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Biomedical subjects

M G Roma

Publications and source records attributed to M G Roma.

28 records · Page 2Linked to original sources
PubMed1994

Effect of oral administration of ursodeoxycholic acid on rat hepatic and intestinal UDP-glucuronosyltransferase.

The effect of oral administration of the bile acid ursodeoxycholic acid on rat hepatic and intestinal microsomal UDP-glucuronosyltransferase was studied. The bile acid was administered during 8 days at a daily dose of 500 mg/kg body weight. Enzyme activity was assessed in native and activated microsomes, using bilirubin and p-nitrophenol as substrates. Activation was achieved either by including UDP-N-acetylglucosamine in the incubation mixture or by preincubating native microsomes with an optimal concentration of Lubrol Px. Irrespective of activation status of the microsomes, ursodeoxycholic acid treatment increased enzyme activities toward both substrates in intestine, but not in liver. The analysis of the degree of activation by Lubrol Px revealed that, at least for bilirubin, ursodeoxycholic acid decreased the latency of the intestinal enzyme. The analysis of the lipid composition of microsomes showed several changes in response to ursodeoxycholic acid in intestine but not in liver. Thus, a decrease in cholesterol/phospholipid ratio and an increase in the unsaturation index of total-lipid fatty acids, which correlated well with a membrane "fluidification," were observed. These modifications appear to be related to the lower latency of bilirubin UDP-glucuronosyltransferase in intestine from treated rats and could be responsible, at least in part, for the improvement of enzyme activity in this group. Whatever the mechanism involved, the increment of intestinal UDP-glucuronosyltransferase activities toward both substrates may be relevant as a complement to the hepatic enzymes in those liver diseases in which ursodeoxycholic acid is used as a therapeutic agent.

Animals↗
PubMed1992

Taurolithocholate-induced inhibition of biliary lipid and protein excretion in the rat.

Taurolithocholate (TLC), a natural bile salt, induces selective impairment on canalicular membrane of the hepatocyte, which seems to be a major determinant of its cholestatic effect in experimental animals. In order to extend existing studies about the effects of TLC on bile secretion, we examined in TLC-treated rats the biliary excretion of compounds that are transported to canalicular membrane via vesicles, such as lipids and proteins. The single intravenous injection of TLC (3 mumol/100 g body wt.) inhibited transiently the biliary bile salt excretion, while the biliary excretion of lipids (i.e., cholesterol and phospholipids) and proteins remained inhibited even though the biliary excretion and composition of bile salts were normalized. Under such a condition, TLC also inhibited the transcellular vesicular pathway to the exogenous protein horseradish peroxidase entry into bile, without altering the paracellular biliary access of the protein. The hepatic uptake of horseradish peroxidase was unaffected by TLC-treatment. The results indicate that TLC can inhibit the biliary excretion of compounds that reach the canaliculus via a vesicular pathway, such as lipids and proteins, by a mechanism not related to a defective bile salt excretion. Possible explanations for these findings are discussed.

Animals↗
PubMed1992

Bile salt-associated electrolyte secretion. A study following a short-term biliary obstruction in the rat.

The mechanisms involved in bile salt-induced choleresis are poorly known. To give an insight in this physiological process, bile salt-associated electrolyte secretion was studied following relief of a short-term (2h) biliary obstruction in the rat, an experimental model that shows an important diminution of bile salt choleretic efficiency. For this purpose, biliary excretion of total bile salts and electrolytes (sodium, chloride and bicarbonate) were studied in such a model during taurocholate infusion at increasing rates. The results showed that bile flow, bile salt output and electrolyte secretion stimulated by taurocholate administration were decreased in the rats that were subjected to biliary obstruction. Besides, the choleretic efficiency of the excreted bile salts, as estimated by the slope of the regression line of bile flow vs. bile salt output, was diminished by 46% (p < 0.005). Multiple regression analysis of bile flow vs. bile salt and electrolyte outputs allowed to detect a selective diminution of the fraction of bile flow related to bile salt-associated electrolyte secretion ("secretory fraction" of the choleretic efficiency of bile salts) (3.2 +/- 0.3 vs. 2.5 +/- 0.2 L/mol, p < 0.05) whereas the "osmotic fraction" of the choleretic efficiency of bile salts was not modified by the treatment (5.0 +/- 0.4 vs. 5.1 +/- 0.3 L/mol, p > 0.05). Since both chloride and bicarbonate biliary concentrations in the volume of bile stimulated by taurocholate were reduced by 53% and 52% respectively, a role of these anions in the generation of bile salt-induced choleresis was suggested. Possible mechanisms involved in such a process and in its early impairment during cholestasis are discussed.

