Ozaki M, Masuda Y
Department of Toxicology, Niigata College of Pharmacy, Niigata, Japan.
Biol Pharm Bull. 2000 Jan;23(1):17-22. doi: 10.1248/bpb.23.17.
The characteristics of isolated guinea-pig ileal contractions of basal tension after tetanic stimulation in the presence of a high concentration of naloxone (NLX) [post-tetanic contraction] were investigated. The post-tetanic contraction did not occur in the absence of NLX, but did occur in a concentration-dependent manner in the presence of a high concentration of NLX (5 x 10(-7), 10(-6), 10(-5) and 5 x 10(-5) M), the concentration of which was higher than that required for antagonizing post-tetanic twitch inhibition. The contraction in the presence of 10(-6) M NLX was diminished by washing NLX from the preparation with Krebs-bicarbonate solution. The contraction under 10(-6) M NLX occurred in a frequency-dependent manner (5, 10 and 20 Hz), but not at 0.1 Hz. Tetanic stimulation (5, 10 and 20 Hz) without NLX did not induce this contraction. The post-tetanic contraction with 10(-6) M NLX had a tendency to be antagonized in the presence of 5 x 10(-6) M atropine. Methysergide (5 x 10(-5) M) had no effect on this contraction. Spantide (10(-5) M) largely inhibited the contraction, and indomethacin (5 x 10(-6) M) and tetrodotoxin (5 x 10(-7) M) completely inhibited this contraction. These results indicate that tetanic stimulation in the presence of a high concentration of NLX induces contraction of the ileal muscle due to the release of endogenous ileal contractile substances (substance P, prostaglandins and acetylcholine), and suggests that these contractions are closely linked to the endogenous opioid system induced by tetanic stimulation in the ileum.
研究了在高浓度纳洛酮（NLX）存在下，强直刺激后豚鼠离体回肠基础张力收缩的特征[强直后收缩]。在无NLX时不发生强直后收缩，但在高浓度NLX（5×10⁻⁷、10⁻⁶、10⁻⁵和5×10⁻⁵M）存在时，以浓度依赖性方式发生，其浓度高于拮抗强直后抽搐抑制所需的浓度。用 Krebs-碳酸氢盐溶液从标本中冲洗NLX后，10⁻⁶M NLX存在时的收缩减弱。10⁻⁶M NLX下的收缩以频率依赖性方式发生（5、10和20Hz），但在0.1Hz时不发生。无NLX的强直刺激（5、10和20Hz）不诱导这种收缩。10⁻⁶M NLX的强直后收缩在5×10⁻⁶M阿托品存在时有被拮抗的趋势。甲基麦角新碱（5×10⁻⁵M）对这种收缩无影响。Spantide（10⁻⁵M）很大程度上抑制了收缩，吲哚美辛（5×10⁻⁶M）和河豚毒素（5×10⁻⁷M）完全抑制了这种收缩。这些结果表明，在高浓度NLX存在下的强直刺激由于内源性回肠收缩物质（P物质、前列腺素和乙酰胆碱）的释放而诱导回肠肌肉收缩，并提示这些收缩与回肠强直刺激诱导的内源性阿片系统密切相关。
