Mechanisms underlying the impairment of endothelium-dependent relaxation in the pulmonary artery of monocrotaline-induced pulmonary hypertensive rats.
1. It has been reported that endothelium-dependent relaxation is impaired in pulmonary hypertensive vessels. The underlying mechanisms for this phenomenon, however, have not yet been identified. In this study, the mechanisms responsible for decreased endothelium-dependent relaxation in the pulmonary artery isolated from monocrotaline (MCT)-induced pulmonary hypertensive rat (MCT rat) were examined. MCT (60 mg kg-1), or its vehicle was administered by a single subcutaneous injection to 6-week-old male Sprague Dawley rats. 2. Endothelium-dependent relaxation induced by carbachol or ionomycin in the MCT rat artery was significantly smaller than that in vehicle-treated rat (control rat) artery. Cyclic GMP levels, measured by enzyme-immunoassay, under resting or stimulation with carbachol or ionomycin were also smaller in the MCT rat artery. However, sodium nitroprusside-induced cyclic GMP accumulation in the endothelium-denuded artery was similar in control and MCT rats. These results suggest that MCT treatment decreases endothelial nitric oxide (NO) production. 3. Resting endothelial Ca2+ levels ([Ca2+]i) in the fura-PE3-loaded MCT rat artery, were not different from those in the control rat. However, the increase in endothelial [Ca2+]i elicited by carbachol was attenuated in the MCT rat. 4. In quantitative RT - PCR analysis, the expression of mRNA encoding endothelial NO synthase was rather increased in the MCT rat artery, suggesting an up-regulation of eNOS expression. 5. These results provide evidence that impaired NO-mediated arterial relaxation in the MCT rat is due to dissociation between eNOS expression and NO production. This dissociation may be derived from an inhibition of receptor-mediated Ca2+ metabolism and also from the apparent decrease in Ca2+ sensitivity of eNOS.
Nakazawa
H
H
Department of Veterinary Pharmacology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
Hori
M
M
Ozaki
H
H
Karaki
H
H
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D006152:Cyclic GMP / Q000378:metabolism; D004730:Endothelium, Vascular / Q000378:metabolism / Q000502:physiology*; D006976:Hypertension, Pulmonary / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D016686:Monocrotaline; D018721:Muscarinic Agonists / Q000494:pharmacology; D009126:Muscle Relaxation / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000378:metabolism / Q000503:physiopathology*; D009569:Nitric Oxide / Q000096:biosynthesis; D019001:Nitric Oxide Synthase / Q000096:biosynthesis / Q000235:genetics; D052250:Nitric Oxide Synthase Type III; D009929:Organ Size / Q000187:drug effects; D011651:Pulmonary Artery / Q000378:metabolism / Q000503:physiopathology*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction
D018721:Muscarinic Agonists; D012333:RNA, Messenger; D009569:Nitric Oxide; D016686:Monocrotaline; D002217:Carbachol; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D006152:Cyclic GMP; D002118:Calcium