In vivo inhibition of hepatitis B viral gene expression by antisense phosphorothioate oligodeoxynucleotides in athymic nude mice

Antisense oligodeoxynucleotides strategies have been used both to study normal gene function and to block gene expression therapeutically. We have previously shown that a number of antisense oligonucleotides against hepatitis B virus (HBV) mRNA are able to inhibit viral gene expression in vitro. Here we report the establishment of an animal model producing HBV markers in athymic nude mice and inhibition of HBV gene expression and replication by antisense DNA in vivo. 2.2.15 cells (Hep-G2 cell line transfected with HBV genomes) were injected subcutaneously (s.c.) into athymic BALB/c nude mice at a total cell number of 0.5-1 x 10(8) per mouse. Transplanted tumours developed about 2 weeks after inoculation. Hepatitis B surface and e antigens (HBsAg and HBeAg), as well as HBV DNA, could be detected in the circulation of tumour-bearing mice. Hepatitis B surface antigen and hepatitis B core antigen (HBcAg) were demonstrated in tumour cells. After 10 days of tumour growth, antisense phosphorothioate oligonucleotide, complementary to the cap site of the SP II promoter of HBV mRNA, were injected by infiltration into or around the tumour as a daily dose of 20 micrograms per gram body weight. Treatment for a total of 10 days resulted in an effective inhibition of viral replication and gene expression. These results suggest therapeutic potential for antisense oligomers in the treatment of patients who are chronically infected with HBV.

Cooperative medical schemes in contemporary rural China

Improvements in rural health care in China in the 1950s, 1960s and 1970s were largely due to the development of cooperative medical schemes (CMSs) and the establishment of a three-tier rural health network. Since the economic reforms were instituted in the late 1970s, the financing and delivery of rural health services have seen many changes, some positive, others not. Most CMSs have collapsed. In the absence of CMSs, the rural population has to pay for health care out-of-pocket and poor families have greater difficulty in getting access to essential health care. In the meantime, emphases of health services have tended to shift from lower to higher levels, from preventive to curative services, and from planning and management to market forces. This paper outlines the evolution of CMSs, reasons for their collapse, and their likely impact on rural health services. The main focus is on the development of a new generation of rural cooperative health care schemes, given their importance in the process of consolidating the rural three-tier health network after the impact of the economic reforms: the characteristics of some schemes, the apparent conditions for success, and government policy towards the development of cooperative health care financing are presented.

[Clinical evaluation of serum collagen type IV in diagnosing liver fibrosis]

Serum collagen type IV (CIV) levels determined by one step sandwich EIA kit were compared with the serum procollagen type III (PCIII) and hyaluronic acid (HA) in 114 patients with various liver diseases, 30 patients without liver diseases (NL) and 30 controls.

RESULTS

serum CIV was significantly increased in chronic active hepatitis, liver cirrhosis and primary hepatic carcinoma. So were PCIII and HA. Serum CIV PCIII and HA were found to be closely related to the degree of fibrosis in 69 patients' liver biopsy studies, but no correlation could be found between these 3 markers. The sensitivity of CIV, PCIII, HA in detecting liver fibrosis were 73.9%, 67.4%, 67.4% with specificity of 95.7%, 91.3%, 100.0% respectively. The early diagnostic value of CIV is better than PCIII and HA; their combination could further raise the diagnostic sensitivity to more than 90.0%.

Intracranial germ cell tumors: detection of p53 gene mutations by single-strand conformation polymorphism analysis

Using polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) analysis, p53 gene mutation was examined in 12 intracranial germ cell tumors (5 yolk sac carcinomas and 7 germinomas), many of which were derived from young patients in the first to the second decade. A total of 10 mutations were detected in 4 of the 12 cases and, in 3 of them, the mutations were multiple or tandem. Among the 10 mutations, 7 were missense, 1 was splicing and 2 were silent. The 7 missense mutations were located at previously proposed hot spot codons or in their vicinity or, when outside the hot spots, at a codon encoding an amino acid conserved in most vertebrates. These findings suggested that all 7 missense mutations may actually give rise to functional alteration of the p53 protein. The splicing mutation was considered to be a germ-line mutation, though its biological effect was equivocal, since the neoplastic tissue contained an additional mutation. The pattern of the mutations was predominancy of G:C-A:T transition with frequent involvement of the CpG site. These mutations were more frequently detected in yolk sac carcinomas (60%; 3/5 cases) than in germinomas (14%; 1/7 cases), suggesting that the contribution of the p53 mutation to carcinogenesis differed with the histological type of the intracranial germ cell tumor.

