Uptake of lactate by the liver: effect of red blood cell carriage.

Multiple-indicator dilution experiments with labeled lactate were performed in the livers of anesthetized dogs. A mixture of (51)Cr-labeled erythrocytes, [(3)H]sucrose, and L-[1-(14)C]lactate or a mixture of (51)Cr-labeled erythrocytes, [(14)C]sucrose, and L-[2-(3)H]lactate was injected into the portal vein, and samples were obtained from the hepatic vein. Data were evaluated using a model comprising flow along sinusoids, exchange of lactate between plasma and erythrocytes and between plasma and hepatocytes, and, in the case of L-[1-(14)C]lactate, metabolism to H[(14)C]O(-)(3) within hepatocytes. The coefficient for lactate efflux from erythrocytes was 0.62 +/- 0.24 s(-1), and those for influx into and efflux from hepatocytes were 0.44 +/- 0.13 and 0.14 +/- 0.07 s(-1), respectively. The influx permeability-surface area product of the hepatocyte membrane for lactate (P(in)S, in ml x s(-1) x g(-1)) varied with total flow rate (F, in ml s(-1) x g(-1)) according to P(in)S = (3.1 +/- 0.5)F + (0.021 +/- 0.014). Lactate in plasma, erythrocytes, and hepatocytes was close to equilibrium, whereas lactate metabolism was rate limiting.

Kinetics of endothelin-1 binding in the dog liver microcirculation in vivo.

Endothelin-1 (ET-1) is a 21-amino acid peptide produced by vascular endothelial cells that acts as a potent constrictor of hepatic sinusoids. Hepatic binding of tracer (125)I-labeled ET-1 was investigated in anesthetized dogs with the multiple-indicator dilution technique with simultaneous measurements of unlabeled immunoreactive ET-1 plasma levels. Despite 80% binding to albumin, tracer (125)I-ET-1 was avidly extracted by the liver, with only 15 +/- 6% of the peptide surviving passage through the organ. Exchange of ET-1 between plasma and binding sites, probably located on the surface of liver cells, was quantitatively described by a barrier-limited, space-distributed variable transit time model. Reversible and irreversible parallel binding sites were found. Reversible and irreversible plasma clearances of unbound (125)I-ET-1 were 0.084 +/- 0.033 ml. s(-1). g liver(-1) and 0.17 +/- 0.09 ml. s(-1). g liver(-1), respectively, and the dissociation rate constant for reversible binding was 0.24 +/- 0.12 s(-1). The specific ET(A) receptor antagonist BMS-182874 did not modify binding to either site. The nonspecific ET(A)/ET(B) antagonist LU-224332 dose-dependently reduced irreversible binding only. ET-1 levels in the hepatic vein were significantly lower than in the portal vein but were not different from those in the hepatic artery. The ratio between hepatic vein and portal vein levels (0.64 +/- 0.31) was considerably higher than survival fractions, suggesting a substantial simultaneous release of newly synthesized or stored ET-1 by the liver. These results demonstrate both substantial clearance and production of ET-1 by the intact liver. Hepatic ET-1 clearance is mediated by the ET(B) receptor, with the presence of reversible, nonspecific ET-1 binding at the liver surface

Hepatic uptake of bromosulfophthalein-glutathione in perfused Eisai hyperbilirubinemic mutant rat liver: a multiple-indicator dilution study.

