PubMed Health⌕ Search

Biomedical subjects

F Kuipers

Publications and source records attributed to F Kuipers.

At least 145 records · Page 8Linked to original sources
PubMed1987

Effect of infusion of "tris-galactosyl-cholesterol" on plasma cholesterol, clearance of lipoprotein cholesteryl esters, and biliary secretion in the rat.

As shown by us previously (van Berkel et al. 1985. J. Biol. Chem. 260: 2694-2699 and van Berkel et al. 1985. J. Biol. Chem. 260: 12203-12207) the clearance of both low density lipoproteins (LDL) and high density lipoproteins (HDL) from the blood can be greatly enhanced by pretreatment of these lipoproteins with a tris-galactosylated cholesterol derivative, which makes these particles recognizable by hepatic galactosyl-receptors. Here we report that intravenous infusion of the (water-soluble) tris-galactosyl-cholesterol in rats caused a dose-dependent decrease of the plasma cholesterol level. This fall was sustained long after termination of the infusion. It was not observed upon infusion of tris-glucosyl-cholesterol. The fall in plasma cholesterol was accompanied by an increase in hepatic cholesterol. Upon injection of rat HDL and LDL labeled in their cholesteryl ester moieties, plasma clearance of label in both lipoproteins was enhanced in rats infused with tris-galactosyl-cholesterol, the stimulation being more pronounced when the label was in HDL. The appearance of label in bile was also enhanced in the rats receiving the compound, again more markedly when the label was given as HDL. Ninety four percent or more of the radioactivity excreted in the bile was in the form of bile salts, with conjugated cholate being the major species in both control and treated rats; 6% or less of the radioactivity in the bile was as free cholesterol. Infusion of tris-galactosyl-cholesterol constitutes a new and defined method of lowering plasma lipoprotein levels by enhancing their uptake in the liver.

Animals↗
PubMed1986

Hepatic processing of the cholesteryl ester from low density lipoprotein in the rat.

Human low density lipoprotein (LDL), radiolabeled in the cholesteryl ester moiety, was injected into estrogen-treated and -untreated rats. The hepatic and extrahepatic distribution and biliary secretion of [3H]cholesteryl esters were determined at various times after injection. In order to follow the intrahepatic metabolism of the cholesteryl esters of LDL in vivo, the liver was subfractioned into parenchymal and Kupffer cells by a low temperature cell isolation procedure. In control rats, the LDL cholesteryl esters were mainly taken up by the Kupffer cells. After uptake, the [3H]cholesteryl esters are rapidly hydrolyzed, followed by release of [3H]cholesterol from the cells to other sites in the body. Up to 24 h after injection of LDL, only 9% of the radioactivity appeared in the bile, whereas after 72 h, this value was 30%. Hepatic and especially the parenchymal cell uptake of [3H]cholesteryl esters from LDL was strongly increased upon 17 alpha-ethinylestradiol treatment (3 days, 5 mg/kg). After rapid hydrolysis of the esters, [3H]cholesterol was both secreted into bile (28% of the injected dose in the first 24 h) as well as stored inside the cells as re-esterified cholesterol ester. It is concluded that uptake of human LDL by the liver in untreated rats is not efficiently coupled to biliary secretion of cholesterol (derivatives), which might be due to the anatomical localization of the principal uptake site, the Kupffer cells. In contrast, uptake of LDL cholesterol ester by liver hepatocytes is tightly coupled to bile excretion. The Kupffer cell uptake of LDL might be necessary in order to convert LDL cholesterol (esters) into a less toxic form. This activity can be functional in animals with low receptor activity on hepatocytes, as observed in untreated rats, or after diet-induced down-regulation of hepatocyte LDL receptors in other animals.

Animals↗
PubMed1986

Lipoproteins and liposomes as in vivo cholesterol vehicles in the rat: preferential use of cholesterol carried by small unilamellar liposomes for the formation of muricholic acids.

