L739,749: a farnesyl-protein transferase inhibitor and antineoplastic compound.

LABA: long-acting β-agonists and compounds used to treat asthma. Examples include salmeterol and eformoterol fumarate.

Labelled: a compound or molecule in which one or more of its component atoms is radioactive. These labelled or hot compounds are often used in ADME studies to observe the fate of a compound after it is administered. Using radiography, radiographs of internal organs can be made to determine the organs in which the compound becomes most concentrated over a fixed period of time following administration.

Labile: chemically unstable and a term used to describe drugs which, for example, are destroyed by gastric acid after oral dosing. Examples include and protein or peptide drugs such as insulin and interferons which must be given parenterally.

Lactam: see lactam-lactim tautomerism under tautomerism.

β-Lactams: an important class of antibacterial compounds. They are cyclic amides with four atoms in the ring and this ring is more accurately referred to as an azetidinone ring. Examples of β-lactams include penicillins (natural and synthetic), cephalosporins (natural and synthetic), cephems (also known as carbacephems), cephams, penems, penams, carbapenems, cephamycins, 1-oxacephems, clavulanic acids (also known as clavams), nocardicins, trinems (also known as tribactams) and monobactams.

Lactulose: a carbohydrate and osmotic laxative. It is broken down by the gut flora to make the gut more acidic causing a reduction in the absorption of ammonia. Normally, the presence of ammonia causes water to be drawn into the lower bowel leading to an increase in the water content and volume of the faeces therefore relieving constipation.

Laetrile: a substance which has been used by individuals in the (self)treatment of cancer. It comprises mainly amygdalin and can be obtained from apricot stones. It is thought to be selectively broken down by β-glucuronidase to form benzaldehyde and hydrocynanic acid which is presumably the cytotoxic component of this substance.

Langendorff heart preparation: an isolated heart preparation usually using a heart usually taken from a rat or frog and used to observe the effects of drugs on the heart muscle and structures. In this preparation the aorta is cannulated and perfused in a retrograde fashion and perfusate containing the drug enters the coronary artery via the ostium so the heart can be maintained for several hours. The heart beats spontaneously and Langendorff studies can be conducted in either constant pressure or constant perfusate flow modes. Transducers can measure the rate and force of contraction. The Langendorff preparation is suitable for the investigation of coronary artery function but it provides only limited information on ventricular function.

Langendorff O. Untersuchungen am uberlebenden Saugetierherzen. Pflugers Archives fur die Gesamte Physiologie des Menschen and der Tiere (1895) 61;291‑332 (article written in German, the English translation of the title is ‘Examinations on the surviving mammalian heart’)

Langley, John Newport (1852‑1925): British physiologist who first suggested that drugs interact with specific components of cells to produce an effect.

Langley JN. On the reaction of cells and nerve-endings to certain poisons, chiefly as regards the reaction of striated muscle to nicotine and to curare (1905) J Physiol 33; 374-413

Lanosterol: a tetracyclic triterpene alcohol present in large amounts in wool fat of sheep. In humans, it is biosynthesized from squalene and is an important intermediate in the synthesis of tetracyclic triterpenes and steroids.

Lansoprazole: a proton pump inhibitor used clinically to reduce gastric acid pH in the treatment of benign gastric ulcer, duodenal ulcer, Zollinger-Ellison syndrome, gastroesophageal reflux disease and acid-related dyspepsia.

Lantibiotics: lanthionine-containing antibiotics, a group of about 30 antimicrobial polycyclic peptides which are produced by and primarily act upon gram‑positive bacteria. Examples include nisin, a naturally occurring antimicrobial used as a food additive to prevent spoilage.

Brotz H, Sahl HG. New insights into the mechanism of action of lantibiotics-diverse biological effects by binding to the same molecular target. Journal of Antimicrobial Chemotherapy (2000) 46; 1‑6

Larkspur toxins: potent norditerpenoid alkaloid neurotoxins which are known to poison cattle and contribute to a significant number of their deaths by respiratory paralysis. Examples include methyllylaconitine and D-tubocurarine.

Larvicide: compounds which kill larval pests and used in the prevention of infections of heartworm and other pests affecting mainly animals. Examples include diethylcarbamazine, ivermectin and milbemycin.

