Electron microscopic autoradiography of the trachea in fetal Syrian golden hamsters treated transplacentally with N-nitrosodiethylamine.

Tritiated N-nitrosodiethylamine (DENA) was administered to female Syrian golden hamsters on each of the last 4 days (days 12--15) of pregnancy. The intracellular distribution of bound radioactivity was monitored by electron microscopic autoradiography in the epithelium of the fetal tracheas, from which transplacentally induced tumors arise in this system. Most of the bound radioactivity was concentrated in the rough endoplasmic reticulum of undifferentiated stem cells and mucous cells. The level of binding on the various days of pregnancy appeared to reflect the degree of differentiation of the endoplasmic reticulum in these cells. Basal cells, which were identified as the origin of DENA-induced tracheal tumors in adult hamsters by one or our earlier studies, demonstrated only little bound radioactivity in the fetal tracheas. The pathogenesis of DENA-induced tracheal tumors in this transplacental system may hence be different from that in adult animals.

Pathogenesis of tumors induced with N-nitrosomethylpiperazine in the olfactory region of the rat nasal cavity.

Tumors in the olfactory region of the nasal cavity of the F344 rat were induced by chronic treatment with N-nitrosomethylpiperazine. The pathogenesis of the neoplasms was studied in a serial sacrifice study by light and electron microscopy. Proliferating basal cells of the olfactory epithelium differentiated into cells with morphologic features of neuroendocrine cells, which then progressed further to become invasive carcinomas. The tumors exhibited areas of neuroendocrine, adenoid, squamous, and neuroblastic morphologies. The variability of morphologic patterns found within the same tumor can be explained by the ability of neuroendocrine cells to differentiate into these different cell types.

Sequential morphologic changes during methapyrilene-induced hepatocellular carcinogenesis in rats.

The pathogenesis of hepatocellular tumors induced in F344 rats by the antihistaminic methapyrilene was investigated by light and electron microscopy in a serial sacrifice study. Eosinophilic foci of altered hepatocytes were found in portal areas after 1 week of treatment, the eosinophilia being caused by proliferation of mitochondria. Eosinophilic neoplastic nodules developed from such lesions after 16 weeks of treatment. Hepatocellular carcinomas developed after 26 weeks of treatment. Mitochondrial proliferation, which had been found as a marker for hepatocytes altered by this compound at 1 week of treatment, was still present in the hepatocellular carcinomas, which therefore met the morphologic criteria of oncocytomas.

Binding of radioactivity after transplacental administration of tritiated N-nitrosodiethylamine to Syrian golden hamsters.

Tritiated N-nitrosodiethylamine (DEN) was administered to two groups of female Syrian golden hamsters on days 11 and 15 of pregnancy. Binding of radioactivity was measured in maternal and fetal organs after various intervals by liquid scintillation counting of dehydrated and combusted tissues. No bound activity was found in the fetal tracheas on day 11 of gestation, when transplacental administration of DEN is known to be noncarcinogenic for the offspring. On day 15, when DEN administration caused a 95% incidence of tracheal tumors in the offspring, bound radioactivity was found in the fetal tracheas. In the respiratory tracts of the mothers, the distribution of bound radioactivity correlated with the distribution of target cell types. Binding was high in segmental bronchi and bronchioles which contain numerous Clara cells, the major source of DEN-induced pulmonary tumors. No binding occurred in the main bronchi, which do not possess Clara cells.

Autoradiography in fetal golden hamsters treated with tritiated diethylnitrosamine.

Tritiated diethylnitrosamine was administered to female Syrian golden hamsters on each of the last 4 days (days 12-15) of pregnancy. The distribution of bound radioactivity was monitored by light microscopic autoradiography of fetal tracheas and livers, the placentas, and the maternal livers. In the trachea, the fetal target organ, bound radioactivity was restricted to the respiratory epithelium, where diethylnitrosamine-induced tracheal tumors arise. Mucous cells and nonciliated stem cells were identified as the principal sites of binding; other cell types within the tracheal epithelium contained only small amounts of bound radioactivity. The level of binding observed in the fetal trachea increased steadily from day 12 to day 15, which correlated well with the levels of differentiation of this tissue during this period. This observation also agrees with the previously reported observation that tumor incidence increases from 40 to 95% in Syrian golden hamsters between days 12 and 15.

