Dose-dependent Positive Effect Research Articles

Effects of Ascorbic Acid Injection in Incubated Eggs Submitted to Heat Stress on Incubation Parameters and Chick Quality

Dose-dependent positive effects on hatchability and hatchling weight have been attributed to ascorbic acid (AA) when eggs were submitted or not to intermittent heat stress during incubation. Fertile breeder (Cobb(r)) eggs were used to determine if the pre-incubation injection of AA in ovo affects the incubation and hatchling quality of egg incubated under thermoneutral or intermittent heat stress conditions. Eggs were not injected or injected with 0, 2,4, or 6% AA/100µL water and incubated at continuous thermoneutral (37.5oC) or hot (39.0oC) temperature. Eggshell temperature (EST) increased in the second half of the incubation period in all experimental groups. The EST of non-injected eggs and of those injected with water was higher when incubated at 39°C than at 37.5°C, but EST was not different among eggs injected with AA. Egg mass loss and eggshell conductance were higher in the eggs incubated at 39°C than at 37.5°C.Hatchability was lower in the eggs injected with AA. Liver and yolk sac weights were higher, whereas heart and liver weights were lower in hatchlings from eggs incubated at 39°C; however, hatchling weight was not affected by incubation temperature. The results showed that AA doses affected egg conductive heat loss and hatchability, and that they did not minimize the effects of high incubation temperature on liver and heart development.

Melatonin: a possible link between the presence of artificial light at night and reductions in biological fitness.

The mechanisms underpinning the ecological impacts of the presence of artificial night lighting remain elusive. One suspected underlying cause is that the presence of light at night (LAN) supresses nocturnal production of melatonin, a key driver of biological rhythm and a potent antioxidant with a proposed role in immune function. Here, we briefly review the evidence for melatonin as the link between LAN and changes in behaviour and physiology. We then present preliminary data supporting the potential for melatonin to act as a recovery agent mitigating the negative effects of LAN in an invertebrate. Adult crickets (Teleogryllus commodus), exposed to constant illumination, were provided with dietary melatonin (concentrations: 0, 10 or 100 µg ml(-1)) in their drinking water. We then compared survival, lifetime fecundity and, over a 4-week period, immune function (haemocyte concentration, lysozyme-like and phenoloxidase (PO) activity). Melatonin supplementation was able only partially to mitigate the detrimental effects of LAN: it did not improve survival or fecundity or PO activity, but it had a largely dose-dependent positive effect on haemocyte concentration and lysozyme-like activity. We discuss the implications of these relationships, as well as the usefulness of invertebrates as model species for future studies that explore the effects of LAN.

The dose-related effects of dexmedetomidine on renal functions and serum neutrophil gelatinase-associated lipocalin values after coronary artery bypass grafting: a randomized, triple-blind, placebo-controlled study.

Acute kidney failure after coronary artery bypass grafting (CABG) is a serious complication that increases morbidity and mortality rates. Early detection and prevention of this complication are very important. A novel biomarker named neutrophil gelatinase-associated lipocalin (NGAL) can play an important role in early diagnosis of acute kidney injury. Recent studies on the favourable effects of Dexmedetomidine on cardiac surgery have been published. The aim of this study is to investigate whether there is a dose-dependent positive effect of Dexmedetomidine on neutrophil gelatinase-associated lipocalin levels and renal functions when used after CABG. Our randomized, triple-blinded, placebo-controlled study was conducted among 295 patients scheduled for CABG surgery between August 2009 and March 2011 in a tertiary cardiac and vascular surgery clinic. A total of 90 consecutive patients who met inclusion criteria were randomized and divided into three groups. The first group received a placebo. The second and the third groups received 4 and 8 µg/cc concentration of the Dexmedetomidine infusion, respectively. Infusion rates were regulated to obtain sedation with a Ramsey sedation score of 2 or 3. Patients were regrouped according to the total Dexmedetomidine dose. Statistical analyses of variables including serum neutrophil gelatinase-associated lipocalin values and conventional renal function tests were made for all six possibilities before the blind was broken. Results of conventional renal function tests were not significantly different. However, neutrophil gelatinase-associated lipocalin levels for the first postoperative day for placebo, low-dose and high-dose Dexmedetomidine groups were 176.8 ± 145.9, 97.7 ± 63.4 and 67.3 ± 10.9 ng/ml, respectively. These values were significantly different among the groups (P <0.001). In our study, we found that Dexmedetomidine infusion for sedation after CABG under cardiopulmonary bypass can be useful in the prevention of kidney injury. Conventional renal function tests, including blood urea nitrogen, serum creatinine, urine output and creatinine clearance rate measurements typically may not detect the development of acute kidney dysfunction in the first 48-h postoperative period. Differences were detected in renal function in the early postoperative period and the development of acute kidney injury, as determined by measurements of blood NGAL levels, was significant and dose-dependent.