Lathyritic rat: a model of deep arterial injury in which the internal elastic lamina can easily be broken by balloon injury because of the fragility of its connective tissue. Lathyrism is characterized by defective collagen synthesis due to inhibition of lysyl oxidase, an enzyme essential for cross‑linking between collagen fibres. Defective collagen leads to defective connective tissues such as artery walls.

Lathyrogens: compounds which inhibit the formation of collagen. Examples include β‑aminoproprionitrile.

Latin square design: a method for assigning a randomised schedule for drug administration in which each animal or individual receives each course of treatment once in a known and random sequence.

α-Latrotoxin (LTX): Black widow spider venom.

Laxative: a substance which facilitates emptying of the bowel. See cathartics.

Lazaroids: also known as 21-aminosteroids, a group of non-glucocorticoid analogues of methylprednisolone synthesized to penetrate the hydrophobic domains of cell membranes in order to inhibit lipid peroxidation. Lazaroids have shown to be effective in the treatment of traumatic injury to the central nervous system, ischaemic reperfusion injury and in haemorrhagic shock. Lazaroids inhibit lipid peroxidation and may directly scavenge hydroxy radicals.

LC₅₀: the (lethal) concentration of a compound which causes the death of 50% of a group of test animals.

LD₅₀: Median lethal dose

LDL receptors: cell surface receptors which bind their natural ligand low-density lipoproteins and which facilitate the transport of cholesterol‑carrying lipoprotein particles into cells by receptor‑mediated endocytosis. Some 65‑70% of plasma cholesterol in humans circulates in the form of a low density lipoprotein/cholesterol particles which comprise a hydrophilic part where LDL molecules are on the outside and a hydrophilic part on the inside where it carries over 1000 cholesterol molecules per particle. This particle contains apolipoprotein B 100 in its outer membrane and this binds to the LDL receptor on the cell surface triggering endocytosis of the LDL/cholesterol complex. The mature LDL receptor is a modular type‑1 transmembrane protein comprising 839 amino acids.

LEC rats: Long-Evans cinnamon rats

Leishmanicidals: drugs used to treat leishmanial infections in humans and animals, ie infections caused pathogenic protozoa of the genus Leishmania. Examples include Leishmania tropica which causes cutaneous leishmaniasis (Oriental sore) and Leishmania donovani which causes visceral leishmaniasis also known as dum-dum fever and cachectic fever. Treatment of this disease is usually with pentavalent antimonials, eg sodium stibogluconate and meglumine antimoniate; pentamidine and amphotericin B have been used in second-line therapy.

Leiurotoxin: a toxin from the venom of scorpions. Leiurotoxin I (also known as scyllatoxin) is a 31‑amino acid polypeptide from the venom of the scorpion Leiurus quinquestriatus hebraeus is a peptide ligand for Ca²⁺‑activated potassium channels. Leiurotoxin has apamine-like actions.

Leprostatic: drugs which suppress infections caused by Mycobacterium leprae and ameliorate the clinical manifestations of leprosy (a chronic and communicable disease occurring in tropical and subtropical regions which is characterized by inflamed nodules beneath the skin and destruction of body parts). Examples of leprostatics include dapsone, clofazimine, thalidomide, rifampicin and ethionamide.

Leptazol: a compound used to induce seizures and to test the effects of anti-epileptic drugs. Typically, a dose of 100mg/kg is given to mice intraperitoneally and the time taken for seizures to occur is compared to that when animals are treated with an anti-epileptic drug.

Leptin: a 16kDa protein cytokine and the product of the Ob gene which is secreted from mature white adipocytes into the plasma after food intake. Leptin inhibits food intake, reduces body weight and stimulates energy expenditure and so plays a key role in energy balance in both rodents and humans. Its expression and secretion follows a circadian rhythm and is closely correlated with body fat mass and adipocyte size. It binds to transmembrane receptors which are similar to the receptors of the cytokine family (type IL-6). Cortisol and insulin are potent stimulators of leptin expression, while expression is attenuated by β-adrenergic agonists, cAMP and thiazolidinediones. Many of its effects on food intake and energy utilization are thought to be mediated centrally via neurotransmitters such as neuropeptide Y.

