The Ruminant sorting mechanism protects teeth from abrasives

Dental wear due to ingestion of dust and grit has deleterious consequences. Herbivores that could not wash their food hence had to evolve particularly durable teeth, in parallel to the evolution of dental chewing surface complexity to increase chewing efficacy. The rumen sorting mechanism increases chewing efficacy beyond that reached by any other mammal and has been hypothesized to also offer an internal washing mechanism, which would be an outstanding example of an additional advantage by a physiological adaptation, but in vivo evidence is lacking so far. Here, we investigated four cannulated, live cows that received a diet to which sand was added. Silica in swallowed food and feces reflected experimental dietary sand contamination, whereas the regurgitate submitted to rumination remained close to the silica levels of the basal food. This helps explain how ruminants are able to tolerate high levels of dust or grit in their diet, with less high-crowned teeth than nonruminants in the same habitat. Palaeo-reconstructions based on dental morphology and dental wear traces need to take the ruminants' wear-protection mechanism into account. The inadvertent advantage likely contributed to the ruminants' current success in terms of species diversity.

No news from old drawings? Stomach anatomy in muroid rodents in relation to body size and ecology

Muroid rodents mostly have a complex stomach: one part is lined with a cornified (non-glandular) epithelium, referred to as a 'forestomach,' whereas the rest is lined with glandular epithelium. Numerous functions for the forestomach have been proposed. We collated a catalog of anatomical depictions of the stomach of 174 muroid species from which the respective non-glandular and glandular areas could be digitally measured, yielding a 'stomach ratio' (non-glandular:glandular area) as a scale-independent variable. Stomach ratios ranged from 0.13 to 20.15, and the coefficient of intraspecific variation if more than one picture was available for a species averaged at 29.7% (± 21.5). We tested relationships of the ratio with body mass and various anatomical and ecological variables, including diet. There was a consistent phylogenetic signal, suggesting that closely related species share a similar anatomy. Apart from classifying stomachs into hemiglandular and discoglandular, no anatomical or ecological measure showed a consistent relationship to the stomach ratio. In particular, irrespective of statistical method or the source of dietary information, dietary proxies did not significantly correlate with the stomach ratio, except for a trend towards significance for invertivory (insectivory). Yet, even this relationship was not convincing: whereas highly insectivorous species had high but no low stomach ratios, herbivorous species had both low and high stomach ratios. Thus, the statistical effect is not due to a systematic increase in the relative forestomach size with invertivory. The most plausible hypotheses so far associate the muroid forestomach and its microbiome with a generic protective role against microbial or fungal toxins and diseases, without evident correlates of a peculiar need for this function under specific ecological conditions. Yet, this function remains to be confirmed. While providing a catalog of published depictions and hypotheses, this study highlights that the function of the muroid rodent forestomach remains enigmatic to date. This article is protected by copyright. All rights reserved.

Stomach serosal arteries distinguish gastric regions of the rat

Because the stomach in situ has few distinctive surface features and changes shape dramatically with food intake, we have used micro-CT imaging combined with two distinct contrast agents to (1) characterize the pattern of arteries, potential landmarks, on the stomach wall and (2) evaluate how meal-related shape changes affect the size of the different regions. Images generated with a contrast agent injected directly into the heart during perfusion enabled a thorough look at the organizational features of the stomach angioarchitecture. The stomach receives its blood supply primarily from two pairs of vessels, the gastric and gastroepiploic arteries. Each of the three regions of the stomach is delineated by a distinctive combination of arterial fields: the corpus, consistent with its dynamic secretory activity and extensive mucosa, is supplied by extensive arterial trees formed by the left and right gastric arteries, travelling, respectively, on the ventral and dorsal stomach surfaces. These major arteries course circularly from the lesser towards the greater curvature, distally along both left (or ventral) and right (or dorsal) walls of the corpus, and branch rostrally to supply the region. The muscular antrum is characterized by smaller arterial branches arising primarily from the right gastroepiploic artery that follows the distal greater curvature and secondarily from small, distally directed arteries supplied by the large vessels of the left and right gastric arteries. The forestomach, essentially devoid of mucosal tissue and separated from the corpus by the limiting ridge, is vascularized predominantly by a network of small arteries issued from the left gastroepiploic artery coursing around the proximal greater curvature, as well as from higher order and smaller branches issued by the gastric and celiac arteries. These distinctive arterial fields appear to distinguish the major gastric regions, irrespective of the degree of fill of the stomach. Volume assessments of stomach compartments were made from images of iodine-stained stomachs. By varying the delay time between eating and perfusion, we were able to probe the emptying behavior of the stomach and demonstrate that the regions of the stomach empty at different rates, thus changing the relative dimensions of the organ regions. Notably, and despite these shape changes, the gastric arteries appear to form a regular, particularly recognizable, and lateralized pattern corresponding to the corpus that should be of use in guiding surgical and experimental interventions.

