DMH Treatment Research Articles

The recombinant congenic strains—a novel genetic tool applied to the study of colon tumor development in the mouse

The development of tumors in mice is under multigenic control, but, in spite of considerable efforts, the identification of the genes involved has so far been unsuccessful, because of the insufficient resolution power of the available genetic tools. Therefore, a novel genetic tool, the RC (Recombinant Congenic) strains system, was designed. In this system, a series of RC strains is produced from two inbred strains, a "background" strain and a "donor" strain. Each RC strain contains a different small subset of genes from the donor strain and the majority of genes from the background strain. As a consequence, the individual genes of the donor strain which are involved in the genetic control of a multigenic trait, become separated into different RC strains, where they can be identified and studied individually. One of the RC strains series which we produced is made from the parental strains BALB/cHeA (background strain) and STS/A (donor strain). We describe the genetic composition of this BALB/cHeA-C-STS/A (CcS/Dem) series and show, using 45 genetic autosomal markers, that it does not deviate from the theoretical expectation. We studied the usefulness of the CcS/Dem RC strains for analysis of the genetics of colon tumor development. The two parental strains, BALB/cHeA and STS/A, are relatively resistant and highly susceptible, respectively, to the induction of colon tumors by 1,2-dimethylhydrazine (DMH). The individual RC strains differ widely in colon tumor development after DMH treatment; some are highly susceptible, while others are very resistant. This indicates that a limited number of genes with a major effect are responsible for the high susceptibility of the STS strain. Consequently, these genes can be mapped by further analysis of the susceptible RC strains. The differences between the RC strains were not limited to the number of tumors, but the RC strains differed also in size of the tumors and the relative susceptibility of the two sexes. Our data indicate that the number of tumors and the size of tumors are not controlled by the same genes. The genetics of these different aspects of colon tumorigenesis can also be studied by the RC strains. The DMH-treated mice of the parental strains and the RC strains also developed anal tumors and haemangiomas in varying numbers. The strain distribution pattern (SDP) of susceptibility for each of the three types of tumors induced by DMH is different, indicating that development of these tumors is under control of different, largely non-overlapping, sets of genes.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantification of acid mucins in the descending colon of rats having simultaneously growing colonic tumors

The acid mucins contained in goblet cells of the descending colon of 34 male Sprague-Dawley rats were histochemically labeled by Alcian blue pH 2.5 and quantified in an image analyzer (Cortex Controller). Twenty-two of these 34 rats were treated with 1,2-dimethylhydrazine (DMH) suspended in EDTA solution as a stabilizing agent and the remaining 12 rats with EDTA only. Of the 22 DMH-treated rats, 11 had concomitantly an adenocarcinoma elsewhere in the colon and the remaining 11 rats had no colonic tumors despite DMH treatment. The results indicated that Alcian blue-positive areas occupied 34.5% of the mucosa of the descending colon in tumor-bearing rats, and 35.2% in non-tumor-bearing DMH-treated rats. For EDTA-treated rats the percentage of mucosa occupied by Alcian blue-positive cells was 48.1%. The difference between DMH-treated rats (with or without tumors) and EDTA-treated rats was significant (p less than 0.001). These results suggest that the decrease of Alcian blue areas is related to the protracted treatment with DMH. Whether the decrease in acid mucins is induced by the carcinogen per se or whether it represents a true biochemical premalignant change at the cytoplasmic level remains to be elucidated.

