errors in analysis and 69 in presentation. Out of 144 manuscripts, the editor-in-chief sent out 30 (21%) for statistical review. Statistics was not satisfactory in 25 of them, including 11 definite errors in analysis and 17 in presentation. Statistical editors comments improved three manuscripts. If the authors had acknowledged all statistical editors suggestions, 9 more manuscripts would have been improved. Statistical editor had a total of 195 comments on 30 published manuscripts. Most numerous were the comments concerning the presentation of the statistical analysis (51%), followed by the general comments (26%), comments on analysis (11%), study design (8%), and interpretation (4%). CONCLUSION: Appointment of a statistical editor is not a guarantee of improvement of statistics in small journals. Other measures are necessary, including strict editorial policy on statistical review, monitoring of revised manuscript versions, and enrollment of formally trained biostatisticians.

Humans↗

Clinical, histopathological and flow-cytometric properties of incidental renal cell carcinomas.

Medical records of 63 patients operated on for renal cell carcinoma (RCC) between 1986 and 1996 in the Karlovac General Hospital were studied retrospectively. In 23 (36.5%) patients, the tumor was incidentally detected. The median patient age was 62 in the incidental group and 64 years in the symptomatic group (P > 0.05). Ultrasonography was the leading technique for incidental detection of RCC. The median tumor diameter was 6 cm in the incidental group and 9 cm in the symptomatic group (P < 0.001). Incidental carcinomas had a lower stage (P = 0.022) and a lower nuclear grade (P < 0.001) than the symptomatic ones. The incidental cases were associated with a more favorable ploidy status (P = 0.027) and a lower proliferative activity (P = 0.005). The 5-year survival rate was significantly higher in incidental (81.4%) than in symptomatic cases (44.3%) (P = 0.020). Univariate analysis showed that tumor stage, ploidy status, and proliferative activity were good prognostic parameters, while patient age, tumor size, and nuclear grade were not. Tumor stage was the only independent prognostic parameter in multivariate analysis. In conclusion, the incidentally detected RCC show more favorable clinical, histopathological, and flow-cytometric characteristics and their prognosis is significantly better than in symptomatic cases.

Adult↗

Croatian Medical Journal at the turn of the millennium.

The turn of the millennium coincided with the inclusion of the Croatian Medical Journal into the bibliographic databases MEDLINE (1998), and Current Contents/Clinical Medicine (1999), which greatly increased the number of submitted manuscripts. The increased pressure on the editorial office prompted us to modify the editorial procedure and sharpen our acceptance criteria. At the same time, we extended our author-friendly policy to all for global medicine and (2) medicine in translational and emerging countries. The Editorial Board and the Advisory Board were critical in developing and improving the Journal and setting the highest standards in all aspects of publication, especially in manuscript selection by high-quality peer review. In this editorial, we finally meet the members of the two Boards in person, or rather, in photographs and short biographies.

Croatia↗

Joining together to combat poverty.

The International Poverty and Health Network (IPHN) was created in December 1997 following a series of conferences organized by the World Health Organization, with the aim of integrating health into plans to eradicate poverty. Around 1.3 billion people live on less than US$1 per day. Of the 4.4 billion people in developing countries nearly 60% lack access to sanitation, 30% do not have clean water, 20% have no health care, and 20% do not have enough dietary energy and protein. Even among rich nations there are gross socioeconomic inequalities. Many children are robbed of their physical and mental potential through poverty. Expressed in constant 1963 US dollars, an average Croatian family needed the annual income of US$894 to meet the poverty line in 1960 and US$9,027 in 1995. Accordingly, 9-25% of Croatian households were below the poverty line between 1960 and 1995. The increase in the poverty rate after 1991 was compounded by the war that destroyed almost a third of industrial capacity and infrastructure. Dissipation of the communist economy and inadequate privatization have contributed to the increase in unemployment rate, corruption, and other social ills. IPHN invited Croatian Medical Journal to publish this editorial to help push the issue of poverty up political and medical agendas on a global level. We argue that a factor contributing to the failure of most large-scale programs against poverty to date is the excessive emphasis on material and infrastructure assistance at the expense of spiritual, moral, and intellectual development.