The hepatocellular uptake of the glutathione conjugate of bromosulfophthalein (BSPGSH) was examined in Eisai hyperbilirubinemic rats (EHBR; originating from Sprague-Dawley rats), which lacked the ATP-dependent canalicular transport for non-bile acid organic anions, a trend common to other mutant rat strains (TR- and GY, originating from Wistar rats). Single-pass perfused rat liver experiments were conducted with BSPGSH (26-257 microM) using the multiple indicator dilution technique. The steady-state extraction ratio of BSPGSH was close to zero due to lack of biliary excretion. After the introduction of a bolus dose containing vascular (51Cr-labeled red blood cells), interstitial (125I-labeled albumin and [14C]sucrose) and cellular space (D2O) indicators and [3H]BSPGSH into the portal vein, the outflow dilution profile of [3H]BSPGSH was found to display a protracted declining profile (tailing) at low input BSPGSH concentrations; the tail disappeared at higher BSPGSH concentrations. When data were fitted with the barrier-limited model of Goresky as used previously for BSPGSH for the Sprague-Dawley rat (SDR), model fitting was found to evoke an additional "deep pool" within the hepatocyte to account for the "tail" component. The deep pool became evident for the EHBR because biliary excretion of BSPGSH was absent and the rate of return from the deep pool was slow. The concentration of BSPGSH within the deep pool was estimated to be 12 +/- 8 times that in the cytosol. The binding of BSPGSH to EHBR S9 (effective binding concentration of 53 microM and a binding association constant KA of 2.4 x 10(4) M-1), however, was found to be lower than that of SDR S9 and could not account for the late-in-time data. The influx permeability-surface area product was concentration dependent and decreased from 0.27 to 0.01 ml.sec-1.g-1 with increasing BSPGSH concentration; the throughput component, or the portion of the dose that goes through the liver without entering the hepatocyte, increased with increasing concentration. The trends were characteristic of carrier-mediated transport and were similar to those found for the uptake of BSPGSH in SDR.

Carrier-mediated entry of 4-methylumbelliferyl sulfate: characterization by the multiple-indicator dilution technique in perfused rat liver.

The hepatocellular entry of 4-methylumbelliferyl sulfate (4MUS) a highly ionized and highly bound anion capable of futile cycling, was examined in the single-pass albumin-free perfused rat liver preparation. Desulfation of 4MUS to 4-methylumbelliferone (4MU) was verified in vitro to be a low-affinity, high-capacity process (Km = 731 micromol/L; Vmax = 414 nmol min(-1) g(-1) liver). With 4MUS given to the perfused rat liver, sulfation of 4MU, the formed metabolite, was attenuated in the presence of 2,6-dichloro-4-nitrophenol (DCNP), a sulfation inhibitor, and when sulfate ion was substituted by chloride ion. 4MU sulfation, being a high-affinity system, was reduced most effectively at the lowest 4MUS concentration (15 micromol/L) used, evidenced by the increased (24%) net hepatic extraction ratio of 4MUS and reduced utilization (72%) of infused tracer 35SO4(2-) by 4MU for 4MU35S formation. Single-pass multiple indicator dilution (MID) studies were thus conducted under identical conditions (DCNP and absence of inorganic sulfate), with injection of [3H]4MUS and a set of noneliminated vascular and cellular reference indicators into the portal vein (prograde) or hepatic vein (retrograde), against varying background bulk concentrations of 4MUS (5 to 900 micromol/L). The steady-state removal rate of 4MUS and formation rates of 4MU and its glucuronide conjugate (4MUG) were not altered with perfusion flow direction, suggesting the presence of even or parallel distributions of 4MUS desulfation and 4MU glucuronidation activities. When the outflow dilution profile of [3H]4MUS was evaluated with the barrier-limited model of Goresky, a slight red cell carriage effect was found for 4MUS. The permeability surface area product for cellular entry for prograde showed a dramatic concentration-dependent decrease (from 0.13 to 0.01 mL sec(-1) g(-1), or 7.4 to 0.56 times the blood perfusate flow rate) and was resolved as saturable and nonsaturable components, while data for retrograde were more scattered, varying from 2.8 to 1 times the blood perfusate flow rate. Efflux (coefficient = 0.0096 +/- 0.0024 and 0.0088 +/- 0.0062 mL sec(-1) g(-1), respectively) was relatively insensitive to concentration and flow direction. The same was observed for the removal capacity for metabolism and excretion (sequestration coefficient: for prograde, 0.0056 +/- 0.0017 mL sec(-1) g(-1); for retrograde, 0.0056 +/- 0.003 mL sec(-1) g(-1)). The decrease in the apparent partition coefficient (ratio of 4MUS concentration estimated in tissue to unbound plasma concentration) and the increase in relative throughput component with concentration further substantiate the claim on the presence of concentrative processes at the sinusoidal membrane.