Reduction of aberrant crypt formation in the colon of CF1 mice by potential chemopreventive agents

Carcinogen-induced aberrant crypts (AC) of the colon are a precancerous state that leads to malignancy. The inhibition of AC formation by chemopreventive agents was evaluated in this study. Colon AC were induced by 1,2-dimethylhydrazine (DMH) in 3 weeks in CF1 mice. The cecum of the large intestine of CF1 mice did not produce more than one AC focus per animal. The effect of DMH and that of the inhibitors in this part of the large bowel were essentially similar to the vehicle control and inhibitor-only controls. The response of DMH treatment in the colorectal portion of the large bowel was found to be different from that of the cecum. The DMH treated mice had 13-17 foci per animal in three different experiments. The average number of AC per focus was greater than one in all three experiments performed. None of the inhibitor-only control animals nor the cottonseed oil vehicle control animals developed AC focus in the colorectal or the cecal part of the large bowel. The known inhibitor of colon carcinogenesis 3-butyl-4-hydroxyanisole reduced DMH-induced average AC formation by 10 and 46% at 1 and 4 mg per dose, respectively. The inhibitors 2-n-butylthiophene and phenylpropylisothiocyanate reduced DMH-induced average AC formation greater than 34 and greater than 40% respectively. The postulated inhibitor 2-n-octylthiophene, which is an eight-carbon homolog of 2-n-butylthiophene, similarly reduced DMH-induced AC formation. The known colon carcinogenesis inhibitor dehydroepiandrosterone, in contrast, has no effect. The inactivity of dehydroepiandrosterone to inhibit colon AC formation was attributed to its mechanism of inhibitory action, which differs from that of the phenol, isothiocyanate and thiophenes. The short duration that is required to produce quantifiable results suggests that the reduction of carcinogen-induced AC formation may be developed into a useful prescreening assay for potential chemopreventive agents against colon cancer.

Dietary Selenium and Antioxidant Status: Toxic Effects of 1,2-Dimethylhydrazine in Rats

Weanling male Sprague-Dawley rats were used to determine whether the mechanism of the previously reported toxicity of 1,2-dimethylhydrazine (DMH) in selenium-deficient rats was related to a diminished capacity for detoxification of reactive oxygen species via glutathione peroxidase (GSH-Px) as well as by other known pathways of detoxification, including catalase (CAT), superoxide dismutase (SOD), glutathione-S-transferase (GST) and levels of glutathione (GSH). A 3 x 3 factorial experimental design was used to examine the acute effects of DMH treatment (0, 10 and 20 mg/kg body weight) interacting with dietary Se levels (less than 0.02, 0.1 and 0.5 mg/kg diet as sodium selenite). Animals were maintained on the test diets for 4 wk prior to challenge with DMH. Preliminary kinetics studies indicated the most appropriate time to examine antioxidant status was 3 h after DMH injection. At that time, livers and colons were analyzed for tissue levels of GSH-Px, CAT, SOD, GST and GSH. Data analysis demonstrated that Se deficiency impaired the ability of both liver and colon to mount an induced detoxification response to the acute oxidative stress generated by DMH challenge and may explain the toxicity of DMH in Se-deficient rats.

Hyperplasia of mouse duodenal crypts and its control by NK cells during the initial phase of DMH carcinogenesis

The possible regulatory role of NK cells on early events in chemical carcinogenesis remains undefined. The present study examined whether NK cells control 1,2-dimethylhydrazine (DMH)-induced hyperplasia of the duodenal crypt in CD1 mice. Mice receiving chronic DMH treatment showed a dose-dependent hyperplasia confined to the proliferative zone, with a parallel increase in mitotic and 3H-TdR-labelled cells and significant suppression of splenic NK activity. Complete ablation of splenic NK activity with anti-asialo GM-I antibody (alpha AGM-I) treatment slightly enhanced hyperplasia. Halving of the DMH dose for 2 weeks led to regression of hyperplasia, which was totally prevented by alpha AGM-I treatment. The alpha AGM-I treatment alone did not influence crypt size in normal mice. Finally, a stimulation of NK activity with Poly I:C treatment in DMH-treated mice caused regression of the DMH-induced hyperplasia. Our results suggest that hyperplastic cells with possible genetic alterations induced by the carcinogen express target structures for NK cells, but that simultaneous carcinogen-induced suppression of NK activity hampers their containment, allowing progression of hyperplasia to neoplasia, possibly owing to additional genetic changes.

