Efficacy of percutaneous fibrin sheath stripping in restoring patency of tunneled hemodialysis catheters.

OBJECTIVE: Our objective was to determine the effectiveness of percutaneous fibrin sheath stripping as a method of restoring function to failing tunneled hemodialysis catheters. SUBJECTS AND METHODS: A total of 131 percutaneous fibrin sheath stripping procedures were performed on 100 failing tunneled hemodialysis catheters in 91 patients. Only the initial stripping procedure of the first catheter inserted in each patient was included for analysis. Patients were excluded if an additional cause of catheter failure was noted at the time of percutaneous fibrin stripping. Failure of the hemodialysis catheter was defined as inability to sustain an average blood flow rate of 250 ml/min or more in a hemodialysis session. Patients were followed up until the time of catheter failure, catheter removal, or a second stripping. Poststripping primary patency and complication rates were determined. RESULTS: The technical success of the procedure was 95.6%. Median follow-up was 16 weeks (range, 0-128 weeks). The overall median duration of primary patency after the first stripping was 89 days (3 months). No statistically significant difference in primary patency rates was seen between patients who underwent fibrin sheath demonstration by contrast injection and those who did not (p = .71). Female patients were statistically more likely to have catheter failure after catheter stripping than were male patients (p = .02). The route of catheter insertion did not significantly influence poststripping patency rates. No complications were associated with the procedure. CONCLUSION: Percutaneous fibrin sheath stripping is a safe, effective method of restoring patency to failing hemodialysis catheters when the failure is due to fibrin sheath formation and other causes are excluded.

The effect of surgical treatment following peritoneal sepsis on hepatic gene expression.

Peritoneal sepsis results in downregulation of the gene that codes for the hepatic mitochondrial enzyme carnitine palmitoyltransferase (CPT). The inhibition of hepatic CPT transcription by sepsis is thought to be mediated, in part, by increased expression of the leucine-zipper DNA transcription factor c-fos. In a cecal ligation and puncture (CLP) model, we examined the temporal effect of surgical treatment (cecal excision) on sepsis-induced inhibition of CPT gene expression. We investigated the hypothesis that Fos protein level will inversely correlate with the regulation of CPT gene expression. Specifically, we studied hepatic Fos nucleoprotein accumulation and CPT gene expression as measured by total mitochondrial CPT activity, CPT protein, and CPT mRNA. We investigated the following groups: (i) CLP followed by cecal excision 6, 12, or 24 hr following initial insult, (ii) concurrent CLP control group, and (iii) concurrent sham CLP reference group. When measured 48 hr following initial surgical insult, we conclude that: (i) in the absence of surgical treatment, peritoneal contamination results in a decrease in hepatic CPT gene expression and an increase in Fos nucleoprotein accumulation; (ii) surgical treatment at 6 or 12 hr following initial insult prevents the downregulation in hepatic CPT gene expression and does not result in Fos nucleoprotein accumulation; and (iii) surgical treatment at 24 hr following insult did not prevent the downregulation of hepatic CPT gene expression and results in an increase in hepatic Fos nucleoprotein accumulation. These data are consistent with the hypothesis that sepsis-induced regulation of hepatic c-fos gene expression, in part, is responsible for the downregulation of CPT gene expression.

Regulation of the transcription factor C/EBP alpha following peritoneal sepsis.