Endothelin-1 myocardial clearance, production, and effect on capillary permeability in vivo.

Myocardial metabolism of endothelin-1 (ET-1) and its effect on coronary microcirculatory exchanges were obtained in anesthetized dogs by combining the indicator-dilution technique with immunoreactive ET-1 measurements. The myocardium extracted 17.7 +/- 4.6% of tracer ET-1 (n = 12). Simultaneously measured ET-1 levels in the aorta (0.97 +/- 0.46 pg/ml) and coronary sinus (0.96 +/- 0.53 pg/ml) were not different, supporting a production of ET-1 by the heart that balances the amount extracted. Intracoronary infusion of ET-1 (5 ng.kg-1.min-1) increased coronary sinus ET-1 levels approximately 50-fold, decreased coronary blood flow per unit of interstitial space by approximately 30% (P = 0.006), and increased myocardial microcirculatory transit times (n = 6). Permeability to albumin was unaffected by ET-1, whereas the permeability-surface area product for sucrose decreased following derecruitment of myocardial capillaries. We conclude that there is a normal myocardial metabolic balance of ET-1 and that the heart marginally contributes to circulating ET-1. Pharmacological doses of ET-1 may adversely affect myocardial metabolism by reducing blood flow and the permeability-surface area product for small circulating substances.

Increased hepatocyte permeability surface area product for 86Rb with increase in blood flow.

Liver cell recruitment (the equivalent of capillary recruitment in other organs) was explored by carrying out multiple indicator dilution experiments with labeled rubidium across the liver of the anesthetized dog under basal conditions and after bleeding with saline replacement infusion, which increases liver blood flow. A mixture of 51Cr-labeled red blood cells (a vascular reference), 22Na (which immediately equilibrates in the extracellular space, the sum of the sinusoidal plasma and Disse or interstitial spaces, the expected distribution space for labeled rubidium in the absence of cellular entry), and 86Rb was injected into the portal vein, and normalized outflow patterns, expressed as outflowing fractions of each injected tracer per milliliter versus time, were obtained. In relation to the labeled red blood cell curve, the labeled sodium curve is displaced by flow-limited distribution into the Disse or interstitial space; it is lower on the upslope, reaches a lower and delayed peak, and decays more slowly. The early part of the labeled rubidium curve lies within the labeled sodium curve; it reaches a much reduced peak, and the later return of tracer entering cells is so slow that it is obscured by recirculation. Modeling of the concentrative cellular uptake of rubidium from the Disse space provided an influx permeability surface area product for labeled rubidium. This increases with flow over the observed flow range, demonstrating that sinusoidal recruitment occurs with increase in hepatic blood flow.

Role of ERCP in the diagnosis of intraductal papillary mucinous neoplasms.

Mucinous cystic neoplasms of the pancreas may present in a "ductectatic" form, which parallels a distinct clinical presentation. We describe six patients with this entity termed mucinous ductal ectasia, or intraductal papillary mucinous neoplasm. All six patients presented with typical clinical and endoscopic findings and subsequently, almost all were found to have mucinous ductal cystadenocarcinomas. The endoscopic and pancreatographic findings associated with an intraductal papillary mucinous neoplasm are characteristic, unique, and yield a high diagnostic accuracy. It is important to recognize these features of intraductal papillary mucinous neoplasm since the tumor has a lower malignant potential than adenocarcinoma of the pancreas, and surgical resection is curative in many cases.

