Roles of function, reminding, and variability in categorization by 3-month-old infants

The roles of function, reminding, and exemplar variability in categorization of a physically dissimilar object were studied with 3-month-old infants trained to move a crib mobile by kicking. Performance on a transfer test with a motionless novel object provided evidence of categorization. In Experiments 1 and 2, infants, like adults, initially categorized novel objects on the basis of physical appearance, but only if trained with multiple exemplars, after delays of 1 and 7 days. In Experiment 3, prior knowledge of an object's functional properties overrode physical dissimilarity as the basis for categorization and enabled reminding of the classification response 2 weeks later. In Experiment 4, postevent contingency information overrode physical and functional properties as the basis for categorization. These findings indicate that expectations and goals influence infants' category decisions and raise the possibility that infants of 3 months respond by analogy.

Schedule-dependent effectiveness of ADM and multiple cycles of DDP on a murine reticulum sarcoma

The therapeutic index of adriamycin (ADM) and cisplatin (DDP) combination versus repeated sequences of the more active drug (DDP) was investigated on a murine reticulum cell sarcoma of ovarian origin (M5) implanted i.m. in C57BL/6 mice. The antitumor efficacy of multiple cycles of DDP according to different regimens at a prefixed time (every 7 days) or at tumor regrowth was also evaluated. Our data demonstrate that the ADM-DDP combination did not improve the antitumoral efficacy of DDP as single agent, while repeated cycles of DDP led to a significant increase in the host life span. Differences in therapeutic effect were elicited by the two schedules: the regimen at a prefixed time showed a major effect on local tumor control, although the regimen at tumor regrowth was better tolerated.

[Surgical cardiac risk in patients with heart diseases. II. Perioperative treatment]

An improvement can be obtained in the surgical prognosis of the cardiopathic by working on the main risk factors. Congestive decompensation must usually be treated with diuretics; digitalis in only indicated in certain cases. In patients with ischaemic cardiopathy, angina therapy should be continued during the perioperative period, replacing the oral route; in the postoperative period. ECG monitoring is advisable up to Day III-V. Valve defects should be assessed carefully, including haemodynamically (especially severe aortic stenosis) because correction of the defect may become a priority. In hypertrophic cardiomyopathy hypovolaemia and loss of sinus rhythm should be avoided. Valve prostheses involve particular problems represented by antibacterial prophylaxis and perioperative anti-coagulation. Congenital cyanogenic cardiopathies often require a lowering of the haematocrit and careful control of hypotension. Postoperative arrhythmias generally have medical causes and require control of the latter before possible antiarrhythmic therapy. The implantation of a temporary prophylactic pacemaker is rarely needed; for patients with definitive pacemakers, some precautions are needed for the use of the thermocautery. It is very important to deal with poor general medical conditions that might affect prognosis. Control of hypertension is less important than control of hypotension.

[Surgical cardiac risk in patients with heart diseases. I. Evaluation of the risk]

To evaluate the cardiac risk in patients undergoing noncardiac surgery, it has been identified by the multivariated analysis some major and independent correlates of fatal or life-threatening cardiac complications. The most important ones were the history of previous myocardial infarction in the preceding six months, clinical signs of congestive heart failure, third heart sound or jugular venous distention, and for some Authors instable angina class IV CCS. Other predictive factors of complications were premature ventricular and atrial contractions or ectopic rhythms within cardiac diseases, age over 70 years, intraperitoneal, intrathoracic, aortic or emergency operation, severe valvular aortic and mitral stenosis and poor general medical conditions. Stable angina, hypertension, hyperlipidemia and smoking habit were less important. The global evaluation of cardiac risk can be performed by multifactorial index subdividing the patients into four very different risk classes. This is obtained by scores assigned to each statistically significant factor.

Myocardial ischemia during stroke: scintigraphic demonstration

In a 74-year old female, admitted to the Acute Stroke Unit for a cerebral reversible ischemic attack, we investigated the occurrence of ischemic alterations on ECG, recorded during an acute relapse, using 99mTc (MIBI) myocardial scintigraphy. Scintigrams showed a transient anteroseptal and inferior hypoperfusion. This is the first direct demonstration of myocardial ischemia occurring during stroke.