Platelet-rich plasma mixed-fat grafting: a reasonable prosurvival strategy for fat grafts?

One of the most interesting developments in practical applications of fat grafting in recent years is the use of prosurvival strategies to improve maintenance of volume. Platelet-rich plasma (PRP) plays a decisive role in the repair and regeneration of different tissues via the activation and secretion of a great variety of growth factors and other cytokines stored in the alpha-granules of the platelets. This review aimed to assess the efficacy of PRP mixed-fat grafting as a prosurvival strategy for fat grafts. Online searches of the Cochrane Library and MEDLINE until January 2014 were conducted. The review included studies with at least one clinical end point in which the effect of PRP on the absorption and viability of the fat graft could be assessed. The review comprised 6 preclinical studies with a control group and 9 clinical studies of humans. It also included comparative studies performed with other prosurvival strategies for fat grafts, such as combination with the stromal vascular fraction and second-generation PRP, also called "platelet-rich fibrin." The results indicate that PRP may have a dose-dependent positive effect on fat grafts and suggest low complication rates. The development of new growth factor delivery systems or cell therapies to enrich fat grafts is an area that merits further research.

TRANSCRANIAL MAGNETIC STIMULATION OF DEEP BRAIN REGIONS IN ALZHEIMER'S DISEASE

sensitive measure for attention (respectively 1.96 (CI -0.86 4.80) and 3.48 (CI 0.54 6.42); figure 1), N-back, a test for working memory (respecitvely 0.09 (CI -0.06 0.24) and 0.12 (CI -0.02 0.27); figure 2) and on the visual verbal learning test, a test for learning and retrieval of information (figure 3 and 4). No differences were found on Stroop test, eye movements, VAS and pharmaco-EEG. Conclusions: The administered doses of Memogain were well tolerated. A dose dependent positive effect on attention and several aspects of memory was observed. Memogain may be a promising treatment for symptoms of Alzheimer’s Disease. Results of the higher doses and comparison with galantamine and donepezil may confirm these results and will be available in April 2014.

Cardiotonic activity of Parotoid gland secretion of common Indian Toad Bufo melanostictus on isolated heart of Frog

The present investigation has been undertaken to study the cardiotonic activity of parotoid gland secretion of common Indian Toad Bufo melanostictus on isolated perfused frog heart (Rana tigrina). Cardiotonic activity of parotoid gland secretion of B. melanostictus in normal as well as when induced with paraoxon (an organophosphate) was studied. For the evaluation of cardiotonic activity, Syme’s technique is being employed, digoxin and propranolol were used as standard drug and β-blocker respectively to characterize the effects on the receptors. The isolated perfused frog heart and hypodynamic frog heart showed dose dependent positive ionotrophic effects. The parotoid gland secretion exihibited cardiac stimulant activities. The propranolol was not able to block the effects of paraoxon induction on toad secretion. Thus, the present investigation reports that the parotoid gland secretion increased the force of contraction, heart beat and cardiac output in perfused frog’s heart, whereas, there was no change on hypodynamic heart, indicating that there may be existence of two components, one with β–receptor stimulating activity and other acting directly on the heart (independent of β1-adrenoreceptors).

Cardiotonic Activity of Alcoholic Bark Extract of Xylocarpus Granatum with Emphasis on Its Mechanism of Action

The aim of the present study was to scan and evaluate cardiotonic activity of alcoholic bark extract of Xylocarpus granatum and to establish its mechanism of action. The alcoholic extract of the bark of Xylocarpus granatum was prepared by the process of continuous extraction (soxhlation). The cardiotonic activity of the extract was evaluated on isolated normal and hypodynamic frog heart using Syme’s technique. Potassium loss was estimated in the effluents collected from the isolated perfused hypodynamic heart (control and inhibitory activity of the extract was estimated using the same frog heart muscle. The extract showed dose dependent positive ionotropic effect on normal and hypodynamic frog heart, loss of potassium ions and the percentage inhibition of Na, K ATPase activity. The percentage inhibition of Na, K ATPase activity with digoxin at a dose of 300 μg was found to be 93.80 ± 1.98%. Similarly, the extract also showed dose dependent (2, 20, 200 mg) percentage inhibition of Na, K ATPase activity and was found to be 35.20 ± 4.96%, 40.10 ± 1.27%, 56.74 ± 3.01% respectively. Results clearly indicated that the bark extract of Xylocarpus granatum possesses significant cardiotonic activity and follows the similar mechanism of digoxin (inhibition of Na, K ATPase enzyme activity).