[Study on the effect of endothelin and nitric oxide on DNA synthesis of pulmonary artery smooth muscle cells and modulation of hypoxia]

Increasing vasoconstriction and vascular remodeling of pulmonary vasculature are main characteristics of hypoxic pulmonary hypertension (HPH). Basal pulmonary circulatory tone is maintained by a dynamic balance of vasoconstrictors and vasodilators acting on the pulmonary vascular smooth muscle cells. Endothelin-1 (ET-1) and nitric oxide (NO) are the most important endothelium-derived vasoconstrictor (EDCF) and vasodilator (EDRF). In this report, we studied the effect of ET-1 and NO on hypoxic pulmonary vascular remodeling. We observed that ET-1 dose dependently increased DNA synthesis of pulmonary artery smooth muscle cells (PASMC), SNP, a NO generating drug, inhibited DNA synthesis of PASMC and its inhibitory effect was mediated by cGMP. Hypoxia increased the proliferative response of PASMS to ET-1 by stimulating autocrine of PASMC and decreased the inhibitory effect of SNP by reducing the activity of intra-cellular soluble guanylate cyclase. Based on the result, it is suggested that the balance of ET-1 and NO and regulation of hypoxia play important roles in hypoxic pulmonary vascular remodeling.

[Preliminary studies on the effects of tumor necrosis factor gene transfer on the growth of human hepatocellular carcinoma cells in nude mice]

An eukaryotic expression vector containing tumor necrosis factor alpha (TNF alpha) gene (psVK3-tnf) was transduced into hepatocellular carcinoma (HCC) cell line, SMMC7721, by calcium phosphate coprecipation method. The TNF-gene-transduced SMMC7721 cell began to secrete TNF after 24h (50 0/ml), reached peak level at 48-72h (90U/ml), and declined after 96h (40U/ml). Three weeks after the pSVK3-tnf DNA entrapped with calcium phosphate was introduced directly into subcutaneous nodules of human HCC in nude mice (treated mice), the growth of HCC was significantly delayed as compared to the pSVK3 group (control mice) (2.5 +/- 1.6 cm vs. 3.2 +/- 1.8 cm, n = 6, P < 0.05). There was a transient increase in TNF alpha level in peripheral blood in the treated but not in the control mice. The survival time of the treated mice was markedly prolonged as compared to the control (44.0 +/- 3.3d vs. 28.2 +/- 2.0d, n = 6, P < 0.01). The above results suggest that TNF alpha gene transfer might be a hopeful therapy for HCC.

p21ras independent down-regulation of ras-induced increases in natural antibody binding during tumor progression

Selective outgrowth of v-H-ras-infected 10T1/2 cells based on the cointroduction of a gene for resistance to geneticin (G418), yielded cells which exhibited an increased capacity to bind polyclonal serum natural antibody (NAb). This demonstrated an NAb-susceptible phase of tumor development which would be a basic requirement for NAb-mediated surveillance of tumors. The ras-oncogene dependence of the high-NAb-binding phenotype provided a model for assessing NAb resistance against ras transformants in vivo and for a comparative analysis of phenotypic and genetic alterations contributing to the progression of ras transformants. Variants were developed through in vitro and in vivo models of tumor progression. T24-H-ras and v-H-ras transformants were isolated in vitro through more rigorous growth conditions, focus formation in the presence of untransformed cells with no selecting drug. These clones expressed p21ras but exhibited little or no increase in NAb binding. Variants recovered following growth from intravenous or threshold subcutaneous (s.c.) inocula of high-NAb-binding ras transformants in syngeneic C3H/HeN mice exhibited decreases in NAb binding but no uniform change in p21ras. Concurring inverse correlations between NAb binding and s.c. tumorigenicity were exhibited by the T24-H-ras transformant clones, the ras transformants grown in vivo, and the v-H-ras-transformed clones isolated in the presence versus the absence of untransformed cells. This consistent inverse correlation, together with the reduced NAb binding of the ras transformants grown in vivo, provides strong evidence that NAb participates in the defense against ras-transformed cells in vivo. The lack of any direct correlation between p21ras expression and the reduction in NAb binding or the increase in tumorigenicity of cells generated through progression in vivo suggested the regulatory action of additional genes. Hybridization studies between high- and low-NAb-binding clones implicated the activation of an additional oncogene and inactivation of an antioncogene in the down-regulation of the ras-induced increases in NAb binding associated with tumor progression.

