Constitutive cyclooxygenase (COX-1) and inducible cyclooxygenase (COX-2): rationale for selective inhibition and progress to date

While a great deal has been discovered concerning the potential physiological and pathological role of prostanoids, much is left to be determined. The widespread distribution of both COX-1 and COX-2 coupled with the capacity of most vascular beds, smooth muscle, as well as leukocytes to respond to prostanoids make drawing generalities difficult. The problems with the majority of currently used NSAIDs are clear and ulcerogenic liability is of obvious concern. Interestingly enough, the mechanism of that damage is still the subject of controversy as illustrated by the recent review and hypothesis of Somasundaram et al. In this treatise, the suggestion is made that the initial gastric damage is the result of uncoupling of oxidative phosphorylation which is independent but simultaneous with COX inhibition. At least two currently marketed NSAIDs have improved G.I. liability (nabumetone and etodolac) with efficacy equivalent to other more ulcerogenic NSAIDs. These drugs appear to have achieved that by a mechanism distinct from selective inhibition of COX-2. Whether or not selective COX-2 inhibitors will demonstrate an improved profile over these compounds remains to be shown. Unfortunately, clinical experience with nimsulide and CGP 28238 suggest that NSAID-like toxicity may still be an issue. The promise of selective COX-2 inhibitors remains largely untested. It is with great interest and expectation that the clinical evaluation of the more selective compounds of different structural types is awaited.     

Role of cyclooxygenase 2 in acute spinal cord injury

Cyclooxygenase, or prostaglandin G/H synthase, is the rate-limiting step in the production of prostaglandins. A new isoform, cyclooxygenase-2 (COX-2), has been cloned that is induced during inflammation in leukocytes and by synaptic activity in neurons. The objectives of this study are to determine the nature of COX-2 expression in normal and traumatized rat spinal cord, and to determine the effects of selective COX-2 inhibition on functional recovery following spinal cord injury. Using a weight-drop model of spinal cord injury, COX-2 mRNA expression was studied with in situ hybridization. COX-2 protein expression was examined by immunohistochemistry and Western analysis. Finally, using the highly selective COX-2 inhibitor, 1-[(4-methylsufonyl)phenyl]-3-tri-fluro-methyl-5-[(4-flur o)phenyl]prazole (SC58125), the effect of COX-2 inhibition on functional outcome following a spinal cord injury was determined. COX-2 was expressed in the normal adult rat spinal cord. COX-2 mRNA and protein production were increased following injury with increases in COX-2 mRNA production detectable at 2 h following injury. Increased levels of COX-2 protein were detectable for at least 48 h following traumatic spinal cord injury. Selective inhibition of COX-2 activity with SC58125 resulted in improved mean Basso, Beattie, and Bresnahan scores in animals with 12.5- and 25-g/cm spinal cord injuries; however, the effect was significant only for the 12.5g/cm injury group (p=0.0001 vs. p=0.0643 in the 25-g/cm group). These data demonstrate that COX-2 mRNA and protein expression are induced by spinal cord injury, and that selective inhibition of COX-2 improves functional outcome following experimental spinal cord injury.     

Differential roles of neurokinin 1 and neurokinin 2 receptors in the development and maintenance of heat hyperalgesia induced by acute inflammation