Spilanthes acmella ethanolic flower extract: LC–MS alkylamide profiling and its effects on sexual behavior in male rats

According to Indian Systems of Medicine, Spilanthes acmella (L.) Murr. (Family – Asteraceae), is considered effective in the treatment of sexual deficiencies especially due to ageing. In the present study, characterization of ethanolic extracts of the Spilanthes acmella flower and its effect on general mating pattern, penile erection and serum hormone levels of normal male Wistar albino rats were investigated and compared with sildenafil citrate. In vitro nitric oxide release was also investigated in human corpus cavernosum cell line. As N-alkylamides are a promising group, their profiling was performed using a gradient reversed phase high performance liquid chromatography/electrospray ionization ion trap mass spectrometry (HPLC/ESI-MS) method on an embedded polar column. MS 1 and MS 2 fragmentation data were used for identification purposes. For assessment of sexual behavior, animals were divided into five groups of eight male rats. The extracts (50, 100 and 150 mg/kg body weight/day) and sildenafil citrate (5 mg/kg body weight/day) (positive control) were administered orally for 28 days. The behavioral and sexual parameters were observed at days 0, 15, 28 and after a lapse of 7 and 14 days of discontinuance of drug treatment. Five N-isobutylamides, one 2-methylbutylamide and one 2-phenylethylamide were identified. The orally administered extract had a dose dependent positive effect on mounting frequency, intromission frequency and ejaculation frequency and the most significant effects ( p < 0.05) were observed at 150 mg/kg treatment, even after a lapse of 7 and 14 days of discontinuance of drug treatment. A dose dependent effect was also observed on the FSH, LH and testosterone serum levels. With 150 mg/kg of ethanolic extract the values for FSH, LH and testosterone were 3.10 ± 0.25 mlU/ml, 6.87 ± 0.18 mlU/ml and 3.72 ± 0.12 ng/ml, respectively. In vitro nitric oxide release was 21.7 ± 2.9 μM, which was significantly higher compared to the control group ( p < 0.01). Sildenafil citrate exhibited also a significant effect on NO release, but no effect on hormone levels of rats was observed. The aphrodisiac potential of an ethanolic Spilanthes acmella extract was demonstrated in vitro and in vivo. N-Alkylamides might attribute to the improved sexual potential. Study lends support to the traditional utilization of S. acmella as a sexual stimulating agent.

Reduced transplant arteriosclerosis after treatment with MMF and MMF in combination with ganciclovir in a mouse aortic transplant model

Objectives: The aim of this study was to investigate whether Ganciclovir and Mycophenolate Mofetil (MMF), alone and in combination, have a beneficial influence on the development of transplant arteriosclerosis (TxA). Methods: Fully allogeneic C57BL/6 (H2b) donor aortas were transplanted into CBA (H2k) recipients. Recipient mice were treated with a single medication of MMF (100mg/kg or 300mg/kg) or a combination of MMF and Ganciclovir (10mg/kg Ganciclovir and 100mg/kg MMF or 72mg/kg Ganciclovir and 300mg/kg MMF) per day. Grafts were analysed by histology and morphometry on day 30 after transplantation. A potential effect of MMF or Ganciclovir on Tregs was investigated by FACS analysis. Results: Two doses of 150mg/kg MMF per day significantly reduced the development of TxA compared to untreated controls (intima proliferation of 23%±8% vs. 68%±7% [control]). 50mg/kg of MMF did not have any effect on the development of TxA. Strikingly, combination of Ganciclovir and low-dose MMF reduced the formation of TxA (intima proliferation of 27%±2% vs. 68%±7% [control]). The high-dose combination group (300mg MMF/72mg Ganciclovir) showed an intima proliferation of 24%±4%. FACS analysis of the spleen within this group revealed 12.73% CD4+cells with 14.70% CD4+CD25+FoxP3+cells. As compared to 17.5% CD4+cells with 11.1% CD4+CD25+FoxP3+cells in the control group. Single treatment with MMF (300mg) showed 10.55% CD4+ cells and 10.87% CD4+CD25+FoxP3+ cells within the analysed spleens. Conclusion: Our results demonstrate a dose-dependent positive effect of MMF on the development of TxA and a synergistic effect of Ganciclovir in combination with MMF.