[The lipid hypothesis in the etiopathogenesis of ischemic heart disease: confirmations and doubts resulting from primary prevention trials]

Sufficient evidence exists today pointing to the relationship between high levels of plasma cholesterol and coronary atherosclerosis. Up to now, however, the last criterion for validating the aetiopathogenetic relationship between dyslipidemia and CHD, i.e., the demonstration that reduction of plasma cholesterol reduced the formation or progression of the plaque and the incidence of its fatal or non-fatal cardiac and vascular complications, has been lacking. For more than two decades, numerous trials have had this aim in mind but until very recently results have not been substantiated owing to various deficiencies in the method. Before publication of the NHLBI Task Force of Atherosclerosis, eleven major randomised clinical studies based on hypolipidemia interventions were completed. The three studies involving dietetic interventions were considered non-conclusive overall because of the lack of a double-blind factor and of other important epidemiological criteria. Of three pharmacological trials only two involved studies of primary prevention carried out on a population of hypercholesterolaemics. These produced partial results on certain cardiac end-points but not on total deaths and at times not even on deaths from CHD. Multifactorial studies, finally, were even less demonstrative. Taken together, however, the trials based on hypolipidemia interventions point to interesting though not definitive evidence of a reduction in blood cholesterol levels to reduce the incidence and mortality from CHD. According to the NHLBI, many of these studies lacked important features that were codified and suggested for later studies.(ABSTRACT TRUNCATED AT 250 WORDS)

[Transesophageal pacing in the diagnosis of accelerated atrioventricular conduction]

The term "enhanced atrioventricular nodal conduction" (EAVN) is used to indicate an electrophysiologic condition characterized by subnormal conduction delay with reduced decremental properties in the AV node, which can be responsible for rapid ventricular rates in the event of fast atrial rhythms. Although identification of such an entity usually requires definition of the AV conduction intervals, some authors have suggested that EAVN can be diagnosed, by means of atrial pacing only, when 1:1 conduction with narrow QRS complexes occurs during atrial pacing at rate higher than 200 bpm. The use of incremental transesophageal atrial pacing (TAP) as a noninvasive tool for identification of EAVN was investigated in 19 patients. Fifteen had a history of supraventricular tachyarrhythmias (11 Wolff-Parkinson-White syndrome; 2 Lown-Ganong-Levine syndrome; 1 intranodal AV reentry tachycardia; 1 sick sinus syndrome); 4 patients exhibited an electrocardiographic pattern of preexcitation without a history of tachyarrhythmias. Analysis of AV conduction at fast induced rates was hampered in 5 patients because of the easy occurrence of reciprocating tachycardia and/or atrial fibrillation during TAP, as well as because of the persistence of delta wave at cycle lengths (CL) shorter than 300 ms. Among the remaining patients, in 7 (50%, Group A), 1:1 AV conduction was present at pacing CL shorter than 300 ms. In 7 patients (50%, Group B), AV block occurred at pacing CL longer than 300 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of the cytotoxic effect of 5-fluorouracil by N-methylformamide on a human colon carcinoma cell line

The cytotoxic effect of the combination of N-methylformamide (NMF) with 5-fluorouracil (5-FU) on cell survival of the human colon cancer line HT29 was assessed. The differentiating activity of NMF was evidenced by morphological maturation and conversion of cell culture characteristics to those consistent with a more benign phenotype. In combination experiments, the noncytotoxic concentration of 1% NMF was chosen and doses of 5-FU ranging from 5 to 25 micrograms/ml were employed. Two main schedules were tested either on exponentially or stationarily growing cells: (a) 1% NMF for 72 h followed by 12-h exposure to 5-FU; (b) 5-FU for 12 h followed by 72-h exposure to 1% NMF. The results obtained demonstrated that the 5-FU----NMF sequence determined a powerful reduction in the surviving fraction of HT29 cells, while the reverse sequence did not increase the killing effect of 5-FU given alone. Immunocytochemical and scanning electron microscopy studies seemed to confirm that the association in which the differentiating agent followed the 5-FU treatment strongly impaired cellular integrity and function and that cytoskeletal elements, particularly microfilaments, and surface structures could play an essential role in the mechanisms of cytotoxicity. Furthermore, the results of this work indicate that drug sequence is a critical factor for the optimal combination of 5-FU and NMF.