In vivo localization and postmortem stability of benzo[a]pyrene-DNA adducts

DNA adducts of carcinogenic polycyclic aromatic hydrocarbons (PAHs) play a critical role in the etiology of gastrointestinal tract cancers in humans and other species orally exposed to PAHs. Yet, the precise localization of PAH-DNA adducts in the gastrointestinal tract, and the long-term postmortem PAH-DNA adduct stability are unknown. To address these issues, the following experiment was performed. Mice were injected intraperitoneally with the PAH carcinogen benzo[a]pyrene (BP) and euthanized at 24 h. Tissues were harvested either at euthanasia (0 time), or after 4, 8, 12, 24, 48, and 168 hr (7 days) of storage at 4°C. Portions of mouse tissues were formalin-fixed, paraffin-embedded, and immunohistochemically (IHC) evaluated by incubation with r7,t8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-DNA antiserum and H-scoring. The remaining tissues were frozen, and DNA was extracted and assayed for the r7,t8,t9-trihydroxy-c-10-(N ² -deoxyguanosyl)-7,8,9,10-tetrahydrobenzo[a]pyrene (BPdG) adduct using two quantitative assays, the BPDE-DNA chemiluminescence immunoassay (CIA), and high-performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ES-MS/MS). By IHC, which required intact nuclei, BPdG adducts were visualized in forestomach basal cells, which included gastric stem cells, for up to 7 days. In proximal small intestine villus epithelium BPdG adducts were visualized for up to 12 hr. By BPDE-DNA CIA and HPLC-ES-MS/MS, both of which used DNA for analysis and correlated well (P= 0.0001), BPdG adducts were unchanged in small intestine, forestomach, and lung stored at 4°C for up to 7 days postmortem. In addition to localization of BPdG adducts, this study reveals the feasibility of examining PAH-DNA adduct formation in wildlife species living in colder climates. Environ. Mol. Mutagen. 61:216-223, 2020. © 2019 Wiley Periodicals, Inc.

Activation of PI3K/Akt/NF-kB Signaling Mediates Swedish Snus Induced Proliferation and Apoptosis Evasion in the Rat Forestomach: Modulation by Blueberry

BACKGROUND AND OBJECTIVES

The present study was undertaken to ascertain whether the modulatory effects of blueberries on cell proliferation induced by Swedish snus in the rat forestomach epithelium is mediated via abrogation of the PI3K/Akt/NFκB signaling axis that regulates cell fate decision.

METHODS

The transcript and protein expression of genes involved in cell cycle progression and apoptosis, as well as canonical PI3K/Akt/NF-κB signaling pathways, were analyzed by qRT-PCR, immunoblotting and ELISA. Expression profiling of noncoding RNAs (ncRNAs) that influence PI3K/Akt/NF-κB signaling was undertaken. TUNEL assay was performed using flow cytometry.

RESULTS

Administration of snus induced basal cell hyperplasia in the rat forestomach with increased cell proliferation and inhibition of apoptosis. This was associated with the activation of PI3K/Akt/NFκB signaling. Coadministration of blueberries significantly suppressed snus-induced hyperplasia. Analysis of the molecular mechanisms revealed that blueberries suppress the phosphorylation of Akt, NF-κB and IKKβ, prevent nuclear translocation of NF-κB and modulate the expression of microRNAs that influence PI3K/Akt/NF-κB signaling.