Isotopic analyses of nitrogenous compounds from the Murchison meteorite: ammonia, amines, amino acids, and polar hydrocarbons

The combined volatile bases (ammonia, aliphatic amines, and possibly other bases), ammonia, amino acids, and polar hydrocarbons were prepared from the Murchison meteorite for isotopic analyses. The volatile bases were obtained by cryogenic transfer after acid-hydrolysis of a hot-water extract and analyzed by combined gas chromatography-mass spectrometry of pentafluoropropionyl derivatives. The aliphatic amines present in this preparation comprise a mixture that includes both primary and secondary isomers through C5 at a total concentration of > or = 100 nmoles g-1. As commonly observed for meteoritic organic compounds, almost all isomers through C5 are present, and the concentrations within homologous series decrease with increasing chain length. Ammonia was chromatographically separated from the other volatile bases and found at a concentration of 1.1-1.3 micromoles g-1 meteorite. The ammonia analyzed includes contributions from ammonium salts and the hydrolysis of extractable organic compounds, e.g., carboxamides. Stable isotope analyses showed the volatile bases to be substantially enriched in the heavier isotopes, relative to comparable terrestrial compounds delta D < or = +1221%; delta 13C = +22%; delta 15N = +93%). Ammonia, per se, was found to have a somewhat lower delta 15N value (+69%) than the total volatile bases; consequently, a higher delta 15N (>93%) can be inferred for the other bases, which include the amines. Solvent-extractable polar hydrocarbons obtained separately were found to be enriched in 15N (delta 15N = +104%). Total amino acids, prepared from a hydrolyzed hot-water extract by cation exchange chromatography, gave a delta 15N of +94%, a value in good agreement with that obtained previously. Nitrogen isotopic data are also given for amino acid fractions separated chromatographically. The delta 15N values of the Murchison soluble organic compounds analyzed to date fall within a rather narrow range (delta 15N = +94 +/- 8%), an observation consistent with their formation, or formation of their precursors, by interstellar chemistry.

Climatic Implications of an 8000-Year Hydrogen Isotope Time Series from Bristlecone Pine Trees

Tree rings from three dendrochronologically dated bristlecone pines were analyzed for stable hydrogen isotopic composition. These trees give a continuous time series from 8000 years ago to the present that indicates the presence of a postglacial climate optimum 6800 years ago and a continuous cooling since then. The qualitative agreement between this record and records from other sources, such as ice cores, pollen, and treeline fluctuations, indicates that these climate changes were global. This record can serve as a reference for other climate indicators throughout the past 8000 years.

p53 gene mutations in pontine gliomas of juvenile onset

Using polymerase chain reaction-single strand polymorphism(PCR-SSCP) and nucleotide analyses, p53 gene mutation was examined in 13 pontine gliomas many of which were of juvenile onset. A total of 15 mutations were detected in 8 cases, of which 5 revealed multiple or tandem mutations. The mutations included 6 G:C-A:T and 4 A:T-G:C transitions and 4 G:C-T:A and 1 A:T-T:A transversions. There was only 1 transition at the CpG site. Normal tissues of the same patients revealed no mutation, suggesting that these mutations were somatic, but not of germ line, in nature. The pattern of mutation characterized by frequent multiple or tandem occurrence, predominancy of transition at non-CpG sites and relatively frequent transversions suggested that pontine glioma might be related with some mutagenic or carcinogenic agents.

Sideband suppression in magic-angle-spinning NMR by a sequence of 5 pi pulses

We report a symmetrical sequence of 5 pi pulses for total sideband suppression in magic-angle-spinning NMR. The sequence is almost evenly spaced and shorter than previous 4 and 6 pi pulse methods.

Neuron-specific enolase (NSE) and non-neuronal enolase (NNE) mRNAs are co-expressed in neurons of the rat cerebellum: in situ hybridization histochemistry

Using in situ hybridization histochemistry, we analysed the localization of mRNAs for neuron-specific enolase (NSE) and non-neuronal enolase (NNE) in the rat cerebellum at various postnatal developmental stages. Synthetic 45 meric oligonucleotides corresponding to partial sequences of the non-coding region of rat NSE or NNE mRNA were 35S-labeled to approximately the same specific activity and used as hybridization probes. On examination of the adult rat cerebellum, both NSE and NNE signals were detected in all identified and presumed neurons which included Purkinje cells, internal granule cells and presumed stellate/basket cells in the cerebellar cortex and neurons of the dentate nucleus. Examination of the cerebellum during postnatal development also revealed coexistence of NSE and NNE signals in these neurons from early stages. During development, both signals coincidentally increased in Purkinje cells and neurons of the dentate nucleus, while only NSE signals showed a gradual increase in the internal granule cells in which NNE signals remained at the same level from early postnatal to adult stages. The external granule cells showed NNE signals until postnatal day 7 but thereafter the signals became less distinct, especially in cells if the inner zone of the external granule cell layer. Thus, it was shown that NSE and NNE were commonly coexpressed at the mRNA level in various neurons of the cerebellum except for very undifferentiated external granule cells which expressed only NNE mRNA.