Failure of antiviral therapy for acquired immunodeficiency syndrome-related cytomegalovirus myelitis

We report the first published case (to our knowledge) of histopathologically documented acquired immunodeficiency syndrome-related cytomegalovirus (CMV) myelitis in which antiviral drug therapy was administered. Despite sensitivity of the patient's CMV isolate to therapy with both ganciclovir and foscarnet, use of neither of these agents halted progression of central nervous system CMV disease. Higher doses of these drugs or combination therapy may be required to treat acquired immunodeficiency syndrome-related CMV myelitis effectively.

Establishment, characterization and chemosensitivity of two human glioma derived cell lines

Two continuous human glioma derived cell lines, LI and DF, were established in our laboratory. Both cell lines showed cytological features and in vitro behavior similar to those of the respective original neoplasms. These two lines were characterized for their main biological properties including in vitro and in vivo growth rate, clonogenic ability and tumorigenicity in nude mice. The plating efficiencies were generally high both during exponential and stationary growth phases and a high tumorigenicity was observed. All injected nude mice developed tumors. The two lines were tested for chemosensitivity to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and cis-Diamminedichloroplatinum II (DDP). Heterogeneity in biological features and in drug sensitivity was observed. Exposure of the two lines to BCNU and DDP showed that the glioblastoma (LI) was less sensitive than the anaplastic astrocytoma (DF). For both lines BCNU was more effective on cells in plateau than in exponential phase, while the killing effect of DDP was not phase-dependent.

The automatic implantable cardioverter/defibrillator: transesophageal atrial pacing discloses the potential for erroneous discharges

We report the occurrence of erroneous discharge from an implanted automatic cardioverter/defibrillator during transesophageal atrial pacing. Transesophageal pacing was performed as part of a study protocol on the inducibility of ventricular tachycardia from the atrium in patients with ischemic heart disease. At an induced heart rate of 166 beats per minute (a value just above the cut-off rate of the device), the cardioverter/defibrillator was triggered. This observation suggests that transesophageal atrial pacing could be utilized to disclose the potential for spurious discharges in the event of fast atrial rhythms in patients with the automatic implantable cardioverter/defibrillator.

[Hypertrophic cardiomyopathy associated with Noonan's syndrome and membranous aortic subvalvular stenosis associated with Turner's syndrome. Report of 2 clinical cases]

Cardiovascular anomalies are found in 50% of the cases of Turner's and Noonan's syndromes-diseases with the same phenotype but with a different genotype. In the former, the most common congenital heart diseases are aortic coarctation (30%) and bicuspid aortic valve (34%), while in the latter they are pulmonary valvular stenosis (60%), interatrial septal defect (25%) and obstructive or non obstructive hypertrophic cardiomyopathy (17%). We have described two cases, respectively of Noonan's and Turner's syndrome. The prominent features of the first case are the transmission of the syndrome on the male line, since father and son--the latter being our patient--are affected with the same syndrome, and the occurrence of a non obstructive hypertrophic cardiomyopathy involving both the ventricles, a situation not yet described in Noonan's syndrome. A subvalvular membranous aortic stenosis has instead been found in our patient with Turner's syndrome: this cardiac anomaly has never been described within the aforementioned syndrome in medical literature.

Effect of sequential application of hyperthermia and chemotherapy on the survival of a thermoresistant human melanoma cell line

The human melanoma cell line M14 has been proven in previous experiments to be much less sensitive to the action of heat (42 degrees C, 60 min) than other melanoma lines. In the present study, we have investigated the possibility of increasing the effect of heat by means of drug treatment. Thermochemotherapy was applied to exponentially growing cells according to different schedulings, and was analyzed in its efficacy by measuring the impairment of the cellular colony-forming ability. Findings of the present study point out that: (a) appropriate sequencing between hyperthermia and cis-diamminedichloroplatinum II(DDP), melphalan (L-Pam), 1,2,4-dichlorobenzyl-1H-indazol-3-carboxylic acid (LNA) or 5-3,3-dimethyl-1-triazeno-imidazole-4-carboxamide (DTIC) strongly influences the cytotoxic effect of the two agents; and (b) the optimal combination appears to be the simultaneous application of heat and drugs. However, as far as thermochemotherapy with DDP is concerned, a synergistic effect may also be achieved when hyperthermia precedes DDP.