The transcription factors C/EBP alpha and C/EBP beta belong to the leucine-zipper C/EBP (CCAAT/enhancer binding protein) family of DNA-binding proteins. C/EBP alpha and C/EBP beta are expressed in the liver and are implicated in the control of transcriptional events following following sepsis. It is hypothesized that inhibition of C/EBP alpha gene expression following sepsis may lead to some of the phenotypic features we recognize as sepsis syndrome such as decreased visceral protein (albumin) synthesis. In this study we demonstrate that C/EBP alpha mRNA accumulation is transiently inhibited 12 hr following peritoneal insult, consistent with previous data. However, we demonstrate that (1) there is increased binding of hepatic nuclear protein to the C/EBP alpha DNA response element 48 hr following insult, (2) a marked increase in C/EBP alpha protein is observed 48 hr following CLP insult compared with no increase in hepatic C/EBP alpha protein at 12 hr postinsult, (3) the increase in hepatic C/EBP alpha protein at 48 hr following cecal ligation and puncture is not associated with an increase in C/EBP alpha mRNA accumulation, (4) the increase in hepatic C/EBP alpha protein is associated with an increase in C/EBP beta protein, and (5) hepatic albumin mRNA accumulation is decreased at 12 and 48 hr following insult and does not correlate with the C/EBP alpha protein synthesis. We conclude that the possible role of the transcription factor C/EBP alpha with respect to decreased albumin gene expression following sepsis must be reevaluated.

Hepatic CCAAT/enhancer binding protein (C/EBP-alpha and C/EBP-beta) expression changes with riboflavin deficiency, diet restriction and starvation in rats.

To study the role of nuclear regulatory proteins in mediating dietary effects, hepatic CCAAT/enhancer binding protein (C/EBP), mRNA and transcription rate were measured for C/EBP-alpha and C/EBP-beta in nutritional states that profoundly alter energy metabolism and growth. Weanling male Sprague-Dawley rats were fed riboflavin-sufficient (R+) or deficient (R-) diets for 4 wk. A diet-restricted, pair-fed (RP) group was maintained concurrently, because riboflavin-deficient rats voluntarily decrease food consumption by approximately 50% compared with controls. Half of each group was deprived of food for 48 h. The 4-wk treatment altered hepatic levels of both proteins (P < 0.05). C/EBP-alpha protein levels were increased -twofold by diet restriction. C/ EBP-beta protein levels were increased nearly threefold by riboflavin deficiency. Starvation had no significant effect on the expression of either protein. We investigated the mechanism responsible for increased protein by measuring steady-state mRNA levels and transcription rates for C/EBP-alpha and C/EBP-beta. In both isoforms, increases in mRNA were parallel to increases in transcription rates. The nutrient-induced changes in protein, mRNA and transcription rates could not be attributed only to alterations in serum glucagon or insulin concentrations. We conclude that 1) C/EBP-alpha and C/EBP-beta expression responds to diet but may involve different dietary signals for diet restriction vs. riboflavin deficiency; 2) the dietary regulation of C/EBP-alpha and C/EBP-beta expression seems to be controlled in part at the level of gene transcription; and 3) C/EBP-alpha and C/EBP-beta nuclear proteins, by virtue of their increased quantities, may participate in regulating altered energy metabolism and growth by influencing hepatic transcription of key metabolic enzymes.

Sepsis-induced release of interleukin-6 may activate the immediate-early gene program through a hypothalamic-hypophyseal mechanism.

BACKGROUND: The immediate-early gene c-fos has been implicated in transcriptional regulation after sepsis. We test the hypothesis that sepsis-induced central nervous system release of interleukin (IL)-6 regulates hepatic c-fos gene expression. METHODS: Using a stereotaxically placed intracerebral-ventricular (ICV) catheter in rats with and without hypophysectomy, we measured hepatic c-fos protein accumulation after treatment with either IL-6 or vehicle control. Using a rat cecal ligation and puncture (CLP) model, we studied the following groups: (1) sham-CLP, (2) CLP, (3) hypophysectomized sham-CLP, and (4) hypophysectomized CLP and measured hepatic c-fos mRNA. RESULTS: ICV IL-6 treatment increased hepatic c-fos protein in the IL-6-treated group compared with the vehicle-treated group, and hypophysectomy inhibited the ICV IL-6-mediated increase in c-fos protein. After peritoneal sepsis, CLP increased hepatic c-fos messenger RNA compared to either the sham-CLP or the hypophysectomized sham-CLP group, and hypophysectomy before CLP inhibited hepatic c-fos mRNA compared with the CLP group. CONCLUSIONS: ICV IL-6 results in an increase in hepatic fos protein that is mediated through a hypothalamic-hypophyseal mechanism. Peritoneal sepsis results in an increase in hepatic c-fos gene expression that may be, in part, mediated by central nervous system release of IL-6 through a hypothalamic-hypophyseal mechanism.

