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M Llobera

Publications and source records attributed to M Llobera.

At least 37 records · Page 2Linked to original sources
PubMed1993

Epidermal growth factor interferes with the effect of adrenaline on glucose production and on hepatic lipase secretion in rat hepatocytes.

We studied the interaction of epidermal growth factor (EGF) and adrenaline in the control of several metabolic functions in isolated hepatocytes from fed rats. EGF did not modulate glucose release, urea production or hepatic lipase secretion, but interfered with the stimulatory effect of adrenaline on both glucose and urea production and also with the inhibitory effect of this hormone on hepatic lipase secretion. EGF also interfered with the effect of both angiotensin II and vasopressin on glucose release and on hepatic lipase secretion. While the effect of EGF interfering with the action of adrenaline on glucose release was potentiated in the absence of extracellular calcium, the effect on the inhibition of hepatic lipase secretion was abolished. These results suggest that EGF interfered with catecholamine actions in the liver at a site distal from the generation of the calcium signal.

Animals↗
PubMed1993

Lipoprotein lipase in developing rat tissues: differences between Wistar and Sprague-Dawley rats.

Lipoprotein lipase in animal tissues is known to be affected by fasting, but contradictory results have been published concerning this effect in particular tissues. For example, we reported that lipoprotein lipase activity expressed in the liver of neonatal rats was either increased or not affected by fasting. To evaluate the influence of the rat strain used as experimental animal model, we studied differences between Wistar and Sprague-Dawley rats in the development and in the effect of fasting on lipoprotein lipase and hepatic lipase activities in tissues of neonatal rats. Beside some minor differences in the development of lipoprotein lipase in some tissues like brown adipose tissue and lungs, we found quite remarkable differences between both strains in the development of lipoprotein lipase and hepatic lipase activities in the liver. In 1-day-old neonates, differences between both strains were also observed in the effect of fasting on lipoprotein lipase activity both in liver and lungs. In the liver of Wistar pups lipoprotein lipase activity was increased by fasting by 350%, but only by 50% in the liver of Sprague-Dawley pups. In contrast, in the lungs of Wistar pups lipoprotein lipase activity was increased by fasting by 280%, but by 580% in lungs of Sprague-Dawley rats. Therefore, our results indicate that quantitative differences exist between Wistar and Sprague-Dawley rats in the regulation of lipoprotein lipase.

Adipose Tissue, Brown↗
PubMed1992

Neonatal extinction of liver lipoprotein lipase expression.

In contrast to the complete absence of lipoprotein lipase (LPL) mRNA in adult rat liver, fetal and neonatal rat liver contain substantial amounts of LPL mRNA, which is translated in active LPL protein as can be deduced from the presence of LPL activity in this organ. At this neonatal stage, both the relative abundance of LPL mRNA and LPL activity increased with starvation. During the suckling period, LPL mRNA and LPL activity gradually decreased until both parameters were undetectable. While the administration of L-thyroxine or hydrocortisone enhanced the disappearance of LPL mRNA, induced hypothyroidism delayed its disappearance. In adult animals induced hypothyroidism could not reactivate LPL mRNA production in the liver. The data presented suggest that liver LPL production responds to changes in the nutritional state and becomes extinguished during development, in a fashion reminiscent to the extinction of alpha-fetoprotein. This extinction of LPL gene expression is influenced by hormonal factors.

Animals↗
PubMed1992

Lipoprotein lipase and hepatic lipase activities are differentially regulated in isolated hepatocytes from neonatal rats.

Lipoprotein lipase and hepatic lipase are members of the lipase gene family sharing a high degree of homology in their amino acid sequences and genomic organization. We have recently shown that isolated hepatocytes from neonatal rats express both enzyme activities. We show here that both enzymes are, however, differentially regulated. Our main findings are: (i) fasting induced an increase of the lipoprotein lipase activity but a decrease of the hepatic lipase activity in whole liver, being in both cases the vascular (heparin-releasable) compartment responsible for these variations. (ii) In isolated hepatocytes, secretion of lipoprotein lipase activity was increased by adrenaline, dexamethasone and glucagon but was not affected by epidermal growth factor, insulin or triiodothyronine. On the contrary, secretion of hepatic lipase activity was decreased by adrenaline but was not affected by other hormones. (iii) The effect of adrenaline on lipoprotein lipase activity appeared to involve beta-adrenergic receptors, but stimulation of both beta- and alpha 1-receptors seemed to be required for the effect of this hormone on hepatic lipase activity. And (iv), increased secretion of lipoprotein lipase activity was only observed after 3 h of incubation with adrenaline and was blocked by cycloheximide. On the contrary, decreased secretion of hepatic lipase activity was already significant after 90 min of incubation and was not blocked by cycloheximide. We suggest that not only synthesis of both enzymes, but also the posttranslational processing, are under separate control in the neonatal rat liver.

