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Comparison of the effects of hydroxocobalamin and oxyhaemoglobin on responses to NO, EDRF and the nitrergic transmitter
Author(s) -
La Mylinh,
Li Chun Guang,
Rand Michael J.
Publication year - 1996
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1996.tb15264.x
Subject(s) - hydroxocobalamin , endothelium derived relaxing factor , acetylcholine , chemistry , aorta , endocrinology , medicine , endothelium , anesthesia , cyanocobalamin , vitamin b12
1 The effects of ranges of concentrations of oxyhaemoglobin (0.01–30 μ m ) and hydroxocobalamin (1–100 μ m ) were compared for their abilities to reduce relaxant responses to EDRF released by acetylcholine in endothelium‐intact rat aortic rings, the nitergic transmitter in rat anococcygeus muscles, and NO in aqueous solution in both tissues (aortic rings were denuded of endothelium). 2 The concentrations of oxyhaemoglobin producing 50% reduction of responses to EDRF and NO in rat aorta correspond closely, the IC 50 values being 0.13 ± 0.02 μ m and 0.11 ± 0.02 μ m respectively. 3 Oxyhaemoglobin was equally effective in inhibiting responses to NO in anococcygeus muscles and in aortic rings with an IC 50 of 0.14 ± 0.05 μ m . However, responses to the nitrergic transmitter were considerably less sensitive to inhibtion by oxyhaemoglobin, the IC 50 being 19.7 ± 5.1 μ m . 4 The IC 50 values for hydroxocobalamin in inhibiting responses to EDRF and NO in aorta were 3.4 ± 0.2 μ m and 8.4 ± 0.63 μ m , respectively, but it was less effective against responses to NO in anococcygeus muscles the IC 50 being 46 ± 9.6 μ m . However, even in the highest concentration used (100 μ m ), it did not reduce responses to the nitrergic transmitter. 5 The findings are compatible with the views that EDRF is NO, but suggest that the nitergic transmitter in the rat anococcygeus muscle does not behave like free NO.