Effect of oxytocin and estradiol on uterine prostaglandin release in nonpregnant and early-pregnant ewes.
The effects of exogenous oxytocin (OT) and estradiol-17 beta (E2) on plasma concentrations of prostaglandin (PG) E2 and 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) were investigated on Day 14-15 (NP) of the estrous cycle and Days 14-16 (PI) and 21-25 (EP) of pregnancy in the ewe. Basal concentrations of PGFM were significantly elevated in utero-ovarian venous (UOV) plasma on Day 14 of pregnancy (4.05 +/- 0.81 nM, mean +/- SEM) compared to that observed on Day 14 of the cycle or Days 21-25 of pregnancy (2.29 +/- 1.3 nM and 1.06 +/- 0.56 nM, respectively). PGFM release increased significantly following intera-arterial bolus injections of 50, 500, and 5000 mU OT at 2-h intervals in all experimental groups. There was no significant difference in area and peak height of the PGFM response between the 3 groups studied. The time to peak PGFM response was, however, significantly longer in the PI group. No significant changes in concentration of PGFM were observed in any experimental group following 1-h infusions of E2 at 5, 50, and 500 pmol/min. Long-term (15-18 h) infusion of E2 at 83 pmol/min increased the peak height of the OT-induced PGFM response at both stages of gestation studied. PGE2 concentrations in UOV plasma were less than 0.05 nM in all samples studied. These results demonstrate that PG release can be induced in response to OT during the period in which ovine trophoblastic protein-1 (oTP-1) is released by the conceptus. During pregnancy, oTP-1 does not appear to inhibit the E2 induction of uterine OT receptors.
Burgess
K M
KM
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Ralph
M M
MM
Jenkin
G
G
Thorburn
G D
GD
D000818:Animals; D004334:Drug Administration Schedule; D004958:Estradiol / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D005260:Female; D010121:Oxytocin / Q000494:pharmacology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011453:Prostaglandins / Q000096:biosynthesis* / Q000097:blood; D012016:Reference Values; D012756:Sheep; D014599:Uterus / Q000187:drug effects / Q000502:physiology*
D011453:Prostaglandins; D004958:Estradiol; D010121:Oxytocin