Animals↗
PubMed1991

Lipoprotein lipase enables triacylglycerol hydrolysis by perfused newborn rat liver.

Fasted 1-day-old rat liver has high heparin-releasable (endothelial) lipoprotein lipase (LPL) activity, and its hepatocytes synthesize LPL protein. To test the physiological role of this LPL, we perfused the isolated organ with a 0.8 mM triacylglycerol (TAG) (Intralipid + glycerol tri[3H]oleate) 6.3% serum medium. Samples of the recirculated perfusate were taken at different times to determine 3H in TAG, free fatty acid (FFA), and water-soluble (WS) fractions. In the medium [3H]TAG disappeared and [3H]FFA and [3H]WS fractions appeared linearly with time. This TAG hydrolysis was 1) absent when medium was recirculated without liver, 2) not affected by chloroquine addition, 3) inhibited by anti-LPL immunoglobulins, 4) absent when serum was omitted from the medium, and 5) restituted when apolipoprotein CII was added to the medium without serum. Therefore, lysosomal lipase is not involved in this TAG hydrolysis, the features of which are characteristic of LPL, not of the so-called "hepatic endothelial lipase." Thus LPL activity enables the neonatal rat liver to hydrolyze and take up circulating TAG, i.e., has the same function as extrahepatic LPL.

Animals↗
PubMed1991

Involvement of catecholamines in the effect of fasting on hepatic endothelial lipase activity in the rat.

The effect of fasting on hepatic endothelial lipase activity in the liver of adult rats was investigated. We found that, both in male and female rats, fasting produced a progressive decrease of the hepatic endothelial lipase activity. Upon refeeding, the activity returned to control values in 48 h. In isolated livers from fed male rats, a sharp peak of hepatic endothelial lipase activity appeared in the perfusate upon heparin addition. It accounted for 75% of the total activity (heparin-released + residual) of the tissue. Fasting (24 h) decreased the heparin-releasable activity, and this effect was responsible for most of the decrease found in whole tissue. We suggest that the effect might be due to a decreased synthesis and/or secretion of the enzyme by hepatocytes, since isolated hepatocytes from fasted rats, incubated at 37 C, released 65% less activity to the incubation medium than hepatocytes from fed rats. Adrenaline, but not insulin, glucagon, dexamethasone, epidermal growth factor, or T3, decreased the amount of hepatic endothelial lipase activity released by hepatocytes isolated from fed rats. The effect of adrenaline appears to be mediated by alpha 1-receptors since phenylephrine but not isoprenaline reproduced, and prazosin but not propranolol blocked, the effect of the catecholamine. In the presence of cycloheximide, adrenaline also decreased the amount of activity released. We suggest that, in our incubation conditions (up to 3 h), the hormone affects the posttranslational processing of the enzyme. In vivo administration of prazosin blocked the effect of both noradrenaline and fasting on hepatic endothelial lipase activity in whole liver. Those results suggest that catecholamines are involved in the decreased hepatic endothelial lipase activity found in the liver of fasted rats, and points out the role of these hormones in the acute modulation of an enzyme involved in reverse cholesterol transport.

Animals↗
PubMed1991

Lipoprotein lipase in lungs, spleen, and liver: synthesis and distribution.

Lipoprotein lipase (LPL, E C 3.1.1.34) is the enzyme responsible for hydrolysis of triacylglycerols in plasma lipoproteins, making the fatty acids available for use by subjacent tissues. LPL is functional at the surface of endothelial cells, but it is not clear which cells synthesize the enzyme and what its distribution within tissues and vessels is. In previous studies we reported that in the major LPL-producing tissues (muscles, adipose tissue, and mammary gland) the enzyme is made by the major cell types. In the present work we have studied in adult guinea pigs some tissues that present LPL activity but in lower amounts (lung, spleen, and liver). On cryosections of these tissues we have searched for specific cell expression of the LPL gene (by in situ hybridization using a RNA probe) and for the corresponding protein distribution (by immunocytochemistry). Based on morphological criteria we can suggest that, contrary to the main LPL-producing tissues, in these tissues the enzyme is made by scattered cells, such as macrophages in the lung and spleen and Kupffer cells in the liver; endothelial cells present but do not synthesize the enzyme, indicating that the endothelial LPL originates in other cells. In the liver strong immunoreaction was detected in the sinusoid in contrast to the low level of mRNA expression, suggesting that liver takes up circulating LPL from blood.

Animals↗
PubMed1990

Effect of starvation on lipoprotein lipase activity in the liver of developing rats.

