Our preceding studies reported using animal liver microsomes that 2, 2', 3, 4, 4', 5'-hexachlorobiphenyl (hexaCB) (CB138), a worldwide and persistent organohalogen pollutant, was metabolized to two major hydroxy (OH)-metabolites, 3'-OH-CB138 (M-3) and 2'-OH-2, 3, 3', 4, 4', 5'-hexaCB (M-4), and two dechlorinated OH-metabolites (M-1 and M-2) in guinea pigs at much faster rate than in rats and hamsters. In this study, the distribution of four CB138 metabolites to the serum and liver 4 days after exposure and their fecal excretion were studied in guinea pigs administered with CB138 intraperitoneally. 3'-OH-CB138 (M-3) was a major metabolite in the liver, serum and feces. M-1 was observed as a minor metabolite in guinea pig feces. In contrast, trace amount of M-2 was present in guinea pig serum. However, 2'-OH-2, 3, 4, 3', 4', 5'-hexaCB (M-4) which was a major metabolite in the in vitro system using guinea pig liver microsomes was not found in all tissues and feces tested in this study. On the other hand, the exact chemical structures of M-1 and M-2 were determined to be 6'-OH-2, 3, 3', 4, 4'-pentaCB and 4'-OH-2, 2', 3, 4, 5'-pentaCB, respectively, by comparison of the retention time and mass fragmentation of the synthetic authentic samples in GC-MS. From these results, it is suggested that the metabolism of CB138 in guinea pigs may proceed by three pathways, a direct hydroxylation at 3'-position, and also the formation of 2',3'- or 3', 4'-epoxide and subsequent dechlorination and that three metabolites show the different mode of distribution and excretion.
Summary 1. The acute effects of isatin, an endogenous monoamine oxidase (MAO) inhibitor, on norepinephrine (NE) and serotonin (5‐HT) concentrations in the brain of stroke‐prone spontaneously hypertensive rats (SHRSP) and Wistar‐Kyoto rats (WKY) were determined in order to elucidate its pathophysiological role. 2. Isatin was identified in purified extracts of SHRSP brain. 3. A single dose of isatin significantly increased NE concentration in the cerebral cortex of WKY. Isatin also significantly increased 5‐HT concentration in WKY brains. 4. After isatin administration NE and 5‐HT levels in the SHRSP brain did not differ from those in WKY. 5. These data suggest that isatin, an endogenous MAO inhibitor, presents in the SHRSP brain and maintains high blood pressure.
The in vitro metabolism of 2, 2', 3, 4', 5, 5'-hexachlorobiphenyl (hexaCB) (CB146) was examined using liver microsomes of rats, guinea pigs, hamsters and human. Untreated animal livers produced one metabolite (M-2) in rats, three metabolites (M-l, M-2and M-3) in guinea pigs and no metabolite in hamsters. Pretreatment of phenobarbital (PB) resulted in a marked increase of M-1 in three animals and of M-2in guinea pigs. In contrast, pretreatment of 3-methylcholanthrene showed a significant increase of M-3 in guinea pigs and a decrease of M-2in rats. Human liver microsomes prepared from nine Caucasians mainly formed M-2and M-3 at a ratio of 2: 1 and two individuals also formed one more metabolite M-1. The formation of M-1 was significantly correlated with CYP2B6 activity. By comparison of the GC-MS data of three metabolites with synthesized authentic samples, M-1 and M-2were determined to be 3'-hydroxy (OH)-CB146 and 4-OH-CB146, respectively. However, M-3 is unclear at present except the fact that it is OH-hexaCB. These results suggest that 3'-OH-CB146 is formed by PB-inducible cytochrome P450 (CYP2B enzymes) in animal and human livers and 4-OH-CB146 is a major metabolite in rat and human liver.
