Effect of pge2 on uterine contractility and tone in mares

A technique for transvaginal, ultrasound-guided intrauterine injection was developed. After preliminary study using different approaches, the procedur e was successful in 24 of 25 (96%) mares, based on detecting fluid in the u terine lumen during and after the injection. The technique was used to stud y the effect of PGE2, reportedly produced by the embryonic vesicle, on uter ine contractility on Day 12 (Day 0=ovulation). Uterine contractility was sc ored (1=minimal, 4=maximal) every 10 min for 1 h and every 30 min for the n ext hour by a continuous 1-min ultrasound examination of a longitudinal sec tion of the uterine body without knowledge of group. In Experiment 1, the m ain effect of group (1-mL vehicle, n=6; 0.25 mu g PGE2, n=7) tended to be s ignificant (P<0.09), and the effect of time was significant (P<0.008). The mean score was higher for the PGE2 group (2.0+/-0.1) than for the vehicle g roup (1.7+/-0.1). An increase in contractility occurred between 0 and 5 min in the vehicle group (P<0.0004) and between 0 and 10 min in the PGE2 group (P<0.04). In Experiment 2, there was a tendency (P<0.08) for effect of gro up (control without injection, n=6; 1-mL vehicle, n=6; 0.025 mu g PGE2, n=6 ). The PGE2 group (2.0+/-0.1) was different from the vehicle group (1.6+/-0 .1) and the control group (1.6+/-0.1). An increase in contractility occurre d between 0 and 20 min in the PGE2 group, and the changes were not signific ant in the other groups. However, scores were higher in the PGE2 group befo re treatment, and there were no significant effects when data were converte d to percentage changes. The results for an effect of intrauterine treatmen t of PGE2 on uterine contractility are considered uncertain because of the transient increase in contractility from vehicle injections in Experiment 1 and the higher score in the PGE2 group before treatment, with no significa nt differences in percentages in Experiment 2. Indirectly, however, an effe ct of PGE2 was suggested by a shorter (P<0.05) period of detectability of i ntrauterine fluid in the PGE2 groups (21+/-31 min) than in the vehicle grou ps (50+/-42 min). The shorter period was attributable to greater dispersion of the fluid as a result of increased contractility. In Experiment 3, PGE2 (10 mg, n=5) and vehicle (4 mL, n=5) were given intravenously. In addition to uterine contractility, uterine tone was scored (1=minimal, 4=maximal) b y transrectal digital compression. The main effect of group was significant (P<0.03) for uterine contractility score, which increased between 0 and 20 min after PGE2 injection. The time effect and interaction were highly sign ificant (P<0.0001) for uterine tone score, and tone increased in the PGE2 g roup between 0 and 20 min after injection. The results indicated that PGE2 should be considered as a potential stimulator of both uterine contractions and uterine tone during the time of embryo mobility in mares. (C) 1998 by Elsevier Science Inc.