Liver lipoprotein lipase activity in neonatal (1- and 5-day-old) rats was 2-3-times than in the liver of adult rats. In mid-suckling (15-day-old) or weaned (30-day-old) animals, it was not significantly different from the low activity detected in adult rats. Starvation resulted in a 3-fold increase of lipoprotein lipase activity in the neonatal liver, but did not affect the activity in the liver of mid-suckling, weaned or adult rats. When isolated livers from both 1- and 5-day-old pups were perfused with heparin, a sharp peak of lipoprotein lipase activity appeared in the perfusate. In fed neonates, the peak area accounted for about 70% of the total (released + non-releasable) activity. In starved neonates, the proportion of heparin-releasable activity increased up to about 90%. These results indicate that neonatal rat liver lipoprotein lipase activity is markedly affected by changes in the nutritional status of the animal, and the effect is restricted to the vascular pool of the enzyme, as was reported in extrahepatic tissues from adult rats.

Animals↗
PubMed1990

Localization of lipoprotein lipase to discrete areas of the guinea pig brain.

Lipoprotein lipase is a key enzyme in lipoprotein metabolism present primarily in extrahepatic tissues with high turnover of fatty acids. Using immunocytochemistry we have explored where lipoprotein lipase is localized in guinea pig brain. The enzyme was found to be associated with neuronal cells and vascular endothelial surfaces. The distribution was strikingly uneven with intense reaction in some areas, and virtually no reaction in adjacent areas. The highest reactivity was in neocortex, in hippocampus, in Purkinje cells of the cerebellum and in some motor nuclei of the brainstem. The results suggest marked differences between individual brain areas in utilization of plasma lipoproteins.

Animals↗
PubMed1990

Lipoprotein lipase: cellular origin and functional distribution.

Lipoprotein lipase (LPL, E.C. 3.3.1.34) is the enzyme responsible for hydrolysis of triacylglycerols in plasma lipoproteins, making the fatty acids available for use by subjacent tissues. LPL is functional at the surface of endothelial cells, but it is not clear which cells synthesize the enzyme and what its distribution is within tissues and vessels. We have searched for specific cell expression of the LPL gene by in situ hybridization using a RNA probe and for the corresponding protein distribution by immunocytochemistry on cryosections of some LPL-producing tissues of guinea pigs. In white and brown adipose tissues, heart and skeletal muscle, and lactating mammary gland, there was positive hybridization for LPL mRNA over all members of the major cell types, indicating that mature and immature adipocytes, muscle cells, and mammary epithelial cells are main sources of LPL. In large vessels, LPL expression was detected in some smooth muscle cells in the media layer. There was no positive hybridization for LPL mRNA over endothelial cells in any of the tissues studied, but there was immunoreaction for LPL protein at endothelial surfaces of all blood vessels. In the kidney, there was strong immunofluorescence at the vascular endothelium, particularly in the glomeruli, but little or no LPL mRNA was detected in the surrounding cells. These observations suggest that in some tissues LPL is synthesized by parenchymal cells and spreads along the vascular mesh. Transfer to the vascular endothelium is, however, not the only route taken by LPL. In the mammary gland most of the enzyme protein appeared to be secreted, partly in association with milk fat droplets.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1990

Lipoprotein lipase activity in the liver of starved pregnant rats.

We have previously described the appearance of lipoprotein lipase (LPL)-like activity in the liver of 24-hour-starved 21-day pregnant rat, but it is not known up to what point the appearance of this activity depends on the gestation stage and/or the length of the starvation period. We found that 24 h of starvation resulted in the appearance of LPL-like activity in the liver of 21-day-pregnant but not in 17-day- or nonpregnant rats. This appearance was found only after 24 h but not after 48 or 72 h of starvation. We demonstrate that this activity actually corresponds to LPL, since it is inhibited by either 1.5 M NaCl or 1.5 mg/ml protamine sulfate, is serum-dependent, and could be separated from hepatic lipase activity by using heparin-Sepharose affinity chromatography. The possible relationship between the appearance of LPL activity in the liver and the enhanced metabolic response to starvation in pregnant rats at term is discussed. It is suggested that the presence of this enzyme in the liver would allow the direct uptake by the liver of circulating triacylglycerols.

Adipose Tissue↗
PubMed1989

Lipoprotein lipase activity in neonatal-rat liver cell types.

