Changes in the secretion of ovarian steroid and pituitary luteinizing hormone in the peri-ovulatory period in the ewe: the effect of progesterone

The secretion rates of oestradiol, androstenedione and progesterone and the peripheral plasma concentration of LH were measured in 12 ewes with ovarian autotransplants before and after luteal regression induced by a single intramuscular injection of a synthetic prostaglandin (PG) analogue, 16-aryloxyprostaglandin F 2alpha (I.C.I. 80996). Luteal regression was followed by a fourfold rise in the basal concentration of LH and increased secretion of oestradiol. In five out of six ewes there was a discharge of LH with the peak occurring 36--78 h after the injection of the PG analogue. The secretion of oestradiol declined from 3-68 +/- 1-08 to 0-33 +/- 0-6 (S.E.M.) ng/min in the 24 h following the LH peak (P less than 0-001). In the remaining six ewes in which progesterone was implanted subcutaneously 24 h after the injection of PG analogue, follicular development was suppressed as indicated by the low secretion of oestradiol and androstenedione. The basal concentration of LH fell to values similar to those observed during the luteal phase after the implant of progesterone. The secretion of androstenedione followed a similar pattern to that of oestradiol in those ewes which showed presumptive evidence of ovulation. These results suggest that progesterone reinforces the negative feedback effects of oestrogen in the ewe.     

Development of Anaplasma marginale in salivary glands of male Dermacentor andersoni

The objective of this study was to clarify the role of oestradiol in luteal function by examining its effect on the oxytocin stimulation of 15-keto-13,14-dihydro-prostaglandin F2 alpha (PGFM) concentrations in cyclic mares. In the first experiment, three groups of mares (4 per group) were given a bolus injection of 17 alpha-oestradiol (1 mg), oestradiol (1 mg) or vehicle on days 7, 9, 11, 13 and 15 of the cycle. Six hours later the mares were challenged with 10 iu oxytocin intravenously and frequent blood samples were taken from 15 min before to 15 min after for measurement of PGFM. Results showed a significant stimulatory effect of oestradiol (five times greater than controls at day 11; P < 0.05), but not of 17 alpha-oestradiol, on the oxytocin stimulation of PGFM. As a relatively large dose was given systemically in this experiment, a second experiment was performed to introduce a dose that was more physiological into the uterus. Small Silastic spheres (1 cm diameter) were impregnated with or without oestradiol at a concentration that gave a release rate similar to that of embryos at day 12 (10 ng h-1). These were inserted (one per mare) into the uterus of two groups of mares (five per group) on day 7. The mares were challenged with oxytocin on days 9, 11, 13 and 15 of the cycle and blood samples were taken as before for determination of PGFM. The results showed that oestradiol enhanced (four times greater than controls at day 13; P < 0.05) the oxytocin stimulation of PGFM concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Uterine secretion of prostaglandin F2 alpha in the ewe: regulation at the cellular level by ovarian hormones and the conceptus

Changes in the ability of the uterus to secrete prostaglandin F2 alpha (PGF2 alpha) in response to oxytocin may play a critical role in determining when endogenous secretion of PGF2 alpha begins. The cellular mechanisms that regulate uterine secretion of PGF2 alpha in response to oxytocin have not been completely defined. Several intracellular components that may contribute to this regulation have been studied, including phospholipase C (PLC), prostaglandin H endoperoxide synthase (PGS) and receptors for oxytocin. All of these components change during the oestrous cycle and are associated with the development of uterine secretory responsiveness to oxytocin. Progesterone appears to play the principal role in regulating oxytocin receptors, PLC and PGS. The conceptus appears to suppress the increase in receptors for oxytocin and PLC activity that typically occurs around the time of luteal regression.     

