Deep parasternal intercostal plane nerve block: an anatomical study.

INTRODUCTION: The superficial and deep parasternal intercostal plane (DPIP) blocks are two new blocks for thoracic pain. There are limited cadaveric studies evaluating the dye spread with these blocks. In this study, we examined the dye spread of an ultrasound-guided DPIP block in a human cadaveric model. METHODS: Five ultrasound-guided DPIP blocks were performed in four unembalmed human cadavers using an in-plane approach with a linear transducer oriented in a transverse plane adjacent to the sternum. Twenty milliliters of 0.1% methylene blue were injected between ribs 3 and 4 into the plane deep to the internal intercostal muscles and superficial to the transversus thoracis muscle layer. The chest muscles were dissected, and the extent of dye spread was documented in both cephalocaudal and mediolateral directions. RESULTS: The transversus thoracis muscle slips were stained in all cadavers from 4 to 6 levels. Intercostal nerves were dyed in all specimens. Four levels of intercostal nerves were dyed in each specimen with variability in number of levels stained above and below the level of the injection. CONCLUSIONS: The DPIP block spreads along the tissue plane above the transversus thoracis muscles to multiple levels to dye the intercostal nerves in this cadaver study. This block may be of clinical value for analgesia in anterior thoracic surgical procedures.

Deep Parasternal Intercostal Plane Block for Intraoperative Pain Control in Cardiac Surgical Patients for Sternotomy: A Prospective Randomized Controlled Trial.

OBJECTIVES: Sternotomy pain is common after cardiac surgery. The deep parasternal intercostal plane (DPIP) block is a novel technique that provides analgesia to the anterior chest wall. The aim of this study was to investigate the analgesic effect of bilateral DPIP blocks on intraoperative pain control in cardiac surgery. DESIGN: This is a double-blinded, prospective randomized controlled trial (Oct 2020-Dec 2022). SETTINGS: This study was conducted in a single institution, which is an academic university hospital. PARTICIPANTS: Eighty-six elective cardiac surgical patients with median sternotomy were recruited. INTERVENTIONS: Patients were randomly divided into DPIP or control group. Either 20ml 0.25% levobupivacaine or 0.9% normal saline was injected for the DPIP under ultrasound guidance after induction of general anaesthesia. MEASUREMENTS AND MAIN RESULTS: The primary outcome was intraoperative opioids consumption and hemodynamic changes at sternotomy. Secondary outcomes included postoperative morphine consumption, postoperative pain and time to tracheal extubation. Intraoperative opioids requirement was reduced from a median (IQR) intravenous morphine equivalence of 21.4mg (13.8-24.3mg) in control group to 9.5mg (7.3-11.2mg) in the DPIP group (P<0.001). Hemodynamic parameters were more stable in DPIP group at sternotomy, as evidenced by lower percentage increase in systolic, diastolic and mean arterial blood pressure from baseline. No difference was observed in time to tracheal extubation, postoperative morphine consumption, postoperative pain score and spirometry. CONCLUSIONS: Bilateral DPIP block provides effective intraoperative analgesia and opioid-sparing. It may be included as part of the multimodal analgesia for enhanced recovery in cardiac surgery.

Preemptive deep parasternal intercostal plane block for perioperative analgesia in coronary artery bypass grafting with sternotomy: a randomized, observer-blind, controlled study.

