D R Compton

Bio: D R Compton is an academic researcher from Virginia Commonwealth University. The author has contributed to research in topics: Cannabinoid & Cannabinoid receptor. The author has an hindex of 11, co-authored 14 publications receiving 2357 citations.

Cannabinoid-induced mesenteric vasodilation through an endothelial site distinct from CB1 or CB2 receptors.

Abstract: Cannabinoids, including the endogenous ligand arachidonyl ethanolamide (anandamide), elicit not only neurobehavioral but also cardiovascular effects. Two cannabinoid receptors, CB1 and CB2, have been cloned, and studies with the selective CB1 receptor antagonist SR141716A have implicated peripherally located CB1 receptors in the hypotensive action of cannabinoids. In rat mesenteric arteries, anandamide-induced vasodilation is inhibited by SR141716A, but other potent CB1 receptor agonists, such as HU-210, do not cause vasodilation, which implicates an as-yet-unidentified receptor in this effect. Here we show that “abnormal cannabidiol” (Abn-cbd) is a neurobehaviorally inactive cannabinoid that does not bind to CB1 receptors, yet causes SR141716A-sensitive hypotension and mesenteric vasodilation in wild-type mice and in mice lacking CB1 receptors or both CB1 and CB2 receptors. Hypotension by Abn-cbd is also inhibited by cannabidiol (20 μg/g), which does not influence anandamide- or HU-210-induced hypotension. In the rat mesenteric arterial bed, Abn-cbd-induced vasodilation is unaffected by blockade of endothelial NO synthase, cyclooxygenase, or capsaicin receptors, but it is abolished by endothelial denudation. Mesenteric vasodilation by Abn-cbd, but not by acetylcholine, sodium nitroprusside, or capsaicine, is blocked by SR141716A (1 μM) or by cannabidiol (10 μM). Abn-cbd-induced vasodilation is also blocked in the presence of charybdotoxin (100 nM) plus apamin (100 nM), a combination of K+-channel toxins reported to block the release of an endothelium-derived hyperpolarizing factor (EDHF). These findings suggest that Abn-cbd and cannabidiol are a selective agonist and antagonist, respectively, of an as-yet-unidentified endothelial receptor for anandamide, activation of which elicits NO-independent mesenteric vasodilation, possibly by means of the release of EDHF.

Behavioral, biochemical, and molecular modeling evaluations of cannabinoid analogs.

Abstract: Numerous cannabinoids have been synthesized that are extremely potent in all of the behavioral assays conducted in our laboratory. An important feature in increasing potency has been the substitution of a dimethylheptyl (DMH) side chain for the pentyl side chain. Our previous studies have shown that (−)-11-OH-Δ8-THC-dimethylheptyl was 80–1150 times more potent than Δ9-THC. Stereospecificity was demonstrated by its (+)- enantiomer which was more than 1400–7500 times less potent. A related series of DMH cannabinoid analogs has recently been synthesized and preliminary evaluations reported here. (−)-11-OH-Δ9-THC-DMH was found to be equipotent with (−)-11-OH-Δ8-THC-DMH. The aldehyde (−)-11-oxo-Δ9-THC-DMH was 15–50 times more potent than Δ9-THC. Surprisingly, (−)-11-carboxy-Δ9-THC-DMH was also active, being slightly more potent than Δ9-THC. In the bicyclic cannabinoid series, the length and bulk of the side chain were found to be equally important. Aminoalkylindoles, which are structurally dissimilar from classical cannabinoids, have been found to exhibit a pharmacological profile similar to Δ9-THC. Though not extremely potent in vivo, they appear to represent an entirely new approach to studying the actions of the cannabinoids. The structural diversity and wide-ranging potencies of the analogs described herein provide the opportunity to develop a pharmacophore for the cannabinoids using molecular modeling techniques.

The pharmacological activity of anandamide, a putative endogenous cannabinoid, in mice.