Regulation of the long-chain carnitine acyltransferases.

Long-chain carnitine acyltransferases are a family of enzymes found in mitochondria, peroxisomes, and endoplasmic reticulum that catalyze the exchange of carnitine for coenzyme A in the fatty acyl-CoA. Conversion of the fatty acyl-CoA to fatty acylcarnitine renders the fatty acid more permeable to the various cellular membranes. The mitochondrial carnitine palmitoyltransferases are considered important in the regulation of mitochondrial beta-oxidation of long-chain fatty acids. However, palmitoylcarnitine produced by peroxisomal carnitine octanoyltransferase or by microsomal carnitine palmitoyltransferase is not different from that produced by the mitochondrial enzyme. Therefore, for there to be control of fatty acid oxidation by the long-chain carnitine acyltransferases, there would have to be some mechanism to coordinately regulate these varied enzymes. The first system of regulation involves inhibition by malonyl-CoA, an intermediate in the synthesis of fatty acids. Malonyl-CoA inhibits long-chain carnitine acyltransferase activity by all three enzymes at similar concentrations in the physiological range. In addition, the mitochondrial and peroxisomal enzymes are known to be regulated at the level of mRNA transcription by a number of shared factors. Although the microsomal enzyme is less well studied, there does, indeed, appear to be a pattern of coordinate regulation for this system.

The regulation of mitochondrial fatty acid oxidation and hepatic gene expression by catecholamine.

We hypothesized that dopamine or dobutamine may alter hepatic mitochondrial fatty acid oxidation secondary to an effect on hepatic gene expression. We investigated the effect of dopamine or dobutamine on hepatic fat oxidation and gene transcription by studying the enzyme carnitine palmitoyltransferase (CPT), the rate-limiting step in hepatic mitochondrial long-chain fat oxidation. We incubated either H4IIE rat hepatoma cells or rat hepatocytes in primary cell culture with either dopamine (1, 0.1, 0.01 microgram/ml), dobutamine (1, 0.1, 0.01 microgram/ml), or vehicle control for 1, 2, 3, or 4 hr. We investigated the effect on (1) CPT mRNA (Northern or dot blotting) and the possible regulatory mechanism by incubating dopamine (0.1 microgram/ml) or dobutamine (0.1 microgram/ml) with propranolol or phentolamine, (2) CPT translation (CPT [35S]methionine incorporation), and (3) hepatic mitochondrial fatty acid oxidation ([1-14C]-palmitate oxidation to acid-soluble products). We conclude that (1) dopamine or dobutamine increases both hepatic CPT mRNA and CPT protein translation, (2) the effect on CPT mRNA is mediated by the beta-receptor, (3) the increase in hepatic mitochondrial fat oxidation induced by dopamine or dobutamine may be, in part, secondary to increased CPT transcription and translation, and (4) the significant difference in hepatic fat oxidation induced by dopamine as compared with that by dobutamine is secondary to factors other than transcriptional or translational mechanisms. We speculate that dopamine treatment in the critically ill may increase hepatic mitochondrial fatty acid oxidation and ketogenesis and that this increase in beta-oxidation may be, in part, secondary to increased CPT gene expression.

Isolation and characterization of the promoter for the gene coding for the 68 kDa carnitine palmitoyltransferase from the rat.