Risk area and infarct area relations in the hypertensive stroke-prone rat

BACKGROUND AND PURPOSE

Our purpose was to characterize the surface area of the infarct and the surface area at risk of infarction as defined spatially by arterial anastomoses to determine whether position, size, or shape of the infarct and the area at risk were related in stroke-prone rats or hybrid rats.

METHODS

Stroke-prone rats (n = 18; mean +/- SEM blood pressure, 182 +/- 8 mm Hg) and hybrid rats (n = 18; mean +/- SEM blood pressure, 147 +/- 6 mm Hg; p < 0.05) were anesthetized and the left middle cerebral artery was occluded with a ligature. The rats were killed 7 days later, arterial anastomoses were made visible with latex, the brains were fixed in formalin, and film recorded the infarct and anastomoses. Anastomoses and infarcts were digitized for measurements of risk area, luminal width, and infarct area.

RESULTS

Mean risk area was similar in size, length, width, and variability in stroke-prone rats (area, 85 +/- 5 mm2) and hybrid rats (area, 84 +/- 7 mm2; p > 0.05), whereas mean infarct area was larger, longer, wider, and less variable in stroke-prone rats (area, 53 +/- 6 mm2) than in hybrid rats (area, 15 +/- 11 mm2; p < 0.05). Infarct length was appreciably greater than infarct width in both groups, indicating that infarct shape was not amorphous. Spatial overlap maps indicated that the infarct area common to all stroke-prone rats was positioned centrally in the risk area and was surrounded by a variable infarct area, which indicated that the likelihood of infarction increased with distance from the anastomoses. Shape factors for both risk area and infarct area were significantly different within each rat group, which indicated that infarct shape did not uniformly parallel the anastomotic sites that determined risk area shape (p < 0.05). Risk area anastomoses and border zone width were linearly correlated in size and both were significantly wider in hybrid rats than in stroke-prone rats (p < 0.05), which suggests that the narrower border zone tissue was perfused by narrower anastomoses.

CONCLUSIONS

We conclude that the position of the infarct within the risk area relates to luminal widths of conterminous anastomoses that define the risk area, but not to the size or shape of the area at risk of infarction defined spatially by the anastomoses.

Identification algorithm for systemic arterial parameters with application to total artificial heart control

A new algorithm for estimating systemic arterial parameters from systolic pressure and flow measurements at the root of the aorta is developed and tested through a systems identification approach. The resulting procedure has direct application to a total artificial heart (TAH) control system currently under development. Identification models, representing the systemic arterial system, are developed from existing work in the area of cardiovascular modeling. The resistive and compliance components of these models are physically significant, representing overall hydraulic properties of the systemic arterial system. A unique method of parameterizing the identification models is designed which operates on the basis of aortic pressure and flow measurements taken exclusively during systole. The estimator is a modified recursive least squares algorithm which utilizes covariance modification to track time-varying parameters and a dead-zone to improve the robustness. Performance of the estimation algorithm was tested on data generated by a higher-order distributed model of the systemic arterial bed using normal canine parameters. Results from model-to-model experiments verify the consistency of the estimates and the ability of the estimator to converge quickly and track dynamically varying parameters.

Comparison of methods for generation of absolute reflectance-factor values for bidirectional reflectance-distribution function studies

Currently, spectrophotometric standard reference materials are calibrated only by using the illumination and viewing geometries recommended by the Commission Internationale de l'Eclairage, and for some geometries the spectral range is limited to the visible wavelengths. A need exists for procedures that calibrate standards at many other geometries and for a broader spectral range. Two methods for calibrating the spectral bidirectional reflectance factor are described. The absolute bidirectional reflectance factor of a sintered polytetrafluoroethylene (PTFE) sample is determined for nearly all the possible illumination and viewing geometries from 400 nm to 2500 nm. The references are a 45/0 reflectance standard calibrated by the National Institute of Standards and Technology and a sintered PTFE sample with a directional, hemispherical reflectance factor traceable to the Institute. The results of the two methods agree to within 0.01 in reflectance factor values. With this PTFE sample as a transfer standard, the instrument described can also be used to measure the absolute bidirectional reflectance factor at nearly all the illumination and viewing geometries from 400 nm to 2500 nm.