The toxic metals appear to use the transport pathways that exist for biologically essential metals. In this regard interactions between the toxic and essential metals are possible. This report summarizes recent findings on the transport of cadmium in rat hepatocytes and renal cortical epithelial cells in the presence or absence of certain essential metals. The transport of cadmium in hepatocytes does not require energy and, therefore, is not an active process. It occurs primarily (80%) by temperature-sensitive processes, i.e., ion channels and carriers, that involve interaction with sulfhydryl groups. These processes apparently exist for the transport of essential metals like copper, zinc and calcium. The remaining 20% of the cadmium in hepatocytes is transported via a temperature-insensitive process, possibly by diffusion. In comparison with the hepatocytes, a smaller fraction (30%) of the cadmium transport through the basolateral membrane and none from the apical membrane of the renal cortical epithelial cells is temperature-sensitive. Total accumulation through the basolateral membrane is about twice that through the apical membrane. A majority of the cadmium transport in the renal cells is by diffusion. As in hepatocytes, copper, zinc and mercury antagonize cadmium transport through the apical membranes of the renal cells. The relative antagonism by copper is the same (25%); however, the antagonism by zinc (16%) and mercury (10%) is 4- to 6-fold lower than in hepatocytes. It appears that the relative contribution of various transport pathways available for cadmium uptake is different in each cell type and apparently depends on the morphological and functional differences between the cell membranes.
Effects of zinc (Zn) and copper (Cu) on cadmium (Cd) accumulation were investigated in LLC-PK1 cells. Coincubation with Zn or Cu decreased Cd uptake by the cells in a concentration-dependent manner. Cd accumulation data suggested that Cd is taken up by the cells via simple diffusion and carrier-mediated transport. Zn and Cu significantly increased the Km of Cd uptake with no or little effect on the Vmax. Pretreatment of the cells with ouabain and a metabolic inhibitor (FCCP) significantly decreased Cd accumulation, and coincubation with Zn or Cu led to an additional decrease in Cd accumulation by these cells. Overall, it seems that, in addition to simple diffusion, Cd is also taken up by LLC-PK1 cells via carrier-mediated mechanisms that are competitively inhibited by Zn and Cu.
The reduction of plastoquinone by NADPH was detected as an increase in the dark level of Chi fluorescence in osmotically ruptured chloroplasts of spinach. This activity was observed only when the chloroplasts were ruptured in a medium containing a high concentration of MgCl2. The activity was suppressed by inhibitors of the respiratory NADH dehydrogenase (NDH) complex in mitochondria, capsaicin and amobarbital, suggesting that the activity was mediated by chloroplastic NDH complex. Antimycin A, an inhibitor of ferredoxin-quinone reductase (FQR), and the protonophore nigericin also inhibited the increase in Chi fluorescence by NADPH. By contrast, JV-ethylmaleimide (NEM), an inhibitor of ferredoxin-NADP+ reductase (FNR), did not suppress the fluorescence increase, showing that FNR is not involved in this reaction. When the osmotically ruptured chloroplasts were washed by centrifugation, a further addition of ferredoxin as well as NADPH was required for an increase in fluorescence. This ferredoxin-de-pendent activity also was suppressed by antimycin A, but only partly inhibited by capsaicin or amobarbital, suggesting that this is mediated mainly by FQR. These findings suggest that the NADPH-binding subunit of NDH complex is easily dissociated from the thylakoid membranes during the process of the washing the thylakoids by centrifugation.
The acetocarmine–Giemsa C-banding technique was used to study heterochromatin distribution in somatic chromosomes of diploid Elymus junceus (= Psathyrostachys juncea) (2n = 14) (genome designation Ju = N) and nine diploid Agropyron species (2n = 14): A. cristatum (C = P), A. imbricatum (C = P), A. elongatum (= Elytrigia elongata = Thinopyrum elongatum) (E = J), A. junceum (= E. bessarabicum = T. bessarabicum) (J = E), A. spicatum (= Pseudoroegneria spicata) (S), A. libanoticum (= P. libanotica) (S), A. ferganense (S), A. stipifolium (= P. stipifolia) (S), and A. velutinum (V). With the exception of A. elongatum and A. velutinum, which were self-fertile, all species were cross-pollinating and self-sterile. The cross-pollinating species showed large terminal C-bands and a high level of C-band polymorphism. Agropyron elongatum, moderately self-fertile, showed small terminal and interstitial bands and a minimal C-band polymorphism. Agropyron velutinum, fully self-fertile, almost totally lacked C-bands. The Ju, C, E, and J genomes appeared to be distinctive and the equivalence of the E and J genomes was not supported from their C-banding patterns. Four species sharing the S genome, A. spicatum, A. libanoticum, A. ferganense, and A. stipifolium had C-band patterns similar to one another, although C-bands were less prominent in A. stipifolium than others.Key words: C-banding, karyotype, wheatgrass, cytology.