CONCLUSION

Taken together, the results of the current study provide compelling evidence that blueberries exert significant protective effects against snus-induced soft tissue changes in the rat forestomach epithelium mediated by inhibiting key molecular players in the PI3K/Akt/NF-κB signaling axis. Long-term studies on the impact of snus exposure on various cellular processes, signaling pathways, and the interplay between genetic and epigenetic mechanisms are however warranted. The results of this investigation may contribute to the development of protection against soft tissue changes induced by smokeless tobacco in the human oral cavity.

Colobine forestomach anatomy and diet

Colobine monkeys have complex, multichambered, foregut-fermenting stomachs with either three ("tripartite") or four ("quadripartite," adding the praesaccus) chambers where a commensal microbiome digests plant cell walls and possibly detoxifies defensive plant chemicals. Although different potential functions for the praesaccus have been suggested, little evidence exists to support any of the proposed functions. To address the issue of the function of the praesaccus, we collated literature data on diet and compared tripartite and quadripartite species. Our results suggest that the praesaccus is an adaptation to a dietary niche with a particularly high reliance on leaves as fallback foods in colobine clades with quadripartite stomachs, and a higher reliance on fruits/seeds as foods at times of high fruit availability in clades with tripartite stomachs. This supports the notion that a large gut capacity is an important characteristic by which folivores survive on a high fiber diet, and that this large gut capacity may not be necessary for some species if there are seasonal peaks in fruit availability.

Effect of increasing the proportion of dietary concentrate on gastrointestinal tract measurements and brush border enzyme activity in Holstein steers

The aim of this study was to determine the time course for adaptation of the reticulo-rumen, omasum, abomasum, and small intestine in response to an abrupt increase in the proportion of grain in the diet. Adaptive responses include tissue and digesta mass, small intestinal length, and brush border enzyme activity in the duodenum, proximal jejunum, and ileum. Twenty-five Holstein steers (213 ± 23 kg; 5 to 7 mo of age) were blocked by body weight, and within block were randomly assigned to 1 of 5 treatments: the control diet (CTRL; 92% chopped grass hay and 8% mineral and vitamin supplement on a dry matter basis) or a moderate grain diet (MGD; 50% chopped grass hay, 42% rolled barley grain, and 8% mineral and vitamin supplement) that was fed for 3 (MGD3), 7 (MGD7), 14 (MGD14), or 21 d (MGD21). Dry matter intake was limited to 2.25% of body weight to ensure that changes in dry matter intake did not confound the results. On the last day of the dietary exposure, steers were slaughtered 2 h after feeding. Reticulo-rumen tissue mass and ruminal epithelium mass in the ventral sac of the rumen were not affected by the MGD. Wet reticulo-ruminal digesta mass decreased from CTRL to MGD7 and then increased, but reticulo-ruminal digesta dry matter mass did not differ between treatments. Omasal mass, omasal tissue mass, and omasum digesta mass decreased linearly with the number of days fed MGD, but abomasal tissue mass tended to increase linearly. Duodenal tissue mass tended to increase linearly, and ileal length increased linearly with the number of days fed MGD. Lactase activity in the proximal jejunum increased linearly and maltase activity in duodenum tended to increase linearly with days fed MGD. Aminopeptidase N activity in the proximal jejunum increased cubically with days fed MGD, and dipeptidylpeptidase IV activity in ileum tended to decrease from CTRL to MGD14 and then tended to increase. Adaptation to a diet with a greater proportion of concentrate involves changes in the mass and length of regions of the gastrointestinal tract and brush border enzyme activity. These changes take place gradually over at least 3 wk.

Epidemiological studies on forestomach disorders in cattle and buffaloes

Aim:

To study epidemiology of forestomach (reticuloruminal, omasal, and abomasal) disorders in cattle and buffaloes.

Materials and Methods:

The 106 buffaloes and 32 cattle referred for treatment to the university large animals teaching hospital with the complaint of gastrointestinal diseases constituted the study material. The cases were diagnosed based on history, clinical examination, hematology, biochemistry, radiography, peritoneal fluid analysis and ultrasonography, rumenotomy, and postmortem. A questionnaire was prepared containing important information on housing, husbandry practices, including feeding practices and individual animal information viz. age, species, month of the year, parity, gestation (month), and recent parturition. The animals were divided into eight groups and analysis of variance was performed to study risk factors associated with each condition.