1. Following induction of acute inflammation by intraarticular injection of kaolin and carrageenan into the knee joint in rats, there was a significant decrease in the withdrawal latency to radiant heat applied to the paw (i.e. heat hyperalgesia), an increased joint circumference and increased joint temperature. 2. A neurokinin1 (NK1) receptor antagonist (CP-99,994, 10 mM) had no effect on the paw withdrawal latency when it was administered spinally through a microdialysis fibre before the induction of inflammation. Pretreatment with a NK2 receptor antagonist (SR48968, 1 mM) administered spinally through the microdialysis fibre prevented the heat hyperalgesia from developing in the early stages of the inflammation. 3. Post-treatment through the microdialysis fibre with the NK1 receptor antagonist (0.01-10 mM) was effective in reversing the heat hyperalgesia. In contrast, post-treatment spinally with the NK2 receptor antagonist (0.01-1 mM) had no effect on the heat hyperalgesia. The inactive stereoisomers of the NK1 receptor antagonist, CP100,263, or the NK2 receptor antagonist, SR48965, administered at the same doses, had no effect on the joint inflammation or the heat hyperalgesia. 4. Pretreatment systemically with the NK1 receptor antagonist (30 mg kg-1) had no effect on the heat hyperalgesia or pain-related behaviour ratings where 0 is none and 5 is non weight bearing and complete avoidance of limb contact. Pretreatment with a NK2 receptor antagonist (10 mg kg-1) systemically prevented the heat hyperalgesia and pain-related behaviour ratings from developing in the early stages of the inflammation. The inactive stereoisomers of NK1 receptor antagonist, CP100,263, or the NK2 receptor antagonist, SR48965, administered at the same doses, had no effect on the joint inflammation or the heat hyperalgesia. 5. Post-treatment systemically with either the NK1 (0.1-30 mg kg-1) or the NK2 (0.1-10 mg kg-1) receptor antagonist resulted in a dose-dependent reversal of the heat hyperalgesia. Pain-related behaviour ratings were reduced by post-treatment only with the NK1 receptor antagonist. The inactive stereoisomers of the NK1 receptor antagonist, CP100,263, or the NK2 receptor antagonist, SR48965, administered at the same doses, had no effect on the behavioural responses. 6. Direct pretreatment of the knee joint with either the NK1 (30 mg) or the NK2 (10 mg) receptor antagonist prevented the heat hyperalgesia from developing without affecting joint swelling. The inactive stereoisomers of the NK1 receptor antagonist, CP100,263, or the NK2 receptor antagonist, SR48965, administered at the same doses, had no effect on the joint inflammation or the heat hyperalgesia. 7. There appears to be a differential role for the spinal tachykinin receptors in the development and maintenance of the heat hyperalgesia associated with acute joint inflammation. The NK2 receptors appear to be activated early in the development of the heat hyperalgesia and NK1 receptors are involved in the maintenance of the heat hyperalgesia. 8. Peripherally, both NK1 and NK2 receptors are involved in the development of heat hyperalgesia and pain-related behaviour ratings induced by acute inflammation.     

The classification of cyclooxygenase inhibitors

In summary, precise classification of COX inhibitors has important clinical implications for efficacy and toxicity. However, classification of these agents clinically is difficult because there are insufficient data to predict correlations between biochemical and pharmacologic properties and the clinical effect of a given agent. In any case, specific COX-2 inhibitors are expected to show antiinflammatory and analgesic activities equivalent to those of NSAID, as well as significant reductions in the incidence of the life threatening side effects (i.e., GI bleeding) associated with COX-1 inhibition. The advantages of preferential COX-2 inhibitors may be more subtle and therefore more difficult to verify in clinical trials.     

The effect of leukotriene synthesis inhibitors in models of acute and chronic inflammation

To define the risk factors related to the occurrence of fungemia in children infected with human immunodeficiency virus (HIV), we performed a matched case-control study. During a 6-year period (1987-1993), fungemia developed in 22 (6.3%) of 347 HIV-infected children observed at the Pediatric Branch of the National Cancer Institute. Each of these 22 cases was matched by age and gender with three controls. Multiple logistic regression indicated that the best predictor of fungemia in this population was the presence of a central venous catheter placed for > 90 days (P < .00001), followed by a group of risk factors composed of 10 independent variables adjusted for a CD4 cell count of < 100/MicroL (P < .045). Those variables included treatment with more than three antibiotics, treatment with more than three parenteral antibiotics, > 30 days of antibiotic treatment, bacterial infections, > 30 days in the hospital, hypoalbuminemia, C3 (Centers for Disease Control and Prevention) classification of HIV infection, and malnourishment. We conclude that prolonged placement of central venous catheters is the most important risk factors for fungemia in HIV-infected children and that the risk of fungemia is further influenced by antibacterial therapy, catheter manipulation, and host response.     

