Showing papers on "Arecoline published in 1989"

Cytotoxic and genotoxic effects of areca nut-related compounds in cultured human buccal epithelial cells.

Abstract: Because betel quid chewing has been linked to the development of oral cancer, pathobiological effects of an aqueous areca nut extract, four areca nut alkaloids (arecoline, guvacoline, guvacine, and arecaidine), and four nitrosated derivatives [N-nitrosoguvacoline, N-nitrosoguvacine, 3-(N-nitrosomethylamino)propionaldehyde and 3-(N-nitrosomethylamino)propionitrile] have been investigated using cultured human buccal epithelial cells. Areca nut extract in a dose-dependent manner decreases cell survival, vital dye accumulation, and membrane integrity, and it causes formation of both DNA single strand breaks and DNA protein cross-links. Depletion of cellular free low-molecular-weight thiols also occurs, albeit at quite toxic concentrations. Comparisons of the areca nut-related N-nitroso compounds and their precursor alkaloids, at concentrations up to 5 mM, indicate that 3-(N-nitrosomethylamino)propionaldehyde is the most potent on a molar basis to decrease both survival and thiol content and to cause significant formation of DNA single strand breaks. Arecoline, guvacoline, or N-nitrosoguvacoline decreases survival and cellular thiols, whereas arecaidine, guvacine, N-nitrosoguvacine, and 3-(N-nitrosomethylamino)propionitrile have only minor effects on these variables. Taken together, the present studies indicate that aqueous extract and, in particular, one N-nitroso compound related to areca nut, i.e., 3-(N-nitrosomethylamino)propionaldehyde, are highly cytotoxic and genotoxic to cultured human buccal epithelial cells, of potential importance in the induction of tumors in betel quid chewers.

The Muscarinic Cholinergic Agonist Arecoline Stimulates the Rat Hypothalamic-Pituitary-Adrenal Axis Through a Centrally-Mediated Corticotropin-Releasing Hormone-Dependent Mechanism

Abstract: Several lines of experimental evidence suggest that acetylcholine and other cholinergic agonists are excitatory to the hypothalamic-pituitary-adrenal (HPA) axis. To examine the site on the HPA axis that is stimulated by cholinergic agents, we evaluated the in vivo and in vitro effects of the muscarinic cholinergic agonist arecoline in intact and pituitary stalk-transected rats as well as on isolated rat hypothalami, dispersed anterior pituicytes, and adrenocortical cells in culture. Arecoline, injected iv to catheterized, freely moving male Sprague-Dawley rats, stimulated plasma ACTH and corticosterone release in a dose-dependent fashion. The muscarinic cholinergic antagonist atropine significantly blunted the ACTH response to arecoline. Pituitary stalk transection led to diminished plasma ACTH and corticosterone responses to arecoline. Similarly, previous administration of anti-CRH serum significantly blunted these responses. These findings suggest that arecoline stimulates the HPA axis centrally, mainly via secretion of CRH. This hypothesis was confirmed by the dose-dependent ability of arecoline to cause hypothalamic CRH secretion in vitro, an effect antagonized by atropine, and its failure to elicit ACTH and corticosterone secretion by dispersed anterior pituicytes and adrenocortical cells in culture, respectively. These data suggest that the muscarinic cholinergic agonist arecoline stimulates the HPA axis in the rat and that this effect is mediated mainly by the release of endogenous CRH. Arecoline, therefore, appears to be a compound suitable to selectively evaluate the responsiveness of the central component of the HPA axis.

Betel nut-induced extrapyramidal syndrome: an unusual drug interaction.

Abstract: Two cases are described of chronic schizophrenic patients maintained on depot neuroleptics, who developed severe extrapyramidal symptoms following a period of heavy betel nut consumption. A mechanism for this effect is proposed based on the pharmacological antagonism of the anticholinergic agent, procyclidine, by the active alkaloid ingredient of the betel, arecoline.

Synthesis and muscarinic activity of a series of tertiary and quaternary N-substituted guvacine esters structurally related to arecoline and arecaidine propargyl ester.

Abstract: A series of tertiary and quaternary N-substituted guvacine (1,2,5,6-tetrahydro-3-carboxy-pyridine) methyl and propargyl esters have been synthesized and tested for muscarinic/antimuscarinic activity on rat ileum and electrically paced left atria. Arecoline and arecaidine propargyl ester (APE) as well as their corresponding N-demethyl derivatives, guvacoline (norarecoline) and guvacine propargyl ester, acted as full agonists at both atrial and ileal muscarinic receptors (range of pD2-values 6.09-8.07). However, in both preparations arecoline and APE were clearly more potent (up to 15-fold) than their N-demethyl analogues. Replacement of the N-methyl group in arecoline and APE by larger substituents (ethyl, n-propyl, n-butyl, benzyl, phenylethyl) as well as N-methylation resulted in a decrease or even a complete loss of agonistic activity. In both organs, the propargyl esters usually showed higher potency than the corresponding methyl ester analogues. N-Ethylguvacine propargyl ester and APE methiodide displayed pronounced agonistic activity in the atria (pD2 approximately 6.5; intrinsic activity = 0.79 and 0.67, respectively) but behaved as competitive antagonists in the ileum (pA2 = 6.06 and 5.62, respectively). Beside the lower sensitivity to muscarinic agonists of the rat ileum as compared to rat atria, the cardioselective stimulant action of both agents may also be due to their ability to recognize structural differences between atrial M2 alpha and ileal M2 beta muscarinic receptor subtypes.

Binding of semirigid nicotinic agonists to nicotinic and muscarinic receptors.

Abstract: Isoarecolone methiodide (1-methyl-4-acetyl-1,2,3,6-tetrahydropyridine methiodide) was previously shown to be among the most potent agonists tested at the frog neuromuscular junction. Because nicotinic receptors from different sources vary in their selectivities, isoarecolone methiodide as well as 19 additional congeners, most of which were also previously tested at the frog neuromuscular junction, were studied in binding assays. Torpedo nobiliana was the tissue source for nicotinic receptors. Two types of experiments were conducted. The first evaluated the affinities of the agonists (including acetylcholine and carbamylcholine) for the recognition site by allowing the agonists to compete for that site with 125I-alpha-bungarotoxin. The inhibition potencies obtained correlated strongly (Spearman's correlation coefficient,-0.91) with the potency obtained at the frog neuromuscular junction. The second type of experiment evaluated the agonists for their ability to activate the receptor. The binding of [3H]perhydrohistrionicotoxin, which was employed as an indicator of the activation of the receptor, was measured in the presence of each of the agonists. Isoarecolone methiodide was the most potent of all. A few of the agonists (partial agonists) were incapable of fully enhancing this binding. For the full agonists, the concentration that produced half of the maximum binding of [3H]perhydrohistrionicotoxin was defined as the EC50. The correlation coefficient (Spearman's) for EC50 versus potency at the frog neuromuscular junction was -0.73, indicating innate differences between Torpedo and frog receptors. In addition, these compounds were tested for their affinity at muscarinic receptors from rat brain. Competition experiments were carried out using [3H]N-methylscopolamine. The affinity of isoarecolone methiodide was only about 7-fold lower than that of acetylcholine and less than 2-fold lower than that of carbamylcholine. In contrast, 1-methyl-4-acetylpiperazine methiodide was much more selective for nicotinic receptors. Its activity was similar to isoarecolone methiodide at the nicotinic receptor, but it was among the weakest compounds in its affinity for the muscarinic receptor.