Complex effects of imatinib on spontaneous and oxytocin-induced contractions in human non-pregnant myometrium

Human myometrium includes two important cell populations involved in its contractility: smooth muscle fibers and interstitial cells. The pacemaking mechanism is not yet identified, but it is possible that myometrial smooth muscle cells contract in response to a signal generated by c-kit positive interstitial cells. The aim of this study was to investigate the effects of imatinib as a c-kit receptor antagonist on the spontaneous or oxytocin (OT) induced contractions of human non-pregnant myometrium in vitro. Myometrial strips were obtained from non-pregnant women (reproductive age) undergoing hysterectomy for benign indications. The strips were suspended in organ baths for recording of isometric tension. Imatinib effects were assessed on spontaneous contraction and after preexposure to OT.Direct exposure of myometrial strips to imatinib inhibits both amplitude and frequency of contractions (80-320 μM) in a dose dependent manner. Amplitude reverted back to 90% of the baseline amplitude by consequent addition of imatinib (until 480 μM). Total inhibition of myometrial contraction was obtained after addition of OT 60 nM. If myometrium was pre-exposed to OT (320 nM), imatinib 80-160 μm increased amplitude, while decreasing frequency. These data provide evidence that telocytes may be involved as modulators of the spontaneous contractions of the non-pregnant human uterus, via a tyrosine-kinase independent signaling pathway.     

The effect of acetylsalicylic acid and indomethacin on the catecholamine- and oxytocin-induced contractility and prostaglandin (6-keto-PGF1 alpha, PGF2 alpha)-production of human pregnant myometrial strips

The effects of acetylsalicylic acid (ASA) and indomethacin (IND) on the epinephrine and oxytocin stimulated contractility and prostaglandin (6-keto-PGF1 alpha, PGF2 alpha) production of superfused myometrial strips from the pregnant human uterus at term are reported. Without preincubation in ASA or IND epinephrine dose-dependently (10 ng/ml to 1 microgram/ml) stimulated the contractility and significantly increased the PG-release of the myometrial strips. The epinephrine induced increase in contractility was correlated to a higher increase in PGF2a production and a decreased 6-keto-PGF1 alpha/PGF2 alpha ratio (5.4 to 1.8). Superfusion of oxytocin increased myometrial contractions and PGF2 alpha release according to dose (3-12 microU/ml). However, 6-keto-PGF1 alpha production was not affected by oxytocin. Myometrial strips preincubated with ASA (100 micrograms/ml) or IND (10 micrograms/ml) demonstrated little spontaneous activity and the PG production was below the detection limit of the RIA. The stimulating effect of epinephrine and oxytocin on the contractility and PGF2 alpha release of the myometrial strips was inhibited significantly. During continuous superfusion of the ASA and IND preincubated myometrial strips with Tyrode's solution the inhibitory effect on spontaneous, epinephrine-, and oxytocin-stimulated contractility and PGF2 alpha release gradually declined over a period of 2 hours. This decrease of the inhibitory effect was more significant in ASA preincubated specimens. Our results demonstrate that spontaneous, epinephrine-, and oxytocin-stimulated contractility and PG release of human myometrial strips can be inhibited by ASA and IND and that this inhibitory effect is reversible. Furthermore our results suggest that in pregnant human myometrium the inhibition of PGF2 alpha production by ASA and IND is more pronounced than that of 6-keto-PGF1 alpha (PGI2).     

In vivo oxytocin release from microdialyzed bovine corpora lutea during spontaneous and prostaglandin-induced regression

The release of luteal oxytocin during spontaneous and prostaglandin-induced luteolysis was investigated in cows. A continuous-flow microdialysis system was used in 11 cows to collect dialysates of the luteal extracellular space between Days 12 and 24 postestrus. Seven cows were untreated and were expected to exhibit spontaneous luteolysis during sampling, whereas 4 cows received prostaglandin F(2alpha) (PGF(2alpha)) systemically between Days 13 and 15 to induce luteolysis during sampling. Oxytocin was detectable in the dialysate of all cows before Day 16 postestrus and occurred as 2 or 3 discrete pulses per 12-h sampling period. For non-PGF(2alpha)-treated cows, dialysate oxytocin content began to decline spontaneously on Day 15 postestrus and was undetectable by Day 17 postestrus. Oxytocin decay curves preceded onset of serum progesterone decline by at least 72 h and were not related temporally with onset of progesterone decline within cow. Exogenous PGF(2alpha) (25 mg, i.m.) produced a 10-fold increase in dialysate oxytocin within 1 h (1.9 +/- 0.3 pg/ml to 20.8 +/- 3.0 pg/ml; P < 0. 01). Dialysate oxytocin then declined to pretreatment concentrations within 2 h and was undetectable within 8 h posttreatment. A second PGF(2alpha) injection given 20 h after the first did not result in a measurable increase in dialysate oxytocin, probably because luteolysis was underway. Although robust luteal oxytocin release was observed after treatment with a pharmacological dose of PGF(2alpha), the lack of detectable oxytocin secretion during spontaneous luteolysis suggests that the contribution of luteal oxytocin in the cow may be less than that proposed for the ewe.     