Animals↗
PubMed1991

Biliary excretion of polyethylene glycol molecular weight 900. Evidence for a bile salt-stimulated vesicular transport mechanism.

Polyethylene glycol molecular weight 900 (PEG-900) has been used as a marker of vectorial water transport into bile canaliculus. However, the mechanisms by which this compound is excreted have not been clarified. To gain more information on this process, we studied the biliary excretion of [3H]PEG-900 in rats during choleresis induced by canalicular choleretics. In addition, the effects of the microtubule inhibitors colchicine and vinblastine, and of the acidotropic agent chloroquine, on PEG-900 excretion were studied to determine whether a vesicular pathway is involved. Continuous i.v. infusion of either dehydrocholate (DHC, a non-micelle forming bile salt choleretic) or 4-methylumbelliferone (4-MU, a non-bile salt canalicular choleretic) at stepwise-increasing rates [0.7, 1.0 and 1.2 mumol.min-1.(100 g body wt)-1] induced a gradual increment in bile flow, whereas a transient increment of [3H]PEG-900 excretion was observed only during DHC-induced choleresis. Furthermore, studies in which two consecutive i.v. injections of DHC (10 mumol/100 g body wt) were administered showed that [3H]PEG-900 excretion induced by a second administration of DHC was 54% lower than that induced by the first one, despite a similar excretion in bile flow. Finally, colchicine (0.5 mumol/100 g body wt), vinblastine (0.5 mumol/100 g body wt) and chloroquine (50 mg/kg body wt) pretreatments inhibited the DHC-induced increment in biliary [3H]PEG-900 output, while DHC-induced choleresis was almost unaffected. Conversely, excretion of [14C]sucrose, when coadministered with [3H]PEG-900, was not impaired by the treatments. These results suggest that, unlike sucrose, PEG-900 excretion is not associated with canalicular water movements. Instead, it may be related to a vesicular transport process followed by a bile acid-stimulated discharge of secretory vesicles into bile through the lysosomal compartment.

Animals↗
PubMed1991

Hepatic handling of photoirradiated bilirubin. A study in isolated perfused Wistar rat liver.

Conjugation has been considered the rate-limiting step for bilirubin hepatic transport, and bypass of this metabolic step could explain why photobilirubins can be rapidly cleared by the liver. In this paper we assessed whether photoirradiation may enhance the bilirubin overall hepatic transport in the isolated perfused Wistar rat liver, a model possessing intact transport and conjugating systems. Bilirubin was administered as a bolus so as to reach a perfusate concentration of approximately 10 microM (bilirubin/albumin molar ratio 1:17). Perfusate light exposure (0.56.10(15) quanta s-1 cm-2) yielded 7-10% of configurational photoisomers, which were further identified as (4Z,15E/4E,15Z)-bilirubin IX alpha. Under such conditions, the perfusate removal rate was increased by 39% over that from dark conditions. Likewise, biliary excretion, estimated as total bilirubin recovery at 60 min, was also increased (+48%). This later improvement was mainly produced at the expense of unconjugated bilirubin, which most likely derived from its configurational photoisomers that, once excreted into bile, readily re-isomerized to the parent compound. In addition, this increment was partially due to a delayed improvement of monoglucuronide pigment excretion. The calculated hepatic pigment content was significantly higher under light conditions. A direct assessment of hepatic content of different bilirubin moieties at 20 min after bilirubin administration confirmed that such an increment was fully accounted for by unconjugated pigment. Our finding that hepatic pigment content rose (despite a higher biliary excretion) when the bilirubin was irradiated suggests a higher net uptake of photoisomers than native pigment. This observation, and the finding that bilirubin photoisomers were usually excreted without undergoing conjugation even if the metabolic system is active, contribute to explain the greater appearance of unconjugated bilirubin in Wistar rat bile under light exposure.