Results:

The forestomach disorders are widely prevalent in cattle and buffaloes between April and October, during summer and rainy season (90%) and constituted a significant proportion of diseased cows and buffaloes (138/1840) at the hospital. Different forestomach disorders and their prevalence was: Diaphragmatic hernia (DH) 17%, traumatic reticuloperitonitis (TRP) 14%, idiopathic motility disorder or vagus indigestion (VI) 22%, adhesive peritonitis (AP) 13%, frank exudative peritonitis (FEP) 12%, reticular abscess (RA) 8%, ruminal and omasal impaction (RI) 5%, and abomaso duodenal ulceration (ADU) 9%. DH and RA were significantly more common in buffaloes as compared to cattle. Similarly, impactions were more in buffaloes but its incidence was very low (5%). ADU was present in buffalo as commonly as in cows. Exclusive feeding of wheat straw was present in an abysmally low number of animals and hence could not be considered the cause of these disorders. DH was significantly higher in buffaloes (>5 years) of 5-8 years of age and TRP, VI and AP were observed in cattle and buffalo of 2-8 years of age during the second half of gestation to 1 month post-calving. FEP (12%) occurred more commonly within 1 month of parturition.

Conclusions:

DH, TRP, frank and AP and ADU are causes of the widely prevalent forestomach (reticuloruminal, omasal and abomasal) disorders in cattle and buffaloes.

Vagal Intramuscular Arrays: The Specialized Mechanoreceptor Arbors That Innervate the Smooth Muscle Layers of the Stomach Examined in the Rat

The fundamental roles that the stomach plays in ingestion and digestion notwithstanding, little morphological information is available on vagal intramuscular arrays (IMAs), the afferents that innervate gastric smooth muscle. To characterize IMAs better, rats were given injections of dextran biotin in the nodose ganglia, and, after tracer transport, stomach whole mounts were collected. Specimens were processed for avidin-biotin permanent labeling, and subsets of the whole mounts were immunohistochemically processed for c-Kit or stained with cuprolinic blue. IMAs (n = 184) were digitized for morphometry and mapping. Throughout the gastric muscle wall, IMAs possessed common phenotypic features. Each IMA was generated by a parent neurite arborizing extensively, forming an array of multiple (mean = 212) branches averaging 193 µm in length. These branches paralleled, and coursed in apposition with, bundles of muscle fibers and interstitial cells of Cajal. Individual arrays averaged 4.3 mm in length and innervated volumes of muscle sheet, presumptive receptive fields, averaging 0.1 mm(3) . Evaluated by region and by muscle sheet, IMAs displayed architectural adaptations to the different loci. A subset (32%) of circular muscle IMAs issued specialized polymorphic collaterals to myenteric ganglia, and a subset (41%) of antral longitudinal muscle IMAs formed specialized net endings associated with the serosal boundary. IMAs were concentrated in regional patterns that correlated with the unique biomechanical adaptations of the stomach, specifically proximal stomach reservoir functions and antral emptying operations. Overall, the structural adaptations and distributions of the IMAs were consonant with the hypothesized stretch receptor roles of the afferents.

Development of a methodology to measure the effect of ergot alkaloids on forestomach motility using real-time wireless telemetry