Leptin modulators: compounds which modulate the effects of leptin or alter tissue sensitivity to it. As leptin levels are many times higher in obese people than in people of normal weight, it appears that obese people are insensitive to its effects and so leptin modulators are being developed as treatments for obesity.

Lethal synthesis: the metabolic conversion of a compound to a form which is toxic.

An example is the conversion of fluoroacetate (an active component of rat poison) to fluorocitrate which inhibits aconitase and is thus toxic to the Krebs cycle and cellular respiration.

Lethargic mouse: a mouse used as an animal model of absence epilepsy. These mice have been shown to exhibit behavioural, electrographic and pharmacological profiles similar to those of humans with absence epilepsy.

Leukotriene receptor antagonists: compounds which inhibit the actions of LTs and their analogues at leukotriene receptor sites (BLT and CysLT sites). They have been developed for the treatment of asthma and include the lukasts, ie ablukast, cinalukast, montelukast, pranlukast and tomelukast.

Lewis rat: originally developed by Margaret Lewis from Wistar stock in the early 1950s, this inbred and very docile strain shows high fertility but low survivability of around 26% survival after 2 years. It is often used an as inbred partner for several congenic strains at the major histocompatibility complex Rt H-1. Albino Lewis rats are susceptible to the occurrence of autologous immune complex glomerulonephritis.

Levamisole: a depolarizing neuromuscular blocker used in veterinary pharmacology for the treatment of nematode infections in ruminants and pigs. It causes paralysis of the worm which is flushed out of the intestines with the normal passage of faeces.

Lidocaine: also known formerly as lignocaine and by the trade name Xylocaine, a local anaesthetic used clinically to treat ventricular arrhythmias particularly following myocardial infarction, neuropathic pain and to treat urethral pain topically. It decreases the action potential duration in hearts with little change in conductivity and is classified as a Class 1B antiarrhythmic for use in both humans and animals (typically dogs and horses). Lidocaine is used in dental anaesthesia and acts by blocking the initiation and propagation of action potentials by inhibiting a voltage-dependent increase in Na⁺ by physically blocking the ion channel.

Ligand: any molecule or structural group with or without biological activity which binds to a receptor or enzyme. The term is often used to refer to a receptor agonist or antagonist.

Ligand binding assay: see receptor binding assay.

Ligand-gated ion channels: transmembrane proteins that can exists in different conformations and forming a channel through the membrane connecting the inside with the outside of a cell. When a ligand binds to these proteins, the confirmation changes in such a way as to open the channel allowing the passage of ions such as Na⁺, K⁺ and Ca²⁺ to pass across the membrane. Thus, ligand binding causes the channel to open or close to ions.

There are three superfamilies of extracellularly activated ligand-gated ion channel subunits and they vary in function and tissue distribution. The cis-loop superfamily of channels are found is nicotinic, 5-HT₃, γ-aminobutyric acid (GABA_A and GABA_C), glycine and some other receptors. The ATP-gated channels which are found in purinoceptors and the glutamate-activated cationic channels which are found in NMDA, AMPA and kainate receptors.

Ligand-gated ion channels mediate fast excitatory or inhibitory neurotransmission. For example, binding of acetylcholine (an excitatory neurotransmitter) to nicotinic receptors induces a conformation change that opens the ion-conducting channel allowing Na⁺ ions to enter the cells and K⁺ ions to exit (so these are sometimes referred to as monovalent ion channels). This process is reversed during repolarization by a Na⁺-K⁺-ATPase pump to bring the membrane back to a state where it is responsive to ACh again.

Leukotrienes (LT): a group of lipid hormone eicosanoids derived from cell membrane phospholipids and arachidonic acid. They are products of lipoxygenases, cytosolic enzymes located in tissues such as the lungs, platelets, mast cells and white blood cells. Leukotrienes are the are potent mediators of inflammation and play important roles in allergic rhinitis, inflammatory bowel disease and asthma. The name leukotriene is derived from the fact that these substances occur in white blood cells (leucocytes) and that they all have 4 double bonds (hence the 4 subscript) in common 3 of these are in a conjugated triene structure.