Nitrosamine-induced lung carcinogenesis and Ca2+/calmodulin antagonists.

This review summarizes recent data which implicate cell membrane receptors and their associated signal transduction pathways as molecular targets of tobacco-related lung carcinogenesis as well as therapy of such cancers. It is shown that the two nitrosamines N-nitrosodiethylamine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone bind to nicotinic cholinergic receptors in hamster lung. Binding of the nitrosamines as well as nicotine to this receptor stimulates proliferation of human lung carcinoid cells in vitro. These data suggest chronic stimulation of nicotinic receptors by nicotine and nitrosamines in smokers as one of the molecular events responsible for stimulation of neuroendocrine cell proliferation and ultimately the development of lung tumors with neuroendocrine differentiation. On the other hand, a selective antiproliferative effect of the dihydropyridine derivative B859-35 on neuroendocrine lung tumor cells in vivo and in vitro suggests the potential use of such agents as cancer therapeutics. The demonstrated inhibition of Ca2+/calmodulin and protein kinase C by B859-35 as reported in other in vitro systems suggests interference with such elements of signal transduction pathways as the molecular mechanism of the observed antiproliferative effects.

Inhibition of N-nitrosodiethylamine-induced respiratory tract carcinogenesis by piperonylbutoxide in hamsters.

The influence of pretreatment with piperonylbutoxide (PIP) on the biological effects of N-nitrosodiethylamine (DEN) in vivo in Syrian golden hamsters was investigated. PIP pretreatment significantly reduced covalent binding of N-[ethyl-1-14C]DEN to tissue macromolecules in trachea, lung, and liver, while it did not change the tissue distribution of the parent compound. In a chronic experiment, hamsters treated with PIP before each DEN injection did not develop any tumors or precancerous changes in the lungs, while 60% of the animals given DEN alone developed lung tumors with the morphology of Clara cells and endocrine cells. Tumor incidence in the trachea was also significantly reduced by PIP, but to a lesser extent than in the lungs.

Transplacental induction of pancreas tumors in hamsters by ethanol and the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.

Epidemiological studies suggest that smoking during pregnancy and passive exposure of children to cigarette smoke may increase the cancer risk in children and young adults. We have previously shown that the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is an active transplacental carcinogen in Syrian golden hamsters when administered by s.c. injections to pregnant females. The majority of tumors in the offspring developed in the respiratory tract. Since in smoking women the respiratory tract is the portal of entry of tobacco-related carcinogens, including NNK, we have investigated the transplacental effects of NNK given by intratracheal instillation to pregnant hamsters. The modulating effect of ethanol on the transplacental carcinogenicity of NNK in this system was also investigated because smoking and consumption of alcoholic beverages are observed in pregnant women. Our data show that exposure to NNK via the maternal respiratory tract causes a similar tumor incidence in the offspring as the s.c. route of administration. Ethanol greatly enhanced the carcinogenic response to NNK, and up to 60% of the offspring exposed in utero to ethanol and NNK developed tumors of the exocrine pancreas.

Modulation of the uptake and metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone by nicotine in hamster lung.

The tobacco-specific carcinogenic nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is formed during the curing and processing of tobacco by nitrosation of nicotine. Nicotine and NNK have structural similarities, and they are both metabolized extensively by lung tissue via several steps known to require oxidative enzyme systems, such as cytochrome P450. On the other hand, nicotine exerts many biological effects similar to those caused by the physiological neurotransmitter acetylcholine, a phenomenon mediated through selective uptake mechanisms via nicotinic cholinergic cell membrane receptors. The aim of this study was to determine if nicotine modulates NKK metabolism in hamster lung explants and if NNK competes with nicotine for binding sites on nicotinic cholinergic receptors in the hamster lung in vivo. Our data show a concentration-dependent inhibition of NNK metabolism in vitro by alpha-carbon hydroxylation and pyridine N-oxidation, whereas the carbonyl reduction of NNK remained unchanged. Radioreceptor assays with membrane receptor fractions of hamster lung after exposure to radiolabeled (S)-(-)-nicotine revealed significant numbers of nicotinic binding sites only in the lungs of hamsters with hyperplasia of pulmonary neuroendocrine cells caused by 4-wk preexposure to hyperoxia. In such animals, radiolabeled nicotine was displaced from the receptor binding sites by NNK. Our data suggest that nicotine can potentially interfere with the carcinogenicity of NNK by competition for enzyme systems essential for the metabolic activation of the nitrosamine and by competition as ligand for nicotinic cholinergic receptors.