Comparison of three treatments for bovine endometritis

Three commercial preparations for the treatment of bovine endometritis were compared: an intrauterine infusion of 1500 mg oxtytetracycline hydrochloride solution, an intramuscular injection of 500 micrograms cloprostenol (a synthetic analogue of prostaglandin F2 alpha), and an intramuscular injection of 3 mg oestradiol benzoate/500 kg estimated bodyweight. A total of 300 cases of endometritis were treated, of which 225 involved first, 67 involved second, and eight involved third or subsequent treatments. The overall success rate of treatment was 68 per cent. Oxytetracycline was successful in 73 per cent of cases, cloprostenol in 67 per cent and oestradiol in 63 per cent of cases. There was no significant difference between the success rates of the treatments, except for cows with mild endometritis in which oxytetracycline was more successful than oestradol (86 v 66 per cent, P < 0.05). Mild cases were treated more successfully than moderate cases (78 v 61 per cent, P < 0.01), and more successfully than severe cases (78 v 44 per cent, P < 0.001). Prostaglandin F2 alpha was more successful if the milk progesterone concentration was > 7 ng/ml at the time of treatment (P < 0.05). The presence of a smelly discharge at the time of treatment reduced the success rate by 17 per cent (P < 0.02). The treatment to conception interval for all successful treatments of endometritis by prostaglandin F2 alpha was 18.1 days shorter than for oestradiol (68.3 v 86.4 days, P < 0.02), and the interval for oxytetracycline was 16.2 days shorter than for oestradiol (70.2 v 86.4 days, P < 0.05).     

Prostaglandins compared with oxytocin for induction of labour at term (author's transl)

12 cases of induction of labour with prostaglandin F2 alpha and 8 with prostaglandin E2 were compared with 14 cases in which induction was undertaken with oxytocin. All inductions were successful, the induction--delivery intervals being slightly shorter in the prostaglandin groups than in the oxytocin group. Both with prostaglandin F2 alpha and with prostaglandin E2 the cardiotocogram showed uterine hyperactivity in most of the cases with an unexpected, episodically-occurring increase in basal uterine tone and remarkable tachysystoly. Uterine hyper-activity led to fetal heart rate alterations of the "dip 2" type in about 50% of the cases. According to these results prostaglandins cannot be considered superior to oxytocin for the induction of labour at term.     

Effects of exogenous recombinant ovine interferon tau on circulating concentrations of progesterone, cortisol, luteinizing hormone, and antiviral activity; interestrous interval; rectal temperature; and uterine response to oxytocin in cyclic ewes

Interferon tau (IFN tau) is the conceptus-produced antiluteolytic signal in ruminants. Three experiments examined the effects of s.c. administration of recombinant ovine (ro)IFN tau on interestrous interval (IEI), oxytocin (OT)-induced uterine prostaglandin F2alpha metabolite (PGFM) production, rectal temperature (RT), respiration rate (RR), and plasma concentrations of progesterone, cortisol, LH, and antiviral activity (AVA) in plasma and uterine flushings. In experiment I, 20 ewes were treated s.c. with either 0, 1, 2, or 4 mg/day roIFN tau (0.7 x 10(8) U/mg; 5 ewes/dosage) from Days 11 to 15 of the estrous cycle (estrus = Day 0) and were challenged with OT (30 IU) on Day 15. Jugular blood samples were collected at -10, 0, 10, 20, 30, 40, 50, and 60 min relative to the OT challenge and assayed for PGFM. Recombinant oIFN tau increased IEI (16.7, 18.7, and 22.6 +/- 0.6 days for 0, 2, and 4 mg roIFN tau, respectively, p < 0.01). Recombinant oIFN tau did not affect peak PGFM response to OT (2309 +/- 172 pg/ml; p > 0.1). However, the 4 mg/day dosage delayed the time to peak PGFM (32.4 vs. 47.5 +/- 3.4 min; p < 0.01, 0 vs. 4 mg) and resulted in approximately 200% higher concentrations of PGFM at 60 min post-OT (0 vs. 4 mg/day, p < 0.07). Experiment II was similar to experiment I, except that only the 0- and 4-mg/day dosages of roIFN tau were administered. Ewes were hysterectomized on Day 16, and assay of uterine flushes detected no AVA from ewes treated with either 0 or 4 mg/day roIFN tau. In experiment III, 20 ewes were treated s.c. with either 0, 2, 4, or 6 mg roIFN tau on Day 12. Blood samples, RT, and RR were obtained at frequent intervals for 24 h, and plasma was assayed for progesterone, cortisol, LH, and AVA. Plasma AVA, which increased in a dose-dependent manner, was detectable within 60 min and remained elevated at 24 h compared to control values. RT (elevated 0.5-1.0 degrees C), RR, and cortisol increased in response to all dosages of roIFN tau, with peak values occurring 150-180 min postinjection. For all dosages of roIFN tau, plasma progesterone declined from 120 to 360 min posttreatment and then returned to pretreatment values by 24 h (p < 0.01) as compared to controls. Overall, exogenous roIFN tau altered uterine PGFM response to OT from a pulse to a gradual and sustained elevation and extended IEI with only a transient decline in progesterone and mild hyperthermia, effects that are not expected to compromise pregnancy.     