Abstract: The arachidonic acid derivative anandamide (arachidonylethanolamide) has been isolated from porcine brain and has been shown to bind competitively to the cannabinoid receptor. Although the pharmacological activity of this compound has not yet been fully determined, preliminary data suggest that it produces several effects similar ot the cannabinoids. In the present experiments anandamide produced effects similar to those of delta 9-tetrahydrocannabinol, including antinociception (as determined in a latency to tail-flick evaluation), hypothermia, hypomotility and catalepsy in mice after i.v., i.t. and i.p. administration. In general, the effects of anandamide occurred with a rapid onset, but with a rather short duration of action. Prominent antinociceptive effects (> 80% maximal possible effect) were measured immediately after i.v. and i.t. administration. Anandamide produced significant decreases in rectal temperature (2-4 degrees C) after either i.v. or i.t. injection. Maximal effects on motor activity (approximately 85% inhibition) were observed immediately after i.v. and i.p. administration and 10 min after i.t. administration. Maximum immobility observed after i.v. administration was over 80%, yet that produced after i.p. and i.t. administration was too small (< or = 20%) to be considered pharmacologically relevant. Anandamide was less potent (1.3 to 18 times) than delta 9-tetrahydrocannabinol in all behavioral assays. Pretreatment with nor-binaltorphimine, a kappa opioid antagonist which blocks i.t. delta 9-tetrahydrocannabinol-induced antinociception, failed to alter antinociception after i.t. anandamide administration. Binding studies demonstrating that anandamide displaces [3H]CP-55,940 from rat whole brain P2 membrane preparations with a KD of 101 +/- 15 nM. These findings demonstrate that anandamide produces effects in a tetrad of tests used to predict cannabimimetic activity and supports the contention of its role as an endogenous cannabinoid ligand. However, there appear to be distinct differences between anandamide and the cannabinoids with regard to their antinociceptive properties, and other properties vary as a function of route of administration.

Pharmacology and stereoselectivity of structurally novel cannabinoids in mice.

Abstract: The pharmacological effects of three stereoisomeric pairs of structurally novel cannabinoids were tested after i.v. administration in mice for depression of spontaneous activity and the production of hypothermia, antinociception and catalepsy. The (-)-enantiomers were as much as 770 times more potent than delta 9-6a,10a-trans-tetrahydrocannabinol and were 7 to 2000 times more potent than their respective (+)-enantiomers. The order of potency for cannabinoid-induced effects was spontaneous activity greater than antinociception greater than hypothermia greater than or equal to catalepsy. Levonantradol was active between 0.123 to 1.5 mg/kg, whereas dextronantradol, its (+)-enantiomer was inactive. (-)-CP 55,244 and (-)-CP55,940 analogs which lack the dihydropyran ring were 5 to 775 times more potent than delta 9-6a,10a-trans-tetrahydrocannabinol and 30 to 2000 times more potent than their respective (+)-enantiomers. Some separation of effects was demonstrated with (+)-CP 55,243 and (-)-CP 56,667 which were inactive in producing hypothermia and catalepsy but were active in the spontaneous activity and tail-flick procedures. The high degree of enantioselectivity and potency of these nonclassical cannabinoids are indicative of a highly specific mechanism of action such as a receptor.

Assessment of Anandamide Interaction with the Cannabinoid Brain Receptor: SR 141716A Antagonism Studies in Mice and Autoradiographic Analysis of Receptor Binding in Rat Brain

