Ojewole J A
Methods Find Exp Clin Pharmacol. 1983 Jun;5(5):299-310.
The effects of some autonomic drugs and transmural electrical stimulation have been investigated on different isolated regions (oesophagus, stomach, duodenum, ileum, colon, and rectum) of the rainbow lizard (Agama agama Linn.) alimentary canal. Acetylcholine and its natural or synthetic analogues (5 X 10(-10)-10(-6)M) contracted the rainbow lizard isolated oesophagus, duodenum, ileum, colon, and rectum (but not the stomach) in a concentration-dependent manner. Acetylcholine cholinoceptors on the lizard gut were classified as "muscarinic" since acetylcholine-induced contractions of the muscle preparations were inhibited or abolished by relatively low concentrations of atropine (10(-9)-10(-6)M), but not by d-tubocurarine or hexamethonium (at the same concentration levels. Atropine exhibited characteristics of competitive antagonism and gave a high mean pA2 value (9.40 +/- 0.25) against acetylcholine on lizard isolated rectum. Physostigmine (eserine, 10(-8)-10(-4)M) did not contract any isolated region of the lizard gut. However, low to medium concentrations of eserine (10(-8)-10(-6)M) potentiated acetylcholine-but not carbachol-induced contractions of the isolated smooth muscle segments taken from different regions of the rainbow lizard alimentary canal. The selective potentiation of ACh-elicited contractions of the muscle preparations by eserine is therefore thought to suggest the presence of acetylcholinesterases in the tissues, and their inhibition by physostigmine. Dimethylphenylpiperazinium (DMPP) or nicotine (10(-8)-10(-5)M) did not contract any of the isolated segments from the different regions of the rainbow lizard alimentary canal. Adrenaline and all its analogues examined (10(-8)-10(-5)M) dose-dependently relaxed isolated segments from different regions (except the stomach) of the rainbow lizard gastrointestinal tract. The catecholamine-induced relaxations of the lizard gut smooth muscles were inhibited or abolished by low concentrations of phentolamine (10(-7)-2.5 X 10(-6)M). This observation probably suggests the presence of "alpha" adrenoceptors on rainbow lizard gastrointestinal tract. Repetitive transmural electrical excitation induced tetrodotoxin- (and atropine-) resistant, frequency-dependent contractions of all isolated segments taken from different regions (except the stomach) of the lizard alimentary canal. The findings that medium to high concentrations of physostigmine (10(-6)-10(-4)M), DMPP and nicotine (10(-6)-10(-5)M) failed to elicit intrinsic nerve-mediated contractions, coupled with the fact that tetanic transmural electrical stimulation caused tetrodotoxin-resistant contractions of the rainbow lizard isolated gut muscles, strongly suggest that the autonomic innervation of this reptilian alimentary canal differs from that of a conventional mammalian (e.g. guinea-pig) gastrointestinal tract...
已对彩虹蜥蜴（变色蜥）消化道的不同离体区域（食管、胃、十二指肠、回肠、结肠和直肠）研究了某些自主神经药物和经壁电刺激的作用。乙酰胆碱及其天然或合成类似物（5×10⁻¹⁰ - 10⁻⁶M）以浓度依赖性方式使彩虹蜥蜴离体食管、十二指肠、回肠、结肠和直肠（但不包括胃）收缩。蜥蜴肠道上的乙酰胆碱胆碱受体被归类为“毒蕈碱型”，因为相对低浓度的阿托品（10⁻⁹ - 10⁻⁶M）可抑制或消除乙酰胆碱诱导的肌肉制剂收缩，而d - 筒箭毒碱或六甲铵（相同浓度水平）则不能。阿托品表现出竞争性拮抗特性，在蜥蜴离体直肠上对乙酰胆碱的平均pA2值较高（9.40±0.25）。毒扁豆碱（依色林，10⁻⁸ - 10⁻⁴M）未使蜥蜴肠道的任何离体区域收缩。然而，低至中等浓度的依色林（10⁻⁸ - 10⁻⁶M）增强了乙酰胆碱（而非卡巴胆碱）诱导的取自彩虹蜥蜴消化道不同区域的离体平滑肌节段的收缩。因此，毒扁豆碱对肌肉制剂中乙酰胆碱引发收缩的选择性增强被认为表明组织中存在乙酰胆碱酯酶，且它们被毒扁豆碱抑制。二甲基苯基哌嗪鎓（DMPP）或尼古丁（10⁻⁸ - 10⁻⁵M）未使彩虹蜥蜴消化道不同区域的任何离体节段收缩。肾上腺素及其所有检测的类似物（10⁻⁸ - 10⁻⁵M）以剂量依赖性方式使彩虹蜥蜴胃肠道不同区域（除胃外）的离体节段舒张。低浓度的酚妥拉明（10⁻⁷ - 2.5×10⁻⁶M）可抑制或消除儿茶酚胺诱导的蜥蜴肠道平滑肌舒张。这一观察结果可能表明彩虹蜥蜴胃肠道上存在“α”肾上腺素能受体。重复性经壁电刺激诱导了取自蜥蜴消化道不同区域（除胃外）的所有离体节段产生对河豚毒素（和阿托品）耐受的、频率依赖性的收缩。中至高浓度的毒扁豆碱（10⁻⁶ - 10⁻⁴M）、DMPP和尼古丁（10⁻⁶ - 10⁻⁵M）未能引发内在神经介导的收缩，再加上强直经壁电刺激导致彩虹蜥蜴离体肠道肌肉产生对河豚毒素耐受的收缩，这些发现有力地表明这种爬行动物消化道的自主神经支配不同于传统哺乳动物（如豚鼠）的胃肠道……