Potassium inhibition of DMH‐induced small intestinal tumors in rats

This is a preliminary report that shows that supplemental potassium partially prevents 1,2-dimethylhydrazine (DMH) induction of tumors of the small intestine in Sprague-Dawley rats. Male rats were injected weekly with 20 mg DMH/kg body wt for 20 weeks. Potassium chloride was provided in the drinking water one week before the first DMH treatment and was continued until sacrifice 14 weeks after the last DMH treatment. There were four groups of rats and they were identified as follows: DMH, DMH + K, K, and untreated control. Based on 24-hour food and water consumption data and food and water compositions, rats provided 0.5% potassium (from KCl in the drinking water) were ingesting 287.5 +/- 9.2 mg potassium per 24 hours (K/Na = 4.18) and the unsupplemented groups were ingesting 180.3 +/- 18.4 mg potassium per 24 hours (K/Na = 2.62). At sacrifice, the incidence of DMH-induced small intestinal tumors was significantly (p less than 0.05) reduced from 46% (6/13) in the DMH group to 6% (1/17) in the DMH + K group (p less than 0.05). The potassium supplement also significantly (p less than 0.05) reduced the cumulative small intestinal tumor incidence from 40% (8/20) in the DMH group to 5% (1/20) in the DMH + K group. The incidence of colon tumors and of zymbal gland tumors appeared to be reduced by the potassium supplement; however, these were not statistically significant observations (p greater than 0.05). Based on the complete blood count and other blood parameters measured, the level of potassium supplement used induced no apparent toxic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary Milk Proteins Inhibit the Development of Dimethylhydrazine-Induced Malignancy

This study investigated the influence of two formula diets containing 20 g/100 g diet of either whey protein concentrate or casein, or Purina mouse chow on 1,2-dimethylhydrazine (DMH)-induced colon carcinoma in A/J mice. Four weeks after the 24th DMH treatment the incidence of tumour and tumour area in the whey protein-fed mice was substantially less in comparison to either the casein or Purina groups. The Purina group exhibited the greatest tumour burden. At the end of the experiment all animals continuously fed the whey protein diet were found to be alive, whereas 33% of those on the casein or Purina diet had died. Animals fed Purina diet for 20 weeks and then switched to either milk protein diet for a further 8 weeks exhibited a decrease in tumour burden as compared to those animals fed the Purina diet continuously. Body weights were similar in all dietary groups. In conclusion, a whey protein diet appears to significantly influence the development of chemically induced colon tumours and the short-term survival of mice.

Effect of plyamine oxidase inhibition on the colonic malignant transformation process induced by 1.2-dimethylhydrazine

Recent studies of colon adenocarcinomas in humans and experimentally induced colonic tumors in rodents have demonstrated selective elevations in the level of N1-acetylspermidine in these malignant tissues. The exact relationship of these alterations in acetylated polyamine levels to the malignant transformation process, however, remains unclear. In order to clarify this issue, rats were given s.c. injections of 1,2-dimethylhydrazine (DMH; 20 mg/kg body wt/week) or diluent for up to 26 weeks. After 10 weeks of carcinogen treatment, one-half of the animals in each group were also concomitantly given i.p. injections of MDL 72527 (20 mg/kg body wt/week), a specific inhibitor of polyamine oxidase, until they were killed. Animals were killed after 15 weeks of DMH treatment and polyamine levels as well as the activities of polyamine oxidase, ornithine decarboxylase and spermidine-N1-acetyltransferase were measured and compared in rat proximal and distal colonic mucosa of each group. Polyamine levels were also assessed in each of these groups after 26 weeks of treatment with this carcinogen +/- MDL 72527. In addition, in view of recent studies that have indicated that polyamines may influence certain oncogenes in human colonic carcinoma cells, tumors from DMH +/- MDL 72527 were analyzed for K-ras mutations. The results of these experiments demonstrated for the first time that: (i) MDL 72527 was a specific inhibitor of polyamine oxidase in normal and malignant colonic tissue; (ii) concomitant administration of this agent with DMH enhanced the elevation of colonic N1-acetylspermidine and significantly reduced the mean colonic tumor burden, as assessed by total tumor area per rat, produced by this carcinogen alone; (iii) analysis of K-ras mutations revealed a similar incidence (62-69%) in adenocarcinomas for both groups (+/- MDL 72527); (iv) however, analysis of the K-ras-mutated and non-mutated tumors revealed that in both carcinogen-treated groups (+/- MDL 72527), tumors with such mutations were smaller than their counterparts without such genetic alterations. Moreover, MDL 72527 reduced the average size of tumors, with and without such mutations, to a similar extent.