Carnitine palmitoyltransferase (CPT) regulates the flux of long-chain fatty acids into the mitochondria for subsequent beta-oxidation. A 485 bp segment of the promoter for the gene encoding the 68 kDa CPT was isolated from a rat lambda DASH genomic library using the polymerase chain reaction. The promoter contained a consensus binding sequence for CREB (cyclic AMP response element binding protein) at -153 to -166, and for C/EBP alpha (CCAAT/enhancer binding protein) at -115 to -128. DNAase I footprinting using proteins isolated from rat liver nuclei indicated the presence of several regions of nuclear protein binding, most notably at -95 to -130, at -273 to -295, and at a wide region encompassing -395 to -465. DNAase I footprinting studies with purified CREB and C/EBP alpha confirmed that protein binding to DNA occurred at the sites predicted by the consensus sequences. The segment containing 481 bp of 5' flanking sequence plus 181 bp of untranslated mRNA was ligated to the structural gene for chloramphenicol acetyltransferase (CAT). When this plasmid was transfected into Hep G2 cells, CAT activity was stimulated 7-fold by addition of 1 mM-8-bromo-cyclic AMP (8-Br-cAMP) or co-transfection of the expression vector coding for the catalytic subunit of protein kinase A (PKA). The ability of several known second messengers and transcription factors to stimulate transcription of 68 kDa CPT promoter-CAT reporter was tested in co-transfection experiments. 68 kDa CPT promoter-CAT reporter transcription activity was stimulated 7-fold by addition of 8-Br-cAMP, and this induction was depressed 50% by the addition of phorbol esters. When the 68 kDa CPT promoter-CAT reporter was co-transfected with an expression vector for CREB or C/EBP alpha, transcription was increased 3- and 10-fold respectively. 8-Br-cAMP caused an additional 8-fold induction in the presence of each factor to yield 25- and 80-fold induction respectively. Co-transfection of the expression vector for c-jun also increased the CAT activity driven by the 68 kDa CPT promoter, while co-transfection with the expression vector for c-fos had no effect. When expression vectors for both c-jun and c-fos were co-transfected with the 68 kDa CPT promoter, c-fos depressed the induction seen with c-jun alone.

The possible inhibitory role of the leucine-zipper DNA binding protein c-fos in the regulation of hepatic gene expression after sepsis.

BACKGROUND: The leucine-zipper c-fos has been implicated in the regulation of gene expression. We investigated the possible role of c-fos in the regulation of hepatic gene expression after sepsis. Based on previous data demonstrating that sepsis inhibits hepatic gene expression of carnitine palmitoyltransferase (CPT), we hypothesized that c-fos may play a role in the inhibition of CPT gene expression after sepsis. METHODS: We studied c-fos gene expression after peritoneal sepsis induced by cecal ligation and puncture (CLP) or sham-CLP. To investigate the possible inhibitory role of c-fos on CPT gene transcription, we investigated the effect of c-fos on c-jun-driven CPT promoter-chloramphenicol acyltransferase reporter gene expression in a HepG2 hepatoma cell cotransfection model. To investigate the possible role of cyclic adenosine monophosphate (cAMP) in the regulation of c-fos in vivo, we treated either the sham-CLP group or the CLP group with either vehicle or cAMP. RESULTS: Peritoneal sepsis in the rat model resulted in a four-fold increase in hepatic c-fos mRNA and c-fos protein. In the cotransfection model, c-fos significantly inhibited c-jun-induced chloramphenicol acyltransferase activity. Treatment with cAMP resulted in a 50% decrease in c-fos protein in either the sham-CLP or CLP group. CONCLUSIONS: We conclude that (1) sepsis increases hepatic c-fos transcription and translation, (2) c-fos inhibits c-jun-induced CPT gene expression, and (3) cAMP probably does not directly mediate the increase in c-fos after sepsis.

The Ca2+ second messenger system and interleukin-1-alpha modulation of hepatic gene transcription and mitochondrial fat oxidation.