Animals↗
PubMed1991

Studies on the mechanism of bile salt-independent bile flow impairment in streptozotocin-induced hepatotoxicity.

The main factors involved in the impairment of formation of the bile salt-independent bile flow (BSIF) in streptozotocin (SZ)-treated rats were examined. Twenty-four hours after SZ injection (50 mg/kg body wt, i.v.) bile flow, bile salt output and biliary excretion of the major inorganic electrolytes (sodium, chloride and bicarbonate) were significantly diminished. The relationship between bile flow and bile salt output obtained during the administration of sodium taurocholate at stepwise-increasing rates indicated that bile salt-independent bile flow (y-intercept) was diminished by 37% in SZ-treated rats. The relationship between electrolyte output and bile salt output showed that the fractions of sodium, chloride and bicarbonate excreted independently of bile salt (y-intercept) decreased to 59%, 47% and 67% of the control values respectively, while the amount of electrolyte secreted per unit of bile salt secreted was unaffected in SZ-treated rats. The hepatic activity of Na+,K(+)-adenosine triphosphatase (Na+,K(+)-ATPase) was decreased by 59% (P less than 0.05) in SZ-treated rats. Nicotinamide administered prior to SZ prevented the hyperglycemia indicative of SZ-induced diabetes, but had no effect on the decrease in Na+,K(+)-ATPase activity caused by the drug. These results suggest that SZ itself, and not its diabetogenic effect, decreases the BSIF by a mechanism that involves impairment of the biliary electrolyte excretion, which could be the result of the inhibition of the hepatic Na+,K(+)-ATPase activity.

Animals↗
PubMed1989

A simple method for the correction of biliary excretion curves distorted by the biliary dead space.

Biliary solute concentrations measured at the tip of the cannula suffer a delay with respect to bile flow due to the transit time through the biliary tree volume. This study proposes a simple method, which is valid under variable bile flow conditions, to correct the distortion introduced by the biliary tree volume on the kinetic curves of the biliary excretion rate. The biliary transit time (tt) was calculated as the time needed to excrete a bile volume equal to the biliary tree volume by means of the interpolation of biliary cumulative volume versus time curves. Such tt permits one to estimate the canalicular concentration at time t, interpolating the biliary concentration curves at time t-tt. The product between the estimated canalicular concentration and the bile flow allows the calculation of the corrected biliary excretion rate. This method was evaluated by a comparison between biliary excretion rate curves of [14C]taurocholate [( 14C]TC) injected as a bolus under basal and sodium dehydrocholate (DHC)-induced choleresis conditions. Since the canalicular excretion rate of [14C]TC is considered independent of bile flow, the significant differences observed in its excretion kinetics under both conditions were attributed to distortion due to the biliary tree volume. After the correction, both curves showed a significant overlapping. This result indicates that the method improves the time-course representation of canalicular events in biliary excretion kinetic studies.

Animals↗
PubMed1988

Comparison of hepatic, renal and intestinal bilirubin UDP-glucuronyl transferase activities in rat microsomes.

1. Bilirubin UDP-glucuronyltransferase activity and its dependence on substrate concentrations in rat liver, renal cortex and intestinal mucosa microsomes were studied. 2. Bilirubin monoglucuronide synthesis from unconjugated bilirubin was a higher capacity, lower affinity step in comparison with bilirubin diglucuronide formation in the three tissues tested. 3. Bilirubin glucuronide formation in liver microsomes showed a higher capacity but a lower affinity than extrahepatic ones. Renal cortex and intestinal mucosa exhibited similar kinetics parameters. 4. In vitro bilirubin glucuronidation in renal cortex and intestinal mucosa was quantitatively important as compared with the hepatic one.

Animals↗