Costs and effectiveness of extracorporeal gallbladder stone shock wave lithotripsy versus laparoscopic cholecystectomy. A randomized clinical trial. McGill Gallstone Treatment Group.

Thirty-five patients were randomized to extracorporeal shock-wave lithotripsy (ESWL) and 25 to laparoscopic cholecystectomy (LC). Stone disappearance occurred in only 12 of 32 ESWL patients [38% (95% CI: 21-56%)] during a 15-month follow-up. Greater incremental gains in quality of life after 6 months were observed among LC patients (p < .01). Total duration of disability was 6.8 +/- 8.5 days for ESWL, and 22.7 +/- 16.6 days for LC (p < .01). Nine (28%) patients crossed over electively to the LC group, but only 44% of these underwent LC within the next 3 years. ESWL cost Can $58.9/ day of disability saved. ESWL is limited by its selective applicability and modest stone disappearance rate. Its cost-effectiveness is largely dependent on patient acceptance of recurrent episodes of biliary colic due to the persistence of stone fragments.

Pulmonary clearance of circulating endothelin-1 in dogs in vivo: exclusive role of ETB receptors.

The pulmonary circulation plays an important role in the removal of circulating endothelin-1 (ET-1). Plasma ET-1 levels are increased in pulmonary hypertensive states of various etiologies (e.g., idiopathic, heart failure, and congenital anomalies) in proportion to the severity of pulmonary hypertension. It is possible that reduced pulmonary clearance of this peptide contributes to the hyperendothelinemia of those pathologies. The ETA and ETB receptors are abundant in lung tissues: on the vascular endothelium, the ETB receptor is predominant and may contribute to ET-1 extraction through receptor-mediated endocytosis. We designed experiments to determine and quantify the importance of the ETA and ETB receptors in the pulmonary extraction of circulating ET-1 in anesthetized dogs. The single-pass cumulative tracer ET-1 extraction by the lung was measured with the indicator-dilution technique before and 5 min after intrapulmonary injection of the specific ETA antagonist BQ-123 (n = 5, 120-960 nmol) and the specific ETB antagonist BQ-788 (n = 6, 1,000 nmol). The inhibitors had no significant effect on pulmonary and systemic hemodynamics. Mean cumulative pulmonary ET-1 extraction was not modified by BQ-123 [control (C): 36 +/- 4%, antagonist (A): 34 +/- 6%] but was completely abolished by BQ-788 (C: 34 +/- 6%, A: 0 +/- 2%, P < 0.001). The pulmonary rate constant (K) for ET-1 removal was also unaffected by BQ-123 (C: 0.050 +/- 0.0085 s-1, A: 0.047 +/- 0.012 s-1) but significantly decreased and became close to zero after BQ-788 (C: 0.058 +/- 0.014 s-1, A: 0.009 +/- 0.007 s-1, P < 0.1). We conclude that the ETB receptor is completely and exclusively responsible for pulmonary ET-1 removal in vivo. Future studies are needed to show whether desensitization or downregulation of the ETB receptor may contribute to the increase in circulating ET-1 levels in conditions associated with pulmonary hypertension. This novel pulmonary endothelial cell function may play a protective role by modulating circulating ET-1 levels in the systemic circulation.

Hepatic uptake of protein-bound ligands: effect of an unstirred Disse space.

Uptake of protein-bound substances by the liver was modeled considering concurrent depletion of unbound ligand (i.e., not bound to protein)along the length of a sinusoid as well as within a 0.5-micron unstirred boundary layer at the surface of the hepatic parenchymal cells. The development completes a previous exploration of Weisiger et al. [Am. J. Physiol. 261 (Gastrointest. Liver Physiol. 24): G872-G884, 1991]. Ligand is carried across the unstirred layer by albumin, producing a deviation from binding equilibrium inside and outside the unstirred layer. The resulting differential equations have a closed solution. In the case of tight binding, the unbound ligand in the sinusoid is in a quasi-steady state, and the unbound fraction becomes constant along the flow path, except for a very short section at its beginning. During hepatic oleate uptake, the unbound oleate concentration rises from 39% of the equilibrium value at 0.1 microM albumin and 0.01 microM oleate to 78% at 0.5 microM albumin and 0.05 microM oleate. diffusion through the unstirred layer and across the cell membrane was found, in the model, to contribute to the overall resistance to oleate uptake in a complementary fashion.