The lipoprotein lipase activity in the liver of neonatal (1 day old) rats was about 3 times that in the liver of adult rats. Perfusion of the neonatal liver with collagenase decreased the tissue-associated activity by 77%. When neonatal-rat liver cells were dispersed, hepatocyte-enriched (fraction I) and haemopoietic-cell-enriched (fraction II) populations were obtained. The lipoprotein lipase activity in fraction I was 7 times that in fraction II. On the basis of those activities and the proportion of both cell types in either fraction, it was estimated that hepatocytes contained most, if not all, the lipoprotein lipase activity detected in collagenase-perfused neonatal-rat livers. From those calculations it was also concluded that haemopoietic cells did not contain lipoprotein lipase activity. When the hepatocyte-enriched cell population was incubated at 25 degrees C for up to 3 h, a slow but progressive release of enzyme activity to the incubation medium was found. However, the total activity (cells + medium) did not significantly change through the incubation period. Cycloheximide produced a time-dependent decrease in the cell-associated activity. Heparin increased the amount of lipoprotein lipase activity released to the medium. Because the cell-associated activity was unchanged, heparin also produced a time-dependent increase in the total activity. In those cells incubated with heparin, cycloheximide did not affect the initial release of lipoprotein lipase activity to the medium, but blocked further release. The cell-associated activity was also decreased by the presence of cycloheximide in those cells. It is concluded that neonatal-rat hepatocytes synthesize active lipoprotein lipase.

Animals↗
PubMed1989

Hepatic endothelial lipase activity in neonatal rat liver.

Hepatic endothelial lipase (HEL) activity is as high in the neonatal (1-day old) rat liver as in adults. Most of the HEL activity is located at the capillaries since 75% of the total activity is released by heparin or collagenase perfusion. The residual activity (non-releasable) is located in hepatocytes and not in hemopoietic cells, which are the major cell type in neonatal liver. Per mg of protein, the HEL activity is 50% higher in neonatal than in adult hepatocytes. We suggest that neonatal hepatocytes have an increased capacity to synthesize and secrete HEL activity, so maintaining a high activity in the whole organ. It might contribute to the hepatic uptake of cholesterol from circulating lipoproteins, in a period in which endogenous cholesterol synthesis is known to be inhibited in the liver.

Animals↗
PubMed1989

Low intestinal lactase activity in offspring from ethanol-treated mothers.

Some aspects of small intestine maturation have been studied in the newborns from chronic ethanol-treated pregnant rats (25% ethanol in drinking fluid) immediately after birth (before suckling) and after 30 days of life. Litters delivered by mothers fed ad libitum with a standard diet diluted 50% with cellulose were used as a nutritional control. At birth, pups from ethanol-treated mothers showed significant decreases in total intestinal length and thickness, low total lactase activity and low somatostatin intestinal content. The intestinal alterations of these neonatal parameters are not present in newborns from mothers on fiber-diluted diet. From delivery, pups from different experimental groups were nursed by normal lactating dams. At 30 days of age neither of those parameters differed among the groups. We propose that the low levels of total lactase activity in newborns from alcoholic mothers, that are a consequence of a lower intestinal mucosa content, are a direct effect of ethanol in utero on the fetal gastrointestinal system.

Aging↗
PubMed1988

Acid lipase activity in neonatal rat liver cell types. Effect of starvation.

The acid lipase activity in the liver of neonatal (1-day-old) rats was studied. It was found that (i) in whole liver, the activity was 50% lower than in adult rats; (ii) in neonatal livers, the activity was 7.7-fold higher in hepatocytes than in hemopoietic cells; (iii) neonatal hepatocytes contained about 25% of the activity detected in adult hepatocytes; (iv) all the differences disappeared when expressed per mg of protein; and (v) starvation did not affect the activity either in adult or in neonatal rat liver.

Animals↗
PubMed1988

Lipoprotein lipase in liver. Release by heparin and immunocytochemical localization.

We have previously demonstrated that infusion of Intralipid to rats causes a pronounced increase of the lipoprotein lipase activity in the liver. In this paper we study where in the liver this lipoprotein lipase is located. When isolated livers from Intralipid-treated rats were perfused with heparin, substantial amounts of lipoprotein lipase were released into the perfusate. The identity of the lipase activity was demonstrated by specific inhibition with antisera to lipoprotein lipase, and to hepatic lipase, respectively, and by separation of the two lipase activities by chromatography on heparin-Sepharose. We have also studied the localization of both enzymes by an immunostaining procedure based on post-embedding incubation of ultrathin tissue sections with specific antibodies which were then visualized using protein A-colloidal gold complexes. There was no marked difference in localization for the two enzymes which were both seen at the luminal side of endothelial cells, at the interdigitations of the space of Disse and inside both hepatocytes and endothelial cells. Thus, lipoprotein lipase is present in the liver in positions similar to where the functional pool of hepatic lipase is located and analogous to where lipoprotein lipase is found in extrahepatic tissues. These results raise the possibility that the enzyme has a functional role in the liver.

Animals↗