Clarithromycin inhibits myometrial contractions in isolated human myometrium independent of stimulus

Erythromycin has a well-known dual effect on the contractility of the gastrointestinal system and recently has also been shown to inhibit contractions of the rat myometrium. The aim of the present study was to investigate the effects of clarithromycin on oxytocin, prostaglandin F2alpha (PGF2alpha) and KCl-induced contractions of human myometrium in vitro. Myometrial strips were obtained from pregnant women undergoing elective Cesarean section and the strips were suspended in a jacketed organ bath filled with Krebs solution at 37 degrees C (pH 7.4) and continuously aired with 95% oxygen and 5% carbon dioxide. Isometric contractions were measured using a force displacement transducer. Oxytocin, PGF2alpha, KCl and clarithromycin were applied to the tissue bath and the amplitude and frequency of contractions were evaluated at 20-min intervals. Freidmann analysis of variance, Kruskal Wallis and Wilcoxon Rank tests were used for statistical analysis of the data. Clarithromycin dose dependently inhibited the amplitude of contractions independent of the stimulus. Pre-treatment with apamin prevented clarithromycin-induced effects on amplitude and frequency of contractions. We conclude that the macrolide antibiotic clarithromycin may have a direct inhibitory effect on contractions of human myometrium.     

Uterine and placental prostaglandins and their modulation of oxytocin sensitivity and contractility in the parturient uterus

The parturient uterus develops a markedly enhanced sensitivity to the uterotonic action of oxytocin (OT). The mechanism leading to this enhanced OT sensitivity is not known. Our previous work suggested that prostaglandins (PGs) may be involved. To define the relationship between OT sensitivity and uterine PG production, we measured uterine sensitivity to OT by a quantitative dose-response procedure in rats on Days 19, 20, 21 and 22 of pregnancy and monitored uterine and placental tissue concentrations of PGF2 alpha and PGE2. In addition, we determined the effects of inhibition of endogenous PG synthesis on OT sensitivity and uterine contractility. We found that both OT sensitivity and spontaneous contractility are positively related to uterine PGF2 alpha production. An abrupt increase in OT sensitivity was observed on Days 21 and 22 of pregnancy. The increase in OT sensitivity was coincidental with the marked increase in PGF2 alpha production in the uterus on Days 21 and 22 of pregnancy. Suppression of in vivo PG synthesis caused a reduction in both spontaneous uterine contractility and OT-induced contractions. Uterine PGE2 concentrations and release were 3-5 times lower than PGF2 alpha. There were no significant fluctuations of uterine PGE2 concentration measured on these last 4 days of gestation. Placental PG levels were also found not to be related to uterine contractility. Placental PGE2 levels were higher than PGF2 alpha and may play a regulatory role in placental perfusion. However, placental PGs did not vary with gestational age.     

Dual actions of prostacyclin (PGI2) on the rat pregnant uterus.

Using strips of rat pregnant uterus, treated with indomethacin to suppress spontaneous contractility, the oxytocic activity of prostacyclin was compared with other prostaglandins. A prostacyclin concentration of 32 ng/ml elicited uterine contractions in all experiments. In this respect prostacyclin was 80 times more active than 6-oxo-PGF1 alpha but less active than PGE2 or PGF2 alpha. Apart from a direct stimulant effect, prostacyclin also exhibited an indirect potentiating action. In threshold concentrations prostacyclin caused a 3-fold potentiation of threshold doses of oxytocin. A lesser 1.5-fold potentiation of PGE2 alpha was also observed. The implications of these findings in relation to prostacyclin playing a role in parturition are discussed.     