Placental transfer of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone instilled intratracheally in Syrian golden hamsters.

The tobacco-specific N-nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone (NNK) is a potent tumorigen in adult Syrian golden hamsters and an active transplacental carcinogen in this species. In this study, we have investigated the biodistribution and metabolism of NNK in maternal and fetal hamster tissues as a function of the dose and the time after NNK treatment. Hamsters on day 15 of gestation were instilled intratracheally with single doses (0.05-100 mg/kg) of [5-3H]NNK and sacrificed 30 min later or treated with a single dose (25 mg/kg) of [5-3H]NNK and sacrificed at various times (5-360 min) after treatment. Total radioactivity was quantified in maternal tissues (liver, lung, kidney, placenta, and stomach), in whole fetus and in fetal tissues (liver and lung). NNK and its metabolites were extracted from selected tissues (maternal plasma, amniotic fluid, fetal liver, and lung) and assayed by high-performance liquid chromatography-scintigraphy. Thirty min after treatment, radioactivity associated with NNK and its metabolites showed similar widespread tissue distribution patterns at all doses, with a linear dose relationship observed in whole fetus and fetal tissues. NNK levels detected in maternal plasma, amniotic fluid, fetal liver, and lung were also related linearly to dose. At high doses (25 mg/kg or more) of NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol was the major metabolite detected in maternal plasma. Pyridine N-oxidation of NNK predominated at the lowest doses (0.05 and 0.5 mg NNK/kg). The toxicokinetics of NNK demonstrated that this carcinogen is rapidly absorbed from the maternal lung (less than 5 min), metabolized mainly to 4-(methylnitrosamino)-1- (3-pyridyl)-1-butanol, and quickly distributed into the maternal-fetal compartment. Both NNK and its main metabolite 4-(methylnitrosamino)-1-(3- pyridyl)-1-butanol were eliminated slowly from the amniotic fluid, with levels still detectable up to 6 h after NNK treatment. These results demonstrated that NNK instilled intratracheally in pregnant hamsters crossed the placental barrier even at low doses. Moreover, NNK quickly reached fetal tissues and amniotic fluid and was eliminated slowly from these tissues, resulting in an extended exposure of the fetus to this tobacco-specific carcinogen.

Beta-adrenergic mitogenic signal transduction in peripheral lung adenocarcinoma: implications for individuals with preexisting chronic lung disease.

Peripheral adenocarcinoma (PAC) of the lung has increased dramatically over the last 20 years and is today the leading histological type of lung cancer in smokers and nonsmokers in industrialized countries. There is no apparent explanation for the steep rise in the number of individuals developing this cancer type. Using assays for the assessment of cell proliferation, receptor binding, and production of cyclic AMP (cAMP), we have identified a beta-adrenergic receptor-mediated mitogenic pathway, which activates cAMP down-stream, in cell lines derived from human peripheral adenocarcinomas that express features of Clara cells. Agonists of beta-adrenergic receptors strongly stimulated cell proliferation, whereas antagonists of this receptor and its associated second messenger, cAMP, were potent inhibitors of this effect. Agonists of beta-adrenergic receptors are the active ingredients of many decongestants and bronchodilators, and such medications are, therefore, likely to stimulate this pathway in vivo. Patients suffering from chronic upper and lower respiratory tract diseases and treated with such medications over many years may, therefore, be at a higher risk than the average population to develop PAC, particularly when simultaneously exposed to carcinogenic environmental factors such as smoking. Because the incidence of chronic respiratory tract diseases has risen in industrialized countries during the same time frame as PAC, a potential etiological link between the therapy of such nonneoplastic diseases with beta-adrenergic agonists and the risk for PAC should be investigated.

The tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone is a beta-adrenergic agonist and stimulates DNA synthesis in lung adenocarcinoma via beta-adrenergic receptor-mediated release of arachidonic acid.