The objectives of these experiments were to characterize rumen motility patterns of cattle fed once daily using a real-time wireless telemetry system, determine when to measure rumen motility with this system, and determine the effect of ruminal dosing of ergot alkaloids on rumen motility. Ruminally cannulated Holstein steers (n = 8) were fed a basal diet of alfalfa cubes once daily. Rumen motility was measured by monitoring real-time pressure changes within the rumen using wireless telemetry and pressure transducers. Experiment 1 consisted of three 24-h rumen pressure collections beginning immediately after feeding. Data were recorded, stored, and analyzed using iox2 software and the rhythmic analyzer. All motility variables differed (P < 0.01) between hours and thirds (8-h periods) of the day. There were no differences between days for most variables. The variance of the second 8-h period of the day was less than (P < 0.01) the first for area and less than the third for amplitude, frequency, duration, and area (P < 0.05). These data demonstrated that the second 8-h period of the day was the least variable for many measures of motility and would provide the best opportunity for testing differences in motility due to treatments. In Experiment 2, the steers (n = 8) were pair-fed the basal diet of Experiment 1 and dosed with endophyte-free (E−) or endophyte-infected (E+; 0 or 10 μg ergovaline + ergovalinine/kg BW; respectively) tall fescue seed before feeding for 15 d. Rumen motility was measured for 8 h beginning 8 h after feeding for the first 14 d of seed dosing. Blood samples were taken on d 1, 7, and 15, and rumen content samples were taken on d 15. Baseline (P = 0.06) and peak (P = 0.04) pressure were lower for E+ steers. Water intake tended (P = 0.10) to be less for E+ steers the first 8 h period after feeding. The E+ seed treatment at this dosage under thermoneutral conditions did not significantly affect rumen motility, ruminal fill, or dry matter of rumen contents.

Ectopic tissue consisting of a mixture of glandular gastric, intestinal, and exocrine pancreatic tissue in the forestomach of a rat

The development of ectopic gastric, intestinal, or pancreatic tissue in the gastrointestinal tract is extremely rare in rats, although it is fairly common in humans. In this report, we describe an unusual case in which a mixture of different types of ectopic tissue was found in the forestomach of a rat. A solitary white nodular/polypoid structure, which measured 5 mm in size, was detected on the luminal surface of the greater curvature of the forestomach in an 8-week-old female Crl:CD(SD) rat. A histological examination revealed that the lesion contained ectopic glandular gastric tissue, including gastric surface mucous cells, parietal cells, and pyloric gland cells, which was confirmed by immunohistochemistry. Moreover, the lesion also contained villin-positive columnar intestinal absorptive cells and chymotrypsin-positive pancreatic exocrine tissue. To the best of our knowledge, this is the first study to detect a mixture of ectopic glandular gastric, intestinal, and exocrine pancreatic tissue in a rat.

Receptors for short-chain fatty acids in brush cells at the "gastric groove"

In the stomach of rodents clusters of brush cells are arranged at the "gastric groove," immediately at the transition zone from the non-glandular reservoir compartment to the glandular digestive compartment. Based on their taste cell-like molecular phenotype it has been speculated that the cells may be capable to sense constituents of the ingested food, however, searches for nutrient receptors have not been successful. In this study, it was hypothesized that the cells may express receptors for short-chain fatty acids, metabolites generated by microorganisms during the storage of ingested food in the murine forestomach, which lacks the acidic milieu of more posterior regions of the stomach and is colonized with numerous microbiota. Experimental approaches, including RT-PCR analysis and immunohistochemical studies, revealed that the majority of these brush cells express the G-protein coupled receptor types GPR41 (FFAR3) and GPR43 (FFAR2), which are activated by short-chain fatty acids. Both, the GPR41 receptor proteins as well as an appropriate G-protein, α-gustducin, were found to be segregated at the apical brush border of the cells, indicating a direct contact with the luminal content of this gastric region. The exposure of microvillar processes with appropriate receptors and signaling elements to the gastric lumen suggests that the brush cells may in fact be capable to sense the short-chain fatty acids which originate from fermentation processes during the retention of ingested food in the anterior part of the stomach.

Immunohistochemical evaluation of the goat forestomach during prenatal development

Here we report the detection and distribution of synaptophysin (SPY), non-neuronal enolase (NNE), glial fibrillary acidic protein (GFAP), vimentin (VIM), neuropeptide Y (NPY), and vasoactive intestinal peptide (VIP) expression in the goat forestomach during prenatal development. A total of 140 embryos and fetuses were examined to evaluate protein expression from the first stage of prenatal life until birth. In all cases, SPY immunoreactivity was detected at 53 days gestation in the lamina propria-submucosa, tunica muscularis, serosa, and myenteric plexuses. Immunoreactivity to NNE was observed at 64 days gestation in the same locations as well as the epithelial layer. Glial cells were found at 64 days as indicated by signals corresponding to GFAP and VIM at 39 days. Positive staining for NPY and VIP was observed at 113, 75, and 95 days in the rumen, reticulum, and omasum, respectively, in the lamina propria-submucosa, tunica muscularis, and myenteric plexuses of each of these gastric compartments. These findings indicate possible preparation of the fetal goat forestomach for postnatal function. Compared to other ruminant species, neuroendocrine cells, glial cells and peptidergic innervations markers were detected earlier compared to sheep but at around the same stage as in deer.