Abstract: Anandamide is the newly discovered endogenous cannabinoid ligand that binds to brain cannabinoid receptors and shares most, but not all, of the pharmacological properties of Δ9-THC. Therefore, this study was undertaken to determine whether its interaction with the CB1 receptor in brain was identical to that of Δ9-THC. Anandamide depressed spontaneous activity and produced hypothermia, antinociception and immobility in mice after i.v. administration. However, none of these effects was blocked by pretreatment with the selective CB1 antagonist, SR 141716A. However, the metabolically stable analog 2-methyl-2′-fluoroethylanandamide produced reductions in motor activity and antinociception in mice, effects that were blocked by the antagonist. To determine whether anandamide’s receptor binding mimicked that of other cannabinoids, an autoradiographic comparison of anandamide, SR 141716A and CP 55,940 competition for [3H]CP55,940 binding was conducted throughout rat brain. The receptor affinities for all three compounds did not change according to brain area. As expected, Bmax values differed dramatically among differ brain areas. However, the Bmaxvalues for each brain area were similar regardless of the compound used for displacement. These data suggest that anandamide, SR 141716A and CP 55,940 compete for the same cannabinoid receptor throughout brain despite SR 141716A’s failure to block anandamide’s pharmacological effects. Although there is no question that anandamide binds to the cannabinoid receptor, failure of SR 141716A to block its pharmacological effects in mice poses a dilemma. The results presented herein raise the possibility that anandamide may not be producing all of its effects by a direct interaction with the CB1 receptor.

International Union of Pharmacology. XXVII. Classification of Cannabinoid Receptors

Abstract: Two types of cannabinoid receptor have been discovered so far, CB(1) (2.1: CBD:1:CB1:), cloned in 1990, and CB(2) (2.1:CBD:2:CB2:), cloned in 1993. Distinction between these receptors is based on differences in their predicted amino acid sequence, signaling mechanisms, tissue distribution, and sensitivity to certain potent agonists and antagonists that show marked selectivity for one or the other receptor type. Cannabinoid receptors CB(1) and CB(2) exhibit 48% amino acid sequence identity. Both receptor types are coupled through G proteins to adenylyl cyclase and mitogen-activated protein kinase. CB(1) receptors are also coupled through G proteins to several types of calcium and potassium channels. These receptors exist primarily on central and peripheral neurons, one of their functions being to inhibit neurotransmitter release. Indeed, endogenous CB(1) agonists probably serve as retrograde synaptic messengers. CB(2) receptors are present mainly on immune cells. Such cells also express CB(1) receptors, albeit to a lesser extent, with both receptor types exerting a broad spectrum of immune effects that includes modulation of cytokine release. Of several endogenous agonists for cannabinoid receptors identified thus far, the most notable are arachidonoylethanolamide, 2-arachidonoylglycerol, and 2-arachidonylglyceryl ether. It is unclear whether these eicosanoid molecules are the only, or primary, endogenous agonists. Hence, we consider it premature to rename cannabinoid receptors after an endogenous agonist as is recommended by the International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification. Although pharmacological evidence for the existence of additional types of cannabinoid receptor is emerging, other kinds of supporting evidence are still lacking.

Determination and characterization of a cannabinoid receptor in rat brain.

Abstract: The determination and characterization of a cannabinoid receptor from brain are reported. A biologically active bicyclic cannabinoid analgetic CP-55,940 was tritium-labeled to high specific activity. Conditions for binding to rat brain P2 membranes and synaptosomes were established. The pH optimum was between 7 and 8, and specific binding could be eliminated by heating the membranes to 60 degrees. Binding to the P2 membranes was linear within the range of 10 to 50 micrograms of protein/ml. Specific binding (defined as total binding displaced by 1 microM delta 9-tetrahydrocannabinol (delta 9-THC) or 100 nM desacetyllevonantradol) was saturable. The Kd determined from Scatchard analysis was 133 pM, and the Bmax for rat cortical P2 membranes was 1.85 pmol/mg of protein. The Hill coefficient for [3H]CP-55,940 approximated 1, indicating that, under the conditions of assay, a single class of binding sites was determined that did not exhibit cooperativity. The binding was rapid (kon approximately 2.6 x 10(-4) pM-1 min-1) and reversible (Koff approximately 0.016 min-1) and (koff' greater than 0.06 min-1). The two Kd values estimated from the kinetic constants approximately 55 pM and exceeded 200 pM, respectively. The binding of the agonist ligand [3H]CP-55,940 was decreased by the nonhydrolyzable GTP analog guanylylimidodiphosphate. The guanine nucleotide induced a more rapid dissociation of the ligand from the binding site, consistent with an allosteric regulation of the putative receptor by a G protein. The binding was also sensitive to MgCl2 and CaCl2. Binding of [3H]CP-55,940 was displaced by cannabinoid drugs in the following order of potency: CP-55,940 greater than or equal to desacetyllevonantradol greater than 11-OH-delta 9-THC = delta 9-THC greater than cannabinol. Cannabidiol and cannabigerol displaced [3H]CP-55,940 by less than 50% at 1 microM concentrations. The (-)-isomer of CP-55,940 displaced with 50-fold greater potency than the (+)-isomer. This pharmacology is comparable to both the inhibition of adenylate cyclase in vitro and the analgetic activity of these compounds in vivo. The criteria for a high affinity, stereoselective, pharmacologically distinct cannabinoid receptor in brain tissue have been fulfilled.

