Humic acid-induced echinocyte transformation in human erythrocytes: characterization of morphological changes and determination of the mechanism underlying damage

Blackfoot disease (BFD) is a peripheral arterial occlusive disease found among human inhabitants along the southwest coast of Taiwan. Well water used for drinking and cooking contains humic acid (HA), which may be a possible etiological factor. In this study, HA toxicity was investigated in human erythrocytes and was found to induce echinocytic formation. Morphological changes occurred in both a concentration- and time-dependent fashion. The presence of HA was also observed to facilitate the loading of erythrocytes with excess Ca(2+) (1 mM), which may have occurred following permeability changes in cell membranes, leading to echinocytic transformations. Sodium dodecyl sulfate (SDS) gel electrophoresis indicated that echinocyte formation was due to the oxidation of normal membrane proteins that were replaced by high-molecular-weight proteins. Humic acid also induced hemoglobin oxidation in erythrocytes. Data show that oxidative stress generated by HA as well as direct effects were exerted on the cytoskeleton of erythrocytes, and these may be significant factors in the etiology of BFD.

Effects of halothane and methoxyflurane on the hypothalamic-pituitary-adrenal axis in rat

Effects of acute exposure (2 h) to either 1.5% halothane or 0.5% methoxyflurane on chemical mediators of the hypothalamic-pituitary-adrenal (HPA) axis were evaluated in male Sprague-Dawley rats immediately after exposure, after the righting reflex (4 h), or 24 h postexposure. Effects of these anesthetics on hippocampal corticotropin releasing factor (CRF) were also evaluated. Methoxyflurane caused significant elevations in pituitary adrenocorticotropin hormone (ACTH)-like immunoreactivities in all three of the experiment's time groups, yet halothane failed to cause the same response immediately after exposure. Serum ACTH-like immunoreactivities were significantly elevated immediately after exposure to both anesthetics, but were not elevated at 4 and 24 h postexposure. Corticosterone (CORT)-like immunoreactivities were significantly elevated by halothane in all experimental groups, and in the 2- and 24-h groups following methoxyflurane exposure. Hippocampal CRF-like immunoreactivities remained unaffected by either anesthetic. Results indicate that a 2-h exposure to either halothane or methoxyflurane results in significant activation of the rat hypothalamic-pituitary-adrenal axis, and that the activation appears to be sustained over a 24-h period.

Alterations in catecholamine turnover in specific regions of the rat brain following acute exposure to nitrous oxide

The effects of nitrous oxide (N2O) on steady-state concentrations and turnover rates of catecholamines in the olfactory bulb, hypothalamus, brain stem, hippocampus, striatum, thalamus, cerebral cortex, and spinal cord were determined in rats. Animals were exposed for 2 h to either 60% N2O or air. Immediately following exposure, all animals were injected intraperitoneally with alpha-methylparatyrosine (alphaMPT), a competitive inhibitor of tyrosine hydroxylase, and sacrificed at 0, 30, or 90 min postinjection. Brain catecholamine concentrations were determined using high-performance liquid chromatography coupled with electrochemical detection (HPLC-EC). Results indicate that N2O exposure significantly elevates steady-state concentrations of norepinephrine (NE) in the hypothalamus and striatum yet decreases amine levels in the brain stem region. Steady-state levels of dopamine (DA) were not significantly altered in any region of the CNS by N2O exposure. Acute exposure to N2O also resulted in significant decreases in the turnover rate of NE in the brain stem, yet it increased turnover of this amine in the olfactory bulb, hypothalamus, and striatum. Acute exposure to N2O resulted in a decreased turnover rate of DA in the hippocampus and striatum. In contrast, N2O appears to increase DA turnover in the olfactory bulb. These results indicate that acute exposure to N2O in rats causes region-specific alterations in steady-state levels and turnover rates of DA and NE within the central nervous system.

Effects of halothane and methoxyflurane on regional brain and spinal cord substance P-like and beta-endorphin-like immunoreactivities in the rat

Effects of acute exposure (2 hr) to either 1.5% halothane or 0.5% methoxyflurane were investigated in the Sprague Dawley rat. Pituitary (PIT) and central nervous system (CNS) substance P (SP)-like and beta-endorphin (beta-end)-like immunoreactivities were evaluated immediately after anesthetic exposure (2 h), after righting reflex (4 h) or 24 hr postexposure (24 h). Only halothane significantly reduced SP-like immunoreactivity in olfactory bulbs in both the 2-h and 4-h groups. Halothane elevated SP-like immunoreactivity of hippocampus at all three time periods, and in the hypothalamus at 2 h. Both anesthetics significantly depleted thalamic concentrations of SP-like immunoreactivity. Methoxyflurane anesthesia resulted in a drastic decrease in SP-like immunoreactivity in PIT at all three time periods periods, while halothane elevated PIT concentrations of this peptide at 4 h. Both anesthetics significantly decreased beta-end-like immunoreactivity in the olfactory bulbs and thalami at 2, 4, and 24 h. However, halothane alone significantly elevated beta-end-like immunoreactivity in the spinal cord at 24 h. Halothane significantly elevated PIT beta-end-like immunoreactivity at 2 and 24 h, while methoxyflurane significantly lowered it in the 4-h group, but elevated the levels of the same in the 24-h group. Brain stem beta-end immunoreactivity were significantly reduced at 2 h by both anesthetics, and at 4 h by methoxyflurane. Results indicate that halothane and methoxyflurane may differ significantly in their actions on SP and beta-end secreting neurons in the CNS.