OBJECTIVE: The precise characteristics of deep parasternal intercostal plane block (DPIP), which is useful for providing analgesia during open heart surgery, have not yet been thoroughly elucidated. In this study, we aimed to establish the efficacy, define the cutaneous sensory block area, and determine the duration of preemptive DPIP block at the T3-4 or T4-5 intercostal spaces in patients undergoing coronary artery bypass grafting (CABG) via sternotomy. DESIGN: A prospective, single-blind, randomized controlled trial. SETTING: Patients were randomly divided into three cohorts, each containing thirty patients. PARTICIPANTS: Ninety patients who underwent elective CABG via sternotomy were included in this study. INTERVENTIONS: The T3-4 and T4-5 groups received a preoperative single-shot DPIP block at the respective intercostal spaces. The principal objective of the study was to ascertain the optimal dosage of sufentanil administered during surgical procedures involving either a DPIP block or its absence, and to conduct a comparative analysis thereof across distinct injection sites, specifically T3-4 and T4-5. Secondary factors considered were the dosage of postoperative analgesics, the extent of sensory block on the skin, pain levels after extubation, time of recovery from anesthesia (time to extubation), duration of the block, and the occurrence of nausea and vomiting. MEASUREMENTS & MAIN RESULTS: Preemptive DPIP block significantly reduced intraoperative sufentanil requirement compared to the control group (T3-4:0.38 ± 0.1, T4-5:0.32 ± 0.10, vs. Control:0.88 ± 0.3 µg/kg/h, p < 0.001). It also resulted in decreased analgesic consumption and numeric rating scale scores on the day of surgery (p < 0.01 compared to the control group). The DPIP block provided accurate anesthetic coverage of the dermatomes in the sternal region and reduced the time to extubation and postoperative nausea. However, the injection point (either via the T3-4 intercostal or the T4-5 intercostal) did not affect the efficacy. Preoperative DPIP block failed to provide adequate analgesia beyond 24 h post-surgery. CONCLUSION: Preemptive bilateral DPIP block provided effective analgesia in patients undergoing CABG during surgery and in the early postoperative period. The analgesic effects of the DPIP block in the T3-4 and T4-5 intercostal spaces were comparable.

Usefulness of monochromatic imaging with metal artifact reduction software for computed tomography angiography after intracranial aneurysm coil embolization.

BACKGROUND: Recently, a newly developed fast-kV switching dual energy CT scanner with a gemstone detector generates virtual high keV images as monochromatic imaging (MI). Each MI can be reconstructed by metal artifact reduction software (MARS) to reduce metal artifact. PURPOSE: To evaluate the degree of metal artifacts reduction and vessel visualization around the platinum coils using dual energy CT with MARS. MATERIAL AND METHODS: Dual energy CT was performed using a Discovery CT750 HD scanner (GE Healthcare, Milwaukee, WI, USA). In a phantom study, we measured the mean standard deviation within regions of interest around a 10-mm-diameter platinum coil mass on MI with and without MARS. Thirteen patients who underwent CTA after endovascular embolization for cerebral aneurysm with platinum coils were included in a clinical study. We visually assessed the arteries around the platinum coil mass on MI with and without MARS. RESULTS: Each standard deviation near the coil mass on MI with MARS was significantly lower than that without MARS in a phantom study. On CTA of a clinical study, better visibility of neighboring arteries was obtained in 11 of 13 patients on MI with MARS compared to without MARS due to metal artifact reduction. CONCLUSION: Dual energy CT with MARS reduces metal artifact of platinum coils, resulting in favorable vessel visualization around the coil mass on CTA after embolization.

Binding of diuretic antihypertensive bendroflumethiazide to human serum albumin studied by ¹9F nuclear magnetic resonance method.