Cytokines have been implicated in the modulation of fat metabolism after sepsis. Carnitine palmitoyltransferase (CPT), the regulatory enzyme of hepatic mitochondrial long-chain fatty-acid oxidation, is involved in the control of hepatic fat oxidation in sepsis. Using either H4IIe rat hepatoma cells or rat hepatocytes in primary culture, we tested the hypothesis that interleukin-1-alpha (IL-1 alpha) would modulate CPT transcription (CPT mRNA), CPT translation (35S-methionine CPT protein incorporation), and hepatic mitochondrial oxidation of 1-Carbon 14-labeled (14C) palmitate to ketone bodies (acid soluble products). We showed that IL-1 alpha significantly increased CPT mRNA, 35S-methionine incorporation CPT protein, and hepatic mitochondrial oxidation of 1-14C-palmitate to acid soluble products. We further hypothesized that the Ca2+ second messenger system may play a role in the IL-1 alpha induction of hepatic CPT gene transcription. We showed that either calcium ionophore (A23187) or phorbol myristate acetate increased CPT gene transcription and that either calcium chelation, protein kinase C inhibition (acridine orange), or chronic exposure to phorbol myristate acetate significantly inhibited IL-1 alpha induction of CPT mRNA. We conclude that the IL-1 alpha increases in hepatic mitochondrial fatty-acid oxidation may be, in part, secondary to increased CPT gene transcription and translation and that the Ca2+ second messenger system may play an important role in IL-1 alpha induction of CPT gene transcription.

Regulation of carnitine acyltransferase synthesis in lean and obese Zucker rats by dehydroepiandrosterone and clofibrate.

The effects of dehydroepiandrosterone (DHEA) and clofibrate on mitochondrial and peroxisomal proliferation and carnitine acyltransferases [mitochondrial carnitine palmitoyltransferase (CPT) and peroxisomal carnitine octanoyltransferase (COT)] were measured in lean and obese female Zucker rats. DHEA increased total hepatic mitochondrial protein twofold; clofibrate increased total hepatic peroxisomal protein more than fivefold. Both DHEA and clofibrate administration increased enzyme activities, immunoreactive protein, messenger RNA levels and transcription rates for the carnitine acyltransferases. Transcription rates and messenger RNA concentration for both carnitine acyltransferases correlated with the increases in activity. These data suggest that the hepatic CPT and COT in female Zucker rats are regulated primarily at the transcriptional level by DHEA and clofibrate.

Turnover of carnitine palmitoyltransferase mRNA and protein in H4IIE cells. Effect of cyclic AMP and insulin.

Regulation of the 68 kDa carnitine palmitoyltransferase (CPT) synthesis by (chlorophenylthio) cyclic AMP (cAMP) and insulin was studied in H4IIE cells in culture. Addition of 0.1 mM- or 1.0 mM-(chlorophenylthio) cAMP induced CPT mRNA and rate of transcription 2-4-fold by 15 min, reaching a plateau at 4-6-fold by 30 min. Addition of 5-15 nM-insulin plus 1.0 mM-cAMP suppressed the increases in transcription rate and mRNA levels occurring with cAMP alone. The t1/2 for CPT mRNA was 70-80 min and was not affected by cAMP. The t1/2 for CPT protein was 70 min, and was increased to 240 min in the presence of cAMP. The rate of CPT synthesis was also increased in the presence of cAMP. The data indicate that CPT synthesis is increased by cAMP via induction of transcription and subsequent increase in the CPT mRNA. Insulin acts to depress transcription and CPT mRNA. In addition, cAMP prolongs the t1/2 of CPT.

Co-ordinate induction of hepatic mitochondrial and peroxisomal carnitine acyltransferase synthesis by diet and drugs.