Physiology of the endocrine pancreas

The endocrine pancreas is composed of nests of cells called the islets of Langerhans, which comprise only about 20% of pancreatic cell mass and secrete insulin, glucagon, somatostatin, and pancreatic polypeptide. Insulin is anabolic, increasing storage of glucose, fatty acids and amino acids, while glucagon namely stimulates hepatic glycogenolysis, gluconeogenesis, and ketogenesis. Somatostatin acts as a paracrine agent to inhibit both insulin and glucagon release, and, therefore, to modulate their output. This article explores factors controlling release of these hormones, as well as the way in which they affect fuel metabolism in the whole animal.

Biochemical and physiological manifestations of acute insulin withdrawal

When insulin is withdrawn acutely from a severely diabetic patient, a sequence of intricately interconnected events begins which, without intervention, can result in coma and death. These events involve not only carbohydrate metabolism, but protein and lipid metabolism, electrolyte and fluid balance as well. Acute insulin withdrawal permits the unopposed action of the counter-regulatory hormones (which are attempting to elevate the plasma glucose concentration), namely glucagon, cortisol, growth hormone, and epinephrine. This article details interrelationships existing between the many biochemical and physiological events that are occurring more or less simultaneously in the animal following acute insulin withdrawal.

Effect of chronic DDC treatment on LHRH and substance P amidation processes in the rat

We examined the effects of chronic diethyldithiocarbamate (DDC) treatment on the concentrations of methionine-enkephalin, mature and unamidated forms (-Gly) of luteinizing hormone releasing hormone (LHRH) and substance P (SP) in various regions of the central nervous system (CNS). Chronic DDC treatment resulted in elevations of LHRH-Gly like immunoreactivity in the preoptic area (POA) and the medial basal hypothalamus (MBH), as well as elevations in SP-Gly like immunoreactivity in all areas of the CNS examined. Castration altered the ratios of SP-G-like/SP-like immunoreactivity in the pons, and LHRH-Gly like immunoreactivity in the MBH. Met-enkephalin concentrations were significantly elevated in the pons and medulla of intact DDC-treated animals, and in the POA of both intact- and castrated DDC-treated animals. Results demonstrate that it is possible to detect basal levels of unamidated LHRH and SP in many areas of the CNS, with ratios of unamidated/amidated peptides representing a unique and sensitive method for determining altered posttranslational processing of these transmitters, especially under altered endocrine states such as castration. Pharmacological blockade of terminal enzymatic processing of these peptides may be useful in studying upstream regulatory events in peptidergic neurons.

Influence of halothane and methoxyflurane on regional brain and spinal cord concentrations of methionine-enkephalin in the rat

Rats were exposed to either oxygen (controls), 1.5% halothane in oxygen, or methoxyflurane (0.5%) in oxygen over a period of 2 h, then sacrificed at the end of exposure (2-h group), 4 h after removal from environmental chamber (4-h group), or at 24 h following anesthetic exposure (24-h group). Pituitary (excluding the neural lobe, Pit), brain, and spinal cord areas were isolated and processed with Met-enkephalin tissue concentrations determined. In halothane-exposed animals, Met-enkephalin concentrations in pit and across CNS areas studied were significantly lower at 2 h following anesthetic exposure than in control animals. Concentrations of Met-enkephalin in many areas of CNS and Pit of 4-h group approached control levels. Concentrations of Met-enkephalin in all areas studied except spinal cord returned to basal levels by 24 h following halothane exposure. Exposure to methoxyflurane resulted in less dramatic changes in Met-enkephalin concentrations across CNS regions examined. Exposure to methoxyflurane resulted in significant decreases in Met-enkephalin levels in olfactory bulb, thalamus, and hippocampus only. Met-Enkephalin levels did not change significantly in other areas of the central nervous system following methoxyflurane exposure. These results indicate that halothane and methoxyflurane may have differential effects on the endogenous opioid system.

Role of intracellular calcium and protein kinases in the activation of hepatic Na+/taurocholate cotransport by cyclic AMP

Glucagon and dibutyryl cyclic AMP (Bt2cAMP) stimulate Na+/taurocholate (TC) cotransport and increase the intracellular Ca2+ concentration ([Ca2+]i) of hepatocytes. Whether the effect of cAMP is mediated via increases in [Ca2+]i, cAMP-dependent protein kinase (PKA), and/or protein kinase C (PKC) was investigated in this study. TC uptake and [Ca2+]i were determined in isolated rat hepatocytes using [14C]TC and the fluorescent dye quin-2, respectively. Bt2cAMP, forskolin, and 8-bromo-cAMP stimulated Na(+)-dependent, but not Na(+)-independent TC uptake. Bt2cAMP increased the maximal rate of Na+/TC cotransport without affecting the apparent Km. Increases in TC uptake and [Ca2+]i by Bt2cAMP were inhibited in hepatocytes preloaded with bis-(2-amino-5-methylphenoxy)-ethane-N,N,N',N'-tetraacetic acid (MAPTA) or preincubated with 8-diethylaminooctyl 3,4,5-trimethoxybenzoate (TMB8). Calmodulin antagonists inhibited Bt2cAMP-induced increases in TC uptake, but not [Ca2+]i. Other Ca(2+)-mobilizing agents (thapsigargin, vasopressin, phenylephrine, and ionomycin) increased [Ca2+]i but failed to stimulate TC uptake, indicating that an increase in [Ca2+]i alone is not a sufficient stimulus for TC uptake. However, increases in TC uptake by 1 and 10 microM Bt2cAMP were further increased by thapsigargin, indicating a permissive role for Ca2+/calmodulin. Bt2cAMP-induced increases in TC uptake and [Ca2+]i were inhibited by known inhibitors of PKA and by an activator of PKC, but they remained unaffected by a specific inhibitor of PKC. Unlike thapsigargin, vasopressin inhibited Bt2cAMP-induced increases in TC uptake. Taken together these results indicate that stimulation of hepatic Na+/TC cotransport by cAMP 1) is mediated via PKA; 2) is potentiated, but not mediated, by Ca2+/calmodulin-dependent processes; and 3) may be down-regulated by PKC.