Several distinct leukotrienes are known. They are generally divided into peptidoleukotrienes including LTC₄, LTD₄ and LTE₄ and dihydroxyleukotrienes including LTB₄. The main LTs are;

• Leukotriene A₄ (LTA₄) - synthesized in mast cells, eosinophils and neutrophils. It is rapidly metabolised by LTA₄ hydrolase to form LTB₄.
• Leukotriene B₄ (LTB₄) - produced predominantly by leukocytes in response to a variety of immunological stimuli, LTB₄ is a potent chemoattractant. In addition, LTB₄ modulates immune responses, is important in host defence against infections and is a key mediator of platelet activating factor (PAF)-induced lethal shock.
• Leukotriene C₃ (LTC₃) - a cysteinyl leukotriene and LT receptor agonist.
• Leukotriene C₄ (LTC₄) - like LTB₄ this is produced predominantly by leukocytes in response to a variety of immunological stimuli.. It is a cysteinyl-containing leukotriene which contract smooth muscle particularly in the peripheral airways and is an important mediator of bronchial asthma. It increases the permeability of post-capillary venules leading to extravasation of plasma. A mixture of LTC₄, LTD₄, LTE₄ make up SRS-A (slow reacting substance of anaphylaxis) a potent bronchoconstrictor.
• Leukotriene C₅ (LTC₅) - a cysteinyl leukotriene and LT receptor agonist.
• Leukotriene D₄ (LTD₄) - like LTB₄ and LTC₄ this is produced predominantly by leukocytes in response to a variety of immunological stimuli. It is a cysteinyl-containing leukotriene which contract smooth muscle particularly in the peripheral airways and is an important mediator of bronchial asthma. It increases the permeability of post-capillary venules leading to extravasation of plasma.
• Leukotriene E₃ (LTE₃) - a cysteinyl leukotriene and LT receptor agonist formed in vitro from LTC₃.
• Leukotriene E₄ (LTE₄) - as above this is produced predominantly by leukocytes in response to a variety of immunological stimuli. It is a cysteinyl-containing leukotriene which contract smooth muscle particularly in the peripheral airways and is an important mediator of bronchial asthma. It increases the permeability of post-capillary venules leading to extravasation of plasma.
• Leukotriene E₅ (LTE₅) - a cysteinyl leukotriene and LT receptor agonist formed in vitro from LTD₅.
• Leukotriene F₄ (LTF₄) - a cysteinyl leukotriene and LT receptor agonist formed in vitro from LTE₄. It causes contraction of isolated guinea pig ileum.

Leukotriene receptors: receptors for the endogenous ligands in the leukotriene family of arachidonic acid metabolites and their analogues. Four receptors are known which fall into two classes, ie cysteinyl (CysLT) receptors and BLT receptors, each appearing to modulate different physiological responses to leukotrienes. They are classified as:

• LTB₄ receptors are also known as BLT receptors are subdivided into BLT₁ and BLT₂ receptors. BLT₁ receptors shows a high degree of specificity for LTB₄ and are only expressed on inflammatory cell.
• CysLT₁ receptors were formerly known as LTD₄ receptors and, like CysLT₂ receptor,  mediate the contraction of bronchiolar smooth muscle.
• CysLT₂ receptors were formerly known as LTC₄ receptors.

http://www.iuphar‑db.org/GPCR/ChapterMenuForward?chapterID=1287

Light/dark box: a type of box used in mouse and rat experiments which comprises two main areas, a lit area and an unlit (dark) area. It is commonly used to test the effects of anxiolytic drugs which, if they are effective, increase the time the animal spends in the unlit part of the box which is something it would normally be reluctant to do.

Lignocaine: see lidocaine.

Limbic system: a complex of brain structures including the hypothalamus, the hippocampus, the amygdala, the cingulate gyrus, the fornicate gyrus and the archicortex and which lies on both sides of the brain and underneath the thalamus just below the cerebrum. The limbic system is primarily responsible for emotions and has a lot to do with the formation of memory.

Lincosamides: bacteriostatic compounds which inhibit bacterial reproduction by binding to the 23S rRNA in the large 50S ribosome subunit and inhibit protein synthesis (protein elongation). Examples include lincomycin (which was isolated from a soil sample near Lincoln, Nebraska) and a semi-synthetic derivative clindamycin. They are active against gram-positive bacterial infections.