Lung cancer is the leading cause of death in the United States, and it demonstrates a strong etiological association with smoking. The nicotine-derived nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) reproducibly induces pulmonary adenocarcinomas (ACs) in laboratory rodents and is considered an important contributing factor to the high lung cancer burden observed in smokers. It has been shown that the development of NNK-induced ACs in mice is reduced by inhibitors of cyclooxygenase and lipoxygenase and that the growth of human AC cell lines is regulated by beta-adrenergic receptors. On the basis of structural similarities of NNK with classic beta-adrenergic agonists, we tested the hypothesis that NNK stimulates the growth of human AC cells via agonist-binding to beta-adrenergic receptors, resulting in the release of arachidonic acid (AA). In support of this hypothesis, radioreceptor assays with transfected CHO cell lines stably expressing the human beta1- or beta2-adrenergic receptor demonstrated high affinity binding of NNK to each of these receptors. Two human AC cell lines expressed beta1- and beta2-adrenergic receptors by reverse transcription-PCR and responded to NNK with the release of AA and an increase in DNA synthesis. Beta-adrenergic antagonists completely blocked the release of AA and increase in DNA synthesis. The cyclooxygenase inhibitor aspirin and the 5-lipoxygenase inhibitor MK-886 both partially inhibited DNA synthesis in response to NNK. Our findings identify the direct interaction of NNK with beta-adrenergic, AA-dependent pathways as a novel mechanism of action which may significantly contribute to the high cancer-causing potential of this nitrosamine. Moreover, NNK may also contribute to the development of smoking-related nonneoplastic disease via this mechanism.

Successful chemotherapy of experimental neuroendocrine lung tumors in hamsters with an antagonist of Ca2+/calmodulin.

The chemotherapeutic effect of B859-35, the (-)-enantiomer of dihydropyrine 3-methyl-5-3-(4,4-diphenyl-1-piperidinyl)-propyl-1,4-dihydro-2,6-dimethy l-4- (3-nitrophenyl)-pyridine-3,5-dicarboxylate-hydrochloride (niguldipine), was tested on tumors induced in Syrian golden hamsters by N-nitrosodiethylamine (DEN). Peripheral pulmonary adenomas/adenocarcinomas were induced in hamsters maintained under ambient air conditions by multiple s.c. injections of DEN for 20 weeks. We have reproducibly shown that within this time interval lung adenomas develop in a significant number of the animals. The carcinogen treatment was discontinued at this point and one group of these hamsters was given B859-35 intragastrically 5 days/week for 20 weeks while the second group of such tumor-bearing hamsters were kept for an identical time interval without further treatment. Neuroendocrine lung tumors were induced in hamsters maintained in an atmosphere of 60% O2 by multiple s.c. injections of DEN for 8 weeks. We have reproducibly shown that within this short time interval neuroendocrine lung tumors develop in a significant number of the animals. The carcinogen treatment was discontinued at this point and the animals were returned to ambient air conditions. One group of these tumor-bearing hamsters was then given B859-35 intragastrically 5 days/week for 20 weeks while a second group of these hamsters was kept untreated for an identical time interval. A control group was given s.c. injections of saline for 20 weeks under ambient air conditions. A dramatic and selective anticarcinogenic effect of B859-35 was observed on the neuroendocrine lung tumors and nasal cavity tumors induced by DEN/hyperoxia while tumors of larynx/trachea were not affected. B859-35 had no effect on peripheral adenomas/adenocarcinomas, nasal cavity tumors, papillary polyps of larynx/trachea, or liver tumors induced by DEN under ambient air conditions.

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone is an active transplacental carcinogen in Syrian golden hamsters.

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent carcinogen in adult laboratory rodents. Our previous studies have shown that NNK crosses the placenta in pregnant hamsters and is metabolized into DNA-methylating and clastogenic intermediates by fetal respiratory tract tissues. Based on these findings, we have tested the transplacental carcinogenicity of NNK in this species. Groups of pregnant hamsters were given s.c. injections of single or multiple doses of NNK (cumulative dose range, 50-300 mg/kg) on day 15 (last day of gestation) or on days 13, 14, and 15 of gestation. Within 1 year after treatment, up to 70% of the offspring developed tumors in various organs, including respiratory tract, nasal cavity, adrenal glands, pancreas, and liver. No tumors were found in the control hamsters treated with the vehicle (trioctanoin) alone. The overall tumor incidence was proportional to the cumulative dose. Females had a generally higher tumor incidence than males.