Effects of calcium channel blocker, mibefradil, and potassium channel opener, pinacidil, on the contractile response of mid-pregnant goat myometrium

The present study was undertaken to investigate the in vitro influence of mibefradil, a calcium channel blocker, and pinacidil, a potassium channel opener, on pregnant goat myometrial spontaneous rhythmic contractility and contractions induced with the agonist, oxytocin. Longitudinal strips from the distal region of uterus, collected from goats at midgestation, were mounted in an organ bath for recording isometric contractions. Mibefradil (10(-8)-10(-4) M) or pinacidil (10(-10)-10(-4) M), added cumulatively to the bath at an increment of 1 log unit, caused concentration-dependent inhibition of the spontaneous rhythmic contractions of isolated uterine strips. The rhythmic contraction was, respectively, abolished at 100 and 10 microM concentrations of mibefradil and pinacidil. In a concentration-dependent manner, mibefradil (1 and 10 microM) antagonized the contractions elicited with oxytocin (10(-5)-10(-2) IU). Pretreatment of uterine strips with glibenclamide (10 microM), a selective KATP channel blocker, caused a rightward shift of the concentration-response curve of pinacidil with a concomitant decrease in its pD2 value. Pinacidil (0.3, 1 and 3 microM), in a concentration-related manner, antagonized the oxytocin (10(-5)-10(-2) IU)-induced contractile response. The inhibition of spontaneous rhythmic contractions and antagonism of oxytocin-induced contraction by mibefradil in the pregnant goat myometrium may be related to the antagonism of voltage-dependent Ca2+ channels, while by pinacidil suggests that KATP channel could be a therapeutic target for tocolysis.     

Inhibitory effect of GnRH on isolated rat uterine muscle contractility

The effect of GnRH upon uterine contractions of both non-pregnant and pregnant rats was examined in vitro. In the non-pregnant rat uterus, GnRH inhibited in a concentration-and-time dependent manner the contractions induced by acetylcholine and oxytocin, but not those caused by bradykinin and angiotensin II. GnRH also inhibited the rhythmic contractions induced by oxytocin in uterine strips from late pregnant rats. These findings show that GnRH has a direct inhibitory effect on the rat uterine contractions, suggesting that GnRH-like substances may exert modulatory influences upon rat uterine contractility.     

Temporal changes in serum prostaglandin F2alpha and oxytocin in dairy cows with short luteal phases after the first postpartum ovulation

Luteolysis in the cow depends upon an interaction between prostaglandin F(2alpha) (PGF(2alpha)) and oxytocin. The objectives of our study were 1) to determine oxytocin concentrations in postpartum dairy cows and 2) to identify the temporal relationship between oxytocin and PGF(2alpha) release patterns during luteolysis in normal and abbreviated estrous cycles in the postpartum period. Serum oxytocin and PGF(2alpha) metabolite (PGFM) concentrations from nine cows which had short estrous cycles (< 17 d) were compared with those of six cows which had normal estrous cycles. Serum basal oxytocin concentrations in short estrous cycle cows (23.7 to 31.1 pg/ml) were higher (P<0.05) than those of normal estrous cycle cows (14.6 to 19.8 pg/ml). Oxytocin concentrations increased to peak values in both short and normal cycle cows, during luteolysis. Basal PGFM concentrations (112.2 to 137.4 pg/ml) were higher in cows with short cycle (P<0.05) than in cows with normal cycles (62.9 to 87.5 pg/ml). The increase in PGFM concentrations during luteolysis was significant in both normal cycle and short cycle cows (P<0.05). Increases in serum PGFM concentrations were always associated with increases in serum oxytocin concentrations in normal cycle and short cycle cows and the levels decreased simultaneously before the subsequent estrus. Results support the idea of a positive relationship between PGF(2alpha) and oxytocin concentration during the estrous cycle as well as a possible synergistic action of these hormones in the induction of luteolysis in dairy cattle.     