Promoter function of carrageenan on development of colonic tumors induced by 1,2-dimethylhydrazine in rats.

In order to understand the function of carrageenan, an indigestible polysaccharide, as a promoter of colonic tumors induced by 1,2-dimethylhydrazine (DMH), molecular weight distribution of fecal carrageenan and amounts of fecal bile acids in rats given carrageenan and DMH treatment were examined. Gel filtration pattern on Sephacryl S-300 of fecal carrageenan was very similar to that of feeding carrageenan, and carrageenan ingested was quantitatively excreted in feces. Hexafluoroisopropyl ester-trifluoroacetyl derivatives of fecal bile acids were analyzed by gas chromatography on QF-1. Although there was a decreased concentration of deoxycholic acid and total bile acids in carrageenan-fed rats compared to control rats, no difference in the daily output was found because carrageenan ingestion increases fecal output. Significant increased concentration and daily output of lithocholic acid, a tumor-promoter, by feeding carrageenan were found. Thus, it was suggested that the promoting effect of carrageenan on colon tumorigenesis by DMH may be mediated by increased excretion of lithocholic acid and may not participate in degradation of carrageenan ingested.

The histogenesis of dmhinduced colonic carcinoma in rats

Twenty-one Donryu male rats of six weeks old were injected with 1,2-dimethyl-hydrazine hydrochloride (DMH), once a week, for 4 to 20 weeks, and sacrificed at intervals of two weeks since a lapse of four weeks after the commencement of the injections. The DMH induced 320 atypia lesions, from 0.03 through 20 mm in size, of grade II or higher. The rate of benign lesions was higher in the group receiving less than 20 injections than in the group of 20 injections of DMH, while in the latter group, the rates of the benign, borderline and malignant lesions were stable, suggesting that benign lesions mainly develop in the earlier period of the DMH treatment, and thereafter various grades of lesions develop at a constant rate. All the benign lesions were less than 1 mm in size, and all lesions greater than 1 mm were malignant. In addition, the size of the lesion was significantly greater when it was occupied by malignant crypts in a greater rate. These results indicate that the benign lesions become cancerous before they reach a certain size (adenoma-carcinoma sequence). Twenty-seven minute lesions (less than 1 mm) were mixed lesions of malignant and benign atypia, suggesting that the adenoma-carcinoma sequence is elicited in any size of lesion. On the other hand, there were 41 minute malignant-only lesions, which constituted 27.7% of the overall minute lesions and included three "single crypt" cancers. In addition, malignant-only lesions were smaller when compared to the malignant-dominant mixed lesions. These results indicate that about 30% of colon cancers develop de-novo.

Vanadate supplements and 1,2-dimethylhydrazine induced colon cancer in mice: Increased thymidine incorporation without enhanced carcinogenesis

Because vanadate ion is a potent mitogen and accumulates in the gut of rodents fed vanadate supplements, effects of ammonium metavanadate in drinking water (10 ppm or 20 ppm) were studied on the development of large bowel neoplasms in mice treated with 1,2-dimethylhydrazine (DMH) (20 mg kg-1 weekly for 20 weeks). In the colon at 30 weeks DMH treatment caused a 14% increase in RNA content, an 18% increase in DNA content, and 33% deeper crypts. Vanadate at either 10 ppm or 20 ppm decreased RNA content by approximately 11%. Although vanadate increased thymidine incorporation 210% to 550% compared with controls, it had no influence on the attack rate, incidence, or histological type of tumours induced by DMH.

