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1.
The intranuclear binding of radioactive 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rat liver has been studied both in vivo and in vitro. Following the intravenous administration of [1,6-3H]TCDD, a maximum uptake by cell nuclei could be observed at 2 h after injection with a concurrent decrease in the cytosolic uptake. Using linear sucrose density gradient centrifugation, dextran-coated charcoal adsorption assay, DEAE-Sepharose ion-exchange chromatography, competition, enzymatic and saturation studies, a high-affinity binding protein for TCDD in liver cell nuclei could be demonstrated both in vivo and after an exchange in vitro of intravenously administered unlabelled 2,3,7,8- tetrachlorodibenzofuran (TCDBF) for [3H]TCDD. Sucrose density gradient analysis showed a size of 4–5 S for both the cytosolic and nuclear TCDD binding entity. The specific binding of [3H]TCDD to nuclear components was heat labile and saturable and had an equilibrium dissociation constant of 1.05 nM. Based on a differential susceptibility to specific hydrolases, i.e. DNAase, RNAase, trypsin and pronase, the binding entity appears to be a 4–5 S salt-extractable protein.  相似文献   

2.
Positive liposomes consisting of phosphatidylcholine, cholesterol and stearylamine and negatively charged liposomes consisting of phosphatidylcholine, cholesterol and phosphatidylserine, were double labelled with either 3H-labelled dipalmitoyl phosphatidylcholine and [14C]cholesterol or with [14C]cholesterol and [3H]methotrexate entrapped in the aqueous phase. The plasma levels and urinary excretion of radioactivity from sonicated and non-sonicated liposomes were then compared with the levels of radioactivity from free [3H]methotrexate during a 4 h experimental period after an initial intravenous injection in cynomolgous monkeys. Tissue uptake at the completion of the 4 h experimental period was also measured.It was found that plasma radioactivity from [3H]methotrexate and [14C]cholesterol in sonicated positive liposomes was cleared more slowly than from comparable non-sonicated liposomes, and considerably slower than from free [3H]methotrexate. Radioactivity from sonicated negative liposomes was cleared more rapidly than from positive sonicated liposomes. Positive liposomes captured considerably more [3H]methotrexate than negative liposomes and showed very low permeability to [3H]methotrexate in in vitro studies, even in the presence of high concentrations of serum.[14C]Cholesterol radioactivity was cleared more rapidly from plasma than 3H-radioactivity from liposome-entrapped [3H]methotrexate for double-labelled sonicated liposomes and generally showed greater uptake into tissues and red blood cells. 3H-labelled dipalmitoyl phosphatidylcholine in sonicated positive liposomes was cleared faster than [14C]cholesterol during the first 3 h. The more rapid disappearance of [14C]cholesterol from the plasma was complemented by greater uptake into a number of tissues, and positive non-sonicated liposomes were taken up to a greater extent by the spleen than equivalent sonicated liposomes.Renal excretion of 3H from liposome-entrapped [3H]methotrexate was considerably less than that of 3H from free [3H]methotrexate. There was insignificant excretion, however, of 14C from cholesterol in the urine.Entrapment in liposomes completely prevented the otherwise considerable breakdown of free methotrexate to 3H-containing products in plasma and partially prevented its breakdown in tissues.These studies indicate marked differences in the distribution of liposomes in vivo due to surface charge and size, and some degree of exchange of the lipid components of the liposome bilayer independent of the distribution of the entrapped species. They also show that entrapment in liposomes can reduce metabolic degradation of a drug, maintain high plasma levels and reduce its renal excretion.  相似文献   

