PubMed Health⌕ Search

Biomedical subjects

R L McLeod

Publications and source records attributed to R L McLeod.

13 recordsLinked to original sources
PubMed1998

Antitussive action of antihistamines is independent of sedative and ventilation activity in the guinea pig.

We studied the oral actions of antihistamines from six chemical classes, namely: the ethanolamines (ENA, diphenhydramine and clemastine); ethylenediamines (EDA, pyrilamine and tripelennamine); piperidines (PPD, terfenadine and astemizole); piperazines (PPZ, hydroxyzine and cetirizine); phenothiazines (PTZ, promethazine), and the alkylamines (ALA, chlorpheniramine and bromopheniramine) on cough reflexes, pentobarbital-induced sedation and minute ventilation in the conscious guinea pig. Antihistamines of the ENA class had minimal effects on capsaicin-induced cough although both diphenhydramine (30 and 100 mg/kg p.o.) and clemastine (30 and 100 mg/kg p.o.) increased sedation time (ST). The PPZ class demonstrated both antitussive and sedating activity. The minimum effective oral antitussive dose (MED) of cetirizine and hydroxyzine was 30 and 10 mg/kg, respectively. The EDA did not exhibit antitussive activity. Tripelennamine (10, 30 and 100 mg/kg p.o.) but not pyrilamine enhanced ST. The MED for the PTZ, promethazine, was 10 mg/kg, and at 100 mg/kg promethazine increased ST. The ALA group displayed antitussive activity but only chlorpheniramine (10 mg/kg p. o.) had any effects on ST. The MED for chlorpheniramine and bromopheniramine was 3 and 10 mg/kg p.o., respectively. The PPD antihistamines, namely terfenadine and astemizole, inhibited cough (MED 30 and 10 mg/kg p.o.) without sedative effects. Of the antihistamines tested only promethazine (100 mg/kg p.o.) depressed ventilation responses; however, this dose of promethazine was associated with adverse behavioral effects. The present findings indicate that the antitussive actions of antihistamines are not directly related to histamine H1-receptor blockade because several antihistamines did not antagonize capsaicin-induced cough. In addition, the antitussive actions of antihistamines are independent of their sedative or ventilation effects.

Administration, Oral↗
PubMed1998

Sch 50971, an orally active histamine H3 receptor agonist, inhibits central neurogenic vascular inflammation and produces sedation in the guinea pig.

We studied the actions of Sch 50971, a novel histamine H3 receptor agonist, in an experimental neurogenic model of migraine and characterized its sedative and respiratory actions. Sch 50971 (i.v. and p.o) inhibited plasma protein extravasation in the dura mater of guinea pigs after electrical stimulation of the trigeminal ganglia. The minimum effective doses of Sch 50971 were 3.0 mg/kg i.v. and 10 mg/kg p.o., which produced a 40% and 42% decrease in plasma protein extravasation, respectively. The effects of Sch 50971 (3.0 mg/kg i.v. ) were blocked by the histamine H3 antagonist thioperamide (3.0 mg/kg i.v.). The 5-HT1D agonist, sumatriptan (0.3 mg/kg i.v.), and the histamine H3 agonist, (R)-alpha-methylhistamine (0.3 mg/kg), also inhibited plasma extravasation by 40 and 46%. In sedation studies, Sch 50971 (1-100 mg/kg p.o.) potentiated pentobarbital-induced sleep. The ED40 min for Sch 50971, the benzodiazepines triazolam and diazepam, the histamine H1 antagonist diphenhydramine and the H3 receptor agonist (R)-alpha-methylhistamine were 7.0, 0.5, 2.3, 14.1 and 23.4 mg/kg p. o., respectively. The sedative effects of oral Sch 50971 was blocked by thioperamide (10 microgram i.c.v.). The sedative activity of Sch 50971 was also examined using EEG activity, locomotor activity and sleep. In conscious guinea pigs, Sch 50971 (10 mg/kg p.o.) depressed locomotor activity, increased total sleep time and produced EEG patterns consistent with physiological sleep. Sch 50971 decreased beta wave activity but had no effects on delta wave activity, theta activity or alpha wave activity. In contrast, triazolam (1.0 mg/kg p. o.) depressed delta and theta wave activity and produced large increases in alpha and beta wave activity. In conclusion, Sch 50971 is an orally active, potent and selective agonist of histamine H3 receptors that may act to ameliorate the sequelae of migraine headaches, where activation of histamine H3 receptors may be beneficial. Sch 50971 also decreases motor activity and promotes EEG activity consistent with physiological sleep.