Impaired erythrocytes deformability in H2O2-induced oxidative stress: Protective effect of L-carnosine

Impaired red blood cell deformability is a hemorheological perturbation induced by many kinds of diseases. An increase in free radicals causes a reduction in erythrocyte flexibility and deformability. Carnosine is a dipeptide abundant in skeletal muscle and brain of humans. One of the main function of carnosine is its antioxidant and free-radical scavenger effect. In this study our aim is to investigate the protective effect of L-carnosine on RBCs in H(2)O(2)-induced oxidative stress in vitro conditions. Twenty male wistar albino rats, 10 were 3 months old, 10 were 12 months old used. The blood from each rat were divided into ten tubes and these blood samples divided into two groups. The first tube of the first group was the control and the rest 4 tubes were treated with different concentrations of L-carnosine. All tubes in the second group were incubated with H(2)O(2) additively. The deformability indexes of the erythrocytes were measured by a laser diffractometer (Myrenne Rheodyne SSD).L-carnosine has improved the RBC deformability significantly which is impaired by H(2)O(2) treatment (p<0.05). Increase in deformability is more significant in young rat group when compared to old rat group.L-carnosine, as an antioxidant molecules, has a dose dependent positive effect on RBC deformability and has improved or protect the deformability of erythrocytes, especially in young rat group which impaired by H(2)O(2)-induced oxidative stress in vitro conditions. The results of this study first suggest that L-carnosine supplemention can be used to improve the RBC quality or to protect them from oxidative damage in survival of RBC in the circulation.

Nitric Oxide-dependent Regulation Of Glut4 Expression In L6 Myotubes

The upregulation of GLUT4 expression is one of the most important exercise-induced adaptations leading to improved glucose disposal in skeletal muscle. The GLUT4 gene is transcriptionally regulated and AMP-activated protein kinase (AMPK) is involved in this process. Previous studies in rats and humans have shown that AMPK is capable of phosphorylating and activating nitric oxide synthase (NOS). PURPOSE We hypothesized that NOS inhibition would prevent AMPK-induced upregulation in GLUT4 mRNA in L6 myotubes. METHODS Myoblasts were cultured in growth medium (10% FBS) until reaching 80% con.uence, then switched to differentiation medium (2%HoS) until myotubes were 80% confluent. At this point, myotubes were exposed to treatment medium (10%HoS + 5%FBS) for 16 h, with or without the AMPK activator, AICAR (5- aminoimidazole-4-carboxamide riboside, 1mM) or AICAR + the NOS inhibitor, LNAME (N(G)-L-nitro-arginine methyl ester,100μm). RESULTS AICAR induced ∼9-fold increase in GLUT4 mRNA levels in comparison to the control group (n=5–6/group; p = .0012), whereas co-treatment with L-NAME prevented this effect (p = .42). A dose-dependent positive effect of nitric oxide on GLUT4 expression was confirmed by incubation of myotubes with the nitric oxide donor, SNAP. Additionally, treatment with the cell permeable cGMP analog, 8-BrcGMP (1mM) for 16 h increased GLUT4 mRNA levels by 85% (n=6/group; p = .002). CONCLUSIONS These findings suggest that nitric oxide plays a role in the AMPK-induced upregulation of GLUT4 mRNA in skeletal muscle, and may do so by increasing intracellular levels of cGMP. Supported by UF Opportunity Fund.

Lignosulfonate promotes the interaction between Scots pine and an ectomycorrhizal fungus Pisolithus tinctorius in vitro

Lignosulfonate (LS) is a lignin-based polymer obtained as a by-product from paper industry, which may have potential as an amendment with macronutrients. We studied effects of LS on the interaction between Scots pine (Pinus sylvestris L.) seedlings and hypocotyl cuttings and the ectomycorrhizal (ECM) fungusPisolithus tinctorius (Pers.) Coker and Couch. The experiments were performed in vitroon the MMN agar medium containing Fe–LS chelate at the concentrations of 0, 5, 10 and 25 mg/L. Inoculation with P. tinctoriusincreased root growth of the seedlings. Fe–LS enhanced P. tinctorius induced formation of lateral roots and had a dose-dependent positive effect on the establishment of mycorrhizas on the seedlings. The growth of the fungal mycelium was improved by Fe–LS, which might cause faster and more intensive contact with the roots and, thus, better root growth and mycorrhiza formation. P.␣tinctorius enhanced also adventitious root formation and subsequent root growth of the hypocotyl cuttings but without any synergistic effect with Fe–LS. Our study with P. tinctorius and Scots pine in vitro indicates that a low-cost by-product Fe–LS, obtained from paper industry, may be a potential tool to improve the efficiency of fungal inoculations, thus, facilitating the early interaction between an ECM fungus and host seedling.