Croatia↗

Effects of tamoxifen on steroid hormone receptors and hormone concentration and the results of DNA analysis by flow cytometry in endometrial carcinoma.

OBJECTIVES: Tamoxifen is a nonsteroidal triphenylethylene derivate with a predominant antiestrogen activity, used in the endocrine treatment of breast and endometrial cancer. It is not known which endometrial carcinomas will respond favorably to tamoxifen and which ones will not. The aim of this study was to find out whether tamoxifen has an effect on hormone steroid receptors, hormone concentration, DNA content, and proliferative activity in endometrial cancer and to correlate the tamoxifen-induced changes with pathologic parameters such as clinical stage, tumor differentiation, depth of invasion, and histologic type. METHODS: Thirty postmenopausal women with endometrial carcinoma were treated with 30 mg of tamoxifen daily for 7-10 days after curettage. Steroid hormone receptors (estrogen and progesterone receptors), levels of follicle-stimulating hormone, luteinizing hormone, prolactin, estradiol, progesterone, testosterone, dehydroepiandrosterone sulfate, sex hormone binding globulin, and DNA ploidy and proliferative activity were determined before and after therapy. The patients were also divided into favorable and unfavorable prognosis groups according to classical histological parameters. The patients in the favorable group consisted of patients with stage I disease, well and moderately differentiated tumors, favorable histologic type, and a depth of myometrial invasion of less than (1/3). The patients with only one of the unfavorable parameters (clinical stage II or III, poorly differentiated tumors, unfavorable histologic types, and deeper invasion of myometrium) were included in the unfavorable prognosis group. RESULTS: After the treatment, there was a net increase in the progesterone receptors and sex hormone binding globulin and a significant decrease in the estrogen receptors. The increase in progesterone receptors and decrease in estrogen receptors occurred in the patient group with favorable prognosis regarding histologic type, degree of differentiation, and clinical stage, but also in the unfavorable prognosis group regarding the depth of myometrial invasion. Statistically significant decrease in the follicle-stimulating hormone concentration was observed in the groups with favorable prognosis regarding histologic type, depth of myometrial invasion, and grade of differentiation. Concentration of sex hormone binding globulin was significantly increased in groups with favorable prognosis if histologic type and grade of differentiation were taken into account. On the other hand, there was a significant decrease in the concentration of luteinizing hormone in the group with unfavorable histologic type and also a decrease in progesterone concentration in patients with unfavorable prognosis regarding the grade of differentiation. There was no statistical significance either in the concentrations of other hormones measured or in the DNA analysis by flow cytometry. CONCLUSIONS: Our results revealed that tamoxifen can increase progesterone receptors and decrease estrogen receptors in endometrial cancer. The effect was most pronounced in tumors with favorable clinicopathologic parameters. We conclude that tamoxifen therapy can induce progesterone receptor synthesis even in tumors with low initial progesterone receptor levels, making such tumors potentially responsive to additional hormonal therapy with progesterone.

Adenocarcinoma↗

Pre-treatment of transplant bone marrow cells with hydrocortisone and cyclosporin A alleviates graft-versus-host reaction in a murine allogeneic host-donor combination.

The aim of the study was to alleviate graft-versus-host reaction (GVHR) by pre-treatment of the bone marrow (BM) transplant with hydrocortisone (HC) and cyclosporin A (CsA) in C57BL/6J (donor) --> CBA/J (recipient) mouse combination. BM cells were exposed to HC and CsA for 1 h at 37 degrees C and then injected into lethally irradiated (9.5 Gy) mice at a dose of 2 x 10(6) BM cells/mouse. Haematopoietic recovery was assessed on day 12, and survival was followed for 100 days. Combinations of 1000 microg/ml HC and 100 microg/ml CsA, and 100 microg/ml HC and 10 microg/ml CsA significantly reduced MLR and additively mitigated GVHR in vivo, achieving 40% and 26% survival rates, respectively. However, HC and CsA altered neither the peripheral blood cell counts nor in vitro and in vivo BM cell clonogenic potential. Additional studies have shown that HC and CsA blocked con A-driven differentiation of CD8+ and CD4+ CD8+ lymph node cells (LNC) and progression of LNC to S + G2/M cell cycle phases, and inhibited IL-1, IL-2 and TGF-beta while enhancing GM-CSF gene expression in BM cells. Taken together, these data indicate that the pre-treatment of the BM transplant with HC and CsA results in inactivation of GVHR effector cells and mitigation of GVHR while sparing BM repopulating capacity.