3.
Intralipid was sonicated with [3H]cholesteryl linoleyl ether (a nonhydrolyzable analog of cholesteryl linoleate) and incubated with rat HDL and d greater than 1.21 fraction of rabbit serum at a ratio of 0.012 mg triacylglycerol to 1 mg HDL protein. 25% of [3H]cholesteryl linoleyl ether was transferred to HDL. The labeled HDL was injected into donor rats and was screened for 4 h. [125I]HDL was subjected to the same protocol as the 3H-labeled HDL, including screening. The screened, labeled sera were injected into acceptor rats and the disappearance of radioactivity from the circulation was compared. The t1/2 in the circulation of [125I]HDL was about 10.5 h, while that of [3H]cholesteryl linoleyl ether-HDL was about 8 h. The liver and carcass were the major sites of uptake of [3H]cholesteryl linoleyl ether-HDL and accounted for 29-41% (liver) and 30% (carcass) of the injected label. Maximal recovery of [3H]cholesteryl linoleyl ether in the liver was seen 48 h after injection, and thereafter there was a progressive decline of radioactivity, which reached 7.8% after 28 days. The maximal recovery of [125I]HDL in the liver was about 9%. Pretreatment of the acceptor rats with estradiol for 5 days resulted in a 20% increase in the hepatic uptake of [3H]cholesteryl linoleyl ether-HDL and a 5-fold increase in adrenal uptake. The present findings indicate that in the rat the liver is the major site of uptake of HDL cholesteryl ester and that part of the HDL cholesteryl ester may be cleared from the circulation separately from the protein moiety. On the basis of our previous findings (Stein, Y., Kleinman Y, Halperin, G., and Stein, O. (1983) Biochim. Biophys. Acta 750, 300-305) the loss of the [3H]cholesteryl linoleyl ether from the liver after 14-28 days was interpreted to indicate that the labeled [3H]cholesteryl linoleyl ether had been taken up by hepatocytes.  相似文献   

4.
Following the intravenous injection of nanomolar amounts of [3H]dolichol into rats, the radioactivity rapidly appeared in the high-density lipoprotein fraction of the plasma and circulated with a half-life of about 9 h. A fraction of the injected activity was excreted in the feces, presumably through the bile, but evidence was obtained that little oxidative breakdown of dolichol occurred. All tissues assayed acquired radioactivity, but the liver attained the highest specific activity and the largest percentage of the total radioactive dolichol. Subcellular fractionation of the liver revealed that mitochondrial preparations contained the bulk of the labeled dolichol at all times tested up to 40 h after injection. Disruption of the mitochondrial structure by two different techniques permitted the isolation of inner and outer membrane fractions and it was found that the [3H]dolichol was concentrated in the outer membrane fraction. The significance of these findings is discussed.  相似文献   

5.
Positive liposomes consisting of phosphatidylcholine, cholesterol and stearylamine and negatively charged liposomes consisting of phosphatidylcholine, cholesterol and phosphatidylserine, were double labelled with either 3H-labelled dipalmitoyl phosphatidylcholine and [14C]cholesterol or with [14C]cholesterol and [3H]methotrexate entrapped in the aqueous phase. The plasma levels and urinary excretion of radioactivity from sonicated and non-sonicated liposomes were then compared with the levels of radioactivity from free [3H]methotrexate during a 4 h experimental period after an initial intravenous injection in cynomolgous monkeys. Tissue uptake at the completion of the 4 h experimental period was also measured.It was found that plasma radioactivity from [3H]methotrexate and [14C]cholesterol in sonicated positive liposomes was cleared more slowly than from comparable non-sonicated liposomes, and considerably slower than from free [3H]methotrexate. Radioactivity from sonicated negative liposomes was cleared more rapidly than from positive sonicated liposomes. Positive liposomes captured considerably more [3H]methotrexate than negative liposomes and showed very low permeability to [3H]methotrexate in in vitro studies, even in the presence of high concentrations of serum.[14C]Cholesterol radioactivity was cleared more rapidly from plasma than 3H-radioactivity from liposome-entrapped [3H]methotrexate for double-labelled sonicated liposomes and generally showed greater uptake into tissues and red blood cells. 3H-labelled dipalmitoyl phosphatidylcholine in sonicated positive liposomes was cleared faster than [14C]cholesterol during the first 3 h. The more rapid disappearance of [14C]cholesterol from the plasma was complemented by greater uptake into a number of tissues, and positive non-sonicated liposomes were taken up to a greater extent by the spleen than equivalent sonicated liposomes.Renal excretion of 3H from liposome-entrapped [3H]methotrexate was considerably less than that of 3H from free [3H]methotrexate. There was insignificant excretion, however, of 14C from cholesterol in the urine.Entrapment in liposomes completely prevented the otherwise considerable breakdown of free methotrexate to 3H-containing products in plasma and partially prevented its breakdown in tissues.These studies indicate marked differences in the distribution of liposomes in vivo due to surface charge and size, and some degree of exchange of the lipid components of the liposome bilayer independent of the distribution of the entrapped species. They also show that entrapment in liposomes can reduce metabolic degradation of a drug, maintain high plasma levels and reduce its renal excretion.  相似文献   