Cannabinoid receptor localization in brain

Abstract: [3H]CP 55,940, a radiolabeled synthetic cannabinoid, which is 10-100 times more potent in vivo than delta 9-tetrahydrocannabinol, was used to characterize and localize a specific cannabinoid receptor in brain sections. The potencies of a series of natural and synthetic cannabinoids as competitors of [3H]CP 55,940 binding correlated closely with their relative potencies in several biological assays, suggesting that the receptor characterized in our in vitro assay is the same receptor that mediates behavioral and pharmacological effects of cannabinoids, including human subjective experience. Autoradiography of cannabinoid receptors in brain sections from several mammalian species, including human, reveals a unique and conserved distribution; binding is most dense in outflow nuclei of the basal ganglia--the substantia nigra pars reticulata and globus pallidus--and in the hippocampus and cerebellum. Generally high densities in forebrain and cerebellum implicate roles for cannabinoids in cognition and movement. Sparse densities in lower brainstem areas controlling cardiovascular and respiratory functions may explain why high doses of delta 9-tetrahydrocannabinol are not lethal.

Characterization and localization of cannabinoid receptors in rat brain: a quantitative in vitro autoradiographic study

Abstract: A potent, synthetic cannabinoid was radiolabeled and used to characterize and precisely localize cannabinoid receptors in slide-mounted sections of rat brain and pituitary. Assay conditions for 3H-CP55,940 binding in Tris-HCl buffer with 5% BSA were optimized, association and dissociation rate constants determined, and the equilibrium dissociation constant (Kd) calculated (21 nM by liquid scintillation counting, 5.2 nM by quantitative autoradiography). The results of competition studies, using several synthetic cannabinoids, add to prior data showing enantioselectivity of binding and correlation of in vitro potencies with potencies in biological assays of cannabinoid actions. Inhibition of binding by guanine nucleotides was selective and profound: Nonhydrolyzable analogs of GTP and GDP inhibited binding by greater than 90%, and GMP and the nonhydrolyzable ATP analog showed no inhibition. Autoradiography showed great heterogeneity of binding in patterns of labeling that closely conform to cytoarchitectural and functional domains. Very dense 3H-CP55,940 binding is localized to the basal ganglia (lateral caudate-putamen, globus pallidus, entopeduncular nucleus, substantia nigra pars reticulata), cerebellar molecular layer, innermost layers of the olfactory bulb, and portions of the hippocampal formation (CA3 and dentate gyrus molecular layer). Moderately dense binding is found throughout the remaining forebrain. Sparse binding characterizes the brain stem and spinal cord. Densitometry confirmed the quantitative heterogeneity of cannabinoid receptors (10 nM 3H-CP55,940 binding ranged in density from 6.3 pmol/mg protein in the substantia nigra pars reticulata to 0.15 pmol/mg protein in the anterior lobe of the pituitary). The results suggest that the presently characterized cannabinoid receptor mediates physiological and behavioral effects of natural and synthetic cannabinoids, because it is strongly coupled to guanine nucleotide regulatory proteins and is discretely localized to cortical, basal ganglia, and cerebellar structures involved with cognition and movement.