Prostaglandin secretion by perifused bovine endometrium: secretion towards the myometrial and luminal sides at day 17 post-estrus as altered by pregnancy

Bilateral perifusion devices were utilized to measure prostaglandin secretion towards luminal and myometrial sides of bovine endometria. Tissues were collected at Day 17 post-estrus from cyclic (n = 4), pregnant (n = 5) and bred but subsequently non-pregnant (n = 6) cows. Tissue from each cow was placed into two perifusion devices, perifused with Krebs-Ringer Bicarbonate solution (3 ml/10 min) for 2.5 h and fractions collected every 10 min. Oxytocin (1 IU/ml) was perifused during fractions 7-12 to the luminal side of one device and to the myometrial side of the other device. Regardless of status, prostaglandin secretion rates (PGF and PGE2) were higher (P less than 0.01) from the luminal side than the myometrial side. Secretion rates of PGF were lower (P less than 0.01) for endometria from pregnant cows than for endometria from cyclic or bred/non-pregnant cows, whereas secretion rates of PGE2 were not affected by pregnancy status. Regardless of the side of perifusion, secretion rates of PGF and PGE2 from endometria of cyclic and bred/non-pregnant cows were elevated (P less than 0.01) throughout the period of oxytocin treatment, whereas prostaglandin secretion by endometria from pregnant cows was not stimulated by oxytocin. Decreased secretion of PGF from endometria of pregnant cows suggests that the corpus luteum and pregnancy are maintained because of an inhibition of endometrial prostaglandin synthesis or an inability to respond to stimulators of prostaglandin synthesis (i.e. oxytocin).     

Morinda lucida reduces contractility of isolated uterine smooth muscle of pregnant and non-pregnant mice.

The present work investigated the effect of Morinda lucida (M. lucida) extract on isolated uterine smooth muscle of pregnant and non-pregnant mice. Pregnant and non-pregnant mice were pretreated with oral stilboesterol (0.1 mg/kg body weight) and killed by cervical dislocation. Thin strips of the uterus were cut and mounted in a 20ml organ bath containing De Jalon solution bubbled with 95%O2-5% CO2 gas mixture. The strips were connected to a force transducer coupled to a Grass 7D Polygraph for the recording of isometric tension. Effects of graded concentrations of oxytocin (OXY; 10-5-10-2 mol/L), acetylcholine (ACh; 10-9-10-5 mol/L) and M. lucida extract (0.015-1.5 mg/ml) were recorded. Fresh uterine strips were then incubated with M. lucida extract for 5mins and cumulative response to OXY was repeated. Another set of fresh strips was incubated in L-NAME for 15mins and the cumulative responses to M.lucida extract were repeated. OXY resulted in increased contractile responses in both pregnant and non-pregnant uterine muscles. M. lucida resulted in relaxation of the uterine smooth muscle in both pregnant and non-pregnant mice at all doses. However, at 1.5mg/ml, M. lucida completely blocked spontaneous uterine contractions. Following incubation with L-NAME, M. lucida extract led to a slightly greater relaxation of the uterine strips. In conclusion, M. lucida reduced contractility of uterine smooth muscle in both pregnant and non-pregnant mice as well as blocking contractile responses to OXY and Ach in uterine smooth muscle of pregnant and non-pregnant mice. There was no significant alteration of M. lucida activity by L-NAME suggesting that the action of the compound on uterine muscle is not associated with impaired nitric oxide synthase.     

Physiological studies on nonpregnant and pregnant uterus in experimentally diabetic rats]

Spontaneous intraluminal pressure waves of diabetic nonpregnant uterus and contractile responses to oxytocin and prostaglandin F2 alpha (PGF 2 alpha) of both diabetic nonpregnant and diabetic pregnant uterus were investigated in vitro. Diabetes was induced by streptozotocin (STZ), 60 mg/kg for nonpregnant and 50 mg/kg for pregnant rats. Frequency of spontaneous intraluminal pressure waves of nonpregnant uterus was reduced in diabetic rats when compared with normal, but amplitude was slightly larger in diabetic than in normal uterus. Pressure-volume curves revealed that the compliance of nonpregnant diabetic uterus was remarkably reduced. Normal tubal side-circular muscle was significantly more sensitive to oxytocin and PGF 2 alpha than cervical one in contractile responses. This tendency was lost in diabetic nonpregnant uterus. Contractile responses of both tubal and cervical circular muscles to oxytocin were lower in nonpregnant diabetic than in normal rats, but those of longitudinal muscles were higher in diabetic nonpregnant than in normal rats. Cervical circular muscle of pregnant diabetic rats was more sensitive to both agents than those of normal. However, contractile responses of diabetic longitudinal muscle to both agents were higher than those of normal as in the case of nonpregnant uterus. The mechanism of diabetic changes of the nonpregnant and pregnant uterus was discussed.     