The present studies examined the effect of agents that induce peroxisomal and mitochondrial beta-oxidation on hepatic mitochondrial carnitine palmitoyltransferase (CPT) and peroxisomal carnitine acyltransferase [CPTs of Ramsay (1988) Biochem. J. 249, 239-245; COT of Farrell & Bieber (1983) Arch. Biochem. Biophys. 222, 123-132 and Miyazawa, Ozasa, Osumi & Hashimoto (1983) J. Biochem. 94, 529-542]. In the first studies, high fat diets containing corn oil or fish oil were used to induce peroxisomal and mitochondrial enzymes. Rats were fed one of three diets for 4 weeks: (1) low fat, with corn oil as 11% of energy (kJ); (2) high fat, with corn oil as 45% of kJ; (3) high fat, with fish oil as 45% of kJ. At the end of 4 weeks, both mitochondrial CPT and peroxisomal CPTs exhibited increases in activity, immunoreactive protein, mRNA levels and transcription rates in livers of rats fed either high-fat diet compared to the low fat diet. Riboflavin deficiency or starvation for 48 h also increased the peroxisomal CPTs mRNA. A second set of studies used the plasticizer 2-(diethylhexyl)phthalate (DEHP), 0.5% clofibrate or 1% acetylsalicylic acid (fed for 3 weeks) to alter peroxisomal and mitochondrial fatty acid oxidation. With DEHP, the mitochondrial CPT and peroxisomal CPTs activity, immunoreactive protein, mRNA levels and and transcription rate were all increased by 3-5-fold. The peroxisomal CPTs activity, immunoreactive protein, mRNA levels and transcription rate were increased 2-3-fold by clofibrate and acetylsalicylic acid, again similar to mitochondrial CPT. The results of the combined studies using both diet and drugs to cause enzyme induction suggest that the synthesis of the carnitine acyltransferases (mitochondrial CPT and peroxisomal CPTs) may be co-ordinated with each other; however, the co-ordinate regulatory factors have not yet been identified.

Regulation of carnitine palmitoyltransferase in vivo by glucagon and insulin.

Carnitine palmitoyltransferase (CPT total) activity and synthesis increase in states where the insulin/glucagon ratio is low, such as starvation and diabetes [Brady & Brady (1987) Biochem. J. 246, 641-646]. However, the effect of glucagon and insulin on CPT synthesis is unknown. The present experiments were designed to determine the effect of glucagon, cAMP [8-(chlorophenylthio) cyclic AMP], and insulin + cAMP on CPT transcription and mRNA amounts over time after injection. The CPT protein that was purified, used to generate antibody, and cloned in these studies was the 68 kDa mitochondrial protein described previously [Brady & Brady (1987) Biochem. J. 246, 641-646; Brady, Feng & Brady (1988) J. Nutr. 118, 1128-1136; Brady & Brady (1989) Diabetes 38, in the press]. Saline-injected control rats exhibited a 2-fold increase in hepatic CPT transcription rate and CPT mRNA over the 5 h experiment from 09:00 to 14:00 h. The effect was most probably due to the fasting state of the rats during the day. Glucagon injection caused an 8-fold increase in transcription rate by 90 min and a 4-fold increase in CPT mRNA by 90-120 min. The cAMP effect had reached a peak by the first time point taken (15 min). Transcription rate was increased 4-fold and CPT mRNA was increased 3-fold at this time. The combination of cAMP + insulin injection did not produce any significant increase in transcription rate or CPT mRNA over the saline-injected controls. CPT mRNA and transcription rate showed a clear dose-response to glucagon injection from 0 to 150 micrograms/100 g body wt. Total CPT activity and immunoreactive CPT were not increased during these experiments. The data indicate that glucagon and insulin interact in control of transcription rate and amount of CPT mRNA, but that increases in CPT immunoreactive protein and activity are temporally delayed. This lag probably relates to the half-life of the CPT protein in vivo, which has been estimated as 2-7 days.

Effects of clofibrate and acetylsalicylic acid on hepatic carnitine palmitoyltransferase synthesis.