Lindane: a hexachlorocyclohexane and pediculicide (an agent to treat lice and scabies infestations). It is toxic and has limited use in humans but is used in veterinary pharmacology to treat screwworm and ear tick infestations in cattle, horses, swine, sheep and goats. Lindane is a GABA antagonist and young animals are sensitive to lindane poisoning.

Linear kinetics: also known as first order kinetics

Lipid A: also known as endotoxin, a glucosamine-based phospholipid which comprises the outer monolayer of the outer membranes of gram-negative bacteria. Lipid A is the hydrophobic anchor for lipopolysaccharide (LPS) in bacterial membranes and is a potent stimulator of the immune system and inflammatory mediator synthesis such as TNF-α and IL-1β. Lipid A and LPS are thought to stimulate cells by activating Toll‑like receptor 4 (TLR4), MD‑2 and CD14 receptors on cell surfaces.

Gram‑negative sepsis is caused by Lipid A and LPS and is the major cause of deaths in intensive care units of hospitals and continues to increase worldwide. Lipid A antagonist reduce the toxicity of Lipid A and LPS.

Lipid A antagonist: compounds which antagonize the effects of Lipid A at its effects cells in the immune system. They are being developed for the treatment of sepsis and septic shock. Example include the Lipid A analogue E5564 9 (and Toll-like 4 receptor antagonist), E5531 and B975.

Lipinski’s rules: also known as the ‘rule-of-five’, a set of rules governing the determination of drugs likely to be absorbed by the intestines. If any two of the following criteria are satisfied by a molecule then intestinal absorption may be a problem: 1) a molecular weight of >500, 2) the number of hydrogen bond acceptors (ie. an N or O atom) is >10, 3) the number of hydrogen bond donors (ie, an NH or OH group) is >5 and the calculated logP (the log of the calculated octanol/water partition coefficient) in >5.0. These rules were devised by Chris Lipinski of Pfizer.

Lipocortins: also known as annexins and calpactins, a family of glucocorticoid‑induced proteins which inhibit the actions of phospholipase and so inhibit the production of arachidonic acid metabolites such as prostaglandins and leukotrienes. There are six known lipocortins (I to VI which are also known as annexins A1 to A6)

Lipopolysaccharide (LPS): see Lipid A.

Liposomes: small vesicles constructed from a phospholipid so that a phospholipid-protein bilayer is formed with the active drug at the centre of the vesicle. Liposomes are highly lipophilic and have been used in the administration of anticancer drugs, in the delivery of genes to tissues in gene therapy and in the delivery of vaccines and insulin.

Lipoxins (LXs): a group of arachidonic acid metabolites and lipid mediators of inflammation. Examples include LXA₄ and LXB₄.Their name is derived from lipoxygenase interaction products and they have anti-inflammatory actions. They antagonize the effects of leukotrienes at CysLT₁ receptor sites and inhibit the production of some interleukins.

Serhan C, Hamberg M, Samuelsson B. Lipoxins: novel series of biologically active compounds formed from arachidonic acid in human leukocytes. Proc Natl Acad Sci USA (1984) 81:5335‑5339

Bonnans C et al. Lipoxins Are Potential Endogenous Antiinflammatory Mediators in Asthma. Am J Resp and Crit Care Med (2002) 165: 1531‑1535

5-Lipoxygenase (5-LO, 5-LOX): also known officially as arachidonate 5-lipoxygenase, an enzyme (EC 1.13.11.34) which catalyzes the formation of leukotriene A₄ from arachidonic acid via the intermediates 5-HPETE (5‑hydroperoxyeicosatetraenoic acid) and an essential enzyme in the formation of leukotrienes.

5-Lipoxygenase inhibitors: compounds which inhibit the actions of 5-lipoxygenase and so inhibit the formation of leukotrienes. They have been developed for the treatment of asthma and examples include zileuton (A‑64077), ABT-761 and CV6504 (used against pancreatic cancer because 5-lipoxygenase inhibitors have been shown to inhibit proliferation of certain types of cancer cell).