Administration, Oral↗
PubMed1998

Studies on the pharmacology of the novel histamine H3 receptor agonist Sch 50971.

Experiments were performed to characterize the pharmacology of Sch 50971 ((+)-trans-4-(4(R)-methyl-3(R)-pyrolidinyl)-1H-imidazole dihydrochloride, CAS 167610-28-8), a novel histamine H3 receptor agonist. The activity of Sch 50971 was compared with that of (R)-alpha-methylhistamine (CAS 75614-87-8), a potent and moderately selective agonist of histamine H3 receptors, in a series of in vitro and in vivo assays. Sch 50971 is a high affinity, selective H3 receptor agonist in vitro and in vivo. Sch 50971 inhibits [3H]-N-alpha-methylhistamine (CAS 673-50-7) binding to the histamine H3 receptor in human brain (Ki = 5.0 nmol/l) and guinea pig brain (Ki = 2.5 nmol/l). Sch 50971 also inhibits electric field stimulated guinea pig ileum contractions (pD2 = 7.47) and decreases [3H]-norepinephrine (CAS 51-41-2) release (pD2 = 7.48) from guinea pig pulmonary artery by activation of presynaptic inhibitory H3 receptors. The in vitro effects of Sch 50971 are antagonized by low concentrations of a selective H3 antagonist, thioperamide (CAS 106243-16-7). Sch 50971 has low affinity (IC50's > 10 mumol/l) for histamine H1, dopamine D1 and D2, serotonin 5-HT2 and muscarinic cholinergic receptors. It also does not exhibit histamine H2-antagonist activity. In guinea pigs and cats, Sch 50971 exhibits in vivo H3 agonist activity. Sch 50971 inhibits sympathetic hypertension evoked by stimulation of the medulla oblongata in anesthetized guinea pigs (ED30 = 0.3 mg/kg i.v., ED30 = 1.0 mg/kg i.d.). Sch 50971 also inhibits the effects of sympathetic nerve stimulation on nasal resistance in cats. In these assays, Sch 50971 exhibits an efficacy and potency comparable to H3-agonist (R)-alpha-methylhistamine. However, under in vivo conditions, Sch 50971 does not exhibit histamine H1-mediated responses that are seen with (R)-alpha-methylhistamine at doses close to those that produce H3 effects. Therefore, Sch 50971 is a novel, potent and selective agonist of histamine H3 receptors with an improved in vitro and in vivo receptor profile selectivity compared with (R)-alpha-methylhistamine.

Airway Resistance↗
PubMed1997

Central antitussive activity of the NK1 and NK2 tachykinin receptor antagonists, CP-99,994 and SR 48968, in the guinea-pig and cat.

