Utero-ovarian venous concentrations of prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) following PGE2 intrauterine infusions

Expression of enzymes of cyclooxygenase pathway and secretion of prostaglandin E2 and F2α by porcine myometrium during luteolysis and early pregnancy

Past studies of uterine prostaglandin (PGs) and pig reproduction have focused on endometrial rather than myometrial PGs. This study documents the synthesis and secretion of myometrial prostaglandins (PGs) in pigs and the involvement of oxytocin (OT) in these processes. Cyclooxygenase-2 (COX-2) expression was similar in myometrial explants from cyclic and pregnant pigs (days 14-16) and OT (10(-7) M) in vitro significantly increased COX-2 protein regardless of reproductive state. Basal expression of prostaglandin E2 synthase (PGES) was higher during pregnancy than during luteolysis. Conversely, prostaglandin F synthase (PGFS) was highest during luteolysis and lower in myometrium from gravid animals. OT had no influence on the expression of PGES and PGFS. In another tissue culture experiment, myometrial slices produced more PGE2 than PGF2alpha regardless of reproductive state of the female. OT stimulated PGE2 production in myometrium harvested during luteolysis and increased PGF2alpha production in all tissues examined. Progesterone (P4; 10(-5) M) blocked stimulatory effect of OT on myometrial PG release. Myometrial OTr mRNA was higher (P=0.03) during luteolysis than during pregnancy.

IN CONCLUSION

(1) oxytocin increases myometrial COX-2 expression, but does not influence the expression of terminal enzymes of PGs synthesis (PGES and PGFS); (2) porcine myometrium preferentially produces PGs during early pregnancy and secretes more PGE2 than PGF2alpha; (3) myometrial OT and OTr support secretion of PGs from myometrium during luteolysis.

Prostaglandins and reproduction in female farm animals

Prostaglandins impact on ovarian, uterine, placental, and pituitary function to regulate reproduction in female livestock. They play important roles in ovulation, luteal function, maternal recognition of pregnancy, implantation, maintenance of gestation, microbial-induced abortion, parturition, postpartum uterine and ovarian infections, and resumption of postpartum ovarian cyclicity. Prostaglandins have both positive and negative effects on reproduction; they are used to synchronize oestrus, terminate pseudopregnancy in mares, induce parturition, and treat retained placenta, luteinized cysts, pyometra, and chronic endometritis. Improved therapeutic uses for prostaglandins will be developed when we understand better their involvement in implantation, maintenance of luteal function, and establishment and maintenance of pregnancy.

Local transfer of prostaglandin E2into the ovary and its retrograde transfer into the uterus in early pregnant sows

This study was designed to establish (a) whether prostaglandin E2 (PGE2) can reach the ovary and oviduct by a local pathway and what is the contribution of lymphatic vessels to this transfer, and (b) whether PGE2 can permeate from venous and lymphatic vessels of the mesometrium to arterial blood and be delivered to the uterine horn during maternal recognition of pregnancy in gilts. The reproductive tract was excised from gilts (n = 10) on day 14 after mating. The uterine horn was isolated with the ovary and broad ligament and perfused with warmed and oxygenated autologous blood. A total dose of 5.5 x 10(7) disintegrations per min (d.p.m.) (49 ng) [3H]PGE2 was infused into the small branches of the uterine vein on the broad ligament or into the lymphatic vessels. Frequent blood samples were collected from the branch of the uterine artery and from the venous effluent. Tissue samples were collected from the uterine horn, the ovary and the broad ligament. The concentration of [3H]PGE2 was significantly higher in the ovary (P < 0.001), oviduct (P < 0.01), endometrium (P < 0.01), myometrium (P < 0.001) and mesometrium (P < 0.001) after infusion of [3H]PGE2 into lymphatic vessels than into the branches of the uterine vein. In contrast, the concentration of [3H]PGE2 was significantly higher in arterial blood supplying the uterine horn (P < 0.01) and in the venous effluent (P < 0.001) after infusion of [3H]PGE2 into the branches of the uterine vein than into lymphatic vessels. These results demonstrated local transfer of [3H]PGE2 into the ovary, oviduct and uterine horn from lymphatic and venous vessels of the mesometrium. However, the efficiency of this transfer was considerably higher after infusion into lymphatic vessels than into branches of the ovarian vein. We conclude that the lymphatic pathway is a fundamental mechanism in the local transfer of PGE2 from the uterus to the ovary and oviduct during early pregnancy in the pig.