Positive association, in local release, of luteal oxytocin with endothelin 1 and prostaglandin F2alpha during spontaneous luteolysis in the cow: a possible intermediatory role for luteolytic cascade within the corpus luteum

Luteolysis is caused by a pulsatile release of prostaglandin F(2alpha) (PGF(2alpha)) from the uterus in ruminants, and a positive feedback between endometrial PGF(2alpha) and luteal oxytocin (OXT) has a physiologic role in the promotion of luteolysis. The bovine corpus luteum (CL) produces vasoactive substances, such as endothelin 1 (EDN1) and angiotensin II (Ang II), that mediate and progress luteolysis. We hypothesized that luteal OXT has an additive function to ensure the CL regression with EDN1 and Ang II, and that it has an active role in the luteolytic cascade in the cow. Thus, the aim of the present study was to observe real-time changes in the local secretion of luteal OXT and to determine its relationship with other local mediators of luteolysis. Microdialysis system (MDS) capillary membranes were implanted surgically into each CL of six cyclic Holstein cows (18 lines total among the six cows) on Day 15 (estrus == Day 0) of the estrous cycle. Simultaneously, catheters were implanted to collect ovarian venous plasma ipsilateral to the CL. Although the basal secretion of OXT by luteal tissue was maintained during the experimental period, the intraluteal PGF(2alpha) secretion gradually increased up to 300% from 24 h after the onset of luteolysis (0 h; time in which progesterone started to decrease). In each MDS line (microenvironment) within the CL, the local releasing profiles of OXT were positively associated with PGF(2alpha) and EDN1 within the CL in all 18 MDS lines implanted in the six CLs (OXT vs. PGF(2alpha), 50.0%; OXT vs. EDN1, 72.2%; P < 0.05). On the other hand, the intraluteal OXT was weakly related to Ang II (OXT vs. Ang II, 27.7%). In the ovarian vein, the peak concentration of PGF(2alpha) increased significantly when the peak of PGF(2alpha) coincided with the peak of OXT after the onset of spontaneous luteolysis (P < 0.05). In conclusion, intraluteal OXT may locally modulate secretion of vasoactive substances, particularly EDN1 and PGF(2alpha) within the CL, and thus might be one of the luteal mediators of spontaneous luteolysis in the cow.     

Effect of the myorelaxant clenbuterol on the oxytocin-induced release of prostaglandin F2 alpha in ovariectomized heifers

Clenbuterol, as other sympathomimetic drugs, relaxes the myometrium, thus causing a short-term inhibition of labor and the delay of parturition. This study has examined the influence of clenbuterol on the release of prostaglandin F2 alpha (PGF2 alpha) induced by oxytocin alone or with estradiol-17 beta. Five bilaterally ovariectomized heifers, primed with progesterone for 14 days, were used in two experiments. In the first they received two i.v. injections of oxytocin 6h apart, with and without an i.v. injection of clenbuterol before the second oxytocin injection; the second experiment was similar to the first except that the animals were given estradiol-17 beta 30 min after the first oxytocin injection. Frequent blood samples were taken for the measurement of 13,14-dihydro-15-keto-PGF2 alpha by radioimmunoassay. The data show that clenbuterol does not influence PGF2 alpha release in response to oxytocin alone or with estradiol-17 beta, and it does not inhibit the basal release of PGF2 alpha. This suggests that clenbuterol does not act on the endometrium to alter the secretion of PGF2 alpha in the non-pregnant cow.     

Prostaglandin secretion by perifused bovine endometrium: Secretion towards the myometrial and luminal sides at day 17 post-estrus as altered by pregnancy

Bilateral perifusion devices were utilized to measure prostaglandin secretion towards luminal and myometrial sides of bovine endometria. Tissues were collected at Day 17 post-estrus from cyclic (n=4), pregnant (n=5) and bred but subsequently non-pregnant (n=6) cows. Tissue from each cow was placed into two perifusion devices, perifused with Krebs-Ringer Bicarbonate solution (3 ml/10 min) for 2.5h and fractions collected every 10 min. Oxytocin (1 IU/ml) was perifused during fractions 7–12 to the luminal side of one device and to the myometrial side of the other device. Regardless of stratus, prostaglandin secretion rates (PGF and PGE₂) were higher (P< 0.01) from the luminal side than the myometrial side. Secretion rates of PGF were lower (P< 0.01) for endometria from pregnant cows than for endometria from cyclic or bred/non-pregnant cows, whereas secretion rates of PGE₂ were not affected by pregnancy status. Regardless of the side of perifusion, secretion rates of PGF and PGE₂ from endometria of cyclic and bred/non-pregnant cows were elevated (P< 0.01) throughout the period of oxytocin treatment, whereas prostaglandin secretion by endometria from pregnant cows wasnot stimulated by oxytocin. Decreased secretion of PGF from endometria of pregnant cows suggests that the corpus luteum and pregnancy are maintained because of an inhibition of endometrial prostaglandin synthesis or an inability to responsd to stimulators of prostaglandin synthesis (i.e. oxytocin).     