Animals↗

[The curriculum plan for the Split University Medical School--a modern concept for a new school].

The transformation of the Zagreb University Medical School into an independent medical school, i.e., Split University Medical School prompted us to develop a new curriculum which had to adapt Zagreb curriculum to the new circumstances and to overcome its weaknesses. Additional reasons for new curriculum were the need for implementation of the current trends in medical education and adaptation to the Split Faculty. Principles according which the curriculum was developed took into account the current international recommendations on medical education, equal treatment of all teaching subjects, flexible curriculum and vertical integration of the elective subjects. New curriculum requires substantial changes in the organization of the undergraduate teaching. Because of the differences between Croatian medical schools, it is impossible and unnecessary to have a unique curriculum. Joint effort of medical schools has to be directed to the development of a common curriculum core and corresponding computer base of questions for examinations, enhancing state examination development, standard for the evaluation of the medical schools' quality.

Croatia↗

Indirect demonstration of the lifetime function of human thymus.

The aim of this study was to test the hypothesis that human thymus maintains its function as the site of early T cell development throughout life, but to a progressively diminishing extent. Mononuclear cell suspensions prepared from the samples of 39 human thymuses were analysed for the total number of cells per gram of thymus tissue, percentage of single marker-positive CD2, CD4 and CD8 cells, percentages of double-positive CD4CD8 and CD2CD8 cells, double-negative CD4CD8 cells, absolute numbers of these cells per gram of tissue, and extent of the in vitro proliferation upon stimulation with concanavalin A (Con A), phytohaemagglutinin (PHA) and pokeweed mitogen (PWM) mitogens. The main outcome measures were flow cytometric data on thymus lymphoid cell composition (according to CD classification), expressed as percentages and numbers of cells per gram of thymus tissue. The total number of mononuclear cells expressed per gram of thymus tissue exponentially decreased with age. The slope of none of the analysed cell subpopulations differed from the slope of the line constructed for age-related decline of the total number of mononuclear cells (-0.024 on a semilogarithmic scale). The thymuses of all ages contained all analysed cell subpopulations in approximately the same proportions: percentages of these cell subpopulations did not change with age, except for all CD4+ (P=0.017) and double-positive CD4+CD8+ (P=0.016) cells, which tended to decrease with age. The extent of proliferation of thymus cells upon stimulation with T and B cell mitogens was unrelated to age. We conclude that the thymus retains its function as the site of differentiation of T lymphocytes throughout life. With respect to the number of involved lymphoid cells, the function exponentially decreases with age.

Adolescent↗

Peer review in the Croatian Medical Journal from 1992 to 1996.

We analyzed the peer review process in the Croatian Medical Journal (CMJ) from 1992 to 1996 by a retrospective analysis of review forms for 319 manuscripts. The forms asked about manuscript's structure (7 questions), its scientific value (7-item scale), clarity and length, and final recommendation (5-item scale). An international manuscript had at least one author affiliated with a non-Croatian institution. The overall rejection rate of manuscripts was 23.5%. National and international manuscripts had similar rejection rates except for original research manuscripts in clinical sciences (34.7% vs. 18.9%, p=0.046). Out-door peer review was asked for 77.4% of the manuscripts; other manuscripts were commissioned and passed an in-house review. Over the years, the number of international reviewers increased, and that of national reviewers decreased. National reviewers more often did not fill in the review form, and international reviewers more often asked for a major revision. The agreement between reviewers ranged from 34.1% (scientific value) to 90.7% (reference citations). Kappa for inter-rater agreement was poor to fair, without difference between national and international manuscripts. International manuscripts had shorter median review time (from receipt to decision) and publishing time (from acceptance to publication) than national manuscripts: 58 vs. 112 days (p<0.001), and 116 vs. 140 days (p<0.009), respectively. Our analysis shows that peer review can be introduced and sustained in a small journal from the scientific periphery. It can be fair both to national and international manuscripts, although work with the authors of national manuscripts may be needed to improve the quality of data presentation.