Hepatic cholesterol metabolism was studied in rats with a permanent biliary drainage. Three cholesterol vehicles were used to discriminate between metabolic pathways of cholesterol in the liver. [3H]Cholesterol was administered intravenously associated with rat serum lipoproteins, multilamellar (MLV) or small unilamellar (SUV) liposomes. The liposomes were made from cholesterol, sphingomyelin and phosphatidylserine in a 5:4:1 molar ratio. Initial blood elimination differed markedly for the three vehicles: 15 min after injection the 3H radioactivity content of blood for MLV, SUV and lipoprotein was 3, 50 and 54% of the injected dose, respectively. After about 30 min, MLV-cholesterol label started to reappear in the blood, probably after processing of the vehicle by the Kupffer cells. For all vehicles about 80% of the cholesterol label had been excreted in bile after 120 h, predominantly as bile acids. Initial biliary excretion was highest for lipoproteins (5.7% at 1 h), followed by MLV and SUV (1.3 and 1.2%, respectively). No differences in the radioactivity of excreted bile acids were detectable between the three vehicles at 12 h after injection. However, at 1 h the radioactivity in the muricholic acid fraction was markedly increased, as compared to the other bile acids after injection of SUV-cholesterol, but not after injection of MLV- or lipoprotein-cholesterol. Also, the glycine/taurine conjugation ratio of bile acids was increased for SUV-cholesterol at 1 h as compared to that for the other two vehicles. Since SUV appear to donate their cholesterol to a pool which preferentially supplies cholesterol for muricholic acid synthesis, we conclude that more than one cholesterol pool exists in the hepatocytes from which cholesterol can be recruited for bile acid synthesis. Zonal heterogeneity might be responsible for the observed differences.

Animals↗
PubMed1986

Intestinal absorption of lithocholic acid sulfates in the rat: inhibitory effects of calcium.

Sulfation of lithocholic acid has been proposed as a mechanism for elimination of this hepatotoxic bile acid from the body by accelerating its fecal excretion. However, quantitative data on the absorption characteristics of sulfated lithocholic acid conjugates in vivo are scarce. We studied the intestinal absorption of 14C-labeled glycolithocholic acid (GLC), taurolithocholic acid (TLC), and their 3 alpha-sulfate esters, SGLC and STLC, respectively. Studies were performed in unanesthetized rats with a permanent biliary drainage. At an intestinal infusion rate of 125 nmol/min, which is comparable to 7% of the normal biliary bile acid output in the rat, the absorption of sulfated lithocholic acid conjugates was delayed when compared with their unsulfated precursors but quantitatively only slightly reduced over a 24-h period: SGLC 90.9 +/- 3.6%, GLC 94.4 +/- 1.1%, STLC 84.4 +/- 3.0%, and TLC 94.2 +/- 2.1%. Urinary excretion of sulfated and unsulfated bile acids was similar and never exceeded 2% of the dose. SGLC absorption was dose dependent, was not altered by coinfusion of rat bile, and was only slightly reduced by a sixfold overdose of taurocholic acid. SGLC and STLC were excreted into bile largely unchanged in form. In contrast, GLC and TLC were extensively metabolized to more polar bile acids, predominantly to beta-muricholic acid conjugates. Replacement of NaCl in the infusion fluid by CaCl2 reduced the absorption of SGLC and STLC by 63 and 52%, respectively. This calcium effect was less pronounced for the unsulfated bile acids: GLC -22%, and TLC -19%. Absorption of taurocholic acid was unaffected by CaCl2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Ketoconazole blocks bile acid synthesis in hepatocyte monolayer cultures and in vivo in rat by inhibiting cholesterol 7 alpha-hydroxylase.