Distribution of catecholamines in the central nervous system of the pig

The objective of this study was to document, through comprehensive means, normal distribution and concentration of catecholamines in various regions of the CNS of pigs, an increasingly popular animal model used for transgenic manipulation of neural genes. The effects of gonadal steroidal status on this distribution were also assessed by comparing CNS catecholamine concentrations among mature male pigs (boars), immature (gilts) and mature female pigs (sows), and adult male pigs castrated prepuberally (barrows). Dissected tissue samples from the CNS were extracted in 2 N acetic acid, filtered through a 0.2 micron filter, then quantitated by reverse-phase high performance liquid chromatography using a C-18 reverse phase column with electrochemical detection. In both boars and sows the highest concentrations of norepinephrine (NE) were found in the diencephalic areas and brain stem. Gilts exhibited elevated concentrations of NE in the olfactory bulbs (OB), hypothalamus, pons, and corpus trapezoideum-locus ceruleus (LC) compared to lower concentrations in corresponding areas of sows. Prepuberal castration of the male was associated with significantly lower NE concentrations in the striatum, periaqueductal area (PAG), pons, LC, and spinal cord. The sow exhibited significantly lower NE concentrations in the mammillary area (Mam), PAG, pons, and spinal cord than those in corresponding areas of the boar. Dopamine concentrations appeared to be similar in all areas of the brain and spinal cord studied in the sow and boar. Results demonstrated that prepuberal castration of the male appears to significantly alter the DA content of the Mam and dorsal spinal cord, in contrast to gilts who possess significantly higher concentrations of DA. It is concluded from our studies that in general, catecholamine concentrations in various regions of the brain and spinal cord of sexually mature pigs parallel distributions of neuropeptides, substance P, and methionine enkephalin, as previously reported. In addition, significant association was found between gonadal activity and catecholamine concentrations in discrete areas of the pig brain.

Cocaine and lidocaine interfere with epinephrine-induced changes in intracellular calcium concentration and glucose efflux from rat hepatocytes

The mechanism of cocaine-induced hepatotoxicity is not clearly understood. Recent studies show that fluctuations in intracellular Ca2+ ([Ca2+]i) and/or cyclic-AMP ([cAMP]) concentration play a major role in hormone action, and sustained elevations in [Ca2+]i may be involved in the initiation of hepatocellular damage. To evaluate the possible involvement of intracellular Ca2+ and/or cAMP, we investigated effects of cocaine and lidocaine on basal, epinephrine and dibutyryl cyclic-AMP (DBcAMP)-induced changes in [Ca2+]i and glucose efflux from isolated rat hepatocytes. [Ca2+]i was monitored continuously using a Ca2(+)-selective fluorescence indicator, Quin-2, and was calculated after correcting for autofluorescence. Neither cocaine nor lidocaine (0.1-5 mmol/l) affected basal [Ca2+]i, yet both agents decreased epinephrine (10 mumol/l) and DBcAMP (100 mumol/l)-induced increases in [Ca2+]i in a dose-dependent fashion. Half-maximal inhibition occurred at 0.75 mmol/l cocaine and 1.7 mmol/l lidocaine. Cocaine and lidocaine also decreased epinephrine and DBcAMP-induced glucose efflux. The dose-dependent effect on epinephrine-induced glucose efflux was similar to that of both anesthetics on epinephrine-induced increases in [Ca2+]i. However, 5 mmol/l cocaine or lidocaine decreased DBcAMP-induced glucose efflux by less than 50%, and [Ca2+]i by more than 80%. Taken together, these results indicate that cocaine and lidocaine decrease the ability of epinephrine to stimulate glucose efflux by interfering with the Ca2(+)-mediated, and not the cAMP-mediated intracellular pathway. It is therefore speculated that alterations in metabolic endocrine regulation may contribute to cocaine's hepatotoxic effect.

Basal and bile salt-stimulated bile flow and biliary lipid excretion in ponies

The role of bile salt in biliary lipid excretion was studied in 3 healthy ponies with chronic external biliary fistulas. After endogenous bile salt pool depletion, micelle-forming taurocholate or taurochenodeoxycholate was infused to replace excreted bile salt. Enterohepatic circulations were held open (total biliary diversion) throughout each study. Results indicated that biliary lipid excretion in ponies (113 +/- 21 nmol/min/kg of body weight) is approximately 10 times less than that reported in rodents. Although the lipid composition (4.4% cholesterol, 5.6% phospholipid, and 90% bile salt) was within the predicted range for a single phase of micellar (or vesicular) liquid in solution, it was supersaturated with cholesterol because of low absolute concentrations of bile salt and phospholipid. Ponies, like guinea pigs, were determined to have a high bile salt-independent secretion of biliary lipid with little (or no) coupling to endogenous bile salt output. However, bile salt excretion induced by higher taurocholate infusion rates (ie, those greater than the physiologic range of 61 to 125 nmol/min/kg) was positively correlated with an increase in biliary phospholipid excretion, but not cholesterol excretion, thus indicating that a threshold intracellular bile salt concentration may be associated with enhanced biliary phospholipid excretion in ponies. The apparent cholerectic effects of endogenous bile salts, taurocholate, and taurochenodeoxycholate (that is, the increment in bile flow per increment in bile salt recovered) were greater in ponies than reported for any other mammal.