Oleate uptake by isolated hepatocytes and the perfused rat liver is competitively inhibited by palmitate.

Competition for uptake between long-chain free fatty acids has been difficult to document, because there has been no algorithm for computing unbound concentrations of two fatty acids simultaneously in solution with albumin. We modified an iterative procedure to permit this computation and studied initial [3H]oleate uptake by isolated hepatocytes and steady-state uptake by the single-pass perfused rat liver from 600 microM bovine serum albumin solutions containing various concentrations of oleate in the presence and absence of palmitate. In both systems, the Michaelis-Menten constant was significantly higher in the presence of palmitate than in its absence, whereas the maximal reaction velocity was unaltered, indicating competitive inhibition. In additional experiments employing the multiple transhepatic indicator-dilution technique, the influx rate constant and permeability-surface area product for oleate influx were significantly reduced by palmitate, confirming that the competition observed in the conventional perfused liver studies was at the influx step. Long-chain fatty acid uptake has now been shown to exhibit all the kinetic properties of facilitated transport and cannot be attributed solely to passive diffusion.

Accumulation of unconjugated bilirubin in cholesterol pellets implanted in swine gallbladders.

BACKGROUND & AIMS: Most cholesterol gallstones have a pigmented center, but it is unclear whether its presence is primary or secondary. This study was performed to determine if bilirubin would accumulate in a gallstone model consisting of cholesterol pellets. METHODS: Cholesterol was compressed into pellets at 2500 psi, producing a pellet that behaved like human cholesterol gallstones in regard to penetration of solutes into the stone. Pellets were implanted into gallbladders of pigs and harvested after 4 weeks. Bilirubin species were measured by high-performance liquid chromatography. RESULTS: The proportions of bilirubin species in bile were not changed by the presence of pellets, i.e., diconjugates (mean +/- SD, 1.9% +/- 1.0% vs. 0.7% +/- 0.8%), monoconjugates (83.8% +/- 5.5% vs. 87.8% +/- 6.6%), and unconjugated bilirubin (14.2% +/- 5.3% vs. 11.5% +/- 5.6%) were similar at the time of implantation and removal. The cut surfaces of the pellets were pigmented. Pellets contained 5.46 +/- 1.38 micrograms bilirubin/g sample at harvesting, and 98.6% +/- 2.3% of bilirubin in pellets was unconjugated. In in vitro studies, there was a large increase in unconjugated bilirubin in the bile. Pellets also became pigmented in vitro, but there was considerable variability in the bilirubin species present in the pellets. CONCLUSIONS: Unconjugated bilirubin accumulates in cholesterol pellets and pigments them. This provides a mechanism by which cholesterol gallstones could become secondarily pigmented.

Kinetics of pulmonary uptake of serotonin during exercise in dogs.

The multiple indicator-dilution technique was employed in the exercising dog to evaluate the effect of increasing activity on the pulmonary extraction and kinetics of removal of tracer 3H-labeled serotonin (5-HT) and on the measured central blood volume and tracer-accessible extravascular lung water. 51Cr-labeled red blood cells, 125I-labeled albumin, and 14C-labeled 1,8-octanediol were injected with labeled 5-HT at rest and at two increasing levels of exercise (lower and higher in 9 dogs). Blood flow approximately tripled at the highest level of exercise, and the central blood volume increased linearly with increasing blood flow. The tracer-accessible extravascular lung water increased in the transition from rest to low-level exercise and stabilized at an average proportion of 0.85 of the gravimetric extravascular lung water at the higher values of blood flow. The average labeled 5-HT extraction at rest was 42 +/- 11%, and this slowly decreased with increase in flow. The calculated permeability-surface area product for 5-HT increased approximately directly with increasing blood flow. We conclude that exercise results in an increase in the central blood volume that is accompanied by an increase in the tracer-accessible extravascular lung water (lung tissue recruitment) over low exercise levels, with no change at higher levels of exercise, and that the pulmonary capillary surface area subserving 5-HT uptake increases almost linearly with flow over the range of flows attained.