1. The purpose of this study was to investigate the antitussive activity and sites of action of the NK1 and NK2 tachykinin receptor antagonists, CP-99,994, SR 48968, and the racemate of SR 48968, SR 48212A in the cat and guinea-pig. 2. Guinea-pigs were dosed subcutaneously (s.c.) with CP-99,994, SR 48212A or SR 48968 one hour before exposure to aerosols of capsaicin (0.3 mM) to elicit coughing. Coughs were detected with a microphone and counted. 3. Intracerebroventricular (i.c.v.) cannulae were placed in the lateral cerebral ventricles of anaesthetized guinea-pigs. Approximately one week later, the animals were dosed with CP-99,994 or SR 48212A (i.c.v.) and exposed to aerosols of capsaicin (0.3 mM) to elicit coughing. 4. Cough was produced in anaesthetized cats by mechanical stimulation of the intrathoracic trachea and was monitored from electromyograms of respiratory muscle activity. Cannulae were placed for intravenous (i.v.) or, in separate groups of animals, intravertebral arterial (i.a.) administration of CP-99,994, SR 48212A or SR 48968. Dose-response relationships for i.v. and i.a. administration of each drug were generated to determine a ratio of i.v. ED50 to i.a. ED50, known as the effective dose ratio (EDR). The EDR will be 20 or greater for a centrally active drug and less than 20 for a peripherally active drug. 5. In the guinea-pig, CP-99,994 (0.1-30 mg kg-1, s.c.), SR 48212A (1.0-30 mg kg-1, s.c.), and SR 48968 (0.3-3.0 mg kg-1, s.c.) inhibited capsaicin-induced cough in a dose-dependent manner. Capsaicin-induced cough was also inhibited by i.c.v. administration of CP-99,994 (10 and 100 micrograms) or SR 48212A (100 micrograms). 6. In the cat, both CP-99,994 (0.0001-0.3 mg kg-1, i.a., n = 5; 0.003-3.0 mg kg-1, i.v., n = 5) and SR 48212A (0.003-1.0 mg kg-1, i.a., n = 5; 0.01-3.0 mg kg-1, i.v., n = 5) inhibited mechanically induced cough by either the i.v. or i.a. routes in a dose-dependent manner. SR 48968 (0.001-0.3 mg kg-1, i.a., n = 5; 0.03-1.0 mg kg-1, i.v., n = 5) inhibited cough when administered by the i.a. route in a dose-dependent manner, but had no effect by the i.v. route up to a dose of 1.0 mg kg-1. Intravenous antitussive potencies (ED50, 95% confidence interval (CI) of these compounds were: CP-99,994 (0.082 mg kg-1, 95% CI 0.047-0.126), SR 48212A (2.3 mg kg-1, 95% CI 0.5-20), and SR 48968 (> 1.0 mg kg-1, 95% CI not determined). The intra-arterial potencies of these compounds were: CP-99,994 (1.0 microgram kg-1, 95% CI 0.4-1.8), SR 48212A (25 micrograms kg-1, 95% CI 13-52), and SR 48968 (8.0 micrograms kg-1, 95% CI 1-32). The derived EDRs for each compound were: CP-99,994, 82; SR 48212A, 92; and SR 48968, > 125. 7. We concluded that CP-99,994 and SR 48968 inhibit cough in the guinea-pig and cat by a central site of action. In the cat, the antitussive action of these compounds appears to be solely by a central site.

Animals↗
PubMed1997

In vivo metabolism-based discovery of a potent cholesterol absorption inhibitor, SCH58235, in the rat and rhesus monkey through the identification of the active metabolites of SCH48461.

SCH48461 is a selective and highly potent inhibitor of cholesterol absorption. In rats, SCH48461 is rapidly and completely metabolized in the first pass through the body. To compare the activity of the metabolites of SCH48461 with SCH48461 itself, an intestinally cannulated, bile duct-cannulated rat model for cholesterol absorption was developed. SCH48461 inhibited the absorption of cholesterol by 70%, whereas bile containing the metabolites of SCH48461 (henceforth, "metabolite bile") inhibited the absorption by greater than 95%. Very little of the recovered radioactive dose of SCH48461 was located in the intestinal lumen (7%) or wall (4%), whereas 85% appeared in bile. However, in rats treated with metabolite bile, 62% of the dose remained in the lumen, 13% was associated with the wall and only 24% reappeared in bile, which suggests that the activity of the metabolite bile may be related to its higher retention in the intestinal wall. Rats treated with metabolite bile had 64% and 84% less drug-related radioactivity in their plasma and livers, respectively, compared with animals treated with SCH48461, which indicates that the metabolites are systemically less available than SCH48461. The metabolites in bile were separated by high-performance liquid chromatography; the most active fraction in the bile duct-cannulated rat model was identified by mass spectrometry as the glucuronide of the C4-phenol of SCH48461. The other fractions had moderate or no activity. Through the identification of the most active biliary metabolites of SCH48461 in the rat, we have discovered SCH58235, a novel cholesterol absorption inhibitor which is 400 times more potent than SCH48461 in the cholesterol-fed rhesus monkey.