In cultured hepatocytes conversion of [4-14C]cholesterol into bile acids was dose dependently reduced by the antimycotic drug ketoconazole, giving half-maximal inhibition at 10 microM ketoconazole in rat hepatocytes and at 1 microM in human hepatocytes. No change was observed in the ratio of produced cholic, beta-muricholic, and chenodeoxycholic acid with increasing amounts of the drug. Conversion of [4-14C]7 alpha-hydroxycholesterol, an intermediate of bile acid pathway, to bile acids was not affected by ketoconazole. These results together with kinetic studies with rat liver microsomes, demonstrating noncompetitive inhibition (Ki = 0.4 microM), indicate that cholesterol 7 alpha-hydroxylase is the main site of inhibition. In bile-diverted rats a single dose of ketoconazole (50 mg/kg) dramatically impaired bile flow and biliary bile acid output (92% inhibition). A similar blockade was observed using [4-14C]cholesterol as precursor for bile acid synthesis. Therefore, treatment of patients with this drug may inhibit bile acid synthesis, resulting in a reduction of the bile acid pool size after long-term ketoconazole therapy.

Animals↗
PubMed1986

Enterohepatic circulation in man. A simple method for the determination of duodenal bile acids.

A method has been developed for easy sampling of duodenal bile acids. For this purpose Entero-Test was used, an encapsulated nylon thread originally used to estimate enteral parasites. This capsule is swallowed by a fasting subject and one end of the thread is taped at a corner of the month. Four hours after swallowing the thread, it is withdrawn and bile acids are eluted with buffer. The solution is applied to a Sep-Pak C18 cartridge to extract bile acids, which are subsequently analyzed by capillary gas-liquid chromatography and liquid chromatography. In vitro analyses showed that there was no preferential binding to the thread of any bile acid and that binding was pH-independent. A high correlation (r = 0.98) was found between direct analyses of bile and analyses by Entero-Test after in vitro incubation. The values obtained by the Entero-Test were similar to those of duodenal bile simultaneously collected with the normal intubation technique (r = 0.99). Duodenal bile acid composition showed a daily variation. In 11 healthy volunteers the following bile acid composition of unstimulated duodenal juice was found (mean +/- SD; %): choleate 44 +/- 12 (glycine/taurine ratio 1.8), chenodeoxycholate: 29 +/- 6 (G/T ratio 2.3); deoxycholate: 25 +/- 11 (G/T ratio 5.7), lithocholate: 1, ursodeoxycholate: less than 1. The described technique turned out to be an easily applicable method for determination of duodenal bile acids in man. This enables longitudinal studies concerning the factors that determine the bile acid pool composition and its relevance to various diseases.

Bile Acids and Salts↗
PubMed1985

Acute effects of pentobarbital-anaesthesia on bile secretion.

Male Wistar rats were equipped with permanent catheters in the bile duct and the duodenum under ether anaesthesia, at least seven days before the experiments. By this technique, the enterohepatic circulation can be interrupted for bile collection without direct surgical intervention. 14C-Pentobarbital (26.6 mumole/100 g body wt) was injected intraperitoneally immediately before interruption of the enterohepatic circulation (NBD, Non-Bile Diverted) or after eight days of bile diversion (BD, Bile Diverted). In NBD rats, bile flow and biliary bile acid excretion were significantly reduced during the first hour after pentobarbital administration when compared to unanaesthetized controls, but markedly increased thereafter. Pentobarbital treatment slightly decreased biliary bile acid excretion in BD rats, but caused a 60% increase in bile flow. Within four hours 22.3 +/- 0.4% and 26.0 +/- 2.7% of the injected radioactivity was excreted into bile in NBD and BD rats, respectively. The calculated osmotic activity of pentobarbital and its metabolites was 47.8 +/- 5.2 microliter/mumole in NBD rats and 37.8 +/- 1.3 microliter/mumole in BD rats. Consequently, pentobarbital treatment affected the bile acid independent fraction of bile flow (BAIF). The calculated BAIF was 2.68 microliter/min/100 g body wt in unanaesthetized animals, but 4.27 microliter/min/100 g body wt in pentobarbital treated NBD rats. Corresponding values for BD rats were 1.70 and 2.38 microliter/min/100 g body wt. It is concluded that pentobarbital anaesthesia affects bile production in the rat by direct and indirect means. Firstly, pentobarbital and its metabolites are rapidly excreted into bile and exert a significant choleretic effect, thereby increasing the BAIF. Secondly, pentobarbital anaesthesia retards the exhaustion of the intestinal bile acid pool, which leads to secondary changes in the biliary excretion process.