Hepatotoxic bile acids increase cytosolic Ca++ activity of isolated rat hepatocytes

Effects of bile acids on cystolic Ca++ activity and cell viability of isolated rat hepatocytes were studied to test the hypothesis that bile acids may produce hepatotoxicity by increasing cystolic Ca++ activity. Changes in cystolic Ca++ activity were calculated from time-dependent changes in fluorescence of quin-2 loaded hepatocytes. Release of lactate dehydrogenase and changes in propodium iodide fluorescence were used to assess cell viability. Bile acids studied were unconjugated and taurine-conjugated cholate, chenodeoxycholate (and taurochenodeoxycholate), deoxycholate (and taurodeoxycholate) and lithocholate (and taurolithocholate). With the exception of cholate and taurocholate, bile acids increased cystolic Ca++ activity within 10 to 30 sec in a concentration-dependent fashion (0.05 to 1.0 mM) and in the order lithocholate = taurolithocholate greater than chenodeoxycholate = taurochenodeoxycholate = deoxycholate = taurodeoxycholate. The initial increase in cystolic Ca++ activity by bile acids was not due to cell damage, since bile acid-induced decreases in cell viability were not significant until 2 to 3 min. At higher concentrations of unconjugated bile acid, there was a secondary increase in quin-2 fluorescence corresponding temporally to the increase in propodium iodide fluorescence, indicating cell damage after the initial increase in cystolic Ca++ activity. The ability of conjugated and unconjugated bile acids to increase cystolic Ca++ activity was abolished and decreased (60 to 90%), respectively, in the absence of extracellular Ca++, indicating that extracellular Ca++ is the major source of the bile acid-induced increase in cystolic Ca++ activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of hepatobiliary scintigraphy to diagnose bile duct atresia in a lamb

A neonatal lamb was admitted with icterus, hypoglycemia, increased liver enzyme activities, and delayed sulfobromophthalein clearance. Biliary and pancreatic duct atresia were documented in this lamb at necropsy. Hepatobiliary scintigraphy was useful in reaching an antemortem diagnosis of bile duct obstruction. Hepatobiliary scintigraphy, using 1.5 mCi of 99m technetium-labeled acid, was performed on the affected lamb and on an age-matched control lamb. Using a large field-of-view camera equipped with a low-energy parallel-hole collimator, right ventral oblique images of the thorax and abdomen were obtained. Images were simultaneously recorded on microdot film by use of a dedicated nuclear medicine computer. In the control lamb, there was rapid clearance of radioactivity from the blood pool, coincident with obvious accumulation of radioactivity in the liver and followed by sequential accumulation in the intrahepatic biliary system, gallbladder, common bile duct, and small intestine. Results of the study in the affected lamb were characterized by prolonged blood-pool radioactivity without appreciable hepatic uptake and by excessive renal and urinary bladder activity in the later phases of the study. Hepatobiliary scintigraphy was a safe and non-invasive procedure that provided quantitative information about the degree of bile duct obstruction in the affected lamb.

Enterohepatic circulation of lorazepam and acetaminophen conjugates in ponies

Adult female ponies (130-225 kg) with chronically implanted external biliary fistulas (T-tubes) participated in three-way cross-over studies using either i.v. lorazepam (10 mg) or acetaminophen (2 g), two model drugs biotransformed mainly by hepatic conjugative reactions. The objectives were to determine the systemic pharmacokinetics, urinary and biliary excretion and degree of enterohepatic circulation (EHC) of these compounds. Trial conditions were: A: EHC intact, with blood and urine, but not bile, collected after i.v. drug administration; B: EHC interrupted, with blood, urine and bile collected after i.v. drug administration; and C: bile infused, EHC open, without i.v. drug administration, with bile collected from trial B (containing biliary excreted drug) infused into the duodenum via the T-tube, followed by collection of blood, urine and bile. At least 2 weeks elapsed between trials. Interruption of the EHC caused lorazepam plasma half-life to shorten (3.4 vs. 2.3 hr with the EHC intact, P less than .1), clearance to increase (9.2 vs. 12.3 ml/min/kg, P less than .1) and total area under the plasma concentration curve for lorazepam glucuronide to decrease (210 vs. 310 ng/ml X hr, P less than .06). Recovery of lorazepam as its glucuronide in bile was 24.5% of the i.v. injected dose. Urinary elimination of lorazepam glucuronide was reduced from 41 to 36% of the dose due to bile collection. Subsequent duodenal infusion of collected bile, containing an average of 2.45 mg of lorazepam as glucuronide, was followed by urinary excretion of 0.48 mg of lorazepam as glucuronide in urine and 0.36 mg re-excreted into bile.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of hepatobiliary disorders in the horse

This article addresses clinical problems that present in equine liver disease. It also discusses the variety of laboratory tests available to the clinician that can differentiate the type and degree of liver dysfunction. This is followed by a more specific discussion regarding unique features of equine bilirubin and bile acid metabolism.

Pharmacokinetics of dantrolene sodium in horses

The pharmacokinetics of dantrolene sodium were investigated in horses following both intravenous (2 mg/kg) and intragastric (4 mg/kg) administration. Two ponies also received dantrolene sodium intravenously (2 mg/kg) in a pilot study to obtain preliminary kinetic data and to determine urinary and biliary excretion of the intact drug. Distribution and elimination of dantrolene was rapid, resulting in an elimination half-life of 129 +/- 8 (SEM) min and a whole body clearance of 4.16 +/- 0.52 ml/min/kg. Following intragastric administration, dantrolene rapidly acheived peak concentrations within 1.5 h, but was incompletely absorbed, with a bioavailability of 39 +/- 10%. Small amounts of intact drug were recovered in urine and bile. Based upon disposition kinetics of dantrolene in these studies, intravenous and intragastric dosage regimens were determined which would maintain blood dantrolene concentrations within the predicted clinically effective range.