Tracer oxygen distribution is barrier-limited in the cerebral microcirculation.

The kinetics of tracer oxygen distribution in the brain microcirculation of the awake dog were investigated with the multiple indicator dilution technique. A bolus containing 51Cr-labeled red blood cells, previously totally desaturated and then resaturated with [18O]2 (oxygen), 125I-albumin, 22Na, and [3H]water, was injected into the carotid artery, and serial anaerobic blood samples were collected from the sagittal sinus over the next 30 seconds. The outflow recovery curves were analyzed with a distributed-in-space two-barrier model for water and a one-barrier model for oxygen. The analysis provided an estimate of flow per gram brain weight as well as estimates for the tracer water and oxygen rate constants for blood-to-brain exchange and tracer oxygen parenchymal sequestration. Flow to tissue was found to vary between different animals, in concert with parallel changes in oxygen consumption. The 18O2 outflow curves showed an early peak, coincident with and more than half the magnitude of its vascular reference curve (labeled red blood cells), whereas the [3H]water curve increased abruptly to a low-in-magnitude curve at low flow values and to a small early peak at high flow values. Analysis indicates that the transfers of both 18O2 and [3H]water indicators from blood to brain are barrier-limited, with the former highly so because of the large red blood cell capacity for oxygen, and that the proportion of the tracer oxygen returning to the circulation from tissue is a small fraction of the total tracer emerging at the outflow.

The 1994 G. Malcolm Brown Lecture. Biological barriers and medicine.

Career support provides the essential element needed for the detailed development of thematic areas of inquiry. Dr Goresky outlines how career support provided for him the substratum for the investigation and definition of tracer exchange processes in the liver. Classical interstitial substances (labeled albumin, inulin, sucrose, and sodium) and labeled water were found to undergo flow limited distribution in the liver. An excluded volume phenomenon created systematic variation in accessible interstitial space (that is, Disse space) values, smaller for larger molecular weight substances. Labeled rubidium entered liver cells in a concentrative fashion (return from cells was very small, early in time). Labeled glucose liver cell entry was found to exhibit the characteristics of a carrier-mediated membrane transport process. Labeled galactose showed saturation of intracellular sequestration, as well as of the cell entry process, the former at much lower galactose concentrations. Straight-chain labeled monohydric alcohols were found to enter liver cells in a flow-limited fashion. Labeled ethanol consumption, when related to underlying steady ethanol values, exhibited Michaelis-Menten kinetics. A substantial extra intracellular enzymic space of distribution was found for the C3- and C4- straight-chain alcohols, predicted by the kinetics. Development of the tracer approach allowed the differentiation and characterization of the processes by which substances penetrate the cell membrane barrier and those resulting in intracellular sequestration.

Carrier-mediated uptake and excretion of bromosulfophthalein-glutathione in perfused rat liver: a multiple indicator dilution study.