Extension of corpus luteum lifespan and reduction of uterine secretion of prostaglandin F2 alpha of cows in response to recombinant interferon-tau

Two experiments tested the effect of recombinant ovine and bovine interferon-tau on corpus luteum lifespan, interestrous interval, and oxytocin-induced uterine secretion of prostaglandin F2 alpha. Cows received intrauterine injections of 100 micrograms of recombinant ovine interferon-tau plus 1.4 mg of BSA or of 1.5 mg of BSA alone in Experiment 1 and 200 micrograms of recombinant bovine interferon-tau plus 1.3 mg of BSA or 1.5 mg of BSA alone in Experiment 2. Twice daily injections (0700 and 1900 h) were split evenly between the uterine horns from d 14 to 24 of the experimental estrous cycle via an AI pipette in Experiment 1 and via intrauterine catheters in Experiment 2. On d 17, cows were injected with 100 IU of oxytocin, and plasma was collected for analysis of 13,14-dihydro-15-keto-prostaglandinF2 alpha. Recombinant ovine interferon-tau extended the lifespan of the corpus luteum (27.5 vs. 19.2 d) and interestrous interval (30.5 vs. 20.6 d) and abolished the oxytocin-induced increase in 13,14-dihydro-15-keto-prostaglandinF2 alpha, which peaked at 30 min for the BSA control group (210.8 pg/ml). Recombinant bovine interferon-tau also extended the lifespan of the corpus luteum (29.0 vs. 21.4 d) and interestrous interval (31.5 vs. 22.6 d) and abolished the oxytocin-induced increase in 13,14-dihydro-15-keto-prostaglandin F2 alpha, which peaked at 30 min for the BSA control group (205.6 pg/ml). In conclusion, recombinant ovine interferon-tau and recombinant bovine interferon-tau were effective antiluteolytic agents in cattle.     

Regulation of oxytocin, oestradiol and progesterone receptor concentrations in different uterine regions by oestradiol, progesterone and oxytocin in ovariectomized ewes