Metabolism and DNA damage induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in fetal tissues of the Syrian golden hamster.

The nicotine derived N-nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent respiratory tract carcinogen in adult Syrian golden hamsters. In this study, the metabolism and genotoxicity of NNK was investigated in fetal hamster trachea and lung tissues. Fetal lung and tracheal explants were cultured in vitro with [5-3H]NNK, and metabolites released into the culture medium were assayed by high-performance liquid chromatography-scintigraphy. Activation of NNK by alpha-carbon hydroxylation and deactivation by pyridine N-oxidation increased from Day 12 to 15 of fetal development. In lung tissues, at Day 12 of fetal development, carbonyl reduction of NNK to 4-(methylnitrosamino)-1-(3-pyridyl)butan-1-ol was the major metabolic pathway. When adult and fetal lung explants were cultured in vitro with [methyl-3H] NNK, explant DNA was methylated at the O6- and N-7 guanine sites. When hamsters were injected i.p. with NNK (0-200 mg/kg) on Day 14 of gestation, chromosome aberrations were observed in epithelial cells established from lung and tracheal explant outgrowths. Most aberrations in lung and tracheal cells were of chromatid types. High frequency of chromatid exchange was observed in tracheal cells. After injection of NNK (200 mg/kg) to 14-day pregnant hamsters, NNK was detected in lung (0.39 +/- 0.16 nmol/mg), placenta (0.72 +/- 0.48 nmol/mg protein) and amniotic fluids (34.07 +/- 7.62 nmol/ml). These results demonstrated that NNK can cross the placental barrier in pregnant hamsters and be activated to genotoxic intermediates in tracheal and lung tissues and suggest that NNK is a transplacental carcinogen in this species.

Metabolic activation and cytotoxicity of 4-ipomeanol in human non-small cell lung cancer lines.

In the normal lungs of many animal species, 4-ipomeanol is transformed to a highly reactive metabolite preferentially in pulmonary bronchiolar Clara cells and to a lesser extent in alveolar type II cells, potentially leading to damage or destruction of these cell types. Since Clara cells and type II cells are suspected sites of origin of certain "non-small cell" lung cancers, the metabolic activation of 4-ipomeanol (measured by the metabolism-dependent covalent binding of 4-ipomeanol to cellular macromolecules) was compared in two human non-small cell carcinoma derived cell lines (NCI-H322 and NCI-H358) and two human small cell carcinoma derived cell lines (NCI-H128 and NCI-H69). Metabolic activation of 4-ipomeanol was evident in the non-small cell lines; the production of covalently bound metabolite was somewhat greater in NCI-H322 (morphology related to Clara cells) compared to NCI-H358 (morphology related to alveolar type II cells), but was entirely undetectable in the small cell lines. The activation pathway was concentration (4-ipomeanol) and time dependent and followed Michaelis-Menten kinetics. Metabolism to the reactive intermediate required oxygen and was strongly inhibited by carbon monoxide. Covalent binding was enhanced in the non-small cell lines by prior incubation with beta-naphthoflavone and by supplementation of the incubate with exogenous reduced nicotinamide adenine dinucleotide phosphate. 4-Ipomeanol was more cytotoxic to the non-small cell lines than to the small cell lines under the in vitro growth conditions used. These studies indicate that certain human non-small cell lung cancers have metabolic characteristics of normal bronchiolar Clara cells and alveolar type II cells; these results would therefore be consistent with an origin of these tumors from Clara cells or type II cells, respectively. The present studies indicate that the further preclinical testing and development of 4-ipomeanol is warranted, with a view toward possible clinical evaluation against human lung cancers.

Metabolism of arachidonic acid in human lung cancer cell lines.