Prostaglandin F2 alpha and oxytocin interactions in ovarian and uterine function

The oxytocin-neurophysin gene is expressed in several nontraditional sites within the endocrine system. In the ovary its expression in the corpora lutea is initiated by ovulation. Ovarian oxytocin concentrations reach maximal levels around day 11 of luteal cycle and fall to a nadir at estrus. PGF2 alpha has the capacity to release oxytocin from the corpus luteum, and oxytocin in turn releases PGF2 alpha from the uterine endometrium or decidua. This positive feedback loop between the ovary and the uterus ensures the completion of luteolysis in species that depend on the presence of the uterus for the termination of luteal lifespan. Immunization against oxytocin has been shown to disrupt this loop, resulting in much-prolonged luteal cycles. In primates and other species in which luteal life span is independent of the uterus, an oxytocin PGF2 alpha interaction may take place within the ovary itself. At parturition a related interaction takes place which ensures the expulsion of the fetus and placenta in an orderly manner. Oxytocin of both pituitary and ovarian origin reaches the uterus via its blood supply and binds to two types of receptors: one on myometrial cells, the occupation of which initiates contractions, and the other on decidual cells, the occupation of which initiates prostaglandin generation. This prostaglandin diffuses into the adjacent myometrium and augments the oxytocin-induced contractions. In conjunction with a direct softening effect by prostaglandins on the cervix the augmented contractions achieve the force needed to dilate the cervix and expel the fetus. An additional source of oxytocin during labor may be the placenta, another non-traditional site for the occurrence of oxytocin.     

Uterokinetic activity of fenprostalene (a prostaglandin F2alpha analog) in vivo and in vitro in the bovine

The luteolytic potency of fenprostalene (a PGF2alpha analog) is about 20-times that of naturally produced PGF2alpha. The objective of this research was to investigate the uterokinetic effects of fenprostalene at a luteolytic dosage (1.0 mg) in the cyclic and early postpartum cow, and in the isolated uterine horn. Uterine motility measurements were conducted on two consecutive days in each cow. Experimental protocol on Day 1 was: spontaneous motility was recorded for 1 h; fenprostalene was injected (1.0 mg i.m.), after which motility was recorded for 2 h; fenprostalene was injected (1.0 mg i.v.) and motility was recorded for 30 min; and oxytocin was injected (40 U i.v.), followed by a 30-min recording period. On Day 2, the treatment sequence was reversed: spontaneous motility was recorded for 1 h; oxytocin was injected (100 U i.m.), after which motility was recorded for 2 h; fenprostalene was injected (1.0 mg i.v.) and motility recorded for 30 min; and oxytocin was injected (40 U i.v.), followed by a 30-min recording period. In the in vitro experiment, different dosages of fenprostalene (5.9, 11.8, 17.6, and 29.4 ng/ml bath solutions) and oxytocin (0.06, 0.12, 0.18, and 0.60 mU/ml bath solutions) were tested in pairs for 1 h. The treatment was then repeated. In a different group, fenprostalene (5.9 ng/ml bath solution) and oxytocin (0.06 mU/ml bath solution) treatments were alternated. Fenprostalene (at luteolytic dosage) was not uterokinetic in either the cyclic or postpartum cow. However, fenprostalene and oxytocin had a significant uterokinetic effect (five- to six-fold pretreatment value) on the isolated uterine horn preparation at all dosages studied. Peak motility occurred between 10 to 15 min, followed by a gradual decrease to 40% at 60 min. When the treatments were repeated at 60 min, oxytocin but not fenprostalene caused a minute, transient contraction. However, fenprostalene-desensitized (by exposure to fenprostalene) uteri reacted significantly to oxytocin, and vice versa.     

