Effects of Intermittent and Continuous Oxytocin Exposure on Myometrial Contractile Activity in Term-Pregnant Rats In Vitro.

Continuous oxytocin exposure to augment labor contractions may cause receptor desensitization and further reduce the uterine response to oxytocin, resulting in an increased risk of uterine atony. This study aimed to investigate and compare the uterine response to continuous and intermittent oxytocin stimulation. We hypothesized that intermittent brief episodes of oxytocin separated by recovery periods rather than continuous oxytocin application improves subsequent uterine contractions. Myometrial strips were isolated from term-pregnant rats (22 days of gestation; n = 11), mounted in tissue bath chambers, and exposed to continuous oxytocin (5 nM) for 2 h or 6 repeated episodes of 10-min oxytocin exposure (5 nM) separated by 10 min of recovery period in Krebs solution. Contractile parameters (force amplitude, frequency, and integral force) significantly decreased during continuous oxytocin exposure compared with control (n = 11; P < 0.01). Interestingly, myometrial contractility significantly increased during subsequent short intermittent oxytocin exposure which was sustained for 6 h compared with control or continuous exposure (n = 11; P < 0.01). Brief intermittent oxytocin stimulations resulted in better uterine response and improved contractile force than continuous exposure, which may be attributed to attenuation of receptor desensitization or recovery of oxytocin receptor function following intermittent exposure. These findings would help maintain adequate strong contractions to avoid postpartum bleeding.