Effect of colon tumor development and dietary fat on the immune system of rats treated with DMH.

We examined the effect of dietary fat and colon tumorigenesis on the morphology and function of the rat mesenteric lymph node (MLN) and spleen at two stages of tumor development. Male Sprague-Dawley rats were fed semipurified diets of varying fat content (5% mixed fat, 24% beef fat, 24% corn oil, or 24% Crisco) and treated for five weeks with either the colon carcinogen 1,2-dimethylhydrazine (DMH) or the vehicle (saline). Animals consuming high-fat diets had an increased incidence of splenic follicular and germinal center hyperplasia. Carcinogen treatment had no significant effect on the histological morphology of the spleen. MLN morphology was not dramatically affected by either diet or DMH treatment. At this time period, the splenic lymphocyte transformation response induced by concanavalin A (Con A), phytohemagglutinin, or pokeweed mitogen was significantly depressed in the group fed 24% corn oil (vehicle-treated) and in the DMH-treated groups fed 5% fat compared with the vehicle-treated group fed 5% fat. In contrast, the MLN transformation response was elevated in the group fed 24% Crisco. DMH treatment did not significantly influence the MLN response. Four months after carcinogen or vehicle treatment, at the point of colon tumor development, no statistically significant differences were seen in the splenic or MLN blastogenic responses of DMH- or saline-treated animals. Splenic natural killer cell cytotoxic activity was also not significantly affected by dietary fat, carcinogen treatment, or tumor development.

The correlation between cholecystectomy and fecal bile acids, and large-bowel cancer induced with 1,2-dimethylhydrazine in mice.

The relationship between cholecystectomy and large-bowel cancer development was investigated in animal models. Female ICR mice underwent cholecystectomy, and received 15 weekly intragastric administrations (Experiment 1) or 10 weekly subcutaneous injections (Experiment 2) of 15 mg/kg body weight of large-bowel carcinogen 1,2-dimethylhydrazine (DMH). Autopsy at 28 weeks after surgery showed that cholecystectomized mice had a nonsignificantly increased incidence of large-bowel carcinomas, compared to sham-operated and/or unoperated control mice (85 vs. 64 percent in Experiment 1; 31 vs. 16 and 20 percent in Experiment 2). Cholecystectomy alone without DMH treatment did not produce any cancer. Cholecystectomized mice excreted a significantly increased level of primary bile acids but an unchanged level of secondary bile acids in the feces, compared with unoperated control mice. It is obvious that cholecystectomy enhanced the development of DMH-induced, large-bowel carcinomas along with the change of fecal bile acid composition, suggesting that changes of bile acid metabolism after cholecystectomy may enhance or promote large-bowel carcinogenesis in man as well. This association of cholecystectomy and large-bowel cancer is not a strong one, however, as presented in epidemiologic as well as experimental studies.

Modifying action of neonatal androgenization on 1,2-dimethylhydrazine-induced carcinogenesis in male CBA mice

Newborn male CBA mice received a single treatment with 0.5 mg testosterone propionate. Weekly subcutaneous injections of 1,2-dimethylhydrazine (DMH) were given to 2-month-old mice. The incidence of pararenal angiosarcomas and colonic tumors in neonatally androgenized mice reached 78.5 and 71.0%, respectively by the 35th week after the DMH treatment was commenced. In DMH-treated control mice, the incidence of the above tumors amounted to 25 and 32%, respectively.

