Myometrial activity ans plasma progesterone and oxytocin concentrations in cycling and early-pregnant ewes

L. Rhodes, P. W. Nathanielsz

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Myometrial activity and plasma progesterone (P) and oxytocin (OT) were measured in erly pregnant (n = 5) and cycling (n = 5) ewes. Electromyograph (EMG) leads and jugular and inferior vena cava (IVC) catheters were surgically plaed in ewes about 1 wk before data collection. When ewes returned to estrus, they were bred to either an intact or vasectomized ram. Continuous EMG data were collected, and blood samples were collected twice daily from day of estrus (Day 0) until Day 18. Ewes bred with an intact ram were checked surgically for pregnancy on Day 20. Computerized, quantitative analysis of EMG events showed no difference in signal from the right to the left uterine horns, and no differences between pregnant and cycling ewes (p < 0.05) until Days 14-18 when nonpregnant ewes returned to estrus and had increased EMG activity. The mean number of EMG events 180-900 s in length decreased in pregnant ewes, but this differncer was not significant (p < 0.05). Jugular plasma progesterone (P) levels confirmed corpus luteum (CL) formation in all ewes, and no differences in P between pregnant and nonpregnant ewes were measured until Days 14-18, when cycling ewes underwent luteolysis and pregnant ewes maintained CL. IVC plasma oxytocin concentrations were increased in pregnant ewes compared to concentrations in nonpregnant ewes on Days 5-13 (p < 0.05), and the difference was largest at Day 6 (x̄ ± SEM pg/ml: pregnant = 68.7 ± 13.9, nonpregnant = 30.9 ± 19.9). In summary, pregnant and nonpregnant ewes had similar P concentrations and EMG activity until Days 14-18, when nonpregnant ewes underwent luteolysis and showed increased EMG activity. Pregnant ewes had increased plasma OT levels, which did not result in measurable increases in uterine EMG activity.

Original languageEnglish (US)
Pages (from-to)834-841
Number of pages8
JournalBiology of reproduction
Issue number5-6
StatePublished - 1990
Externally publishedYes

ASJC Scopus subject areas

  • Reproductive Medicine
  • Cell Biology


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