Drugs online research references
Br J Pharmacol. 1986 Mar;87(3):587-94.
Adrenoceptor blocking properties of atropine-like agents anisodamine and anisodine on brain and cardiovascular tissues of rats.
Varma DR, Yue TL.
The cholinoceptor antagonists anisodamine and anisodine are widely used in the People's Republic of China for the management of acute circulatory shock but the mechanism of their beneficial effects is not fully known; we therefore investigated if these agents possessed adrenoceptor blocking properties. The antagonistic effect of anisodamine and anisodine against the specific binding of the alpha 1-adrenoceptor ligand [3H]-WB-4101 to cardiac and brain tissue membrane preparations and against the effects of phenylephrine on isolated aortic strips and left atria of rats were compared with classical muscarinic receptor and adrenoceptor blocking agents. Both anisodamine and anisodine possessed alpha 1-adrenoceptor blocking properties; the order of potency of various agents in displacing the binding of [3H]-WB-4101 to receptors and in antagonizing the effects of phenylephrine on aortic strips and left atria was: prazosin greater than atropine greater than anisodamine greater than scopolamine greater than anisodine. It is concluded that both anisodamine and to a lesser extent anisodine possess alpha 1-adrenoceptor blocking properties; this antagonistic activity of anisodamine may contribute to its salutary effects on the microcirculation. However, it is unlikely that anisodine produces a significant adrenoceptor blockade in the clinically used dose-range.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2879586&dopt=Abstract
J Pharmacol Exp Ther. 1988 Aug;246(2):548-52.
Reversal of inhibition of prolactin secretion in cultured pituitary cells by muscarinic antagonists.
Beach JE, Smallridge RC, Chiang PK, Fein HG.
Department of Clinical Physiology, Walter Reed Army Institute of Research, Washington, DC.
We investigated whether the inhibition of prolactin secretion from pituitary cells by carbachol, a cholinergic agonist resistant to hydrolysis by cholinesterases, would be a useful bioassay to explore an important nonneuronal action of antimuscarinic agents. Carbachol inhibited prolactin secretion from cultured rat anterior pituitary cells in a dose-dependent manner with a mean IC50 of 1.5 +/- 0.6 (S.E.) microM and maximal inhibition at 10(-5) M. Prolactin levels in media were significantly reduced by 30 min of incubation with carbachol. This inhibition persisted for 24 hr and was reversed by 2 microM atropine. The stimulation of prolactin secretion by 10(-6) M thyrotropin releasing hormone (to 1.5 times control) was inhibited by the addition of carbachol (10(-5) M). Addition of atropine (2 microM) to these agents restored maximal stimulation by thyrotropin releasing hormone. The inhibition of carbachol by atropine was competitive, whereas the inhibition of thyrotropin releasing hormone by carbachol was noncompetitive. The apparent affinities (Ki) of several antimuscarinic agents in pituitary cells were determined by their ability to reverse the carbachol inhibition of prolactin secretion: atropine 0.14 nM, scopolamine 0.26 nM, azaprophen 0.3 nM, aprophen 3.0 nM, pirenzepine 42 nM, benactyzine 80 nM and adiphenine 198 nM. These potencies correlated positively with those previously determined for inhibition of alpha amylase secretion from pancreatic acinar cells as well as with those for behavioral depressant actions of the antimuscarinics. Cultured anterior pituitary cells thus provide an effective system for testing the relative potencies of muscarinic antagonists in pituitary cells.(ABSTRACT TRUNCATED AT 250 WORDS)
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3404446&dopt=Abstract
Biochemistry. 1986 Nov 4;25(22):6995-7008.
Assessment of mechanistic proposals for the binding of agonists to cardiac muscarinic receptors.
Wong HM, Sole MJ, Wells JW.
N-[3H]Methylscopolamine has been used to characterize muscarinic receptors in crude homogenates prepared from hearts of Syrian golden hamsters. The Hill coefficient is one for specific binding of the radioligand itself and for its inhibition by muscarinic antagonists; markedly lower values are obtained for its inhibition by muscarinic agonists. The binding patterns of agonists have been analyzed in terms of a mixture of sites differing in affinity for the drug and reveal the following. All agonists discern at least two classes of receptor in atrial and ventricular homogenates. The number of classes and the relative size of each differ for different agonists in the same region and for the same agonist in different regions. Atrial and ventricular affinities are in good agreement for some agonists but differ for others. Guanylyl imidodiphosphate (GMP-PNP) is without effect on the specific binding of the radioligand but alters the binding of carbachol via an apparent redistribution of receptors from one class to another; the apparent affinity at either class remains unchanged. Carbachol reveals two classes of sites in ventricular preparations, and the nucleotide mediates an interconversion from higher to lower affinity; three classes are revealed in atrial preparations, and the nucleotide eliminates the sites of highest affinity with a concomitant increase in the number of sites of lowest affinity. Taken together, the data are incompatible with the notion of different, noninterconverting sites; rather, there appear to be several possible states of affinity such that the equilibrium distribution of receptors among the various states is determined by the tissue, by the agonist, and by neurohumoral modulators such as guanylyl nucleotides. The effects of agonists and GMP-PNP cannot be rationalized in terms of a ternary complex model in which the low Hill coefficients arise from a spontaneous equilibrium between receptor (R) and G protein (G) and in which agonists bind preferentially to the RG complex.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3801407&dopt=Abstract
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