Croatia↗

Prognostic significance of cell cycle parameters in infiltrative ductal breast carcinoma.

Flow-cytometric DNA analysis was performed retrospectively from paraffin-embedded blocks in 158 consecutive ductal infiltrative breast carcinoma patients grades I-III. Normal breast tissue was used as control. Tumor proliferative activity, cell ploidy, and DNA index (DI) were related to age of patients, histological grade of tumor, tumor size, axillary lymph node status, estrogen and progesterone receptor status, menopausal status,TNM clinical classification, and survival. There was a significant association between DNA aneuploidy and a high cellular proliferative activity, increased DI, poor differentiation of tumor, primary tumor size, number of positive lymph nodes, and postmenopausal state. Increased proportion of cells in S-phase was associated with positive lymph node status and higher number of positive lymph nodes. The cell cycle parameters had no prognostic value either for overall survival of disease-free survival of the patients.

Adult↗

Prognostic relevance of non-Hodgkin's lymphomas cell cycle data.

Determination of proliferative activity of non-Hodgkin's lymphomas (NHL), aimed at improving the prediction of their clinical behavior, has gained considerable attention in the recent years. Flow cytometry has allowed rapid measurement of the cellular DNA content in terms of ploidy and proliferative activity. Flow cytometric DNA analysis was performed on paraffin embedded biopsy specimens taken from 125 patients with NHL. In 90 of them, proliferative index (PI) could be accurately measured and correlated with histology grade of the Working Formulation (WF). Intermediate and high grade NHL (54 patients) were analyzed together as HG-NHL. With the discrimination point for PI of 10%, the survival of high and low proliferative lymphomas was compared in the whole NHL group and within the WF prognostic groups. The median PI was 5% in LG (low grade) NHL and 10% in HG (high grade) NHL group. Acturial survival in NHL with high proliferative activity (39 patients) was 31% at 5 years and 15% at 10 years, and in NHL with low proliferative activity (51 patients) 53% and 18%, respectively (p = 0.002). In HG-NHL, survival at 5 years for low proliferative cases was 55% and for high proliferative cases 28% (p = 0.065), whereas in the LG-NHL group it was 54% and 28%, respectively (p = 0.059). The survival at 10 years was nearly equal in all groups. Proliferative index was associated with the overall survival of NHL in the whole group, as well as within the LG and HG prognostic categories. PI could differentiate more and less aggressive NHLs both within LG-NHL and HG-NHL. A tendency of survival curves toward continuous relapse was observed in low proliferative NHL and a tendency toward "plateau" in high proliferative NHL, irrespective of the histology grade.

Cell Cycle↗

Prognostic parameters for survival of patients with malignant mesenchymal tumors of the uterus.

BACKGROUND: Malignant mesenchymal uterine neoplasms are the most aggressive type of primary uterine tumors, with most patients dying within a few years of diagnosis. Thus, it would be very important to define prognostic factors for predicting the malignancy potential of at least some of their subtypes. METHODS: Flow cytometric cell cycle analysis (proliferative activity, DNA ploidy, and DNA index) was performed on archival paraffin embedded blocks from 80 patients with malignant mesenchymal uterine neoplasms (endometrial stromal sarcomas, malignant smooth muscle tumors, and malignant Müllerian mixed tumors). The Cox proportional hazards regression model was used to assess relative effects of the following factors on patient survival: clinical stage, mode of therapy, DNA+proliferative activity, DNA index, histologic type, cellularity, degree of atypia, mitotic activity, and depth of myometrial invasion. RESULTS: There were 9 low grade stromal sarcomas, 17 high grade stromal sarcomas, 8 smooth muscle neoplasms with uncertain malignant potential, 23 leiomyosarcomas, and 16 homologous and 7 heterologous malignant Müllerian mixed tumors. In univariate analysis for stromal sarcomas, statistical significance was found for DNA ploidy+proliferative activity (P < 0.001), histologic type (P = 0.005), and DNA index (P < 0.001). In multivariate analysis, DNA index appeared to be the only significant parameter influencing patient survival (P = 0.005). In univariate analysis for malignant smooth muscle neoplasms, statistical significance was detected for mitotic activity (P = 0.049) and International Federation of Gynecology and Obstetrics classification (P = 0.021), but in multivariate analysis, clinical stage appeared to be the only significant parameter influencing patient survival (P = 0.032). In univariate analysis for malignant Müllerian mixed tumors, statistical significance was found for the depth of myometrial invasion (P = 0.039), DNA index (P = 0.037), and clinical stage (P = 0.013), but in multivariate analysis, only the depth of myometrial invasion (P = 0.036) and clinical stage (P = 0.025) were of statistical significance. CONCLUSIONS: The most powerful prognostic indicator for stromal sarcomas was the DNA index, for malignant smooth muscle neoplasms it was the clinical stage, and for malignant Müllerian mixed tumors it was the depth of myometrial invasion.