Gastric tumor development in Smad3-deficient mice initiates from forestomach/glandular transition zone along the lesser curvature

SMAD proteins are downstream effectors of the TGF-β signaling pathway. Smad3-null mice develop colorectal cancer by 6 months of age. In this study, we have examined whether the loss of Smad3 promotes gastric neoplasia in mice. The stomachs of Smad3⁻/⁻ mice were compared with age-matched Smad3 heterozygous and wild-type mice. E-cadherin, Ki-67, phosphoSTAT3, and TFF2/SP expression was analyzed by immunohistochemisty. The short hairpin RNA (ShRNA)-mediated knockdown of Smad3 in AGS and MKN28 cells was also performed. In addition, we examined alterations in DCLK1-expressing cells. Smad3⁻/⁻ mouse stomachs at 6 months of age revealed the presence of exophytic growths along the lesser curvature in the proximal fundus. Six-month-old Smad3⁻/⁻ mouse stomachs showed metaplastic columnar glands initiating from the transition zone junction between the forestomach and the glandular epithelium along the lesser curvature. Ten-month-old Smad3⁻/⁻ mice all exhibited invasive gastric neoplastic changes with increased Ki-67, phosphoSTAT3 expression, and aberrant cytosolic E-cadherin staining in papillary glands within the invading submucosal gland. The shRNA-mediated knockdown of Smad3 in AGS and MKN28 cells promoted the expression of phosphoSTAT3. DCLK1-expressing cells, which also stained for the tuft cell marker acetylated-α-tubulin, were observed in 10-month-old Smad3⁻/⁻ mice within tumors and in fundic invasive lesions. In conclusion, Smad3-null mice develop gastric tumors in the fundus, which arise from the junction between the forestomach and the glandular epithelium and progress to prominent invasive tumors over time. Smad3-null mice represent a novel model of fundic gastric tumor initiated from forestomach/glandular transition zone along the lesser curvature.

Comparison of reversibility of rat forestomach lesions induced by genotoxic and non-genotoxic carcinogens

Reversibility of forestomach lesions induced by genotoxic and non-genotoxic carcinogens was compared histopathologically. Groups of 30 to 33 male F344 rats were given dietary 0.1% 8-nitroquinoline, dietary 0.4-0.2% 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide, an intragastric dose of 20 mg/kg body weight N-methyl-N'-nitro-N-nitrosoguanidine once a week, or 20 ppm N-methylnitrosourethane in the drinking water as a genotoxic carcinogen, or 2% butylated hydroxyanisole, 2% caffeic acid, 2% sesamol or 2% 4-methoxyphenol in the diet as a non-genotoxic carcinogen for 24 weeks. Ten or 11 rats in each group were killed at week 24. Half of the remainder were maintained on basal diet alone for an additional 24 weeks and the other half were given the same chemical for 48 weeks, and then killed. Forestomach lesions induced by genotoxic carcinogens did not regress after removal of carcinogens. In contrast, simple or papillary hyperplasia (SPH), but not basal cell hyperplasia (BCH), induced by non-genotoxic carcinogens clearly regressed after cessation of insult. SPH labeling indices in the non-genotoxic carcinogen-treated cases decreased after removal of the carcinogenic stimulus whereas BCH values were low irrespective of treatment. Atypical hyperplasia (AH), observed at high incidences in rats treated with genotoxic carcinogens, was also evident in animals receiving non-genotoxic agents, even after their withdrawal, albeit at low incidences. AH labeling indices remained high even without continued insult. These results indicate that even with non-genotoxic carcinogens, heritable alterations at the DNA level could occur during strong cell proliferation and result in AH development. This putative preneoplastic lesion might then progress to produce carcinomas.