Pharmacokinetics of antipyrine, acetaminophen and lidocaine in fed and fasted horses

Previous studies demonstrated that plasma clearance of organic anions such as bilirubin, bile acid, sulfobromophthalein (BSP) and indocyanine green (ICG), was reduced from 36% (bile acid) to 55% (ICG) in fasted (3 days) horses. It is believed that a general decline in carrier-mediated hepatic uptake may have accounted for those changes. However, fasting may also affect hepatic blood flow, thereby contributing to reduced clearance of these compounds. In order to test this hypothesis, plasma clearance of antipyrine, acetaminophen and lidocaine, drugs known to be cleared by the liver yet not suspected of undergoing carrier-mediated hepatic uptake, were investigated in nine healthy adult mares (three horses/drug group) before and following a 3-day fast. Results demonstrate that fasting decreased clearance of organic anions from previous studies more than clearance of drugs used in these studies. In addition, clearance of lidocaine, the drug with the highest plasma clearance and therefore the drug most likely to be affected by reduced hepatic blood flow, was affected least by fasting. Therefore, reductions in clearance of these compounds due to fasting must not be due entirely to reductions in hepatic blood flow, but must also involve reductions in intrinsic hepatic clearance.

Antipyrine and lidocaine are cleared faster in horses than in humans: acetaminophen may be handled similarly

The following studies were designed to evaluate plasma elimination kinetics of intravenously administered antipyrine, acetaminophen and lidocaine among 9 healthy adult horses and 9 healthy drug-free humans (3 each per drug group), in order to compare potential species differences in drug-metabolizing ability. Acetaminophen is largely biotransformed in humans by hepatic glucuronide and sulfate conjugation, whereas both antipyrine and lidocaine are oxidized by hepatic microsomal mixed-function oxidases. Thus, plasma clearances of these drugs are thought to reflect differences in hepatic oxidative and conjugative activity, and possibly hepatic blood flow in the case of lidocaine. Results showed that mean (+/- SD, n = 3) acetaminophen clearance was similar in both horses (4.84 +/- 0.637 ml/min/kg) and humans (4.68 +/- 0.691 ml/min/kg). However, antipyrine clearance was 10 times greater in horses (5.83 +/- 2.21 ml/min/kg) than in humans (0.536 +/- 0.110 ml/min/kg), which may reflect enhanced hepatic microsomal activity in horses. Although lidocaine clearance in humans was similar to estimated hepatic blood flow (20.6 +/- 5.81 ml/min/kg), clearance in horses was more than 2 times greater (52.0 +/- 11.7 ml/min/kg). The cause of the higher clearance of lidocaine in horses (like dogs) remains unexplained, and may involve significant metabolism of lidocaine at extrahepatic, extravascular sites, for intravascular degradation and renal excretion of intact lidocaine in horses was negligible. Although precise biochemical mechanisms underlying pharmacokinetic parameters for these drugs in horses were not determined, it is nonetheless concluded from antipyrine results that horses may have an enhanced ability (compared with humans) to clear drugs from the circulation that are primarily metabolized in the liver by phase I oxidative reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of plasma sample storage on blood ammonia, bilirubin, and urea nitrogen concentrations: cats and horses

Ten horses, a pony, and 13 cats were used to evaluate base-line blood ammonia, bilirubin, and urea nitrogen concentrations and to determine The effects of prolonged cold storage (-20 degrees C) before assay. Base-line plasma ammonia concentrations in cats (0.992 +/- 0.083 [SE] micrograms/ml) did not change significantly after 48 hours of storage (0.871 +/- 0.073 micrograms/ml); however, they were increased 4.2- and 13-fold after 168 and 216 hours of storage, respectively. In contrast to base-line plasma-ammonia values in cats, those of horses were significantly (0.265 +/- 0.044 micrograms/ml) lower, and significantly increased from base-line values after 48 hours of storage (0.861 +/- 0.094 micrograms/ml) and continued to increase 25.6-fold at 168 hours and 18.4-fold at 216 hours. Plasma urea nitrogen concentrations in cats (25.8 +/- 1.06 mg/dl) and horses (11.2 +/- 0.749 mg/dl) did not change significantly during 168 hours of storage. Total plasma bilirubin values from both cats (0.19 +/- 0.049 mg/dl) and horses (0.75 +/- 0.064 mg/dl) also did not change significantly during storage. These results indicate that feline plasma samples for ammonia determinations may be stored at -20 degrees C for up to 48 hours, whereas equine plasma ammonia values tend to increase during that time. The reason for the increase remains unexplained. Both feline and equine plasma urea nitrogen and total bilirubin are stable for at least 168 hours of storage at -20 degrees C.

Hepatobiliary transport of indocyanine green and sulfobromophthalein in fed and fasted horses

Fasting is associated with unconjugated hyperbilirubinemia in several species, including the horse. Studies in ponies showed that a 3-day fast decreased plasma clearance of bilirubin, cholic acid, and sulfobromophthalein (BSP). Since these organic anions are conjugated with different substrates, it is possible that observed differences in plasma clearance result from a general decrease in hepatic conjugating capacity during the animals' fasting. To test this hypothesis, the effects of a 3-day fast on plasma clearance of IV injected BSP (4.4 to 5.1 mg/kg), which is conjugated to glutathione, and indocyanine green (ICG; 0.8 to 1.1 mg/kg), which is not conjugated, were studied in 10 healthy horses and 2 ponies with diverted enterohepatic circulations (indwelling T tubes). Blood samples were obtained for 30 minutes after injection, and bile samples from ponies were obtained for 3 hours. Fasting increased plasma bilirubin concentration in all animals studied (from 1.03 +/- 0.337 mg/dl in control animals to 3.49 +/- 1.01 mg/dl in fasted animals). Kinetic values of ICG disappearance were determined from single exponential functions, and those for BSP were determined from both single and curvilinear (2-exponential) functions. Plasma clearance of BSP in fed horses (8.65 +/- 1.02 ml X min-1 X kg-1) was greater than clearance of ICG (3.54 +/- 0.67 ml X min-1 X kg-1), results similar to those reported in dogs, cats, rats, and persons. Fasting significantly decreased fractional plasma disappearance rate of both BSP (-36%) and ICG (-58%) and similarly reduced plasma clearance (BSP,-48%; ICG,-55%).(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced biliary bilirubin excretion after heparin-induced erythrocyte mass depletion

