Effect of cholinergic agonists on muscular tonus of the lizard small intestine and esophagus.
The underlying mechanisms of acetylcholine-induced intestinal relaxation in the lizard Liolaemus tenuis tenuis are still unknown. By using a classical model of intestinal recording of isometric contraction and relaxation in conjunction with specific pharmacological tools, this article studies the possible influence of EDRF/NO and nicotinic ganglionar receptors on the Ach-induced relaxation in an effort to elucidate the probable mechanisms involved in ACh effect. It was observed that the relaxation of the lizard intestine elicited by ACh (10(-7) - 4 x 10(-4) M) was not affected by hexametonium (5 x 10(-4) M) or tetrodotoxin (10(-6) M). Nicotine (10(-7) to 10(-4) M) induced relaxation was significantly antagonized by hexametonium; however, it was not influenced by tetrodotoxin. These results allow us to discard a neuronal pathway in cholinergic-induced relaxation, suggesting a more direct cholinergic effect on the smooth muscle, perhaps mediated by an unknown substance released by some specialized tissue. N-nitro-L-arginine, used to block NO-synthase and NO production, induced no changes in ACh-induced relaxation. Methylene blue, a soluble guanylate cyclase inhibitor, induced no changes in ACh-induced relaxation. These results allow us to discard a probable role of EDRF/nitric oxide in the ACh-induced relaxation of lizard small intestine, providing evidence that this mechanism could be different from that reported in other species.
Wacyk
J
J
Institute of Biomedical Sciences (ICBM), Faculty of Medicine, University of Chile, Santiago de Chile.
Fuenzalida
M
M
Morales
M
M
Acuña
O
O
Lemus
D
D
D000818:Animals; D018679:Cholinergic Agonists / Q000494:pharmacology*; D004947:Esophagus / Q000187:drug effects*; D005260:Female; D007421:Intestine, Small / Q000187:drug effects*; D008116:Lizards; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects*; D009129:Muscle Tonus / Q000187:drug effects*
D018679:Cholinergic Agonists