Kinetic and survival response of the M14 cell line to lonidamine associated with adriamycin or hyperthermia

Lonidamine (LND), an indazole-carboxylic acid derivative, was delivered alone and together with adriamycin (ADM) or hyperthermia to the human melanoma cell line M14, and cell survival was assessed. Cell cycle-specific effects were investigated by analyzing sequences of DNA content histograms by means of a suitable mathematical procedure. LND delivered for 1 h at a dose of 50 micrograms/ml did not affect proliferation and survival of the cells. Exposure of the cells for 1 h to ADM (1.0 microgram/ml) followed by LND for 1 h (50 micrograms/ml) produced the highest effect on the survival. Kinetic parameters were affected by the combined treatment slightly more than by ADM exposure alone. Simultaneous delivery of LND (50 micrograms/ml) with hyperthermia (42 degrees C, 1 h) reduced the survival and enhanced the block of cells in the G2M phase, as compared with the heat treatment alone. The effect of the treatments on cell survival appeared to be related to the perturbation of the G2M phase of the cycle.

Biological features and in vitro chemosensitivity of a new model of human melanoma

The M14 human melanoma cell line was characterized either for some biological features in vitro and in vivo or for responsiveness to a panel of anti-tumor agents of clinical interest. The results of our study show that the M14 cells in culture resemble the in vivo melanomas both biologically and functionally, thus suggesting the usefulness of employing this line as a preclinical model for cancer treatment studies.

In vitro and in vivo potentiation by lonidamine of the antitumor effect of adriamycin

Lonidamine (LND), a powerful antispermatogenic compound, has been shown to impair differentially the energy metabolism of normal and neoplastic cells and to increase significantly the survival of animal bearing experimental tumors. Clinical trials are presently ongoing and preliminary favourable results have been obtained with LND as a single agent or associated with other antineoplastic drugs. In this work the effect of the combination LND plus ADM was investigated on in vitro and in vivo tumors. The in vitro effect was analysed by the colony forming technique and the in vivo antitumor activity was assessed by means of local control parameters, increase in host lifespan and weight reduction of metastasing target organs (liver, kidney, ovary). The results obtained indicate that LND is poorly effective when used alone, while a very high cytotoxicity is observed when it is combined with ADM. Exposure of cells to different time-sequences and schedules of both drugs elicits a different response. In particular a synergistic effect is obtained when ADM precedes LND. These results have been preliminarily confirmed by in vivo studies.

The plasma atrial natriuretic peptide response to treatment of acute cardiac failure, spontaneous supraventricular tachycardia and induced re-entrant tachycardia in man

Patients with acute congestive cardiac failure had elevated plasma concentrations of atrial natriuretic peptide (ANP) which fell towards normal levels with successful diuretic therapy. The plasma ANP concentration was closely correlated with the clinical condition of the patients as assessed by serial clinical measurement of the jugular venous pressure and body weight. Plasma ANP concentrations were also raised in patients with a spontaneous acute onset of supraventricular tachycardia but to a lesser extent in patients with chronic tachycardia. Again, successful treatment with d.c. cardioversion returned plasma ANP concentrations towards normal. Induction of atrioventricular re-entrant tachycardia produced an acute and marked rise in plasma ANP concentrations, which rapidly returned to normal when the sinus rhythm was restored. This acute ANP rise probably mediates the known acute natriuretic effect of paroxysmal tachycardia. All the data are consistent with the hypothesis that atrial distension, whatever the cause, releases ANP into plasma.

Etoposide prior to cis-diamminedichloroplatinum in combination chemotherapy: in vitro and in vivo studies

Antitumor effect and toxicity of etoposide (VP 16) in combination with cis-diamminedichloroplatinum (DDP) were studied on the in vitro C108 line and its in vivo counterpart, the M1087 line, both deriving from Lewis lung carcinoma. A colony-forming assay was used to assess the in vitro cytotoxicity of each drug and, on the basis of survival curve shape indications, different drug sequences were analyzed in order to find the optimal combination. Tumor growth inhibition, growth delay, metastasis reduction and percentage increase in lifespan were considered as parameters of therapeutic effect. From the present work it can be derived that the VP 16-DDP combination produces a poor antitumour effect against the Lewis lung carcinoma lines, otherwise associated with a highly acute toxicity. The sequence in which VP 16 is given before DDP induces a significant antimetastatic effect together with acceptable toxicity.