The effect of large-dose heparin therapy on erythrocyte mass depletion in ponies was investigated to determine whether stimulation of reticuloendothelial cell activity and catabolic function would be evidenced by enhanced catabolism of heme to bilirubin. Ponies with chronic external biliary fistula were used to examine biliary excretion of bilirubin both before and after heparin loading (107 U/kg, IV, plus 320 U/kg, subcutaneously) and at maintenance dosages of 320 U/kg given (subcutaneously) at 12 and 24 hours after initial loading with heparin. Results indicated that by 48 hours after ponies were first treated with heparin, catabolism of heme increased, resulting in a 35% increase in plasma bilirubin concentration and a 65% enhancement in biliary bilirubin excretion. During this period, both hematocrit and blood hemoglobin concentrations decreased by 35%. After the last heparin treatment at 24 hours after initial heparin loading, all measured variables returned toward base line within 48 hours. These studies indicated that heparin augments phagocytosis of erythrocytes, resulting in enhanced plasma bilirubin concentration and biliary bilirubin excretion.

Essential role of sodium and chloride for theophylline-induced choleresis in the isolated perfused rat liver

Active secretion of electrolytes by hepatocytes is believed to be responsible for bile acid-independent canalicular bile flow (BAICF). Theophylline, which enhances BAICF, has been shown to enhance electrogenic Cl- secretion in a number of other epithelia. Such transport is dependent on Na+ and Cl-. Thus, the mechanism of theophylline choleresis may also involve stimulation of electrogenic Cl- secretion of the liver. This hypothesis was tested by studying the effect of ion substitution on theophylline choleresis in isolated perfused rat livers. Addition of theophylline (0.1 mmol) and dibutyryl cAMP (0.05 mmol) to 100 ml perfusate, in a single dose, increased bile flow and biliary secretion of Na+ and Cl- reversibly. These effects of theophylline were virtually abolished when perfusate Na+ (146 mM) was replaced by Li+ (146 mM) or choline+ (120 mM), and when Cl- (127 mM) was replaced by 120 mM NO-3, acetate- or isethionate-. Since even the permeable ions like Li+ and NO-3 could not substitute for Na+ and Cl-, these results show that the effect of theophylline on BAICF is specifically dependent on the presence of Na+ and Cl- in the perfusate. We propose, by analogy to other epithelia, that an electrogenic Cl- secretion mechanism is present in the liver. Theophylline, acting via cAMP, stimulates this transport process, thereby enhancing BAICF.

Effects of isoflurane anesthesia on equine liver function

The acute 2-hour effects of isoflurane anesthesia on liver function and biliary excretion were examined in 2 ponies prepared surgically with chronic external biliary fistulas (T-tubes). Studies were conducted 2 to 8 months postoperatively with the enterohepatic circulation held intact between studies. Bile acid infusion IV (8.1 to 8.8 mumol/min) helped maintain bile flow and bile acid and bilirubin excretion during complete biliary diversion throughout each study. Following 3-hour control periods, anesthesia was induced and maintained at 1.3 to 1.5 minimal alveolar concentration plus O2 (spontaneous breathing) for 2 hours. Compared with the immediate 2-hour preanesthesia values, isoflurane caused significant increases in PCV (27%) and biliary bilirubin excretion (24%). However, no significant differences were detected in plasma or biliary bilirubin concentrations, biliary bile acid concentration or excretion, bile flow, or plasma aspartate aminotransferase concentrations between preanesthesia control and anesthesia periods. The results indicate that although isoflurane anesthesia enhanced hepatic bilirubin excretion, its effects on hepatic bilirubin formation and/or clearance are modest, compared with effects of halothane anesthesia which have previously been shown to enhance equine bilirubin excretion by 138% and reduce bile acid excretion by 27%. Isoflurane anesthesia in ponies does not appear to affect hepatic bile acid transport or bile formation significantly.

Effects of halothane anesthesia on equine liver function

Effects of halothane anesthesia were investigated in ponies prepared surgically with chronic external biliary fistulas (T tubes) to determine the effects on liver function and biliary excretion during 2 hours of anesthesia. Four studies were performed on 2 ponies, 2 to 6 months after surgery with the enterohepatic circulation held intact between studies. Intravenous bile acid infusion was used to maintain steady-state bile flow, bilirubin, and bile acid excretion during each study. Compared with the immediate 2-hour preanesthesia values (base line), halothane caused a 138% increase in bilirubin excretion, a 60% increase in biliary bilirubin concentration, and a 43% increase in PCV. Halothane anesthesia also caused a 16% reduction in plasma bilirubin, a 46% reduction in biliary bile acid concentration, and a 27% reduction in bile acid excretion. The bile acid independent fraction of bile flow appeared to increase. Plasma aspartate transaminase concentration did not change during anesthesia. The ratio of conjugated bilirubin fractions in bile [82% to 83% disconjugates of glucuronide and glucoside (2 forms) and 17% to 18% monoconjugates of glucoside, glucuronide, and xyloside] did not change during anesthesia and less than 1% was excreted unconjugated. Halothane anesthesia did not appear to affect adversely the activity of the transferase-conjugating enzymes in the presence of an increased bilirubin load. Seemingly, greatly increased conjugated bilirubin excretion observed during halothane anesthesia was most likely the result of a combination of increased hepatic clearance from plasma and increased hepatic bilirubin production from turnover of free hepatic heme or heme from the induced cytochrome P-450 system.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of glucose administration on equine fasting hyperbilirubinemia