Reversibility of carcinogen-induced rat forestomach basal cell hyperplasia is due to squamous cell differentiation

The mechanisms of reversibility of basal cell hyperplasia in the rat forestomach were investigated. Male F344 rats were given an initial single gastric intubation of N-methyl-N'-nitro-N-nitorosoguanidine and then received 2% butylated hydroxyanisole in the diet from the third week to the 26th week. Rats were killed at weeks 26 and 46 after return to basal diet and their forestomachs were removed. Bromouracil deoxyriboside (BUdR) was administered as a single i.p. injection 1 h before death or by osmotic minipump (120 micrograms/h) continuously for 7 days before death. Additional animals were maintained for 2 or 4 weeks after removal of osmotic minipumps to allow assessment of the fate of proliferating populations. In each case BUdR-labeled cells were demonstrated by immunohistochemistry by immunohistochemistry. At week 26, hyperplastic changes were more pronounced than at week 46. Squamous cells above basal cell hyperplasias were strongly labeled even 4 weeks after cessation of continuous BUdR Three-dimensional reconstruction of persisting basal cell hyperplasias showed almost all basal cells limited to a thin sheet in direct contact with the squamous cell layer, occasional separate islands demonstrating differentiation to squamous cells and formation of epidermal cysts. The results thus showed that the mechanism of reversibility of basal cell hyperplasia involves differentiation of basal cells to squamous cells.

Effect of butylated hydroxyanisole on the level of DNA adduction by aristolochic acid in the rat forestomach and liver

Administration of butylated hydroxyanisole (BHA) orally at either 0.5 g or 1 g/kg daily for 14 days to rats did not produce any DNA adducts in the forestomach as measured by the 32P-postlabeling method using (1) limiting concentrations of 32P-ATP; (2) nuclease P1 enhancement; or (3) butanol extraction. Experiments were conducted to establish the effects of BHA administration on aristolochic acid (AA) DNA adduct formation in the forestomach and liver, when BHA was administered prior to, together with or after AA administration. Adduct levels per 10(9) nucleotides in the liver after oral dosing daily for 5 days with 1 mg/kg AA and BHA (1 g/kg) or corn oil (5 ml/kg) for 7 days were as follows: (a) BHA and AA given simultaneously; 235 +/- 71, (b) AA + corn oil; 63 +/- 39, (c) AA followed by BHA; 57 +/- 13, (d) AA followed by corn oil; 91 +/- 38, (e) BHA followed by AA; 90 +/- 12, (f) corn oil followed by AA; 83 +/- 24. For the forestomach the values were: (a) 236 +/- 86, (b) 77 +/- 25, (c) 367 +/- 97, (d) 296 +/- 47, (e) 217 +/- 81, (f) 70 +/- 64. These data suggest that BHA could have an enhancing effect on AA-induced lesions in the forestomach if dosed together with, or prior to, AA as adduct levels are significantly higher than in controls.

Co-carcinogenic effect of retinyl acetate on forestomach carcinogenesis of male F344 rats induced with butylated hydroxyanisole

The potential modifying effect of retinyl acetate (RA) on butylated hydroxyanisole (BHA)-induced rat forestomach tumorigenesis was examined. Male F344 rats, 5 weeks of age, were maintained on diet containing 1% or 2% BHA by weight and simultaneously on drinking water supplemented with RA at various concentrations (w/v) for 52 weeks. In groups given 2% BHA, although marked hyperplastic changes of the forestomach epithelium were observed in all animals, co-administration of 0.25% RA significantly (P less than 0.05) increased the incidence of forestomach tumors (squamous cell papilloma and carcinoma) to 60% (9/15, 2 rats with carcinoma) from 15% (3/20, one rat with carcinoma) in the group given RA-free water. In rats given 1% BHA, RA co-administered at a dose of 0.05, 0.1, 0.2 or 0.25% showed a dose-dependent enhancing effect on the development of the BHA-induced epithelial hyperplasia. Tumors, all papillomas, were induced in 3 rats (17%) with 0.25% RA and in one rat (10%) with 0.05% RA co-administration. RA alone did not induce hyperplastic changes in the forestomach. These findings indicate that RA acted as a co-carcinogen in the BHA forestomach carcinogenesis of the rat.