Induction of cyclooxygenase (COX)-2 but not COX-1 gene expression in apoptotic cell death

In this study we assessed the regulation of cyclooxygenase (COX)-2 in models of apoptotic cell death in vivo and in vitro. By 6 h after hippocampal colchicine injection in rat, COX-2 (but not COX-1) mRNA expression was elevated. The induction of COX-2 mRNA expression preceded temporally and overlapped anatomically the cellular morphological features of apoptosis in the granule cell layer of the dentate gyrus. Similarly, in an established in vitro model of apoptosis in P19 cells, COX-2 induction preceded apoptosis in response to serum deprivation by 12 h. These studies suggest that COX-2 may be involved in the early mechanisms leading to apoptosis.     

Differential expression of vasoactive intestinal peptide receptors 1 and 2 (VIP-R1 and VIP-R2) mRNA in murine lymphocytes

Vasoactive intestinal peptide (VIP), a neuropeptide present in the lymphoid microenvironment, modulates cytokine expression and affects T cell proliferation. Recent molecular studies identified two VIP receptors. VIP-R1 and VIP-R2, primarily in nonlymphoid cells. In this study, we investigate the expression of VIP-R1 and VIP-R2 mRNA in unstimulated and stimulated lymphocytes and thymocytes, and in various lymphocyte subpopulations. In contrast to VIP-R1 which is constitutively expressed, the expression of VIP-R2 is induced only following stimulation through the TCR-associated CD3 complex. Both CD4+ and CD8+ T cells express VIP-R1 and VIP-R2. Two T cell lines, EL-4.IL-2 and D10.G4.1 express exclusively VIP-R2. VIP induces the expression of the VIP-R2 gene in the absence of additional stimuli. Differential expression and regulation of the two VIP receptors in T lymphocytes suggests different physiological roles in mediating the immunomodulatory activities of VIP and related neuropeptides.     

Differential signaling by insulin receptor substrate 1 (IRS-1) and IRS-2 in IRS-1-deficient cells

Mice made insulin receptor substrate 1 (IRS-1) deficient by targeted gene knockout exhibit growth retardation and abnormal glucose metabolism due to resistance to the actions of insulin-like growth factor 1 (IGF-1) and insulin (E. Araki et al., Nature 372:186-190, 1994; H. Tamemoto et al., Nature 372:182-186, 1994). Embryonic fibroblasts and 3T3 cell lines derived from IRS-1-deficient embryos exhibit no IGF-1-stimulated IRS-1 phosphorylation or IRS-1-associated phosphatidylinositol 3-kinase (PI 3-kinase) activity but exhibit normal phosphorylation of IRS-2 and Shc and normal IRS-2-associated PI 3-kinase activity. IRS-1 deficiency results in a 70 to 80% reduction in IGF-1-stimulated cell growth and parallel decreases in IGF-1-stimulated S-phase entry, PI 3-kinase activity, and induction of the immediate-early genes c-fos and egr-1 but unaltered activation of the mitogen-activated protein kinases ERK 1 and ERK 2. Expression of IRS-1 in IRS-1-deficient cells by retroviral gene transduction restores IGF-1-stimulated mitogenesis, PI 3-kinase activation, and c-fos and egr-1 induction in proportion to the level of reconstitution. Increasing the level of IRS-2 in these cells by using a retrovirus reconstitutes IGF-1 activation of PI 3-kinase and immediate-early gene expression to the same degree as expression of IRS-1; however, IRS-2 overexpression has only a minor effect on IGF-1 stimulation of cell cycle progression. These results indicate that IRS-1 is not necessary for activation of ERK 1 and ERK 2 and that activation of ERK 1 and ERK 2 is not sufficient for IGF-1-stimulated activation of c-fos and egr-1. These data also provide evidence that IRS-1 and IRS-2 are not functionally interchangeable signaling intermediates for stimulation of mitogenesis despite their highly conserved structure and many common functions such as activating PI 3-kinase and early gene expression.     