The effects of several treatments and their routes of administration on the reduction of hyperbilirubinemia in 9 pony mares after a 3-day fast were studied. Treatments were as follows: glucose given at doses of 1.2, 2.4, and 3.7 mg/min/kg of body weight; refeeding the base-line diet; feeding straw; and IV administration of taurocholic acid at a dosage of 0.07 mumol/min/kg. The 3 glucose dosages were each given by 3 different routes: IV, intraduodenal, and intragastric. The smallest dosage of glucose given by IV route reduced the plasma bilirubin concentration only 7%, even though other measured values associated with fasting returned toward their base line; increased free fatty acid concentration was reduced by 50%; plasma insulin increased above base-line values. Except for the smallest glucose dose given by IV route, the effects of the routes of administration (IV less than intraduodenal less than intragastric) and of the doses of glucose were not significantly different. Taurocholic acid (given IV) was ineffective in reducing the plasma fasting bilirubin concentration. Refeeding the base-line diet reduced the hyperbilirubinemia by 66% in 12 hours, which was a significantly greater reduction than the effect of all other treatments except the largest dose of glucose given by intragastric route. Feeding straw was less effective than refeeding, causing only about a 30% reduction.

Determination of the pool size and synthesis rate of bile acids by measurements in blood of patients with liver disease

1. A simplified technique for the measurement of bile-acid pool size and synthesis rate has been developed in patients with liver disease. Isotope dilution studies in blood and bile were performed after intravenous injection of [24-14C]cholic acid with radioimmunoassay for the measurement of the bile-acid concentration. The interpolated pool sizes and synthesis rates, determined from results from both blood and bile, were not significantly different. The concentration of bile acids in the blood of healthy controls was not sufficiently elevated to permit application of this technique. 2. Three out of six patients with cirrhosis had a markedly reduced pool size compared with that of controls, whereas those with cholestasis had an unchanged pool size. The daily synthesis rate was reduced in both groups. Liver disease caused a redistribution (0.5-16%) of the bile-acid pool to the blood, which was associated with enhanced urinary excretion of cholic acid and its metabolites.

Effect of dehydrocholic, chenodeoxycholic, and taurocholic acids on the excretion of bilirubin

The effects of IV bile acid infusion (at approx 20% of normal excretion rate) on the biliary excretion of 3-alpha-hydroxy bile acids and bilirubin were investigated in ponies prepared surgically with chronic external biliary fistulas. Endogenous bile acid excretion (approx 45 mumol/min) decreased to the hepatic synthesis rate (approx 1.5 mumol/min) during the initial 4 to 5 hours of bile drainage. In type 1 studies, both chenodeoxycholic and taurocholic acid infusion (8 to 9 mumol/min) increased bilirubin excretion by 58% to 82% following 5 hours of biliary diversion. During type 2 studies, 3-hour IV infusions (10.5 mumol/mon) of dehydrocholic acid, 4 hours following biliary diversion, increased bile flow by 45% to 62% and excretion of 3-alpha-hydroxy bile acid by 34% to 36% above preinfusion (hepatic synthesis) levels. Bilirubin excretion was not significantly changed during those increases in bile flow and bile acid excretion. Immediately after dehydrocholic acid infusion, taurocholic acid infusion (8.1 mumol/min) greatly increased bilirubin excretion for 1 hour (a reversal of hepatic storage identical to that found during type 1 studies), prolonged excretion (mg/2 hours) being two to three times that caused by dehydrocholic acid infusion. Bilirubin excretion appeared to correlate with the micelle-forming capacity of endogenous bile acids as opposed to the nonmicelle-forming characteristic of synthestic dehydrocholic acid.

Within-day fluctuations in serum bile-acid concentrations among normal control subjects and patients with hepatic disease

Under carefully controlled conditions in a clinical research ward, conjugated primary bile-acid concentrations were measured by a 125I-radioimmunoassay every eight hours for four days in seven healthy control subjects and ten patients with hepatic disease (five with cirrhosis, three with primary biliary cirrhosis and two with sclerosing cholangitis). Two meals of approximately equal composition were consumed daily at 10 A.M. and 6 P.M., and blood was drawn at 4 A.M., 12 noon and 8 P.M.. With the exception of one patient, all subjects had greater postprandial than fasting serum bile-acid concentrations, with all healthy control subjects and most of those with hepatic disease showing evening values equal to or greater than the noon values. For the healthy control subjects, the mean values were 0.8, 1.4 and 1.9 microM, and for those with hepatic disease, 108, 140 and 133 microM. There were large fluctuations in serum bile acids (up to sevenfold) among patients with hepatic disease. These fluctuations were independently validated by finding corresponding changes in serum radioactivity derived from injection of a tracer (24-14C cholic acid) at the start of each study. To be consistent, especially for serial measurements, bile acids should be measured in blood taken at the same time of the day and at the same time relative to meals.

Direct measurement of biliary bilirubin excretion in ponies during fasting

Biliary excretion of bilirubin, including the conjugate composition, was studied during feeding and during a 2.5-day fast of three pony mares with chronic external biliary (T-tube) fistulas. Fasting bilirubin excretion (1.96 +/- 0.74 microgram/min/kg of body weight), after establishing a new steady state, was not different from excretion during feeding (1.99 +/- 0.45 microgram/min/kg). Hyperbilirubinemia of fasting resulted from a reduced removal of plasma bilirubin rather than from an increased input of bilirubin into the plasma. Relative plasma excretion of the individual conjugate fractions of biliary bilirubin was not changed by fasting.