Absorption↗
PubMed1996

Hemodynamic profile of activation of histamine H3 receptors by R-alpha-methylhistamine in the guinea pig.

1. The effect of R-alpha-methylhistamine, a histamine H1 receptor agonist, was studied on cardiovascular hemodynamics in bilateral vagotomized, anesthetized guinea pigs. 2. R-alpha-methylhistamine (100 micrograms/kg, IV) a dose that selectively activates histamine H3 receptors, produced hypotension and bradycardia. Total peripheral resistance (TPR) and rate pressure product (RPP) were also decreased at this dose. 3. Pretreatment with the ganglionic blocker hexamethonium (20 mg/kg, IV) blocked the blood pressure (BP), heart rate (HR), TPR, and RPP effects of R-alpha-methylhistamine (100 micrograms/kg, IV). Hexamethonium did not block the hypotensive and TPR lowering actions of the muscarinic agonist methacholine (1 and 3 micrograms/kg, IV). 4. Pretreatment with the alpha 1-adrenoceptor antagonist prazosin (0.5 mg/kg IV), blocked R-alpha-methylhistamine's (100 micrograms/kg, IV) effects on BP, TPR, and RPP. Prazosin did not antagonize the bradycardia effect of R-alpha-methylhistamine. 5. Pretreatment with the beta-adrenoceptor antagonist atenolol (1 mg/kg, IV) did not alter the BP, TPR, or RPP actions of R-alpha-methylhistamine. The HR effects of R-alpha-methylhistamine were blocked by atenolol. 6. The hemodynamic effects of R-alpha-methylhistamine were compared to the hemodynamic profile of the calcium channel blocker, verapamil (0.5 mg/kg, IV). Verapamil had little effect on TRP and had a greater cardiac depressant effect as evidenced by a significant reduction in HR and cardiac output (CO). 7. In summary, these results show that activation of prejunctional H3 receptors with R-alpha-methylhistamine decreases basal, BP, HR, TPR, and RPP in anesthetized guinea pigs. The fall in BP is mediated by a decrease in TPR. Furthermore, the inhibitory effects of R-alpha-methylhistamine on sympathetic control of the vasculature appears to impart a greater physiologic effect on the H3-histamine mediated hypotension than its inhibitory effects on sympathetic agents to the heart.

Animals↗
PubMed1996

Resolution of intracranial calcifications in infants with treated congenital toxoplasmosis.

PURPOSE: To determine the natural history of intracranial calcifications in infants with treated congenital toxoplasmosis. MATERIALS AND METHODS: Between January 1982 and March 1994, cranial computed tomography was performed in 56 infants with treated congenital toxoplasmosis when they were newborns and approximately 1 year old. Locations and sizes of intracranial calcifications were noted. RESULTS: Forty newborns had intracranial calcifications. By 1 year of age, calcifications diminished or resolved in 30 (75%) and remained stable in 10 (25%) of these treated infants. Ten (33%) of the 30 infants whose calcifications diminished versus seven (70%) of the 10 infants with stable calcifications received less intensive antimicrobial treatment than the other treated infants. In contrast, a small number of infants who were untreated or treated 1 month or less had intracranial calcifications that increased or remained stable during their 1st year of life. CONCLUSION: Diminution or resolution of intracranial calcifications was an unexpected and remarkable finding in infants with treated, congenital toxoplasmosis, consonant with their improved neurologic functioning.

Anti-Infective Agents↗
PubMed1994

Species differences in the cardiovascular responses to histamine H3 receptor activation.

Potential species differences in cardiovascular responses to histamine H3 receptor activation were studied in the conscious guinea pig, rabbit, normotensive rat and the spontaneously hypertensive rat. R-alpha-Methylhistamine (100 micrograms/kg i.v.) decreased blood pressure in both the guinea pig and the rabbit. In the guinea pig, R-alpha-methylhistamine decreased heart rate, whereas in the rabbit it produced a tachycardia. In the normotensive rat and spontaneously hypertensive rat, R-alpha-methylhistamine (100 micrograms/kg i.v.) had no effect on blood pressure and heart rate. The cardiovascular action of R-alpha-methylhistamine in the guinea pig and rabbit was blocked by pretreatment with thioperamide (1.0 mg/kg i.v.) but not by chlorpheniramine (0.3 mg/kg i.v.) or cimetidine (3.0 mg/kg i.v.), respectively. These results indicate species differences in cardiovascular responses to histamine H3 receptor activation.