Retroactive interference in rats: independent effects of time and similarity of the intervening event with respect to acquisition

Events occurring during the retention intervals for a 5-min delayed alternation task were used to investigate the factors that influence retroactive interference. Appetitive reinforcement in an E-maze was employed to train rats on the delayed alternation task consisting of a forced-choice (target event) trial followed by a free-choice (test) trial. Occasional probe trials added a potentially interfering event either at the beginning, middle, or end of the retention period. These events also varied in similarity to the target events, ranging from low similarity to the converse of the target event. Interference increased both with the interval between the target and intervening events and with the similarity between the converse of the target event and the intervening event; however, there was no tendency, significant or otherwise, towards an interaction between stimulus similarity and the interval between the target and intervening events. Control groups demonstrated that the interference was of an associative nature and that the interval between the intervening event and the test trial was little consequence. These results are discussed in terms of two separate types of interference: similarity interference which depends on stimulus similarity of the intervening event to the converse of the target event but not on the temporal location of the intervening event, and processing interference which depends on the temporal location of the intervening event but not on its similarity to the converse of the target event.

Surgical-adjuvant chemotherapy with AMSA in Lewis lung carcinoma bearing mice

The effect of 4'-(9-Acridinylamino) methanesulfon-m-anisidide (AMSA) in combination with surgery was studied on Lewis lung carcinoma-bearing mice. The surgical removal of the primary tumor was performed at a late stage of growth and the drug was administered i.p. according to different schedules. Results of the present study indicate that the AMSA-surgery combination displays a modest effect against the Lewis lung carcinoma, slightly improved when chemotherapy is given before tumor removal, and that double courses of AMSA, given both before and after surgery, prove to be equally effective as a single preoperative chemotherapy.

Lewis lung carcinoma lines with different metastatic behavior: response to ICRF-159

Three Lewis lung carcinoma lines (3LL) with different metastatic behavior have been investigated with regard to their response to Razoxane (ICRF-159). The effects of different schedules were tested both on primary and secondary tumors. Results show that the lines are heterogeneous in their response to this antimetastatic agent and that, in particular, BM21548 the least metastatic line is also less sensitive to ICRF-159. A better response can be achieved with this line by a proper fractionation regimen which takes into account the delayed metastasis release from primary tumor. As far as M1087, the most metastatic line is concerned, secondaries are greatly affected by ICRF-159 treatment if performed at a moderately advanced stage of growth. On the contrary, metastases from early tumor stages can be better controlled by radical surgery of the primary implant than by treatment with ICRF-159.

Influence of scheduling on therapeutic and toxic effect of AMSA in Lewis lung carcinoma

The antitumor activity and toxic effect of AMSA were studied in Lewis lung carcinoma (3LL) at various stages of growth. The total dose of drug injected IP was 15 mg/kg, which is equivalent to the LD10. Different administration schedules were tested, these being single-injection schedules (day 1, 7, or 10 after tumor implantation) and repeated low-dose-injection regimens (days 1, 4, and 7 and days 1-7 after tumor implantation). Tumor weight inhibition, retardation of growth, reduction in the number of metastases, and median survival time of treated mice over controls were analyzed as end-points to evaluate the antitumor activity of AMSA. Early deaths and changes in white blood cell count were considered as parameters of toxicity. Our findings can be summarized as follows: (1) AMSA is only minimally effective against primary 3LL tumor at all the growth stages examined and no schedule-dependency is detected; (2) a greater reduction in metastases (70%-77%) is found when the drug is administered fractionally than when it is given in a single dose (39%-60%); (3) irreversible leukopenia is induced by the single-dose schedule of AMSA administration while after repeated low doses the white blood cell counts are in the same range of those of the control groups. Therefore, because of the schedule-dependency of toxicity and reduction in metastases, fractionated administration of AMSA at this dose level would be suitable for adjuvant chemotherapy.