The regulation of oxytocin, oestradiol and progesterone receptors in different uterine cell types was studied in ovariectomized ewes. Animals were pretreated with a progestogen sponge for 10 days followed by 2 days of high-dose oestradiol to simulate oestrus. They then received either low-dose oestradiol (Group E), low-dose oestradiol plus progesterone (Group P) or low-dose oestradiol, progesterone and oxytocin (via osmotic minipump; Group OT). Animals (three to six per time-point) were killed following ovariectomy (Group OVX), at oestrus (Group O) or following 8, 10, 12 or 14 days of E, P or OT treatment. In a final group, oxytocin was withdrawn on day 12 and ewes were killed on day 14 (Group OTW). Oxytocin receptor concentrations and localization in the endometrium and myometrium were measured by radioreceptor assay, in situ hybridization and autoradiography with the iodinated oxytocin receptor antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]-vasotocin. Oestradiol and progesterone receptors were localized by immunocytochemistry. Oxytocin receptors were present in the luminal epithelium and superficial glands of ovariectomized ewes. In Group O, endometrial oxytocin receptor concentrations were high (1346 +/- 379 fmol [3H]oxytocin bound mg protein-1) and receptors were also located in the deep glands and caruncular stroma in a pattern resembling that found at natural oestrus. Continuing low-dose oestradiol was unable to sustain high endometrial oxytocin receptor concentrations with values decreasing significantly to 140 +/- 20 fmol mg protein-1 (P < 0.01), localized to the luminal epithelium and caruncular stroma but not the glands. Progesterone treatment initially abolished all oxytocin receptors with none present on days 8 or 10. They reappeared in the luminal epithelium only between days 12 and 14 to give an overall concentration of 306 +/- 50 fmol mg protein-1. Oxytocin treatment caused a small increase in oxytocin receptor concentration in the luminal epithelium on days 8 and 10 (20 +/- 4 in Group P and 107 +/- 35 fmol mg protein-1 in Group OT, P < 0.01) but the rise on day 14 was not affected (267 +/- 82 in Group OT and 411 +/- 120 fmol mg protein-1 in Group OTW). In contrast, oestradiol treatment was able to sustain myometrial oxytocin receptors (635 +/- 277 fmol mg protein-1 in Group O and 255 +/- 36 in Group E) and there was no increase over time in Groups P, OT and OTW with values of 61 +/- 18, 88 +/- 53 and 114 +/- 76 fmol mg protein-1 respectively (combined values for days 8-14). Oestradiol receptor concentrations were high in all uterine regions in Group O. This pattern and concentration was maintained in Group E. In all progesterone-treated ewes, oestradiol receptor concentrations were lower in all regions at all time-points. The only time-related change occurred in the luminal epithelium in which oestradiol receptors were undetectable on day 8 but developed by day 10 of progesterone treatment. Progesterone receptors were present at moderate concentrations in the deep glands, caruncular stroma, deep stroma and myometrium in Group O. Oestradiol increased progesterone receptors in the luminal epithelium, superficial glands, deep stroma and myometrium. Progesterone caused the loss of its own receptor from the luminal epithelium and superficial glands and decreased its receptor concentration in the deep stroma and myometrium at all time-points. There was a time-related loss of progesterone receptors from the deep glands of progesterone-treated ewes between days 8 and 14. These results show differences in the regulation of receptors between uterine regions. In particular loss of the negative inhibition by progesterone on the oxytocin receptor by day 14 occurred only in the luminal epithelium, but is unlikely to be a direct effect of progesterone as no progesterone receptors were present on luminal epithelial cells between days 8 and 14.     

Adrenomedullin, amylin, calcitonin gene-related peptide and their fragments are potent inhibitors of gastric acid secretion in rats

A release of radio-immunoassayable LHRH from the stalk-median eminence of neonatal piglets and prepubertal gilts was measured using an in vitro incubation system. The stalk-median eminence was collected from one-week-old male (n = 19) and female (n = 21) piglets and from 6-month-old prepubertal ovariectomized gilts given oestradiol benzoate (20 micrograms/kg b.w.; n = 52) or left untreated (control; n = 25) 30 or 68 h before slaughter. Each vial, containing the stalk-median eminence in 2 ml of Krebs-Ringer bicarbonate buffer, was incubated for 30 min, followed by 30 min incubations during which either basal release or the effect of adrenoreceptor antagonists and agonists on LHRH output was evaluated. There were no differences between the basal release of LHRH (x +/- SEM; pg/ml) from the stalk-median eminence of male (65.5 +/- 9.8) and female (66.3 +/- 9.6) newborn piglets. The addition of propranolol (10(-6) M) caused a 250% increase in LHRH release from the stalk-median eminence explants of neonatal males (p = 0.08) and females (p < 0.05). Neither norepinephrine nor phentolamine affected LHRH release from the stalk-median eminence of newborn males and females. The basal release of LHRH (pg/ml) from the stalk-median eminence explants collected from ovariectomized gilts given oestradiol benzoate 30 and 68 h before slaughter or left untreated was similar (147.5 +/- 36.1, 236.4 +/- 77.7 and 202.0 +/- 41.6, respectively). Propranolol evoked a significant increase in LHRH secretion from the stalk-median eminence in the control group, but not in the groups given oestradiol benzoate. Norepinephrine (10(-6) M) increased LHRH release from the stalk-median eminence collected from the control animals, 30 h and 68 h after oestradiol benzoate treatment by 48, 78 and 73 percent, respectively. Phentolamine (10(-6) M) did not affect LHRH release from the stalk-median eminence in control animals and ovariectomized gilts primed with oestradiol benzoate. Urapidil (10(-6) M, alpha 1-adrenoreceptor antagonist) did not affect the basal LHRH release from the stalk-median eminence of gilts from the control group and group slaughtered 30 h after oestradiol benzoate treatment, but caused a rapid increase of LHRH release from the stalk-median eminence 68 h after oestradiol benzoate treatment. Phenylephrine (10(-6) M) did not affect LHRH output from the stalk-median eminence collected at various time periods after oestradiol benzoate administration in vivo. These results suggest that in pigs, nerve terminals releasing LHRH at the stalk-median eminence level are sensitive to adrenergic stimulation or inhibition and that the adrenergic system can be modulated by estrogens in the prepubertal gilts.     