6.
125I-labeled albumin or poly(vinyl pyrrolidone) encapsulated in intermediate size multilamellar or unilamellar liposomes with 30–40% of cholesterol were injected intravenously into rats. In other experiments liposomes containing phosphatidyl[Me-14C]choline were injected. 1 h after injection parenchymal or non-parenchymal cells were isolated. Non-parenchymal cells were separated by elutriation centrifugation into a Kupffer cell fraction and an endothelial cell fraction. From the measurements of radioactivities in the various cell fractions it was concluded that the liposomes are almost exclusively taken up by the Kupffer cells. Endothelial cells did not contribute at all and hepatocytes only to a very low extent to total hepatic uptake of the 125I-labels. Of the 14C-label, which orginates from the phosphatidylcholine moiety of the liposomes, much larger proportions were recovered in the hepatocytes. A time-dependence study suggested that besides the involvement of phosphatidylcholine exchange between liposomes and high density lipoprotein, a process of intercellular transfer of lipid label from Kupffer cells to the hepatocytes may be involved in this phenomenon. Lanthanum or gadolinium salts, which effectively block Kupffer cell activity, failed to accomplish an increase in the fraction of liposomal material recovered in the parenchymal cells. This is compatible with the notion that liposomes of the type used in these experiments have no, or at most very limited, access to the liver parenchyma following their intravenous administration to rats.  相似文献   

7.
—The urinary excretion of labelled metabolites was measured in dogs which had been injected intravenously or intraventricularly with [3H]norepinephrine or [14C]dopamine. [3H]Norepinephrine injected by either route produced more labelled 3-methoxy-4-hydroxy-phenylglycol than 3-methoxy-4-hydroxymandelic acid, as did [14C]dopamine after intravenous administration. In contrast, following the intraventricular injection of [14C]dopamine, more [14C]3-methoxy-4-hydroxymandelic acid was formed than [14C]3-methoxy-4-hydroxyphenylglycol. These observations suggest that the metabolism of exogenously-administered and endogenously-formed norepinephrine may proceed through different routes and that the predominant metabolite of norepinephrine in canine brain may be 3-methoxy-4-hydroxymandelic acid rather than 3-methoxy-4-hydroxyphenylglycol.  相似文献   

8.
Incorporation of 8 mol% lactosylceramide in small unilamellar vesicles consisting of cholesterol, dimyristoylphosphatidylcholine and phosphatidylserine in a molar ratio of 5:4:1 and containing [3H]inulin as an aqueous-space marker resulted in a 3-fold decreased half-life of the vesicles in blood and a corresponding increase in liver uptake after intracardial injection into rats. The increase in liver uptake was mostly accounted for by an enhanced uptake in the parenchymal cells, while the uptake by the non-parenchymal cells was only slightly increased. The uptake of both the control and the glycolipid-containing vesicles by the non-parenchymal cell fraction could be attributed completely to the Kupffer cells; no radioactivity was found in the endothelial cells. The effect of lactosylceramide on liver uptake and blood disappearance of the liposomes was effectively counteracted by desialylated fetuin, injected shortly before the liposome dose. This observation supports the notion that a galactose-specific receptor is involved in the liver uptake of lactosylceramide liposomes.  相似文献   