Anesthesia↗
PubMed1985

Enterohepatic circulation in the rat.

Several compounds, in particular bile acids, undergo enterohepatic circulation (EHC). Limited data are available on the pathophysiologic aspects of this circulation. In the present study we describe a surgical technique in rats that allows a long-term, reversible interruption of the EHC and monitoring of peripheral blood levels without direct surgical intervention. This technique excludes the effects of anesthesia and surgical trauma. The model's validity has been tested extensively. We used this animal model to investigate acute and chronic effects of interruption and subsequent restoration of the EHC on (a) nutritional status, (b) plasma cholesterol levels and hepatic cholesterol synthesis, and (c) biliary bile acid, phospholipid, and cholesterol excretion. Interruption of the EHC resulted in an increased food intake and enhanced fecal energy loss, caused by a less efficient intestinal absorption. Plasma cholesterol concentrations declined immediately after the interruption of the EHC, but returned to almost control values during bile diversion. A marked overshoot followed the subsequent restoration of the EHC. Hepatic cholesterol synthesis showed a five-fold increase after 8 days of bile diversion but returned to control values within 2 days after restoration of the EHC. After interruption of the EHC, bile acid, phospholipid, and cholesterol excretion decreased sharply but stabilized after 3 h at 7.6%, 20%, and 23%, respectively, of their initial values. Bile acid output, representing hepatic synthesis, slowly increased over 4 days, but never exceeded 13% of its value during intact EHC. Subsequent restoration of the EHC could rapidly reverse the observed effects of the interruption. The animal model described in the present study is an excellent tool in studying the acute and chronic effects of disturbances of the EHC.

Animals↗
PubMed1985

Cholestasis induced by sulphated glycolithocholic acid in the rat: protection by endogenous bile acids.

Sulphated glycolithocholic acid (SGLC) causes cholestasis in experimental animals, despite its sulphated form. In the present study, the cholestatic potency and the pharmacokinetics of SGLC were investigated in rats under two conditions: (a) in the presence of an intact circulating bile acid pool and (b) after exhaustion of the bile acid pool by 24 h of bile diversion. Intravenous administration of SGLC (8 mumol/100 g body weight) to rats with an intact bile acid pool did not cause cholestasis. However, biliary phospholipid and cholesterol concentrations were reduced by 40% and 29% respectively during the first hour after administration. When the same dose of the bile acid was injected in rats with a 24 h biliary drainage, a complete cessation of bile production was observed within 1 h. Twelve hours after the onset of cholestasis, bile production gradually increased again, showed a marked overshoot, and reached control levels after 3 days. In the recovery phase, biliary phospholipid and cholesterol concentrations were greatly reduced. The absence of endogenous bile acids did not change the hepatic clearance rate of a tracer dose of radiolabelled SGLC, but markedly decreased its biliary excretion rate. It was concluded that the hepatotoxic effect of SGLC is much more pronounced in rats with an exhausted bile acid pool, possibly due to a slower biliary excretion of the toxic compound. This phenomenon may have clinical implications for patients with a contracted bile acid pool.

Animals↗
PubMed1985

Sulphated lithocholic acid conjugates in serum from children with hepatic and intestinal diseases.