Simultaneous specific and nonspecific binding of bendroflumethiazide (BFZ) to human serum albumin (HSA) and concentration profile of BFZ in HSA buffer (pH 7.40) solution were investigated by ¹9F nuclear magnetic resonance (NMR) method. The ¹9F NMR spectrum of BFZ (200 µM) in a buffer solution showed a sharp signal of its CF3 group at 17.8 ppm from the reference trifluoroethanol. Addition of 0.60mM HSA to the sample solution caused the CF(3) signal splitting into three broadened peaks at 18.4 (A), 17.9 (B) and 17.4 ppm (C). By its chemical shift and spectral behavior, B was assigned to unbound BFZ. Competition experiments with Site I and II ligands lead to C being assigned to Site II bound BFZ. However, the peak intensity (areas) of A was not reduced by these ligands, suggesting that A arises from nonspecific binding. Using the peak intensities at several total concentrations of BFZ, Scatchard plot was performed. The plot for A provided a straight line parallel to the x-axis confirming nonspecific binding and that for C was consistent with specific binding. The binding constants for nonspecific and specific Site II binding were 1.02 and 1.00 × 104 (M⁻¹) (n=1.1), respectively. The presence of 0.10 M Cl⁻ in the sample solution affected the binding constant of Site II binding, but not that of nonspecific binding. The concentration profile of BFZ calculated using the binding constants revealed that nonspecific binding is more effective than Site II binding for the binding of BFZ to HSA. It was also confirmed that considerable amounts of BFZ liberated from Site II by the Site II ligands or Cl⁻ ions bind again nonspecifically.

Crystallographic analysis reveals the structural basis of the high-affinity binding of iophenoxic acid to human serum albumin.

BACKGROUND: Iophenoxic acid is an iodinated radiocontrast agent that was withdrawn from clinical use because of its exceptionally long half-life in the body, which was due in part to its high-affinity binding to human serum albumin (HSA). It was replaced by Iopanoic acid, which has an amino rather than a hydroxyl group at position 3 on the iodinated benzyl ring and, as a result, binds to albumin with lower affinity and is excreted more rapidly from the body. To understand how iophenoxic acid binds so tightly to albumin, we wanted to examine the structural basis of its interaction with HSA. RESULTS: We have determined the co-crystal structure of HSA in complex with iophenoxic acid at 2.75 Å resolution, revealing a total of four binding sites, two of which--in drugs sites 1 and 2 on the protein--are likely to be occupied at clinical doses. High-affinity binding of iophenoxic acid occurs at drug site 1. The structure reveals that polar and apolar groups on the compound are involved in its interactions with drug site 1. In particular, the 3-hydroxyl group makes three hydrogen bonds with the side-chains of Tyr 150 and Arg 257. The mode of binding to drug site 2 is similar except for the absence of a binding partner for the hydroxyl group on the benzyl ring of the compound. CONCLUSIONS: The HSA-iophenoxic acid structure indicates that high-affinity binding to drug site 1 is likely to be due to extensive desolvation of the compound, coupled with the ability of the binding pocket to provide a full set of salt-bridging or hydrogen bonding partners for its polar groups. Consistent with this interpretation, the structure also suggests that the lower-affinity binding of iopanoic acid arises because replacement of the 3-hydroxyl by an amino group eliminates hydrogen bonding to Arg 257. This finding underscores the importance of polar interactions in high-affinity binding to albumin.

Analysis by LC/ESI-MS of iophenoxic acid derivatives and evaluation as markers of oral baits to deliver pharmaceuticals to wildlife.

Iophenoxic acid and its derivatives (methyl, ethyl, and propyl) are organic chemicals used as markers in baiting campaigns to deliver vaccines, pharmaceuticals, contraceptives or poisons to wildlife. In this study we develop a method of detection of IPA derivatives by LC/ESI-MS (using butyl-IPA as internal standard) obtaining a limit of detection and quantification in wild boar (Sus scrofa) serum of 0.037 microg/ml and 0.123 microg/ml, respectively. The average recovery of IPA derivatives was 88% at levels >0.2 microg/ml, with coefficients of variation <15%. Wild boars in captivity were orally treated with 5 mg/kg b.w. (three adults) or 15 mg/kg b.w (two piglets and three adults) of methyl-, ethyl- and propyl-IPA and the serum levels of these were monitored during 18 months after dosing. Ethyl- and propyl-IPA were detected up to 18 months after a single oral dose in wild boar, especially at 15 mg/kg. Methyl-IPA was detected until 9 months after dosing. Half-lives of methyl-, ethyl- and propyl-IPA were (mean+/-SD) 41+/-5, 183+/-85 and 165+/-45 days, respectively. One control piglet not exposed to IPA, but housed in the same facility than treated animals showed detectable IPA levels in serum. Piglets born from mothers exposed to marked baits also showed detectable IPA levels in serum. The high persistence of Et- and Pr-IPA must be considered in the field trials, because the presence of the product at low levels in one animal may not reflect a real ingestion of the marked bait.