The influence of polychlorinated biphenyls (PCBs) and phytoestrogens in vitro on functioning of reproductive tract in cow

Ovarian, endometrial and myometrial cells and strips of longitudinal myometrium from cows on defined days of estrous cycle were treated for 24-72 h with different doses (1-100 ng/ml) of PCBs mixture (Aroclor 1248) or with one of PCB congeners (126, 77, 153). The administered doses of PCBs neither affected the viability of cells nor influenced the ovarian steroidogenesis as measured by progesterone (P(4)), estradiol (E(2)) and testosterone secretion from luteal, granulosa and theca cells, respectively. In contrast, PCBs clearly inhibited a FSH and LH-stimulated effect on steroids secretion from granulosa and luteal cells. Moreover, PCBs significantly stimulated oxytocin (OT) secretion from the studied ovarian cells, and at least part of this effect is elicited through activation of glucocorticoid receptors. Further, PCBs were found to increase basal intracellular concentrations of Ca(2+) and both spontaneous and OT-stimulated contractions of myometrial strips. Concomitantly, PCBs increased endometrial secretion of PGF(2alpha), hence the ratio of PGF(2alpha):PGE(2) was also increased. Phytoestrogens (genistein, daidzein, coumestrol), with a different intensity, reduced the effect of PCBs on PGF(2alpha) secretion and myometrial contractions. Genistein inhibited PCBs' effect on OT secretion from granulosa cells, while PCB's effect on OT release from luteal cells was reduced mainly by genistein and daidzein. We conclude that PCBs can impair both ovarian functioning and uterine contractility, while phytoestrogens are able to reduce this effect.     

Secretory patterns of LH and FSH and follicular growth following administration of PGF(2)alpha during the early luteal phase in cattle

Two studies were conducted to determine the changes in gonadotropin secretion associated with growth and development of the largest follicle and the ability of the largest ovarian follicle present on Day 5 following estrus to ovulate if luteal regression is induced. In both studies, cows received either saline (i.m.) or prostaglandin F(2)alpha (PGF(2)alpha; 25 mg i.m.) on the fifth day post estrus. Frequency of LH pulses declined (P<0.01) with increasing day of cycle, while pulse amplitude and duration increased (P<0.05) in saline-treated cows. In PGF(2)alpha-treated cows, LH remained as high frequency-low amplitude pulses. Secretory patterns of FSH were similar between the two groups. In Experiment 2, the largest ovarian follicle present was marked around its periphery with sub-epithelial injections of charcoal. In saline-treated cows, the size of the charcoal marked follicles generally decreased, indicating atresia. A corpus luteum was present within the area of a previously marked follicle in three PGF(2)alpha-treated cows. The size of the marked follicles either decreased or increased in the remaining PGF(2)alpha-treated cows, with ovulation occurring at a different site. In summary, PGF(2)alpha-induced luteal regression on the fifth day of estrus subsequently alters the frequency, amplitude and duration of LH pulses, but not FSH pulses, and the largest follicle present on Day 5 either increases or decreases in size or ovulates when PGF(2)alpha is given on Day 5 following estrus.     

Changes in plasma concentrations of arginine vasotocin after intrauterine injections of prostaglandin F-2 alpha and acetylcholine at various times during the oviposition cycle of the domestic hen (Gallus domesticus)

Prostaglandin F-2 alpha (PGF-2 alpha, 1 microgram) and acetylcholine (10 mg) were injected into the uterus of chickens 23, 21, 16, 8 or 4 h before expected oviposition. Plasma concentrations of immunoreactive arginine vasotocin and PGF were measured in relation to the time of administration of PGF-2 alpha or acetylcholine or to the premature oviposition that was induced. PGF-2 alpha or acetylcholine administration caused premature oviposition and a marked increase in plasma arginine vasotocin levels only when an egg was present in the uterus. Changes in plasma PGF concentrations were not observed. After premature oviposition was induced, plasma values of PGF and arginine vasotocin increased at the expected time of oviposition. Manual stimulation of the uterus 4 h after oviposition also stimulated arginine vasotocin release. During spontaneous oviposition, a rise in plasma PGF concentration preceded increases in uterine contractility and plasma arginine vasotocin concentration. These results suggest that PGF may stimulate uterine contractility which in turn causes the release of arginine vasotocin to provide an additional contractile stimulus during oviposition.