Analysis of Variance↗

Binding of anti-double stranded (ds) DNA-positive sera to denatured (d) DNA and synthetic poly[dA-dT] x poly[dA-dT] double stranded copolymer in an ELISA format.

Using an ELISA assay anti-nuclear antibody-positive sera from 300 patients with various immune-related diseases and 64 anti-nuclear antibody-negative sera were analysed for binding to S1-nuclease-treated double stranded (ds) DNA. In addition, the pattern of reactivity of 50 selected anti-dsDNA-positive sera was established using denatured (d) DNA and poly[dA-dT] X poly[dA-dT] double-stranded alternating copolymer (dAT) as additional DNA antigens. None of the 64 anti-nuclear antibody-negative sera and 76 of the 300 anti-nuclear antibody-positive sera (25%) were anti-dsDNA-positive. Of the anti-nuclear antibody-positive and anti-dsDNA-positive sera, 48 (63%) were from systemic lupus erythematosus patients, and 7 (9%) from rheumatoid arthritis patients, whereas 21 patients (27.6%) suffered from various immune and non-immune related diseases. Anti-dsDNA-positive reactivity was highly correlated with dDNA and dAT reactivity (r = 0.906, p < 0.0001 and r = 0.93, p < 0.0001, respectively). Although the majority of the 50 selected (37 systemic lupus erythematosus and 13 non-systemic lupus erythematosus) anti-dsDNA-positive sera concomitantly bound to both additional antigens, 7 of these (14%) did not bind to dAT, and 2 (4%) did not bind to dDNA. Anti-dsDNA-positive sera (n = 37) showed a similar pattern, in which 8.1% and 2.7% of sera did not bind to dAT and to dDNA, respectively. In contrast, anti-dsDNA-negative sera from various immune-related diseases bound either ssDNA (12.5%) or dDNA and dAT (12.5%). These data suggest that dsDNA and dAT-based assays detect similar but not identical specificities in the sera of patients suffering from systemic lupus erythematosus and in a proportion of non-systemic lupus erythematosus patients.

Antibodies, Antinuclear↗

Phorbol 12-myristate 13-acetate-mediated signalling in murine bone marrow cells.

Phorbol 12-myristate 13-acetate (PMA)-mediated signalling was investigated in relation to the ability of murine (CBA) bone marrow cells to form colonies in vitro. Treatment of marrow cells with PMA did not influence the 1,2-diacylglycerol or cyclic AMP concentrations, the intracellular Ca2+ concentration or phospholipase D activity. PMA increased particulate phospholipase A2 (PLA2) activity, lysophosphatidylcholine formation and arachidonic acid release from bone marrow cells; these effects were abolished when cells were pretreated with the putative PLA2 inhibitors heparin and mepacrine. While indomethacin and nordihydroguaiaretic acid inhibited either the cyclo-oxygenase or lipoxygenase pathway of arachidonic acid metabolism, as measured by their products prostaglandin E2 and leukotriene B4, they did not influence PMA-mediated PLA2 activation or translocation of protein kinase C (PKC) from the soluble to the particulate fraction. Treatment of cells with PMA increased the amounts of membrane-bound alpha, beta, delta, epsilon and zeta isoforms of PKC in bone marrow cells. Pretreatment of cells with PLA2 inhibitors reduced the amount of membrane-bound PKC-zeta in unstimulated cells and diminished PMA-induced translocation of PKC-zeta to membranes without affecting other PKC isoforms. This effect could be overcome by exogenous addition of arachidonic acid, suggesting that PKC-zeta may operate downstream of the activated PLA2. On the other hand, wortmannin, an inhibitor of phosphatidylinositol 3-kinase, did not influence the amount of PKC-zeta associated with particulate fractions in control cells and could not abolish the PMA-mediated translocation of this isoform. Short-term exposure (45 min) of bone marrow cells to PMA, phorbol 12,13-dibutyrate or arachidonic acid increased the number of colonies formed over 7 days in a methylcellulose-based culture in vitro. The effects of PMA, but not those of arachidonic acid, could be prevented by putative PLA2 inhibitors. This suggests that PMA-mediated activation of conventional PKCs and novel PKCs leads to PLA2 activation which, by releasing arachidonic acid from phospholipids, activates PKC-zeta. This signalling pathway appears to be mitogenic for bone marrow cells.