Vaccination of feral pigs (Sus scrofa) using iophenoxic acid as a simulated vaccine.

OBJECTIVES: To develop an encapsulation method for delivery of vaccines to feral pigs, and quantify the effect of iophenoxic acid on captive feral pig blood iodine concentrations to assist in investigation of factors affecting vaccine uptake. DESIGN AND METHODS: Feral pigs were administered iophenoxic acid by oral gavage, and consumption was assessed for different encapsulation methods in baits. Blood iodine concentrations were monitored for eight days after consumption. The relationship between dose rate, time since dosing and blood iodine concentration was assessed for gavaged and baited captive feral pigs. Wild feral pigs were baited with PIGOUT baits containing 20 mg of encapsulated iophenoxic acid to simulate a vaccination program. Using knowledge from the pen studies, bait uptake and factors affecting bait uptake were investigated. RESULTS: Bait-delivered iophenoxic acid led to variable and inconsistent changes in blood iodine concentrations, in contrast to pigs receiving iophenoxic acid by gavage. This precluded accurate assessment of the quantity consumed, but still allowed a conservative determination of bait uptake. Iophenoxic acid in smaller capsules was consumed readily. Increasing baiting intensity appeared to increase bait uptake by wild feral pigs, and pigs of varying sexes, ages and weights appeared equally likely to consume baits. CONCLUSIONS: Encapsulated liquids can be delivered to feral pigs within baits, should the need to vaccinate feral pigs for fertility or disease management arise. High baiting intensities may be required.

Liquid chromatography-electrospray ionization mass spectrometry for direct identification and quantification of iophenoxic acid in serum.

A liquid chromatographic-electrospray ionization mass spectrometric technique was developed for direct quantitation of iophenoxic acid (IA) in serum. IA was spiked into canine, feline, bovine, equine, and porcine sera, extracted, and quantified using negative ion monitoring following chromatographic separation on a Luna C18(2) 3 microm (100 mm x 2.1mm) reversed-phase column. The limit of detection was 25 ng/mL and the limit of quantification was 50 ng/mL. Inter- and intra-assay accuracy (86-113% and 87-115%, respectively) and precision (1.8-7.7%) were calculated. Analysis of serum collected from feral pigs, raccoons, and opossums following ingestion of IA-marked baits confirmed the appropriateness of this method for bait acceptance studies.

Long-lasting systemic bait markers for Eurasian badgers.

This study was carried out to assess whether Rhodamine B, ethyl-iophenoxic acid (EtIPA), and propyl-iophenoxic acid (PrIPA) can be used as long-lasting systemic bait markers for free-living badgers (Meles meles). Between June and November 2003, these chemicals were incorporated into bait distributed around badger setts. Serum, hair, and whiskers from individually marked badgers were collected in the following 4 to 24 wk. Rhodamine B was detectable as fluorescent bands up to 24 wk after ingestion of the bait. Individual badgers were found positive for EtIPA and PrIPA up to 20 wk and 18 wk after exposure, respectively. This study indicates that Rhodamine B, PrIPA, and EtIPA could be used as long-lasting markers for badgers.

Thin-section multiplanar reformats from multidetector-row CT data: utility for assessment of regional tumor extent in non-small cell lung cancer.

