Changes in electrical activity of myometrium during intrauterine distribution of rat blastocysts and after prazosin administration
In the early pregnant rat, electrical activity of the myometrium consisted of regular bursts of spike potential, which appeared well propagated on Day 2 of pregnancy. During Day 3, there was a gradual disappearance of propagated activity. Concomitantly, there was a 7-fold increase (P < 0\m=.\001) of uterine progesterone concentrations. At this stage, mean duration of bursts was 15\m=.\2\ m=+-\0\m=.\9sec and intervals of complete quiescence between bursts were 84\m=.\2\m=+-\7\m=.\0sec. At 10:00
... m=.\0sec. At 10:00 h on Day 4, there were peaks in the uterine concentrations of oestradiol and progesterone, + 36% and + 654%, respectively, compared with values on Day 2 (P < 0\m=.\05). Between 10:00 and 20:00 h on Day 4, EMG activity exhibited a rapid and transient rise: bursts were of longer duration at the utero-tubal end of the horn (+ 60%, p < 0\m=.\05) with an increased amplitude of spike potentials ( + 67% and +90% respectively at the tubal and cervical ends of the uterus, P < 0\m=.\05). The administration of prazosin depressed EMG activity reversibly in a dose-dependent manner with maximal inhibition at about 2\p=n-\3h later. It is concluded that the changes observed during EMG recordings are relevant to the intrauterine distribution of blastocysts and related to changes in the steroidal environment and/or to catecholamine effects via \g=a\1-adrenoceptors.