Animals↗
PubMed1993

Production by R-alpha-methylhistamine of a histamine H3 receptor-mediated decrease in basal vascular resistance in guinea-pigs.

1. The effect of the selective histamine H3 receptor agonist, R-alpha-methylhistamine given intravenously (10-100 micrograms kg-1) was examined on baseline total peripheral resistance (TPR), and cardiovascular haemodynamics in bilaterally vagotomized, anaesthetized guinea-pigs. 2. R-alpha-methylhistamine produced a dose-dependent hypotension and fall in TPR at 30 and 100 micrograms kg-1. A decrease in heart rate (HR) was observed at a dose of 100 micrograms kg-1. R-alpha-methylhistamine (10-100 micrograms kg-1) also produced a dose-dependent fall in rate pressure product (RPP). There was no effect on cardiac output (CO) or stroke volume (SV) at these doses. 3. Histamine H1 and H2 blockade in animals pretreated with a combination of chlorpheniramine (0.3 mg kg-1) and cimetidine (3.0 mg kg-1) did not alter the haemodynamic actions of R-alpha-methyl-histamine (100 micrograms kg-1, i.v.). Pretreatment with the selective H3 antagonist, thioperamide (1 mg kg-1), completely blocked the action of R-alpha-methylhistamine on haemodynamic parameters. 4. To study the mechanism of action of R-alpha-methylhistamine, the vasodilator hydralazine (1 mg kg-1, i.v.) was used. Hydralazine lowered BP, TRP and RPP in guinea-pigs pretreated with ipratropium (50 micrograms kg-1, i.v.). Hydralazine had no effect on HR, SV or CO. 5. R-alpha-methylhistamine (100 micrograms kg-1) did not affect the vasopressor action and increases in TPR produced by adrenaline (1 and 3 micrograms kg-1). On the other hand, the vasodilator hydralazine (1 mg kg-1, i.v.) inhibited the effects of adrenaline (3 micrograms kg-1) on TPR and RPP. The effect of both doses of adrenaline on BP were attenuated by hydralazine. Therefore, the inhibitory effects of R-alpha-methylhistamine are not mediated through a direct action on vascular smooth muscle.6. In adrenalectomized guinea-pigs, R-alpha-methylhistamine (100 microg kg-1) produced a drop in BP and HR.There was no difference between the effects of R-alpha-methylhistamine on blood pressure and heart rate in adrenalectomized and non-adrenalectomized guinea-pigs.7. These results show that activation of peripheral H3 receptors lowers basal BP, HR and TPR, most likely by a peripheral prejunctional mechanism. The fall in BP and TPR is probably due to a decrease in noradrenaline release from sympathetic effector nerves innervating the resistance blood vessels.

Adrenalectomy↗
PubMed1978

Monozygotic twins with Klinefelter's syndrome discordant for systemic lupus erythematosus and symptomatic myasthenia gravis.

Monozygotic twins with Klinefelter's syndrome were evaluated for two distinct illnesses. One subject had clinical and serologic evidence of systemic lupus erythematosus and no symptoms of muscle weakness. His identical twin had typical symptoms and laboratory evidence of myasthenia gravis. Antibodies to acetylcholine receptors were present in both subjects. These patients are discussed in relation to genetic, hormonal, and immunologic mechanisms involved in the pathogenesis of these two disorders.

Diseases in Twins↗
PubMedDate not supplied

Combined histamine H1 and H3 receptor blockade produces nasal decongestion in an experimental model of nasal congestion.