5-Lipoxygenase activating protein (FLAP, ALOX5AP): a membrane-associated 18 kDa protein which is necessary in the activation of 5-lipoxygenase the primary enzyme in the leukotriene cascade.

Lipoxygenases: a family of enzymes of which about four are important, ie arachidonate 5-lipoxygenase (EC 1.13.11.34), arachidonate 8-lipoxygenase (EC 1.13.11.40), arachidonate 12-lipoxygenase (EC 1.13.11.31) and arachidonate 15-lipoxygenase (EC 1.13.11.33). They all catalyze the breakdown of arachidonic acid to form various active metabolites.

Lisinopril: an angiotensin converting enzyme (ACE) inhibitor used clinically to treat essential and renovascular hypertension

Lithium salts: salts of this alkali metal such as lithium carbonate and lithium citrate which are used clinically in the prophylaxis and treatment of mania, in the prophylaxis of bipolar disorders (manic-depressive disorders) and in the prophylaxis of recurrent depression. Lithium appears to alter the balance between excitatory and inhibitory neurotransmitters and signaling activities which regulate second messengers, transcription factors and gene expression.

Litholytic: a drug which can breakdown calculi (ie, renal and gall bladder stones) into a for which can be excreted. Examples include chenodeoxycholic acid.

L-NAME: N(omega)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor used as a pharmacological tool.

LLR: Lower lip retraction

LNMMA: L-N^G-monomethyl arginine, a nitric oxide synthase inhibitor used as a pharmacological tool.

Loading dose: sometimes referred to as a priming dose, a the dose of a drug given as the first of a series of doses and one which is high enough to ensure the blood concentration level rapidly rises to a therapeutic concentration. It is usually higher than a maintenance dose as the body concentration of the drug, when the loading dose is given, is zero, whereas drug is present in most tissues when maintenance doses are given.

Lobeline: a tertiary amine alkaloid obtained from Indian tobacco (Lobelia inflata) and other members of this genus. It is a nicotine receptor agonist with CNS stimulant, expectorant, respiratory stimulant, anti-asthmatic and diuretic effects.

Local anaesthetic: a type of anaesthetic.

Local hormone: also known as autacoid, a short-acting, locally produced and locally effective hormone.

Loewi, Otto (1873 - 1961): German-born physiologist who shared the Nobel prize for Physiology or Medicine in 1936 with Dale "for their discoveries relating to chemical transmission of nerve impulses". He demonstrated in 1921 using two frog hearts, set up in such a way that the Ringer's solution flowing over the first heart was allowed to flow over the other, that when the vagus nerve (parasympathetic) to the first heart was stimulated it slowed and the beats became weaker. A short while later the second heart responded in a similar way which led him to postulate that a substance which he called Vagustoff was released from the nerve endings in the first heart and carried to the second to produce the same effects. Vagustoff is know known to be acetylcholine.

Loewi also showed that when the sympathetic nerve to the first heart was stimulated it beat faster and more forcefully and that this effect was also seen shortly after in the second heart. He termed the substance producing this effect Acceleranstoff now known to be noradrenaline although the effects he observed were actually caused by adrenaline which is present in amphibian hearts.

http://www.nobel.se/medicine/laureates/1936/loewi-bio.html

Lomustine: a lipid-soluble nitrosurea used clinically to treat Hodgkin’s disease and some solid tumours. It is an alkylating agent and so alkylates DNA in reproducing cells inhibiting DNA replication.

Long-Evans rats: a hybrid rodent strain showing little innate susceptibility to the development of audiogenic seizures.

Long-Evans Cinnamon (LEC) rats: an inbred mutant strain of rat which accumulates copper due to a defective copper-transporting ATPase gene resulting in defective incorporation of copper into the copper-transporting protein ceruloplasmin. LEC rats show decreased biliary excretion of copper and develop acute hepatitis, liver tumours and chronic liver injury as a result of copper-induced oxidative stress, lipid peroxidation and DNA damage. They are used in animals models of Wilson’s disease.

Loop diuretics: also known as high-ceiling diuretics.

Loperamide: a phenylpiperidine and centrally-acting emetic used to induce emesis in experimental animals. It is an opioid receptor agonist used clinically in the symptomatic treatment of acute diarrhoea.