Radiolabelled bile acid clearance in control subjects and patients with liver disease

1. The serum bile acid disappearances of tracer doses of [24-14C]cholic acid and [1-14C]-glycocholic acid were studied in eight normal subjects and 11 patients with chronic liver disease (with or without cholestasis) in order to determine the effect of liver disease on hepatic clearances, reflux of conjugated cholic acid and initial distribution volume of each tracer.

2. Total cholic acid clearance was significantly reduced from normal (7·2 ± 0·7 ml min−1 kg−1, mean ± se) in patients with liver disease (69–88%, group means) as were unconjugated cholic acid (51–68%) and glycocholic acid (66–83%) clearance.

3. Extensive regurgitation of labelled conjugated cholic acid (after unconjugated cholic acid tracer injection) among cholestatic patients accounted for 69 ± 5% of total 14C remaining in serum at 70 min, thus masking a less-impaired uptake process.

4. The hepatic extraction efficiency for conjugated cholic acid among controls (86 ± 8%) was greater than that for unconjugated cholic acid (60 ± 4%), and was greatly reduced among patients (7–27%, group means).

5. Normal subjects and patients with cirrhosis without cholestasis did not distribute the isotope to extravascular, extrahepatic spaces, in contrast to cholestatic patients with serum bile acid concentration > 149μmol/l.

6. Careful evaluation of serum disappearance of bile acids as well as chromatographic separation of regurgitated metabolites, could provide investigators with indirect evidence of defects in the rate-limiting steps (uptake, conjugation or excretion) of hepatic bile acid transport.

Bile acid clearance in sheep with hereditary hyperbilirubinemia

The disappearance of IV injected [24-14C]cholic acid from plasma was studied in normal and mutant Corriedale and Southdown sheep exhibiting hereditary defects in hepatic organic anion transport. Hepatic cholic acid clearance was determined from the integral of the 40-minute disappearance curves fit to the sums of two exponential functions. Cholic acid clearance among Corriedale sheep was significantly less (P less than 0.05) for mutant sheep (8.44 +/- 0.86 SEM ml/minute/kg of body weight) than for normal sheep (12.7 +/- 0.58 ml/minute/kg). Cholic acid clearance in the Southdown mutant (1.97 +/- 0.59 ml/minute/kg) was less than 15% of normal clearance rate (13.3 +/- 2.2 ml/minute/kg). Clearance of [14C]taurocholic acid (curves fit to three exponential function) in the Southdown mutant (10.8 +/- 0.4 ml/minute/kg) was significantly greater (P less than 0.01) than cholic acid clearance, yet was not significantly different (P greater than 0.05) from normal taurocholate clearance (17.8 +/- 2.5 ml/minute/kg). Hepatic regurgitation of conjugated bile acid was not detected after [14C]cholic acid injection. Both the mutant Corriedale and Southdown sheep, which exhibited inherited defects in hepatic bilirubin transport similar to Dubin-Johnson syndrome and Gilbert's disease in man, exhibited defects in hepatic bile acid clearance.

Plasma bile acid elevation following CCI4 induced liver damage in dogs, sheep, calves and ponies

Plasma bile acid concentration was determined in normal dogs,sheep, calves and ponies for three days before and six days after liver damage, induced by carbon tetrachloride. In all species, a significant increase in plasma bile acid concentration was associated with a concomitant significant increase in plasma sorbitol dehydrogenase and transferase activity. Plasma bilirubin also significantly increased in all animals except the dogs. Results suggested that plasma bile acid levels could be used to test liver function in domestic animals.

Effect of bile acid on hepatic excretion and storage of bilirubin in ponies

Endogenous bilirubin uptake from plasma and biliary bilirubin excretion were determined in ponies with chronic biliary T-tube fistulas. Excreted bile was quantitatively recovered. Uptake was calculated from the plasma disappearance of 14C-labeled bilirubin. Biliary bilirubin excretion was determined directly in excreted bile. When bile acid excretion was low (during continuous drainage without bile acid replacment), bilirubin excretion was 37% less than uptake. Uptake and excretion were essentially identical when taurocholic acid was infused to replace bile acids. After depletion of the bile acid pool, replacement of bile acids (by taurocholic acid infusion) greatly increased both bilirubin excretion and its biliary concentration for approximately 1 hour. After this initial increase, bilirubin excretion was maintained at a rate approximately 30% greater than the preinfusion rate. Bile acid excretion was found to be essential for normal, endogenous bilirubin excretion.

Bile acid kinetics and bile secretion in the pony

Bile acid pool size and synthesis rate were determined by both isotope-dilution and washout methods in ponies with chronic external biliary fistulas. Bile acid pool size (10.9 mumol/kg) and synthesis rate (11.2 mumol/day per kg) estimated by the isotope-dilution method did not differ significantly from pool size (9.4 mumol/kg) and synthesis rate (9.5 mumol/day per kg) estimated by washout method. Bile acid-dependent and -independent fractions of bile flow, determined by a method that circumvents any inevitable correlation of flow to bile acid secretion due to common factors in both parameters, did not differ from those values obtained by linear regression of bile flow versus bile acid secretion. The choleretic effect of infused chenodeoxycholic acid was higher than that of both endogenous bile acid and infused taurocholic acid.

Bile secretion in ponies with biliary fistuals

Surgically placed bile duct cannulas allowed collection of secreted bile from nonanesthetized ponies. UNINTERRUPTED ENTEROPHEPATIC CIRCULATION WAS PERMITTED BETWEEN COLLECTIONS. Deleterious effects of cannulation were not observed. Average bile flow was 18.6 plus or minus 1.72 (standard error) mul/minute/kg, bile acid excretion was 0.179 plus or minus 0.0212 mumole/minute/kg, and bilirubin excretion averaged 1.22 plus or minus 0.136 mug/minute/kg.