We studied the pharmacological actions of combined histamine H1/H3 receptor blockade on the increase in nasal airway resistance (NAR) and decrease in nasal cavity volume produced by nasal exposure to compound 48/80, a mast cell degranulator. In the anesthetized cat compound 48/80 (1%) produced a maximum increase in NAR of 9.1 +/- 0.7 cmH20.L/minute. The increase in NAR in animals pretreated with a combination of the H1 antagonist, chlorpheniramine (CTM; 0.8 mg/kg i.v.) and increasing doses of the H3 antagonist, thioperamide (THIO; 1.0, 3.0, and 10.0 mg/kg i.v.) were 6.1 +/- 2.1, 4.2 +/- 1.0 and 2.2 +/- 0.7 cmH20.L/minute, respectively. A second H3 antagonist, clobenpropit (CLOB; 0.03, 0.3, and 1.0 mg/kg i.v.) combined with CTM (0.8 mg/kg i.v.) also inhibited the nasal effects of compound 48/80. When the nonsedating H1 antihistamine, loratadine (3.0 mg/kg i.v.), was substituted for CTM, it also reduced nasal congestion when given in combination with THIO (10 mg/kg i.v.). In contrast, treatment with CTM (1.0 mg/kg i.v.) and the H2 antagonist, ranitidine (RAN; 1.0 mg/kg i.v.) were without activity. Loratadine, CTM, CLOB, RAN, or THIO administered alone were inactive. The alpha-adrenergic agonist, phenylpropanolamine (PPA; 1.0 mg/kg i.v.) demonstrated decongestant effects, but in contrast to H1/H3 blockade, PPA produced a significant hypertensive effect. Using acoustic rhinometry (AcR) we found that combined i.v. CTM (1.0 mg/kg) and THIO (10 mg/kg) and combined oral CTM (10 mg/kg) and THIO (30 mg/kg) blocked the decrease in nasal cavity volume produced by intranasal compound 48/80 (1%, 50 microL). We conclude that combined H1/H3 histamine receptor blockade enhances the efficacy of an H1 antagonist by conferring decongestant activity to the H1 antihistamine. We propose that the decongestant activity of combined H1/H3 blockade may provide a novel approach for the treatment of allergic nasal congestion without the hypertensive liability of current therapies.

Airway Resistance↗
PubMedDate not supplied

Changes in nasal resistance and nasal geometry using pressure and acoustic rhinometry in a feline model of nasal congestion.

This is the first report describing the use and pharmacological characterization of nasal patency by both pressure rhinometry and acoustic rhinometry (AcR) in an experimental cat model of nasal congestion. In pressure rhinometry studies, aerosolized compound 48/80 (0.1-3.0%), a mast cell liberator, increased nasal airway resistance (NAR) 1.2 +/- 0.6, 5.8 +/- 0.5, 8.6 +/- 1.1 and 7.9 +/- 1.5 cmH2O.L/minute, respectively. Increases in NAR produced by compound 48/80 were associated with a 395% increase in histamine concentration found in the nasal lavage fluid. Pretreatment with the alpha-adrenoreceptor agonist, phenylpropanolamine (PPA; 0.1-3.0 mg/kg, i.v.), and the NO synthetase inhibitor, NG-nitro-L-arginine (L-NAME; 10 mg/kg, i.v.) attenuated the increases in NAR produced by compound 48/80. The histamine H1 antagonist chlorpheniramine (1.0 mg/kg, i.v.) and the H2 antagonist, ranitidine (1.0 mg/kg, i.v.) had no decongestant activity. Also without decongestant activity were the muscarinic antagonist atropine, the cyclooxygenase inhibitor indomethacin, and the 5-HT blocker methysergide. Aerosolized histamine (0.1-1.0%) also produced a dose dependent increase in NAR. In studies using acoustic rhinometry (AcR), intranasal application of compound 48/80 (0.1-1.0%) elicited pronounced decreases in nasal cavity volumes and minimum cross-sectional area (Amin). Pretreatment with PPA (3 mg/kg, i.v. or 10 mg/kg, p.o.) attenuated the decreases in nasal volume and Amin. The effects of topical intranasal histamine (0.1-1.0%) on nasal geometry were similar to compound 48/80. We conclude that the cat is a useful model for evaluating the pharmacological actions of potential nasal decongestants. Furthermore, we also conclude that AcR is a useful method for noninvasive assessment of nasal patency in a preclinical setting.

Acoustics↗