The hepatic removal of the glutathione conjugate of bromosulfophthalein (BSPGSH) was studied in the single-pass perfused rat liver with the multiple indicator dilution (MID) technique against various background concentrations of BSPGSH (20 to 214 mumol/L) over which nonlinear binding to both plasma (albumin) and tissue proteins with two classes of binding sites was found. A bolus containing 51Cr-labeled red blood cell (a vascular reference), [125I]albumin and [14C]sucrose (large and small molecular weight interstitial references, respectively), D2O (a cellular space reference), and [3H]BSPGSH was injected into the portal vein during steady-state. The eliminated fraction of dose, obtained by subtracting the survival fraction of [3H]BSPGSH in plasma from one, corresponded to the steady state extraction ratio (E) with bulk data, which declined from 0.74 +/- 0.04 to 0.27 +/- 0.01 with concentration. The major portion of the tracer outflow profile was a throughput component, which is the proportion of tracer that did not enter liver cells during its transit through the liver. The influx, efflux, and sequestration coefficients, evaluated with previously developed barrier-limited models, provided the corresponding influx (k1), efflux (k-1) and excretion (kseq) rate constants. Concentration-dependent influx (Vmax = 83 nmol min-1 g-1 and Km = 3.7 mumol/L), efflux (Vmax = 15 nmol min-1 g-1 and Km = 1.8 mumol/L), and excretion (Vmax = 94 nmol min-1 g-1 and Km = 1.8 mumol/L) were obtained for BSPGSH, when Km values are expressed in terms of the unbound concentrations. In these calculations, the observed unbound tissue concentration was not used for estimation of the Vmax and Km for efflux and excretion because of overestimation, because of the presence of highly concentrated BSPGSH in ductular elements present in liver homogenates; rather, the unbound tissue concentration was calculated from the influx, efflux, and removal rate coefficients. Because of carrier-mediated entry, the unbound tissue concentration does not equal the unbound plasma concentration, and kinetic parameters for BSPGSH excretion could be alternately estimated when the rate of excretion or net rate of loss of BSPGSH from plasma was regressed against the estimated tissue unbound concentration. This yielded a Vmax of 97 nmol min-1 g-1 and a Km of 3.6 mumol/L, values similar to those obtained from MID.(ABSTRACT TRUNCATED AT 400 WORDS)

Sulfation of acetaminophen by the perfused rat liver: the effect of red blood cell carriage.

Acetaminophen uptake and conversion in the perfused rat liver to acetaminophen sulfate was studied with the multiple indicator dilution technique (MID). Because acetaminophen is avidly bound to red blood cells and not albumin, a pre-equilibrated MID dose containing the noneliminated references (51Cr-labeled red blood cells [RBC, a vascular reference], [58Co]EDTA [a small molecular weight interstitial reference that does not enter cells], and D2O [a cellular reference]) and [3H]-acetaminophen was introduced into the portal vein of the single-pass perfused rat liver (1 mg/L acetaminophen) under varying conditions of hematocrit, with observation of timed outflow profiles in the hepatic venous blood. The [3H]acetaminophen curve exhibited an early high peak, paralleling that for red cells and varying with hematocrit, followed by a prolonged decline, with the late appearance of acetaminophen sulfate product; the early peak disappeared when red cells were absent from the dose and perfusate. Analysis demonstrated a slow release of acetaminophen from the red blood cells and rapid liver cell entry, so that red cell binding was displayed as a red cell carriage effect that reduced the rate of liver cell entry and hence of sulfation of [3H]-acetaminophen. The liver cells exhibited a concomitant very low permeability to product acetaminophen sulfate, leading to protracted product outflow curves. An inferred slow efflux-mediated storage phenomenon for product was found to evolve as a result.

Effects of second messengers on the permeability and morphology of eel rete capillaries.