Differential induction of peroxisomal enzymes by hypolipidaemics in human (HepG2) and rat (MH1C1) hepatoma cell lines

Human (HepG2) and rat (MH1C1) hepatoblastoma cells were incubated with different concentrations of the hypolipidaemics cetaben, clofibrate and thyroxine. The enzymatic activities of catalase, peroxisomal bifunctional enzyme, succinate dehydrogenase, and 3-oxoacyl-CoA thiolase were measured. In order to determine the point of regulation of the enzymatic activities Northern and Slot blot experiments with probes for peroxisomal bifunctional enzyme, catalase and fatty acyl CoA oxidase were performed on total RNA. Catalase activity was enhanced in HepG2 cells treated with 3 mmol/l clofibric acid to 135% of control and the mRNA value to 2.6 fold, whereas in cetaben treated cells the enhancement (up to 119% of control) was less pronounced. In MH1C1 cells catalase activity was not changed by any of the drugs. The activity of the peroxisomal bifunctional enzyme was not affected in HepG2 cells by clofibric acid and cetaben, whereas the mRNA level was elevated to 2.3 fold by 10 micromol/l cetaben. At high concentrations of cetaben all enzyme activities were decreased in both cell lines due to its high cytotoxicity. Our data show that, due to the differences in the genomic organisation, the regulation of the enzyme activities is different in human and rat, but the results from the human and rat hepatoblastoma cells correlate with the findings in whole man and rat, so that a human in vitro system is more suitable for pharmacological tests. These results suggest that the human hepatoma cell line HepG2 may be a useful model system for studies of the influence of hypolipidaemics on the peroxisomal enzyme system.     

An update on eicosanoids and inhibitors of cyclooxygenase enzyme systems

There are 3 main enzymatic pathways for synthesis of eicosanoids from arachidonic acid, however, some compounds are also formed non-enzymatically. Among the enzymatic pathways, cyclooxygenase (COX) also known as prostaglandin synthase (PGHS), generates endoperoxides (PGG/H). These are converted into prostaglandins (PGs) and thromboxanes (TXs). The second pathway involves lipooxygenase (LOX) group of enzymes to provide hydroperoxyeicosatetraenoic acid (HpETEs) which in turn can be converted into leukotrienes (LTs), hepoxilins (HXs), trioxilins and lipoxins (LXs). The third pathway involves cytochrome P-450 which catalyses the formation of a number of monohydroxy fatty acids (hydroxyeicostetraenoic acids or HETEs) dihydroxy fatty acids (dihydroxyeicostetrienoic acids or DiHETrEs) and epoxyeicosatrienoic acids (EpETrEs: formerly called EETs). This system also provides leukotoxins. The non-enzymatic pathway leads to the formation of isoprostanes by free radical catalysed peroxidation of arachidonic acid. In addition, brain cells also convert arachidonic acid into arachidonylethanolamide (anandamide) which have the ability to bind to cannabinoid receptors. Most of these eicosanoids are either biologically active or are converted into metabolites which have biological activities. Cyclooxygenase is now known to exist in two separate isoforms which are called COX-1 and COX-2. While both isoforms catalyse the same reactions, the former is a constitutive enzyme and its activity is not markedly changed once the cell is fully grown. The later isoform is however inducible and its activity is several fold increased following the exposure of body cells to a number of stimuli and its contribution in the process of inflammation is now well documented. It is now believed that eicosanoids produced by COX-1 activity are essential for the physiological (house keeping) functions while those produced by COX-2 lead to various pathological changes in body tissues. Older nonsteroidal antiinflammatory drugs like aspirin and indomethacin are non selective inhibitors of COX activity and therefore, in addition to inhibiting COX-2 activity, inhibit the formation of eicosanoids by COX-1. The later are required for normal house keeping functions such as secretion of mucus for protection of gastrointestinal mucosa, maintenance of renal function and control of haemostasis. Use of older non-selective NSAIDs has been associated with a number of gastrointestinal, renal and other side effects. Recently drugs such as nimesulide and meloxicam with selective action on COX-2 have been discovered and introduced into medicine. Evidence available so far has indicated the low incidence of side effects with these drugs. While being useful for various arthritic and other conditions, it is unlikely that these drugs will replace aspirin for the cardiovascular disease.     