PURPOSE: To determine the clinical utility of thin-section multiplanar reformats (MPRs) from multidetector-row CT (MDCT) data sets for assessing the extent of regional tumors in non-small cell lung cancer (NSCLC) patients. MATERIALS AND METHODS: Sixty consecutive NSCLC patients, who were considered candidates for surgical treatment, underwent contrast-enhanced MDCT examinations, surgical resection and pathological examinations. All MDCT examinations were performed with a 4-detector row computed tomography (CT). From each raw CT data set, 5mm section thickness CT images (routine CT), 1.25 mm section thickness CT images (thin-section CT) and 1.25 mm section thickness sagittal (thin-section sagittal MPR) and coronal images (thin-section coronal MPR) were reconstructed. A 4-point visual score was used to assess mediastinal, interlobar and chest wall invasions on each image set. For assessment of utility in routine clinical practice, mean reading times for each image set were compared by means of Fisher's protected least significant difference (PLSD) test. A receiver operator characteristic (ROC) analysis was performed to determine the diagnostic capability of each of the image data sets. Finally, sensitivity, specificity and accuracy of the reconstructed images were compared by McNemar test. RESULTS: Mean reading times for thin-section sagittal and coronal MPRs were significantly shorter than those for routine CT and thin-section CT (p<0.05). Areas under the curve (Azs) showing interlobar invasion on thin-section sagittal and coronal MPRs were significantly larger than that on routine CT (p=0.03), and the Az on thin-section sagittal MPR was also significantly larger than that on routine CT (p=0.02). Accuracy of chest wall invasion by thin-section sagittal MPR was significantly higher than that by routine CT (p=0.04). CONCLUSION: Thin-section multiplanar reformats from multidetector-row CT data sets are useful for assessing the extent of regional tumors in non-small cell lung cancer patients.

Inhibition of drug binding to human serum albumin by cholecystographic agents.

The binding of two cholecystographic agents to human serum albumin (HSA) was evaluated by means of two different complementary methodologies. In particular, the inhibition of drug HSA binding caused by iopanoic- and iophenoxic-acid was investigated by circular dichroism (CD) and resonant mirror (RM) optical biosensor techniques. The CD study allowed to obtain information both on the cholecystographic agent binding site and on the effect of the binding on the protein conformation. Iopanoic acid (IOP), a drug potentially useful for thyrotoxic disorders, resulted a direct competitor for ligands that selectively bind to site II, in agreement to literature data. No definite evidence was obtained for the highest affinity binding site of iophenoxic acid (IOPH), however, this diagnostic tool markedly affected the binding of ligands to the most characterized high affinity sites on HSA, namely sites I, II and III. Binding parameters were obtained by optical biosensor analysis: K(D) values were 3.6 x 10(-7) and 2.8 x 10(-8) M for IOP and IOPH, respectively.

Use of oral cholecystography agents in the treatment of hyperthyroidism of subacute thyroiditis.

AIM: In this study, we describe our experience in treating subacute thyroiditis patients with 2 OCAs (sodium ipodate and sodium iopanoate). METHODS: We studied 10 consecutive patients with subacute thyroiditis treated with 1 of the 2 oral cholecystography agents (OCAs). RESULTS: Hyperthyroidism was controlled and symptoms improved markedly in each case without any evidence of subsequent relapse of thyroiditis after withdrawal of OCAs. Three of the 10 patients had been treated previously with corticosteroids and had demonstrated relapse of thyroiditis and hyperthyroidism after tapering or withdrawal of steroids. We observed no side effects of treatment with OCAs. CONCLUSION: Our data suggest that OCAs are effective and safe agents for management of hyperthyroidism in patients with subacute thyroiditis, even when they have relapsed after treatment with corticosteroids.

Recombinant lysine:N(6)-hydroxylase: effect of cysteine-->alanine replacements on structural integrity and catalytic competence.