9.
In the present study the tissue distribution of [3H]methotrexate was studied after intravenous injection of [3H]methotrexate-containing liposomes in normal and macrophage-depleted mice. Elimination of macrophages was performed by treatment with dichloromethylene diphosphonate- (DMDP)-containing liposomes. After thorough elimination of the macrophages from spleen and liver, by two intravenous injections of DMDP liposomes 6 and 4 days before tissue distribution studies, we found dramatic changes in the localization pattern of [3H]methotrexate liposomes in the blood, due to a decreased uptake of [3H]methotrexate liposomes by the DMDP liposome-treated liver. Because of the absence of these macrophages that are able to clear the blood of liposomes, and because of the resulting higher blood level of liposomes, we found an enhanced uptake of [3H]methotrexate liposomes by the spleen. It may be concluded that, in the spleen, apart from uptake of liposomes by macrophages, at least one other mechanism is responsible for the clearance of liposomes from the circulation. When comparing cholesterol-rich with cholesterol-poor liposomes, we found basically the same results, although uptake of cholesterol-rich liposomes by macrophages was smaller than that of cholesterol-poor liposomes, as found in several other studies. We suggest that pretreatment with DMDP liposomes can help to maintain a high level of intravenous-injected liposome-entrapped material in the blood, which otherwise would be removed by macrophages.  相似文献   

10.
Rats were given intravenous injections of 125I-labelled human α2-macroglobulin·trypsin. The half-time of disappearance of radioactivity from arterial blood was 2 min. External counting showed that radioactivity in the liver was maximal by 10 min and then decreased slowly. 87% of the injected dose was recovered in the liver by 10 min. Light- and electron microscopic autoradiography carried out on samples of liver fixed with glutaraldehyde 3 min or 30 min after the injection showed that 85–90% of the grains were over the hepatocytes and 4–9% were over the Kupffer cells. Thus, uptake into hepatocytes, and not into Kupffer cells as believed previously, appears to account for the major part of the uptake of α2-macroglobulin·trypsin by the liver and thereby for its rapid removal from the blood.  相似文献   

11.

Background

Phosphatidylcholine (PC) is the predominant phospholipid associated with high density lipoproteins (HDL). Although the hepatic uptake of cholesteryl esters from HDL is well characterized, much less is known about the fate of PC associated with HDL. Thus, we investigated the uptake and subsequent metabolism of HDL-PC in primary mouse hepatocytes.

Methods and results

The absence of scavenger receptor-BI resulted in a 30% decrease in cellular incorporation of [3H]PC whereas [3H]cholesteryl ether uptake was almost completely abolished. Although endocytosis is not involved in the uptake of cholesteryl esters from HDL, we demonstrate that HDL internalization accounts for 40% of HDL-PC uptake. Extracellular remodeling of HDL by secretory phospholipase A2 significantly enhances HDL lipid uptake. HDL-PC taken up by hepatocytes is partially converted to triacylglycerols via PC-phospholipase C-mediated hydrolysis of PC and incorporation of diacylglycerol into triacylglcyerol. The formation of triacylglcerol is independent of scavenger receptor-BI and occurs in extralysosomal compartments.

Conclusions and general significance

These findings indicate that HDL-associated PC is incorporated into primary hepatocytes via a pathway that differs significantly from that of HDL-cholesteryl ester, and shows that HDL-PC is more than a framework molecule, as evidenced by its partial conversion to hepatic triacylglycerol.  相似文献   

12.
Human plasma α1-antitrypsin (α1-AT) was labeled with either 3H [3H-labeled NANA (N-acetyl-neuraminic acid)-7] residues in the carbohydrate moiety) or 14C (?-N-methyl-[14C]lysyl residues in the protein backbone) or with both isotopes in the corresponding residues. After intravenous injection into rats of the doubly labeled partially (50%) desialylated (methyl-[14C]·[3H]NANA-7)-α1-AT, the rates of disappearance from the plasma of both isotopes were very rapid and yielded essentially the same circulatory half-life of 5 min. The rapid disappearance of the doubly labeled glycoprotein from the plasma was accompanied by concomitant fast and equal accumulations of 14C and 3H in the liver which constituted about 70% of the administered dose 15 min after the injection. The asialo (methyl-[14C])-α1-AT·trypsin complex or methyl-[14C]-α1-AT·trypsin complex had a plasma survival time (45 min) that was intermediate between methyl-[14C]-α1-AT and its desialylated derivative. These complexes were removed from the plasma by the liver (45% of the injected dose 60 min after injection), although not as rapidly as asialo (methyl-[14C])-α1-AT. Blockade of the reticuloendothelial (Kupffer) cells by simultaneous injection of heat-denatured albumin inhibited the liver uptake of the inhibitor·trypsin complexes but not that of the uncomplexed asialo α1-AT. Radioactive ?-N,N-dimethyllysine, ?-N-monomethyllysine, methionine, choline, and betaine were separated and identified from the trichloro-acetic acid-soluble fraction of rat livers 25 min after injection of asialo (methyl-[14C])-α1-AT.  相似文献   