Early prostaglandin release from the ischemic myocardium in the dog

Cellular consequences of myocardial ischemia were studied in anesthetized dogs. Confirmation of myocardial ischemia was provided by electrocardiographic and biochemical indexes. Prostaglandin F2alpha release into coronary venous blood was significantly elevated during myocardial ischemia, whereas indomethacin treatment prevented this increase in coronary venous prostaglandin F2alpha concentrations. No significant increase in prostaglandin E2 release was observed in response to myocardial ischemia, but indomethacin treatment significantly reduced coronary venous prostaglandin E2 concentrations below those of control values. Within one hour after occlusion of the coronary artery, the S-T segment was significantly altered, and coronary venous prostaglandin F2alpha had increased significantly above the control concentration. These changes persisted during four hours of myocardial ischemia. Plasma creatine phosphokinase activity increased significantly after two hours of myocardial ischemia and remained elevated for the subsequent two hours of ischemia. After four hours of myocardial ischemia, myocardial creatine phosphokinase activity of ischemic myocardium was significantly reduced, and labilization of myocardial treatment prevented increases in prostaglandin release but did not influence other biochemical changes or the electrocardiographic response to ischemia. Thus, prostaglandin release by ischemic myocardial tissue is an early response to the ischemic stimulus.     

Regulation of messenger ribonucleic acid encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase in the ovine corpus luteum

Three experiments were conducted to determine how steady-state levels of mRNA encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) in the ovine corpus luteum vary 1) between the two steroidogenic luteal cell types, 2) during the estrous cycle, and 3) during prostaglandin F2 alpha (PGF2 alpha)-induced luteolysis. In the first experiment, RNA (10 micrograms) was isolated from purified preparations (n = 4) of large or small steroidogenic luteal cells. Large luteal cells contained 42% more (p < 0.05) message for 3 beta-HSD per microgram RNA than did small luteal cells, while the amount of mRNA for tubulin did not differ between the two types of luteal cells. To determine whether luteal levels of mRNA for 3 beta-HSD differ during the estrous cycle, corpora lutea were collected from cycling ewes (n = 3/day) on Days 3, 6, 9, 12, and 15 postestrus. Levels of mRNA for 3 beta-HSD were similar on Days 3, 6, 9, and 12 but were lower (p < 0.05) on Day 15 postestrus, while levels of mRNA for tubulin were unchanged. In the final experiment, ewes were treated on Day 10 postestrus with two injections of PGF2 alpha (5 mg each) or saline (control) at a 4-h interval. Corpora lutea were collected from ewes (n = 4/treatment) 1 h or 8 h after the second injection of PGF2 alpha or 8 h after the second saline injection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exogenous interferon delays luteal regression in red deer hinds (Cervus elaphus) by suppressing steroid-induced endometrial oxytocin sensitivity

Three groups of intact hinds (n = 10-18) and one group of ovariectomized hinds were treated with progesterone by mean, of Controlled Internal Drug Releasing (CIDR) devices for 13 days (device removal = Day 0). Group 1 served as controls; group 2 received injections of 4 mg recombinant bovine interferon-alpha,1 twice daily from Days 13 to 21; group 3 was run with a stag from Days 0 to 3, and all hinds were subsequently diagnosed pregnant; group 4 (ovariectomized) was treated with CIDR devices and estradiol to mimic steroid secretion during the estrous cycle. Progesterone profiles were determined from thrice-weekly plasma samples from Days -13 to 28. Rectal temperature was measured in a subset of groups 1 and 2 from Days 9 to 21. Oxytocin-induced prostaglandin F2 alpha release was measured in a subset of groups 1, 2, and 4 on Days 2, 4, 10, 16, and 18. Data are presented as means +/- SEM. Exogenous interferon delayed luteolysis (> or = 28 vs. 21.2 +/- 0.55 days, P < 0.0005) and induced transient pyrexia after the first injection (39.89 +/- 0.11 vs. 38.88 +/- 0.19 degrees C, p < 0.0005). Incidence of oxytocin-induced PGF2 alpha release in control hinds was greater on Days 2 and 18 than on Days 4 and 10 (8/8 and 7/8 vs. 3/8 and 0/8, respectively; p < 0.05) and was greater in control than in interferon-treated hinds on Days 16 and 18 (5/8 and 7/8 vs. 1/8 and 1/8, respectively; p < 0.05). Profiles of plasma progesterone concentration and oxytocin sensitivity in steroid-treated ovariectomized hinds did not differ from those in control hinds. These results suggest that steroid-controlled uterine oxytocin sensitivity is important in luteolysis and is suppressed by the administration of interferon, the putative embryonic pregnancy recognition signal in red deer.     

