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Objective: This study aimed to examine the role of nitric oxide
(NO) as mediator of non-adrenergic non-cholinergic (NANC) system in coronary arteries of sheep. Design: In vitro study.
Samples: Sixtheen hearts of sheep aged 8-10 months.
Procedure: In vitro experiments were conducted using isolated
tissue preparations. The isolated tissues were obtained from the left coronary arteries of hearts collected from lambs aged 8-10 months. They were mounted in organ bath system to record the
isometric forces by a physiograph. The tissues were suspended in
37CC Krebs’ solution bubbled with 95% oxygen and 5% CO2. Four experimental groups were prepared and the isolated tissues were treated with 5x l0 M acetyl choline (Ach), an inhibitor of NO synthethase, nitro- L- arginine methyl ester (L-NAME) and L- arginine (L-arg) as precursor for NO.
Statistical analysis: Student t-test. Results: The tissues treated with Ach contracted for a short time before they were relaxed permanently. The relaxation induced by
Ach was dependent on the viability of endothelium. The pretreatment
of tissues with L-NAME, not only decreased the relaxation induced
by Ach, but also significantly (P<0.02) increased the level of tissue
contraction. It was also found that L-arg was significantly able to decrease the primary contraction induced byAch (P<0.Ol) as well as reducing the effects of L-NAME on coronary arteries of sheep
and the results of this study further suggest that there are different
types of muscarinic receptors in sheep coronary arteries.
Conclusion: The results of this study showed that a NANC system mediated by No is present in sheep coronary arteries and also
approved the findings that there are dufferent Achreceptors in these
arteries.