Morphology and Distribution of 1,2-Dimethylhydrazine Dihydrochloride-Induced Colon Tumors and Their Relationship to Gut-Associated Lymphoid Tissue in the Rat<xref ref-type="fn" rid="FN1">2</xref>

The histopathology and relationship of sym-dimethylhydrazine dihydrochloride [(DMH) CAS: 306-37-6; 1,2-dimethylhydrazine dihydrochloride]-induced colon tumors to colonic lymphoid aggregates were examined in outbred male Sprague-Dawley rats treated with saline or DMH and sacrificed at three intervals after treatment. The ratio of polypoid:sessile tumors was 71:29 four months after DMH treatment and 62:38 when tumors were fully developed. Colonic lymphoid aggregates were found 3-5 cm from the cecal-colonic junction, near the flexure of the ascending and transverse colon, and 3-5 cm from the rectum. There were no significant differences between saline-treated and DMH-treated rats regarding the size, cellularity, and number of lymphoid aggregates per rat. A significant association (P less than .001) was seen between tumor development and the presence of a lymphoid aggregate in a given segment of the colon. Sessile adenocarcinomas, but not polypoid tumors, were significantly associated (P less than .001) with lymphoid aggregates and usually presented as mucinous tumors adjacent to or intermixed with the lymphoid tissue.

The effect of 1,2-dimethylhydrazine (DMH) carcinogenesis on peripheral T cell subsets in the Wistar Furth rat.

1,2-dimethylhydrazine (DMH)-induced colon cancer in Wistar/Furth (W/Fu) rats is analogous in many ways to human colorectal cancer. As part of our attempt to understand the immunobiology of these tumors, we have utilized the recently available monoclonal antibodies W3/25 and OX8 to monitor helper (Th) and suppressor (Ts) lymphocyte subpopulations. Normal untreated male W/Fu rats of less than 1 year of age were phenotyped (n = 43). The mean percentage of Th and Ts was 42 +/- 1 (mean +/- SEM) and 33 +/- 1, respectively. The mean Th/Ts ratio was 1.3 +/- 0.1. A Th/Ts equal to or greater than 1 is considered "normal" in the W/Fu rat. The DMH-treated rats (20 mg/kg/wk) were evaluated in initial experiments at various intervals after treatment. Rats studied 24 hours after a single DMH injection had no alterations in T cell subsets. Rats studied 28, 32, and 65 weeks after the start of 16 weekly DMH injections were found to have a decrease in the percentage of Th and a relative increase in Ts, with Th/Ts ratios of 0.6 +/- 0.2, 0.7 +/- 0.1, and 0.7 +/- 0.1, respectively (each P less than 0.01). In a separate experiment in which rats were studied after 4, 8, and 16 weeks of DMH injections, no alterations in T cell subsets were noted. Rats (n = 5) studied at 20 weeks after the start of DMH were found to have 41 +/- 3% Th and 36 +/- 2% Ts and a Th/Ts ratio of 1.2 +/- 0.1. Three of five rats were found to have adenocarcinomas. Four of five rats had Th/Ts less than 1. One rat with Th/Ts equal to 0.9 had metastatic disease. Rats studied at 25 weeks (n = 8) were found to have more advanced carcinomas (4/8) that were causing obstruction or bleeding in the animal. There was a significant decrease in Th and Ts in this group, with 24 +/- 3% and 26 +/- 3% respectively (P less than 0.001). The Th/Ts ratio for this group was 0.9 +/- 0.1 (P less than 0.01). In other experiments, rats were treated with DMH or placebo over a 16-week period and serially bled during and after treatment. No effect of DMH treatment on T cell subsets was noted. Repeated bleeding alone was noted to cause persistent alterations of T cell subpopulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Selective inhibition of replicative and repair DNA synthesis in mouse colon following administration of 1,2-dimethylhydrazine.

Early alterations in normal semiconservative and repair DNA synthesis were determined in gastrointestinal tissues of HalCR mice following administration of the colon carcinogen 1,2-dimethylhydrazine (DMH). Following DMH injections of 60 and 200 mg/kg, normal DNA synthesis was rapidly inhibited in all tissues. The greatest depressions were observed in the descending colon, followed closely by the ascending colon. DNA repair was estimated by measuring unscheduled DNA synthesis. No repair was observable in the descending or ascending colon. The esophagus, forestomach, jejunum, and ileum demonstrated significant amounts of DNA repair, while the duodenum and gastric stomach displayed nominal or insignificant amounts of repair. Repair DNA synthesis was inhibited by simultaneous administration of caffeine and DMH. The degree of inhibition of normal replicative DNA synthesis and the amount of repair DNA synthesis in response to DMH treatment correlate closely with the incidence of DMH-induced tumors. Most tumors occur in the descending colon, followed by the ascending colon, and only a few in the duodenum and gastric stomach area. Neoplasms are rarely found in the remainder of the gastrointestinal system.