Clofibrate and acetylsalicylic and have both been reported to increase carnitine palmitoyltransferase (CPT) activity when administered to rats. The purpose of the present study was to determine the mechanism of the increase in CPT activity. Rats (150-200 g) were fed one of the following: chow, chow with 0.5% clofibrate, or chow with 1% acetylsalicylic acid for 2 weeks. At the end of this time, hepatic CPT activity was increased 4-fold over control in the clofibrate group and 3.6-fold over control in the acetylsalicylic acid group. Immunoreactive protein increased 4.0- and 3.6-fold, respectively, over control. Transcription rates of hepatic nuclei were increased 2.8- and 1.9-fold over control in the clofibrate and acetylsalicylic acid groups, and hepatic mRNA levels increased 2.8- and 2.0-fold respectively. These data indicate that increases in CPT activity caused by clofibrate and acetylsalicylic acid administration are due, at least in part, to increased CPT protein, resulting from increased transcription rate and levels of mRNA specific for CPT.

Regulation of carnitine palmitoyltransferase synthesis in spontaneously diabetic BB Wistar rats.

The long-term regulation of hepatic mitochondrial carnitine palmitoyltransferase (CPT) was studied in control, insulin-treated, and untreated spontaneously diabetic BB Wistar rats. The activity of CPT was elevated approximately twofold in the untreated diabetic rats. This corresponded to an approximately equivalent elevation in the immunoreactive CPT activity. mRNACPT was assayed by reticulocyte lysate translation and by dot blot to a CPT oligonucleotide probe. The level of mRNACPT was approximately proportional to the observed CPT activity. A cDNA probe to CPT was developed, and transcriptional activity for CPT was assessed in isolated hepatic nuclei. Again, transcription of CPT mRNA was approximately proportional to the observed activity. We therefore conclude that at least part of the long-term regulation of hepatic CPT in spontaneously diabetic BB Wistar rats is the product of increased de novo synthesis of CPT protein brought about by regulation at the transcriptional level. Additional control of the amount of CPT may be via the regulation of RNA processing and turnover and enzyme insertion into the mitochondrial membrane.

Hemipalmitoylcarnitinium, a strong competitive inhibitor of purified hepatic carnitine palmitoyltransferase.

We have synthesized (2S,6R:2R,6S)-6-carboxymethyl-2-hydroxy-2-pentadecyl-4,4-dimethylmorp holinium bromide (hemipalmitoylcarnitinium, HPC) which is a conformationally restricted analog inhibitor of carnitine palmitoyltransferase (CPT; EC 2.3.1.21). rac-HPC inhibits catalytic activity in purified rat liver CPT. In the forward reaction, HPC competes with both (R)-carnitine (Ki(app) = 5.1 +/- 0.7 microM) and palmitoyl-CoA (Ki(app) = 21.5 +/- 4.9 microM). In the reverse reaction, inhibition by HPC is competitive with palmitoyl-(R)-carnitine (Ki(app) = 1.6 +/- 0.6 microM), but inhibition is uncompetitive with CoA. The forward reaction is also competitively inhibited by its product, palmitoyl-(R)-carnitine, Ki(app)'s 14.2 +/- 2.1 microM relative to (R)-carnitine and 8.7 +/- 2.6 microM relative to palmitoyl-CoA. rac-HPC is the most potent synthetic reversible inhibitor of purified CPT. HPC fails to inhibit carnitine acetyltransferase (CAT; EC 2.3.1.7). Palmitoylcholine also inhibits CPT in the forward reaction, competing with (R)-carnitine (Ki(app) = 18.6 +/- 4.5 microM) and with palmitoyl CoA (Ki(app) = 10.4 +/- 2.5 microM). Choline is not an effective CPT inhibitor. We have shown [R.D. Gandour et al. (1986) Biochem. Biophys. Res. Commun. 138, 735-741] that hemiacetylcarnitinium inhibits CAT but not CPT. The combined data demonstrate further differences between the carnitine recognition sites in CPT and CAT.