Effect of LH on prostaglandin F2α and prostaglandin E2 secretion by cultured porcine endometrial cells

LH appears to be a potent stimulator of the release of endometrial prostaglandins (PGs) in the pig. The aim of the present studies was to examine the effect of LH on PGF2αand PGE2secretion by cultured porcine endometrial cells on days 10–12 and 14–16 of the oestrous cycle and to compare its action with oxytocin. A time-dependent effect of LH (10 ng/ml) on PGF2αrelease from luminal epithelial and stromal cells on days 10–12 was observed (experiment 1). The highest increase in PGF2αsecretion in response to LH was detected in stromal cells after 6 h of incubation (P< 0.001). Epithelial cells responded to LH after a longer exposure time (P< 0.01). A concentration-dependent effect of LH (0.1–100 ng/ml) on PGF2αrelease from stromal cells was examined after 6 h and from epithelial cells after 12 h (experiment 2). Effective concentrations of LH were 10 and 100 ng/ml. LH (10 ng/ml) and oxytocin (100 nmol/l) affected PGF2αand PGE2secretion from endometrial cells on days 10–12 and 14–16 of the oestrous cycle (experiment 3). LH stimulated PGF2αsecretion from both cell types and its action was more potent on days 10–12. LH induced PGE2release, especially in epithelial cells on days 14–16. A stimulatory effect of oxytocin on PGF2αwas confirmed in stromal cells, but this hormone was also shown to enhance PGE2output. These results indicated that LH, like oxytocin, a very effective stimulator of PGF2αrelease, could play an important role in the induction of luteolysis.

Total content of prostaglandin F2 alpha in the endometrium and myometrium from various sections of the porcine uterine horn during the estrous cycle

The purpose of this study was to determine effects of various stages of the estrous cycle on the content and concentration of PGF2 alpha in endometrium and myometrium in different segment of the uterine horn and whether different methods of expressing PGF2 alpha data would affect interpretation of results. Total content of PGF2 alpha in the endometrium and myometrium of the entire uterine horn, and PGF2 alpha concentrations in five sections of uterine horn each of equal length (1 to 5 beginning from the ovarian end) were measured in gilts during three different phases of the estrous cycle: the early luteal phase (Days 3 to 6 of the estrous cycle), mid-luteal phase (Days 9 to 12), and during luteolysis (Days 15 to 18). The total content of PGF2 alpha in the early and mid-luteal phases was similar (P > or = 0.05) in both the endometrium and myometrium. During luteolysis the content of PGF2 alpha in the endometrium and myometrium increased 7-fold and 4-fold, respectively, when compared to the early luteal phase. The distribution of PGF2 alpha was similar throughout the length of the uterine horn and this did not change during the phases of the cycle studied. The PGF2 alpha concentrations during different phases of the estrous cycle differed with methods of expressing the data i.e. ng g-1 tissue, ng mg-1 DNA, ng mg-1 protein, but the relative differences were not appreciably altered.

Luteal maintenance during early pregnancy in the pig: role for prostaglandin E2

We previously demonstrated that prostaglandin E2 (PGE) directly inhibits prostaglandin F2 alpha (PGF)-induced regression of individual pig corpora lutea (CL) in a dose dependent manner. The present experiments were conducted to 1) characterize and compare uterine secretion of PGE and PGF during the estrous cycle and early pregnancy and 2) evaluate the local effect of the conceptus on uterine prostaglandin secretion and associated CL function in unilaterally pregnant pigs. In Experiment 1, utero-ovarian venous blood samples were collected from two nonpregnant and two pregnant gilts at 3-h intervals from day 10 through 16 (first day of estrus or mating = day 0) for quantitation of uterine PGE and PGF secretion. In Experiment 2, gilts (n = 4) were made unilaterally pregnant on day 2, and utero-ovarian venous catheters were placed bilaterally to determine if differences in PGE and/or PGF secretion might account for the known luteotrophic/antiluteolytic effect of the gravid uterine horn on the CL of the ipsilateral ovary. During the estrous cycle (Experiment 1), pulsatile secretion of PGF increased markedly on day 13 and continued to increase through day 16. PGE secretion also increased from day 13 to 16 of the estrous cycle; however, concentrations of PGE remained at least 3-fold lower than those of PGF. In contrast to changes in non-mated gilts, prostaglandin secretion in mated gilts peaked earlier (day 11-12), with PGE predominating. Thereafter, both PGE and PGF secretion declined to basal levels where they remained through day 16 of pregnancy. During unilateral pregnancy (Experiment 2), PGF concentration in nongravid and gravid horns was similar (P > 0.8). In contrast, PGE concentrations were greater (P < 0.06) in utero-ovarian venous blood draining the gravid uterine horn. This increase in PGE was associated with enhanced CL function on the ipsilateral ovary as evidenced by an elevated progesterone content and concentration as well as increased CL weights. These data are consistent with a role for conceptus-associated increases in uterine PGE secretion in the local stimulation of luteal function during early pregnancy in the pig.