Sulphated lithocholic acid conjugates (SGLC) were measured in the sera of 268 children with various hepatic and intestinal disorders. Two groups were distinguished: (I) SGLC concentration less than or equal to 1.2 mumol/l, n = 198, and (II) SGLC concentration greater than 1.2 mumol/l, n = 70. In 28 patients of the latter group the SGLC concentration was less than 25% of the concentration of glycocholic acid (GC) in the same serum sample. This group (IIA) consisted predominantly of patients with cholestasis, as characterized by high serum bile acid levels and deviating liver function tests. The rest of the group (IIB), with SGLC levels exceeding 25% of the GC concentration and relatively low serum bile acid concentrations, showed no clear cholestatic symptoms. A postprandial increase in serum SGLC (delta SGLC) greater than 1.0 mumol/l was found in only 1 of 32 patients of group I (3%), in 1 of 6 patients of group IIA (17%), but in 9 of 11 patients of group IIB (81%). delta SGLC did not correlate with delta GC in the same test, which indicated that a general hepatic bile acid clearance defect was not responsible. In two patients with intermittent cholestasis, the distinct postprandial rise in serum SGLC that was always found during anicteric periods could be prevented by adding cholestyramine to the test meal. We conclude that elevated serum concentrations of SGLC develop during the course of cholestasis but may also be caused by influx of this bile acid from the intestine. Because of its hepatotoxic properties, SGLC may be involved in the initiation or perpetuation of specific cholestatic phenomena.

Adolescent↗
PubMed1984

Hypothalamically-induced insulin release and its potentiation during oral and intravenous glucose loads.

Male Wistar rats were provided with bilateral cannulas in the lateral hypothalamic area (LHA) and cannulas in the left and right jugular vein. Freely moving rats provided in this way with cannulas were infused with transmitters in the LHA and with various substances in the blood circulation during simultaneous sampling of blood without disturbing the animals. Infusion of norepinephrine (NE) in the LHA resulted in increased insulin levels while plasma glucagon and blood glucose were nearly not affected. This LHA mediated insulin release was suppressed by atropine injection in the blood circulation suggesting a vagal contribution to the observed phenomenon. Administration of either an oral or i.v. glucose load during noradrenergic stimulation of the LHA elicited an exaggerated insulin response when compared to their controls. This LHA potentiated insulin response during an oral and i.v. glucose load could be suppressed by atropinization of the rats. It is concluded that meal-related stimuli are relayed to the NE-stimulated area of the LHA and that these stimuli modulate the output from this area of the LHA that is concerned with the release of insulin.

Animals↗
PubMed1984

Descending pathways from hypothalamus to dorsal motor vagus and ambiguus nuclei in the rat.

The anatomical pathways between the hypothalamus and cell groups of the lower medulla that are involved in the neural control of endocrine pancreas activity were investigated. As part of this control system the descending pathways originating from lateral, dorsomedial and ventromedial hypothalamic nuclei towards the dorsal motor vagus and ambiguus nuclei, were studied by retrograde transport of horseradish peroxidase. Very small injections of the tracer, by means of the iontophoretic delivery method, were placed in the dorsal motor vagus, ambiguus and solitary tract nucleus as well as in the various nuclei of the medullary reticular formation. Subsequent retrograde labeling was studied in the hypothalamus and the brainstem. The appearance of considerable retrograde labeling in mesencephalic periventricular grey and rostral mesencephalic reticular formation indicated a possible role for these structures as intermediates in an indirect hypothalamo-medullary control circuitry. This led us to extend the peroxidase injections to these mesencephalic areas after which the hypothalamus was investigated for retrograde labeling. All data combined indicated the existence of three descending pathways, direct and indirect, between hypothalamus and the parasympathetic motor nuclei of the lower medulla.

Animals↗
PubMed1982

Organization of diencephalic and brainstem afferent projections to the lateral septum in the rat.

Ascending diencephalic and brainstem afferents to the lateral septal column were studied by retrograde transport of horseradish peroxidase following microiontophoretic injections in the various subdivisions of the lateral septal area. Predominantly ipsilateral cells, of which several coincide with reported monoaminergic cell groups, appeared in the preoptic area, several hypothalamic nuclei, periventricular nuclei, raphe nuclei, pontine area and medulla oblongata. It is concluded that there is a heterogeneous monoaminergic input to the lateral septal area organized in a complicated pattern along the longitudinal axis of the lateral septum.

Afferent Pathways↗