Contractility of late pregnant rat myometrium is refractory to activation of soluble but not particulate guanylate cyclase

OBJECTIVE: Our purpose was to compare the effects of agents activating part iculate or soluble guanylate cyclases on the spontaneous contractile activi ty of the isolated pregnant rat uterus. STUDY DESIGN: Uterine rings from midpregnant (14-day) and late pregnant (21 -day) rats were suspended in organ chambers to record spontaneous contracti le activity. Concentration-response curves were obtained for the following natriuretic peptides: atrial, brain, and C-type; concentration-response cur ves were also obtained for diethylamine nitric oxide, 3-morpholino-sydnomin ine, and authentic nitric oxide. RESULTS: All 3 natriuretic peptides inhibited spontaneous uterine contracti ons equally at midgestation and late gestation. The inhibitory effects of t he nitric oxide donors diethylamine nitric oxide, 3-morpholino-sydnominine, and authentic nitric oxide were attenuated in uterine tissues from animals in late stages of pregnancy. CONCLUSION: Agents activating either soluble or particulate guanylate cycla se inhibit contractions of uterine rings from midgestation rats, whereas th e effects of soluble guanylate cyclase are attenuated at late pregnancy. Th us spontaneous uterine contractions are under the control of both soluble a nd particulate guanylate cyclases; the former is dependent on gestational a ge but the latter is not.