Differential expression of human high-molecular-weight salivary mucin (MG1) and low-molecular-weight salivary mucin (MG2)

Two distinct mucin components of saliva, MG1 and MG2, have been identified based on chemical composition and molecular weights (high and low, respectively) in saliva. With the aim of characterizing the expression pattern of salivary mucins, we have prepared monoclonal antibodies (MAbs) directed against the peptide core of MG1 and against a synthetic peptide derived from the MG2 (MUC7) sequence. MAb PANH2 raised against partially deglycosylated MG1 stained a high-molecular-weight smear in Western blots of partially purified MG1. PANH2 binding was increased by deglycosylation with trifluoromethanesulfonic acid as well as with subsequent periodate treatment, and was eliminated by pronase treatment, strongly suggesting that MAb PANH2 was directed to a peptide epitope of MG1. MAb PANH3 raised against a synthetic peptide derived from the MG2 (MUC7) sequence reacted with the native molecule and stained a narrow smear of ca. 200,000 to 210,000 in Western blots of concentrated saliva and a lower-molecular-weight smear of trifluoromethanesulfonic-acid-treated MG2. Immunohistology on frozen sections of human salivary glands showed that MAb PANH2 selectively labeled mucous cells, whereas MAb PANH3 labeled subpopulations of serous cells. Double-direct immunofluorescence staining with PANH2 and PANH3 demonstrated that the staining patterns were non-overlapping. The development of these antibody probes will facilitate studies of mucin expression in diseases of salivary glands.     

Cyclooxygenase-2 inhibitors in tumorigenesis (Part II)

The rate-limiting step in arachidonate metabolism is mediated by enzymes known as cyclooxygenases (COXs). These enzymes catalyze the biosynthesis of prostaglandin H2, the precursor of molecules such as prostaglandins, prostacyclin, and thromboxanes. The COX enzyme family consists of the classical COX-1 enzyme, which is constitutively expressed in many tissues, and a second isozyme, i.e., COX-2, which is induced by various stimuli, such as mitogens and cytokines, and is involved in many inflammatory reactions. Because nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit both COX-1 and COX-2, these drugs also cause unwanted side effects, exemplified by gastrointestinal bleeding. Accumulating evidence indicates that NSAIDs can reduce the incidence of colorectal cancers in human and experimental animals and can reduce the number and size of polyps in patients with familial adenomatous polyposis. This Part II (of a two-part review) focuses on the growing clinical and experimental evidence that NSAIDS and COX-2 inhibitors can influence the risk of colon (and possibly of other) cancers.     

Differential effects of GABA(A) and GABA(B) agonists on sensitization to the locomotor stimulant effects of ethanol in DBA/2 J mice