13.
In the present study the tissue distribution of [3H]methotrexate was studied after intravenous injection of [3H]methotrexate-containing liposomes in normal and macrophage-depleted mice. Elimination of macrophages was performed by treatment with dichloromethylene diphosphonate- (DMDP)-containing liposomes. After thorough elimination of the macrophages from spleen and liver, by two intravenous injections of DMDP liposomes 6 and 4 days before tissue distribution studies, we found dramatic changes in the localization pattern of [3H]methotrexate liposomes in the blood, due to a decreased uptake of [3H]methotrexate liposomes by the DMDP liposome-treated liver. Because of the absence of these macrophages that are able to clear the blood of liposomes, and because of the resulting higher blood level of liposomes, we found an enhanced uptake of [3H]methotrexate liposomes by the spleen. It may be concluded that, in the spleen, apart from uptake of liposomes by macrophages, at least one other mechanism is responsible for the clearance of liposomes from the circulation. When comparing cholesterol-rich with cholesterol-poor liposomes, we found basically the same results, although uptake of cholesterol-rich liposomes by macrophages was smaller than that of cholesterol-poor liposomes, as found in several other studies. We suggest that pretreatment with DMDP liposomes can help to maintain a high level of intravenous-injected liposome-entrapped material in the blood, which otherwise would be removed by macrophages.  相似文献   

14.
The disappearance of [8-3H]-adenosine 3′,5′-monophosphate (cAMP) from plasma of the intact rat has been investigated. Thirty minutes after the i.v. injection of a pulse of [3H] cAMP with 3 μmole cAMP into 300–400 g rats, more than 99% of the isotope had been removed from the plasma. The disappearance of isotope from the plasma was retarded by probenecid (20–200 mg/kg body weight), bilateral nephrectomy and bilateral nephrectomy plus hepatectomy, in increasing order of their effectiveness. Ligation of both ureters did not alter the rate of isotope disappearance. After the pulse injection, the amount of isotope in the plasma and tissues was determined and the ratio, cpm per g wet tissue/cpm per ml plasma, was calculated. Kidney cortex, kidney inner medulla and liver showed the most striking accumulations of isotope with ratios of 250, 19 and 18, respectively. Probenecid produced a dose-dependent reduction in the accumulation of isotope in kidney cortex and liver. Other tissues which showed some, albeit small, accumulation of isotope were heart (2.0), lung (2.9) and small intestine (1.6). From the accumulation of isotope in the various tissues it was estimated that the kidney cortex accounted for 39%, liver 15%, and urinary excretion 5% of the injected dose of isotope in the untreated rat. It is concluded that in the rat, at least, the kidney cortex is the principal tissue involved in cAMP removal (and degradation) from the plasma.  相似文献   

15.
The mechanisms of HDL-mediated cholesterol transport from peripheral tissues to the liver are incompletely defined. Here the function of scavenger receptor cluster of differentiation 36 (CD36) for HDL uptake by the liver was investigated. CD36 knockout (KO) mice, which were the model, have a 37% increase (P = 0.008) of plasma HDL cholesterol compared with wild-type (WT) littermates. To explore the mechanism of this increase, HDL metabolism was investigated with HDL radiolabeled in the apolipoprotein (125I) and cholesteryl ester (CE, [3H]) moiety. Liver uptake of [3H] and 125I from HDL decreased in CD36 KO mice and the difference, i. e. hepatic selective CE uptake ([3H]125I), declined (–33%, P = 0.0003) in CD36 KO compared with WT mice. Hepatic HDL holo-particle uptake (125I) decreased (–29%, P = 0.0038) in CD36 KO mice. In vitro, uptake of 125I-/[3H]HDL by primary liver cells from WT or CD36 KO mice revealed a diminished HDL uptake in CD36-deficient hepatocytes. Adenovirus-mediated expression of CD36 in cells induced an increase in selective CE uptake from HDL and a stimulation of holo-particle internalization. In conclusion, CD36 plays a role in HDL uptake in mice and by cultured cells. A physiologic function of CD36 in HDL metabolism in vivo is suggested.  相似文献   

