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Nitric oxide formation from glyceryl trinitrate by rabbit aortic strip: detection by rabbit taenia coli concurrent with vasorelaxation
Author(s) -
Hussain Aman S.,
PoklewskaKoziell Margo,
Brien James F.,
Marks Gerald S.,
Nakatsu Kanji
Publication year - 1994
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.1476-5381.1994.tb17167.x
Subject(s) - rabbit (cipher) , nitric oxide , taenia , nitric oxide synthase , taenia coli , lagomorpha , chemistry , pharmacology , medicine , guinea pig , helminths , immunology , statistics , mathematics
1 The purpose of the present study was to assay NO formation from GTN biotransformation by the rabbit aortic strip (RAS) at times concurrent with its vasorelaxation. Such an assay is an important test of the prodrug hypothesis where it is postulated that glyceryl trinitrate (GTN) is biotransformed to nitric oxide (NO), the active species that initiates vascular smooth muscle relaxation. To test such a hypothesis, we propose that a sample of smooth muscle, poorly responsive to GTN, yet sensitive to the effects of NO could be used to detect RAS production of NO from GTN. 2 Muscle strips of rabbit taenia coli (RTCS) and RAS in close apposition, were mounted in tissue baths, and muscle relaxation was recorded with isometric force transducers. Tissues were submaximally precontracted with 30–35 m m K + depolarizing solution and exposed to increasing concentrations of GTN (0.1 n m ‐10 μ m ). 3 EC 25 for GTN‐induced relaxation of RTCS in the presence of RAS was significantly decreased to that for RTCS in the absence of RAS (5.9 ± 3.0 × 10 −8 m and 5.5 ± 3.7 × 10 −6 m , respectively). Mean maximal levels of GTN‐induced relaxation of similarly precontracted RTCS also differed in the presence and absence of RAS, viz., 80.8 ± 2.1% and 29.8 ± 8.3% respectively. 4 RTCS was found to relax upon administration of NO gas bubbled through the incubation medium. Analysis of tissue bath medium revealed that the NO concentration to which RTCS was exposed attained a maximum of 33 n m . Relaxation of RTCS by NO gas was inhibited by 1 μ m reduced haemoglobin. 5 For GTN‐incubation with intestinal and vascular smooth muscle preparations, NO formation was greater with RAS compared to RTCS. Thus, in the two‐issue bioassay, the RAS was the predominant source of NO formation from GTN. 6 Reduced deoxyhaemoglobin (1 μ m ), a potent extracellular NO scavenger, was found to decrease the augmented GTN‐induced relaxation in the RTCS‐RAS sandwich preparation from 17.3 ± 1.8% to 8.0 ± 0.8%. The augmented RTCS response was restored upon washout and subsequent addition of GTN, in the absence of reduced Hb. 7 These data indicate that nitric oxide or a closely related NO‐donor is produced by vascular biotransformation of GTN as seen by the increased sensitivity of RTCS to GTN when in the presence of RAS. The results of this bioassay thus support the GTN‐NO prodrug hypothesis.