Effects of nitric oxide donors on non-pregnant and pregnant rat uterine and aortic smooth muscle.

OBJECTIVE: To compare the effects of nitric oxide (NO) donors, diethylamine/nitric oxide (DEA/NO) and nitroglycerin (NTG), on isolated uterine and aortic tissues from non-pregnant, mid and late pregnant rats. METHODS: The uterus and thoracic aorta were obtained from non-pregnant (estrous cycle) and pregnant Sprague-Dawley rats on day 14 and day 21. The uterine and aortic rings were incubated in organ chambers filled with Krebs-Henseleit solution bubbled with 5% CO2 in air for isometric tension recordings. Cumulative concentration-response relationships to DEA/NO and NTG were obtained in the aortic rings contracted with phenylephrine and in spontaneously contracting uterine rings. RESULTS: The sensitivity and the maximal inhibitory effects of DEA/NO did not differ in aortic tissues of any group. DEA/NO-induced Maximal inhibition of spontaneous contractions of uterine tissues from mid-pregnant rats was greater (although not significantly) than in the tissues from non-pregnant animals (with similar sensitivity), but it was significantly depressed in tissues from late pregnant rats. The sensitivity to and maximal inhibitory effects of NTG were less in aortic tissues from late pregnant versus mid-pregnant and non-pregnant rats. In uterine tissues from late pregnant rats the effect of NTG was negligible. The inhibitory action of both NO donors was much more pronounced in aortic versus uterine tissues. CONCLUSIONS: Uterine smooth muscle is less sensitive than vascular smooth muscle to NO. Uterine smooth muscle from late pregnant animals demonstrates refractoriness to both DEA/NO and NTG, while vascular smooth muscle from late pregnant animals demonstrates refractoriness to NTG, but not to DEA/NO.