16.
The sites of tissue uptake of human lipoprotein(a) (Lp(a] were studied in rats using [3H]cholesteryl linoleyl ether [( 3H]CLE) as a marker. Since rat plasma has no cholesteryl ester transfer activity, the amount of label in various tissues should reflect the quantitative uptake of Lp(a). Isolated Lp(a) was labeled with [3H]CLE by incubation overnight of Lp(a), a source of cholesteryl ester transfer activity (1.23 g/ml infranate of human plasma), and [3H]CLE-labeled Intralipid. Following labeling, the homogeneity and integrity of Lp(a) was shown by agarose electrophoresis and immunoblotting. Intact Lp(a) was injected via the tail vein of rats (120-170 g, n = 4 at each time point), and tissues were collected at various times thereafter (4-48 h). The disappearance curve of [3H]CLE-labeled Lp(a) from rat plasma was bimodal and had an initial rapid t1/2 of 1.8 h followed by a slower component, t1/2 = 13.3 h. Tissue uptake at all sampling times was greatest in liver (28.5% at 48 h of total dpm injected), followed by the intestine (9-12%), with less than 3% uptake by spleen. The small intestine was divided into four segments, and while the 3H radioactivity was similar in the proximal segments, a time-related increase in [3H]CLE was seen in its most distal portion. These studies indicate that the tissue sites of degradation in the rat of human Lp(a) are similar to human low-density lipoproteins (LDL); the increase in label in the distal portion of the small intestine with time may represent [3H]CLE excreted through the bile and absorbed by the mucosal cells.  相似文献   

17.
Abstract— A new procedure is described for the estimation of [3H]noradrenaline (NA) and its major metabolites free and conjugated 3-methoxy-4-hydroxyphenylglycol (MOPEG) and free and conjugated 3,4-dihydroxyphenylglycol (DOPEGI in the rat brain. The procedure involves adsorption on to alumina, cation exchange chromatography. enzymatic hydrolysis of conjugates and thin-layer-chromatography after intraventricular (IVT) or intravenous injection of [3H]tyrosine. In a time-course study the formation and accumulation of the metabolites have been measured from 15min to 23h after IVT injection of [3H]tyrosine. [3H]MOPEG and [3H]DOPEG were found in almost equal amounts during the synthesis phase of [3H]NA as well as during the storage and disappearance phase of [3H]NA. The maximum levels of conjugated [3H]MOPEG and conjugated [3H]DOPEG were found 2 h after IVT [3H]tyrosine. At this time interval the levels of free [3H]MOPEG and free [3H]DOPEG amounted to 25% and 11%, respectively of the corresponding conjugates. Increasing doses of IVT injected [3H]tyrosine (10-90 °Ci) revealed that the accumulation of [3H]NA and metabolites was linear up to about 50 °Ci. Following intravenous instead of IVT injection of [3H]tyrosine. much higher doses (325 °Ci) were needed to obtain measurable amounts of total [3H]MOPEG and [3H]DOPEG-SO4 in the rat brain. The formation of labelled NA metabolites from [3H]NA in the rat brain in vim measured as total [3H]MOPEG and [3H]DOPEG-SO4 was influenced by drugs affecting [3H]NA synthesis, release and metabolism. Synthesis inhibition with a-methyltyrosine (250mg-kg?1) or FLA-63 (30mg-kg?1) and inhibition of monoamine oxidase with pargyline (75mg-kg?1) or clorgyline (2mg-kg?1) strongly decreased the accumulation of total [3H]MOPEG and [3H]DOPEG-SO4. Noradrenaline receptor blockade with phenoxybenzamine (20mg-kg?1) increased both total [3H]MOPEG and [3H]DOPEG-SO4 to about 160% of the control values. NA release and uptake inhibition induced by d-amphetamine (10mg-k?1) or phenylethylamine (two doses of 80mg-kg?1) decrease strongly the levels of [3H]NA and [3H]DOPEG-SO4. whereas total [3H]MOPEG was only very slightly decreased or even increased as compared to controls.  相似文献   