Contemporary theories of drug abuse suggest that behavioral sensitization plays an important role in addiction. However, few studies have examined the mechanisms underlying behavioral sensitization to ethanol. The present study examined the ability of THIP (2, 4, or 8 mg/kg) and baclofen (5.0, 6.25, or 7.5 mg/kg), GABA(A) and GABA(B) agonists, respectively, to prevent development of sensitization to the locomotor stimulant effects of ethanol (2 g/kg) in DBA/2 J mice. Ethanol was administered immediately before four 5-min activity trials conducted at 48-h intervals. Administration of ethanol on each of the four trials resulted in behavioral sensitization in control groups. While having few effects on activity when given alone, both GABA agonists completely blocked the acute stimulant response to ethanol on the first trial. Administration of THIP prior to ethanol on each trial failed to prevent development of sensitization. In contrast, all doses of baclofen blocked sensitization. Assessment of blood ethanol levels 15, 50 and 100 min after administration of ethanol indicated that baclofen did not change the pharmacokinetics of ethanol. These results indicate an important role for GABA(B) receptors, but not GABA(A) receptors, in development of sensitization to the locomotor stimulant effects of ethanol.     

Enantioselectivity of some 1-(benzofuran-2-yl)-1-(1-H-imidazol-1-yl) alkanes as inhibitors of P450Arom

The low stereospecificity of the enantiomers of 1-[(benzofuran-2-yl)-4-chlorophenylmethyl]imidazole (6, R=H, R'=4'-Cl) and the corresponding 4-fluoro compound as inhibitors of aromatase (P450Arom) has been explored using 1-(5,7-dichlorobenzofuran-2-yl)-1-(1H-imidaz-1-yl)ethane (7, R1=R2=Cl, R=CH3), -propane (7, R1=R2=Cl, R=C2H5), and the corresponding 5,7-dibromo compounds resolved as their dibenzoyl-D (or -L) tartrates. Low enantioselectivity ratios of 4.8 (5,7-diCl) and 12.6 (5,7-diBr) were shown for the ethanes. The values for the corresponding propanes were 8.3 and 5.2, respectively, and for these compounds the stereoselectivity was reversed.     

Differential activities of secreted lymphotoxin-alpha3 and membrane lymphotoxin-alpha1beta2 in lymphotoxin-induced inflammation: critical role of TNF receptor 1 signaling

Lymphotoxin (LT, LT alpha, TNF beta) is a member of the immediate TNF family that also includes TNF-alpha and lymphotoxin-beta (LT beta). LT is produced by activated lymphocytes and functions as either a secreted homotrimer or a membrane-associated heterotrimer that includes the transmembrane protein LT beta. Secreted LT alpha3 can bind to two cell surface receptors, TNFR1 and TNFR2, while the membrane-bound heterotrimer LT alpha1beta2 has been shown to interact with a distinct receptor, LT betaR. LT alpha induces inflammation at the sites of expression of a rat insulin promoter-driven lymphotoxin (RIPLT) transgene in the pancreas and kidney. To determine the role of the various ligands and their receptors in LT-induced inflammation, mice deficient in either TNFR1, TNFR2, or LT beta were crossed to RIPLT-transgenic mice. Our results indicate that LT alpha-induced inflammation is dependent on the interaction of LT alpha3 with TNFR1, and there is no obvious role for TNFR2, since in its absence, LT alpha-induced inflammation is quantitatively and qualitatively similar to that seen in the wild type. However, the absence of LT beta results in accentuated infiltration of the kidney with an increase in the proportion of memory cells in the infiltrate. These data show a crucial role for the secreted LT alpha3 signaling via TNFR1 in LT alpha-induced inflammation, and a separate and distinct role for the membrane LT alpha1beta2 form in this inflammatory process.     

Functional stability of hippocampal slices after treatment with cyclooxygenase inhibitors

The influence of cyclooxygenase inhibitors on functional stability of hippocampal slices, determined by electrophysiological criteria of recovery after slicing and long-term maintainence of population activity, was studied. Transient (3 min) treatment of slices during slicing with indomethacin (45 microM) or aspirin (0.5 mM) allowed registration of the population responses from the second minute. The activity reached 100% after 15 min incubation and could be registrated for 3 days under conditions of overnight hypothermia. The presence of the same drugs for the entire incubation period had the same effect. The present findings suggest that slicing is a crucial point for triggering of pathological events mediated by cyclooxygenase products and that blockade of cyclooxygenase provides for the further high longterm functional stability of brain slices.     