Recombinant lysine:N(6)-hydroxylase, rIucD, catalyzes the hydroxylation of L-lysine to its N(6)-hydroxy derivative, with NADPH and FAD serving as cofactors in the reaction. The five cysteine residues present in rIucD can be replaced, individually or in combination, with alanine without effecting a major change in the thermal stability, the affinity for L-lysine and FAD, as well as the k(cat) for mono-oxygenase activity of the protein. However, when the susceptibility to modification by either 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) or 2,6-dichlorophenol indophenol (DPIP) serves as the criterion for monitoring conformational change(s) in rIucD and its muteins, Cys146-->Ala and Cys166-->Ala substitutions are found to induce an enhancement in the reactivity of one of the protein's remaining cysteine residues with concomitant diminution of mono-oxygenase function. In addition, the systematic study of cysteine-->alanine replacement has led to the identification of rIucD's Cys166 as the exposed residue which is detectable during the reaction of the protein with DTNB but not with iodoacetate. Substitution of Cys51 of rIucD with alanine results in an increase in mono-oxygenase activity (approx. 2-fold). Such replacement, unlike those of other cysteine residues, also enables the covalent DPIP conjugate of the protein to accommodate FAD in its catalytic function. A possible role of rIucD's Cys51 in the modulation of its mono-oxygenase function is discussed.

A surface-modified chylomicron remnant-like emulsion for percutaneous computed tomography lymphography: synthesis and preliminary imaging findings.

RATIONALE AND OBJECTIVES: To assess a surface-modified emulsion as a percutaneous CT lymphographic agent in normal dogs. METHODS: An iodinated chylomicron remnant-like microemulsion was formulated with a mean particle size of 91.3 nm and an iodine concentration of 91 mg I/mL. Contrast material (2 mL) was injected into the subcutaneous tissues of the metatarsus and metacarpus of six normal dogs to enhance popliteal and cervical lymph nodes, respectively. CT images were acquired at 0, 15, 30, 45, 60, 240, 480, and 1440 minutes. RESULTS: Significant lymph node enhancement occurred in as little as 15 minutes after injection and persisted at least 8 hours. Node opacification was most pronounced at 1 to 4 hours postinjection and exceeded 200 HU in some nodes (precontrast attenuation = 45 HU). Marked enhancement of popliteal efferent lymphatics and of iliac and sacral node groups also occurred indicating distribution to second order nodes. Attenuation of enhanced nodes reverted to precontrast levels by 24 hours. CONCLUSION: The new surface-modified, chylomicron remnant-like emulsion provided marked, selective enhancement of targeted lymph nodes after subcutaneous administration. Moreover, the formulation produced significant opacification of more distant node groups from a single injection.

Incorporation of an (125)I-labeled hexa-iodinated diglyceride analog into low-density lipoprotein and high specific uptake by cells of cervical carcinoma cell lines.

The feasibility of using low-density lipoprotein (LDL) to deliver cytotoxic drugs to tumor cells has been explored since the 1980s, when cells of a number of cancer cell lines were found to have higher LDL receptor activity than normal cells. Such differential uptake between tumor and normal cells may provide a unique opportunity to use LDL as a tumor-specific carrier of radiopharmaceuticals for the clinical management of cancer. In this study, an (125)I-labeled hexa-iodinated diglyceride analog, 1, 3-dihydroxypropan-2-one 1,3-diiopanoate (DPIP), was synthesized and incorporated into LDL using a fusion technique. It was found that approximately 500 [(125)I] DPIP molecules were incorporated into each LDL particle. Cells of three human cervical tumor cell lines, HeLa, SiHa and C-33A, were used to examine the cellular uptake of the [(125)I]DPIP-LDL conjugate. It was shown that the [(125)I]DPIP-LDL conjugate was specifically bound to and taken up by cervical tumor cells through an LDL receptor-mediated endocytosis pathway. The results suggest that LDL may be a selective carrier for delivering hydrophobic radiopharmaceuticals to cancer cells and particularly for the diagnosis of cervical tumors.

High-performance liquid chromatographic determination of iophenoxic acid in serum.