The effects of second-messenger concentration changes on capillary diffusion capacity (permeability-surface area product [PS]) to cellular and paracellular tracers and on capillary ultrastructure were studied during countercurrent perfusion of the rete of the eel swim bladder. Cyclic nucleotide effects were investigated with isoproterenol, forskolin, and dibutyryl cAMP. Isoproterenol (5 x 10(-6) mol/L) did not modify water and solute permeability or capillary structure. Forskolin (10(-4) mol/L) immediately raised the concentrations of cAMP in the rete and produced interstitial edema but did not change permeability. The addition of dibutyryl cAMP (10(-6) mol/L) to the perfusate had rapid effects: it reduced the PS of [3H]water and oxygen and increased the PS of [125I]albumin, [14C]sucrose, and 22Na. No structural changes were observed. Phosphoinositide effects were studied with 1,2-dioctanoyl-sn-glycerol (DG) and phorbol 12-myristate 13-acetate (PMA). DG (10(-5) mol/L) had no effect on the permeability of the rete to water and solutes, while inducing cell membrane vacuolization. PMA (10(-5) mol/L) progressively reduced the PS of [3H]water. In contrast, PS values of [125I]albumin, [14C]sucrose, and 22Na rose gradually. Membrane vacuoles bulging into the lumen and in the cytoplasm were a common feature. The Ca2+ effect was investigated with the Ca2+ ionophore A23187. At 5 x 10(-6) mol/L, unsteady permeability changes and extensive cytolysis were observed. At 5 x 10(-7) mol/L, the PS of [125I]albumin, [14C]sucrose, and 22Na rapidly increased. The PS values for water were not modified. No structural changes were identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of flow, perfusion pressure, and oxygen consumption on cardiac capillary exchange.

The roles of blood flow, local oxygen consumption, and perfusion pressure on cardiac transcapillary exchange were characterized in closed-chest anesthetized dogs by use of the multiple-indicator dilution technique. Occlusion of the carotid arteries or injection of dipyridamole increased coronary flow to significantly higher values compared with a group of animals in a basal state obtained in a previous study. Carotid occlusion resulted in a significant increase in perfusion pressure and myocardial oxygen consumption, whereas these two variables were significantly reduced after dipyridamole. For the whole group of animals, the capillary permeability-surface area product for sucrose increased with coronary flow, which appeared to be the important controller for this microcirculatory exchange parameter. Perfusion pressure and myocardial oxygen consumption also regulated permeability-surface area product values, although to a lesser extent than flow. The heterogeneity of transit times in the capillaries was reduced at high coronary flow values, despite large differences in the cardiac utilization of oxygen. The data suggest that cardiac capillary exchange responds mostly to hemodynamic changes originating at the precapillary level.

Bilirubin conjugate changes in the bile of gallbladders containing gallstones.

Gallbladder bile was obtained at laparoscopic cholecystectomy from 31 patients with gallstones, and duodenal aspirates from 18 normal controls. Bile pigments (9 conjugates and unconjugated bilirubin) were analyzed by high-performance liquid chromatography. The average proportional composition of the bile pigments from the patients with gallstones was characteristically different from the controls. Whereas the average values for the principal conjugates in the controls were bilirubin diglucuronide 83.4%, bilirubin monoglucuronide 10.1%, bilirubin monoglucuronide monoglucoside 4.5%, and bilirubin monoglucuronide monoxyloside 1.0%, the corresponding values in the biles from the patients with gallstones were 66.3%, 20.6%, 6.5%, and 2.8%, respectively. Values from the more minor conjugates and unconjugated bilirubin were less than 2% in either data set. In samples obtained in 9 of the gallstone patients early and late in the procedure, no significant change was found. Over the spectrum of findings in the gallstone patients, as the proportion of bilirubin diglucuronide became smaller, that of bilirubin monoglucuronide increased substantially, whereas those of bilirubin monoglucuronide monoglucoside and bilirubin monoglucuronide monoxyloside increased to a small extent. The findings suggest that bilirubin diglucuronide hydrolysis occurs in the gallbladder bile of gallstone patients, with the production of bilirubin monoglucuronide, and that if further hydrolysis of bilirubin monoglucuronide occurs with the formation of unconjugated bilirubin, the latter does not ordinarily increase because it is being absorbed. Stasis with increased gallbladder residence time was likely present in some of the patients.(ABSTRACT TRUNCATED AT 250 WORDS)