Early Histopathologic Events to Evolution of Colon Cancer in C57BL/6 and CF1 Mice Treated With 1,2-Dimethylhydrazine<xref ref-type="fn" rid="FN2">2</xref>

After administration of the intestinal carcinogen 1,2-dimethylhydrazine (DMH), C57BL/6J and CF1 mice were observed for early precursor lesions to large bowel cancer. Among the initial events seen following DMH treatment, an abrupt reduction in colonic DNA synthesis was the earliest lesion detectable. The frequency of aberrant colonic nuclei rose shortly after DMH treatment, reaching a maximum value 24 hours later and remaining elevated for 3 days following the exposure. Mucin changes, detected histochemically, and cell kinetic alterations in crypt proliferation rates were observed much later and were a constant feature for both strains following 4 weekly treatments with DMH, while carcinomas appeared in all animals 32 weeks after the start of DMH treatment. The quantitative comparison of these histopathologic observations for the early detection of colon cancer suggests that the induction of colonic nuclear aberrations in the mucosa of the large bowel might provide a sensitive and rapid indication of genotoxicity to this organ and thus might provide the basis for a screening methodology for colon carcinogens.

Development and cell kinetics of colonic tumors induced in mice by dimethylhydrazine.

Colonic adenomas and carcinomas were induced in mice by intermittent injections of 1,2-dimethylhydrazine for 30 weeks and cell kinetic characteristics of different tumor types were studied by 3H-thymidine autoradiography. Labeling indices of adenomas and several carcinoma types after a single injection of 3H-thymidine were similar, both showing about 20%–23%. There was a tendency for the small adenomas and the poorly differentiated carcinomas to show higher labeling indices than the large adenomas and the well differentiated adenocarcinomas, respectively. By repeated injections of 3H-thymidine, it was shown that all adenoma and carcinoma cells became labeled within 60–70 h after the start of the injections, thereby suggesting a large growth fraction of the DMH-induced adenomas and carcinomas in the mouse colon. No remarkable differences in the labeling patterns were found between the adenomas and carcinomas, on the one hand, and intramucosal carcinomas and invasive carcinomas, on the other. The growth rate of the small adenomas appeared to be greater than that of the large adenomas and the poorly differentiated carcinomas may grow more rapidly than the well differentiated adenocarcinomas. The squamous-cell carcinomas arising in the anal region were shown to grow more rapidly than the adenocarcinomas of the colon. The changing patterns of tumor development were also studied at various times after DMH treatment with special reference to the minute neoplasms and their histogenesis and it was shown that the adenoma cells arising in the crypts accumulate in the upper part of the crypt to form an aberrant proliferative focus from which a neoplasm develops by expansion. The lesions considered to be benign on histological grounds may possibly change into adenocarcinomas of a well differentiated type. The poorly differentiated carcinomas were suggested to arise as de novo malignancy.

Surgical Resection of the Rat Colon: Effects on Carcinogenesis by 1,2-Dimethylhydrazine<xref ref-type="fn" rid="fn2">2</xref>, <xref ref-type="fn" rid="fn3">3</xref>

Following a 3-month treatment with 1,2-dimethylhydrazine (DMH) given weekly (sc), outbred Sprague-Dawley rats were subjected to partial resection of the transverse colon. After surgery, DMH treatment was continued for 6 months, after which the rats were killed. At autopsy, 63% of the tumors were found in the transverse colon. By contrast, only 29% of the tumors found in the "sham-operated" control animals occurred in the transverse colon. Surgical trauma in the colon mucosa subjected to the action of carcinogenic agents appeared to promote the conditions suitable for the development of tumors in that organ.