Effect of bromocriptine on uterine contractility in near-term pregnant rats

Treatment of pregnant albino rats at gestation day 9 with the dopamine agonist, bromocriptine, in a dose of 0.7 mg kg-1 day-1, i.p. for 11 days produced a significant increase in the normal uterine contractions both in vitro and in vivo. The increase in frequency (F), amplitude (A) and area under the curve (AUC) in the in vitro experiment amounted to 35, 80 and 58%, respectively; while the increase in F and A in the in vivo experiment was 36 and 25%, respectively, in comparison with the corresponding control group. Addition of oxytocin (5x10(-12)-4x10(-11) m) to the uterus isolated from rats pretreated with bromocriptine resulted in marked uterotonic effect (24, 35 and 49% increase in F; 25, 35 and 46% increase in A and 42, 62 and 122% increase in AUC of contractions). Also, the in vivo experiment showed that an injection of oxytocin at the time of investigation (0.125-1.0 I.U. kg-1, i.v.) into rats pretreated with bromocriptine caused a marked increase in F (33, 40 and 81%) and A (33, 37 and 75%) of uterine contractions compared to the values of bromocriptine-treated animals. These results indicate that bromocriptine should be used with caution during pregnancy. In addition, this must be considered when using oxytocin during delivery of females pretreated with bromocriptine.