Iophenoxic acid (IPA), a marker used to investigate the feeding behaviour of bait-consuming animals has previously been indirectly determined by measuring protein-bound iodine levels in serum or plasma. For the first time a method is reported for the direct determination of IPA in biological fluids. IPA was determined in de-proteinized serum by high-performance liquid chromatography (HPLC) on a C18 column with a mobile phase of acetonitrile-water. Isocratic and gradient systems are described with limits of detection of 0.2 microgram/ml (isocratic) and 0.05 microgram/ml (gradient). Recoveries from fox serum were 85% at 0.5 microgram/ml, 95% at 5 micrograms/ml and 91% at 50 micrograms/ml.

Diagnostic and therapeutic potential of poly(benzyl L-glutamate).

Poly(benzyl L-glutamate) (PBLG) microcapsules, prepared by a solvent evaporation technique for intravenous injection, are evaluated for their potential use in diagnostic computed tomographic enhancement of liver images. The smaller microcapsules, < 3 microns, loaded with a radiopaque contrast material, ethyl iopanoate (IOPAE), produced prolonged opacification of the liver when delivered intravenously. In vivo tissue distribution studies of PBLG-131I-IOPAE (5 microCi/rat, iv) showed that liver had the highest uptake (percent of injected dose/g of tissue) among other organs 24 h postinjection. An in vitro estrogen receptor assay in pig uteri indicated that PBLG conjugated with estrone did not interfere with estrogen receptor affinity, suggesting the estrogen therapy potential of PBLG-estrone.

The plasma pharmacokinetics of iophenoxic and iopanoic acids in goat.

1. The comparative plasma pharmacokinetics of two organic iodine-containing compounds were evaluated in the goat for their suitability as markers in wildlife studies. 2. After oral administration of a single dose, the plasma elimination half-life for iopanoic acid was considerably more rapid (t1/2 of 1-2 days) than that of iophenoxic acid (t1/2 of 81 days). 3. Similar peak plasma concentrations were obtained after administration of iophenoxic acid (1.5 mg/kg) and iopanoic acid (25 mg/kg); however, the AUC0----infinity for iopanoic acid at doses of 25, 50, and 100 mg/kg were 201 +/- 39, 604 +/- 225, and 1292 +/- 721 (micrograms h/ml +/- SD), respectively, which were less than the value of 36,600 +/- 6387 for the oral administration of iophenoxic acid at 1.5 mg/kg. 4. Iophenoxic acid was chosen as a suitable marker because of its persistence at detectable concentrations in the plasma for 5 months.

Synthesis and evaluation of iodinated analogues of diacylglycerols as potential probes for protein kinase C.

Analogues of diacylglycerol containing a 3-(3-amino-2,4,6-triiodophenyl)-2-ethylpropanoyl or 3-(3-amino-2,4,6-triiodophenyl)propanoyl group in the 2-position (1a and 1b, respectively) were synthesized and shown to compete with [3H]phorbol dibutyrate [( 3H]PDBu) for binding in a crude rat brain preparation. Phorbol diesters have been shown to bind specifically to protein kinase C and the PDBu receptor has been copurified with protein kinase C activity. The four diastereomers of 1a (1c-f) were synthesized from chiral starting material and studied in the same assay. The affinities for the [3H]PDBu binding site of 1a, 1b, and two isomers of 1a with naturally occurring L configuration were comparable to that of 1-oleoyl-2-acetyl-rac-glycerol (OAG), but the D isomers of 1a were essentially inactive. The chirality of the side chain did not influence the binding affinity. Activation of protein kinase C by 1a, 1c, and 1e demonstrated the same stereochemical requirements, but none were as active as OAG. For the 1,3-isomers 2, 2a, and 2b, the competitive binding studies gave different results. The racemic mixture and the D isomer, 2b, were able to compete for binding, but the L isomer, 2a, did not compete. These studies demonstrate that diacylglycerol binding to and activation of protein kinase C is stereospecific for the glycerol backbone, but not the side chain. Furthermore, the D-1,3-isomer must exist in a conformation such that the acyl and hydroxyl oxygens assume a spatial relationship similar to that in the L-1,2-isomers.