Spatial features of focal infarction after hydralazine treatment in stroke-prone spontaneously hypertensive rats

BACKGROUND AND PURPOSE

Rapid occlusion of the middle cerebral artery above the rhinal fissure produces a large ischemic infarct in hypertensive rats, but this occlusion results in a minimal lesion in young normotensive rats. Our purpose was to attenuate rising blood pressure in young stroke-prone spontaneously hypertensive rats with hydralazine before the occlusion to determine if the gross infarct volume is smaller, and if it is, to determine whether length, width, depth, or surface area of the infarct changes, which could suggest a mechanism of protection.

METHODS

Untreated rats (n = 6) and rats receiving hydralazine for 1.5 (n = 6) or 5 (n = 5) weeks were anesthetized, and the middle cerebral artery was rapidly occluded with a ligature. One day later the rats were killed and the brains were fixed in formalin. Fine-grain-release film that is sensitive to spectral properties of the infarct was used to photograph the tissue. Infarcted areas were traced on paper and then digitized for measurements and computations with a microcomputer.

RESULTS

Compared with untreated rats, tail systolic blood pressure (120 +/- 3 versus 138 +/- 4 mm Hg), infarct volume (61 +/- 4 versus 93 +/- 6 mm3), infarct surface area (39 +/- 1 versus 54 +/- 2 mm2), infarct width (3.8 +/- 0.1 versus 4.8 +/- 0.2 mm), and infarct length (6.0 +/- 0.3 versus 8.1 +/- 0.3 mm) were less in rats receiving hydralazine for 5 weeks (p < 0.05). No change was detected in infarct depth.

CONCLUSIONS

Treatment of young stroke-prone spontaneously hypertensive rats with hydralazine for 5 weeks before middle cerebral artery occlusion results in a smaller infarct. The narrower, shorter dimensions indicate increased protection against lateral enlargement of the infarct and the possibility that protection was due to increased collateral blood flow through modified blood vessels.

Simple technique for determining substrate indices of isotropic materials by a multisheet Brewster angle measurement

When an H-polarized light is incident upon a substrate at the Brewster angle, the reflected light becomes zero. Stacking many identical substrates together forms a multisheet structure. The valley of this reflected intensity pattern centered at the Brewster angle becomes narrower owing to the overlap of these similar reflections from many parallel interfaces of air and substrates. Therefore measuring the Brewster angle of this multisheet structure leads to an accurate determination of the substrate index, which is up to the third decimal place (0.00075).

Isolation of a DNA endonuclease complex in XPD cells which is defective in ability to incise nucleosomal DNA containing pyrimidine dimers

A DNA endonuclease complex which recognizes predominantly pyrimidine dimers in UVC irradiated DNA has been isolated from the chromatin of normal human and xeroderma pigmentosum, complementation group D (XPD) lymphoblastoid cells. The activity of the normal complex on UVC irradiated DNA was increased approximately 2.5 and 1.5 fold over activity on damaged naked DNA, when core (histones H2A, H2B, H3, H4) and total (core+histone H1) nucleosomal DNA, respectively, was used. In contrast, the XPD complex showed no increase in activity on UVC irradiated total and only a 1.4 fold increase on UVC irradiated core nucleosomal DNA, indicating that the XPD complex is defective in its ability to incise UVC irradiated nucleosomal DNA. The normal complex was able to correct this defect in the XPD complex at the nucleosomal level.

Assessment of the molluscicidal activities of Tribromosalan, Cartap and Chlorothalonil against Oncomelania hupensis

Molluscicidal activities of Tribromosalan, Cartap and Chlorothalonil were evaluated in the laboratory and the field against Oncomelania hupensis, the intermediate host of Schistosoma japonicum in China. The three chemicals were very effective against O. hupensis in the laboratory. The molluscicidal activities found in the field trials suggest that Tribromosalan and Cartap may be used as practical molluscicides. Dosage of 10 g/m2 of Tribromosalan in spring only and 20 g/m2 of Cartap in both spring and autumn would be recommendable as practical mollusciciding doses for the control of O. hupensis.