The metabolism of arachidonic acid (AA) was studied in two pulmonary bronchioloalveolar-carcinoma cell lines (NCI-H322 and NCI-H358) and two small cell lung carcinoma cell lines (NCI-H69 and NCI-H128). Exogenous AA was metabolized only in the NCI-H322 and NCI-H358 cells. There was no detectable metabolism of AA in NCI-H69 or NCI-H128 cells, either in the presence or the absence of the calcium ionophore A23187. The major metabolite of AA isolated from both NCI-H322 and NCI-H358 cells was prostaglandin E2 (PGE2). Prostaglandin endoperoxide synthase activities, expressed as immunoreactive PGE2 (pmol/min/mg protein), were 10.3 +/- 0.28 (SD) and 4.8 +/- 0.48 in NCI-H358 and NCI-H322 cells, respectively. The rate of production of PGE2 by both NCI-H358 and NCI-H322 cells was linear up to 10 min. Production of PGE2 in both cell lines was dependent upon substrate concentration and was maximal above 17 microM AA. Moreover, PGE2 did not undergo further metabolism by either the NCI-H358 or the NCI-H322 cells. Aspirin (0.1 mM), a cyclooxygenase inhibitor, decreased PGE2 production by 77 and 60% in NCI-H358 and NCI-H322 cells, respectively. In the presence of exogenous AA the calcium ionophore, A23187 (20 microM), stimulated PGE2 production in NCI-H322 cells by almost 2-fold, although it did not affect PGE2 production in the NCI-H358 cells. In contrast, A23187 stimulated the endogenous production of PGE2 in both NCI-H322 and NCI-H358 cells by 4- and 9-fold respectively. In addition, both the NCI-H358 and NCI-H322 cell lines were susceptible to the cytotoxic effects of the anticancer agent mitoxantrone in both a time and concentration dependent manner. In contrast, the two cell lines lacking detectable prostaglandin synthesis activity, NCI-H69 and NCI-H128 were unaffected by treatment with mitoxantrone. These results illustrate that there are major differences in the abilities of human lung cancer cell lines to biosynthesize and release PGE2. It is conceivable that such differences might have exploitable diagnostic and/or therapeutic implications.

Pathobiology of lung tumors induced in hamsters by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and the modulating effect of hyperoxia.

Neuroendocrine lung cancer is among the most common types of lung cancers in smokers. We have recently shown that exposure of hamsters to N-nitrosodiethylamine and hyperoxia causes a high incidence of this tumor type. In this study, we show that the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone also causes neuroendocrine lung tumors in hyperoxic hamsters. Animals maintained in ambient air while being treated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone developed pulmonary adenomas composed of Clara cells and alveolar type II cells. Pathogenesis experiments provide evidence for the tumors caused by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in ambient air being derived from Clara cells. In the hyperoxic hamsters, the neuroendocrine carcinogenesis appears to involve two stages: (a) transformation of focal alveolar type II cells into neuroendocrine cells and (b) development of neuroendocrine lung tumors from such foci.

Electron microscopic autoradiography of the pancreas in the hamster treated with tritiated N-nitroso-2,6-dimethylmorpholine.

Syrian golden hamsters were given a single dose of [3H]-N-nitroso-2,6-dimethylmorpholine and killed 8 hr later. The pancreas was processed for electron microscopic autoradiography to detect binding of radioactivity to cellular constituents. The pancreatic acinar cells and duct epithelia were found to be labeled, while islet cells, centroacinar cells, and all nonepithelial elements were not. Acinar cells active in secreting zymogen had a high concentration of grains over the zymogen granules and the rough endoplasmic reticulum. Their nonsecreting counterparts contained abundant bound material in the nuclei and rough endoplasmic reticulum. Labeling was lower in the duct epithelia than in acinar cells, with the majority of grains associated with the heterochromatin. Our findings suggest that the acinar cells are the principle site of metabolic activation in this organ.

Autoradiographic study of the distribution of bound radioactivity in the respiratory tract of Syrian hamsters given N-[3H]nitrosodiethylamine.

Adult Syrian golden hamsters received a single intragastric dose of N-[3H]nitrosodiethylamine. Their tracheas, extrapulmonary stem bronchi, and lungs were processed for high-resolution light-microscopic autoradiography to monitor the distribution of bound radioactivity. In the trachea and extrapulmonary stem bronchi, mucous cells contained the most bound radioactivity, while in the lobar and segmental bronchi and bronchioles, Clara cells were the major site of binding. In conjunction with earlier conducted studies on the pathogenesis of N-[3H]nitrosodiethylamine-induced respiratory tract tumors, these findings indicate that metabolic competence and a preexisting capacity for proliferation are important factors in determining the target cell types of this compound.