Placenta Detachment: Unexpected High Concentrations of 5-Hydroxytryptamine (Serotonin) in Fetal Blood and its Mitogenic Effect on Placental Cells in Bovine

The purpose of this study was twofold: (1) to determine whether there is a profile of 5-hydroxytryptamine (5-HT, serotonin) concentrations in fetal bovine blood and tissues during pregnancy, parturition and the early neonatal period and (2) to determine whether 5-HT has a ‘mitogenic’ effect on cultured placentome cells in bovine. Results revealed a 5-HT concentration profile in fetal blood. Overall concentrations of 5-HT in fetal blood were 6.6 times (P< 0.001) that of adult cows and 2.8 times (P< 0.001) that of blood collected during caesarean section (from umbilical veins) and from 18–72h old calves. Mid-term and full-term pregnancy fetuses were not statistically different from each other. Overall concentrations of 5-HT in the intestinal wall of the fetus were 4.4 times higher (P< 0.05) than in the 24h calf. Concentration of 5-HT in full-term muscle was 3.5 times higher than in mid-term muscle and 2.8 times higher than in 24h old calf muscle (P< 0.05). Concentrations of 5-HT in mid-term and full-term cotyledon were 4.4 times higher (P< 0.05) than in post partum cotyledon.Characterized trophoblast cells and a heterogeneous population of bovine cotyledon cells treated with 5-HT (2.5, 5.0 and 10.0μm) incorporated between 2.0 and 3.0 times more3[H]-thymidine than untreated controls, indicating a dose-dependent (r=0.94) positive mitogenic effect of 5-HT. Both groups of cultured cells responded equally. Five-HT treatment did not affect either cell number or cell size. It was concluded that a 5-HT concentration profile exists in fetal bovine blood and tissues and that 5-HT has the ability to act as a mitogen in bovine placental cells.

Effects of some plant growth regulators on the growth of the seagrass Cymodocea nodosa (Ucria) Ascherson

The effect of three auxins (indole-3-acetic acid, α-naphthaleneacetic acid, 2,4-dichlorophenoxyacetic acid), three cytokinins (6-furfurylaminopurine, 6-benzylaminopurine, 6-(γ-γ-dimethylallylamino)purine) and one gibberellin (gibberellic acid) at external concentrations from 0.01 to 10 mg l −1 on the leaf and rhizome growth of fragments of the seagrass Cymodoceanodosa (Ucria) Ascherson was assessed in the laboratory. Only the treatment with gibberellic acid showed a dose-dependent positive effect on leaf growth at external concentrations between 0.01 and 10 mg l −1. Rhizome growth, however, was higher ( P < 0.05) at 0.01–0.1 mg l −1 and decreased with increasing external concentrations of gibberellic acid.

Effects of transferrin receptor antibody—NGF conjugate on young and aged septal transplants in oculo

The purpose of this study was to investigate the effects of nerve growth factor (NGF) conjugated to a monoclonal transferrin receptor antibody (OX-26) on septal transplants in oculo. Three different doses of OX-26-NGF conjugate (0.3, 3, and 50 μg/injection) were injected into the tail vein of young adult hosts 2, 4, and 6 weeks following intraocular transplantation of fetal forebrain tissue containing septal nuclei. Intravenous injections of OX-26 alone, NGF alone, and saline served as controls. An increase in intraocular tissue growth, as well as an increase in the intensity of immunoreactivity for p75 receptors and acetylcholinesterase, was observed following peripheral OX-26-NGF administration at the two highest doses tested. In addition, aged host rats with 16-month-old intraocular septal grafts were injected intravenously with OX-26 or OX-26-NGF (10 μg NGF/injection) every 2 weeks until the transplants were 24 months old. The intensity of choline acetyltransferase-like (ChAT) staining appeared to be greater and the cell bodies were larger with more processes in aged transplants in hosts treated with the OX-26-NGF conjugate than in aged OX-26-treated subjects. The present results suggest that peripheral OX-26-NGF can deliver biologically active NGF across the blood—brain barrier and have dose-dependent positive effects on both aged and developing cholinergic neurons in septal transplants.