Animals↗

Significance of aneuploidy in non-Hodgkin lymphomas.

The incidence of aneuploidy was determined by flow cytometric analysis in paraffin-embedded tumor samples of 125 patients with non-Hodgkin lymphoma (NHL). There were 48 low-grade (LG) and 77 high-grade (HG) tumors. Aneuploidy was found in 34 (27%) NHL, 15 (31%) LG, and 19 (25%) HG tumors. The analysis of patient survival showed a significantly better survival of patients with LG than HG NHL, but the presence of aneuploidy did not influence the survival on the level of all patients, patients with LG or patients with HG NHL. In patients with LG NHL a tendency of diploid vs. aneuploid patients to survive longer was observed, but only at P = 0.056 significance level.

Aneuploidy↗

Short-term and long-term-effects of phorbol 12-myristate 13-acetate and different inhibitors on the ability of bone marrow cells to form colonies in vitro.

The process of signal transduction responsible for the phorbol 12-myristate 13-acetate mediated increase in the colony-forming potential of murine (CBA) bone marrow cells was studied using known modulators of the mitogenic signal. Pretreatment of cells for 60 minutes with staurosporine (1 mumol/l), an inhibitor of protein kinase C, completely prevented colony formation in the control group of cells and significantly reduced the number of colonies formed in the phorbol ester-treated group. Brief exposure (60 min) of cells to the phospholipase A2 inhibitors, mepacrine (500 mumol/l) and heparin (1 g/l), reduced the number of colonies formed in the control group and completely abolished the increase in the number of colonies formed after treatment of the cells with phorbol ester. When inhibitors of protein kinase C or phospholipase A2 were present during the entire period of the colony forming assay (7 days), no colonies could be scored in either the control or phorbol ester-treated groups of bone marrow cells. Long-term treatment or temporary exposure (60 min) of cells to indomethacin (50 mumol/l), an inhibitor of cyclooxygenase, or nordihydroguaiaretic acid (50 mumol/l), an inhibitor of lipoxygenase, had no effect on colony formation in both groups. Pretreatment of cells for 45 min with calcium ionophore A23187 (10 mumol/l) failed to increase the number of colonies, compared with the control group. Moreover, simultaneous treatment of cells for 45 min with phorbol ester (500 nmol/l) and A23187 (10 mumol) did not produce any further increase in the number of colonies, compared with the phorbol ester-treated group, suggesting that elevation of intracellular calcium is unimportant in the phorbol ester-mediated response. Dibutyryl cyclic adenosine monophosphate (50 mumol/l) in the presence or absence of phorbol ester, failed to stimulate colony formation, indicating that cyclic AMP-dependent protein kinases are not involved in the signalling process. Temporary exposure (75 min) of bone marrow cells to okadaic acid (1 mumol/l), a potent inhibitor of serine/threonine phosphatases, or to tyrphostine AG-115 (20 mumol/l), a tyrosine kinase inhibitor, did not effect colony growth in the control or phorbol ester-treated group. The results indicate that phospholipase A2 activation is involved in the phorbol ester-mediated increase in colony formation, since, of the different agents applied, only staurosporine, an inhibitor of protein kinase C, and mepacrine and heparin, putative inhibitors of phospholipase A2, were capable of abolishing phorbol ester-mediated effects.

Animals↗