Signaled tailshock is perceived as similar to a stronger unsignaled tailshock: implications for a functional analysis of classical conditioning

Water-deprived rats given fixed-electrode, variable-intensity tailshock at random times rated each trial by pressing either a "high-aversiveness" or "low-aversiveness" lever in order to obtain water. Trials on which a warning signal preceded tailshock resulted in more "high-aversiveness" leverpressing than did otherwise equivalent unsignaled trials. The magnitude of this effect increased and decreased as a function of several parameters including signal-shock interval, signal duration, and range and absolute value of shock intensities but was never reversed despite efforts to achieve such a reversal. Variation in the size of the effect as a function of signal parameters as well as lick suppression scores indicated that the signal had acquired aversive characteristics, which suggests that the effect of the signal on lever choice was due largely to the aversiveness of the signal summating with the aversiveness of the tailshock. Several hypotheses concerning factors that might have either masked or prevented classically conditioned preparatory responses elicited by the signal from reducing tailshock aversiveness were tested and rejected. Despite the greater aversiveness of the signaled condition, when given the choice of receiving or not receiving the signal, the animals displayed a preference for signaled tailshock. Implications for the role of preparatory responding both in the preference-for-signaled-shock phenomenon and in classical conditioning are discussed.

DNA content distribution of in vivo and in vitro lines of Lewis lung carcinoma

The kinetic features of Lewis lung carcinoma (3LL) and of two in vitro and two in vivo derivative lines were studied by flow cytometry. The in vitro lines C108 and BC215 show the same tetraploid DNA content and a very similar cell cycle structure, characterized by a prevalent S fraction. Also, the in vivo lines, the original 3LL and M1087, show a tetraploid DNA content, while the BM21548 is characterized by a hyperdiploid DNA mode and a broader distribution of DNA values. No difference in the modal DNA value is found between each primary tumor and the corresponding lung metastases for all the in vivo lines. In addition, an increase in the G1 component corresponding to a decrease in the S fraction is observed during the tumor growth. These kinetic features were related to some malignant properties of 3LL lines, such as growth pattern and metastatic potential. Our findings indicate that a direct correlation is not always possible to establish.

Extracellular paraprotein globules in a patient with monoclonal gammopathy

A patient with a plasma cell disorder and IgA lambda paraprotein had the unusual finding of numerous, large, opaque, extracellular globules in her bone marrow and liver. While plasma cell intracellular inclusions are well documented, identification of such material in extracellular sites is not. These globules were of various sizes, stained light to dark blue with Wright's stain, were gray in hematoxylin-eosin preparations, and were fluorescent when stained with conjugated antibodies to lambda, but not to kappa, light chains. They strongly resembled the inclusions (Russell bodies) seen in plasma cells and are believed to be massive accumulations of immunoglobulin. The clinical significance of this morphological finding is unknown, but physicians interpreting bone marrow specimens should be aware of this unusual feature.

Study on protein content of rabbit reticulocyte ribosomal subunits: correlation with functional activity

The correlation between chemical composition (protein content) of native and derived ribosomal subunits and their activity in a cell-free system, programmed with haemoglobin messenger RNA, has been investigated. On the basis of isodensity sedimentation of formaldehyde fixed particles in CsC1 and of two-dimensional gel electrophoresis of ribosomal proteins, it appears that the native ribosomal subparticles contain a large protein complement than the derived subparticles and, correspondingly, they are less dependent on an external supply of initiation factors for haemoglobin synthesis in vitro.

Structural Analysis and in Vitro Function of 80 s Ribosomes Isolated from Mouse Tumor Cells

Investigations were conducted on the RNA/protein ratio and in vitro functional activity of the large pool of 80 s ribosomes and their subunits isolated from some mouse tumors. No differences in the capacity of these ribosomes for polyU-directed polyphenylalanine synthesis were observed. On the other hand, the large subunit of Ehrlich and Sarcoma 180 tumors was found to have a different RNA/protein ratio (corresponding to a loss of about 5 % of its protein content) from the 60 s subunit of mouse liver.

Stimulation of Protein Synthesis and of RNA Polymerase Activity in the Liver of 3-Methylcholanthrene-Treated Rats

Following a single dose of 3-methylcholanthrene in rat liver the RNA polymerase activity of Mg++and Mn++/(NH4)2SO4- dependent forms is stimulated in isolated nuclei and particularly in the chromatin of extranucleolar fraction. The early enhancement of N-2-fluorenylacetamide microsomal hydroxylating activity does not parallel the shift of the monomer-polysome equilibrium to more aggregated forms. It is suggested that the rate of synthesis and the transport mechanism of RNA messengers into the cytoplasm can be selectively regulated by 3-methylcholanthrene and its metabolites.