Nitric oxide in the contractile action of bradykinin, oxytocin, and prostaglandin F2 alpha in the estrogenized rat uterus

Experiments were performed on uteri from estrogen-primed female rats. Bradykinin (BK) (10(-8) M) significantly augmented biosynthesis of prostaglandin F2 alpha (PGF2alpha) and prostaglandin E2 (PGE2), and this synthesis was completely blocked by NG-monomethyl L-arginine (NMMA) (300 microM), a competitive inhibitor of nitric oxide synthase (NOS). Blockade of prostaglandin synthesis by indomethacin caused rapid dissipation of isometric developed tension (IDT) induced by BK. Blockade of NOS with NMMA had similar but less marked effects. Combining the two inhibitors produced an even more rapid decay in IDT, suggesting that BK-induced NO release maintains IDT by release of prostanoids. The decline of frequency of contraction (FC) was not significantly altered by either indomethacin or NMMA but was markedly accelerated by combination of the inhibitors, which suggests that PGs maintain FC and therefore FC decline is accelerated only when PG production is blocked completely by combination of the two inhibitors of PG synthesis. The increase in IDT induced by oxytocin was unaltered by indomethacin, NMMA or their combination indicating that neither NO nor PGs are involved in the contractions induced by oxytocin. However, the decline in FC with time was significantly reduced by the inhibitor of NOS, NMMA, suggesting that FC decay following oxytocin is caused by NO released by the contractile process. In the case of PGF2alpha, NMMA resulted in increased initial IDT and FC. The decline in FC was rapid and dramatically inhibited by NMMA. Receptor-mediated contraction by BK, oxytocin, and PGF2alpha is modulated by NO that maintains IDT by releasing PGs but reduces IDT and FC via cyclic GMP.     

Effect of the vascular endothelium on contractions induced by prostaglandin F2 alpha in isolated pregnant guinea pig uterine artery

The purpose of this study was to examine the influence of endothelium on prostaglandin F2 alpha-mediated contractions in pregnant guinea pig uterine artery. Consequently, the effects of prostaglandin F2 alpha on pregnant guinea pig uterine arterial rings with both intact and denuded endothelium were studied. In vessels with denuded endothelium prostaglandin F2 alpha (0.1-10 microM) induced contraction (pD2 = 6.17) with greater potency than in vessels with intact endothelium (pD2 = 5.68). NG-Monomethyl-L-arginine (10 microM) did not affect the concentration-response curve for prostaglandin F2 alpha, regardless of endothelial condition. In contrast, in both types of preparation, indomethacin (10 microM) increased the maximal response value obtained with prostaglandin F2 alpha, but this effect was significantly greater in preparations with intact than in those with denuded endothelium (128.3 versus 206.5%). Moreover, indomethacin shifted the concentration-response curve for prostaglandin F2 alpha to the left only in preparations with intact endothelium. The pKA values for prostaglandin F2 alpha itself did not differ between preparations: 5.41 and 5.52 for pregnant guinea pig uterine artery with and without endothelium, respectively. The receptor reserve expressed as KA/EC50 was significantly greater in rings with denuded (4.44) compared to those in rings with intact endothelium (1.86). We conclude that prostaglandin-F2 alpha-induced contraction in pregnant guinea pig uterine artery is modulated by the vascular endothelium. It is probable that cyclooxygenase products relating to vasodilatation and derived from endothelium mediate this effect, acting as a functional endogenous antagonist and thereby reducing the apparent efficacy and potency of prostaglandin F2 alpha.     

