Drugs online research references
Neuropharmacology. 1987 Jul;26(7A):743-52.
Presynaptic and postsynaptic effects of histamine and histamine agonists in the superior cervical ganglion of the rat.
Snow RW, Weinreich D.
Extracellular and intracellular recording techniques were used to study the effects of histamine and the histamine agonists [impromidine (IMP) and 2-thiazolylethylamine (2-TH)] on synaptic transmission in the superior cervical ganglion of the rat in vitro. At the concentrations employed (up to 10(-5) M) these compounds did not produce detectable effects on the electrical properties of the postsynaptic neurons. Histamine produced a dose-dependent reduction in the amplitude of the extracellularly-recorded presynaptic and postsynaptic compound action potential. The H2 receptor agonist impromidine reduced only the postganglionic compound action potential. Cimetidine, a specific H2 receptor antagonist, produced parallel shifts in the log dose-response curves for impromidine. Impromidine also reduced the average size of the evoked excitatory postsynaptic potential. The reduction of the mean amplitude of the excitatory postsynaptic potential was due to a decrease in the amount of acetylcholine (ACh) liberated by each preganglionic volley (mean quantal content, m) and a diminution in quantal size. The H1 receptor agonist, 2-TH produced a dose-dependent increase in the presynaptic and postsynaptic compound action potential and in m. The increase in m was not associated with changes in quantal size. The H1 antagonists, pyrilamine and promethazine, did not prevent facilitation of ganglionic transmission induced by 2-TH. It is concluded that histamine H1 and H2 receptors exist on preganglionic axons, or terminals in sympathetic ganglia of the rat. Activation of H1 receptors facilitates release of ACh whereas H2 receptor activation results in depressed release.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2888039&dopt=Abstract
Arch Int Pharmacodyn Ther. 1987 Dec;290(2):267-77.
Effects of antihistamines on the spinal reflex in rats.
Tasaka K, Kitazumi K, Kamei C.
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Okayama University, Japan.
The effect of antihistamines on the spinal reflex in rats was studied. When H1-blocking agents such as pyrilamine, promethazine and diphenhydramine were given intravenously, both monosynaptic reflex (MSR) and polysynaptic reflex potentials (PSR) were inhibited in a dose-dependent fashion without affecting the dorsal root reflex and dorsal root-dorsal root potential. The extent of suppression of the MSR and PSR measured in spinal rats was smaller than that of intact rats. When H1-blocking agents (0.25-5.0 nmol) were applied by intraspinal microinjection close to the motoneuron, the MSR and PSR were depressed dose-dependently. Simultaneous application of carbachol partially blocked the inhibitory effects of H1-blocking agents induced by intraspinal microinjection. Also, the motoneuron discharges evoked by microinjection of glutamic acid or acetylcholine were depressed by simultaneous administration of any of H1-blocking agents tested. However, H2-blocking agents, such as cimetidine and ranitidine, given either intravenously or intraspinally had a scarcely measurable effect on the spinal reflex. The depression of H1-blocking agents on the spinal reflex is due to a direct inhibition of the motoneuron on the one hand. On the other hand, there is also an involvement of higher centers in the central nervous system increasing potential depression.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2895615&dopt=Abstract
J Pharm Pharmacol. 1988 Mar;40(3):176-80.
Transport characteristics of propantheline across rat intestinal brush border membrane.
Saitoh H, Kawai S, Miyazaki K, Arita T.
Department of Pharmacy, Hokkaido University Hospital, School of Medicine, Sapporo, Japan.
The transport mechanism of propantheline, an anti-acetylcholine quaternary ammonium compound, has been studied using brush border membrane vesicles isolated from rat small intestine. The uptake of propantheline was facilitated by the transmembrane electrical potential difference (cell interior negative) induced by NaSCN, NaI or valinomycin. But this effect was a secondary action; in the initial phase of propantheline uptake (less than 5 min), there was no facilitating effect. When the transmembrane potential difference was induced after propantheline uptake had reached a steady state, there was an overshoot of the drug. Therefore, it is suggested that the transport of propantheline across the brush border membrane consists of at least two processes. In the first, propantheline rapidly binds to the brush border membrane, in the second it enters into epithelium driven by the negative transmembrane electrical potential difference. Cationic tertiary amines such as chlorpromazine, imipramine and promethazine markedly inhibited propantheline uptake. These results suggest that there is a common absorption process for tertiary amines and quaternary ammonium compounds.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2899146&dopt=Abstract
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