High-Level Nuclear-Waste Borosilicate Glass: A Compendium of Characteristics

With the imminent startup, in the United States, of facilities for vitrification of high-level nuclear waste, a document has been prepared that compiles the scientific basis for understanding the alteration of the waste glass products under the range of service conditions to which they may be exposed during storage, transportation, and eventual geologic disposal. A summary of selected parts of the content of this document is provided.

Waste glass alterations in a geologic repository may include corrosion of the glass network due to groundwater and/or water vapor contact. Experimental testing results are described and interpreted in terms of the underlying chemical reactions and physical processes involved. The status of mechanistic modeling, which can be used for long-term predictions, is described and the remaining uncertainties associated with long-term simulations are summarized.

[The natural variance of transient myocardial ischemia in coronary artery patients]

Sixty patients of CAD were studied with 24 and 48 hours ambulatory electrocardiogram monitoring. The day-to-day natural variances of transient myocardial ischemia in this group were analysed. The ranges of variation of myocardial ischemia based on a 95% confidence interval were confirmed. The results showed that the day-to-day variances of ischemia between the different days were: (1) 43% in number of ischemia episodes, (2) 76% in duration, (3) 53% in integration, and (4) 48% in maximal degree of ST depression.

[Studies on the identification of mineral medicine wumingyi]

In the paper the morphological characters, physical properties and spectral analyses(IR,AES) of seven samples collected from different regions are investigated by means of comparison with reference standard pyrolusite. The result indicates that the domestic commercial traditional medicine Wumingyi is practically limonite, therefore further investigations should be made to find out the correct mineral sources.

Resibufogenin-induced delayed afterdepolarization in rabbit heart in situ

The pharmacological effects of resibufogenin (RGB), an effective cardiotonic obtained from a famous traditional Chinese medicine, on the electrical activity of the rabbit heart (n = 12) in situ were studied by using a new technique of recording monophasic action potential (MAP). RBG (0.3 mg/kg IV) induced DAD in 3/12 animals. DAD appeared within the first 0.5 to 1 min after RBG and lasted about 20-30 min. The position of DAD was in the end of phase 3 of MAP. The DADs of rabbit epicardium showed a transient, regular and phasic depolarization process. The triggered arrhythmias were not recorded in these experiments, as amplitudes of DAD were lower and did not reach the threshold. The results indicate that DADs are induced by RBG at first time in situ in rabbits. The characteristics of DAD were similar to those previously described in single cardiac fibers in vitro.

Intestinal metabolism of nitrosamines. 1. Transport and metabolism of six nitrosamines in isolated perfused rat small intestinal segments

Possible relationships between structure and metabolism of nitrosamines have been investigated in the rat small intestine. Isolated segments of jejunum and ileum were perfused from the luminal side for 2 h with a Tyrode solution containing one of four symmetrical dialkylnitrosamines with 2-5 carbon atoms per side chain, all 14C-labeled at the alpha position, or one of two unsymmetrical nitrosamines, N-nitroso-tert-butylmethylamine and N-nitrosomethylbenzylamine, 14C-labeled in the methyl group. Besides measurement of 14CO2 production and covalent binding of 14C to intestinal tissue, the absorbed fluid (absorbate) as well as the perfusion medium and tissue homogenates were analysed by h.p.l.c. for the presence of polar metabolites to assess the intestinal metabolism of nitrosamines. Neither N-nitrosodiethylamine nor the two unsymmetrical nitrosamines were metabolized to any significant extent. With increasing chain length of symmetrical dialkylnitrosamines small intestinal metabolism increased dramatically. At a concentration of 1 microM up to 60% and 30% of N-nitrosodipropylamine (NDPA) in jejunal and ileal segments, respectively, and greater than 90% of N-nitrosodibutylamine (NDBA) and N-nitrosodipentylamine (NDAA) in both intestinal segments were metabolized during absorption. Metabolites were found also in perfusate and tissue homogenate but generally at lower percentages as compared with the absorbate. With increasing concentrations the percentage of metabolites decreased, the decrease being more pronounced in ileal as compared with jejunal segments. CO2 production and covalent binding were negligible in ileal segments but amounted up to 5-8% and 0.1-0.4% of the dose in jejunal segments perfused with NDPA, NDBA or NDAA. With NDBA and NDAA no concentration-dependent decrease could be observed, the highest amounts of 14CO2 and bound 14C being found at intermediate concentrations. At concentrations below 10 microM metabolic pathways other than alpha-hydroxylation seem to be of greater importance. The toxicological evaluation of the high intestinal first-pass metabolism of NDPA, NDBA and NDAA must await the identification and quantitation of the metabolites formed.