Spontaneous coronary artery dissection

The effect of an intra-luteal injection of the 5-lipoxygenase (5-LO) inhibitor BWA4C (2 mg in 50 microl DMSO) on the secretion of oxytocin (OT) from the corpus luteum in response to a close-arterial infusion of prostaglandin (PG)-F2alpha (5 ng min(-1)) was examined in anaesthetised sheep. Within 30 minutes of administration both basal (pre-infusion) and PGF2alpha-stimulated OT release into the posterior vena cava were significantly (P<0.01) reduced. These results are consistent with the proposition that 5-LO products of arachidonic acid may modulate OT secretion from the ovine corpus luteum.     

Intraovarian pressure changes during ovulation in rabbits

Contractile elements are found in the ovaries of many species, but it has not been possible to ascertain whether these elements are of importance in the process of ovulation. In this report, we describe changes in intraovarian pressure recorded continuously in vivo in unanesthetized rabbits under normal conditions and under the influence of intravenously injected human chorionic gonadotropin (hCG), as well as following the ovulatory stimulus of normal copulation. The recordings were made by means of small latex balloons (0.02- to 0.04-ml volume) attached to indwelling catheters, inserted into the ovarian stroma, and secured with 6-0 nylon sutures. All 24 rabbits studied showed changes in intraovarian pressure indicative of ovarian contractile activity. The intraovarian pressure changes followed a characteristic pattern which was different from the changes in intratubal pressure, recorded simultaneously from the lumen of the ipsilateral fallopian tube, indicating that the contractions of both organs occurred independently. In normal animals, before an ovulatory stimulus was applied, the ovarian contractility pattern consisted of a series of rapid contractions (average amplitude, 6 mm Hg; average frequency; 8 per minute) occurring with intervals of quiescence lasting from 11 to 36 minutes. The base line tonus was frequently elevated during these series of contractions. Mating or an injection of hCG had no immediate effect on intraovarian pressure but, 6 to 8 hours after the stimulus was applied, ovarian contractile activity increased significantly in all rabbits. This enhanced activity persisted for several hours before returning to initial levels approximately 15 to 18 hours after mating or the hCG injection. This demonstration of increased contractile activity about the time of ovulation suggests that ovarian contractions participate in the process of follicular rupture and the extrusion of ova at ovulation. Prostaglandin F2alpha, norepinephrine, and oxytocin were effective in inducing ovarian contractions.     

Indomethacin reduces contraction of isolated non-pregnant human uterine artery induced by prostaglandin F2 alpha

The purpose of this study was to explore whether cyclooxygenase products derived from endothelium or vascular smooth muscle participate in the response of human uterine artery to prostaglandin F2 alpha. Experiments were performed using human uterine arterial rings. Prostaglandin F2 alpha (0.4 nM-1 microM) induced contraction of human uterine arteries with both intact and denuded endothelium with similar potency and efficacy (pD2 values: 7.93 +/- 0.01 and 8.07 +/- 0.03 for vessels with and without endothelium respectively; maximal response values: 89.1 +/- 4.7% and 92.3 +/- 3.8% for vessels with and without endothelium respectively). Indomethacin (10 microM) significantly suppressed the maximum effects of prostaglandin F2 alpha and induced a shift towards the right of the prostaglandin F2 alpha concentration-response curves, regardless of the endothelial condition. On the other hand, in both types of preparations, OKY-046 (10 microM), an inhibitor of thromboxane synthesis, did not affect prostaglandin F2 alpha-induced contraction of human uterine arteries. It is concluded that in human uterine artery prostaglandin F2 alpha-induced contraction is mediated, at least in part, through constrictor prostanoid(s) of vascular smooth muscle origin that is not thromboxane A2.     

Does prolactin mediate induced nest-building behaviour in pseudopregnant gilts treated with PGF2alpha?