18.
Within 4 h after injection of [3H]ecdysone, almost all tritiated material has disappeared from the haemolymph, indicating that the uptake by the tissues is very fast. After only 15 min, 19% of the label was found in the ecdysterone fraction and 4% in the highly polar products (HPP) fraction. The uptake of [3H]ecdysone by the ovary (mid-vitellogenic) is almost complete within 1 h after injection. The pattern of [3H]ecdysteroids in the ovaries follows a well ordered sequence: firstly, [3H]ecdysone is the major component of the [3 H]ecdysteroids but it disappears within 2 h, next a peak value of [3H]ecdysterone was found at 1 h, whereafter this also disappeared, and from 2 h on, there was a considerable increase in HPP. The HPP consisted of 3 fractions (A, B and C). Glusulase treatment revealed that apparently only fraction B consisted of glucuronide and/or sulphate-conjugates of ecdysteroids. Autoradiographic experiments confirmed that the uptake of [3H]ecdysone was a very rapid process. In ovaries fixed 1 h after injection, the silver grains were abundant in the ooplasm but were also found in the follicle cell cytoplasm and in trophocytes. In follicles examined 16 h after injection, only a few silver grains were observed in the trophocytes and follicle cells. However, the cytoplasm of the oocyte was labelled. The border cells also accumulated label.

The major results indicate that all cell types of the follicle seem to be able to absorb ecdysone from the haemolymph and that there seems to be a rather selective uptake of ecdysone. In the ooplasm, ecdysone is converted to highly polar conjugates.  相似文献   

19.
Fluid endocytosis in rat liver parenchymal (hepatocytes) and non-parenchymal cells was studied by measuring uptake of [125I]polyvinylpyrrolidone (PVP). Radioactive sucrose preparations were also tested but turned out to be unsuitable because of impurities of radioactive glucose and fructose. Fluid endocytosis was temperature dependent without any transition temperature. The rate of endocytosis was inhibited by inhibitors of the glycolytic and the respiratory pathway. Colchicine, but not cytochalasin B, inhibited the uptake of [125I]PVP in hepatocytes. Therefore, intact microtubuli, but not microfilaments may be required for normal rate of fluid endocytosis in hepatocytes. Colchicine reduced the rate of fluid endocytosis in the non-parenchymal liver cells. Subcellular fractionation by isopycnic centrifugation in sucrose gradients indicated that [125I]PVP taken up by the hepatocytes accumulated in the lysosomes. The rate of uptake expressed as volume of fluid internalized per unit time (endocytic index) was calculated to 0.08 μl/h/106 cells for hepatocytes and 0.07 μl/h/106 cells for non-parenchymal liver cells.  相似文献   

20.
We have studied the hepatic uptake of human [14C] cholesteryl oleate labeled acetyl low density lipoprotein (LDL). Acetyl-LDL injected intravenously into rats was cleared from the blood with a half-life of about 10 min. About 80% of the injected acetyl-LDL was recovered in the liver after 1 h. Initially, most of the [14C]cholesterol was recovered in liver endothelial cells (about 60%). Some radioactivity (about 15%) was also recovered in the hepatocytes, while the Kupffer cells and stellate cells contained only small amounts of the label (less than 5%). About 1 h after injection, radioactivity started to disappear from endothelial cells and appeared instead in hepatocytes. Radioactivity subsequently declined in hepatocytes as well. After a lag phase of 4 h, significant amounts of radioactivity were recovered in bile. The in vitro uptake and hydrolysis of [14C]cholesteryl oleate-labeled acetyl-LDL were saturable in isolated rat liver endothelial cells. Native LDL does neither affect the uptake nor the hydrolysis of acetyl-LDL. Ammonia and monensin reduced the hydrolysis of acetyl-LDL in isolated liver endothelial cells. Furthermore, monensin at concentrations above 10 microM completely blocked the binding of acetyl-LDL to the liver endothelial cells, suggesting that the receptor for acetyl-LDL is trapped inside the cells. The liver endothelial cells may be involved in the protection against atherogenic lipoproteins, e.g. liver endothelial cells may mediate uptake of cholesterol from plasma and transfer of cholesterol to the hepatocytes for further secretion into the bile.  相似文献   

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