Effect of Inosine on Function and Adenine Nucleotide Content of the Isolated Working Rat Heart

Inosine added to the perfusion medium for isolated working rat heart induced a dose-dependent coronary vasodilator and positive functional effect. Inosine increased coronary flow (ml/min) from 11.8 +/- 0.5 (control, n = 16) to 15.6 +/- 0.6 (0.1 mM, n = 10), to 18.2 +/- 1.1 (0.5 mM, n = 6), and to 18.4 +/- 0.8 (1.0 mM, n = 14). Left ventricular systolic pressure was increased (LVSP, mm Hg) from 72.5 +/- 1.1 (control) to 75.4 +/- 1.7 (0.1 mM) to 78.7 +/- 2.1 (0.5 mM) and to 82.6 +/- 1.5 (1.0 mM). and cardiac output (CO, ml/min) from 26.4 +/- 2.0 (control) to 29.6 +/- 2.3 (0.1 mM), to 30.2 +/- 3.5 (0.5 mM), and to 37.4 +/- 2.0 (1.0 mM). At the end of 30-min reperfusion after a 15-min period of global total ischemia (n = 9), the functional parameters were significantly reduced (coronary flow 8.5 +/- 0.4 ml/min, LVSP 63 +/- 1.9 mm Hg, CO 13.6 +/- 1.9 ml/min). When inosine was present in the perfusion medium during the entire experimental protocol, coronary flow and heart function were also enhanced in a dose-dependent manner. The content of cardiac ATP (mumol/g) was decreased at the end of the 15-min ischemic period (1.89 +/- 0.17, n = 7; control 3.85 +/- 0.05, n = 4), and inosine had no effect. At the end of the 30-min postischemic reperfusion period, the ATP pool had recovered to an appreciable extent (3.01 +/- 0.11, n = 9) and was higher when 1.0 mM inosine had been infused (3.44 +/- 0.11, n = 7). Thus, inosine increased coronary flow dose dependently and, as a consequence, the function of the isolated perfused working heart both under control conditions and during the postischemic reperfusion period.

The effect of Zotepine on productive and negative symptoms in schizophrenic patients

RésuméZotepine was studied in 15 schizophrenic patients over a period of 28 days with regard to its antipsychotic efficacy, effect on negative schizophrenic symptoms, tolerability and adverse effects. Nine patients received Zotepine in a high dosage of 230 mg/die±52 mg, 6 patients in a low dosage of 168 mg/die ± 18 mg. Two patients receiving the high dosage dropped out after 21 days because of worsening of symptomatology and suicide attempts. Zotepine had rapid antipsychotic effects with sedative properties during the initial days of treatment. Minimal adverse effects and extra-pyramidal motor disturbances as well as dose-dependent positive effects on negative schizophrenie symptoms were found.

Analysis of the interlaboratory and intralaboratory reproducibility of the enhancement of simian adenovirus SA7 transformation of Syrian hamster embryo cells by model carcinogenic and noncarcinogenic compounds.

The intralaboratory and interlaboratory reproducibility of a DNA virus (SA7) transformation enhancement assay was investigated using nine carcinogenic and noncarcinogenic compounds representing a variety of chemical classes. By the use of standardized procedures designed to limit assay variables, replicate assay data were collected in two independent laboratories and analyzed for concurrence. The carcinogens, 7,12-dimethylbenz(a)anthracene, benzo(a)pyrene, and N-methyl-N'-nitro-N-nitrosoguanidine yielded reproducible dose-dependent cytotoxicity and positive transformation effects (defined as statistically significant [p less than or equal to 0.05] enhancement of virus transformation at two or more consecutive dose levels) in all experiments in both laboratories. The carcinogens lead chromate, diethylnitrosamine, 4-nitroquinoline-N-oxide, and 2-acetylaminofluorene demonstrated enhancement of SA7 transformation at two or more dose levels in 40-50% of the assays. The noncarcinogenic structural analogs anthracene and pyrene consistently did not produce positive assay responses when tested at dose levels up to the limits of solubility. Good interlaboratory concurrence was demonstrated for these model compounds in the Syrian hamster embryo cell-SA7 assay.