Nest-building behaviour occurs 6-24 h before parturition in pigs (gestation=116 days). Pseudopregnancy in pigs (induced with oestradiol valerate injections) lasts 50-80 days. We have shown that prostaglandin F2alpha (PG) administration on day 47 of pseudopregnancy induces nest-building and changes to plasma prolactin, oxytocin, cortisol and progesterone similar to those seen before normal parturition. Peripheral prolactin has been proposed as a modulator of nest-building. This study assessed nest-building behaviour in prolactin-deprived gilts. Jugular vein catheters were inserted on day 39 of pseudopregnancy and blood samples collected daily from days 40-48. Animals were injected im with either 40 mg bromocriptine in 2 ml 70% ethanol (n=8) or vehicle (n=7) at 17.00 h on day 46 and 09.00 h on day 47 of pseudopregnancy. PG (15 mg Lutalyse: Upjohn) was injected im at 11.00 h on day 47. Blood and behavioural samples were taken from 90 min before PG to 6 h post-PG. Plasma prolactin increased in control but not bromocriptine treated animals following PG (P<0.05). Elevations in oxytocin, cortisol and progesterone (P<0.05) above pre-PG concentrations were also seen, but of these only progesterone showed between group differences [greater (P<0.05) in control gilts on both days 47 and 48]. PG significantly (P<0.05) increased both the rate and proportion of total time spent performing straw/floor-directed behaviours not including foraging (an index of nesting behaviour) in both treatment groups with no significant differences between groups. There were also no significant differences between groups in time spent performing pen fixture directed activities before or after PG. Bromocriptine suppressed the rise in prolactin concentrations after PG without suppressing nest-building behaviour. We conclude that peripheral prolactin is not an essential component of the nest-building complex in pigs.     

In vivo phosphorylation of phosphofructokinase from the bivalve mollusk Mytilus galloprovincialis

The objective of this study was to determine whether progesterone prevents the stimulatory effects of oestradiol on GnRH receptor gene expression. In Expt 1, ewes were treated during the luteal phase (days 10-12 of the oestrous cycle) with either one or five subcutaneous implants containing oestradiol (n = 6 per group). Control ewes received no treatment (n = 6). Anterior pituitary glands were collected 16 h after treatment with oestradiol. Steady-state amounts of GnRH receptor mRNA were similar among all three treatment groups despite increased circulating concentrations of oestradiol in implanted ewes at the time of pituitary collection (4.3 +/- 0.6 and 24.7 +/- 2.6 pg ml-1 in ewes treated with one or five implants, respectively, compared with 0.5 pg ml-1 in controls). Experiment 2 was designed to determine whether progesterone was the ovarian factor preventing the stimulatory effects of oestradiol on expression of the GnRH receptor gene in Expt 1. Twenty-five ewes were ovariectomized on day 6 or day 7 of the oestrous cycle and assigned to one of five treatment groups (n = 5 per group). Control ewes received no further treatment. Endogenous luteal phase concentrations of progesterone were replaced in three groups of ewes at the time of ovariectomy via intravaginal implants. Three days after ovariectomy, one group of progesterone-treated ewes received one oestradiol implant, while another group of progesterone-treated ewes received five oestradiol implants. An additional group was treated with five oestradiol implants only, and anterior pituitary glands were collected from all ewes 16 h later. Compared with untreated ovariectomized ewes, treatment with progesterone alone did not affect amounts of GnRH receptor mRNA. In ewes treated with progesterone and either one or five oestradiol implants, steady-state amounts of GnRH receptor mRNA were increased twofold (P < 0.01). Treatment with oestradiol in the absence of progesterone increased amounts of GnRH receptor mRNA threefold (P < 0.001). These results provide evidence that the stimulatory effects of oestradiol on the expression of the GnRH receptor gene are prevented during the natural luteal phase in ewes. However, progesterone does not appear to act independently to mediate this effect.     

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The effect of a slow-releasing oxytocin preparation on the ovulation rate of Merino ewes was investigated. Synchronised Merino ewes were subcutaneously injected with a slow-releasing preparation containing 10 IU oxytocin, 48 hours after sponge withdrawal. Laparoscopic examination of the ovaries of all ewes was performed 10 d after the oxytocin treatment in order to determine the number of corpora lutea per ewe. The ovulation rate of the adult ewes of the treated and control groups was 179.1% and 159.1% respectively (p < 0.05) while that of the 2-tooth ewes was 108.3% and 112.8% respectively (p > 0.05). It would appear that a higher ovulation rate can be obtained by a single injection of a slow-releasing oxytocin preparation at the onset of oestrus. The lack of response in the 2-tooth ewes was probably due to their relatively low body weight.