New non-steroidal anti-rheumatic drugs: selective inhibitors of inducible cyclooxygenase

MODE OF ACTION OF NON-STEROIDAL ANTI-INFLAMMATORY DRUGS: Non-steroidal anti-inflammatory drugs (NSAID) exert their major therapeutic and adverse effects by inhibition of prostanoid synthesis. Also the interactions with antihypertensive drugs and lithium are caused by this mechanism of action. Cyclooxygenation is a key enzymatic step in the synthesis of prostanoids. 1990 2 isoforms of the enzyme cyclooxygenase have been identified: Prostanoids synthesized by the constitutive cyclooxygenase (COX-1) are involved in physiological homeostasis. In contrast, the inducible cyclooxygenase (COX-2) produces large amounts of prostanoids, mainly contributing to the pathophysiological process of inflammation. COX-2 SELECTIVE NSAID: The discovery of the cyclooxgenase-isoenzymes ushered in a new generation of NSAID: A drug with selectivity for COX-2 would inhibit proinflammatory prostanoid synthesis while sparing physiologic prostanoid synthesis. Thus, a selective COX-2 inhibitor should be anti-inflammatory with less or no gastrointestinal or other NSAID-typical adverse effects. The experiences with currently used NSAID, which show an increasing incidence of side effects as COX-1 inhibition increases, and studies with the COX-2 selective NSAID salsalate and meloxicam, which have less adverse effects than nonselective COX inhibitors in equivalent antiphlogistic dosage, prove the concept of selective COX-2 inhibition to avoid the NSAID typical side effects. Newly developed drugs with a very high selectivity for COX-2 are now tested in clinical trials. CONCLUSION: So far the results suggest, that selective and highly selective COX-2 inhibitors have significantly fewer gastrointestinal and renal adverse effects and do not inhibit platelet aggregation.     

Differential expression of G1 cyclins and cyclin-dependent kinase inhibitors in normal and transformed melanocytes

The myocardial concentration of many cardioactive drugs has been identified as an important determinant of their short-term effects in previous studies. Although sotalol is frequently administered via short-term intravenous injection, no previous studies had sought to correlate its uptake by the heart with its various effects. We determined the time course of short-term uptake of d,l-sotalol by human myocardium in vivo and investigated the relation between myocardial content of sotalol and the short-term hemodynamic, electrocardiographic, and electrophysiologic effects of the drug. Sixteen patients received a 20-mg intravenous bolus of sotalol at the time of diagnostic cardiac catheterization. Myocardial content of d- and l-sotalol (by using a paired transcoronary sampling technique) and the short-term hemodynamic and electrophysiologic effects of the drug were determined < or = 20 min after injection. Myocardial accumulation of sotalol was not enantioselective, proceeded very rapidly (maximal at 0.74 +/- 0.10 min, representing 2.05 +/- 0.45% of the total injected dose), and was not significantly influenced by left ventricular systolic function or the extent of coronary artery disease. Approximately one third of peak myocardial content was still present 17.5 min after sotalol administration. Maximal effects of the drug (reduction in spontaneous heart rate, p < 0.005; reduction in maximal rate of LV pressure increase (LV+dP/dtmax, p < 0.005); and prolongation of PR intervals, p < 0.02) were delayed by approximately 10 min relative to maximal myocardial sotalol content. The significant prolongation of AH intervals (p < 0.01) and atrioventricular nodal effective refractory periods (p < 0.0002) that was observed was also maximal 10 min after administration of sotalol. Thus a consistent delay between myocardial sotalol content and the short-term effects of the drug was observed. In conclusion, the accumulation of both d- and l-sotalol by the human myocardium is more rapid than that of any other agent studied to date, with considerable hysteresis between myocardial drug uptake and subsequent cardiac effects.