Lorazepam: a benzodiazepine and anxiolytic used clinically to treat anxiety or insomnia and status epilepticus and to induce sedation as a premedication in surgery. It is a benzodiazepine-binding site agonist with similar properties to diazepam.

Losartan: a sartan and an angiotensin II receptor antagonist used clinically to treat hypertension and diabetic retinopathy in type II diabetes mellitus.

LOX: Lipoxygenase

Lower lip retraction (LLR): a method to determine the efficacy of 5-HT_1A receptor agonists and the effects of antagonists at this receptor site.

Berendsen HH et al. Selective activation of 5HT1A receptors induces lower lip retraction in the rat. Pharmacol Biochem Behav. (1989) Aug 33(4): 821‑7

LPS: Lipopolysaccharide

LSD: Lysergic acid diethylamide

Lukasts: the name given to a group of drugs acting at leukotriene receptors sites. Examples include montelukast, zafirlukast, pranlukast and pobilukast.

Lusitropic: a drug which alters the rate of relaxation of cardiac muscle. Positive lusitropic drugs shorten the time taken for the heart to relax making the heart relax for longer and negative lusitropic drugs prolong relaxation time making the time the heart spends relaxed shorter. For example, ketamine and β-adrenoceptor agonists such as adrenaline and noradrenaline have positive lusitropic effects because they speed up relaxation and endothelin receptor agonists have negative lusitropic effects.

Luteolytic: drugs which inhibits the implantation of an ovum in the corpus luteum. They actually cause breakdown or degradation of the corpus luteum. Examples of luteolytics include cloprostenol, a prostaglandin F_2α analogue.

Luzindole: a competitive melatonin receptor antagonist (N-[2-[2-(phenylmethyl)-1H-indol-3-yl]ethyl]acetamide) which has been shown to have anti-depressant effects in animals.

Dubocovich ML. Luzindole (N-0774): a novel melatonin receptor antagonist. J Pharmacol Exp Ther (1988) 246; 902-910

LY-225910: a potent cholecystokinin-B (CCK_B) receptor antagonist (2-[2-(5-bromo-1H-indol-3-yl) ethyl]-3-[3-(1-methylethoxy)phenyl]-4-(3H)-quinazolinone).

17-20 Lyase: officially known as steroid 17‑alpha‑monooxygenase, a hydroxylase enzyme (EC 1.14.99.9) which catalyzes the 17‑hydroxylation of steroids such as progesterone or pregnenolone (the direct precursor to all C₁₈, C₁₉ and C₂₁ steroids) in the presence of NADPH and molecular oxygen. It is an important enzyme in the biosynthesis of steroid hormones.

17-20 Lyase inhibitors: compounds which inhibit 17-20 lyase and so inhibit the production of steroid hormones particularly sex steroid biosynthesis. They are being developed for the treatment of polycystic ovary syndrome and cancers of the breast and prostate. Examples include abiraterone.

LY-294002: a neurotoxin used to determine the neuroprotectant effects of test compounds. It is a potent, specific and cell permeable inhibitor of phosphatidylinositol 3‑kinase.

Lymphokines: proteins which are released from activated immune cells and which activate immune cells. Examples include interferon which initiates virus defence reactions and the interleukins which activate specific immune cells.

Lysergic acid diethylamide (LSD): a semisynthetic ergot alkaloid and hallucinogenic drug of abuse. It acts as a partial serotonin receptor agonist and/or antagonist. It has some sympathomimetic actions and has been used as a psychotropic in the treatment of psychoses. It produces exaggerated imagination and visual illusions. LSD is known by a variety of common and slang names including acid, L, blotter, tabs, LAD, doses, trips and microdots.

http://www.erowid.org/chemicals/lsd/lsd.shtml

Lysophospholipid (LP): metabolites of the biosynthesis of membrane phospholipids having a variety of metabolic anc cell signaling actions.

Lysophospholipid receptors: receptors for lysophospholipids such as lysophosphatidic acid and sphingosine 1-phosphate which mediate a variety of cellular functions.

Fukushima N et al. Lysophospholipid receptors. Ann Rev Pharmacol Toxicol (2001) 41; 507-534

http://www.iuphar‑db.org/GPCR/ChapterMenuForward?chapterID=1338